Hydrophobically Modified Alginate-Based Biomatrix for Temperature- and pH-Stabilization of Encapsulated Protein

Sodium alginate (SA) was hydrophobically modified with stearyl methacrylate (C18) to develop a novel biopolymer matrix, SA-g-C18, for protein encapsulation and stabilization. Successful modification was confirmed by FTIR and NMR spectroscopy. The grafting process altered the polymer’s interfacial and colloidal properties, significantly increasing its contact angle and producing a more negative zeta potential, validating the hydrophobic integration. Spheroids of both pristine SA and modified SA-g-C18 were fabricated through ionic crosslinking using calcium chloride at varying concentrations, where lower crosslinking densities yielded greater swelling behavior. Rheological strain sweeps revealed that the SA-g-C18 matrix possesses a lower crosslink density than pristine SA, directly accounting for its enhanced porosity and swelling capacity, while simultaneously exhibiting superior mechanical ductility and a delayed yield point. An in vitro viability study using L929 fibroblast cell lines confirmed the excellent cytocompatibility of these systems. Bovine serum albumin (BSA) was encapsulated within these spheroids, and its structural integrity was comprehensively evaluated under severe environmental stress conditions across a wide temperature range (40–80 °C) and a pH range (3–9) using circular dichroism (CD) spectroscopy. This BSA-encapsulated biomatrix offers highly promising potential for safe, controlled protein-delivery applications, enabling robust structural monitoring.