Synthesis and characterization of biocompatible zwitterionic sulfobetaine polypeptides and their resistance to protein adsorption

A zwitterionic polypeptide derivative was successfully synthesized using 3-dimethylaminopropylamine as the ring-opening reagent to react with polysuccinimide, and a poly(alpha,beta-L-dimethylamino propyl aspartamide) was obtained with tertiary amine side groups; the ring-opening reagent then reacted with 1,3-propanesultone to prepeare the poly(alpha,beta-3-dimethyl propyl ammonium propanesulfonate aspartamide) (PSBA). PSBA possessed both cationic moiety in the form of quaternary ammonium and anionic functionality in the form of a sulfo-group on the same repeat unit; it also exhibited an isoelectric point (pI) and opposite charges at pH values far high or below the pI. FT-IR and H-1 NMR spectroscopy were used to confirm the chemical structure of PSBA. Zwitterionic polypeptides were coated onto the amino functional silica wafers via electrostatic attraction. The PSBA-coated silica wafers were characterized by water contact angle analysis, X-ray photoelectron spectroscopy (XPS), and atomic force microscope (AFM). Protein adsorption measurements indicated that polypeptides with zwitterionic sulfobetaine structure had good anti-protein-fouling property. The amount of protein adsorbed on the coated surface could be controlled, depending on the pre-coated polymer concentration. Because of its good biocompatibility and anti-protein-fouling property, this zwitterionic polypeptide is a promising candidate for surface modification in many biomedical applications, such as medical implants, drug delivery carriers, and biosensors.