Non-mulberry silk fibroin functionalization enhances charge-transfer efficiency in aligned polypyrrole-silk composites for electrically stimulated neurite outgrowth
Electroconductive biomaterials (ECBs) replicate the natural bioelectrical environment of nerve tissue, promoting action potential propagation after injury and enhancing nerve regeneration through therapeutic electrical stimulation (ES). We present a highly electroactive Faradaic ECB with exceptional electrical conductivity and charge density, alongside low electrochemical impedance. These ECBs trigger action potentials at low stimulation voltages by regulating redox reactions through their intrinsic reversible behavior, thereby preventing electrode degradation and tissue damage. Our biohybrid scaffold consists of aligned microfibrous matrices of polypyrrole (PPy) and Bombyx mori silk fibroin (BmSF), functionalized with Antheraea assamensis silk fibroin (AaSF) rich in the cell-affinitive RGD tripeptide. Serving as an anionic dopant for PPy, AaSF significantly enhances the scaffolds electrical properties ([~]9.18 mS cm-1) and charge-transfer efficiency ([~]25.27 {Omega}). The scaffolds exhibit superior charge injection capacity at low potentials compared to conventional bioelectrodes (e.g., 0.46 mC cm-2 at 50 mV). Under pulsed ES at 50 mV cm-1, these scaffolds support remarkable neurite outgrowth of dorsal root ganglion (DRG) neurons up to 830 m (7 days). Notably, higher current densities and voltages decrease the rate of neurite outgrowth, highlighting the importance of optimizing ES parameters to effectively evoke functional action potentials without causing any neuronal damage. Biocompatibility assessments reveal that AaSF functionalization improves cellular behavior while minimizing immunomodulatory responses. Enhanced neuronal and glial differentiation is attributed to better cell communication facilitated by excellent adhesion and increased conductivity. In essence, this study provides a strategy for selecting optimal ES parameters for electrically excitable tissues using established electrochemical techniques. The fabricated biohybrid scaffolds hold significant promise as smart nerve guidance channels (NGCs) for future nerve regeneration therapies.