Incorporation of new carboxylate functionalized co-monomers to temperature-responsive polymer-grafted cell culture surfaces

Abstract

Several cultured cell types are easily detached from poly( N-isopropylacrylamide) (PIPAAm)-grafted surfaces only by reducing culture temperature without traditional proteolytic treatments that might damage certain cell functions. We have exploited these novel surfaces for tissue engineering applications where harvested intact cell sheets are useful for fabricating tissue-like constructs. We now extend the polymer chemistry of such grafted surfaces with new charged co-monomers. Functional carboxylate groups are incorporated into temperature-responsive surfaces with newly designed analogous carboxylate co-monomers, 2-carboxyisopropylacrylamide (CIPAAm) and 3-carboxy- n-propylacrylamide (CNPAAm), which have a small structural difference in the placement of the carboxylate group ( iso or normal to the monomer propyl group). P(IPAAm- co-CIPAAm) demonstrates a similar phase transition behavior to that of pure PIPAAm, and the ionic dissociation of carboxyl groups is suppressed (elevated p K′a) even under physiological conditions. By contrast, P(IPAAm- co-CNPAAm) exhibits a higher charge density (lower p K′a), higher hydration, and reduced temperature-sensitivity under identical conditions. Introduction of 5 mol% CNPAAm into PIPAAm grafted surfaces produces no cell attachment under typical cell culture conditions, while identical introductions of CIPAAm into grafted copolymers functions well for cell attachment. Cultured cell spreading efficiency was essentially similar on PIPAAm-grafted surfaces as on copolymer-grafted surfaces with 1 mol% introduction of either carboxylate co-monomer. Accelerated cell detachment upon reducing culture temperature was observed for the 1 mol% these copolymer-grafted surfaces since polymer hydration and swelling kinetics are enhanced by the increased ionizable moiety in these grafted surfaces.