Cell loaded 3D bioprinted GelMA hydrogels for corneal stroma engineering.

Tissue engineering aims to replace missing or damaged tissues and restore their functions. Three-dimensional (3D) printing has been gaining more attention because it enables the researchers to design and produce cell loaded constructs with predetermined shapes, sizes, and interior architecture. In the present study, a 3D bioprinted corneal stroma equivalent was designed to substitute for the native tissue. Reproducible outer and inner organization of the stroma was obtained by optimizing printing conditions such as the nozzle speed in the x-y direction and the spindle speed. 3D printed GelMA hydrogels were highly stable in PBS during three weeks of incubation (8% weight loss). Live-Dead cell viability assay showed 98% cell viability on day 21 indicating that printing conditions were suitable for keratocyte printing. Mechanical properties of the cell loaded 3D printed hydrogels increased 2-fold during this incubation period and approached those of the native cornea (ca. 20 kPa vs. 27 kPa, respectively). Expression of collagens types I and V, and proteoglycan (decorin) in keratocytes indicates maintenance of the phenotype in the hydrogels. Transparency of cell-loaded and cell-free hydrogels was over 80% (at 700 nm) during the three week culture period and comparable to that of the native cornea (85%) at the same wavelength. Thus, GelMA hydrogels bioprinted with keratocytes mimic the biological and physical properties of the corneal stroma with their excellent transparency, adequate mechanical strength, and high cell viability.