Nanosilica cross-linked polyurethane hybrid hydrogels to stabilize the silicone rubber based invasive...

An unstable electrode-neural tissue interface induced by tissue inflammatory response hinders the application of invasive brain-computer interfaces (BCIs). In this work, nanosilica cross-linked polyurethane (SiO₂/PU) hybrid hydrogels were prepared to serve as the coatings and to modify silicone rubber (SR), which is a commonly used encapsulation material of invasive electrodes for neural recording/stimulation. The hydrophilicity, swelling ratio, and bulk ionic conductivity of SiO₂/PU hybrid hydrogels were tailored by incorporating different amount of SiO₂ serving as the cross-linking agent. Correspondingly, the optimized SiO₂/PU hybrid hydrogel coatings have less impact on the electrochemical properties of invasive electrodes relative to PU hydrogel. Cell affinity assays with rat pheochromocytoma cells reveal that coatings made of SiO₂/PU hybrid hydrogels are more effective in enhancing their adhesion and neurite outgrowth than those made of PU hydrogels. The adsorption amount of non-specific proteins on SR is significantly reduced by 81.6 % and 92.6 % upon coating with PU hydrogels and SiO₂/PU hybrid hydrogels, respectively. Histological assessment indicates that the SR implants with a SiO₂/PU hybrid hydrogel coating provoke the mildest tissue response. Collectively, the SiO₂/PU hybrid hydrogel is highly promising for the stabilization of electrode-neural tissue interface, which is crucial for the development of invasive BCIs.