Tuning Human Serum Albumin (HSA) Hydrogels through Albumin Glycation.

The changes of technological properties of albumin-based hydrogels induced by increasing degrees of post-translational modification of the protein are reported. Maillard-type modification of amino acids arginine and lysine of albumin is achieved through glyoxal as an α-dicarbonyl compound. The degrees of modification are fine-tuned using different molar ratios of glyoxal. Hydrogels are thermally induced by heating highly concentrated precursor solutions above the protein's denaturation temperature. While the post-translational modifications are determined and quantified with mass spectrometry, continuous-wave (CW) electron paramagnetic resonance (EPR) spectroscopy shed light on the protein fatty acid binding capacity and changes thereof in solution and in the gel state. The viscoelastic behavior is characterized as a measure of the physical strength of the hydrogels. On the nanoscopic level, the modified albumins in low concentration solution reveal lower binding capacities with increasing degrees of modification. On the contrary, in the gel state, the binding capacity remains constant at all degrees of modifications. This indicates that the loss of fatty acid binding capacity for individual albumin molecules is partially compensated by new binding sites in the gel state, potentially formed by modified amino acids. Such, albumin glycation offers a fine-tuning method of technological and nanoscopic properties of these gels.

Serum albumin hydrogels in broad pH and temperature ranges: characterization of their self-assembled structures and nanoscopic and macroscopic properties.

We report extended pH- and temperature-induced preparation procedures and explore the materials and molecular properties of different types of hydrogels made from human and bovine serum albumin, the major transport protein in the blood of mammals. We describe the diverse range of properties of these hydrogels at three levels: (1) their viscoelastic (macroscopic) behavior, (2) protein secondary structure changes during the gelation process (via ATR-FTIR spectroscopy), and (3) the hydrogel fatty acid (FA) binding capacity and derive from this the generalized tertiary structure through CW EPR spectroscopy. We describe the possibility of preparing hydrogels from serum albumin under mild conditions such as low temperatures (notably below albumin's denaturation temperature) and neutral pH value. As such, the proteins retain most of their native secondary structure. We find that all the combined data indicate a two-stage gelation process that is studied in detail. We summarize these findings and the explored dependences of the gels on pH, temperature, concentration, and incubation time by proposing phase diagrams for both HSA and BSA gel-states. As such, it has become possible to prepare gels that have the desired nanoscopic and macroscopic properties, which can, in future, be tested for, e.g., drug delivery applications.