Hofmeister Effects of Anions on Self-assembled Thermogels

Thermogels are smart, temperature-responsive soft biomaterials with numerous biomedical applications. They possess high water content, and can spontaneously gelate by forming non-covalent physical crosslinks between their constituent amphiphilic polymers when warmed. However, despite the ubiquity of salts in biological fluids and buffer media, the influence of salts on thermogelling polymers and the overall physical properties of the resulting hydrogels are poorly understood. Herein, we elucidate the effects of common inorganic salts on the gelation and micellisation properties of a thermogelling polymer containing poly(ethylene glycol), poly(propylene glycol) and poly(caprolactone) components. The identity of the salts’ anions and their concentrations were found to exhibit significant effects on the thermogel properties, in some cases being able to decrease the sol-to-gel phase transition by up to 10 oC. We demonstrate that these notable influences are likely brought about by the changes in solvation of both the polymer’s hydrophobic and hydrophilic segments, as well as by direct interactions of poorly-hydrated anions with the hydrophobic polymer segments. Our findings demonstrate that the effects of salts on amphiphilic thermogelling polymers are non-negligible, and hence need to be taken into account for engineering and optimisation of thermogel properties for different biomedical applications.热凝胶（thermogels）是一类智能型温度响应性软质生物材料，具备广泛的生物医学应用前景。该类材料含水量极高，当温度升高时，其构成单元两亲性聚合物（amphiphilic polymers）之间可形成非共价物理交联，从而自发发生凝胶化。然而，尽管盐类广泛存在于生物体液与缓冲介质中，但学界对盐类影响热凝胶聚合物以及所得水凝胶（hydrogels）整体物理性能的机制仍不甚明晰。本研究阐明了常见无机盐对一款含聚乙二醇（poly(ethylene glycol)）、聚丙二醇（poly(propylene glycol)）与聚己内酯（poly(caprolactone)）组分的热凝胶聚合物的凝胶化与胶束化性能的影响。研究发现，盐类阴离子的种类及其浓度对热凝胶性能具有显著调控作用，在部分场景下可使溶胶-凝胶相转变温度最多降低10 ℃。本研究证实，这类显著影响可能源于聚合物疏水段与亲水段的溶剂化状态改变，以及水合能力较弱的阴离子与聚合物疏水段之间的直接相互作用。本研究结果表明，盐类对两亲性热凝胶聚合物的影响不容小觑，因此在针对不同生物医学应用场景开发与优化热凝胶性能时，必须将该因素纳入考量范围。