Crosslinked Hydrogel Capsules for Cell Encapsulation Formed Using Amino/Betaine Dual-Functional Semibatch Copolymers

Abstract

Robust hydrogel capsules consisting of calcium alginate beads with shells reinforced via crosslinked amino/betaine copolymers of N-(3-aminopropyl) methacrylamide hydrochloride (APM) with 2-methacryloyloxyethyl phosphorylcholine (MPC) are described. These capsules are designed to support future use in immunoisolation of therapeutic cells for transplant purposes. The poly[APM-co-MPC] copolymers were prepared by semibatch free radical copolymerization to reduce the significant compositional drift and the resulting diffusional spread within alginate beads, observed for analogous batch copolymers. Fluorescent labeling was used to track copolymer distribution within the alginate hydrogels. Semibatch copolymers led to better shell confinement and lower cationic charge density on the capsule surface. Three reagents were used to covalently cross-link the resulting poly(amino/betaine) shells: cationic tetrakis(hydroxymethyl)phosphonium chloride (THPC), charge-neutral genipin and anionic partially hydrolyzed poly(methyl vinyl ether-alt-maleic anhydride) (PMM50). Genipin-crosslinked capsules were found to be remarkably robust in pipet aspiration tests. Selected capsules were exposed to FITC-labeled bovine serum albumin to assess the relative degree of protein adhesion, as a proxy for immune recognition; genipin crosslinked capsules were found to have very low levels of BSA binding and good mechanical robustness.