Foreign Body Reaction to Neural Implants: A Comparative Study of Polymer Toxicity and Tissue Response

This study investigated the toxicity of ten polymer materials intended for the development of invasive neural interfaces improving the treatment of neurological diseases. Most of the materials for neural implants can cause traumatization of the surrounding tissue, inflammation, and foreign body reaction. In this study, in vitro and in vivo toxicity assessment was performed for nylon 618 (NY), polycaprolactone (PCL), polyethylene glycol diacrylate (PEGDA), polydimethylsiloxane (PDMS), polyethylene terephthalate (PET), polylactide (PLA), thermoplastic polyurethane (TPU), polypropylene (PP), polyethylene terephthalate glycol (PET-G), and polyimide (PI). The biocompatibility of these ten materials was assessed based on cell adhesion, growth and cytotoxicity on neural (PC-12) and fibroblast (NRK-49F) cultures. Furthermore, brain tissue responses to the implanted phantom scaffolds were analyzed in rats. According to these measurements, PI showed the highest compatibility for both cell types. PEGDA exhibited cytotoxic effects, low cell adhesion and the strongest foreign body reaction, including fibrosis and multinucleated cell formation. The other polymers showed lower pathological responses which makes them potentially usable for neural interfacing. We conclude that PEGDA appears to be unsuitable for long-term use due to adverse tissue and cellular reactions, whereas PI, PLA, PDMS and TPU hold promise as materials for safe and effective neural interface applications.