title: Synthesis and characterization of a novel PNIPAAm-based copolymer with hydrolysis-dependent thermosensitivity.
abstract: The aim of this work was the synthesis and characterization of a novel poly(N-isopropylacrylamide)-based copolymer, with hydrolysis-dependent thermosensitivity, for bioengineering applications. For this purpose, N-isopropylacrylamide (NIPAAm) and 2-hydroxyethylmethacrylate-6-hydroxyhexanoate (HEMAHex) monomers were chosen. The poly(NIPAAm-co-HEMAHex) copolymer was synthesized by radical polymerization. The physicochemical, mechanical, functional and biological properties of the copolymer were investigated. The physicochemical characterization confirmed that the copolymerization was successfully carried out. In addition, the newly synthesized poly(NIPAAm-co-HEMAHex) copolymer showed temperature sensitivity, with a phase separation temperature under body temperature (at 23 °C). Fourier transform infrared spectroscopy and differential scanning calorimetry results after hydrolysis tests indicated that the incorporation of the HEMAHex ester groups provides the cleavage of the lateral chain, which leads to an increase in the hydrophilicity of the copolymer and, consequently, to an increase in the lower critical solution temperature (LCST) with time. Since the LCST increases above body temperature (up to 40.4 °C), the copolymer becomes soluble again and diffuses away. It was also demonstrated that the hydrolysis occurred on the peripheral ester bond of the lateral chain, with the release of 6-hydroxyhexanoic acid, whose bioresorbibility has been reported in the literature. Therefore, the properties of this copolymer are very interesting and make it particularly attractive for biomedical applications.
authors.affiliation: Department of Chemical Engineering, Industrial Chemistry and Materials Science, University of Pisa, Via Diotisalvi 2, 56126 Pisa, Italy.
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Rosellini
authors.forename: Caterina
authors.initials: C
authors.lastname: Cristallini
authors.forename: Giulio D
authors.initials: GD
authors.lastname: Guerra
authors.forename: Niccoletta
authors.initials: N
authors.lastname: Barbani
authors.forename: Paolo
authors.initials: P
authors.lastname: Giusti
mesh_terms: D000180:Acrylic Resins / Q000138:chemical synthesis*; D001672:Biocompatible Materials / Q000138:chemical synthesis*; D006868:Hydrolysis; D057927:Hydrophobic and Hydrophilic Interactions; D008422:Materials Testing; D011109:Polymethacrylic Acids / Q000737:chemistry*; D013696:Temperature
chemical_list: D000180:Acrylic Resins; D001672:Biocompatible Materials; D011109:Polymethacrylic Acids; C031453:aminohexyl-2-hydroxyethylmethacrylate polymer; C052970:poly-N-isopropylacrylamide