Investigating the Use of Cellular Precision Biopatterning for Generating Functional Skin Equivalents

Abstract

The production of skin equivalents for treating full-thickness wounds has been a long-standing challenge in the field of skin tissue engineering. Although several techniques (e.g., skin substitutes and cell-based therapies) have shown promise in restoring extensive skin loss, these approaches are cost-prohibitive and require a large number of autologous cells to accelerate wound healing. As a result, precision biopatterning approaches have been used to improve epidermal regeneration. One of the most commonly used biopatterning approaches for printing cells is extrusion-based bioprinting (EBP). While efficient, the standard bioinks can result in loss of pattern fidelity on moist and irregular, complex substrates. This limitation can be overcome using aqueous two-phase systems (ATPSs). ATPSs involve two or more phase-separating polymers, such as PEG and DEX, that can pattern cells precisely and retain pattern fidelity. Using this approach, ATPS EBP was applied as a novel cell delivery method to promote growth and differentiation of human epidermal keratinocytes cells (HEK001) on both standard tissue culture plates and acellular dermal matrices (DermGEN™). In order to demonstrate the application of ATPS EBP, optimal concentrations of PEG and DEX were identified for stable pattern formation and cell viability. The results from these experiments suggested that 5.0% PEG and 5.0% DEX resulted in a stable interface and pattern formation on wet substrates. This formulation was selected for precise patterning of cells. Using 5.0% PEG and 5.0% DEX, cells were patterned in colonies to promote cell expansion and differentiation in culture. As a control, the same number of cells were dispersedly-seeded on standard tissue culture plates. The efficiency of the ATPS EBP method was evaluated by comparing the differences in growth properties of keratinocytes between the patterned and dispersedly-seeded conditions. Cells patterned in colonies on tissue culture plates displayed superior cell viability as well as improved barrier formation than cells in the dispersedly-seeded condition. Finally, the clinical application of ATPS EBP was demonstrated by patterning the cells directly on DermGEN™ (an acellular dermal matrix that retains the properties of native dermal tissue) as a model for patterning cells directly on tissues. Cells patterned in discrete colonies on acellular dermal matrices were able to preserve their pattern fidelity, suggesting that ATPS EBP can be used to print biomolecules on complex, non-uniform substrates. Moreover, cells patterned in colonies on DermGEN™ demonstrated improved cellular engraftment and stratum basale formation compared to cells in the dispersedly-seeded condition. These findings suggest that biopatterned cells using ATPS EBP holds promise in promoting epidermal regeneration, which may be useful for generating functional skin equivalents.