New thermothickening copolymers were synthesized by grafting responsive poly(ethylene oxide-co-propylene oxide) [PEPO] onto three different polysaccharide backbones: carboxymethylcellulose [CMC], alginate [ALG], and carboxylated dextran [DEX]. The coupling reaction between carboxylic groups of biopolymers and the terminal amine of PEPO was activated at low temperature (T < 10 °C) in water by using carbodiimide and N-hydroxysuccinimide. In these conditions it was shown that the formation of amide bonds strongly depends on the concentration of reactive groups, which is limited by the viscosity of the polymer sample. While a full conversion was obtained for the low molecular weight dextran, the efficiency of grafting remains low (between 30 to 40%) for CMC and alginate, which give a solution of high viscosity even at low concentration. When studied in the semidilute regime, all the copolymer solutions clearly exhibit thermothickening behavior with a large and reversible increase of viscosity upon heating. The association temperature and the gelation threshold were shown to depend on polymer concentration as it is expected from the phase diagram of PEPO precursor. Similarly, the influence of added salt on PEPO solubility in water has been used to control the self-assembling behavior of copolymer formulations. The relative comparison between the three copolymers reveals that the amplitude of the viscosity jump induced by heating mainly depends on the proportion of responsive material inside the macromolecular architecture rather than the dimensions of the main chain. The high increase of viscosity, which can reach several orders of magnitude between 20 °C and body temperature, clearly demonstrates the potentiality of these copolymers in biomedical applications like injectable gels for tissue engineering.
A new reversible gelation pathway is described for alginates in aqueous media. From various samples differing by their mannuronic/guluronic content (M/G), both enthalpic and viscoelastic experiments demonstrate that alginates having a high M content are able to form thermoreversible assemblies in the presence of potassium salts. The aggregation behavior is driven by the low solubility of M-blocks at low temperature and high ionic strength. In semidilute solutions, responsive assemblies induce a strong increase of the viscosity below a critical temperature. A true physical gel is obtained in the entangled regime, although the length scale of specific interactions between M-blocks decreases with increasing density of entanglements. Cold setting takes place at low temperatures, below 0 °C for potassium concentrations lower than 0.2 mol/kg, but the aggregation process can be easily shifted to higher temperatures by increasing the salt concentration. The self-assembling process of alginates in solution of potassium salts is characterized by a sharp gelation exotherm and a broad melting endotherm with a large hysteresis of 20-30 °C between the transition temperatures. The viscoelastic properties of alginate gels in potassium salts closely depend on thermal treatment (rate of cooling, time, and temperature of storage), polymer and salt concentrations, and monomer composition as well. In the case of alginates with a high G content, a similar aggregation behavior is also evidenced at higher salt concentrations, but the extent of the self-assembling process remains too weak to develop a true gelation behavior in solution.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.