Lyophilized pathogen-inactivated platelet lysate enriched hydrogel for cartilage tissue engineering

Platelet-derived products are increasingly investigated for cartilage regeneration because of their high content of bioactive factors. While rapid clearance after direct injection has been partly addressed by hydrogel encapsulation, many platelet-enriched hydrogels still rely on variably processed platelet derivatives, leaving challenges in standardization and storage stability. Here, we developed a gelatin-based hydrogel enriched with lyophilized, pathogen-inactivated human platelet lysate (L-PIPL) as an off-the-shelf platelet-derived reservoir for localized delivery of chondrogenic cues. L-PIPL was produced from expired pathogen-inactivated platelet units by freeze-thaw lysis and lyophilization, then incorporated into a gelatin-based hydrogel at 5, 10, and 15% (w/v). Composite hydrogels were characterized by scanning electron microscopy (SEM), attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), rheology, transforming growth factor beta 1 (TGF- $\beta$ 1) release, and soluble protein analysis. Cytocompatibility and early chondrogenic response were assessed in extruded, crosslinked cell-laden constructs using C20A4 chondrocytes and adipose-derived mesenchymal stromal cells (AD-MSCs). L-PIPL preserved the core hydrogel chemistry while modulating microarchitecture and viscoelastic properties. Moderate enrichment, particularly 5%-10% (w/v), maintained gel-like behavior and cytocompatibility, whereas 15% L-PIPL reduced network stability and cell viability. Release of bioactive factors was dose-dependent, with an initial burst followed by slower release over time. In AD-MSC-laden constructs, L-PIPL increased metabolic activity, with the 10% formulation showing the highest activity, and the 5% formulation showing the most favorable early chondrogenic commitment. L-PIPL-enriched hydrogels provide a standardized, cytocompatible, and bioactive matrix for localized delivery of platelet-derived factors. Overall, 5% L-PIPL emerged as the most promising formulation for further development in cartilage tissue engineering.