Facile preparation of tertiary amine grafted poly (α,β-L-aspartic acid) with zwitterionic property to limit nonspecific protein adsorption

A series of poly (amino acid) with zwitterionic character was prepared for surface coating to avoid protein adsorption, by modifying the poly (aspartic acid) side chain with tertiary amine groups. An interesting and facile procedure is described with starts with polysuccinic acid which is followed by ring-opening with amino functions and finally hydrolysis of the remaining succinic acid groups achieving the polyaspartic acid structure as backbone. The degree of cationic tertiary amino group was easily varied by the degree of ring-opening with amines. The materials show isoelectric point between pH 4 and 9, have a typical zwitterionic character, and can be used to coat negatively as well as positively charged surfaces, depending on composition. The protein adsorption behavior is thus pH dependent and was studied with various proteins mainly available in blood. The adsorption test proved that a significant reduction of protein adsorption could be found for fibrinogen and albumin, and this protein-repellent behavior is strongly dependent on the amount of the absorbed polymer (adsorbed at pH = 7.4). This is a nice additional contribution to polymers with zwitterionic character used as coating reducing nonspecific protein adsorption.