Development of 3D-printing composite inks based on photoreactive cartilage extracellular matrix and gelatin nanoparticles

Decellularized extracellular matrix (dECM)-based materials possess innate biochemical cues to drive cell recruitment and differentiation and are of interest for cartilage tissue engineering. While 3D-printing (3DP) provides a means for achieving the precise architecture needed for cartilage tissue engineering, dECM hydrogels have proven difficult to translate to 3DP due to low viscosity and weak mechanical properties. In this study, a cartilage dECM (cdECM, 3 w/v%) was combined with varied amounts of gelatin nanoparticles (GNPs; 10, 12.5, 15 w/v%) to form novel hydrogel-colloidal composite materials for 3DP. The addition of GNPs increased the viscosity and rheological properties of the cdECM hydrogel in a dose-dependent manner, directly improving the printability of cdECM 3DP inks. Additionally, functionalization of both materials yielded a UV-crosslinkable material for post-printing crosslinking, and increased GNP content increased post-UV storage moduli with 15 w/v% GNPs yielding a storage modulus 26x greater than that of cdECM alone. 3DP construct swelling and degradation were decreased as a function of increased UV-crosslinking dosage (0, 1.5, and 3 J/cm²). After 14 d of swelling in PBS, construct non-porous area was increased by ∼40 % and pore area was increased by ∼30 % for uncrosslinked (0 J/cm²) constructs versus highly crosslinked (3 J/cm²) constructs. Roughly 40 % higher mass retention was observed across GNP content groups for 3 J/cm² versus 0 J/cm² UV exposure after 14 d of enzymatic degradation, showing the potential for tuning physicochemical properties via UV exposure. Likewise, the retention of key biochemical components of cdECM over the course of degradation was evaluated. Sulfated glycosaminoglycans, a key reservoir for tissue-specific growth factors, were found to be retained within scaffolds over 14 d of degradation and to be released relative to construct degradation and UV-crosslinking. The results suggest that a photoreactive dECM and colloidal composite material provides a platform for increasing the printability of dECM inks and the delivery of complex biochemical cues for regenerative medicine applications.