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.

In recent years, additive manufacturing of polydimethylsiloxane (PDMS) has gained interest for the development of soft electronics. To build complex electrical devices, fabrication of multilayered structures is required. We propose here a straightforward digital printing fabrication process of silicone rubber-based, multilayered electronics. An inkjet-printable PDMS solution was developed for the digital patterning of elastomeric structures. The silicone ink was used together with a highly conductive silver nanoparticle (Ag NP) ink for the fabrication of all-inkjet-printed multilayered electrical devices. The application of the multilayered circuit board was successful. The sheet resistances were below 0.3 Ω/□, and the conductive layer thickness was less than 1 μm. The electrical insulation between the conductive layers was done by printing a 20−25 μm-thick dielectric PDMS layer selectively on top of the bottommost conductive layer.

A functional limbal epithelial stem cells (LSC) niche is a vital element in the regular renewal of the corneal epithelium by LSCs and maintenance of good vision. However, little is known about its unique structure and mechanical properties on LSC regulation, creating a significant gap in development of LSC‐based therapies. Herein, the effect of mechanical and architectural elements of the niche on human pluripotent derived LSCs (hPSC‐LSC) phenotype and growth is investigated in vitro. Specifically, three formulations of polyacrylamide gels with different controlled stiffnesses are used for culture and characterization of hPSC‐LSCs from different stages of differentiation. In addition, limbal mimicking topography in polydimethylsiloxane is utilized for culturing hPSC‐LSCs at early time point of differentiation. For comparison, the expression of selected key proteins of the corneal cells is analyzed in their native environment through whole mount staining of human donor corneas. The results suggest that mechanical response and substrate preference of the cells is highly dependent on their developmental stage. In addition, data indicate that cells may carry possible mechanical memory from previous culture matrix, both highlighting the importance of mechanical design of a functional in vitro limbus model.

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