Bioinspired seeding of biomaterials using three dimensional microtissues induces chondrogenic stem cell differentiation and cartilage formation under growth factor free conditions.

Cell laden biomaterials are archetypically seeded with individual cells and steered into the desired behavior using exogenous stimuli to control growth and differentiation. In contrast, direct cell-cell contact is instructive and even essential for natural tissue formation. Namely, microaggregation and condensation of mesenchymal progenitor cells triggers chondrogenesis and thereby drives limb formation. Yet a biomimetic strategy translating this approach into a cell laden biomaterial-based therapy has remained largely unexplored. Here, we integrate the microenvironment of cellular condensation into biomaterials by encapsulating microaggregates of a hundred human periosteum-derived stem cells. This resulted in decreased stemness-related markers, up regulation of chondrogenic genes and improved in vivo cartilage tissue formation, as compared to single cell seeded biomaterials. Importantly, even in the absence of exogenous growth factors, the microaggregate laden hydrogels outperformed conventional single cell laden hydrogels containing supraphysiological levels of the chondrogenic growth factor TGFB. Overall, the bioinspired seeding strategy described herein represents an efficient and growth factor-free approach to efficiently steer cell fate and drive tissue formation for biomaterial-based tissue engineering strategies.

Enzymatically-crosslinked injectable hydrogels based on biomimetic dextran-hyaluronic acid conjugates for cartilage tissue engineering.

Polysaccharide hybrids consisting of hyaluronic acid (HA) grafted with a dextran-tyramine conjugate (Dex-TA) were synthesized and investigated as injectable biomimetic hydrogels for cartilage tissue engineering. The design of these hybrids (denoted as HA-g-Dex-TA) is based on the molecular structure of proteoglycans present in the extracellular matrix of native cartilage. Hydrogels of HA-g-Dex-TA were rapidly formed within 2 min via enzymatic crosslinking of the tyramine residues in the presence of horseradish peroxidase and hydrogen peroxide. The gelation time, equilibrium swelling and storage modulus could be adjusted by varying the degree of substitution of tyramine residues and polymer concentration. Bovine chondrocytes incorporated in the HA-g-Dex-TA hydrogels remained viable, as shown by the Live-dead assay. Moreover, enhanced chondrocyte proliferation and matrix production were observed in the HA-g-Dex-TA hydrogels compared to Dex-TA hydrogels. These results suggest that HA-g-Dex-TA hydrogels have a high potential as injectable scaffolds for cartilage tissue engineering.