Poly[(N-isopropylacrylamide-co-acrylamide-co-(hydroxyethylmethacrylate))] thermoresponsive microspheres: An accurate method based on solute exclusion technique to determine the volume phase transition temperature |
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Authors: | G. Fundueanu M. Constantin R. Cortesi P. Ascenzi |
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Affiliation: | a Department of Pharmaceutical Sciences, University of Ferrara, I-44100 Ferrara, Italy b Department of Bioactive and Biocompatible Polymers, “Petru Poni” Institute of Macromolecular Chemistry, 700487 Iassy, Romania c Department of Biology and Interdepartmental Laboratory for Electron Microscopy, University “Roma Tre”, I-00146 Rome, Italy |
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Abstract: | Poly[(N-isopropylacrylamide-co-acrylamide-co-(hydroxyethylmethacrylate))] [poly(NIPAAm-co-AAm-co-HEMA)] copolymer was synthesized as a new thermoresponsive material possessing a lower critical solution temperature (LCST) around 37 °C in phosphate buffer, pH 7.4, at a solution concentration of 1%, w/v. The influence of polymer concentration on LCST was determined by cloud point measurements and by microcalorimetric analysis. The copolymer was transformed in hydrogel microspheres by suspension reticulation of OH groups with glutaraldehyde. The volume phase transition temperature (VPTT) of microspheres was determined by a new approach, which involves measurement of the increase in concentration of a blue dextran (BD) solution at different temperatures in the presence of dry microspheres. The minimum BD concentration that gives reliable and reproducible results was determined to be 1 mg/ml. However, the higher is the concentration of BD in solution the smaller is the error. Contrary to solution of the linear polymer which displays a sharp phase transition temperature, the dependence of water regain of the hydrogel with temperature lasts from 4 °C to 50 °C. |
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Keywords: | AAm, acrylamide AIBN, N,N&prime -azobisisobutyronitrile BD, blue dextran CP, cloud point D2O, deuterated water GA, glutaraldehyde HEMA, 2-hydroxyethyl methacrylate ISEC, inverse size exclusion chromatography LCST, lower critical solution temperature NIPAAm, N-isopropylacrylamide VPTT, volume phase transition temperature |
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