Corneal transplantation remains gold standard for the treatment of severe cornea diseases, however, scarcity of donor cornea is a serious bottleneck. 3D bioprinting holds tremendous potential for cornea tissue engineering (TE). One of the key technological challenges is to design bioink compositions with ideal printability and cytocompatibility. Photocrosslinking and ionic crosslinking are often used for the stabilization of 3D bioprinted structures, which can possess limitations on biological functionality of the printed cells. Here, we developed a hyaluronic acid (HA)-based dopamine containing bioink using hydrazone crosslinking chemistry for the 3D bioprinting of corneal equivalents. First, the shear thinning property, viscosity, and mechanical stability of the bioink were optimized before extrusion-based 3D bioprinting for the shape fidelity and self-healing property characterizations. Subsequently, human adipose stem cells (hASCs) and hASC -derived corneal stromal keratocytes (hASC-CSKs) were used for bioprinting corneal stroma structures and their cell viability, proliferation, microstructure and expression of key proteins (lumican, vimentin, connexin 43, α-SMA) were evaluated. Moreover, 3D bioprinted stromal structures were implanted into ex vivo porcine cornea to explore tissue integration. Finally, human pluripotent stem cell derived neurons (hPSC-neurons), were 3D bioprinted to the periphery of the corneal structures to analyze innervation. The bioink showed excellent shear thinning property, viscosity, printability, shape fidelity and self-healing properties with high cytocompatibility. Cells in the printed structures showed good tissue formation and 3D bioprinted cornea structures demonstrated excellent ex vivo integration to host tissue as well as in vitro innervation. The developed bioink and the printed cornea stromal equivalents hold great potential for cornea TE applications.

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Microphysiological systems (MPS) are drawing increasing interest from academia and from biomedical industry due to their improved capability to capture human physiology. MPS offer an advanced in vitro platform that can be used to study human organ and tissue level functions in health and in diseased states more accurately than traditional single cell cultures or even animal models. Key features in MPS include microenvironmental control and monitoring as well as high biological complexity of the target tissue. To reach these qualities, cross-disciplinary collaboration from multiple fields of science is required to build MPS. Here, we review different areas of expertise and describe essential building blocks of heart MPS including relevant cardiac cell types, supporting matrix, mechanical stimulation, functional measurements, and computational modelling. The review presents current methods in cardiac MPS and provides insights for future MPS development with improved recapitulation of human physiology.