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

New hydrogels based on N-isopropylacrylamide copolymerized with an activate d monomer have been developed as vesicle immobilizing devices. in order to provide a strong and reversible interaction between the solid support and t he lipid vesicles, we chose polylysine, a cationic polypeptide as the ancho ring element. Our systems are based on N-isopropylacrylamide copolymerized with an activated monomer and then crosslinked with polylysine. The innovat ive 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 site s; and (iii) as an hydrophilic molecule, polylysine improves the swelling p roperties of the gel and therefore the capacity of vesicle binding. Several hydrogels were synthesized with varying monomer ratios and polylysine leng ths. The characterization of the systems includes an estimation of the abil ity 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 polymeri zation of 288). This hydrogel can immobilize up to 1000 mu mol of lipids pe r 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 in crease of the temperature. (C) 2000 Elsevier Science Ltd. All rights reserv ed.