Invasive intraneural electrodes implanted in peripheral nerves are neural prosthetic devices that are exploied to control advanced neural-interfaced prostheses in human amputees. One of the main issues to be faced in chronic implants is represented by the gradual loss of functionality of such intraneural interfaces due to an electrical impedance increase caused by the progressive formation of a fibrotic capsule around the electrodes, which is originally due to a nonspecific inflammatory response called foreign body reaction (FBR).

In this in vitro work, we tested the biocompatibility and ultra-low fouling features of the synthetic coating - poly(ethylene glycol) (PEG) - compared to the organic polymer - zwitterionic sulfated poly(sulfobetaine methacrylate) (SBMA) hydrogel - to prevent or reduce the first steps of the FBR: plasma protein adsorption and cell adhesion to the interface.

Synthesis and characterization of the SBMA hydrogel was done. Preliminary biocompatibility analysis of the zwitterionic hydrogel, using hydrogel-conditioned medium, showed no cytotoxicity at all vs. control. We seeded GFP-labelled human myofibroblasts on PEG- and SBMA hydrogel-coated polyimide surfaces and evaluated their adhesion and cell viability at different time-points. Because of the high hydration, low stiffness reflecting the one of neural tissue, and ultra-low fouling characteristics of the SBMA hydrogel, this polymer showed lower myofibroblast adhesion and different cell morphology compared to adhesion controls, thereby representing a better coating than PEG for potentially mitigating the FBR.

We conclude that soft SBMA hydrogels could outperform PEG coatings in vitro as more suitable dressings of intraneural electrodes. Furthermore, such SBMA-based antifouling materials can be envisioned as long-term diffusion-based delivery systems for controlled release of anti-inflammatory and anti-fibrotic drugs in vivo.