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

This study investigated whether articular chondrocyte microenvironmental stiffness could be tuned independently from bulk construct stiffness to improve cartilage tissue engineering outcomes. The authors compared articular chondrocytes cultured directly in low-stiffness GelMA, directly in high-stiffness GelMA, or encapsulated in soft agarose microgels embedded within high-stiffness GelMA. Articular cartilage-derived progenitor cells were also evaluated as an alternative cell source using the same encapsulated microgel approach. These constructs were placed into porcine osteochondral defects and cultured for 28 days under dynamic compression-sliding stimulation intended to mimic gait. The study found that encapsulating cells in soft agarose microgels within a stiffer bulk hydrogel improved pericellular matrix structure and depth uniformity, particularly through increased perlecan synthesis and more complete PCM coverage around cells. While low-stiffness GelMA produced the highest overall GAG content, matrix deposition in the non-encapsulated groups was more depth-dependent, with stronger ECM synthesis near the top surface and weaker Type-II collagen staining in deeper regions. Encapsulated chondrocytes showed more homogeneous ECM and PCM formation throughout construct depth, suggesting that a soft local cell microenvironment combined with a stiffer load-transmitting bulk material can improve tissue-depth uniformity. Encapsulated articular cartilage-derived progenitor cells behaved similarly to encapsulated chondrocytes, supporting their potential as an alternative cell source, although their total GAG content was lower after 28 days. Overall, the study supports differential tuning of local and bulk hydrogel mechanics as a promising strategy for more functional articular cartilage tissue engineering.