New hydrogels based on N-isopropylacrylamide copolymers crosslinked with polylysine:: membrane immobilization systems

New hydrogels based on N-isopropylacrylamide copolymerized with an activated monomer have been developed as vesicle immobilizing devices. in order to provide a strong and reversible interaction between the solid support and the lipid vesicles, we chose polylysine, a cationic polypeptide as the anchoring element. Our systems are based on N-isopropylacrylamide copolymerized with an activated monomer and then crosslinked with polylysine. The innovative feature of this approach is that the polypeptide plays many key roles: (i) it is used as crosslinker; (ii) its positive charges act as anchor sites; and (iii) as an hydrophilic molecule, polylysine improves the swelling properties of the gel and therefore the capacity of vesicle binding. Several hydrogels were synthesized with varying monomer ratios and polylysine lengths. The characterization of the systems includes an estimation of the ability of the gels to immobilize vesicles and of the integrity of the adsorbed vesicles. The most efficient gel is made of a copolymer containing 6 mol% of activated monomer crosslinked with a long polylysine (degree of polymerization of 288). This hydrogel can immobilize up to 1000 mu mol of lipids per gram of dry gel. Control experiments show clearly that the nature of the anchoring interaction is electrostatic. As an illustration of the potential applications of such a system, we show that vesicles can be immobilized in a gel-packed column and the release of their content is triggered by an increase of the temperature. (C) 2000 Elsevier Science Ltd. All rights reserved.