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Performance of rapid tooling molds for thermoformed sockets

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Title:
Performance of rapid tooling molds for thermoformed sockets
Physical Description:
Book
Language:
English
Creator:
Chimento, Jairo R
Publisher:
University of South Florida
Place of Publication:
Tampa, Fla
Publication Date:

Subjects

Subjects / Keywords:
Pneumatic permeability
Flexural strength
Three dimensional printing
Prosthetics
Residual limbs
Dissertations, Academic -- Mechanical Engineering -- Masters -- USF   ( lcsh )
Genre:
non-fiction   ( marcgt )

Notes

Abstract:
ABSTRACT: Traditional prosthetic socket fabrication is a laborious and time consuming process that involves physical measurements, plaster wrapping of the stump, plaster casting for positive mold preparation, and a thermoforming process. During the mold preparation stage, significant modifications are performed subjectively based on the prosthetist's experience to transmit an optimum load to the residual limb through the socket. Rapid Prototyping techniques have advanced rapidly during the recent decades emerging as a computer aided socket design alternative which promises a potential reduction in the fabrication time, and a more systematic design approach. In addition, 3-D scanning provides accurate and fast virtual replica of the stump which can be imported in CAD environments. Within 3-D CAD software, prosthetists are able to perform modifications precisely and store files indefinitely. This work examines the potential use of ZCorp 3-D printers to directly manufacture the thermoforming mold required for prosthetic socket manufacture. This work analyses the performance of Rapid Tooling molds for thermoformed socket based on three main parameters: pneumatic permeability, flexural strength and wear rate. The traditional material for mold casting, Plaster of Paris, is compared to materials used for three dimensional printing by Zcorp printers: zp130 and zp140 untreated as well as using them with custom and novel post treatments. To obtain the flexural strength of the different materials, three point bend tests were performed in a universal test machine using ASTM Standard D790-03 requirements. In addition, pneumatic permeability tests were performed to cylindrical specimens of the different materials following ASTM Standard D6539-00. Thermoforming tests confirm that Zcorp 3-D printed parts can serve as effective molds for thermoforming of prosthetic socket.
Thesis:
Thesis (M.S.M.E.)--University of South Florida, 2009.
Bibliography:
Includes bibliographical references.
System Details:
Mode of access: World Wide Web.
System Details:
System requirements: World Wide Web browser and PDF reader.
Statement of Responsibility:
by Jairo R. Chimento.
General Note:
Title from PDF of title page.
General Note:
Document formatted into pages; contains 66 pages.

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University of South Florida
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Resource Identifier:
aleph - 002029629
oclc - 437010655
usfldc doi - E14-SFE0002950
usfldc handle - e14.2950
System ID:
SFS0027267:00001


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ABSTRACT: Traditional prosthetic socket fabrication is a laborious and time consuming process that involves physical measurements, plaster wrapping of the stump, plaster casting for positive mold preparation, and a thermoforming process. During the mold preparation stage, significant modifications are performed subjectively based on the prosthetist's experience to transmit an optimum load to the residual limb through the socket. Rapid Prototyping techniques have advanced rapidly during the recent decades emerging as a computer aided socket design alternative which promises a potential reduction in the fabrication time, and a more systematic design approach. In addition, 3-D scanning provides accurate and fast virtual replica of the stump which can be imported in CAD environments. Within 3-D CAD software, prosthetists are able to perform modifications precisely and store files indefinitely. This work examines the potential use of ZCorp 3-D printers to directly manufacture the thermoforming mold required for prosthetic socket manufacture. This work analyses the performance of Rapid Tooling molds for thermoformed socket based on three main parameters: pneumatic permeability, flexural strength and wear rate. The traditional material for mold casting, Plaster of Paris, is compared to materials used for three dimensional printing by Zcorp printers: zp130 and zp140 untreated as well as using them with custom and novel post treatments. To obtain the flexural strength of the different materials, three point bend tests were performed in a universal test machine using ASTM Standard D790-03 requirements. In addition, pneumatic permeability tests were performed to cylindrical specimens of the different materials following ASTM Standard D6539-00. Thermoforming tests confirm that Zcorp 3-D printed parts can serve as effective molds for thermoforming of prosthetic socket.
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Performance of Rapid Tooling Molds for Thermoformed Sockets by Jairo R Chimento A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Mechanical Engineering Department of Mechanical Engineering Colle ge of Engineering University of South Florida Major Professor: Nathan Crane, Ph.D. Rajiv Dubey, Ph.D. Muhammad Rahman, Ph.D. Date of Approval: March 25 2009 Keywords: pneumatic permeability, flexural strength, three dimensional printing, prosth etics, residual limbs, rapid prototyping Copyright 2009, Jairo Chimento

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Dedication This thesis is dedicated to my parents who have supported and encouraged me from the beginning of this path. Especially, I hope to inspire my brother and sister who ha ve been a tremendous source of motivation to continue moving forward during difficult times I look at this achievement as a family effort rather than an individual triumph. Also, this th esis is dedicated to Yisset who believed in my dreams and never aban doned me.

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Acknowledgements The author wishes to acknowledge all the efforts and support of the people who contributed to this thesis. Without Dr. Nathan Crane patience, guidance and encouragement, I would have never been able to finish this work. The ti me and effort devoted from Dr. Rajiv Dubey and Dr. Muhammad Rahman as committee members is deeply appreciated. My thanks to t he prosthetic research group and lab mates that helped through this research suggesting solutions to occasional problems. I want to thank all my family members who reside in the US that w ere tremendously supportive. Finally, warm gratitude is devoted to Silvi a Blanco and her family for their encouragement and support.

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i Table of Contents List of Tables ................................ ................................ ................................ ................................ .... ii i List of Figures ................................ ................................ ................................ ................................ .. iv ABSTRACT ................................ ................................ ................................ ................................ ..... vi C hapter 1: Introduction ................................ ................................ ................................ ..................... 1 1.1. Thesis Statement ................................ ................................ ................................ ... 1 1.2. Background ................................ ................................ ................................ ............ 2 1.2.1. Prosthesis for Residual Limbs ................................ ............................... 2 1.2.1.1. Terminology and Basic Components ................................ .... 3 1.2.2. Socket ................................ ................................ ................................ .... 8 1.2.2.1. Importance of Socket Fit ................................ ....................... 8 1.2.2.2. Problems in the Socket Wearing ................................ ........... 8 1.2.2.3. Traditional Socket Manufacturing ................................ .......... 9 1.2.2.4. Socket Fitting Process ................................ ......................... 11 1.2.2.5. Computer Aid ed Socket Design and Manufacturing ........... 11 1.2.2.6. Rapid Manufacturing Methods ................................ ............ 12 1.2.2.7. Potential for New Approaches ................................ ............. 13 1.3. Thesis Outline ................................ ................................ ................................ ...... 14 Chapter 2: Literature Review ................................ ................................ ................................ ......... 16 2.1. Socket Modeling ................................ ................................ ................................ ... 16 2.1.1. FEA Simulation Based ................................ ................................ ......... 16 2.1.2. 3 D Scanning Based ................................ ................................ ............ 18 2.2. Socket Manufacturing T echnologies ................................ ................................ .... 19 2.2.1. Thermoforming ................................ ................................ .................... 19 2.3. Why 3 D Printing for Rapid Tooling in Prosthetics? ................................ ............. 19 2.3.1. Rapid Prototyping ................................ ................................ ................ 21 2.3.1.1. Three Dimensio nal Printing ................................ ................. 24 2.3.1.2. Fused Deposition Modeling ................................ ................. 27 2.4. Material Property Requirements of Socket Molds ................................ ............... 28 2.4.1. Flow through Porous Media ................................ ................................ 28 2.4.2. Mechanical Strength ................................ ................................ ............ 28 2.4.3. Wear Rate ................................ ................................ ............................ 29 2.5. Conclusions ................................ ................................ ................................ .......... 30 Chapter 3: Material Characterization ................................ ................................ ............................. 31 3.1. Introduction ................................ ................................ ................................ .......... 31 3.2. Materials and Preparation Methods ................................ ................................ ..... 31 3.3. Determination of Pneumatic Permeability ................................ ............................ 32 3.3.1. ................................ ................................ ...................... 32

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ii 3.3.1.1. Pneumatic Permeability ................................ ....................... 33 3.3.2. ASTM Standard for Pneumatic Permeability Measurements .............. 34 3.3.2.1. Specimen Fabrication ................................ .......................... 34 3.3.3. Apparatus Configuration ................................ ................................ ...... 36 3.3.4. Results ................................ ................................ ................................ 38 3.4. Determination of Flexural Strength ................................ ................................ ...... 39 3.4.1. Specimen Fabrication ................................ ................................ .......... 39 3.4.2. Apparatus Configuration ................................ ................................ ...... 41 3.5. Wear Testing ................................ ................................ ................................ ........ 43 Chapter 4: Evaluation of Alternative Materials ................................ ................................ ............... 46 4.1. 3 D Printing Powder ................................ ................................ ............................. 46 4.1.1. List of Materials and Post treatments ................................ .................. 46 4.1.2. Zp 130 ................................ ................................ ................................ .. 47 4.1.3. Zp 140 ................................ ................................ ................................ .. 48 4.2. Measurements of Performance ................................ ................................ ............ 48 4.2.1. Strength ................................ ................................ ............................... 49 4.2.2. Permeability ................................ ................................ ......................... 50 4.2.3. Wear ................................ ................................ ................................ .... 51 4.2.4. Dimensional Stability ................................ ................................ ........... 52 4.3. Build Up Test ................................ ................................ ................................ ....... 53 4.4. Comparison to Traditional Materials ................................ ................................ .... 55 4.5. Therm oforming Tests Using Rapid Tooling Molds ................................ ............... 56 4.6. Ease of Integration into Current Processes ................................ ......................... 58 4.6.1. Discussion ................................ ................................ ........................... 59 Chapter 5: Conclusion and Future Work ................................ ................................ ........................ 60 5.1. Size I ssues ................................ ................................ ................................ ........... 60 5.2. Solid/Hollow Parts Designs ................................ ................................ .................. 61 References ................................ ................................ ................................ ................................ ..... 62 Appendices ................................ ................................ ................................ ................................ .... 65 Appendix A ................................ ................................ ................................ ........................ 66

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iii List of Tables Table 1: Technical specifications of Zcorp printers 29 ................................ ................................ ... 26 Table 2: Typical data obtained from pne umatic permeability test. ................................ ................ 38 Table 3: Available material with different post treatments. ................................ ............................ 48 Table 4: Relative error of thickness and width with respect of nominal dimensions. .................... 53 Table 5: Comparison of performance of different materials. ................................ .......................... 55 Table 6: Me asured dimensions of specimens. ................................ ................................ .............. 66

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iv List of Figures Figure 1: Lower extremity level of amputation 12 ................................ ................................ ............ 4 Figure 2: Upper extremity levels of amputation 13 ................................ ................................ ........... 5 Fig ure 3: Above the knee prosthesis 14 ................................ ................................ ........................... 6 Figure 4: Below the knee prosthesis 14 ................................ ................................ ........................... 6 Figure 5: Below the elbow prosthesis 15 ................................ ................................ .......................... 7 Figure 6: Above the elbow prosthesis 14 ................................ ................................ ......................... 7 Figure 7: Traditional prosthetic socket manufacturing stages 9, 18, 19 ................................ ............ 10 Figure 8: Traditional socket fitting process. ................................ ................................ ................... 11 Figure 9: Potential for new approaches in socket manufacturing. ................................ ................. 14 Figure 10 : Thermoforming process schematic 28 ................................ ................................ .......... 19 Figure 11: Rapid tooling, rapid manufacturing and traditional socket manufacturing compar ison. 20 Figure 12: Comparison between rapid tooling and rapid manufacturing. ................................ ...... 23 Figure 13: 3 D ink jet printing apparatus schematic and process 21 ................................ ............. 25 Figure 14: Fused deposition manufacturing apparatus 20 ................................ ............................. 27 Figure 15: Darcy's experiment 35 ................................ ................................ ................................ ... 33 Figure 16: Plaster of Paris based specimens in PVC pipes. ................................ ......................... 35 Figure 17: Rapid prototyped specimen for pneumatic permeability test. ................................ ....... 35 Figure 18: Pneumatic permeability set up. ................................ ................................ ..................... 37 Figure 19: Pneumatic permeability schematic apparatus. ................................ ............................. 37 Figure 20: Molded plaster specimen. ................................ ................................ ............................. 40 Figure 21: Zcorp printed specimen for three point bending test. ................................ ................... 40 Figure 22: Three point bend test schematic apparatu s. ................................ ................................ 41 Figure 23: MTS universal testing machine with bending fixtures and low force sensor. ............... 42

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v Figure 24: Typical load vs. displacement graph from three point bend test. ................................ 42 Figure 25: Wear test set up. ................................ ................................ ................................ ........... 43 Figure 26: Free body diagram of wear test setup. ................................ ................................ ......... 44 Figur e 27: Scanned images of exposed areas after wear rate test. ................................ .............. 44 Figure 28: Wear comparison of traditional materials. ................................ ................................ .... 45 Figure 29: Flexural strength of the different material configurations. ................................ ............ 49 Figure 30: Pneumatic permeability of different material configurations. ................................ ........ 51 Figure 31: Wear test results from the different material configurations. ................................ ........ 52 Figure 32: Reinforced specimen for flex ural strength test. ................................ ............................ 53 Figure 33: Flexural strength comparison between regular and reinforced specimens. ................. 54 Figure 34: CAD image of the preliminary mold tested. ................................ ................................ .. 56 Figure 35: Preliminary thermoformed socket using 3 D printed mold. ................................ .......... 57 Figure 36: CAD image of t he preliminary mold tested. ................................ ................................ .. 57 Figure 37: Preliminary thermoformed socket using 3 D printed mold. ................................ .......... 57 Figure 38: Schematic process of rapid tooling of molds. ................................ ............................... 58

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vi Performance of Rapid Tooling Molds for Thermoformed Sockets Jairo Chimento ABSTRACT Traditional prosthetic socket fabrication is a laborious and time consuming process that involves physical measurements plaster wrapping of the stump plaster casting for positive mold preparation and a thermoforming process. During the mold preparation stage, significant modifications are performed subjective ly based on the to transmit a n optimum load to the residual limb through the socket Rapid Prototyping techniques have advanced rapidly during the recent decades emerging as a computer aided socket d esign alternative which promises a potential reduction in the fabrication time and a more systematic design approach In addition, 3 D scanning provides accurate and fast virtual replica of the stump which can be imported in CAD environments Within 3 D CAD software prosthetists are ab le to perform modifications precisely and store files indefinitely. This work examines the potential use of ZCorp 3 D printers to directly manufacture the thermoforming mold required for prostheti c socket manufacture. T his work analyses the performance of Rapid Tooling molds for thermo fo rmed socket based on three main parame ters: pneumatic permeability, flexural strength and wear rate The traditional material for mold casting, P laster of Paris, is compared to material s used for three dimensional printing b y Zcorp printers: zp130 and zp140 untreated as w ell as using them with custom and novel post treatments. To obtain the flexural strength of the different materials t hree point bend tests were performed in a universal test machine using ASTM Standard D790 03 requirements In addition, pneumatic permeabi lity tests were performed to cylindrical specimens of the different materials following ASTM Standard D6539 00

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vii Thermoforming tests confirm that Zcorp 3 D printed parts can serve as effective molds for thermo forming of prosthetic socket.

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1 C hapter 1 : I ntroduction 1.1. Thesis Statement Th e overa ll goal of this thesis is to evaluate the suitability of a modified commercial 3 D printing process to produce socket molds. The socket manufacturing process is analyzed based on material comparison between standard and alt ernative materials used in rapid tooling versus traditional materials and processes in prosthetics Currently, Zcorp three dimensional printers offer the lowest cost and higher speeds available in the m arket. This work addresses the integration of 3 D scanning and rapid prototyping t echniques 3 D printing in this case, in prosthetic sockets molds manufacturing as an alternative to potentially reduce fabrication time and increase accuracy in molds shape T o evaluate suitability the key propertie s of standard and modified materials are measured. The main parameters analyzed are pneumatic permeability and flexural strength due to their relevance in the vacuum process and applied loads involved in the therm oforming process of the socket. In addition, other properties were tested such as surface wear rate and volumetric stability to assess part accuracy and ease of modifications. T ime, costs, and process implications of the proposed approach are also examined This chap ter will review the overall concept of prosthesis on residual limbs, terminology and basic components, socket fitting issues and the motivation for considering new techniques in socket design and manufacturing.

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2 1.2. Background 1.2.1. Prosthesis for Residual Limbs Approximately 1.6 million people in the United States currently live with limb lo ss. There are approximately 135, 000 new amputees each year. Amputa tion statistical incidents show : 53% of amputations are of the leg below the knee, 33% are of the leg above the knee, 2% are of the arm above the elbow and 4% are of the arm below the elbow. Lower limb amputations are caused due to several reasons such as disease (70%), trauma (22%), birth defects (4%) and tumors (4%). Following amputation, there are seve ral aspects that may diminish the recovering and rehabilitation of the patient including inactivity, lack of physical and counseling therapy, improper gait and socket fitting. Secondary conditions may further impede amputee recovery. Moreover, these condit ions may include lack of body temperature control, obesity retention of liquids and lack of flexibility. As a result, an increasing necessity to provide comfort and rehabilitation to the amputees creates the space for continuous resear ch in the prosthetic field 1, 2 Prosthesis is a device emulat ing a missing part of the body connected to residual limbs which are remaining extremities th at have suffered amputation. The prosthetic socket is the cavity of the prosthesis where the residual limb is inserted. In addition, p rosthetic socket s are needed in order to align stabilize and support prosthesis in t he residual limb Researche r s and pro sthetists have agreed that appropriate socket fitting is the most important element in the rehabilitation of an amputee 3, 4 An individual can recover the ability to function normally if the p rosthetic socket fits well with the stump. For example, if a lower limb amputee prosthet ic socket fits correctly, the individual will develop a near normal gait providing the ability to continue daily activities with independence 3 However, if the prosthetic socket fits improperly, unnat ural conditions result from the frictional interaction between the soft tissue of the residual limb a nd the prosthetic socket. These conditio ns lead the amputee to suffer pain, b listers, edema, pressure ulcers, and sometimes flap necros is and osteomyelitis 5, 6

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3 Various improvement opportunities in the design and manufacturing of prosthetic sockets have motivated different investigations in the prosthetic field. The majority are related to the analysis of the stump socket surface interface using finite element a nalysis (FEA) to find the regions where the normal and shear stresses could affect the patient comfort 7, 8 Other studies have been devoted to implement three dimensional reconstruction of the residual limb using MRI and CT images 3, 4, 9 Moreover, R apid prototyping, a new manufacturing technology, has been used to aid in the prosthetic socket design and manufacturing 9 11 One particular study des cribed the process of digitalization of the positive mold using 3 D scanning technology followed by m odeling of the socket using computer aided d esign (CAD) software, and the further Computer Aided Manufacturing software/machine interfaces The technol ogy used for fabricating the socket was fused deposition modeling (FDM). 1.2.1.1. Terminology and Basic Components P ros thetic terminology will be used t hroughout this work. A brief explanation of some components and specific terms are described next. Amputation: Partia l or complete removal of a limb. Residual limb: Portion of the extremity remaining after amputation. Upper limb a mputee: Individual that has lost any segment of the arm(s) by accident or due to a surgery. Lower limb a mputee: Individual that has lost any se gment of his/her leg(s) by accident or due to a surgery. Transhumeral amputation (TH) : Above the elbow amputation (AE). Transradial amputation (TR): Below the elbow amputation (BE). Transfemoral amputation (TF): Above the knee amputation (AK). Transtibial amputation (TT) : Below the knee amputation (BK).

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4 Socket: C avity that fits around the residual limb which works as an i nterconnecting device prosthesis. Shank : Leg section between knee and ankle Suspension s ystems: System that hold s the prosthesis on to residual limbs. Terminal devices, sockets, shanks, suspension systems are the common basic components of a prosthesis. Moreover devices simulating joint motions are used depending on the level of amputation on the residual limb. F igure 1 illustrates the leve l s of amputation on lowe r limb amputees. Figure 2 illustrate s the leve l s of amputation on upp er limb amputees. Figure 1 : Lower extremity level of a mputation 12

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5 Figure 2 : Upper extremity levels of a mputation 13 In fact, prostheses for trans tibi al (below the knee) ampu tee s should include: a socket, foot ankle assembly and a shank. Prostheses for transfe mor al (above the knee) amputee s should include the components listed above in addition a thigh and a prosthetic knee. The following two images illustrate the basic components of lower limb prostheses.

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6 Figure 3 : Abov e the knee prosthesis 14 Figure 4 : Below the knee prosthesis 14

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7 In the case of upper limb prostheses the most common prostheses ar e fabricated for transhumeral (above the elbow) and transradial (below the elbow) amputees. The components of a below the elbow prostheses are: socket, suspension, control cable sys tem and a terminal device such as a mechanical hand or a hook. Prostheses f or transhumeral amputees should include the previously mentioned components in addition to a prosthetic elbow. Figure 5 : Below the elbow p rosthesis 15 Figure 6 : Above the elbow p rosthesis 14

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8 1.2.2. Socket The s ocket serves as an interconnecting component between the residual limb and the prosthesis The main object ives of the socket are to hold the prosthesis at the residual lim b and distribute the pressure due to the forces generated when standing or walking in the case of lower limb prosthesis at the socket residual limb interface. An optimal socket should deliver alignment, stability and comfort. 1.2.2.1. Importance of Socket Fit Socket fitting plays a key role in the rehabilitation and normal recovery of activities developed by the patients. The interface between the socket and the residual limb is an area exposed to norm al and shear stresses that can affect comfort with painful symptoms. The socket design should aim to decrease the pressure along intolerant areas and promote higher stresses at more tolerant areas In addition, the socket should stay in place to provide the alignm ent needed to operate in a natural fashion 16 1.2.2.2. Problems in the Socket Wearing The major drawback of the socket fitting is the skin traumas that it generates. In fact, s kin ruptures and irritation are caused by large shear loads and friction respectively. Large normal and shear loads blocks the natural blood circulation at the residual limb area contributing to skin traumas. Also, tightness of the socket fit produces a perspiration increment at cer tain areas causing humid environments which lead to discom fort and skin damage. A tighter fit socket will prevent the socket from slipping off the residual limb Looser fit sockets will cause it to slip off

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9 easier. Finally, r egardless of the load transfer of the socket to the residual limb efficiency, the socket will not be used if it generates pain or any discomfort on the patient 7, 17 1.2.2.3. Traditional Socket Manufacturing In prosthetics the ai m when designing a socket is creating a comfortable weight bearing socket that enables the soft tissue of the stump to be compressed at pressure tolerant areas, and relieved at pressure intolerant areas. The following principles should be addressed in the production of the socket: accurate measurement of the stump geometry, close fitting o f the prosthesis to the stump, good response to forces and mechanical stress, safety, and minimal impact on blood circulation 4 As a result, generating sockets is high skill process. The socket fabrication follows several stages: wrapping, casting, modifying thermoforming and assembly The first stage consists in recording physical inf ormation of the residual limb and casting a nega tive mold using plaster wraps ( Figure 7 a, Figure 7 b ). The second stage implies the generation of a positive mold by pouring a mixture of plaster of Paris, vermiculite if needed and water into the previous cast ( Figure 7 c ) Before pouring the mixture, a st eel pipe is placed at the center of the negative mold 1 inch from the bottom. This tube will connect the mold to the vacuum system The positive mold is then modified by adding or removing material from the mold. These adjustments are based on the physiolo ( Figure 7 d ) Finally, a flat thermoplastic sheet is heated and deformed onto the positive mold connected to a vacuum line that helps the heated sheet reproduce ( Figure 7 e ). The vacuum is used to prevent the formation of air cavities in the interface between the thermoformed plastic and the plaster mold. The desired shape of the socket is acquired by removing the excess of thermoformed material a ttached to the plaster mold ( Figure 7 f ) After the socket is generated, the socket is assembl ed to the other elements of the prosthesis ( Figure 7 g ). Finally, the patient tries and evaluates the fitting of the socket in the residual limb ( Figure 7 h ) If the socket is rejected, the physician modifies the plaster

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10 acceptable. Later, the fin al socket is thermoformed again. O ther components of the artificial limb are assem bled to the socket to provide functionality and cosmetic appearance 10 Figure 7 : Traditional prosthetic socket m anufacturing s tages 9, 18, 19

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11 1.2.2.4. Socket Fitting Process The following chart describes the sequence flow of the processes undertaken during the socket manufacturing and fitting. Figure 8 : Traditional socket fitting p rocess 1.2.2.5. Computer Aided Socket Design and Manufacturing Computer aided design (CAD) and computer aided m anufacturing (CAM) technology is well known to help in the automation and the precision of a manufact uring process resu lting in a

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12 substantial increase in final product quality and a reduction of fabrication process time. The CAD software will help to generate and visualize a three dimensional ( 3 D ) model that enables rapid virtual modifications of the pro ducts. The CAM software/hardware interface will generate the codes that control the automated machines. CAD/CAM technology has been widely used in many applications where a CNC machine is needed. However, the increasing influence of this technology has pen etrated in the medical field. A new research field of computer aided socket design (CASD) and computer aided socket manufacturing was subsequently born. The aim of this research field is to shorten and automate the traditional and laborious fabrication pro cess of the prosthetic socket manufacturing 9 1.2.2.6. Rapid Manufacturing Methods class of machine technology. It involves adding and b onding materials in layers to form objects, RP include the fact that objects can be formed with any geometric complexity or intricacy, reducing the const ruction of complex objects to a manageable, straightforward, and relatively fast 20 (CAD) based automated additive manuf acturing process to construct parts that are used directly as finished products or components 21 However, it is wise to mention that some references define the fabrication of molds using rapid prototyping techniqu es as rapid manufacturing. On the other hand, fabricated using rapid prototyping techniques 22 Ano ther approach availabl e in the market is fabricating the molds using foam blank CNC milling machines. These are computer numerically controlled machines which are capable to produce complex geometries on a foam block with high accuracy. However, molds produced by

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13 this technique do not tolerate high temperatures similar to those app lied in thermoforming processes (). Rapid prototyping and rapid manufacturing of sockets have been done previously. This work is focused on rapid tooling as a new alternative to facilitate prosthetic s ocket fabrication ( ) 1.2.2.7. Potential for New Approaches Three dimensional s canning is a new technique that collects data from the surface of physical objects and generates a 3 D model file compatible to CAD software Under the CAD environment, prosthetists have the opportunity to precisely modi fy the geometry of the model to create the appropriate fit between the socket and residual limb. When the model is finished, STL file is generated to be printed using any rapid prototyping technique depending on the applic ation. Rapid Prototyping (RP) is a technology that enables to automatically produce a 3 D physical object from a virtual CAD model. 3 D scanning and RP have the potential to substantially decrease the time spent by the prosthetists and technicians to fabri cate the mold of the sockets for prosthetic applications. Figure 9 describes the socket manufacturing process using rapid tooling. Moreover, the CAD models of residual limbs can be annexed to patient medical hist ory file and can be reprinted at any time if the socket fitting is appropriate The 3 D printing mold can be modified and reprinted after the original mold is destroyed saving storage space in prosthetists clinics. In addition an electronic medical recor d of the patient can keep track of all the changes made from the original residual limb scanned mold. The resulting history will enable improved fitting methods. S cheduled scans could provide important information to prosthetists to analyze precisely the c hronological changes on the residual limb therefore preventive modifications can be made on the thermoforming mold to ensure a better fit and better patient care More complete discussion of the potential benefits of using rapid tooling for prosthetic sock et mold manufacturing is presented on Chapter 2.

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14 Figure 9 : Potential for new approaches in socket manufacturing 1.3. Thesis Outline The thesis proceeds as desc ribed next. Chapter 1 introduced the importance of prosthesis for resid ual limbs, terminology and basic components in prosthetics, the concept of computer aided socket design and manu facturing. Chapter 2 reviews research efforts in the different socket modeling approaches, available socket manufacturing techniques, material

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15 p roperties required in socket performance, and the value of three dimensional printing of rapid tooling molds for thermoforming of prosthetic sockets Chapter 3 describes the tests and specimens fabrication by which the material s were characterized to analy ze their performance. Chapter 4 presents and evaluates alternative materials with different post treatments for rapid tooling mold fabrication Chapter 5 recommends future research areas of study.

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16 Chapter 2 : Literature Review Th is section will desc ribe the current alternatives on socket modeling and manufacturing. It will also provide theoretical background regarding to the rapid prototyping techniques and material properties involved in the mold fabrication and socket thermoforming. 2.1. Socket Modelin g Several studies have focused their attention on the improvement of the comfort, fabrication time and appearance of prosthetic sockets This section provides an insight of relevant works conducted in the socket design and fabrication process. 2.1.1. FEA Simulat ion Based F inite element a nalysi s (FEA) ha s been used to achieve better understanding of the behavior of the socket stum p interface, internal loads, shear and normal stresses at skin tissues FEA usually approximate complex engineering problems, and its ac curacy to predict relevant results will depend on the determination of the material properties boundary conditions and simplifications of the model 23 During the last decades, many research efforts have been d evoted to create three dimensional residual limbs models to be analyzed using FEA. One challenge is gathering residual limb data. Colombo et al 4 proposed the acquisition of stump morphology using a combination of Mag netic Resonance Images (MRI), Computer Tomography (CT) and Laser Scanner techniques. MRI and CT provide information of the internal structure including bones, m uscles, fat tissue and skin. A noncontact laser acquires the data of

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17 the external geometry of th e residual limb providing a high accuracy three dimensional representation of the stump anatomical shape. Then the three different models are assembled to generate a definite model. Indentation tests are performed for material characterization of the soft tissue. Finally, the 3 D model is used for donning and gait simu lation that aims to verify wear rate and analyze the biomechanical behavior of the socket limb interface respectively. Stereolithography (SLA) rapid p rototyping technique was chosen to create the model of the socket. However, SLA material properties are inferior to traditional socket manufacturing methods. Winson et al 24 illustrates the use of computational analysis to predict prosthetic socket fit b ased on the pressure distribution during single support stand. An indenter was use d to record s stump. In addition, MRI technique is used to build a residual FE model. I ts simulation reveals the pressure distribution on the residual limb at the surface underlying the indenter. The socket fabrication is carried out by replicating the residual limb mold using foam carving machine. The prosthetic socket is thermoformed over the liner using a plastic material. As a result a prosthetic socket was made that induced no pain in the amputee subject. Shuxian et al 3 proposes an innovative reverse engineering application for 3 D reconstruction of residual limb. The process start s with CT scanning of the residual limb. The contours of skin and bones are achieved through image processing. The drawback form this approach is the elevated costs. However, it can provide higher accuracy, visible bony structure and less laborious work for the phy sician. Lee et al 25 proposed the modeling of the contact interface including the friction/slip conditions and pre stresses applied on the limb within a rectified socket. The residual limb and socket were modeled as two separate. It was found that peak normal and shear stresses over the regions where socket undercuts were made reduced. Faustini et al 23 analyzed a patellar tendon bearing prosthetic sockets with integra ted compliant features designed to relieve contact pressure between the residual limb and socket.

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18 The quasi static FEM model was composed of a socket, liner and residual limb and. The geometry of the residual limb, liner and socket were acquired from compu ted tomography (CT) data of a transtibial amputee. The compliant mechanism consisted of thin wall sections and two variations of spiral slots integrated within the socket wall. The results suggest that the integration of local compliant features is an effe ctive method to reduce local contact pressure and improve the functional performance of prosthetic sockets. 2.1.2. 3 D Scanning Based Francis et al 9 described a CASD/CASM method for prosthetic socket. The proposed method rotated and several data poin ts are acquired horizontally by the sensor. The data collection will generate a CAD model subject to modifications under any CAD software e nvironment and conversion to an STL file for CAM convenience. After further transformations, an SML file, which contains a list of instructions for the head movements and material flow rate, is generated to begin the fabrication stage supported in a Rapid Prototyping technique Fused Deposition Modeling (FDM) provided good appearance and merely acceptable material properties to the fabricated socket. The major drawback of the method relies on the manufacturing time (about 30 hrs) which was not considered to be cost effective. The method considered here improves on this by manufacturing a mold that admits to rapid modifications. Cheng et al 26 presented an approach that combines scanning technology, computer aided des ign and Rapid Prototyping. Residual limb casts from transtibial amputee s are scanned using a 3 D laser d igitalizer. Af ter the CAD data is generated, m odifications are performed prior fabrication using FDM technique.

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19 2.2. Socket Manufacturin g Technologies 2.2.1. Thermo forming Thermoforming is a well known manufacturing process in which a thermoplastic sheet is exposed to elevated temperature and then deformed onto the desired mold shape. The process starts heating the thermoforming material by radiant electric heaters l ocated on both sides of the plastic surface sheet. The duration of the heating cycle will depend on the polymer, its thickness, and color. Then, the softened plastic is placed onto the molds. In which negative pressure (vacuum generated) is used to draw a preheated sheet into the mold cavity. Normally, thermoforming molds have holes, so the vacuum line can apply a negative pressure. In prosthetic thermoformed socket the molds are inherently porous since they are plaster based 27 Figure 10 : Thermoforming process schematic 28 2.3. Why 3 D Printing for Rapid Tooling in Prosthetics? Three dimensional printing provides a great alternative for RP applications in prosthetics because is the fastest, lowest cost of all RP methods, and it produces inherently porous prototypes. This technique is ideal to emulate the plaster based molds that are used for thermoforming sockets due to the following reasons. Plaster an d the Zcorp powder have are both gypsum based

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20 Both 3 D Printing and plaster casting produce porous parts. 3 DP is an inexpensive high speed rapid prototyping process with an average build time of one vertical inch per hour, even a part several inches tall can be built within a normal work day. 3 D printed molds can be thermoformed and vacuumed using the traditional approach that has been performed by prosthetists for many years. In the case the mold needs to be slightly modified, regular plaster mixture ca n be adhered to the mold surface therefore the mold does not have to be reprinted. C urrent rapid prototyping technology cannot replicate the mechanical properties of a traditionally manufactured socket. Given the critical lo ad bearing role of the socket, i t is easier to generate rapid tooling of th e molds than the socket itself. Figure 11 : Rapid tooling, rapid manufacturing and traditional socket manufacturing comparison

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21 The rapid manufacturing of a socket is the generation o f an end user element that is going to be permanently worn by the patient. The material properties of the current RP methods are not good enough to overcome the performance of the thermoformed polymer sockets. The rapid tooling of the molds is the reproduc tion of the residual limb being printed in a porous material that has properties similar to the t raditional plaster based molds. Due to normal physical changes, residual limb shape tend s to change slightly with time. Therefore, socket fabrication becomes a n iterative process aiming to find the most comfortable fitting for the patient. The main advantage s of rapid to oling over rapid manufacturing processes are not only that RT has the fastest fabrication speed but also the flexibility t o make modifications f aster In order to make these modifications 3 D printed molds can be physically modified in the traditional way that plaster casted molds are modified This affects new sockets fabricated via thermoforming using these molds. On the other hand, r apid manufa ctured sockets cannot be modified at all after fabrication The modifications have to be done digitally to the CAD design and the s ocket has to be remanufactured increasing the fabrication time due to slow rates of this rapid prototyping technique. 2.3.1. Rapid P rototyping Kenneth Cooper states that Rapid Prototyping (RP) refers to the layer by layer fabrication of three dimensional physical models directly from a computer aided design (CAD). This additive manufacturing process provides designers and engineers the capability to literally print out their ideas in three dimensions. The RP processes provide a fast and inexpensive alternative for producing prototypes and functional models as compared to the conventional routes for part production 22 Dr. Frank Liou, professor in the mechanical engineering department at the University of Missouri Rolla, considers RP is based on layered manufacturing, which builds a part in a layered fashion typically from the bottom up. It makes use of an old technology printing. A layer of

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22 material is printed or laid down on a substrate with careful control. When various layers are stacked together, it forms a 3 D object. Conceptually, it is like stacking many tailored pieces of cardboard o n top of one another. Part geometry needs to be sliced, and the geometry of each slice determined. It is computer controlled and fully automated. Therefore, it is fully compatible with the CAD/CAM system for concurrent product development 20 Rapid Prototyping (RP) is a technology that enables to automatically re pro duce a 3 D physical object from CAD data It consists of a 3 D printer that constructs the physical prototype commanded by the CAD data. The application s of RP are endless such as in the automotive, aerospace, medical, and consumer products industries. For instance, it can be used to test shape, size or strength of designs, produce complicated geometry shapes and fabricate end user products. RP decreases the time spent in manufacturing processes allowing the manufacturers to commercialize their products faster and cheaper. Even though RP can be performed through various techniques, a common process is taken in this technology. First, a 3 D model is generat ed using a Computer Aided Design software package such as Solid Edge, Solid Works or PROEngineer. Next, the model is converted to a STL file which is a file format commonly used in the RP industry. This format represents three dimensional models as an asse mbly of triangles. Then, the STL files are sliced into layers that will be 3 D printed in an automated fashion. Post processing may be needed to improve the product quality. Rapid prototyping can be used to generate parts directly. This technique is calle d rapid manufacturing and has been previously used in prosthetics. Previous research efforts have used fused deposition manufacturing for socket fabrication. Other approach of rapid prototyping is rapid tooling which is the fabrication of the tooling for t he further manufacturing of the final part. This work considers rapid tooling of the molds because it offers several advantages in the process fabrication. These include improved material properties of final socket, ease to perform modifications, lower cos ts and faster fabrication times. Next are described the most common RP techniques.

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23 Figure 12 : Comparison between rapid tooling and rapid manufacturing Figure 12 shows the schematic co mparison between rapid tooling and rapid manufacturing. This thesis considers rapid tooling of molds as the best option of rapid prototyping for sockets manufacturing in prosthetics due to the following reasons. Current fused deposition modeling materials do not meet the requirements needed in a prosthetic socket in terms of strength and comfort. In addition, Rapid tooling of the molds creates a more flexible process which is ideal for such an iterative process as socket manufacturing. This method provides the

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24 opportunity to physically modify the 3 D printed mold or digitally modify the mold and reprint it Finally, Rapid tooling offers lower costs and faster fabrication rates than rapid manufacturing preserving the mechanical properties of traditional metho ds. 2.3.1.1. Three Dimensional Printing Three Dimensional Printing (3 DP ) technology was originally developed at Massachusetts Institute of Technology (MIT) in 1993 and now commercialized by ZCorporation. The process starts with a bin filled of powder in a platform An ink jet head prints a liquid binder material over desired regions to be transformed as solid parts. Additional powder layers are applied and selectively printed after the platform has been lowered. The process is repeated until the part geometry is ob tained. In other words, this technique prints 2 D images per layer on the powder bed from bottom to top. Recently, a new gypsum based material and a new binder system have replaced the initial starch based powder and the water based binder. It is important to state 3 D printing produces weak parts initially when removed from the powder bed, but the porosity characteristic of the material enable s the improvement of the mechanical properties. T he final porous prototype is post treated to improve strength, sur face finish, durability and overall quality. P ost processing consists of removing excess of unbound powder with pressurized air and inf iltrating the parts using wax, epoxy, C yanoacrylate (CA) or other sealants. The main advantage of using inkjet printing t echnology is that the process is able to operate at high speeds with minimal costs.

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25 Figure 13 : 3 D ink jet p rinting apparatus s chematic and p rocess 21

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26 Current Zcorp printers availabl e in the market are described in the following table Table 1 : Technical s pecifications of Zc orp printers 29

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27 2.3.1.2. Fused Deposition Modeling Fused deposition m odeling (FDM) is a layer by layer extru sion based rapid prototyping process. This process extrudes a previously liquefied thermoplastic polymer through a controlled nozzle that travels throughout the XY plane The nozzle deposits small quantities of the polymer tracing the cross sectional bound ary layer and subsequently fills it with parallel filaments of the thermoplastic. The material deposited is used to create the part itself and supports where required. Recently, water solu ble supports have been developed for complex geometries. The lower p latform is maintained at a lower temperature to promote the polymer solidification. Then the platform lowers to initiate the deposition process again over the previous layer. This technique uses a wide variety of materials including polycarbonate, polyphen ylsulfone (PPSF) and, most commonly acrylonitrate butadiene styrene (ABS) 21 Figure 14 : Fused deposition manufacturing a pparatus 20

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28 2.4. Materi al Propert y Requirements of Socket Molds This thesis examines potential replacement mold materials suitable for rapid prototyping of the thermoforming molds. T he next sections will be devoted to overview the different material properties taken into account for the material characterization of the different materials and post treatments available for the rapid tooling molds. 2.4.1. Flow through Porous M edia Porous medium presents a rigid or microscopic deformable solid matrix with interconnected voids in the inner structure. Conventionally, the pore size is much smaller than the length of the specimen. Laboratory samples of porous medium are generally homogeneous, in the sense of the irregular pore structure reproduces itself in the various portions of the sample 30 F luid s fill the voids and find their way through the channeled interior structure suffering a significant pressure drop due to the narrow passages, but reaching a stable flow rate. Flow through porous media phenomena is important in traditional prosthetic socket manufacturing. The molds used for thermoforming the plastic sheet are connected to vacuum lines, and air has to travel through the micro channels of the material. Measurements and results related to the flow t hrough porous media will be discussed in chapter 3 and 4. 2.4.2. Mechanical Strength Mechanical properties are usually calculated from a stress strain curve obtained by measuring the response of the material under specific loads. For ductile materials, the mechan ical properties are obtained from a tensile test. The curve typically goes through an

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29 elastic region, which its maximum point is called yield strength, and a plastic region, which its maximum point is called tensile strength, followed by a breaking point o r failure. For brittle materials, the tensile test is not suitable since the material usually cracks when is placed in the grips of the tensile test machine. Instead, a bend test is more appropriate to test brittle materials where a stress deflection curv e can be obtained to calculate the mechanical properties of the material. The material strength is described by the flexural strength and the modulus of elasticity by the flexural modulus 31 Porous materials can be classified as brittle due to their mechanical behavior. In these materials, the yield strength, flexural strength and breaking strength are all the same. Porous materials usually have a better performance under compression loads than tensile loads. In fact, in the three points bending test the fracture of the specimen starts on the side exposed to tensile stress. Since plaster of Paris and Zcorp materials are brittle, three point bending tests will be used to assess flexural strength as described in chapter 3 and 4. 2.4.3. Wear Rate During the modification stage of the mold manufacturing, prosthetists remove material from the molds using sand paper and rasp. Adding vermiculite to the plaster of Paris mixture is a common practice when generating the mold. In addition, this material adds enhanced pneumatical permeability, reduces the overall weight of the mo ld and increases the wear rate of the mold. However, the mold cannot wear to easily or it would not survive the necessary handling without undesired changes Wear rate measures the ability to remove material from the outer surface of a component. This process can be achieved by mechanical attack of solids or liquids. Wear is known as the surface damage or removal of material form one or both of two solid surf aces in a sliding, rolling, or impact motion relative to one another 32 In the case of the rapid tooling molds,

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30 the wear obtained can be defined as abrasive wear. This type of wear occurs when material is removed from a surface by contact with hard particles. 2.5. Conclusions Throughout this chapter the state of the art on the socket modeling and manufactu ring were described. In addition, the most important material properties involved during the thermoforming process were analyzed. Finally, several reasons were stated to demonstrate the potential suitability o f 3 D printing technique for rapid tooling mold manufacturing.

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31 Chapter 3 : Material Characterization One objective of this work was to analyze the perfo rmance of the different materials available for socket molds manufacturing on the Zcorp printer This chapter illustrates the material characterization process including specimen fabric ation, apparatus configuration and testing methods. It also documents t he results of plaster of Paris based specimens. 3.1. Introduction The aim of material characterization in this work is to provide a quantitative comparison of the materials properties relevant in the socket manufacturing. Fo r this matter, tests have been selec ted to obtain the necessary da ta from the candidate material s. 3.2. Materials and Preparation Methods Plaster of Paris is a powder obtained from heating gypsum to 150C. It is used for the molding application to its particular characteristics that when mixed w ith water forms a paste which liberates heat and hardens 33 Vermiculite is a natural mineral that has the property to expand in the presence of heat creating a process called exfoliation. Vermiculite is the mineralogical na me given to hydrated laminar magnesium aluminum ironsilicate which resembles mica in appearance 34 For preliminary tests the main material used was a solidified mixture of plaster of Paris, water and vermiculate when appro priate. The mixture recipe proposes 1.7 grams of plaster per milliliter of water in the case of 100 % plaster concentration. Vermiculate is added to water plaster

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32 mixtures to decrease the weight of the socket molds due to its incredibly low specific weight Moreover, the inclusion of vermiculate facilitates the manual removal of material that is performed manually by the prosthetists when performing mold modifications. In this study, different concentration s o f plaster water vermiculate were tested. The fir st material analyzed was plaster of Paris since it is the material traditionally used by prosthetists for mold manufacturing. 3.3. Determination of Pneumatic Permeability The determination of the pneumatic permeability provides information concerning to the air flow through the porous media. This is relevant to the socket manufacturing since the thermoforming pr ocess includes vacuum pumping of the mold. 3.3.1. In this model, the pneumatic permeability is obtained as the coefficient of various components such as average flow of air trough the material, differential pressure across the material, length and area of the specimen to be tested. es the flow of homogeneous fluids in porous media. A schematic of the classical experiment setup is shown in Figure 15 It consist of a filter bed of height h bounded by horizontal plane areas of equal size A If o pen manometer tubes are attached at the upper and lower boundaries of the filter bed, the liquid rises to the heights h 2 and h 1 respectively from an arbitrary datum level.

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33 Figure 15 : Darcy's experiment 35 pressure and a constant of proport ionality Q= (1) w here, Q is the v olumetric flow rate [ m 3 /s or ft 3 /s] A is the flow a rea perpendicular t o L [ m 2 or ft 2 ] k is the permeability [m/s or ft/s] L is the s pecimen length [m or ft] p is the fluid pressure [Pa or psi] g is gravity [ m/s 2 or ft/s 2 ] and, z is the elevation [m or ft] 3.3.1.1. Pneumatic Permeability Pneumatic permeability is the capacity of a porous medium to conduct gas in the presence of a gas pressure gradient measured as the ratio of volumetric flow through a specimen to the resultant pressure drop across it. It is also known as pneumatic conductivity or permeability to air. Generally, Pn eumatic permeability is calculated from experimental data obtained from a

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34 3.3.2. ASTM Standard for Pneumatic Permeability Measurements The apparatus set up, specimen preparatio n, measurements and testing procedures were supported from ASTM Standard D6539 00: Test Method for Measurement of Pneumatic Permeability of Partially Saturated Porous Materials by Flowing Air The following formulae are provided by the Standard ( 2 ) where, Q av is the v olumetric flow at specimen average pressure and test temperature [m 3 /s], Q is the f low of air out of specimen [m 3 /s], P B is the t est barometric pressure [Pa], P I is the s pecimen inlet g age pressure [Pa], and is the s pecimen pressure drop [Pa]. ( 3 ) w here K p is the p neumatic permeability, [darcy] Q av is the v olumetric flow at specimen average pressure and test temperature [m 3 /s], is t he s pecimen pressure drop [Pa] L is the s pecimen length [m] A is the s pecimen cross sectional area [m 2 ], and is the viscosity of air at the test temperature [Pas]. 3.3.2.1. Specimen Fabrication (length) cylindrical specimen fulfills the ASTM requirements. After several experimentations, the test specimens are obtained from pouring the desired mixture of Plaster water vermiculate into a PVC pipe with the previously mentioned dimensions. After at least 2 days of curing time at room temperat ure the specimens can be tested.

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35 Figure 16 : Plaster of Paris based specimens in PVC pipes The rapid prototyped parts are printed in the 3 D printer Zcorp using an STL file extension. The prototype is modeled using any CAD s oftware and saving the file in the STL extension. In this case the specimens were designed using Solid Edge. Figure 17 : Rapid prototyped specimen for pneumatic permeability test

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36 After the rapid prototyped specimens were cleane d and post treated if needed, they were dip coated in rubber coating. This treatment was applied to ensure the air is going to flow through the specimens and not through the clearance between the specimen and the PVC pipe. Masking tape was applied to the e nds to avoid the coating clogging the pores where the air was going to flow. After one day of drying at room temperature, one end of a 2 in diameter 3 in length PVC pipe was covered with masking tape and partially filled with rubber coating T he already se aled specimen was immersed into the pipe and placed in the center of the pipe. The excess of the rubber coating that overflows after the specimen was embedded was cleaned. The specimens were cured overnight and the proper fittings were attached to both end s of the PVC pipes that enable the connection to the pneumatic permeability apparatus. Finally, the perimeter of the channels. 3.3.3. Apparatus Configuration This experimental through several fittings to achieve amplifications from the air line to the specimens and reductions from the specimens to the outlet. A differential pressure gage was installed to acquire th e pressure drop along the specimens. The differential pressure sensor provides an output voltage proportional to the pressure being applied. For this set up, the sensor used was the PX26 030DV from omega with a range of 0 30 psid. The most important measur ements in this experiment were pressure and volumetric flow rate. The data acquisition for these two parameters is described next. The pressure sensor was used to measure the pressure gradient and pressure at the inlet of the specimens. The pressure senso r generates an output voltage proportional to the pressure applied. The excitation voltage for the sensor was 5 Volts DC. The voltage was measured using a voltmeter that has the capability to measure DC voltage in millivolts.

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37 The volumetric flo w rate was c alculated using a bubble meter technique. This technique uses a container with a fixed volumetric capacity and a stopwatch. For this experiment, the time recorded was the time needed to replace one litter of water with the air that went through the specime ns. The stopwatch was able to record data with a resolution of ten th s of seconds. Figure 18 : Pneumatic permeability set up Figure 19 : Pneumatic permeability schematic apparatus To verify that t he pneumatic permeability set up was perfectly sealed preliminary steps had to be undertaken. Initially, the complete set up was immersed in wate r to identify any leakage while the air was flowing across the apparatus If a leakage was found in a permanent

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38 connection, silicone was applied to the connection. However, if the leakage was found in an interchangeable connection Teflon tape was applied to the internal threads of the connections. Finally, the set up was run using identical specimens expecting to o btain similar readings in the pressure differences and flow rate. After the apparatus was calibrated, the specimen to be tested was coupled to the system. After the air line was open Three to five minutes were need by the system to become stable and record the voltage output and time. Next, the pressure was slightly increased and the process is repeated until 4 readings are recorded for each specimen. 3.3.4. Results The following table is a typical table of results from the data obtained in the pneumatic permeabil ity tests. The first column labeled V1 is the reading from the output of the differential pressure placed at the ends of the specimens in millivolts The second column labeled conversion from millivolts to units of pressure using the PX 26 differ ential pressure transducer specifications of output range. The third column displays th e amount of time spent to fill one liter of air using bubble meter technique. The next column is the air flow rate across the specimens. The column labeled as V2 display s information of the absolute pressure obtained from the transducer. The next column is the conversion from millivolts to pressure units using the sensor specifications. The last two columns display the results using the average flow rate and the pneumatic permeability using the formulas form the ASTM standard. Table 2 : Typical data obtained from pneumatic permeability test V1 (mv) (Pa) time (s) flow (m^3/s) V2 (mv) inlet press (Pa) AVG FLOW (m^3/s) K (darcy) 2.5 0 5171 40.63 2.46 E 05 2.74 5667 2.38 E 05 0.807 2.03 4198 50.35 1.98 E 05 2.25 4653 1.93 E 05 0.806 1.5 0 3102 68.8 0 1.45 E 05 1.7 0 3516 1.42 E 05 0.803 1.28 2647 81.09 1.2 3 E 05 1.48 3061 1.21 E 05 0.800

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39 3.4. Determination of Flexural Strength In the three point bending test a load is applied at three points causing the bending of the specimen followed by the final failure of the specimen. In this arrangement, the load is applied by a loading nose at midspan of the two supports. The curve obtained from a bending test is commonly plotted showing the relationship between stress and deflection. The apparatus set up, specimen preparation, measurements and testing procedures were suppo rted from ASTM Standard D790 03: Test Method for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials. The following formulas are provided by the Standard (4 ) where, is the stress in t he outer fiber at midpoint, [psi] P is the l oad at a given point on the load deflection curve, [lbf] L is the support span, [in.] ,b and d are the width and depth of beam tested, [in.] Specimen preparation, measurements and testing procedures were suppo rted from ASTM Standard D790 03: Test Method for Flexural Properties of Unreinforced and Reinforced Plastics and Ele ctrical Insulating Materials. The most important characteristics of the test are Specimen Geometry: 6 in x 1.5 in x 0.35 in. Rate of crosshe ad motion: 0.0125 in/s Support span: 5.25 in. 3.4.1. Specimen Fabrication Plaster mixture specimens were fabricated using the following sequence. A negative silicone mold is previously sprayed with a mold release agent and filled with the appropriate mixture of plaster and vermiculate. The excess of material is removed carefully so a horizontal

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40 surface is obtained. The curing time for the plaster mixture is about 3 hours before the specimen can be released from the mold. The specimen can be tested after 2 days . Figure 20 : Molded plaster specimen The rapid prototyped specimens were printed in a standard ZCorp printer using STL files with the appropriate dimensions. Both rapid prototyped and molded specimens are prismatic bars with Figure 21 : Zcorp printed specimen for three point bending test

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41 3.4.2. Apparatus Configuration MTS Universal Testing Machine was the equipment used for the execution of the three point bending test. An exter purchased in omega, was added to the system in order to obtain more accurate readings at lower forces The bending fixtures were installed onto the testing machine with a span of 5.25 in. on the lower supports. The crosshead motion rate was fixed to be 0.00125 inches per seconds. Figure 22 : Three point bend test schematic apparatus

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42 Figure 23 : MTS universal testing machine with bending fixtures and low force sensor The data recorded using the MTS data acquisition software. The software writes a .txt file with the information of the displacement and force app lied during the test. This data can be easily imported in excel software spreadsheet to perform calculations. dimensions was measured with a caliper to be used in the stress calculations. The following graph displays the information obtained from a three point bend test of a specimen. F igure 24 : Ty pical load v s. displacement graph from three point bend test 0 2 4 6 8 10 12 0.06 0.065 0.07 0.075 0.08 0.085 0.09 load vs displacemet

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43 In this load vs displacement graph, it can be observed the brittle behavior o f the porous samples since no plastic deformation ocurred during the test 3.5. We ar Testing Traditionally, vermiculate was added to the plaster of Paris mixture to facilitate the removal of material from the porous material molds. In order to improve socket fit t his material property has a key role in the socket manufacturing since res haping is fundamental in the final stages of the socket mold fabrication. The three point bending test specimen s were used to directly measure the wear rate of the different materia ls and post treated materials. The following f igure shows in detail the app aratus and experimental set up that was used during the tests. Figure 25 : Wear test set up

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44 Figure 26 : Free body diagram of wear test setup From the summation of moments at the pin joint, it ca n be found that F N = W only if F F acts through the pin line of action. Therefore this distance was minimized in the wear test setup to maintain constant normal forces over the specimen and avoid moment due to friction force. The motion rate of the specime n s over the sand paper was 2 in/sec and the wear rate was obtained only in on e direction covering 8 inches over the sand paper Each pass of the specimen was done using fresh sand paper. The specimen rests in a 45 angle which minimizes frictional forces tha t tend to elevate the specimen form the sanding surface. The specimens are sanded over 3 M coarse grain sand paper with reference 332U 60 made of aluminum oxide Five specime ns were tested for each available material To quantify the wear obtained on th e s pecimens, the resulting worn surface area was scanned. The area of each specimen was obtained from each scanned image using a dimension tool in Canvas software. Figure 27 : Scanned images of exposed areas after wear rate test.

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45 The following graph illustrates the substanti al difference in the wear rate of the specimens using pure plaster of Paris and the mixture using 30% of vermiculite in volume. These two materials were analyzed due to their importance in real life prosth etic application. Figure 28 : Wear comparison of traditional materials The results illustrated in the graphs are the measured area exposed at the corner where the specimens were sanded. Needless to say the amount of area expo sed is proportional to the wear rate of the material. It can be observed that including vermiculate in the plaster water m ixtures increases the wear rate of the hardened material. 0.185 0.19 0.195 0.2 0.205 0.21 0.215 0.22 0.225 0.23 0.235 100 P 70 P Area (in 2 ) Materials Wear Comparison

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46 Chapter 4 : Evaluation of Alternative Materials 4.1. 3 D Printing Powder Two different powder were analyzed during this work. The basic information and advantages of each powder are mentioned next. Zp 130 is the traditional powder used by the three dimensional printers commercialized by Zcorp. The main advantages from this mate rial are the high feature and color definition, excellent dimension accuracy and great strength if infiltrated. The prototypes printed with this powder do not stand water because in presence of water they disintegrate. Zp 140 is a material that produces hi gh definition three dimensional parts with the possibility of water curing. Another outstanding property of zp 1 40 is its brightness. In fact, z p 140 prototypes are 180% whiter than zp 130 prototypes 36 The water curing can be performed using two techniques that include dipping or misting. However, this powder is not widely used 4.1.1. List of M aterials and Post treatments Cyanoacrylate is a high strength adhesive used to bond surfaces and is commonly named as CA. Generally, CA is an acrylic resin which rapidly polymerizes in the presence of water forming long, strong chains, joining the bonded surfaces together 37 CA is commercializ ed as super glue or krazy glue. The infiltration of the specimens us ed in this work was done using the commercially distributed Cyanoacrylate from Zcorp called ZBond which has a special slow cure formula.

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47 Another traditional infiltrant used in 3 D printed parts is epoxy. However, using epoxy as a post treatment for this mo ld rapid tooling is not convenient. The post treated layer will become significantly strong making it harder for further modifications. Also, the epoxy will completely seal the pores of the material making impossible the flow through the molds which is und esirable in this application. 4.1.2. Zp 130 Different post treatments were applied to the rapid prototyped specimens. For the zp130 specimens two approaches were used. Using different mixture ratios of acetone and Cyanoacrylate, 4:1 and 8:1, the specimens were in filtrated. The idea of these mixtures is to infiltrate the porous material with the Cyanoacrylate but leaving some of the pores open, so the air can travel through the micro channels inside the material. Experimental data has proven that specimens treated with pure Cyanoacrylate performed poorly in the pneumatical permeability test since all the pores were clogged and no flow was obtained through the specimens The 3 D printed specimens were cleaned and slightly sanded without affecting the original dimensi ons. The infiltrant mixture was applied slowly over the surface using a pipette providing sufficient time to penetrate the material. Infiltrant over saturation of the specimen was avoided by applying small amounts of infiltrant and removing it after the ma terial was unable to absorb it. The additional post treatment applied to the zp 130 specimen s was steaming the surface using a steam generator commercially used to remove wrinkles from clothing. This procedure was performed in a closed container for 2 3 mi nutes to allow the vapor to treat the surface. A special care has to be taken to avoid condensate water get in contact with the printed parts. Zp 130 printed parts will disintegrate if water is directly applied to them.

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48 4.1.3. Zp 140 Water was applied by two diff erent ways to the zp 140 prototyped specimens. Dipping the specimens in water for a short period until no bubbles came out from inside and misting the surface using a regular spray bottle. Since the specimens were small only 30 45 minutes drying time was required after dipped. The drying time for the sprayed specimens was 10 15 minutes. The following list shows the available materials and their proper post treatments that were used to fabricate the testing specimens. Table 3 : Avail able material with different post treatments Material Post treatment Reference Plaster of Paris None 100% Plaster Plaster of Paris 30% Vermiculate None 70% Plaster Plaster of Paris 50% Vermiculate None 50% Plaster Plaster of Paris 70% Vermiculate None 30% Plaster zp 130 None zp 130 untreated zp 130 Infiltrated with pure CA zp 130 CA zp 130 infiltrated with Acetone: CA (4:1 ratio) zp 130 CA (4:1) zp 130 infiltrated with Acetone: CA (8:1 ratio) zp 130 CA (8:1) zp 130 Steamed surface zp 130 V zp 140 N one zp 140 untreated zp 140 Misted with water zp 140 M zp 140 Dipped in water zp 140 D 4.2. Measurements of Performance The performance of the Zcorp materials were analyzed and compared to traditional plaster based materials in the areas of flexural streng th, permeability, and wear rate using the methods described in chapter 3. The results are summarized in the following sections.

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49 4.2.1. Strength The following graph was obtained from the three point bending tests applied to different materials with different post treatments. Figure 29 : Flexural st r ength of the different material configurations The results show that the post treated material flexural strength was increased compared to untreated Zcorp materials. The most important infor mation that can be observed in this chart is that the post treated Zcorp materials are in the same range of traditional plaster based materials. This means that 3 D printing materials after being post treated have acceptable strengths for the socket thermo forming application. Zp 130 infiltrated with p ure Cyanoacrylate has the highest flexural strength over all the RP materials, but is left out of the analysis since it has no pneumatic 0 100 200 300 400 500 600 700 800 900 1000 100% Plaster 70% Plaster 50% Plaster 30% Plaster zp130 CA zp130 CA (8:1) zp130 CA (4:1) zp130 V zp130 untreated zp140 D zp140 untreated zp140 M PLASTER BASED Zp 130 Zp 140 Flexural Strength (Psi) Flexural Strength

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50 permeability. However, t he parts infiltrated with mixtures of Cyanoacryla te and Acetone performed better than other Zcorp materials and do have flow of air through them. 4.2.2. Permeability The following graph was obtained from the pneumatic permeability tests applied to different materials with different post treatments. It is clear that the rapid prototyping materials, zp 130 and zp 140, exhibit the highest pneumatic permeability characteristics. Depending on the different post treatment and the corresponding material, the rapid p rototyping materials can approach the performance of t he traditional plaster of Paris vermiculate mixtures Thus, the traditional socket thermoforming process will not be affected by using rapid tooling molds. For the pneumatical permeability tests, zp 130 CA and 50% plaster were not tested. The 130 CA specim ens showed no permeability and 50% plaster is not clinically used in mold casting. Zp 30% was used in this test only for reference to see the effects of vermiculate addition to the pneumatic permeability.

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51 Figure 30 : Pneumatic pe rmeability of different material configurations 4.2.3. Wear The specimens used for the wear test were the same specimens used for three point s bend test. The test performed on these specimens was described in the previous chapters. The follo wing chart shows th e wear rate of the different materials and post treatments. 50% and 30 % plaster were not included in the experiment because they have no clinical application in the socket thermoforming process. Also, zp 130 CA was excluded from the test due to the fact t hat it does not have pneumatic permeability. The results are promising due to the fact that all the materials exhibit a similar wear rate to the traditional plaster based materials The final mold for 0.00E+00 2.00E 01 4.00E 01 6.00E 01 8.00E 01 1.00E+00 1.20E+00 1.40E+00 1.60E+00 1.80E+00 100% Plaster 70% Plaster 30% Plaster Zp 130 untreated Zp 130 V Zp 130 CA (1:4) Zp 130 CA (1:8) Zp 140 untreated Zp 140 M Zp 140 D Plaster Based Zp 130 Zp 140 Pneumatic Permeability (darcy) Pneumatic Permeability

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52 thermoforming the sockets should not be too soft becaus e it will loss dimensional accuracy, but it cannot be to hard that will prevent to make modifications at the surface of the mold. Figure 31 : Wear test results from the different material configurations 4.2.4. Dimensional S tability A fter the bars for three point bend testing were printed and post treated, measurement of the thickness and width were taken to compare the dimensional stability after post treatment. It is highly important to conserve the original dimensions of the printed parts in terms of accuracy. The following table show s calculated values from the obtained data, attached in the appendix, where it can be observer that no significant change in dimensions has occurred after post treatment for the two different materials 0 0.05 0.1 0.15 0.2 0.25 0.3 100 P 70 P 130 P 130 (1: 8) 130 (1: 4) 130 V 140 P 140 M 140 D Plaster Based Zp 130 Zp 140 Area (in 2 ) Materials Wear Comparison

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53 Table 4 : Relative error of thickness and width with respect of nominal dimensions Material Thickness Width Avg.Error (%) Stdev Error (%) Avg.Error (%) Stdev Error (%) zp 130 1.26 0.12 0.13 0.26 zp 130 CA 0.63 0.63 0.26 0.23 zp 130 CA (4:1) 0.83 0.16 0.54 0.43 zp 130 CA (8:1) 0.71 0.46 1.87 0.41 zp 130 V 1.75 0.81 0.35 0.36 zp 140 1.09 0.37 1.51 0.15 zp 140 D 1.26 1.04 1.38 0.15 zp 140 M 0.46 0.38 1.49 0.20 4.3. Build Up Test Additional flexural strength analysis was dev oted in this work to Zcorp printed specimens reinforced with plaster. The interest of this analysis is to observe the behavior of failure and compare the maximum strengths of the reinforced specimens. The specimens are reinforced with a thick layer of plas ter of Paris on one side to emulate the interface of a hollow mold backfilled with plaster. The specimens have the same dimensions and were tested using the same parameters employed on the three point bend test to obtain the flexural strength proposed by t he ASTM Standard D790 03 Additional plaster was added to one side of the specimens after post treated. Figure 32 : Reinforced specimen for flexural strength test The following graph shows the comparison between the tested spe cimens and non reinforced specimens

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54 Figure 33 : Flexural strength comparison between regular and reinforced specimens Unexpectedly some of the reinforced specimens showed lower strength T his could be due to the fact of poor adhesion between the plaster and the specimen. Another reason could be the moist ure from the plaster mixture may have affected the internal structure of the rapid prototyped parts. S pecimens that performed better were the zp 140 series since they can be p ost treated using water. 0 50 100 150 200 250 300 350 400 450 500 zp130 CA (8:1) zp130 CA (4:1) zp130 V zp130 untreated zp140 D zp140 M Zp 130 Zp 140 Flexural Strength Regular Specimens Reinforced Specimens

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55 4.4. Comparison to Traditional Materials 3 D printed prototypes using powder base d materials can be post treated to improve different mechanical properties. For the socket thermoforming manufacturing process the traditional socket mo ld has medium high flexural strength low pneumatic permeability and medium high wear rate The following table will summarize the performance of the different materials in terms of those three characteristics. Table 5 : C omparison o f performance of different materials. Material Flexural Strength Pneumatic Permeability Wear rate 100% plaster High Low Medium 70% plaster Medium Low High 30% plaster Low Low High zp 130 untreated Medium High Medium zp 130 CA High N one Low zp 130 C A (4:1) Medium Low Medium zp 130 CA (8:1) Medium Medium Medium zp 130 V Medium High Medium zp140 untreated Medium Medium High zp 140 D Medium Low Medium zp 140 M Medium Low Medium From the analysis of this table, it can be observed that the post trea tments applied to the different materials approximate the behavior of the 3 D printed molds to plaster casted molds. From the variety of comb inations of treatments on the Zcorp materials, zp 130 V, zp 130 CA(4:1) and zp 130 CA(8:1) should be a great altern ative because of their good fle xural strength, wear rate low cost and repeatability

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56 4.5. Thermoforming Tests Using Rapid Tooling Molds Since the enormous difference in the pneumatic permeability between plaster based mixtures and the pure zp 130, two thermofo rming molds were tested to analyze if the rapid prototyping material could be thermoformed when most permeable before post treatment Mold was produced by 3 D printing in zp 130 powder, with approximate dimensions to an forearm without a wrist. After the mold was printed, no post treatment was applied to it. The mold was thermoformed by a n experienced prosthetist The prosthetist suggested that no noticeabl e difference in the process was observed comparing it from thermoforming with a plaster based thermof orming process. The resulting socket from the rapid tooling mold was normal in shape appearance and thickness of the plastic layer. The experienced prosthetist performing the thermoforming did not detect any problems due to the increased permeability. Figure 34 : CAD image of the preliminary mold tested.

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57 Figure 35 : Preliminary thermoformed socket using 3 D printed mold Figure 36 : CAD i mage of the preliminary mold tested Figure 37 : Preliminary thermoformed socket using 3 D printed mold

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58 4.6. Ease of Integration into Current Processes Figure 38 : Schematic process of rapid tooling of molds Ease of integration into the t raditional process is the great advantage of 3 D printing technique over other rapid prototyping techniques on socket manufacturing application. Prosthetists traditionally make the negative mold using plaster wraps. After the mold is manufactured, prosthet ists reduce in about 4% the volume of the plaster based mold. However,

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59 this process can be performed in an easier and more accurate fashion using a CAD software tool With the proposed method, the prosthetist will manually scan the residual limb with a han d held optical device. After that step, the prosthetist will give the cast to technicians to reproduce the positive mold. Using the 3 D printing method, the prosthetist would open the file and create a solid CAD version of the scanned image and then send i t to the Zcorp printer. I f further modifications are required after printing the mold can be easily reshaped using traditional processes including removal of material using a rasp, sanding the surface or adding material using plaster of Paris. When the de sired shape is obtained the 3 D printed mold can be thermoformed as well as a plaster casted mold. The final part can be 3 D scanned again to record the geometry in medical patient files. This will facilitate future adjustments of the socket. 4.6.1. Discussion Th is chapter provided meaningful data to compare the different materials and post treatments available for 3 D powder based printing technique. As well as thermoforming test that demonstrated the suitability to integrate the rapid tooling molds into the trad itional thermoforming process of socket manufacturing in prosthetics ap plications. The zp 130 V, zp 130 CA(4:1), zp 130 CA(8:1) an d zp 140 dipped show promising performance in the properties analyzed.

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60 Chapter 5 : Conclusion and Future Work Throughou t this thesis the suitability and integration of 3 D printing technique for molds manufacturing has been discussed and demonstrated. Different characterization methods were employed to analyze the performance of the different materials and available post t reatments to enhance specific properties. Flexural strength, pneuma tic permeability and wear rate were evaluated in this thesis to compare the combinations of materials and post treatments. The use of the 3 D printing for the fabrication of molds for therm oformed sockets can bring several advantages including higher accuracy in the acquisition of the anatomical geometry of the stump due to the 3 D scanning process. In addition, an electronic file of the scanned residual limb can be attached to the patient m edical history. This file can be reprinted at any time using the Zcorp printer. The following section will discuss some of the potential issues that can have a negative impact on the proposed method. 5.1. Size I ssues The biggest Zcorp printer available has a printing area capability of 10 in x 15 in. With this limitation, some of the mold might not be able to be printed as one solid piece. To overcome this disadvantage, the molds are printed in multiple pieces that can be assembled together to produce an integ ral mold with the original shape. This process can bring alignment issues on the surface and also on the longitudinal axis. To integrate multiple pieces plaster of Paris can be used or glue type substances. However, special care needs to be dedicated to th e joint lines to avoid ridges

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61 that can be reflected in the final thermoformed socket and can create high stress lines at the residual limb. It is suggested to analyze in the future different design solutions for the alignment fixtures. This is a key point to ensure the rapid prototyping molds are acceptable to be used for thermoforming sockets. It is imperative to not lose the precision obtained by the 3 D printing technique due to rotational or longitudinal misalignments. 5.2. Solid/Hollow P arts D esigns To be a ble to thermoform a plastic sheet onto a 3 D printed mold, the mold need to have inserted an air line pipe at the base. Hence, during the design stage at the CAD environment a 1.5 in diameter whole needs to be created from the base of the mold. This space will allow clearance for the pipe to be inserted freely, and the void filled with plaster to support the pipe that will be connected to the vacuum line. With this inevitable step in the process, an alternative for low cost mold production appears. The prod uction of hollow designed molds could substantially reduce the cost of printing, but conserving the high accuracy of 3 D printing technique. The final properties of the mold will be more similar to plaster casted molds since the volume occupied by the plas ter of Paris will be dominant. Again, future research should investigate the effects of backfilling the rapid prototyped shells with plaster. Initial observations showed no noticeable changes in the volume or surface of the molds. However, more investigati on should be focused on effects of this alternative.

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62 References 1. Jeffrey J. Cain, MD, and Paddy Rossbach ACA President & CEO. Special report: Paving the way toward better health. In Motion: A Publication of the Amputee Coalition of America 2005 September/October 2005;15(5). 2. Amputation, Handobook of Disabilities [Internet]; c2001. Available from: http://www.rcep7.org/projects/handbook/amputation.pdf 3 Shuxian Z, Wanhua Z, Bingheng L. 3D reconstruction of the structure of a residual limb for customising the design of a prosthetic socket. Medical Engineering & Physics, 2005 1;27(1):67 74. 4. Giorgio Colombo, Stefano Filippi, Paolo Rissone, Caterina Rizz i. ICT methodologies to model and simulate parts of human body for prosthesis designs. Lecture Notes in Computer Science [Internet]. ;4561/2007. 5. Lyon CC, Kulkarni J, Zimerson E, Van Ross E, Beck MH. Skin disorders in amputees. Journal of the American Ac ademy of Dermatology, 2000 3;42(3):501 7. 6. Mak State of the art research in lower limb prosthetic biomechanics socket interface: A review. Journal of Rehabilitation Research and Development 2001;38(2):161. 7. Portnoy S, Yizhar Z, Shabshin N, Itzchak Y, Kristal A, Dotan Marom Y, Siev Ner I, Gefen A. Internal mechanical conditions in the soft tissues of a residual limb of a trans tibial amputee. Journal of Biomechanics, 2008;41(9):1897 909. 8. Zhang M, Turner Smith AR, Roberts VC, Tanner A. Frictional act ion at lower limb/prosthetic socket interface. Medical Engineering & Physics, 1996 4;18(3):207 14. 9. Francis E.H. Tay., M.A. Manna., L.X. Liu. A CASD/CASM method for prosthetic socket fabrication using the FDM technology. Rapid Prototyping Journal [Intern et]. ;8(4)Available from http://www.emeraldinsight.com/1355 2546.htm 10. P. Ng, bP.S.V. Lee, J.C. Goh. Prosthetic sockets fabrication using rapid prototyping technology. Rapid Prototypi ng Journal [Internet]. ;8(1)Available from http://www/emeraldinsight.com/1355 2546.htm 11. Herbert N. A preliminary investigation into the development of 3 D printing of prosthetic sock ets. Journal of Rehabilitation Research and Development 2005;42(2):141.

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63 12. Comrie JD, Marcovitch H, Thomson WAR. Black's medical dictionary. London: A. & C. Blackv. : ill. (some col.) ; 23 cm.; Frequency: Irregular; Publishing history: Began in 1906.; A lternate title: Medical dictionary; 50011 Description based on: 6th ed., published in 1920.; 50021 Latest issue consulted: 41st ed., published in 2006; 50022 Editors: 1953, J.D. Comrie ( 1953) with W.A.R. Thomson; 1955 W.A.R. Thomson; Dr. Harvey Marcovit ch.; 58023 Issued also in the USA: Totowa, N.J. : Barnes & Noble Books, ; Lan ham, MD. : Scarcrow Press Inc 13. Upper Limb Prosthetics [Internet]: eMedicine; c2007 [cited 2008 06/15]. Available from: http://www.emedicine.com/pmr/TOPIC174.HTM#section~Multimedia 14. Prosthetics [Internet]; c2005 [cited 2008 06/15]. Available from: http://www.opinmotion.co m/services.htm 15. Below Elbow Prosthetics Wrist Disarticulation [Internet] [cited 2008 06/15]. Available from: http://www.amannoandp.com/products/ 16. Lee WC, Zhang M, Mak AF. Regional dif ferences in pain threshold and tolerance of the transtibial residual limb: Including the effects of age and interface material. Archives of Physical Medicine and Rehabilitation, 2005 4;86(4):641 9. 17. Hachisuka K, Nakamura T, Ohmine S, Shitama H, Shinkoda K. Hygiene problems of residual limb and silicone liners in transtibial amputees wearing the total surface bearing socket. Archives of Physical Medicine and Rehabilitation 2001 9;82(9):1286 90. 18. New Fitting Techniques At Swanson For Amputees Gives Rise to the Swanson Fitting Method [Internet]06/20]. Available from: http://www.swansonopcenter.com/swanson_method.htm 19. [Internet]; c2006 [cited 2008 06/2]. Available from: http://www.copelaos.org/pdevices.html 20. Liou FW. Rapid prototyping and engineering applications: A toolbox for prototype development. CRC Press; 2008. 21. Hopkinson N. Rapid manufacturing: An indu strial revolution for the digital age. John Wiley & Sons Inc.; 2006. 22. Cooper KG. Rapid prototyping technology: Selection and applicati on. Marcel Dekker, Inc.; 2001. 23. Faustini MC, Neptune RR, Crawford RH. The quasi static response of compliant prosthe tic sockets for transtibial amputees using finite element methods. Med Eng Phys 2006 3;28(2):114 21. 24. Lee WCC, Zhang M. Using computational simulation to aid in the prediction of socket fit: A preliminary study. Medical Engineering & Physics, 2007 10;29 (8):923 9. 25. Lee WCC, Zhang M, Jia X, Cheung JTM. Finite element modeling of the contact interface between trans tibial residual limb and prosthetic socket. Med Eng Phys 2004 10;26(8):655 62. 26. Tan Kim Cheng, Peter Lee Vee Sin, Tam Kock Fye, Lye Sau Li n. Automation of prosthetic socket design and fabrication using computer aided Design/Computer aided engineering and rapid prototyping techniques. The First Symposium of Prosthetic and Orthotics 1998.

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64 27. Mikell P. Groover. Fundamentals of modern manufactu ring: Materials, processes and systems. 3rd ed. ; 2006. 28. Tutorial:The thermoforming process [Internet] [cited 2009 1/27/2009]. Available from: http://www.oshore.com/pro ducts/archived/thermoforming.html 29. Z Corp. Homepage [Internet] [cited 2009 3/12/2009]. Available from: http://www.zcorp.com/ 30. Dagan G. Flow and transport in porous formations. Berlin ; New York: Spri nger Verlag; 1989. G. Dagan. : G. Dagan.; 50411 Includes bibliographical references (p. 451 461). 31. Askeland DR, Phul PP. The science and engineering of materials. 4th ed. Pacific Grove, CA: Thomson Brooks/Cole; 2003. Donald R. Askeland, Pradeep P. Phul . : Donald R. Askeland, Pradeep P. Phul.; 50411 Includes bibliographical references (p. 975) and index. 32. Bhushan B. Principles and applications of tribology. New York: John Wiley; 1999. Bharat Bhushan. : Bharat Bhushan.; 50011 "A Wiley Interscience pu blication."; 50412 Includes bibliographical references and index. 33. A Brief History of Pla ster [Internet] [cited 2009 3/3 /2009]. Available from: http://www.artmolds.com/ali/history _plaster.html 34. Vermiculite Home Page for Information about Vermiculite --A Mineral with Many Uses [Internet] [cited 2009 3/3/2009]. Available from: http://www.vermiculite.net/ 35. Modeling Groundw ater Flow and Contaminant Transport (MGFC) Computer Mediated Distance Learning course by Jacob Bear [Internet] [cited 2009 2/18/2009]. Available from: http://www.cmdlet.com/dem os/mgfc course/mgfcdarcy.html 36. Material Options [Internet] [cited 2009 3/18/2009]. Available from: http://www.zcorp.com/Products/3D Prin ters/Material Options/spage.aspx 37. Cyanoacrylates Health Information Library Penn State Her shey [Internet] [cited 2009 3/3 /2009]. Available from: http://pennstatehersh ey.org/healthinfo/hie/1/002894.htm

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65 Appendi ces

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66 Appendix A Table 6 : Measured dimensions of specimens. # Material Thickness (inches) Width (inches) 1 zp130 pure 0.345 1.251 2 zp130 pure 0.3455 1.253 3 zp130 pure 0.3455 1.255 4 zp130 pure 0.346 1.2525 5 zp130 pure 0.346 1.2465 1 zp130 4:1 0.347 1.255 2 zp130 4:1 0.3475 1.253 3 zp130 4:1 0.3485 1.2495 4 zp130 4:1 0.345 1.252 5 zp130 4:1 0.351 1.257 1 zp130 8:1 0.347 1.261 2 zp130 8:1 0.348 1. 251 3 zp130 8:1 0.347 1.259 4 zp130 8:1 0.3465 1.251 5 zp130 8:1 0.347 1.262 1 zp130 CA 0.354 1.277 2 zp130 CA 0.3545 1.279 3 zp130 CA 0.3515 1.268 4 zp130 CA 0.351 1.268 5 zp130 CA 0.3515 1.275 1 zp130 V 0.3473 1.251 2 zp130 V 0.3425 1.257 3 zp 130 V 0.3415 1.261 4 zp130 V 0.3465 1.251 5 zp130 V 0.3415 1.252 1 zp140 pure 0.352 1.271 2 zp140 pure 0.355 1.269 3 zp140 pure 0.355 1.267 4 zp140 pure 0.354 1.267 5 zp140 pure 0.353 1.2705 1 zp140 M 0.353 1.268 2 zp140 M 0.356 1.269 3 zp140 M 0 .36 1.264 4 zp140 M 0.351 1.268 5 zp140 M 0.352 1.267 1 zp140 D 0.353 1.273 2 zp140 D 0.35 1.268 3 zp140 D 0.351 1.267 4 zp140 D 0.353 1.267 5 zp140 D 0.351 1.268