Calcium-Structured Alginate Hydrogels: Network Formation, Rheology, Swelling, and Collagen Release

Combined hydrogels based on interpenetrating polymer networks of sodium alginate, hydrolyzed collagen, hydroxypropyl methylcellulose, and the calcium salt of lightly crosslinked poly(acrylic acid) were developed for potential use as wound dressings. The effects of the alginate-to-collagen ratio on network formation and the functional properties of the materials were evaluated by extraction-based gel-fraction determination, Fourier-transform infrared spectroscopy, mechanical and rheological measurements, swelling studies in water and simulated wound exudate, collagen-release analysis, and in vitro cytocompatibility assessment. Extraction analysis and spectroscopic data confirmed the incorporation of collagen into the polymer network and revealed a nonlinear relationship between composition and network-formation efficiency. Structural stability was governed by the balance between calcium-mediated ionic crosslinking, electrostatic interactions, and hydrogen bonding, whereas an excess of unbound low-molecular-weight collagen fragments reduced the insoluble network fraction. All hydrogels exhibited predominantly elastic behavior, while their stiffness and mechanical strength varied nonmonotonically with the biopolymer ratio. Swelling was determined by network composition and density; in simulated wound exudate, ionic screening, limited matrix expansion and promoted shape retention. Collagen-release kinetics were also composition-dependent: a more hydrophilic, mobile, alginate-rich network provided faster release, whereas a higher collagen content promoted prolonged diffusion. Cytocompatibility assessment of the representative formulation (Sample 2) indicated no reduction in cell viability in the applied in vitro model, although alterations in oxidative enzyme activity were observed. These findings demonstrate that the structural, mechanical, sorption, and release properties of alginate–collagen hydrogels can be tailored for the development of promising wound dressings.