Mechanical Tuning of the Cell Microenvironment Using a Biomimetic Hydrogel System for Articular Cartilage Tissue Engineering.

Providing a functional pericellular matrix (PCM) by fine-tuning the microenvironment of the articular chondrocytes (ACs) can greatly improve the outcomes of articular cartilage tissue engineering. While harvesting ACs with their PCM (chondrons) results in a low cell yield and a heterogeneous mixture of ACs and chondrons, microscale hydrogels could be used for mechanical tuning of the cell microenvironment. This may enable the use of stiffer bulk materials, improving the load-bearing capacity of the construct. This study investigates the effect of microenvironmental stiffness, independent of total construct stiffness, on the regenerative performance of ACs (ECM and PCM synthesis). Additionally, we explored articular cartilage-derived progenitor cells (ACPCs) as a possible alternative to ACs in the presented system. ACs were cultured in a soft or stiff bulk hydrogel (GelMA) or were encapsulated in soft microgels and seeded into the stiff GelMA. Constructs were seeded in an ex vivo porcine chondral defect model and cultured for 28 days with dynamic mechanical stimulation using a compression-sliding bioreactor. PCM and ECM quality were assessed through cell content analysis, immunofluorescent staining, histology, and measurements of GAG and collagen content. Cell encapsulation influenced ECM synthesis and PCM amount and completeness throughout the construct. Although the nonencapsulated groups showed stronger overall alcian blue staining, the encapsulated groups demonstrated more uniform matrix deposition throughout the depth of the tissue. Furthermore, ACPCs performed similarly to ACs. These findings suggest that the approach to differentially tune encapsulating and bulk hydrogel properties holds potential for future articular cartilage tissue engineering, and that ACPCs could be used as an alternative cell source.