Engineering biomimetic zonal properties in fibre-reinforced hydrogels for functional cartilage tissue engineering in vitro

The functional regeneration of human articular cartilage is hampered by a lack of biomaterials and tissue engineering strategies that adequately capture the physiological depth-dependent compression properties of native tissue. Here, we demonstrate that photocrosslinkable gelatin-hyaluronic acid hydrogels reinforced with multiphasic polycaprolactone microfibre scaffolds form biomimetic soft network composites that serve as <i>in vitro</i> models mimicking the compressive and depth-dependent deformation characteristics of human cartilage. Mono- and multi-phasic gradient scaffolds with fibre spacings of 200, 400, and 800 μm were manufactured using melt electrowriting and embedded in the photocrosslinkable hydrogel system. Mechanical testing combined with finite element analysis revealed how defined microfibre architecture is altered and influences compressive moduli and interstitial fluid load support to mimic the loading response of native articular cartilage in our <i>in vitro</i> model. Digital image and volume correlations demonstrated depth-dependent strain fields in the fibre-reinforced constructs in response to compression, demonstrating biomimetic depth-dependent behaviour. Lastly, we demonstrate that these fibre-reinforced hydrogels support high cell viability, chondrogenic redifferentiation and hyaline-like tissue formation by expanded human articular chondrocytes <i>in vitro</i>. Together, this study demonstrates that, <i>in vitro</i>, these hydrogels reinforced with gradient scaffolds successfully recapitulate key biomechanical traits of native articular cartilage, toward the development of improved models for functional cartilage tissue engineering.