Rheological study of albumin and hyaluronan-albumin hydrogels: Effect of concentration, ionic strength, pH and molecular weight

Albumin and hyaluronic acid are biodegradable, endogenous substances with potential use as drug carriers. These properties combined with the physical structure of the gel can lead to the formation of biologically active materials with application in medicine. This work investigated the gelation process of albumin solutions and mixed solutions of albumin and hyaluronan due to heating. The influence of the polymer concentration, weight ratio of hyaluronan and albumin, ionic strength, pH and molecular weight of hyaluronan is discussed. The study was carried out by measuring the rheological properties of the solutions, formed gels, and the gelation process. With increasing albumin concentration, the gel point was shifted towards lower temperature values. The resulting gels exhibited higher values of loss and storage moduli. For the mixed solutions of protein and polysaccharide, the effect of the polysaccharide concentration was observed. Based on the measurements, it can be assumed that the dependence of the complex modulus on the polysaccharide concentration has a peak at the certain hyaluronan: albumin weight ratio. The measured data showed, that increasing the ionic strength led to higher complex modulus values of the gels, and also to the increase of the temperature of the gel point. The gelation proceeded significantly faster when pH < pIBSA in comparison with the samples with pH > pIBSA. Increasing the pH of the solution (with respect to the albumin stability) led to higher complex modulus values of the gels formed. As a result of lowering the molecular weight of hyaluronan, the gel point was shifted towards lower temperature values, and resulting gels exhibited higher values of complex modulus. In addition, the ability of mixed BSA-HA solutions to bind hydrophobic substances was proven.