Are any typical 3D printed (extrusion based 3D printer) materials, such as ABS or PLA (or slightly more exotic ones, such as kevlar, fibreglass, or carbon fiber), safe for implantation in the human body? Or in medical terms, are they biocompatible (biofunctionality is not topical for this question)? If not, why not? If most of them are safe, then please explain which ones are NOT safe.
Highly relevant, and perhaps even more interesting is: Are there any peer reviewed medical papers that have investigated what materials are safe for implantation in the human body? A paper which answers this unambiguously would be the ideal answer to this question. Another concern is if the process of 3D printing itself adversely influences the properties of the material in the context of implantation applications.
I've tried to determine the answer to this question myself, but I cannot find any papers or studies which answer it. I can easily find that ABS plastic is "non-biodegradable", but I suppose the issue of adverse host responses is more crucial, e.g. causing inflammation or it being a bacterial growth substrate to promote infections seems like plausible concerns. I'm sure there might be other dangerous complications too, which I'm not aware of.
I found a paper dealing with corrosion issues for implantable metals: DOI: 10.1089/end.1997.11.383
I found a paper dealing with silicone-urethane being prone to breakdown: DOI: 10.1021/ma301965y
I found a paper describing the properties and history of ultra-high molecular weight polyethylene (UHMWPE), which appears to be commonly used as implants: DOI: 10.1109/EEIC.2005.1566331
By extension, a 3D printer using UHMWPE might be safe, barring any adverse chemical or mechanical issues as a result of the 3D printing process itself. However, it is not clear to me if any 3D printers can actually reliably print UHMWPE. Furthermore, it is unclear if UHMWPE is a sane choice, as it appears to be useful in applications where strength is required, such as for joints. What about other applications where load bearing properties are not required (e.g. a simple enclosure for implantable electronics)?
I'm aware that titanium appears to be frequently used for implants, and while titanium 3D printers do exist, they are beyond the scope of this question. The valid context is extrusion based 3D printers in the sub $10,000 range (arbitrarily chosen to make the question avoid being tagged as "too broad").