Page 269 - IJB-10-6

International Journal of Bioprinting Skin bioprinting: Keratinocytes and stem cells

Keywords: Keratinocytes; Stem cells; Bioprinting; Skin substitution; Wound healing; Hydrogel

1. Introduction promotes healing. Studies revealed that Alg promotes cell
11
adhesion, proliferation, and vascularization. HA plays a
8,12
The skin, the largest organ of the human body, plays a major role in skin regeneration by increasing keratinocyte
crucial role in our interaction with the environment and migration and proliferation and facilitating the repair and
protection against pathogens. Extensive damage to the remodeling of the extracellular matrix. A previous study
9,11
skin and tissue loss from trauma, infection, or surgical examined the influence of Alg/HA-based hydrogels on
intervention are not only difficult to treat but also can be ADSCs and HaCaT cell cultures. Alg/HA-based hydrogel
life-threatening, especially for large-scale and deep tissue promoted gap closure in an in vitro scratch assay, and in
1,2
burns from thermal, electrical, or chemical injuries. Their vivo testing on a rat model revealed a promoting effect in
2
prognosis is determined by the affected skin surface area, wound healing. 11
the depth of the lesion, and the patient’s age. The primary
3
goal in the treatment of large-scale burns is to provide rapid Gelatin (Gel) is a popular hydrogel component
surgical intervention with necrosectomy combined with because of its low immunogenicity and good mechanical
1
adequate temporary wound coverage to prevent excessive properties. It contains integrin-binding motif (RGD)
fluid loss and maintain optimal moisture levels. 1,4,5 This sequences, which improve cell adhesion and stimulate
temporary wound coverage must prevent desiccation angiogenesis. Furthermore, it contains target sequences
of the wound bed, function as a bacterial barrier, be for matrix metallopeptidases (MMPs) that support
13
semipermeable to allow gas exchange and drainage of wound healing. Additionally, Gel has good printability,
wound exudate, and provide good adherence to the wound increases shape fidelity, and functions as a temperature-
bed. 1,3,4 If uninjured skin areas suitable for skin grafting thickener. Nevertheless, a polymeric additive, like Alg,
are available during treatment, the temporal wound or chemical functionalization is necessary to attain
coverage can be replaced with definitive autologous skin suitable mechanical strength. 13–16 GelMA is a photo-
grafts. In some cases, there may be insufficient uninjured crosslinkable Gel that is biodegradable and allows high
3,4
tissue for complete autologous treatment. Autograft cell viability. 13,17,18 Methacrylation of Gel allows the
2
treatment can be supported by skin tissue engineering. polymerization, improving its mechanical properties and
Many commercially available biological or synthetic skin slowing degradation. 13,19 Fib hydrogels possess excellent
1,20
substitutes have been developed over the past decades. biocompatibility and biodegradation properties.
For example, cultured epithelial autografts have been used Previous studies demonstrated that the formation of the
in the treatment of burn injuries for almost four decades dermo-epidermal junction can be enhanced by the use
and have since become part of the standard treatment of a Fib-glue matrix. 21,22 Other studies indicated the good
protocol. Nevertheless, there are problems regarding graft attachment properties of keratinocytes in a Fib net for
4
23
stability and resilience. The use of tissue-engineered skin rapid healing of full-thickness skin defects.
substitutes, such as cultured epithelial sheet grafts, remains To adequately support skin healing, a dermal equivalent
limited due to insufficient dermal elasticity, inadequate mimicking the skin’s natural properties is needed. Ideally,
regeneration of skin appendages, and long-term the graft would provide sufficient nutrient diffusion
postoperative scarring. Ideally, an exemplary skin graft combined with optimal cell ingrowth into a construct that
6
substitute would enable sufficient nutrient diffusion into is adapted to the depth and size of the wound surface.
1,9
the graft, exhibit healing and revascularization rates equal The utilized biomaterials must be biologically compatible
to or better than those of full-thickness skin grafts, and and not adversely impact wound healing. Therefore,
cause minimal donor site morbidity. Bioprinted constructs natural or synthetic polymer-based hydrogels can be
for skin graft substitution provide an ideal framework for combined with skin cells. Optimally, stem cells are
1,6
optimal cell ingrowth due to their 3D structure. Unlike incorporated into the graft to synergistically influence
sprayed hydrogels or prefabricated substitutes, they can keratinocyte metabolic activity and proliferation. Given
be adapted to the shape and depth of the wound surface. the above, we aim to develop a customized 3D bioprinted
7
Hydrogels can mimic the extracellular matrix and allow construct containing immortalized HaCaT keratinocytes
the diffusion of nutrients, cytokines, and growth factors and ADSCs. Keratinocytes were initially cultivated in
throughout the construct. Alg is commonly used in and on various hydrogels (e.g., containing Alg, Fib,
bioprinting due to its non-antigenicity and favorable collagen, and HA), as well as a prefabricated collagen-
polymerization properties. 8–10 It has a high absorption elastin-matrix. Furthermore, the metabolic activity of
capacity, allowing it to resorb wound exudate while keratinocytes was evaluated during the co-cultivation of
maintaining a physiologically moist environment that keratinocytes in the upper chamber and ADSCs in the

Volume 10 Issue 6 (2024) 261 doi: 10.36922/ijb.3925