Influence of fibrin matrices and their released factors on epidermal substitute phenotype and engraftment

In vitro comparison of human plasma-based and self-assembled tissue-engineered skin substitutes: two different manufacturing processes for the treatment of deep and difficult to heal injuries

Background

The aim of this in vitro study was to compare side-by-side two models of human bilayered tissue-engineered skin substitutes (hbTESSs) designed for the treatment of severely burned patients. These are the scaffold-free self-assembled skin substitute (SASS) and the human plasma-based skin substitute (HPSS).

Methods

Fibroblasts and keratinocytes from three humans were extracted from skin biopsies (N = 3) and cells from the same donor were used to produce both hbTESS models. For SASS manufacture, keratinocytes were seeded over three self-assembled dermal sheets comprising fibroblasts and the extracellular matrix they produced (n = 12), while for HPSS production, keratinocytes were cultured over hydrogels composed of fibroblasts embedded in either plasma as unique biomaterial (Fibrin), plasma combined with hyaluronic acid (Fibrin-HA) or plasma combined with collagen (Fibrin-Col) (n/biomaterial = 9). The production time was 46-55 days for SASSs and 32-39 days for HPSSs. Substitutes were characterized by histology, mechanical testing, PrestoBlue™-assay, immunofluorescence (Ki67, Keratin (K) 10, K15, K19, Loricrin, type IV collagen) and Western blot (type I and IV collagens).

Results

The SASSs were more resistant to tensile forces (p-value < 0.01) but less elastic (p-value < 0.001) compared to HPSSs. A higher number of proliferative Ki67+ cells were found in SASSs although their metabolic activity was lower. After epidermal differentiation, no significant difference was observed in the expression of K10, K15, K19 and Loricrin. Overall, the production of type I and type IV collagens and the adhesive strength of the dermal-epidermal junction was higher in SASSs.

Conclusions

This study demonstrates, for the first time, that both hbTESS models present similar in vitro biological characteristics. However, mechanical properties differ and future in vivo experiments will aim to compare their wound healing potential.

Cellular human tissue-engineered skin substitutes investigated for deep and difficult to heal injuries

Wound healing is an important function of skin; however, after significant skin injury (burns) or in certain dermatological pathologies (chronic wounds), this important process can be deregulated or lost, resulting in severe complications. To avoid these, studies have focused on developing tissue-engineered skin substitutes (TESSs), which attempt to replace and regenerate the damaged skin. Autologous cultured epithelial substitutes (CESs) constituted of keratinocytes, allogeneic cultured dermal substitutes (CDSs) composed of biomaterials and fibroblasts and autologous composite skin substitutes (CSSs) comprised of biomaterials, keratinocytes and fibroblasts, have been the most studied clinical TESSs, reporting positive results for different pathological conditions. However, researchers' purpose is to develop TESSs that resemble in a better way the human skin and its wound healing process. For this reason, they have also evaluated at preclinical level the incorporation of other human cell types such as melanocytes, Merkel and Langerhans cells, skin stem cells (SSCs), induced pluripotent stem cells (iPSCs) or mesenchymal stem cells (MSCs). Among these, MSCs have been also reported in clinical studies with hopeful results. Future perspectives in the field of human-TESSs are focused on improving in vivo animal models, incorporating immune cells, designing specific niches inside the biomaterials to increase stem cell potential and developing three-dimensional bioprinting strategies, with the final purpose of increasing patient's health care. In this review we summarize the use of different human cell populations for preclinical and clinical TESSs under research, remarking their strengths and limitations and discuss the future perspectives, which could be useful for wound healing purposes.

Combined adipose mesenchymal stromal cell advanced therapy resolved a recalcitrant leg ulcer in an 85-year-old patient

Venous leg ulcers (VLU) represent an uphill economic, health and social burden, aggravated in the elderly. Best-practice care interventions are often insufficient and alternative therapies need to be explored. Herein, we have treated for the first time a chronic VLU in an elderly patient by combining cell therapy and tissue engineering in the context of a compassionate use. The administration of allogeneic adipose-derived mesenchymal stromal cells (MSCs) embedded in a plasma-based bioengineered dermis covering the ulcer bed and also injected into the ulcer margins led to the complete closure of a 10-year recalcitrant VLU in an 85-year-old patient. Regenerative properties of MSCs might be boosted by the use of bioengineered matrices for their delivery.

IL-1β-Primed Mesenchymal Stromal Cells Improve Epidermal Substitute Engraftment and Wound Healing via Matrix Metalloproteinases and Transforming Growth Factor-β1

Since the 1980s, deep and extensive skin wounds and burns are treated with autologous split-thickness skin grafts, or cultured epidermal autografts, when donor sites are limited. However, the clinical use of cultured epidermal autografts often remains unsatisfactory because of poor engraftment rates, altered wound healing, and reduced skin functionality. In the past few decades, mesenchymal stromal cells (MSCs) have raised much attention because of their anti-inflammatory, protrophic, and pro-remodeling capacities. More specifically, gingival MSCs have been shown to possess enhanced wound healing properties compared with other tissue sources. Growing evidence also indicates that MSC priming could potentiate therapeutic effects in diverse in vitro and in vivo models of skin trauma. In this study, we found that IL-1β-primed gingival MSCs promoted cell migration, dermal-epidermal junction formation, and inflammation reduction in vitro, as well as improved epidermal substitute engraftment in vivo. IL-1β-primed gingival MSCs had different secretory profiles from naive gingival MSCs, characterized by an overexpression of transforming growth factor-β and matrix metalloproteinase (MMP) pathway agonists. Eventually, MMP-1, MMP-9, and transforming growth factor-β1 appeared to be critically involved in IL-1β-primed gingival MSC mechanisms of action.