3D bioprinted light responsive hydrogel materials for cartilage tissue analogues

Articular cartilage defects are a significant and health problem for millions worldwide, especially in an aging population. Effective cartilage regeneration remains elusive. A promising approach is to combine bioinks with human pluripotent stem cells that can be 3D printed to form hydrogels, as responsive, chondroprogenitor-containing materials for eventual transplantation into articular cartilage defects. A significant step towards this is the development of improved chondrogenic tissue analogues.
To generate articular chondrocytes from human pluripotent stem cells (hPSCs) in vitro chondrogenesis protocols rely on timed addition of growth factors to drive differentiation. Transforming growth factor-beta (TGF-b) and bone morphogenic protein (BMP) signals are crucial in specification of an articular phenotype over a hypertrophic phenotype. Optogenetics can be used as a tool for precise cell signalling manipulation. For example, recently an optogenetic BMP (optoBMP) system has been engineered into hPSCs, providing precise, spaciotemporal and reversible (blue) light driven activation of the BMP signalling pathway. Light will be harnessed to generate 3D chondrogenic tissue analogues with stable articular chondrocyte phenotype. Optogenically engineered hPSCs that can be stimulated by red and blue light will be combined with bioinks and fabricated into hydrogel structures using digital light processing (e.g., projection printing). Projection printing allows for the fabrication of spatially patterned regions in 3D, including stiffness, as well as patterned light stimulation of cells. Responsive inks, based on gelatin and hyaluronan will be developed that can change stiffness in response to light (for example, to increase in stiffness in defined regions to green light). This will enable signalling and stiffness to be orthogonally controlled in cell culture, and realise more realistic cartilage tissue analogues. The ability to control stiffness is particularly interesting...