Immunocompatible polymers

A biocompatible cross-linked polymer matrix encapsulating live cells, said matrix comprising a primary amine-containing polyampholyte covalently cross-linked with an electrophilic polymer or a small molecule crosslinking agent that is reactive to covalently crosslink primary amine groups within the polyampholyte to result in a matrix comprising live cells and having a net neutral or anionic charge, wherein the polyampholyte lacks cationic charge dense patches because it is prepared by copolymerization of cationic primary amine-containing monomers with anionic monomers, or by modifying negatively charged monomer units in a polyanion to positively charged monomer units, or by modifying positively charged monomer units in a polycation to negatively charged monomer units, to yield a polyampholyte comprising both negatively and positively charged monomer units.