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Introduction
Prosthesis and implants are integral parts of modern healthcare, with silicones widely used for their chemical inertness, tissue-like mechanical properties, and adaptability. However, conventional techniques in silicone processing face limitations in structural complexity and patient specificity. 3D printing has emerged as a promising technique for creating personalized medical devices, but the use of medical-grade silicone is limited due to multiple challenges.
Methods
A customized 3D printer was used to print medical-grade silicone. Printing parameters like print bed temperature (e.g., 90°C) and print orientation (e.g., 45°) were varied systematically. The printed samples were characterized for their mechanical performance (tensile properties), defect formation (X-Ray μCT), leachable moieties (NMR), and cytotoxicity.
Results.
Mechanical testing of the samples by tensile mode indicates that the specimens printed at 90°C with 45° orientation showed the lowest tensile strength and modulus. X-ray μCT confirmed increased pore volume fraction for these specimens. These samples also showed lower sphericity values, indicating elongated defects. Both 13C and 29Si NMR detected -CH3 and dimethylsiloxane groups within the leached samples. AlamarBlue and Live/Dead analysis revealed that the leached moieties do not adversely affect the cells. The cells proliferate well from day 1 to day 7 without significant differences between the control and printed samples.
Discussion
The results of this study demonstrated that the print bed temperature and layer orientation influenced the mechanical properties and defect formation of the 3D-printed silicones. Lower tensile strength and modulus for the samples printed at a higher bed temperature and 45° orientation can be attributed to the formation of pores of defects within the 3D-printed samples. This is corroborated by the X-ray μCT analysis, which shows higher pore volume fraction and elongated pores. These defects arise from the printing conditions where entrapped air does not have time to escape before complete curing. The NMR studies show the presence of some precursor moieties that may have been part of either of the two-part silicone systems. These moieties do not show any cytotoxic effect, as seen from the AlamarBlue and Live/Dead assay.
Conclusion
This study successfully demonstrated the feasibility of 3D printing medical-grade silicones using a customized printer. By optimizing printing parameters, it is possible to achieve desirable mechanical properties, minimize defects, and ensure the biocompatibility of the printed silicone parts. These findings have significant implications for fabricating patient-specific implants, prostheses, and other biomedical devices.
References
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J. Herzberger, J.M. Sirrine, C.B. Williams, T.E. Long, Polymer Design for 3D Printing Elastomers: Recent Advances in Structure, Properties, and Printing, Prog. Polym. Sci. 97 (2019) 101144.
J.A.G. Clet, N.-S. Liou, C.-H. Weng, Y.-S. Lin, A Parametric Study for Tensile Properties of Silicone Rubber Specimen Using the Bowden-Type Silicone Printer, Materials 15 (2022) 1729.
R. Menzel, A. Korzun, C. Golz, T. Maier, I. Pahl, A. Hauk, Dimethylsilanediol from silicone elastomers: Analysis, release from biopharmaceutical process equipment, and clearance studies, Int. J. Pharm. 646 (2023) 123441
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