Design of a self-cleaning thermoresponsive nanocomposite hydrogel membrane for implantable biosensors.

Following implantation of a biosensor, adhesion of proteins and cells and eventual fibrous encapsulation will limit analyte diffusion and impair sensor performance. A thermoresponsive nanocomposite hydrogel was developed as a self-cleaning biosensor membrane to minimize the effect of the host response and its utility for an optical glucose sensor, demonstrated here. It was previously reported that thermoresponsive nanocomposite hydrogels prepared from photopolymerization of an aqueous solution of N-isopropylacrylamide (NIPAAm) and polysiloxane colloidal nanoparticles released adhered cells with thermal cycling. However, poly(N-isopropylacrylamide) hydrogels exhibit a volume phase transition temperature (VPTT) of approximately 33-34 degrees C, which is below body temperature. Thus, the hydrogel would be in a collapsed state in vivo, which would ultimately limit diffusion of the target analyte (e.g., glucose) to the encapsulated sensor. In this study, the VPTT of the nanocomposite hydrogel was increased by introducing N-vinylpyrrolidone (NVP) as a comonomer, so that the hydrogel was in the swollen state in vivo. This thermoresponsive nanocomposite hydrogel was prepared by the photopolymerization of an aqueous solution of NIPAAm, NVP, and polysiloxane colloidal nanoparticles. In addition to a VPTT a few degrees above body temperature, the hydrogel also exhibited good mechanical strength, glucose diffusion, and in vitro cell release upon thermal cycling. Thus, this nanocomposite hydrogel may be useful as a biosensor membrane to minimize biofouling and extend the lifetime and efficiency of implantable glucose sensors and other biosensors.