Fibroblast sheets enable epithelialization of sounds that do not support keratinocyte migration

Stem and Somatic Cell Monotherapy for the Treatment of Diabetic Foot Ulcers: Review of Clinical Studies and Mechanisms of Action

Diabetic foot ulcer (DFU) is one of the most severe complications of diabetes mellitus, often resulting in a limb amputation. A cell-based therapy is a highly promising approach for an effective DFU treatment. However, there is no consensus regarding the most effective cell type for DFU treatment. Various cell types contribute to chronic wound healing via different mechanisms. For example, application of keratinocytes can stimulate migration of native keratinocytes from the wound edge, while mesenchymal stem cells can correct limb ischemia. To assess the effectiveness of a certain cell type, it should be administered as a monotherapy without other substances and procedures that have additional therapeutic effects. In the present review, we described therapeutic effects of various cells and provided an overview of clinical studies in which stem and somatic cell-based therapy was administered as a monotherapy. Topical application of somatic cells contributes to DFU healing only, while injection of mesenchymal stem cells and mononuclear cells can break a pathophysiological chain leading from insufficient blood supply to DFU development. At the same time, the systemic use of mesenchymal stem cells carries greater risks. Undoubtedly, cell therapy is a potent tool for the treatment of DFU. However, it is vital to conduct further high-quality clinical research to determine the most effective cell type, dosage and way of administration for DFU treatment. Ischemia, neuropathy and neuro-ischemia are underlying factors of diabetic foot ulcer. Stem and somatic cells monotherapy can improve chronic wound healing via different mechanisms.

Improving skin integration around long-term percutaneous devices using fibrous scaffolds in a reconstructed human skin equivalent model

The interface between synthetic percutaneous devices and skin is a common area for bacterial infection, which may ultimately result in failure of the device. Better integration of percutaneous devices with skin may help reduce infection rates due to the creation of a dermal seal. However, the mismatch in material and chemical properties of devices and skin presents a challenge for closing the dermal gap at the skin-device interface. Here, we have used a tissue engineering approach to tissue integration by creating a highly fibrous poly(ε-caprolactone) scaffold using melt electrowriting and seeding this with dermal fibroblasts, followed by maturation and insertion into a full-thickness defect made in an ex vivo skin model. The integration of seeded scaffolds was compared with controls including a non-seeded scaffold and a polymer tube with a smooth surface. Dermal fibroblast inclusion in the scaffold and epidermal upgrowth versus downgrowth/marsupialization around the device were used as measures of integration. Based on these measures, almost all pre-seeded scaffolds performed better than both the non-seeded scaffolds and smooth tubes. The hypothesis is that the fibroblasts act as a barrier to epithelial downward migration, and provide healthy tissue for nascent epidermal development.

A Novel Bioreactor Microcarrier Cell Culture System for High Yields of Proliferating Autologous Human Keratinocytes

Rapid and efficient resurfacing of various skin defects by autologous keratinocyte transplantation is significant in skin wound healing. We developed a novel bioreactor microcarrier cell culture system (Bio-MCCS) to produce autologous human keratinocytes on a large scale. In this Bio-MCCS we used porcine gelatin microbeads as microcarriers for autolgous keratinocytes and spinning bottles as fermentation tanks. First, the microbeads were modified by culturing them with autologous dermal fibroblasts that were subsequently killed when they proliferated to confluence on the microbeads. We then performed the Bio-MCCS by expanding ketatinocytes on the microbeads in spinning bottles at 37°C, 5% CO2. Our results showed that keratinocytes rapidly attached to and actively proliferated on the modified microbeads in the Bio-MCCS, achieving high cell densities on the modified microbeads (MTT assay and PI staining). Keratinocytes cultured on the modified microbeads in the Bio-MCCS remained proliferating potentials as shown by positive PCNA staining and BrdU labeling. In contrast, keratinocytes cultured on nonmodified microbeads in the Bio-MCCS proliferated slowly, rapidly ceased to proliferate, and finally dislodged from the microbeads. When removed from the Bio-MCCS and cultured under static conditions, keratinocytes were able to leave the modified microbeads and formed a multilayered epidermal equivalent on the culture surfaces. While stored at room temperature, keratinocytes remained at higher viabilities on the modified microbeads when compared to those on nonmodified microbeads. The achievement of high yields of proliferating autologous keratinocytes by this Bio-MCCS offers a practical potential of resurfacing various skin defects by direct administration of autologous keratinocyte microbeads on various skin defects.

Bioglass Activated Skin Tissue Engineering Constructs for Wound Healing

Wound healing is a complicated process, and fibroblast is a major cell type that participates in the process. Recent studies have shown that bioglass (BG) can stimulate fibroblasts to secrete a multitude of growth factors that are critical for wound healing. Therefore, we hypothesize that BG can stimulate fibroblasts to have a higher bioactivity by secreting more bioactive growth factors and proteins as compared to untreated fibroblasts, and we aim to construct a bioactive skin tissue engineering graft for wound healing by using BG activated fibroblast sheet. Thus, the effects of BG on fibroblast behaviors were studied, and the bioactive skin tissue engineering grafts containing BG activated fibroblasts were applied to repair the full skin lesions on nude mouse. Results showed that BG stimulated fibroblasts to express some critical growth factors and important proteins including vascular endothelial growth factor, basic fibroblast growth factor, epidermal growth factor, collagen I, and fibronectin. In vivo results revealed that fibroblasts in the bioactive skin tissue engineering grafts migrated into wound bed, and the migration ability of fibroblasts was stimulated by BG. In addition, the bioactive BG activated fibroblast skin tissue engineering grafts could largely increase the blood vessel formation, enhance the production of collagen I, and stimulate the differentiation of fibroblasts into myofibroblasts in the wound site, which would finally accelerate wound healing. This study demonstrates that the BG activated skin tissue engineering grafts contain more critical growth factors and extracellular matrix proteins that are beneficial for wound healing as compared to untreated fibroblast cell sheets.

Cell sheet technology-driven re-epithelialization and neovascularization of skin wounds

Skin regeneration remains a challenge, requiring a well-orchestrated interplay of cell-cell and cell-matrix signalling. Cell sheet (CS) engineering, which has the major advantage of allowing the retrieval of the intact cell layers along with their naturally organized extracellular matrix (ECM), has been poorly explored for the purpose of creating skin substitutes and skin regeneration. This work proposes the use of CS technology to engineer cellular constructs based on human keratinocytes (hKC), key players in wound re-epithelialization, dermal fibroblasts (hDFb), responsible for ECM remodelling, and dermal microvascular endothelial cells (hDMEC), part of the dermal vascular network and modulators of angiogenesis. Homotypic and heterotypic three-dimensional (3-D) CS-based constructs were developed simultaneously to target wound re-vascularization and re-epithelialization. After implantation of the constructs in murine full-thickness wounds, human cells were engrafted into the host wound bed and were present in the neotissue formed up to 14 days post-implantation. Different outcomes were obtained by varying the composition and organization of the 3-D constructs. Both hKC and hDMEC significantly contributed to re-epithelialization by promoting rapid wound closure and early epithelial coverage. Moreover, a significant increase in the density of vessels at day 7 and the incorporation of hDMEC in the neoformed vasculature confirmed its role over neotissue vacularization. As a whole, the obtained results confirmed that the proposed 3-D CS-based constructs provided the necessary cell machinery, when in a specific microenvironment, guiding both re-vascularization and re-epithelialization. Although dependent on the nature of the constructs, the results obtained sustain the hypothesis that different CS-based constructs lead to improved skin healing.

Dermal templates and the wound-healing paradigm: the promise of tissue regeneration

Dermal regeneration templates arguably represent the first and most clinically successful 'tissue engineering' solution designed for organ reconstruction. Wound healing in the skin normally occurs on a continuum. At one extreme of the continuum lies the promise of tissue regeneration and the complete restoration of normal structure and function. Unfortunately, in the adult, all too often, wound healing occurs at the other extreme of the continuum and the dermis is reconstituted as scar tissue. Dermal regeneration templates are designed to manage the wound-healing process and tip the scales toward regeneration. This review discusses the architecture and molecular composition of the skin and the events that mediate wound healing and scar formation. The development, evolution and commercialization of dermal templates are examined and the clinical and business considerations that drive the product-development cycle are discussed. In the near term, dermal templates cannot be expected to dramatically change in overall composition. Product development will be dominated by continued refinements of existing templates and the field of use will continue to expand as manufacturers seek to increase revenue and capture market share. Continued exploration of novel processing strategies, such as electrospinning, that can be used to fabricate nanoscale biomaterials, may provide a gateway to the next generation of dermal templates.

Bioengineered skin in diabetic foot ulcers

OBJECTIVE

Bioengineered skin (BS) has been shown to play an important role in the treatment of diabetic foot ulcers (DFUs). Whether BS in the therapy of DFU can improve the outcomes still remains uncertain. We performed a quantitative meta-analysis of available randomized controlled trials to determine the effectiveness and safety of BS in the treatment of patients with DFUs.

DESIGN AND METHODS

Comprehensive search strategies of various electronic databases were used for this study to evaluate the effectiveness and safety between BS and conventional treatment (CT) in patients with DFU, and only randomized controlled trials were adopted in our review. Search terms included 'bioengineered skin', 'tissue-engineering skin', 'human-tissue graft', 'human-skin device', 'living-skin equivalent' and 'diabetic foot', 'diabetic ulcer', 'diabetic wound'. Analysis outcomes included complete wound closure, complications, ulcer recurrence and adverse severe events (ASEs).

RESULTS

Seven randomized controlled trials on BS vs. CT were included, and 880 participants met inclusion criteria. Pooled analysis showed a significant effectiveness and safety advantages for BS treatment compared to CT for patients with DFUs. In analysis of complications, only statistically significant difference of infection was noted. And no included trials reported ASEs related to these treatments.

CONCLUSIONS

Based on the meta-analysis, patients with DFUs may benefit from the BS because of its high effectiveness and safety and reduced risk for infections in comparison to CT.

Skin tissue engineering

The major applications of tissue-engineered skin substitutes are in promoting the healing of acute and chronic wounds. Several approaches have been taken by commercial companies to develop products to address these conditions. Skin substitutes include both acellular and cellular devices. While acellular skin substitutes act as a template for dermal formation, this discussion mainly covers cellular devices. In addressing therapeutic applications in tissue engineering generally, a valuable precursor is an understanding of the mechanism of the underlying pathology. While this is straightforward in many cases, it has not been available for wound healing. Investigation of the mode of action of the tissue-engineered skin substitutes has led to considerable insight into the mechanism of formation, maintenance and treatment of chronic wounds. Four aspects mediating healing are considered here for their mechanism of action: (i) colonization of the wound bed by live fibroblasts in the implant, (ii) the secretion of growth factors, (iii) provision of a suitable substrate for cell migration, particularly keratinocytes and immune cells, and (iv) modification of the immune system by secretion of neutrophil recruiting chemokines. An early event in acute wound healing is an influx of neutrophils that destroy planktonic bacteria. However, if the bacteria are able to form biofilm, they become resistant to neutrophil action and prevent reepithelialization. In this situation the wound becomes chronic. In chronic wounds, fibroblasts show a senescence-like phenotype with decreased secretion of neutrophil chemoattractants that make it more likely that biofilms become established. Treatment of the chronic wounds involves debridement to eliminate biofilm, and the use of antimicrobials. A role of skin substitutes is to provide non-senescent fibroblasts that attract and activate neutrophils to prevent biofilm re-establishment. The emphasis of the conclusion is the importance of preventing contaminating bacteria becoming established and forming biofilms.

High yields of autologous living dermal equivalents using porcine gelatin microbeads as microcarriers for autologous fibroblasts

Permanent skin replacement requires a dermal component to ensure adequate long-term graft stability and to prevent wound contraction. This study was to construct a bioreactor microcarrier cell culture system (Bio-MCCS) to produce autologous living dermal equivalents on a large scale. Autologous fibroblasts were isolated from split-thickness skin biopsy from a leg ulcer patient, inoculated onto macroporous porcine gelatin microbeads, and incubated in a bioreactor (Cellspin) in serum-free fibroblast growth medium or in DMEM medium containing 10% fetal calf serum (FCS). Fibroblasts rapidly adhered to and actively proliferated on the microbeads in the bioreactor in both serum-free and serum-containing medium. MTT assay showed the number of fibroblasts on the microbeads reached up to 5.3- or 4.0-fold the cells seeded in DMEM medium containing 10% FCS or serum-free medium, respectively. When removed from Bio-MCCS and cultured under static conditions, fibroblasts were able to leave the microbeads and proliferate to confluence on the bottom of tissue culture flasks. When stored at room temperature in DMEM containing 10% FBS, fibroblast cultured on the microbeads retained highest viabilities for at least 3 weeks, up to 82% of originals. This Bio-MCCS using porcine gelatin microbeads as carriers for fibroblasts offers a new option of mass production of autologous living dermal equivalents.

The efficacy and safety of Dermagraft in improving the healing of chronic diabetic foot ulcers: results of a prospective randomized trial

OBJECTIVE

To determine if a human fibroblast-derived dermal substitute could promote the healing of diabetic foot ulcers.

RESEARCH DESIGN AND METHODS

A randomized, controlled, multicenter study was undertaken at 35 centers throughout the U.S. and enrolled 314 patients to evaluate complete wound closure by 12 weeks. Patients were randomized to either the Dermagraft treatment group or control (conventional therapy). Except for the application of Dermagraft, treatment of study ulcers was identical for patients in both groups. All patients received pressure-reducing footwear and were allowed to be ambulatory during the study.

RESULTS

The results demonstrated that patients with chronic diabetic foot ulcers of >6 weeks duration experienced a significant clinical benefit when treated with Dermagraft versus patients treated with conventional therapy alone. With regard to complete wound closure by week 12, 30.0% (39 of 130) of Dermagraft patients healed compared with 18.3% (21 of 115) of control patients (P = 0.023). The overall incidence of adverse events was similar for both the Dermagraft and control groups, but the Dermagraft group experienced significantly fewer ulcer-related adverse events.

CONCLUSIONS

The data from this study show that Dermagraft is a safe and effective treatment for chronic diabetic foot ulcers.

Healing of chronic foot ulcers in diabetic patients treated with a human fibroblast-derived dermis

A prospective, multicenter, randomized, controlled 12-week study was undertaken to evaluate the effectiveness of a human fibroblast-derived dermis for treating foot ulcers in the diabetic patient. This report summarizes the findings from one center. Following a 2-week screening period, patients were randomized to either human fibroblast-derived dermis (HFDD) (Dermagraft) plus saline-moistened gauze or to the control group (CT) of saline-moistened gauze alone. Effectiveness end points were: 1) wound closure by week 12, 2) time to wound closure, and 3) percent wound closure by week 12. Safety was assessed by review of adverse events and laboratory findings. Patients randomized to HFDD received an application at day 0 and up to seven additional treatments. All patients in each group received shoes with custom-molded inserts and were seen weekly. The study population was comprised of 28 patients (14 HFDD/14 CT) with chronic ulcers (>6 weeks' duration at time of screening). By week 12, significantly more chronic ulcers healed in the HFDD group than in the CT group (71.4% versus 14.3%, p = .003). Healed HFDD patients achieved wound closure significantly faster than CT patients (p = .004). Patients treated with HFDD showed a statistically significant higher percent of wound closure by week 12 than did CT patients (p = .002). The percent of patients who experienced an infection involving their study wound was less in the HFDD group than in the CT group. It was concluded that HFDD is a safe and effective treatment for chronic foot ulcers in diabetic patients.