Thermoresponsive hydrogels with comb-type architecture for "self-cleaning" glucose biosensor membranes
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2019 Omnipress - All rights reserved. Statement of Purpose: Hydrogels, crosslinked polymer networks with high water content, can be used as biocompatible membranes towards creating implantable devices. Previously, double network (DN) hydrogels were used to house a liquid, fluorescent glucose sensing assay to construct an implantable continuous glucose monitor (CGM)1. These DN hydrogels, based on poly(N-isopropylacrylamide) (PNIPAAm), limited cell adhesion (i.e. biofouling) through a "self-cleaning" mechanism in which cyclical dimensional changes were induced by temperature fluctuation above or below their volume phase transition temperature (VPTT). The DN hydrogel membranes ("DN-25%") exhibited requisite properties for a long-term implantable biosensor, including mechanical robustness, high water content (~80%) and minimal fibrous capsule formation2. However, DN membrane mesh size (~4-7 nm) was greater than that of an assay component (fluorescent labeled mannotetarose, ~3 nm), resulting in leaching and hence decreased sensor accuracy and lifetime. Common methods used to decrease hydrogel mesh size (e.g. increasing crosslink density or polymer concentration) would simultaneously diminish biocompatibility by increasing modulus and decreasing water content. In order to maintain the membranes biocompatibility while improving assay encapsulation, a comb-type architecture was introduced into the 1st network of the DN, thereby altering mesh size without affecting mechanical properties or hydration. Combs that contained different charges were evaluated (i.e. negative, positive and neutral). Comb DN hydrogels with optimized comb charges, length and concentration achieved a mesh size < 3 nm, while maintaining a similar robust modulus (~1 MPa) and high water content (~80%).
