Mesoscopic cellular hydrogel scaffolds for bioartificial 3D tissue structures

Abstract

This dissertation presents novel biofabrication strategies for construction of mesoscopic cellular hydrogel scaffolds for bioartificial 3D tissue structures. The ultimate goal of tissue engineering is the restoration of the tissue functions. For the repair or restoration of the tissue functions, the intrinsic macro- to micro-scale 3D environment of the specific tissues is needed to be reconstructed. In conventional methods for 3D tissue engineering, cell aggregations, solid scaffolds, and gel scaffolds have been mainly utilized. However, the controls of microscale 3D environment were lacking or limited in the conventional approaches. Recently, to overcome the limitation, bottom-up tissue engineering, which builds up 3D tissue structures based on meso- to micro-scale cell-containing composites, has been proposed. In this dissertation, I developed facile and distinctive bottom-up tissue engineering methods compared to the related state-of-the-art studies. At the first parts of the dissertation, on-demand 3D freeform fabrication (FF) strategy was studied by utilizing newly built robotic equipment, the 3D cell-hydrogel bioprinter. By using the 3D bioprinter, cell suspension and collagen hydrogel precursor could be directly dispensed as nanoliter droplets at on-demand 3D locations. A printed layer of collagen, either along or combined with cells, was crosslinked by coating the layer with nebulized aerosol of aqueous sodium bicarbonate. The process was repeated in layer-by-layer fashion, resulting in multi-layered cell-hydrogel scaffolds. By utilizing this 3D FF strategy, multi-layered culture of human skin fibroblasts and keratinocytes, multi-layered rat embryonic neural cells with desired 3D cell patterns, and perfusible fluidic hydrogel scaffolds were demonstrated. At the latter parts of this dissertation, facile 3D micromodular fabrication (??MF) strategy was proposed through construction of free-standing cellular hydrogel micromodules, mainly in sheet forms. ...