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

Abstract

Smart hydrogels (SH) were prepared by thermal free radical polymerization of N-isopropyl acrylamide (NIPAAm), acrylamide (AAm) with acrylic acid (A) or maleic acid (M), and N, N′-methylene bisacrylamide. Spectroscopic and thermal characterizations of SHs were performed using FTIR, TGA, and DSC. To determine the effects of SHs on swelling characteristics, swelling studies were performed in different solvents, solutions, temperatures, pHs, and ionic strengths. In addition, cycle equilibrium swelling studies were carried out at different temperatures and pHs. The temperature and pH transition points of SHs are calculated using a sigmoidal equation. The pH transition points were calculated as 5.2 and 4.2 for SH-M and SH-A, respectively. The NIPAAm/AAm hydrogel exhibits a critical solution temperature (LCST) of 28.35 °C, while the SH-A and SH-M hydrogels exhibit the LCST of 34.215 °C and 28.798 °C, respectively, and the LCST of SH-A is close to the body. temperature. Commercial (CHSA) and blood human serum albumin (BHSA) were used to find the adsorption properties of biopolymers on SHs. SH-M was the most efficient SH, adsorbing 49% of CHSA while absorbing 16% of BHSA. In conclusion, the sigmoidal equation or Gaussian approach can be a useful tool for chemists, chemical engineers, polymer and plastics scientists to find the transition points of smart hydrogels.

Intelligent hydrogels and their biomedical applications

“…41 To biotransform the conventional hydrogel into an intelligent hydrogel, different crosslinking methods are carried out physically/chemically to fabricate hydrogels. 42 The modification is caused by covalent interactions such as differently charged ions, hydrophobic interactions, π–π interactions, electrostatic interactions, van der Waals as dipole–dipole interactions, and London dispersion forces. 43,44 Further, some injectable hydrogels can be prepared by physical self-crosslinking via exchanges such as host–guest interactions.…”

“…43,44 Further, some injectable hydrogels can be prepared by physical self-crosslinking via exchanges such as host–guest interactions. 42–44 Also, the diverse environmental stressors frequently impact crosslinking-induced gelation. 45…”

“…PNIPAM is a classic thermo-responsive intelligent biomaterial that can perform a changeable volume phase transition near the LCST. 11,42,80 The alternatives to invasive operations include hybrid thermal hydrogels made of chitosan with collagen, PEG, and carboxy methylcellulose. Additionally, polymers can be used to deliver specific drugs into the bloodstream via fluid administration.…”