Droplet-Based Bioprinting Enables the Fabrication of Cell-Hydrogel-Microfibre Composite Tissue Precursors

Abstract

Composites offer an opportunity to couple particular benefits of their constituents to achieve unique material properties that can be of extra value in many tissue engineering applications. Strategies combining hydrogels with fibre-based scaffolds can create more biologically and structurally functional tissue constructs. However, developing efficient and scalable approaches to manufacture such composites is challenging. Here, we use a droplet-based bioprinting system called Reactive Jet Impingement (ReJI) to integrate a cell-laden hydrogel with a microfibrous mesh. The ReJI system uses microvalves that are connected to different bio-ink reservoirs and directed to continuously jet bio-ink droplets at one another in mid-air where the droplets react and form a hydrogel that lands on a microfibrous mesh. We produce cell-hydrogel-fibre composites by embedding human dermal fibroblasts at two different concentrations (5 x 106 and 30 x 106 cells/ml respectively) in a collagen-alginate-fibrin hydrogel matrix and bioprint it onto a fibre-based substrate. Our results show that both types of cell-hydrogel-microfibre composites maintain high cell viability and promote cell-cell and cell-biomaterial interactions. The lower fibroblast density thereby triggers cell proliferation whereas the higher fibroblast density facilitates faster cellular organisation and infiltration into the microfibres. Additionally, the fibrous component of the composite is characterised by its high swelling properties and quick calcium ions release. The data indicate that the composite constructs we create offer an efficient way to create highly functional tissue precursors for laminar tissue engineering in particular wound healing and skin tissue engineering applications.