Highly hydroresponsive nacre-like oligo proanthocyanidin-intercalated Ca–Al-Layered double hydroxides/graphene oxide/polyvinyl alcohol as a potential neural implant material

Neural implantation with a microscale electrode permits a real-time neuromoduration to enhance the treatment of neural disorders. However, the penetration of a neural microprobe into soft brain tissues always resulted in the invasive tissue damage and mechanical tissue-device friction, which further induced the extensive chronic inflammation that limited the device lifetime. To develop a biocompatible and biocompliant neural implant, this study presented a smart substrate with bioinspired nacre-like structure that can exhibit ultra-hydroresponsive mechanical strength transition, sustained anti-inflammatory drug delivery, and anti-biofouling ability. An organic-inorganic composite, called LOG-P, was synthesized with oligo proanthocyanidin (OPC)-intercalated Ca–Al layered double hydroxide (Ca–Al-LDH) and graphene oxide (GO), followed by crosslinked with linear structural polyvinyl alcohol (PVA) to form a brick-and-mortar architecture. LOG-P exhibited strong mechanical strength of ~ 5 GPa in Young's modulus at dehydrated state, while showing ~99% decrease of Young's modulus when getting hydrated. In addition, the intercalation of OPC in LDH led to zero-order release with duration up to 80 days. LOG-P with negatively charged surfaces inhibited the adhesion of astrocytes, while the released OPC led to robust neuronal cell viability. Finally, integrated with Ag circuits by aerosol jet printing, the fabricated LOG-P-based microelectrode arrays showed stable electroactivity, also permitting a complete penetration into brain-tissue phantoms without bending. Such organic-inorganic nanocomposite-based neural interface with physical, chemical, and biological compatibility was expected to be a revolutionary platform for development of next-generation neural implants.