Bioprinting a Tri-layered Skin Analogue.

Although it is now possible to use tissue engineering approaches to regenerate the dermis and epidermis of the skin, replicating the cellular framework and functions of the skin's three primary layers-epidermis, dermis, and hypodermis remains challenging. Here, we describe the use of a bioprinting method known as suspended layer additive manufacturing (SLAM) to produce a structure with a gradient of mechanical properties, supporting the growth of various cell types, to create a continuous tri-layered skin substitute that closely mimics human skin. SLAM utilizes fluid gels as a temporary support matrix to facilitate the extrusion bioprinting of soft hydrogel-based bioinks into complex, functional, three-dimensional (3D) tissue structures. The printed structures are initially designed using computer-aided design (CAD) and may be printed using a variety of bioinks that can replicate the three primary skin layers: epidermal, dermal, and hypodermal. To accurately reproduce the cellular framework and functions of human skin, it is crucial to use materials that can duplicate the natural extracellular matrix (ECM) structure. This structure provides structural support and appropriate biochemical cues to the embedded cells. Here we describe a method that uses pectin to mimic ECM polysaccharides, along with collagen, which is a major component of human skin ECM. The resulting structure is supported within an agarose support-bed and ionically cross-linked prior to removal. To accurately replicate the cellular framework of human skin, human epidermal keratinocytes (hEKs), human dermal fibroblasts (HDFs), and adipose-derived stem cells (ADSCs) were integrated into the scaffold. A 21-day culture of the skin construct showed that the cellular components were crucial in remodelling the printed structure into architectures resembling those of healthy skin. Integration of the implant, demonstrated by the mobilization of adipose tissue from the surrounding area into the construct, occurred within 7 days post-ex vivo implantation into a simulated porcine wound.