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Fabrication of low cost soft tissue prostheses with the desktop 3D printer

Fabrication of low cost soft tissue prostheses with the desktop 3D printer OPEN Fabrication of low cost soft tissue prostheses with the desktop 3D printer SUBJECT AREAS: MECHANICAL 1,2 1,2 1,2 Yong He , Guang-huai Xue & Jian-zhong Fu ENGINEERING IMPLANTS The State Key Lab of Fluid Power Transmission and Control Systems, Department of Mechanical Engineering, Zhejiang University, BIOMEDICAL ENGINEERING Hangzhou 310027, China, Zhejiang Province’s Key Laboratory of 3D Printing Process and Equipment, Department of Mechanical Engineering, Zhejiang University, Hangzhou 310027, China. Received 12 August 2014 Soft tissue prostheses such as artificial ear, eye and nose are widely used in the maxillofacial rehabilitation. In this report we demonstrate how to fabricate soft prostheses mold with a low cost desktop 3D printer. The Accepted fabrication method used is referred to as Scanning Printing Polishing Casting (SPPC). Firstly the anatomy is 16 October 2014 scanned with a 3D scanner, then a tissue casting mold is designed on computer and printed with a desktop 3D printer. Subsequently, a chemical polishing method is used to polish the casting mold by removing the Published staircase effect and acquiring a smooth surface. Finally, the last step is to cast medical grade silicone into the 27 November 2014 mold. After the silicone is cured, the fine soft prostheses can be removed from the mold. Utilizing the SPPC method, soft prostheses with smooth surface and complicated structure can be fabricated at a low cost. Accordingly, the total cost of fabricating ear prosthesis is about $30, which is much lower than the current Correspondence and soft prostheses fabrication methods. requests for materials should be addressed to oft tissue prostheses are widely used in maxillofacial rehabilitation. Patient numbers is ever increasing due Y.H. (yongqin@zju. to the advancements in medicine, surgical techniques and in particular cancer survival rates . However, the edu.cn) or J.F. (fjz@zju. S high fabrication cost of traditional prostheses prompted the researchers to explore alternatives to reduce the edu.cn) cost and time of fabrication. Three-dimensional (3D) printing or rapid prototyping (RP) is a layered manufac- turing method that can be used to fabricate complex structures. It is an additive manufacturing (AM) process, fundamentally different from the conventional subtractive manufacturing processes. Using 3D printing a phys- ical object can be fabricated from a 3D computer-aided design (CAD) model layer by layer, more conveniently and more rapidly than other manufacturing means. Additionally, it is easy to customize a product according to personal requirement, consequently a wide variety of applications of 3D printing technology in soft matter 2–8 fabrication have emerged recently . The use of 3D printing can help in the development of omnibearing 4 5 biodevices . Such as described in the report by Wang et al., , who used hydrogel and cells to fabricate models that mimic complex soft organs in vitro with the help of 3D printing. Also, Landers et al., printed a hydrogel scaffolds using 3D plotter to attain a designed external shape and a well-defined internal pore structure . Many reports also discussed the fabrication of soft tissues for implant, and scaffolds with cell-seeded hydrogel 9–12 or collagen matrix for clinical application were developed . High-fidelity ears with collagen type I hydrogel scaffolds were fabricated by injection. Even following an extended period after implantation, they continue to effectively mimic the native auricle both biomechanically and histologically . To improve the mechanical properties of the fibrous collagen matrix, composite ear scaffolds with wire frameworks were used to ensure a 11 12 3D shape after implantation . Mannoor, M. S., et al printed bionic ears able to gather inductively-coupled signals from cochlea-shaped electrodes, demonstrating the merging capabilities of biological and nanoelectronic functionalities. However, because scaffolds or soft tissues based on tissue engineering are designed to acquire real tissues after implanting, further clinical study and a thorough ethics evaluation are still needed. 13,14 Furthermore, in 2003 Cheah et al., integrated CAD/CAM techniques for developing facial prostheses and described a complete fabrication process using the selective laser sintering (SLS) 3D printing technology. It is worth noting, they and Eggbeer et al. also discussed the difference between indirect mold production via silicone rubber molding and direct mold production via RP fabrication. In addition, a template-based framework was proposed to rebuild the nasal 3D model with the data from 3D and computed tomography (CT) scans . The results showed that this method had advantages over other rebuilding methods in terms of accuracy, speed, safety and cost. E. Bassoli et al., reported a combined 3D printing/indirect replication method to fabricate 3D vascular- like structures of soft tissue ; using the ProJet HD 3000 3D printer from 3D Systems Inc. to print the negative mold of the vascular structure. SCIENTIFIC REPORTS | 4 : 6973 | DOI: 10.1038/srep06973 1 www.nature.com/scientificreports A team from Italy led by De Crescenzio and Ciocca made a sig- in education, DIY manufacturing, research and industry. As illu- 18–20 nificant contribution to the facial rehabilitation field when they strated by the successful production of micro- and milli-scale reac- tionware with a desktop 3D printer (3DTouch) . reported a comprehensive solution to the design and fabrication of prosthesis. They created a real anatomic reference model library, The main task during the manufacture of soft prostheses is the namely the ‘‘Ear & Nose Digital Library’’, which can be very useful making of the casting mold, which is also the main component of the for the reconstruction of the facial defects. In addition, they described cost incurred during the whole prostheses fabrication process. If the casting mold can be fabricated using a desktop 3D printer, and as how the definitive acrylic ear cast mold was printed by Z Printer 310 (Z Corp, taken over by 3D system Inc. in 2012), which was then such printers become readily affordable, then doctors could fabricate the prostheses in their offices, or the patients could do it at home. transformed into a wax ear with the vinyl polysiloxane material. Nevertheless the staircase effect (contour like structure) caused by A team from UK led by Eggbeer and Bibb performed a long term the layered manufacturing is a challenge which impedes the acquisi- and remarkable research to study how to apply digital technologies in 1,15,21–25 tion of smooth surface in 3D printing. This drawback is especially maxillofacial prosthetics . Eggbeer et al., compared the pros- serious in the desktop 3D printer due to the layer thickness, as shown theses fabricated by 3D printing against a prosthesis made by con- in Fig. 1. ventional techniques . In their nasal prosthesis case study, 3D In this study, we focus on how to apply the low cost desktop 3D printing enabled the prosthetics to work in a more flexible manner. printer to print the casting mold. The fabrication method used is However, they determined that the directly printed prosthesis has called Scanning Printing Polishing Casting (SPPC). The key consid- poor mechanical properties and untested biological responses, and eration when using SPPC is how to fabricate a negative casting mold suggested that the best way is to print the prosthesis mold and cure with smooth surface inside, and will be addressed in this report. To the prosthesis with silicone rubber. Worth mentioning, skin features that end, the polishing method, which can ensure that the surface such as wrinkles and texture in auricular and nasal prostheses have quality of the mold is adequate to be used in the prostheses casting, been successfully fabricated by 3D printing . The time required for was systematically investigated. Moreover, it is proven that the soft prosthesis fabrication by 3D printing was found to be considerable prostheses can be affordably manufactured, under $30 each, at home shorter than that required by the conventional methods. or in a personal lab setting without any expensive technical equip- As the prosthesis is personally customized, mass fabrication meth- ment. SPPC also can be widely used in the fabrication of soft muscle, ods such as metallic mold casting or injection molding are typically hydrogel structure in tissue engineering, artificial skin, customized not suitable. A conventional process for the construction of pros- jewel, etc. theses is particularly lengthy, as it includes many steps: impression, plaster replica, base plate fabrication, mold fabrication, mold pack- ing, curing, and extrinsic finishing. The process is laborious and Methods The typical process of SPPC is shown in Fig. 2. Firstly, 3D data for the prostheses are expensive in addition to time-consuming. The maxillofacial prostho- acquired with a 3D scanner. Once acquired, the datasets are used to generate a digital dontist determines the correct size, shape, and position of the pros- 3D model of the negative mold for casting by using a 3D modeling software such as thesis for each individual patient, hand-sculpts an impression in wax, 3D max, Rhinoceros, or SolidWorks, etc. Subsequently, the 3D model is converted then casts the shape in silicone. A handmade silicone ear or nose into G code language by a slicing software tool, which can then be read by a desktop 3D printer. A common polymer filament, Acrylonitrile Butadiene Styrene copoly- costs up to $4000, and requires 5–7 hospital visits for customization. 26 mers (ABS), is applied for 3D printing. Since the multi-strip-like structure caused by The process takes 5–10 weeks in total . 3D printing will affect the prostheses surface quality, acetone vapor is used to elim- Many researchers have previously demonstrated 3D printing/RP inate the layer thickness effect of the mold, as ABS is soluble in acetone. After technology as an effective way to accelerate the prostheses fabrication polishing, silicone is poured into the mold. The soft prostheses can be easily pulled out/demolded from the mold because the solidified silicone provides extra strength process and reduce its cost. The primary material used in prostheses, and elasticity. either silicon or Polydimethylsiloxane (PDMS), is more suited to A Kinect depth sensor for Microsoft Windows was used to scan the original model, casting. The so-called rapid tool, soft tool or bridge tool fabricated and its digital dataset was saved as a STL file . The negative mold model was then by 3D printing is commonly used to cast prostheses. It should be designed using the Rhinoceros V4.0 software. The slice software Slic3r was used to generate G code files for the desktop 3D printer, RepGo X1, which was purchased noted, however, that the 3D printers used in this previous research from Xiangtan Dot Go 3D technology Corporation for about $570. were industrial-grade and therefore quite expensive. Indeed, the cost Silicone part A and part B (Dongguan Hongfeng Silicone Materials Co., LTD) were of fine prostheses mold-fabricated by an industrial 3D printer is still mixed in a 151 (weight: weight) ratio and stirred for 2 minutes, and then the mixture high, which has hindered the wider use of 3D printing. According to was degassed in a vacuum chamber for 10–15 minutes. ABS is a thermoplastic polymer material with high strength, good toughness and easy to machine. Nowadays the quote given by Magicfirm, LLC. Hangzhou, China, the fabrica- 3 it is widely used in FDM printing. However the poor surface finish quality has limited tion price is $2.2 per cm using the stereolithography apparatus the development of 3D printing, in both appearance and performance. A simple (SLA) of a 3D printer, indicating a cost of $411.80 for an ear mold polishing device has been assembled, as shown in Fig. 3. It includes a heater to with a size of 7.8 3 5.0 3 4.8 cm. A prosthetic product fabricated by 3D printing from Fripp Design & Research in the UK costs around $4,000 each, almost as much as a handmade product . If such pros- theses could be manufactured at home, the cost would drop dramat- ically, greatly benefiting patients. The desktop 3D printer (personal 3D printer), also known as the open source 3D printer, is very popular among the do it yourself (DIY) variants. The advantages of desktop 3D printer include low cost and as a result, many people can afford a small size printer with extremely low to zero toxicity and waste. With the expiration of the key patents of Fused Deposition Modeling (FDM), the technology used in desktop 3D printer, a large open-source development com- munity has emerged, and a desktop 3D printer now only cost $200– $1000. Two standard types of desktop 3D printer are the RepRap and the Fab@Home; however, everyone can change the desktop 3D printer design according to their requirements thanks to its open source Figure 1 | Staircase behavior in 3D printing (Ear negative mold, layer development. At present the desktop 3D printer is being widely used height 0.3 mm, taken by the author, Guang-huai Xue). SCIENTIFIC REPORTS | 4 : 6973 | DOI: 10.1038/srep06973 2 www.nature.com/scientificreports Figure 4 | Working principle of polishing device. The surface quality of the ABS mold is influenced by many polishing parameters such as temperature, vapor pressure, layer height of 3D printing, polishing time and model structure. A box mold was chosen as a standard sample, shown in Fig. 5. Figure 2 | Typical SPPC process (All photographs were taken by the Different layer-thickness ABS models were polished for different times to study how author, Guang-huai Xue). to achieve a better surface finish. The surface quality was assessed using an inductance type roughness tester, a SRT6200 (Guangzhou Landtek Instruments Co. Ltd. Guangzhou China), and a digital microscope (KEYENCE. SRT6200). The surface generate acetone vapor, a beaker to contain liquid acetone, a sealed container to roughness tester can measure a surface with Ra 0.05 , 10.00 mm and Rz 0.020 , control acetone vapor pressure, a temperature sensor to monitor polishing temper- 100.0 mm and an accuracy of not more than 65%. ature, a support frame to fix ABS mold. As shown in Fig. 4, when the heater is on, the beaker containing the acetone is heated to a temperature higher than boiling point of acetone (56.5uC) as it is set to Results and discussion 80uC for the experiment. Heated acetone vapor rises from beaker and washes the ABS Polish process analysis. In order to study the polish effect in sample. Since ABS is soluble in acetone, the surface of the mold is gradually dissolved. different parts of the mold, eight 0.2 mm layer-high samples were By the influence of gravity and liquid surface tension, the staircase surface slowly becomes smoothed. The longer the mold is polished, the more ABS is dissolved, printed and polished for different times. Afterward they were taken which may affect the precision of the mold and its surface roughness. However out and allowed to dry out for about 1 hour. The polish process can acetone will no longer be evaporated when the pressure inside the sealed container be clearly revealed with the help of a digital microscope, as shown in reaches its saturated vapor pressure. A simple equation (State Equation of Ideal Gas) Fig. 6. The wall of a sample is piled up with 0.2 mm high filaments was used to calculate the reasonable acetone volume. (which Fig. 6 part a), while the bottom is lined up with 0.68 mm width filaments (which Fig. 6 part b). The polish effect is not obvious m rV acetone PV~ RT~ RT ð1Þ until the 6 minutes point. When enough ABS is dissolved, the M M grooves between adjacent filaments are filled and the boundaries of filaments become indistinguishable because of the gravity and liquid Saturated vapor pressure of acetone in 80uC: P 5 224 KPa, Volume of the sealed surface tension. Finally all boundaries disappear and a smooth container V~ d h~1:445L, Molecular weight of acetone M 5 58, Scale factor R 5 surface is acquired at about the 12 minutes point. However, if the 8.31 J/(mol?K),T 5 353 K, acetone density r 5 0.788 g/cm . process is allowed to continue, extra ABS is dissolved which causes We can calculate V ~8:12 ml, which means that the pressure of acetone in the acetone pits on the surface, and subsequently it randomly redeposit on the sealed container reaches its saturated vapor pressure. So 10 ml acetone is added into surface resulting in some peaks. These pits and peaks will damage the beaker before every experiment to ensure there is enough acetone in the container smooth surface and as a result surface roughness increases. when the mold is polished. According to the analysis described above, the sample needs to be taken out from the sealed container in timely fashion for a smooth surface. Both the wall and bottom of sample seem to attain a rather low surface roughness at about 12 minutes. However a surface rough- ness tester is required for quantitative analysis. Surface roughness is quantified by the vertical deviations of a real surface from its ideal form. It is usually characterized by the arith- Figure 5 | Box mold (standard sample) for studying polishing effect Figure 3 | Polishing device (Taken by the author, Guang-huai Xue). (Taken by the author, Guang-huai Xue). SCIENTIFIC REPORTS | 4 : 6973 | DOI: 10.1038/srep06973 3 www.nature.com/scientificreports Figure 6 | Surface quality changing over time, 0.2 mm layer-high (a) sample wall, (b) sample bottom. metical mean deviation of profile, Ra, and the maximum height of profile, Rz. Ra~ jj y ð2Þ i~1 th Where y is the vertical distance from the mean line to the i data point. Rz~Rp{Rv, maximum peek high Rp~ max y , maximum valley high Rv~ min y . The surface roughness of the 0.2 mm layer-high samples polished for different times are measured and shown in Fig. 7. The polish curve is quite similar to what we can see under the digital microscope. Figure 8 | Surface roughness of different layer high samples change over It can been seen that the roughness of the sample from the bottom polish time, (a) Ra, (b) Rz. starts to drop dramatically at the beginning, likely as a result of the bottom being in a vertical position relative to the direction of the polishing with a 1.0 mm Ra,which rivals the glossy smooth surface acetone vapor and thus totally exposed to the vapor. The sample achieved by finish tuning or accurate grinding with traditional from the wall is horizontal to the vapor and its polish effect is not machine. Surface roughness increases at 20 minutes as extra ABS is obvious until the 6 minutes point. ABS surface can be smoothed by dissolved resulting in pits and peaks. Samples of 0.1 mm, 0.2 mm and 0.3 mm layer height were printed and polished to study the relationship between the layer height and the polishing effect. The roughness of samples walls were measured and are shown in Fig. 8. Generally speaking, the higher the sample layer height is, the bigger surface roughness will be. However all layer height samples attain their finest smooth surface at about 12–15 minutes. The sample of 0.1 mm layer height from the wall can be polished to a surface as smooth as 0.8 mm. The ear mold is structurally much more complex than these sam- ples. Several molds of 0.2 mm layer height were printed and polished for different times. The staircase effect is very clear when the mold is unpolished, as shown in Fig. 9a. A smooth surface can be acquired at about 15 minutes, as shown in Fig. 9b. For better assessment of the polishing effect, both polished and unpolished ear molds were cast with translucent silicone. Silicone ear prosthesis cast in unpolished mold is full of streaks on its surface, making it look coarse and opaque to light, Fig. 9c. However, when the staircase effect on the surface of ear mold is eliminated, the ear prosthesis looks much smoother and Figure 7 | Surface roughness of 0.2 mm layer-high samples change over more transparent, Fig. 9d, and the fine soft ear with skin color is polish time. shown in Fig. 9e. SCIENTIFIC REPORTS | 4 : 6973 | DOI: 10.1038/srep06973 4 www.nature.com/scientificreports Table 1 | The fabrication cost of silicone ear with SPPC method for first timers Item Amount Cost Silicone 23.7 g $1.2 ABS 63.5 g $0.8 Acetone 10 ml $0.1 Sealed Container 1 $2.5 Power Consumption $0.5 <1kW?h Labor cost 2 h $20 Others (machine wear, beaker, etc.) – $4 Total cost $29.1 comparative analysis of 3D-printed prostheses fabrication using a variety of materials is shown in Tab. 2. Silicon solidifies slowly, so fabricating silicon prostheses by direct writing is not favorable; how- ever, silicon can be fabricated effectively by bioprinter. Maxillofacial rehabilitation is not the most suitable research area for bioprinted tissue engineering, currently, though scaffold fabricated by bioprin- ter is quite promising. Mold-casting prostheses is most preferable. Almost all commercial 3D printers, including the SLA, inkjet, and SLS, can print a casting mold with a variety of materials. Basically, SLA and SLS printers have a high resolution and can fabricate a mold with a surface roughness less than 10 mm, but they are very expensive – sometimes more than $200,000. Inkjet 3D printers print using gypsum powder, which decreases cost but requires further process after printing. Compared to other methods, SPPC dramatically drops costs and creates products with fine surface quality. Mechanical performance. The mechanical and physical properties of silicone prostheses made by SPPC are shown in Tab. 3. Compared to the properties of a range of other commercially-available silicone rubber maxillofacial materials , this silicone prosthesis possesses considerable advantages in its tensile strength and tear strength. Its elongation percentage rivals that of other commercial materials, its hardness ranges from 0 to 60 Au, and its heat resistance is above 200uC, all of which meet the general requirements of prosthetic products. Parting fabrication. Fabricating an ear prosthesis is much simpler than fabricating a hand prosthesis, as only one mold is required. The prosthesis can be easily pulled out of the ear mold, due to the structure of the ear, and the high elasticity and low hardness of silicone. Two or more part molds are necessary, however, when an ear prosthesis with low elasticity and high hardness is needed. It is impossible to cast a silicone hand with only one mold. Upper and lower molds are designed and printed, then tightened by bolts, as shown in Fig. 10. A hand prosthesis looks much like a real human hand in shape and color; nevertheless, it requires much further process and refinement for detail, such as hair and varying texture. Figure 9 | Silicone ear (a) Unpolished mold (b) Polished mold (c) Ear Technically speaking, any shape of silicone prosthesis can be cast by casted with unpolished mold (d) Ear casted with polished mold (e) fine parting fabrication. silicone ear (All photographs were taken by the author, Guang-huai Xue). Conclusion Cost analysis. The biggest merit of the SPPC method is low cost, the As a desktop 3D printer is very cheap, it is also referred to as a mold fabrication cost could be negligible, as it is printed by a desktop personal 3D printer and it will become as popular and common as 3D printer and it can be reused many times. The materials, reagents the personal computer, this means that almost everyone can afford and apparatus used in the mold fabrication and casting of the and use their desktop 3D printer to print whatever they want. It is prosthesis are cheap and readily available. As shown in Tab. 1, the every interesting and creative to develop research applications with a fabrication cost of the first silicone ear can be as low as $29.1. After desktop 3D printer. the mold is printed and polished, fabricating the next prosthesis will In this study we aimed to fabricate the soft prostheses with the help only require 23.7 g silicone, 10 min of labor cost and additional of a desktop 3D printer and succeeded in attaining this goal. The minor costs incurred for machinery ownership, operation wear printing costs of negative mold were negligible when compared to the and tear; which means that the final cost is less than $5. traditional methods. In this report, a cheap and convenient method The material most commonly used to fabricate prostheses is sil- (SPPC) of fabricating silicone prosthesis is demonstrated. The stair- icon, considering its long-term stability, strength and softness. A case effect of the mold caused by the desktop 3D printer is eliminated SCIENTIFIC REPORTS | 4 : 6973 | DOI: 10.1038/srep06973 5 www.nature.com/scientificreports Table 2 | Comparative analysis of prostheses fabrication with 3D printing 3D printer Material Used Cost Surface roughness Fabricating method SLA Ultraviolet resin Expensive High Mold Casting SLS Powder Expensive High Mold Casting Inkjet Gypsum powder Middle Middle Mold Casting Bioprinter Hydrogel Middle High Direct Writing SPPC Polymer silk Cheap Low Mold Casting Table 3 | Mechanical properties of prostheses Density Viscosity Percentage (g/cm ) (kPa.s) Elongation(%) Tear Strength(kN/m) Tensile Strength(kN/m) Hardness (Au) Heat Resistance(uC) Value 1.12 10 450 27 10 0 , 60 200 , 300 Figure 10 | Parting fabricating of hand prosthesis (All photographs were taken by the author, Guang-huai Xue). 16. Sun, J., Chen, X., Liao, H. & Xi, J. Template-based framework for nasal prosthesis to produce a prosthesis with smooth surface. 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Mech. Eng. H. 226, 718–728 (2012). of China(no. 51375440), Fundamental Research Funds for the Central Universities (no. SCIENTIFIC REPORTS | 4 : 6973 | DOI: 10.1038/srep06973 6 www.nature.com/scientificreports 2013QNA4007), and Zhejiang Provincial Natural Science Foundation of China (no. How to cite this article: He, Y., Xue, G. & Fu, J. Fabrication of low cost soft tissue prostheses LY12E05018). with the desktop 3D printer. Sci. Rep. 4, 6973; DOI:10.1038/srep06973 (2014). This work is licensed under a Creative Commons Attribution-NonCommercial- Author contribution NoDerivs 4.0 International License. The images or other third party material in Y.H. proposed the SPPC method, wrote the main manuscript text and G.X. performed this article are included in the article’s Creative Commons license, unless indicated experiments, prepared figures 1–5, 9–10. J.F. planned the research, prepared figures 6–8, otherwise in the credit line; if the material is not included under the Creative and edited the paper. Commons license, users will need to obtain permission from the license holder in order to reproduce the material. To view a copy of this license, visit http:// creativecommons.org/licenses/by-nc-nd/4.0/ Additional information Competing financial interests: The authors declare that they have no competing financial interests. SCIENTIFIC REPORTS | 4 : 6973 | DOI: 10.1038/srep06973 7 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Scientific Reports Springer Journals

Fabrication of low cost soft tissue prostheses with the desktop 3D printer

He, Yong; Xue, Guang-huai; Fu, Jian-zhong
Scientific Reports , Volume 4 (1) – Nov 27, 2014
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Springer Journals
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Copyright © 2014 by The Author(s)
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Science, Humanities and Social Sciences, multidisciplinary; Science, Humanities and Social Sciences, multidisciplinary; Science, multidisciplinary
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10.1038/srep06973
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Abstract

OPEN Fabrication of low cost soft tissue prostheses with the desktop 3D printer SUBJECT AREAS: MECHANICAL 1,2 1,2 1,2 Yong He , Guang-huai Xue & Jian-zhong Fu ENGINEERING IMPLANTS The State Key Lab of Fluid Power Transmission and Control Systems, Department of Mechanical Engineering, Zhejiang University, BIOMEDICAL ENGINEERING Hangzhou 310027, China, Zhejiang Province’s Key Laboratory of 3D Printing Process and Equipment, Department of Mechanical Engineering, Zhejiang University, Hangzhou 310027, China. Received 12 August 2014 Soft tissue prostheses such as artificial ear, eye and nose are widely used in the maxillofacial rehabilitation. In this report we demonstrate how to fabricate soft prostheses mold with a low cost desktop 3D printer. The Accepted fabrication method used is referred to as Scanning Printing Polishing Casting (SPPC). Firstly the anatomy is 16 October 2014 scanned with a 3D scanner, then a tissue casting mold is designed on computer and printed with a desktop 3D printer. Subsequently, a chemical polishing method is used to polish the casting mold by removing the Published staircase effect and acquiring a smooth surface. Finally, the last step is to cast medical grade silicone into the 27 November 2014 mold. After the silicone is cured, the fine soft prostheses can be removed from the mold. Utilizing the SPPC method, soft prostheses with smooth surface and complicated structure can be fabricated at a low cost. Accordingly, the total cost of fabricating ear prosthesis is about $30, which is much lower than the current Correspondence and soft prostheses fabrication methods. requests for materials should be addressed to oft tissue prostheses are widely used in maxillofacial rehabilitation. Patient numbers is ever increasing due Y.H. (yongqin@zju. to the advancements in medicine, surgical techniques and in particular cancer survival rates . However, the edu.cn) or J.F. (fjz@zju. S high fabrication cost of traditional prostheses prompted the researchers to explore alternatives to reduce the edu.cn) cost and time of fabrication. Three-dimensional (3D) printing or rapid prototyping (RP) is a layered manufac- turing method that can be used to fabricate complex structures. It is an additive manufacturing (AM) process, fundamentally different from the conventional subtractive manufacturing processes. Using 3D printing a phys- ical object can be fabricated from a 3D computer-aided design (CAD) model layer by layer, more conveniently and more rapidly than other manufacturing means. Additionally, it is easy to customize a product according to personal requirement, consequently a wide variety of applications of 3D printing technology in soft matter 2–8 fabrication have emerged recently . The use of 3D printing can help in the development of omnibearing 4 5 biodevices . Such as described in the report by Wang et al., , who used hydrogel and cells to fabricate models that mimic complex soft organs in vitro with the help of 3D printing. Also, Landers et al., printed a hydrogel scaffolds using 3D plotter to attain a designed external shape and a well-defined internal pore structure . Many reports also discussed the fabrication of soft tissues for implant, and scaffolds with cell-seeded hydrogel 9–12 or collagen matrix for clinical application were developed . High-fidelity ears with collagen type I hydrogel scaffolds were fabricated by injection. Even following an extended period after implantation, they continue to effectively mimic the native auricle both biomechanically and histologically . To improve the mechanical properties of the fibrous collagen matrix, composite ear scaffolds with wire frameworks were used to ensure a 11 12 3D shape after implantation . Mannoor, M. S., et al printed bionic ears able to gather inductively-coupled signals from cochlea-shaped electrodes, demonstrating the merging capabilities of biological and nanoelectronic functionalities. However, because scaffolds or soft tissues based on tissue engineering are designed to acquire real tissues after implanting, further clinical study and a thorough ethics evaluation are still needed. 13,14 Furthermore, in 2003 Cheah et al., integrated CAD/CAM techniques for developing facial prostheses and described a complete fabrication process using the selective laser sintering (SLS) 3D printing technology. It is worth noting, they and Eggbeer et al. also discussed the difference between indirect mold production via silicone rubber molding and direct mold production via RP fabrication. In addition, a template-based framework was proposed to rebuild the nasal 3D model with the data from 3D and computed tomography (CT) scans . The results showed that this method had advantages over other rebuilding methods in terms of accuracy, speed, safety and cost. E. Bassoli et al., reported a combined 3D printing/indirect replication method to fabricate 3D vascular- like structures of soft tissue ; using the ProJet HD 3000 3D printer from 3D Systems Inc. to print the negative mold of the vascular structure. SCIENTIFIC REPORTS | 4 : 6973 | DOI: 10.1038/srep06973 1 www.nature.com/scientificreports A team from Italy led by De Crescenzio and Ciocca made a sig- in education, DIY manufacturing, research and industry. As illu- 18–20 nificant contribution to the facial rehabilitation field when they strated by the successful production of micro- and milli-scale reac- tionware with a desktop 3D printer (3DTouch) . reported a comprehensive solution to the design and fabrication of prosthesis. They created a real anatomic reference model library, The main task during the manufacture of soft prostheses is the namely the ‘‘Ear & Nose Digital Library’’, which can be very useful making of the casting mold, which is also the main component of the for the reconstruction of the facial defects. In addition, they described cost incurred during the whole prostheses fabrication process. If the casting mold can be fabricated using a desktop 3D printer, and as how the definitive acrylic ear cast mold was printed by Z Printer 310 (Z Corp, taken over by 3D system Inc. in 2012), which was then such printers become readily affordable, then doctors could fabricate the prostheses in their offices, or the patients could do it at home. transformed into a wax ear with the vinyl polysiloxane material. Nevertheless the staircase effect (contour like structure) caused by A team from UK led by Eggbeer and Bibb performed a long term the layered manufacturing is a challenge which impedes the acquisi- and remarkable research to study how to apply digital technologies in 1,15,21–25 tion of smooth surface in 3D printing. This drawback is especially maxillofacial prosthetics . Eggbeer et al., compared the pros- serious in the desktop 3D printer due to the layer thickness, as shown theses fabricated by 3D printing against a prosthesis made by con- in Fig. 1. ventional techniques . In their nasal prosthesis case study, 3D In this study, we focus on how to apply the low cost desktop 3D printing enabled the prosthetics to work in a more flexible manner. printer to print the casting mold. The fabrication method used is However, they determined that the directly printed prosthesis has called Scanning Printing Polishing Casting (SPPC). The key consid- poor mechanical properties and untested biological responses, and eration when using SPPC is how to fabricate a negative casting mold suggested that the best way is to print the prosthesis mold and cure with smooth surface inside, and will be addressed in this report. To the prosthesis with silicone rubber. Worth mentioning, skin features that end, the polishing method, which can ensure that the surface such as wrinkles and texture in auricular and nasal prostheses have quality of the mold is adequate to be used in the prostheses casting, been successfully fabricated by 3D printing . The time required for was systematically investigated. Moreover, it is proven that the soft prosthesis fabrication by 3D printing was found to be considerable prostheses can be affordably manufactured, under $30 each, at home shorter than that required by the conventional methods. or in a personal lab setting without any expensive technical equip- As the prosthesis is personally customized, mass fabrication meth- ment. SPPC also can be widely used in the fabrication of soft muscle, ods such as metallic mold casting or injection molding are typically hydrogel structure in tissue engineering, artificial skin, customized not suitable. A conventional process for the construction of pros- jewel, etc. theses is particularly lengthy, as it includes many steps: impression, plaster replica, base plate fabrication, mold fabrication, mold pack- ing, curing, and extrinsic finishing. The process is laborious and Methods The typical process of SPPC is shown in Fig. 2. Firstly, 3D data for the prostheses are expensive in addition to time-consuming. The maxillofacial prostho- acquired with a 3D scanner. Once acquired, the datasets are used to generate a digital dontist determines the correct size, shape, and position of the pros- 3D model of the negative mold for casting by using a 3D modeling software such as thesis for each individual patient, hand-sculpts an impression in wax, 3D max, Rhinoceros, or SolidWorks, etc. Subsequently, the 3D model is converted then casts the shape in silicone. A handmade silicone ear or nose into G code language by a slicing software tool, which can then be read by a desktop 3D printer. A common polymer filament, Acrylonitrile Butadiene Styrene copoly- costs up to $4000, and requires 5–7 hospital visits for customization. 26 mers (ABS), is applied for 3D printing. Since the multi-strip-like structure caused by The process takes 5–10 weeks in total . 3D printing will affect the prostheses surface quality, acetone vapor is used to elim- Many researchers have previously demonstrated 3D printing/RP inate the layer thickness effect of the mold, as ABS is soluble in acetone. After technology as an effective way to accelerate the prostheses fabrication polishing, silicone is poured into the mold. The soft prostheses can be easily pulled out/demolded from the mold because the solidified silicone provides extra strength process and reduce its cost. The primary material used in prostheses, and elasticity. either silicon or Polydimethylsiloxane (PDMS), is more suited to A Kinect depth sensor for Microsoft Windows was used to scan the original model, casting. The so-called rapid tool, soft tool or bridge tool fabricated and its digital dataset was saved as a STL file . The negative mold model was then by 3D printing is commonly used to cast prostheses. It should be designed using the Rhinoceros V4.0 software. The slice software Slic3r was used to generate G code files for the desktop 3D printer, RepGo X1, which was purchased noted, however, that the 3D printers used in this previous research from Xiangtan Dot Go 3D technology Corporation for about $570. were industrial-grade and therefore quite expensive. Indeed, the cost Silicone part A and part B (Dongguan Hongfeng Silicone Materials Co., LTD) were of fine prostheses mold-fabricated by an industrial 3D printer is still mixed in a 151 (weight: weight) ratio and stirred for 2 minutes, and then the mixture high, which has hindered the wider use of 3D printing. According to was degassed in a vacuum chamber for 10–15 minutes. ABS is a thermoplastic polymer material with high strength, good toughness and easy to machine. Nowadays the quote given by Magicfirm, LLC. Hangzhou, China, the fabrica- 3 it is widely used in FDM printing. However the poor surface finish quality has limited tion price is $2.2 per cm using the stereolithography apparatus the development of 3D printing, in both appearance and performance. A simple (SLA) of a 3D printer, indicating a cost of $411.80 for an ear mold polishing device has been assembled, as shown in Fig. 3. It includes a heater to with a size of 7.8 3 5.0 3 4.8 cm. A prosthetic product fabricated by 3D printing from Fripp Design & Research in the UK costs around $4,000 each, almost as much as a handmade product . If such pros- theses could be manufactured at home, the cost would drop dramat- ically, greatly benefiting patients. The desktop 3D printer (personal 3D printer), also known as the open source 3D printer, is very popular among the do it yourself (DIY) variants. The advantages of desktop 3D printer include low cost and as a result, many people can afford a small size printer with extremely low to zero toxicity and waste. With the expiration of the key patents of Fused Deposition Modeling (FDM), the technology used in desktop 3D printer, a large open-source development com- munity has emerged, and a desktop 3D printer now only cost $200– $1000. Two standard types of desktop 3D printer are the RepRap and the Fab@Home; however, everyone can change the desktop 3D printer design according to their requirements thanks to its open source Figure 1 | Staircase behavior in 3D printing (Ear negative mold, layer development. At present the desktop 3D printer is being widely used height 0.3 mm, taken by the author, Guang-huai Xue). SCIENTIFIC REPORTS | 4 : 6973 | DOI: 10.1038/srep06973 2 www.nature.com/scientificreports Figure 4 | Working principle of polishing device. The surface quality of the ABS mold is influenced by many polishing parameters such as temperature, vapor pressure, layer height of 3D printing, polishing time and model structure. A box mold was chosen as a standard sample, shown in Fig. 5. Figure 2 | Typical SPPC process (All photographs were taken by the Different layer-thickness ABS models were polished for different times to study how author, Guang-huai Xue). to achieve a better surface finish. The surface quality was assessed using an inductance type roughness tester, a SRT6200 (Guangzhou Landtek Instruments Co. Ltd. Guangzhou China), and a digital microscope (KEYENCE. SRT6200). The surface generate acetone vapor, a beaker to contain liquid acetone, a sealed container to roughness tester can measure a surface with Ra 0.05 , 10.00 mm and Rz 0.020 , control acetone vapor pressure, a temperature sensor to monitor polishing temper- 100.0 mm and an accuracy of not more than 65%. ature, a support frame to fix ABS mold. As shown in Fig. 4, when the heater is on, the beaker containing the acetone is heated to a temperature higher than boiling point of acetone (56.5uC) as it is set to Results and discussion 80uC for the experiment. Heated acetone vapor rises from beaker and washes the ABS Polish process analysis. In order to study the polish effect in sample. Since ABS is soluble in acetone, the surface of the mold is gradually dissolved. different parts of the mold, eight 0.2 mm layer-high samples were By the influence of gravity and liquid surface tension, the staircase surface slowly becomes smoothed. The longer the mold is polished, the more ABS is dissolved, printed and polished for different times. Afterward they were taken which may affect the precision of the mold and its surface roughness. However out and allowed to dry out for about 1 hour. The polish process can acetone will no longer be evaporated when the pressure inside the sealed container be clearly revealed with the help of a digital microscope, as shown in reaches its saturated vapor pressure. A simple equation (State Equation of Ideal Gas) Fig. 6. The wall of a sample is piled up with 0.2 mm high filaments was used to calculate the reasonable acetone volume. (which Fig. 6 part a), while the bottom is lined up with 0.68 mm width filaments (which Fig. 6 part b). The polish effect is not obvious m rV acetone PV~ RT~ RT ð1Þ until the 6 minutes point. When enough ABS is dissolved, the M M grooves between adjacent filaments are filled and the boundaries of filaments become indistinguishable because of the gravity and liquid Saturated vapor pressure of acetone in 80uC: P 5 224 KPa, Volume of the sealed surface tension. Finally all boundaries disappear and a smooth container V~ d h~1:445L, Molecular weight of acetone M 5 58, Scale factor R 5 surface is acquired at about the 12 minutes point. However, if the 8.31 J/(mol?K),T 5 353 K, acetone density r 5 0.788 g/cm . process is allowed to continue, extra ABS is dissolved which causes We can calculate V ~8:12 ml, which means that the pressure of acetone in the acetone pits on the surface, and subsequently it randomly redeposit on the sealed container reaches its saturated vapor pressure. So 10 ml acetone is added into surface resulting in some peaks. These pits and peaks will damage the beaker before every experiment to ensure there is enough acetone in the container smooth surface and as a result surface roughness increases. when the mold is polished. According to the analysis described above, the sample needs to be taken out from the sealed container in timely fashion for a smooth surface. Both the wall and bottom of sample seem to attain a rather low surface roughness at about 12 minutes. However a surface rough- ness tester is required for quantitative analysis. Surface roughness is quantified by the vertical deviations of a real surface from its ideal form. It is usually characterized by the arith- Figure 5 | Box mold (standard sample) for studying polishing effect Figure 3 | Polishing device (Taken by the author, Guang-huai Xue). (Taken by the author, Guang-huai Xue). SCIENTIFIC REPORTS | 4 : 6973 | DOI: 10.1038/srep06973 3 www.nature.com/scientificreports Figure 6 | Surface quality changing over time, 0.2 mm layer-high (a) sample wall, (b) sample bottom. metical mean deviation of profile, Ra, and the maximum height of profile, Rz. Ra~ jj y ð2Þ i~1 th Where y is the vertical distance from the mean line to the i data point. Rz~Rp{Rv, maximum peek high Rp~ max y , maximum valley high Rv~ min y . The surface roughness of the 0.2 mm layer-high samples polished for different times are measured and shown in Fig. 7. The polish curve is quite similar to what we can see under the digital microscope. Figure 8 | Surface roughness of different layer high samples change over It can been seen that the roughness of the sample from the bottom polish time, (a) Ra, (b) Rz. starts to drop dramatically at the beginning, likely as a result of the bottom being in a vertical position relative to the direction of the polishing with a 1.0 mm Ra,which rivals the glossy smooth surface acetone vapor and thus totally exposed to the vapor. The sample achieved by finish tuning or accurate grinding with traditional from the wall is horizontal to the vapor and its polish effect is not machine. Surface roughness increases at 20 minutes as extra ABS is obvious until the 6 minutes point. ABS surface can be smoothed by dissolved resulting in pits and peaks. Samples of 0.1 mm, 0.2 mm and 0.3 mm layer height were printed and polished to study the relationship between the layer height and the polishing effect. The roughness of samples walls were measured and are shown in Fig. 8. Generally speaking, the higher the sample layer height is, the bigger surface roughness will be. However all layer height samples attain their finest smooth surface at about 12–15 minutes. The sample of 0.1 mm layer height from the wall can be polished to a surface as smooth as 0.8 mm. The ear mold is structurally much more complex than these sam- ples. Several molds of 0.2 mm layer height were printed and polished for different times. The staircase effect is very clear when the mold is unpolished, as shown in Fig. 9a. A smooth surface can be acquired at about 15 minutes, as shown in Fig. 9b. For better assessment of the polishing effect, both polished and unpolished ear molds were cast with translucent silicone. Silicone ear prosthesis cast in unpolished mold is full of streaks on its surface, making it look coarse and opaque to light, Fig. 9c. However, when the staircase effect on the surface of ear mold is eliminated, the ear prosthesis looks much smoother and Figure 7 | Surface roughness of 0.2 mm layer-high samples change over more transparent, Fig. 9d, and the fine soft ear with skin color is polish time. shown in Fig. 9e. SCIENTIFIC REPORTS | 4 : 6973 | DOI: 10.1038/srep06973 4 www.nature.com/scientificreports Table 1 | The fabrication cost of silicone ear with SPPC method for first timers Item Amount Cost Silicone 23.7 g $1.2 ABS 63.5 g $0.8 Acetone 10 ml $0.1 Sealed Container 1 $2.5 Power Consumption $0.5 <1kW?h Labor cost 2 h $20 Others (machine wear, beaker, etc.) – $4 Total cost $29.1 comparative analysis of 3D-printed prostheses fabrication using a variety of materials is shown in Tab. 2. Silicon solidifies slowly, so fabricating silicon prostheses by direct writing is not favorable; how- ever, silicon can be fabricated effectively by bioprinter. Maxillofacial rehabilitation is not the most suitable research area for bioprinted tissue engineering, currently, though scaffold fabricated by bioprin- ter is quite promising. Mold-casting prostheses is most preferable. Almost all commercial 3D printers, including the SLA, inkjet, and SLS, can print a casting mold with a variety of materials. Basically, SLA and SLS printers have a high resolution and can fabricate a mold with a surface roughness less than 10 mm, but they are very expensive – sometimes more than $200,000. Inkjet 3D printers print using gypsum powder, which decreases cost but requires further process after printing. Compared to other methods, SPPC dramatically drops costs and creates products with fine surface quality. Mechanical performance. The mechanical and physical properties of silicone prostheses made by SPPC are shown in Tab. 3. Compared to the properties of a range of other commercially-available silicone rubber maxillofacial materials , this silicone prosthesis possesses considerable advantages in its tensile strength and tear strength. Its elongation percentage rivals that of other commercial materials, its hardness ranges from 0 to 60 Au, and its heat resistance is above 200uC, all of which meet the general requirements of prosthetic products. Parting fabrication. Fabricating an ear prosthesis is much simpler than fabricating a hand prosthesis, as only one mold is required. The prosthesis can be easily pulled out of the ear mold, due to the structure of the ear, and the high elasticity and low hardness of silicone. Two or more part molds are necessary, however, when an ear prosthesis with low elasticity and high hardness is needed. It is impossible to cast a silicone hand with only one mold. Upper and lower molds are designed and printed, then tightened by bolts, as shown in Fig. 10. A hand prosthesis looks much like a real human hand in shape and color; nevertheless, it requires much further process and refinement for detail, such as hair and varying texture. Figure 9 | Silicone ear (a) Unpolished mold (b) Polished mold (c) Ear Technically speaking, any shape of silicone prosthesis can be cast by casted with unpolished mold (d) Ear casted with polished mold (e) fine parting fabrication. silicone ear (All photographs were taken by the author, Guang-huai Xue). Conclusion Cost analysis. The biggest merit of the SPPC method is low cost, the As a desktop 3D printer is very cheap, it is also referred to as a mold fabrication cost could be negligible, as it is printed by a desktop personal 3D printer and it will become as popular and common as 3D printer and it can be reused many times. The materials, reagents the personal computer, this means that almost everyone can afford and apparatus used in the mold fabrication and casting of the and use their desktop 3D printer to print whatever they want. It is prosthesis are cheap and readily available. As shown in Tab. 1, the every interesting and creative to develop research applications with a fabrication cost of the first silicone ear can be as low as $29.1. After desktop 3D printer. the mold is printed and polished, fabricating the next prosthesis will In this study we aimed to fabricate the soft prostheses with the help only require 23.7 g silicone, 10 min of labor cost and additional of a desktop 3D printer and succeeded in attaining this goal. The minor costs incurred for machinery ownership, operation wear printing costs of negative mold were negligible when compared to the and tear; which means that the final cost is less than $5. traditional methods. In this report, a cheap and convenient method The material most commonly used to fabricate prostheses is sil- (SPPC) of fabricating silicone prosthesis is demonstrated. The stair- icon, considering its long-term stability, strength and softness. A case effect of the mold caused by the desktop 3D printer is eliminated SCIENTIFIC REPORTS | 4 : 6973 | DOI: 10.1038/srep06973 5 www.nature.com/scientificreports Table 2 | Comparative analysis of prostheses fabrication with 3D printing 3D printer Material Used Cost Surface roughness Fabricating method SLA Ultraviolet resin Expensive High Mold Casting SLS Powder Expensive High Mold Casting Inkjet Gypsum powder Middle Middle Mold Casting Bioprinter Hydrogel Middle High Direct Writing SPPC Polymer silk Cheap Low Mold Casting Table 3 | Mechanical properties of prostheses Density Viscosity Percentage (g/cm ) (kPa.s) Elongation(%) Tear Strength(kN/m) Tensile Strength(kN/m) Hardness (Au) Heat Resistance(uC) Value 1.12 10 450 27 10 0 , 60 200 , 300 Figure 10 | Parting fabricating of hand prosthesis (All photographs were taken by the author, Guang-huai Xue). 16. Sun, J., Chen, X., Liao, H. & Xi, J. Template-based framework for nasal prosthesis to produce a prosthesis with smooth surface. 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Mech. Eng. H. 226, 718–728 (2012). of China(no. 51375440), Fundamental Research Funds for the Central Universities (no. SCIENTIFIC REPORTS | 4 : 6973 | DOI: 10.1038/srep06973 6 www.nature.com/scientificreports 2013QNA4007), and Zhejiang Provincial Natural Science Foundation of China (no. How to cite this article: He, Y., Xue, G. & Fu, J. Fabrication of low cost soft tissue prostheses LY12E05018). with the desktop 3D printer. Sci. Rep. 4, 6973; DOI:10.1038/srep06973 (2014). This work is licensed under a Creative Commons Attribution-NonCommercial- Author contribution NoDerivs 4.0 International License. The images or other third party material in Y.H. proposed the SPPC method, wrote the main manuscript text and G.X. performed this article are included in the article’s Creative Commons license, unless indicated experiments, prepared figures 1–5, 9–10. J.F. planned the research, prepared figures 6–8, otherwise in the credit line; if the material is not included under the Creative and edited the paper. Commons license, users will need to obtain permission from the license holder in order to reproduce the material. To view a copy of this license, visit http:// creativecommons.org/licenses/by-nc-nd/4.0/ Additional information Competing financial interests: The authors declare that they have no competing financial interests. SCIENTIFIC REPORTS | 4 : 6973 | DOI: 10.1038/srep06973 7

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Scientific Reports – Springer Journals

Published: Nov 27, 2014

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