Systematic evaluation of photoinitiating systems for engineering tunable gelma hydrogels

Over the years, biomaterials have become central to the development of advanced biomedical therapies, offering customizable platforms for tissue engineering, regenerative medicine, and controlled drug delivery. Among these, gelatin, a denatured derivative of collagen, has emerged as a highly promising candidate owing to its inherent biocompatibility, biodegradability, and cell-interactive features that facilitate cell adhesion, migration, and remodeling. However, native gelatin suffers from lack of tunability, poor mechanical strength and rapid dissolution at physiological conditions, limiting its use in tissue engineering applications without further modification. To overcome these drawbacks, gelatin methacryloyl (GelMA) was developed by introducing methacryloyl groups onto gelatin backbones, thereby enabling light-mediated covalent cross-linking and yielding hydrogels with adjustable mechanical properties and high cytocompatibility, making GelMA an exceptionally versatile biomaterial for wide range of biomedical applications. While GelMA's photo-crosslinkability offers precise spatiotemporal control, its final properties are highly dependent on the photoinitiator system and its concentration. Despite the broad use of both UV- and visible-light-sensitive initiators, the field still lacks rigorous side-by-side evaluations under standardized conditions, limiting our understanding of how initiator chemistry shapes hydrogel performance. To address this, the present thesis study systematically compares the effects of three commonly used systems Eosin Y (EY), Lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP), and Ruthenium/Sodium Persulfate (Ru/SPS), on the mechanical, degradation, swelling, and cytocompatibility properties of 5% and 10% (w/v) GelMA hydrogels. A comprehensive experimental workflow was employed, including real-time rheometry, enzymatic degradation studies, swelling and porosity analysis, and NIH-3T3 fibroblast viability assays. GelMA synthesis yielded a high degree of methacrylation (~81%), ensuring consistent cross-linking performance. The study identified system-specific threshold photoinitiator concentrations beyond which mechanical or biological performance was compromised, thereby elucidating critical trade-offs among stiffness, stability, and cytocompatibility. Distinct polymerization kinetics and structure–function relationships were revealed: LAP enabled rapid UV crosslinking with broad cytocompatibility, EY supported uniform visible-light-mediated networks with controlled gelation, and Ru/SPS, despite cytotoxicity at elevated concentrations, provided a degradable and highly swellable scaffold ideal for transient biomedical applications. Collectively, this work provides an essential resource for rational photoinitiator selection and hydrogel design, offering actionable insights for the engineering of GelMA-based constructs tailored to specific biomedical applications.