Equilibrium Swelling of Biocompatible Thermo-Responsive Copolymer Gels

Abstract

Biomedical applications of thermo-responsive (TR) hydrogels require these materials to be biocompatible, non-cytotoxic, and non-immunogenic. Due to serious concerns regarding potential toxicity of poly(N-isopropylacrylamide) (PNIPAm), design of alternative homo- and copolymer gels with controllable swelling properties has recently become a hot topic. This study focuses on equilibrium swelling of five potential candidates to replace PNIPAm in biomedical and biotechnological applications: poly(N-vinylcaprolactam), poly(vinyl methyl ether), poly(N,N-dimethyl amino ethyl methacrylate), and two families of poly(2-oxazoline)s, and poly(oligo(ethylene glycol) methacrylates). To evaluate their water uptake properties and to compare them with those of substituted acrylamide gels, a unified model is developed for equilibrium swelling of TR copolymer gels with various types of swelling diagrams. Depending on the strength of hydrophobic interactions (high, intermediate, and low), the (co)polymers under consideration are split into three groups that reveal different responses at and above the volume phase transition temperature.

Equilibrium Swelling of Thermo-Responsive Gels in Mixtures of Solvents

“…The experimental dependence χ(T) is determined from Equation (18). Given "universal" values of χ T0 and χ T1 (these parameters were found in [74,75] for several TR gels), the coefficients g 1 and Q 0 are calculated from the best-fit condition by matching the dependence χ(T) with the help of Equations ( 13) and (14). At the other step, experimental data above T c are fitted by the means of two parameters, ḡ2 and β.…”

Smart Hydrogels: Preparation, Characterization, and Determination of Transition Points of Crosslinked N-Isopropyl Acrylamide/Acrylamide/Carboxylic Acids Polymers

“…Three-dimensional cross-linked polymeric structures that love water are called hydrogels [1][2][3], and those that respond to external stimuli (such as pH, temperature, ionic strength, electric field, light, magnetic field, and so forth) as volume changes are called smart or intelligent or stimuli-responsive hydrogels [4][5][6][7][8][9][10][11][12][13][14][15].…”

“…These gels are used in biological sensing, drug release and tissue degeneration, artificial muscles, micro-electromechanical-system instruments such as microvalves, and microfluidity controllers. In addition to these, diapers, irrigation, and smart windows can be given as examples in daily life [11][12][13][14][15]. In the temperature-responsive gels, when the temperature rises above a certain value, phase separation occurs, and the gel shrinks.…”

“…Below the LCST, the compatibility of the gel with water increases, and swelling is observed. This is explained by the strengthening of hydrogen bonds between water molecules and hydrophilic groups [4][5][6][7][8][9][10][11][12][13][14][15].…”

“…The resulting positive charges repel each other, water diffusion is achieved, and swelling is observed in the gel. This swelling shrinkage transition pH is called the inflection point (IP) [4][5][6][7][8][9][10][11][12][13][14][15].…”