Visible-light-triggered BMP-2 release from enzymatically crosslinked marine collagen-alginate hydrogel blends...

Achieving spatiotemporal control over osteoinductive signaling remains a key challenge in craniofacial tissue engineering. Conventional BMP-2 delivery from photocrosslinked hydrogels often leads to uncontrolled burst release and cytotoxic by-products from radical initiators. Here, we designed an enzymatically crosslinked marine collagen-alginate hydrogel blend that enables visible-light-triggered, on-demand release of BMP-2 while promoting oxygen diffusion through leachable porosity.

Marine collagen functionalized with thiol groups (collagen-SH) was crosslinked by microbial transglutaminase (mTG) under physiological conditions, avoiding light-initiated polymerization. Recombinant BMP-2 was conjugated via a coumarin-based 405 nm-cleavable linker (BMP-2_pc) and covalently tethered to the collagen network. Non-crosslinked sodium alginate (0.6% w/v) was incorporated as a sacrificial porogen to create micropores upon diffusion. DPSC were encapsulated (1.5 × 10⁶ cells/mL) and subjected to daily blue-LED pulses (405 ± 10 nm, 25 mW cm^-2, 60 s) for up to 14 days. BMP-2 release (ELISA), porosity (SEM), oxygen diffusivity (Clark microelectrode), viability, and osteogenic differentiation (ALP, qPCR, Alizarin Red) were assessed.

Blue-light stimulation induced stepwise BMP-2 release (≈23% per pulse; 60% cumulative at 72 h), while mTG crosslinking preserved coumarin integrity. Alginate leaching generated an interconnected microporosity (20-60 µm pores) and increased oxygen diffusion coefficient by 42% ± 9%. DPSC viability remained >90%. Light-pulsed composites exhibited 2.4-fold ALP activity and 2.8-fold higher mineral deposition versus dark controls (p < 0.01).

The orthogonally crosslinked marine collagen-alginate composite supports visible-light-controlled BMP-2 delivery and oxygen-enhanced osteogenesis without photoinitiator toxicity. This platform provides a modular, sustainable route toward clinically programmable scaffolds for dental and craniofacial regeneration.