Provided herein are biocompatible polymers having a polymer backbone and one or more repeating units, and methods of making and using the same. The repeating units can each be individually selected from a zwitterionic precursor repeating unit of Formula (1). Also provided are systems for nucleic acid delivery including the biocompatible polymers, the systems having a cationic core and a polysaccharide-anionic peptide conjugate adsorbed to the cationic core.