Question: What are the differences between designing a medical silicone part vs. a medical plastic part?
Answer: The largest difference in design between silicone and plastic is the properties. Understanding the application and the material properties can help designers better utilize silicone in all applications. Silicone and plastic both have implantable and non-implantable grades and your application will dictate what grade you need. Applications may be medical in nature but not contact people but devices may also be implantable for a few days, weeks, or years or just contact skin or blood.
Designers trying to determine tolerances and fitting may want to keep in mind that silicone can deform more readily than most plastics to fit an assembly so your tolerance level may be dependent on the level of performance. For example a strain relief or compressed seal may not need as tight of tolerances as an optical lens or a pressure membrane. Silicone generally has high elongation and low hardness compared to most plastics so specifications may need to be adjusted accordingly. For example regrinding of silicone is not practical but straight walls and undercuts that may be difficult in plastics may not pose an issue due to the low hardness and high elongation of silicone. Flash and cuts which may not be a significant issue with most plastics is common in silicone.