In Situ Biofabrication of Skin Substitutes
The development of in situ biomanufacturing strategies, such as in situ skin fabrication, represents one of the major challenges in tissue engineering.[69,77,140–143] Contrary to the traditional biofabrication approaches, in which constructs are produced based on predesigned models and then cultured in in vitro conditions for subsequent implantation into the patient, in situ biofabrication involves the fabrication of substitutes for tissue repair and regeneration directly in the lesion of the patient. In this case, biofabrication systems are combined with real-time imaging techniques and path-planning devices, enabling the controlled deposition of biomaterials with or without encapsulated cells into the lesion site. In situ biofabrication has great potential for clinical applications, due to its minimally invasive nature, the possibility of eliminating the need for postprocessing operations, ability to fabricate patient-specific biological substitutes and reduced intervention time. Theoretically, this new concept can be applied for the regeneration of different tissues, but recent works are only focused on osteochondral,[141] bone[142] and skin[140] defects. Owing to its layered structure and multiple cell composition, the regeneration of healthy and vascularized skin remains a huge challenge. The current strategies for skin regeneration still present major pitfalls such as inadequate vascularization, poor adherence to the wound bed, inefficient elasticity, inability to reproduce hair follicles, sweat, sebaceous glands and pigmentation, the possibility of rejection and high manufacturing costs. Some of these limitations could be addressed by the development of an in situ biofabrication device, enabling the direct deposition of cell-laden constructs in a layer-by-layer fashion, in this way mimicking the structural and compositional organization of the skin tissue. The printed skin substitute covers the wound to prevent contamination, provides adequate moisture to avoid dehydration, gives immediate and effective relief to patients, and induces skin regeneration, due to its functional composition and cell combination. Recently, Sofokleous et al. developed a portable electrohydrodynamic multineedle system and proposed its use for the in situ fabrication of polymeric meshes in the damaged skin site of a patient (Figure 6).[143] These meshes can be coated, thus encapsulating drugs, and therapeutic and clotting agents. Poly(lactic-co-glycolic) acid meshes with an average diameter of 2.3 ± 0.5 µm were reported. The use of a coaxial needle device allowed the fabrication of bimaterial fibers (average diameter of 3.9 ± 0.7 µm), with a core structure made by polymethysilsesquioxane coated with a thin layer of poly(lactic-co-glycolic) acid.
Figure 6.
Electrohydrodynamic multineedle system printing a polymeric mesh directly into the lesion site on the patient.
Reproduced with permission from [143].
Binder et al. developed a portable inkjet delivery system for the in situ printing of skin cells into the lesion site.[140] The potential of the system to induce the skin regeneration was evaluated through the printing of human keratinocytes and fibroblasts into full-thickness skin lesions (3 × 2.5 cm) created on mice. Results showed the complete closure of the wound after 3 weeks, as well the formation of skin with similar properties to the healthy skin. Histological analysis revealed that the new skin contained organized dermal collagen and a fully formed epidermis.
Despite the tremendous potential of in situ biofabrication of skin substitutes, this concept is still in its infancy. To be effective, great challenges need to be addressed: the integration between biomanufacturing technologies and imaging techniques; the development of dedicated software to control the deposition of different biomaterials and cells, and planning the surgical intervention; and the development of advanced multifunctional biomaterials, capable of entrapping different cells types and maintaining their viability and functionality.
Currently, several strategies are being explored to promote skin regeneration. The most commonly used are autografts and allografts, wound dressings and tissue-engineered skin substitutes. Although these strategies result in products with distinct characteristics, they have been used in combination to improve the healing process. For example, wound dressings, either traditional or modern and tissue-engineered skin can be applied on top of autografts and allografts, providing a better adhesion to the defect site and protecting it from fluid loss and contamination.[144,145] Another approach involves the fabrication of electrospun meshes on top of commercial wound dressings in order to obtain a nanofibrous scaffold with morphological and architectural features similar to the natural ECM in the skin.[136] Despite the great potential of the in situ biofabrication of skin substitutes, this strategy may also require the combined use of dressings or cell-free tissue-engineered skin substitutes to ensure initial adhesion to wound bed and prevent biomaterial (hydrogel) dehydration.
Nanomedicine. 2013;8(4):603-621. © 2013 Future Medicine Ltd.
