Novel macro-microporous gelatin scaffold fabricated by particulate leaching for soft tissue reconstruction with adipose-derived stem cells.

The restoration of body contours as shaped by adipose tissue remains a clinical challenge specifically in patients who have experienced loss of contour due to trauma, surgical removal of tumours or congenital abnormalities. We have developed a novel macro-microporous biomaterial for use in soft tissue re-bulking and augmentation. Alginate beads provided the pore template for the construct. Incorporation, and subsequent dissolution, of the beads within a 7 % (w/v) gelatin matrix, produced a highly porous scaffold with an average pore size of 2.01 ± 0.08 mm. The ability of this scaffold to support the in vitro growth and differentiation of human adipose-derived stem cells (ADSCs) was then investigated. Histological analysis confirmed that the scaffold itself provided a suitable environment to support the growth of ADSCs on the scaffold walls. When delivered into the macropores in a fibrin hydrogel, ADSCs proliferated and filled the pores. In addition, ADSCs could readily be differentiated along the adipogenic lineage. These results therefore describe a novel scaffold that can support the proliferation and delivery of ADSCs. The scaffold is the first stage in developing a clinical alternative to current treatment methods for soft tissue reconstruction.

The effect of topical analgesics on ex vivo skin growth and human keratinocyte and fibroblast behavior.

The application of topical analgesics to the donor site of split thickness skin grafts has been proven to be an effective method of pain management but little is known about their effects on wound reepithelialization. This study compares the effect of four analgesics on human keratinocytes and fibroblasts and whole skin explants in vitro to determine whether epithelial cell behavior is affected by topical analgesics. The effect of diclofenac, bupivacaine, lidocaine, and ketorolac was studied at concentrations between 10 mM and 1 nM. The effect on epithelial growth was measured using an ex vivo skin explant model. In addition, cell proliferation, and cytotoxicity were measured in cultured primary human keratinocytes and fibroblasts. Epithelial growth from the explant model was most inhibited by diclofenac with a significant reduction at 100 microM (p=>0.001). Diclofenac also exhibited the strongest inhibitory effect on cell proliferation especially in keratinocytes. Ketorolac was the most cytotoxic. Bupivacaine showed cytotoxicity in a dose-dependent manner with only the very highest concentrations having a significant inhibitory effect. Lidocaine showed no evidence of cytotoxicity at the concentrations tested in either the in vitro cell studies or the ex vivo explant model. Topical analgesics alter keratinocyte and fibroblast behavior and such inhibition may affect wound healing.

Use of a novel porcine collagen paste as a dermal substitute in full-thickness wounds.

A commercially available porcine collagen sheet material has been found previously to be useful as an implant for reconstructive surgery. However, its use as a dermal substitute has been hindered by slow cell penetration and vascularization. A novel paste formulation of this material was investigated for its potential role as a dermal substitute in full-thickness wounds. A porcine punch biopsy model was initially used to assess the integration of a wide range of material formulations. Selected formulations were then assessed further in a larger wound-chamber model. Paste formulations were compared with those of sheet and another commercially available dermal regeneration template. The porcine collagen paste became integrated into full-thickness wounds without rejection and without excessive inflammation. It was detected in wounds up to day 27 postimplantation. Porcine collagen paste was readily infiltrated by host cells by day 2 and supported migrating keratinocytes on its surface. Staining for endothelial cells indicated neovasculature formation as early as day 4 and functional newly formed microvessels were noted at day 7. This was comparable with neovascularization of an alternative and clinically proven dermal regeneration template and was significantly superior to the sheet material formulation at the same time points. Our findings suggest that porcine collagen paste may be suitable as an alternative to current dermal substitutes in full-thickness wounds.

Survival of cultured allogeneic limbal epithelial cells following corneal repair.

In this study a technique for determining donor cell fate following corneal grafting was evaluated. Patients treated for limbal deficiency with allogeneic cultured corneal epithelial cells were studied to determine the fate of the grafted cells. The technique was evaluated initially through the use of donor eyes and then applied to the clinical analysis of 7 patients who had received a cultured corneal epithelial allograft. Cells removed from the cornea and any retrieved tissue were analyzed via polymerase chain reaction (PCR) genotyping to determine the origin of the cells populating the patients' healed cornea. A mixture of genotypes was detected in a cornea retrieved from a patient following a fully penetrating keratoplasty who had received a mixture of allogeneic tissue. Donor cells were no longer detected on the corneal surface of all 7 cases beyond 28 weeks postgraft. At these later time points, only patient genotype could be detected. These results demonstrate that PCR genotyping can be used to determine the origin of cells populating the surface of the cornea following the grafting of cultured allogeneic cells and demonstrates that transplanted cultured limbal epithelial cells do not persist on the surface of the host cornea for more than 28 weeks.

Outcomes and DNA analysis of ex vivo expanded stem cell allograft for ocular surface reconstruction.

PURPOSE: To investigate the outcome of a new technique of ex vivo expanded stem cell allograft for limbal stem cell deficiency (LSCD), and to characterize the ocular surface genotype after surgery. DESIGN: Retrospective noncomparative case series. PARTICIPANTS: Ten eyes of 10 patients with profound LSCD arising from ectodermal dysplasia (3 eyes), Stevens-Johnson syndrome (3 eyes), chemical injury (2 eyes), thermal injury (1 eye), and rosacea blepharoconjunctivitis (1 eye). INTERVENTION: Allogeneic corneal limbal stem cells were cultured on plastic and transplanted to the recipient eye after removal of conjunctival pannus. Amniotic membrane was applied in a bandage capacity. The procedure was combined with other reconstructive surgery in 2 cases. Nine patients received systemic cyclosporin A immunosuppression, and the DNA genotype was investigated with surface impression cytology. MAIN OUTCOME MEASURES: Parameters of LSCD, including vascularization, conjunctivalization, inflammation, epithelial defect, photophobia, and pain. RESULTS: The mean follow-up period was 28 months (range, 12-50). Seven of 10 eyes (70%) had improved parameters of LSCD at final follow-up and were considered successes. Four (40%) had improved visual acuity, including 3 having had further procedures for visual rehabilitation. Three patients failed to improve-1 with a thermal burn and lid deformity, 1 with Stevens-Johnson syndrome and severe dry eye, and 1 with ectodermal dysplasia who developed an epithelial defect at 26 months. DNA analysis of the first 7 cases showed no ex vivo donor stem cell DNA present beyond 9 months. CONCLUSIONS: Ex vivo expanded stem cell allograft is a useful technique for restoring the ocular surface in profound LSCD. The absence of donor DNA beyond 9 months suggests that ongoing immunosuppression may be unnecessary and raises questions regarding the origin of the host corneal epithelium.

Scarring, stem cells, scaffolds and skin repair.

The treatment of full thickness skin loss, which can be extensive in the case of large burns, continues to represent a challenging clinical entity. This is due to an on-going inability to produce a suitable tissue engineered substrate that can satisfactorily replicate the epidermal and dermal in vivo niches to fulfil both aesthetic and functional demands. The current gold standard treatment of autologous skin grafting is inadequate because of poor textural durability, scarring and associated contracture, and because of a paucity of donor sites in larger burns. Tissue engineering has seen exponential growth in recent years with a number of 'off-the-shelf' dermal and epidermal substitutes now available. Each has its own limitations. In this review, we examine normal wound repair in relation to stem/progenitor cells that are intimately involved in this process within the dermal niche. Endothelial precursors, in particular, are examined closely and their phenotype, morphology and enrichment from multiple sources are described in an attempt to provide some clarity regarding the controversy surrounding their classification and role in vasculogenesis. We also review the role of the next generation of cellularized scaffolds and smart biomaterials that attempt to improve the revascularisation of artificial grafts, the rate of wound healing and the final cosmetic and functional outcome.

A comparison of keratinocyte cell sprays with and without fibrin glue.

Fibrin glue is an excellent template for cellular migration and has been shown to be an effective delivery system for cultured autologous keratinocytes. We have investigated whether fibrin glue has any benefit on the percentage of epithelial cover when cultured autologous keratinocytes are sprayed onto a freshly debrided wound bed. Three pigs were used for this study. This provided a total of 18 full thickness, vertically orientated wounds, each 4cm in diameter and isolated in PTFE chambers to prevent re-epithelialisation from the wound margins. Eight wounds were sprayed with cultured autologous keratinocytes suspended in 2ml culture medium and eight wounds were sprayed with cultured autologous keratinocytes suspended in 1ml of the fibrin/aprotinin component of Tisseel fibrin glue (Baxter) mixed with 1ml of culture medium. In the latter group the thrombin component of the fibrin glue kit was applied to the wound bed immediately prior to grafting. The remaining two wounds were used as controls and sprayed with either culture medium or fibrin glue without cells. Epithelial cover was calculated in whole-wound biopsies at 3 weeks using image analysis, histology and immunohistochemistry. The cell suspension in fibrin glue appeared to spread more evenly over the wound surface, with no pooling in the inferior aspect of the wound. However, mean epithelial area at 3 weeks in the fibrin group was 1.6cm(2) per wound compared with 1.8cm(2) for the non-fibrin group, as measured by image analysis of digital photographs. There was no statistically significant difference between the two groups (P=0.802). This surprising result was confirmed by histological analysis of the wound biopsies, with a good correlation between histological and image analysis data (R=0.967). There was no observable difference in the quality of the epithelium on histological and immunohistological analysis of either group.

Luminescent dual sensors reveal extracellular pH-gradients and hypoxia on chronic wounds that disrupt epidermal repair.

Wound repair is a quiescent mechanism to restore barriers in multicellular organisms upon injury. In chronic wounds, however, this program prematurely stalls. It is known that patterns of extracellular signals within the wound fluid are crucial to healing. Extracellular pH (pHe) is precisely regulated and potentially important in signaling within wounds due to its diverse cellular effects. Additionally, sufficient oxygenation is a prerequisite for cell proliferation and protein synthesis during tissue repair. It was, however, impossible to study these parameters in vivo due to the lack of imaging tools. Here, we present luminescent biocompatible sensor foils for dual imaging of pHe and oxygenation in vivo. To visualize pHe and oxygen, we used time-domain dual lifetime referencing (tdDLR) and luminescence lifetime imaging (LLI), respectively. With these dual sensors, we discovered centripetally increasing pHe-gradients on human chronic wound surfaces. In a therapeutic approach, we identify pHe-gradients as pivotal governors of cell proliferation and migration, and show that these pHe-gradients disrupt epidermal barrier repair, thus wound closure. Parallel oxygen imaging also revealed marked hypoxia, albeit with no correlating oxygen partial pressure (pO2)-gradient. This highlights the distinct role of pHe-gradients in perturbed healing. We also found that pHe-gradients on chronic wounds of humans are predominantly generated via centrifugally increasing pHe-regulatory Na+/H+-exchanger-1 (NHE1)-expression. We show that the modification of pHe on chronic wound surfaces poses a promising strategy to improve healing. The study has broad implications for cell science where spatial pHe-variations play key roles, e.g. in tumor growth. Furthermore, the novel dual sensors presented herein can be used to visualize pHe and oxygenation in various biomedical fields.

Strategies Demonstrating Efficacy in Reducing Wound Contraction In Vivo.

SIGNIFICANCE: Scarring continues to present a significant clinical problem. Wound contraction leads to scarring and is mediated by myofibroblasts and contractile forces across the wound bed. Contracture formation can have a significant impact on the quality of life of the patient, particularly where function and appearance are affected. RECENT ADVANCES: Novel tissue-engineered matrices, cell-based therapies, and medicinal therapeutics have shown significant reduction in wound contraction in in-vivo models, particularly at early time points. These have been accompanied in many cases by reduced numbers of myofibroblasts, and in some by increased angiogenesis and improved neodermal architecture. CRITICAL ISSUES: There are no animal models that replicate all aspects of wound healing as seen in patients. Therefore, information obtained from in vivo studies should be assessed critically. Additional studies, in particular those that seek to elucidate the mechanisms by which novel therapies reduce contraction, are needed to gain sufficient confidence to move into clinical testing. FUTURE DIRECTIONS: The use of knockout mouse models in particular has generated significant advances in knowledge of the mechanisms behind myofibroblast conversion and other factors involved in generating tension across the wound. Medicinal therapeutics and tissue-engineering approaches that seek to disrupt/alter these pathways hold much promise for future development and translation to clinical practice.

Progression of wound pH during the course of healing in burns.

The aim of this study was to measure the pH on the wound surface of 30 burn patients and test the hypothesis that wound surface pH is correlated to healing time and burn depth. Inclusion criteria were any adult outpatient with burn injury. Patient age was 17 to 75 years (mean, 44), burn depth ranged from superficial to full thickness with a TBSA of 0.4 to 4%. Cause of burn included scalds, flame burn, and contact burns. On admission, and at each dressing change, the pH on the wound surface was measured. The pH in both healing and nonhealing wounds was found to decrease with each dressing change. At the second dressing change, wounds that went on to heal were found to have a significantly lower pH of 7.32 in comparison with pH 7.73 in wounds that failed to heal and therefore required subsequent grafting (P = .004). Wound pH was also correlated to depth at the second dressing change (superficial = pH 6.05, full thickness = pH 8.0). The correlation between pH and wound outcome could be used as an additional diagnostic tool to predict poor healing in wounds. Early identification of a nonhealing wound may allow a more aggressive treatment regimen, including skin grafting, to bring about rapid wound healing.

Wound contraction is significantly reduced by the use of microcarriers to deliver keratinocytes and fibroblasts in an in vivo pig model of wound repair and regeneration.

In full-thickness injuries caused by extensive burns or penetrating traumatic injuries, the natural epidermal stem cell niche is destroyed, and wound healing occurs through migration of cells from the wound edges and wound contraction. This can lead to significant contracture formation, especially in large full-thickness injuries, causing lack of mobility and pain. Contraction is reduced when wounds are treated using split-thickness skin grafts (STSG) or dermal substitutes, particularly in combination with cultured autologous keratinocytes, delivered as confluent sheets or sprayed as a single cell suspension (SAK). Here, we show that the application of keratinocytes alone or keratinocytes with fibroblasts, delivered on microcarriers, in combination with STSG or a dermal substitute, significantly reduces contraction of wounds in vivo in a porcine model of wound repair and regeneration. A decrease in alpha-smooth muscle actin-positive myofibroblasts, the cell type responsible for wound contraction, accompanies the reduction in contraction. These findings demonstrate the potential for a significant clinical advantage in the treatment of full-thickness injuries.

Microcarriers and their potential in tissue regeneration.

Microcarriers are a versatile tool with applications across a wide range of disciplines within tissue engineering. Large numbers of cells of appropriate phenotypes are required in engineering the many different tissues of the body, and microcarriers facilitate not only the expansion of many cell types but also the investigation of cell behavior in vitro. Microcarriers can also be used to directly deliver cells in vivo to repair and regenerate tissues. This review summarizes and discusses the use of microcarriers in diverse applications of tissue repair, including bone, cartilage, skin, vascular, central nervous system, adipose tissue, and liver repair. It also considers how microcarriers can be used to bulk-culture and deliver stem cells for tissue regeneration. Microcarriers thus have multidisciplinary use and advances in their use are of benefit to the entire tissue engineering field.

Effect of artificial dermal substitute, cultured keratinocytes and split thickness skin graft on wound contraction.

In this study, the effect of different wound treatments on contraction was evaluated in an established porcine model. In two separately conducted experiments full thickness wounds treated with artificial dermal substitute, split thickness skin graft (STSG), meshed STSG applied in combination with cultured keratinocytes or meshed STSG alone were compared with untreated wounds. The surface area of all wounds was quantified at regular time intervals. After 20 days wounds from some groups were subjected to histological analysis to establish the degree of epithelialization. Wounds treated with STSG contracted more than with artificial dermal substitute until day 21. From day 21 to day 35 wounds treated with STSG showed the least contraction. Wounds sprayed with cultured keratinocytes demonstrated a slower rate of contraction than those with meshed STSG alone after 20 days. The untreated control wounds showed a greater rate of contraction and had almost closed by day 20. This study demonstrates that there is a significant difference in contraction between wounds treated with artificial dermal substitute and control wounds and between wounds treated with STSG with cultured keratinocytes and meshed STSG alone. STSG with cultured keratinocytes, unmeshed STSG, and artificial dermal substitute all reduced wound contraction significantly.