Improving SiC surface properties by hyaluronic acid hydrogel deposition for neural probe applications

Abstract

The reliability and long-term stability of neural probes after in vivo implantation depend first and foremost on the tissue-device interface, which can be improved by the development of hybrid inorganic/organic material interfaces. We report the deposition process of hyaluronic acid (HA) hydrogel film as a biomimetic polymer on amorphous SiC (a-SiC) film. This is a two-step process involving first the covalent immobilization of an azide-modified HA derivative (HA-N₃) which is followed by deposition of a cross-linked HA hydrogel film obtained by a strain-promoted azide-alkyne cycloaddition (SPAAC) reaction. Prior the a-SiC surface was modified with an amino-silane (APTES) enabling the covalent grafting of HA-N₃ on a-SiC. The step-by-step modification of the a-SiC surface properties has been investigated. The chemical modification is evidenced by XPS measurements and Raman spectra, which demonstrate the presence of an homogeneous HA film with expected chemical environments for C, N and O elements. The surface morphology modification is characterized by an increase of roughness going from 1 nm to 45 ± 3 nm (RMS). These changes in chemical composition and roughness result in an increase in wettability giving a low contact angle value of 26.4° with low dispersion, indicating that the HA layer is hydrophilic and homogeneous. The high initial stiffness of the a-SiC film is reduced by 10³, leading to a Young's modulus of ∼6 kPa obtained from nano-indentation measurements. This local AFM data was compared to the bulk rheological properties to get insights about deformation modes in the HA network. These preliminary results demonstrate the success of the process and pave the way for further experiments, which will focus on the in vitro and in vivo impact of the biopolymer coating on neural cell attachment and growth.