Un-cross-linked fibrin substrates inhibit keratinocyte spreading and replication: correction with fibronectin and factor XIII cross-linking

Self-Assembled Fibrinogen Scaffolds Support Cocultivation of Human Dermal Fibroblasts and HaCaT Keratinocytes

Self-assembled fibrinogen scaffolds are highly attractive biomaterials to mimic native blood clots. To explore their potential for wound healing, we studied the interaction of cocultures of human dermal fibroblasts (HDFs) and HaCaT keratinocytes with nanofibrous, planar, and physisorbed fibrinogen. Cell viability analysis indicated that the growth of HDFs and HaCaTs was supported by all fibrinogen topographies until 14 days, either in mono- or coculture. Using scanning electron microscopy and cytoskeletal staining, we observed that the native morphology of both cell types was preserved on all topographies. Expression of the marker proteins vimentin and cytokeratin-14 showed that the native phenotype of fibroblasts and undifferentiated keratinocytes, respectively, was maintained. HDFs displayed their characteristic wound healing phenotype, characterized by expression of fibronectin. Finally, to mimic the multilayered microenvironment of skin, we established successive cocultures of both cells, for which we found consistently high metabolic activities. SEM analysis revealed that HaCaTs arranged into a confluent top layer after 14 days, while fluorescent labeling confirmed the presence of both cells in the layered structure after 6 days. In conclusion, all fibrinogen topographies successfully supported the cocultivation of fibroblasts and keratinocytes, with fibrinogen nanofibers being particularly attractive for skin regeneration due to their biomimetic porous architecture and the technical possibility to be detached from an underlying substrate.

Protein nanocoatings on synthetic polymeric nanofibrous membranes designed as carriers for skin cells

Protein-coated resorbable synthetic polymeric nanofibrous membranes are promising for the fabrication of advanced skin substitutes. We fabricated electrospun polylactic acid and poly(lactide-co-glycolic acid) nanofibrous membranes and coated them with fibrin or collagen I. Fibronectin was attached to a fibrin or collagen nanocoating, in order further to enhance the cell adhesion and spreading. Fibrin regularly formed a coating around individual nanofibers in the membranes, and also formed a thin noncontinuous nanofibrous mesh on top of the membranes. Collagen also coated most of the fibers of the membrane and randomly created a soft gel on the membrane surface. Fibronectin predominantly adsorbed onto a thin fibrin mesh or a collagen gel, and formed a thin nanofibrous structure. Fibrin nanocoating greatly improved the attachment, spreading, and proliferation of human dermal fibroblasts, whereas collagen nanocoating had a positive influence on the behavior of human HaCaT keratinocytes. In addition, fibrin stimulated the fibroblasts to synthesize fibronectin and to deposit it as an extracellular matrix. Fibrin coating also showed a tendency to improve the ultimate tensile strength of the nanofibrous membranes. Fibronectin attached to fibrin or to a collagen coating further enhanced the adhesion, spreading, and proliferation of both cell types.

The role of stem cells in the treatment of diabetic foot ulcers

Diabetic foot ulcers (DFUs) are a significant and rapidly growing complication of diabetes and its effects on wound healing. Over half of diabetic patients who develop a single ulcer will subsequently develop another ulcer of which the majority will become chronic non-healing ulcers. One-third will progress to lower extremity amputation. Over the past decade, the outcomes for patients with DFUs ulcers have not improved, despite advances in wound care. Successful treatment of diabetic foot ulcers is hindered by the lack of targeted therapy that hones in on the healing processes dysregulated by diabetes. Stem cells are a promising treatment for DFUs as they are capable of targeting, as well as bypassing, the underlying abnormal healing mechanisms and deranged cell signaling in diabetic wounds and promote healing. This review will focus on existing stem cell technologies and their application in the treatment of DFUs.

High thrombin concentrations in fibrin sealants induce apoptosis in human keratinocytes

Over the last century many studies have been performed to assess the impact of fibrin sealant (FS) components on cells. Because of the noncovalent bonding of thrombin to fibrin during fibrin clot formation, we wanted to further evaluate the impact of fibrin bound thrombin on cell viability. Initially, we quantified the activity of thrombin in three different, commercially available FS. This information was used to prepare fibrin clots covering a range of thrombin concentrations from 4 to 820 IU mL(-1), but which were identical with respect to all other constituents. Although these fibrin clots did not differ in their three-dimensional structure, clots prepared with highly concentrated thrombin (820 IU mL(-1)) failed to support adhesion and spreading of primary human keratinocytes (NHEK). The number of attached cells was also significantly reduced on high thrombin activity clots. We hypothesized that these observations are not only the consequence of decreased proliferation but of apoptotic mechanisms, since the expression of cleaved caspase 3 and 7 was strongly enhanced on fibrin clots with high thrombin activity. This was accompanied by an induction of expression of Trail-R2 which is a receptor known to mediate apoptosis signals. Blocking of thrombin activity by hirudin led to an improvement of cell morphology and to an increase in number of attached cells. In addition, the induction of caspase 3 and 7 was also reduced. Thus, here we report for the first time that fibrin bound thrombin does not only decrease proliferation (as already published by others), it also does induce NHEK apoptosis when present at high concentrations.

Mesenchymal stem cell therapy and delivery systems in nonhealing wounds

OBJECTIVE

The objective of the study was to inform wound care practitioners of mesenchymal stem cell application for nonhealing wounds. Recent advances in delivery systems are also discussed in order to highlight potential improvements toward clinical application of stem cell therapy for chronic wounds.

DATA SOURCES

MEDLINE and PubMed Central were searched for scientific studies regarding the use of mesenchymal stem cells and delivery systems in wound healing.

STUDY SELECTION

Preclinical studies using stem cells as therapeutic modality for chronic wounds were selected for this review.

DATA EXTRACTION

Information on study design, sample size and characteristics, stem cell source, type of delivery systems, and rate and time of wound closure was abstracted.

DATA SYNTHESIS

Application of mesenchymal stem cells improved wound healing in experimental and clinical settings. Advances in stem cell therapy and delivery vehicles offer promising alternatives to current limited therapeutic modalities for chronic wounds.

CONCLUSIONS

Stem cell therapy has recently emerged as a promising therapeutic strategy for nonhealing wounds. Further research is needed to evaluate the relationship between the various delivery systems and stem cells in order to maximize their therapeutic effects. Development of novel delivery vehicles for stem cells can open new opportunities for more effective cell therapy of chronic wounds.

Cell Compatibility of Fibrin Sealants: In Vitro Study with Cells Involved in Soft Tissue Repair

Fibrin sealants can be used to support tissue regeneration or as vehicles for delivery of cells in tissue engineering. Differences in the composition of fibrin sealants, however, could determine the success of such applications. The results presented in this article show clear differences between Fibrin sealant A (FS A) clots and Fibrin sealant B (FS B) clots with respect to their compatibility with primary human cells involved in soft tissue repair. FS A clots, which are characterized by a physiological coarse fibrin structure, promoted attachment, spreading, and proliferation of keratinocytes, fibroblasts, and endothelial cells. In contrast, FS B clots displaying a fine to medium clot structure failed to support spreading of all three cell types. Adhesion of keratinocytes was decreased on FS B clots compared to FS A clots after 3 h incubation, whereas number of attached fibroblasts and endothelial cells was initially comparable between the two fibrin sealants. However, all three cell types proliferated on FS A clots but no sustained proliferation was detected on FS B clots. We further demonstrate that the observed differences between FS A and B clots are partly based upon 1 M sodium chloride extractable constituents, like thrombin, and partly on nonextractable constituents or the fibrin structure. In conclusion, our in vitro results demonstrate that FS A clots serve as a provisional matrix that encourages adhesion and growth of keratinocytes, fibroblasts, and endothelial cells. Therefore, FS A seems to be well suited for applications in tissue engineering.

The use of fibrin based matrices and fibrin microbeads (FMB) for cell based tissue regeneration

BACKGROUND

Due to its good cell attachment capabilities and promotion of cell migration, fibrin serves as an interim cell-binding matrix in wounded tissues. Due to their fast degradation, unprocessed fibrin matrices have limited use in tissue engineering.

OBJECTIVE

To describe stable fibrin-based matrices for isolation, growth and delivery of stem cells for implantation to enhance tissue regeneration.

METHODS

Fibrin microbeads (FMB) were produced by moderate-heat condensation of fibrin particles in oil without compromising the cell binding capability of the fibrin.

RESULTS

Mesenchymal stem cells (MSC) were separated from different sources at much higher yields with FMB. They were further expanded on them in suspension without trypsinization and passages. Cells on FMB could be induced to differentiate into different phenotypes, such as bone and cartilage. This enabled implantation of the cells on FMB for cell-based tissue regeneration.

CONCLUSIONS

FMB technology provides a simple and effective method for cell separation, expansion in suspension and delivery for tissue regeneration.

Evaluation of dermal pericapillary fibrin cuffs in venous ulceration using confocal microscopy

Dermal pericapillary fibrin is a hallmark of venous disease and is thought to play a pathogenic role in the development of ulceration. However, the actual spatial configuration of pericapillary fibrin is unknown, and it remains unclear whether it truly represents a barrier that can impair physiological exchanges between the blood and dermis. Using confocal microscopy on tissue specimens taken from the edges of venous ulcers in six patients, we report a detailed analysis of dermal pericapillary fibrin deposits. Sections were evaluated with an antibody to human fibrinogen/fibrin and viewed, vertically and horizontally, with confocal microscopy. The distribution of fibrin deposition was highly variable and patchy, with areas of great intensity next to others of marginal intensity. Vertical cut sections showed the highest concentration of fluorescent material next to the lumen of dermal capillaries. Horizontal sections showed that maximal fluorescence was distributed at random. Our findings indicate that fibrin deposits in venous ulcers are patchy and discontinuous around dermal vessels. As such, these deposits are unlikely to act as a true and stable anatomic barrier as originally proposed. However, pericapillary fibrin may still act as a physiological barrier under conditions of poor blood flow where even marginal or patchy fibrin deposition might have a greater effect on the exchange of oxygen and other nutrients between blood and dermis.

Autologous bone marrow-derived cultured mesenchymal stem cells delivered in a fibrin spray accelerate healing in murine and human cutaneous wounds

The nonhematopoietic component of bone marrow includes multipotent mesenchymal stem cells (MSC) capable of differentiating into fat, bone, muscle, cartilage, and endothelium. In this report, we describe the cell culture and characterization, delivery system, and successful use of topically applied autologous MSC to accelerate the healing of human and experimental murine wounds. A single bone marrow aspirate of 35-50 mL was obtained from patients with acute wounds (n = 5) from skin cancer surgery and from patients with chronic, long-standing, nonhealing lower extremity wounds (n = 8). Cells were grown in vitro under conditions favoring the propagation of MSC, and flow cytometry and immunostaining showed a profile (CD29+, CD44+, CD105+, CD166+, CD34-, CD45-) highly consistent with published reports of human MSC. Functional induction studies confirmed that the MSC could differentiate into bone, cartilage, and adipose tissue. The cultured autologous MSC were applied up to four times to the wounds using a fibrin polymer spray system with a double-barreled syringe. Both fibrinogen (containing the MSC) and thrombin were diluted to optimally deliver a polymerized gel that immediately adhered to the wound, without run-off, and yet allowing the MSC to remain viable and migrate from the gel. Sequential adjacent sections from biopsy specimens of the wound bed after MSC application showed elongated spindle cells, similar to their in vitro counterparts, which immunostained for MSC markers. Generation of new elastic fibers was evident by both special stains and antibodies to human elastin. The application of cultured cells was safe, without treatment-related adverse events. A strong direct correlation was found between the number of cells applied (greater than 1 x 10(6) cells per cm2 of wound area) and the subsequent decrease in chronic wound size (p = 0.0058). Topical application of autologous MSC also stimulated closure of full-thickness wounds in diabetic mice (db/db). Tracking of green fluorescent protein (GFP)+ MSC in mouse wounds showed GFP+ blood vessels, suggesting that the applied cells may persist as well as act to stimulate the wound repair process. These findings indicate that autologous bone marrow-derived MSC can be safely and effectively delivered to wounds using a fibrin spray system.

Interaction of a blood coagulation factor on electrically polarized hydroxyapatite surfaces

Although the polarization treatment of hydroxyapatite (HA) remarkably enhances the osteoconductivity, the mechanisms have not yet been completely understood. The interaction of proteins in blood and tissue fluids with biomaterials are reportedly triggers for later cellular responses and played a major role in osteoconductive processes. Considering this, we disclosed the interaction of polarized HA surface with a coagulation factor, fibrin stabilizing factor XIII (FXIII). The HA activated FXIII even in Ca2+ free buffer, based on the SDS-PAGE detections of alpha-polymer and gamma-dimer bands assigned to stabilized fibrin. The Ca2+ ions, possibly released from the HA surfaces, were examined whether they initiate the activation of the FXIII. It was experimentally proved by ICP analysis that the induced large negative charges on the electrically polarized HA significantly increased the released Ca2+ concentration for the short pre-incubation time of 3 min. The more Ca2+ ions released from the negatively charged HA (N-HA) surfaces were more effective in the activation of the FXIII, resulting in the rapider disappearance of the gamma-chain bands in fibrin. The slightly lower Ca2+ concentration in the positively charged HA, compared to the nonpolarized HA activated the FXIII at an almost equal rate. The accelerated activation contributed to the stabilization of fibrin scaffold. Therefore, the polarity difference of the induced charges of the polarized HA surface altered the rate of the FXIII activation. The early stage interaction of the HA surfaces with blood proteins was considered to be an essential process of the accelerated new bone formation near implanted N-HA surface.

Tissue engineering: current and future approaches to ocular surface reconstruction

Although cells have been cultured outside the body for many years, research has only recently begun to develop complex three-dimensional tissue constructs that will, ideally, mature into fully functional tissues and organs. Tissue engineering is an emerging field in the area of biotechnology that combines the principles and methods of life sciences with those of engineering for the purpose of regenerating, repairing, or replacing diseased tissues. In this review, we describe the recent advances and current development of tissue engineering approaches as related to the ocular surface system, which comprises the three main integrated tissue units: conjunctiva, cornea and lacrimal glands.

Synergistic effect of keratinocyte transplantation and epidermal growth factor delivery on epidermal regeneration

Both keratinocyte transplantation and epidermal growth factor (EGF) delivery stimulate epidermal regeneration. In this study, we hypothesized that the combined therapy of keratinocyte transplantation and EGF delivery accelerates epidermal regeneration compared to the single therapy of either keratinocyte transplantation or EGF delivery. To test this hypothesis, we utilized fibrin matrix as a keratinocyte/EGF delivery vehicle for epidermal regeneration. Full-thickness wounds were created on the dorsum of athymic mice, and human keratinocytes and EGF in fibrin matrix were sprayed onto the wounds to regenerate epidermal layers (group 1). As controls, human keratinocytes in fibrin matrix (group 2), EGF in fibrin matrix (group 3), or fibrin matrix alone (group 4) was sprayed onto the wounds. Spraying keratinocytes suspended in fibrin matrix did not affect the keratinocyte viability, as the cell viabilities before and after spraying were not different. EGF was released from fibrin matrix for 3 days. The wounds were analyzed with histology and immunohistochemistry at 1 and 3 weeks after treatments. Compared with the control groups, initial wound closure rate was highest in group 1. Histological analyses indicated that group 1 exhibited faster and better epidermal regeneration than the other groups. Immunohistochemical analyses showed that regenerated epithelium in groups 1 and 2 stained positively for human involucrin at 3 weeks, whereas the tissue sections of the groups 3 and 4 stained negatively. Human laminin was detected at the dermal-epidermal junction of the regenerated tissues in groups 1 and 2 at 3 weeks and was not detected in groups 3 and 4. The epidermal thickness of the regenerated tissues in group 1 was significantly thicker than that of the other groups at all time points. These results suggest that the combined therapy of keratinocyte transplantation and EGF delivery is more efficacious for epidermal regeneration than each separate therapy alone.

Evaluation of a fibrin-based skin substitute prepared in a defined keratinocyte medium

The purpose of this study was to evaluate the influence of fibrin glue and aprotinin on the growth of adult human skin keratinocytes in defined serum-free conditions. The keratinocytes were cultured on cell culture plastics and on a fibrin matrix prepared from fibrin glue. The cell growth was measured by MTT assay, while the growth of clonogenic keratinocytes was evaluated by colony assay and expressed as colony-forming efficiency (CFE). The clonogenic potential of keratinocytes released from subconfluent and confluent cultures grown on fibrin glue was also studied by the colony assay. In comparison to a plastic culture surface the fibrin glue had significantly (P<0.05) increased the clonogenic potential of keratinocytes, as well as enhanced their growth. Keratinocytes released from subconfluent cultures grown on fibrin glue attained a significantly (P<0.05) higher percentage of clonogenic cells than their confluent parallels. At 75, 150, 300 and 450 KIU/ml aprotinin did not influence the growth of keratinocytes (P>0.2). A fibrin-based skin substitute produced in the defined keratinocyte medium could be safely used to treat a number of skin defects.

Composition and characteristics of an autologous thrombocyte gel

BACKGROUND

The purpose of the current study was to characterize and compare an autologous thrombocyte gel containing several blood components with a commercially available glue.

MATERIALS AND METHODS

Twenty-five volunteers had blood drawn, and lab values, characteristics of the platelet-enriched plasma (PRP), thrombocyte aggregation, electron microscopic examinations, and the breaking strength were determined and compared to a commercial glue.

RESULTS

Overall 65% of the total thrombocytes could be isolated from the volunteers and an enrichment of 300% with an autotransfusion device could be achieved. Thrombocyte aggregation as a marker for thrombocyte function decreased from 92% in patients to 71% in the PRP. The autologous glue demonstrated a significant reduced breaking strength (0,76 N/cm(3)) compared to the commercial glue (7.42 N/cm(2)), P < 0.05. The decrease in breaking strength could be correlated with the thrombocyte concentration, P < 0.05.

CONCLUSIONS

In the present study we have shown that an autologous platelet-enriched plasma cannot be used as a glue in the common sense to seal stitches or prosthesis. Platelet gels, however, have a high concentration of platelets that release the bioactive proteins and growth factors are necessary to initiate and accelerate tissue repair and enhance dermal and epidermal regeneration. To evaluate the possible clinical implication prospective, randomized studies should be performed to examine the effect of autologous plasma platelet-enriched plasma on wound healing.

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.

A Novel Role of Fibrin in Epidermal Healing: Plasminogen-Mediated Migration and Selective Detachment of Differentiated Keratinocytes

Recent studies have shown that fibrin promotes epidermal regeneration in vitro and maintains the stem cell population after transplantation of keratinocytes in vivo. As epidermal keratinocytes do not express integrin alpha(v)beta3, the receptor for fibrin and fibrinogen, the mechanism through which fibrin affects epidermal cells remains elusive. To investigate the role of fibrin in epidermal wound healing, we developed an in vitro model in which fibrin was added to the top of wounded keratinocyte monolayers grown on collagen. With this matrix topology, keratinocytes migrate between the collagen on their basal side and fibrin on their apical side mimicking migration of the epidermis in vivo. Using this model, we found that fibrin promoted keratinocyte migration in low and high calcium concentrations by exposing the cells to plasminogen. The migration rate depended strongly on the concentration of fibrinogen and the rate of plasmin-mediated fibrin degradation. Surprisingly, fibrin and fibrinogen caused significant detachment of keratinocytes which was prevented by the addition of calcium. Further examination using flow cytometry revealed that the detached cells were larger, more granular, and had very low levels of beta1 integrin, which are all signs of differentiated keratinocytes. Our results suggest a novel dual role of fibrin in epidermal healing. First, fibrin promotes keratinocyte migration indirectly by exposing plasminogen to migrating cells, and second, fibrin selectively disrupts adhesion of differentiated keratinocytes. Our data are novel and may have important implications in understanding wound healing and in the use of fibrin as a biomaterial for protein and gene delivery.

A fibrin-based bioengineered ocular surface with human corneal epithelial stem cells

PURPOSE

The purpose of the investigation was to prepare a bioengineered ocular surface tissue replacement consisting of (presumed) human corneal epithelial stem cells in a cross-linked fibrin gel for potential transplant.

METHODS

Presumed human epithelial stem cells were harvested, isolated, and cultivated as previously described from adult donor corneas obtained from a tissue and organ bank. The cultured corneal epithelial stem cells were suspended in a fibronectin/fibrin gel cross-linked by factor XIII. Plasma components were derived from a fibrinogen-rich cryoprecipitate of human plasma. Suspended cells proliferated in the fibrin gel, giving rise to colonies that eventually coalesced to near confluence over the 15 days of cultivation. The gels were sectioned and immunostained for keratin 3 (AE5) and keratin 19.

RESULTS

The fibrin gel product with corneal stem cells was easily manageable and maneuverable. Addition of the protease inhibitor aprotinin to the incubation medium prevented gel degradation; once it was removed, gels disintegrated within 24 hours. All of the cells cultivated in the fibrin gel stained positively for keratin 3 (AE5), indicating differentiation along the corneal epithelium lineage. Cells located in the center of the colonies were keratin 19-positive, suggesting a more primitive cell type. Growth kinetics were documented.

CONCLUSIONS

A bioengineered ocular surface with a combination of presumed corneal epithelial stem cells in a cross-linked fibrin gel represents a potential improvement in current attempts to create a transportable, pliable, and stable tissue replacement. Since both the cells and the plasma components of the fibrin gel are of human origin, this technique provides the potential for a totally autologous bioengineered replacement tissue.

Fibrinogen and fibrin are anti-adhesive for keratinocytes: a mechanism for fibrin eschar slough during wound repair

During cutaneous wound repair the epidermis avoids the fibrin-rich clot; rather it migrates down the collagen-rich dermal wound margin and over fibronectin-rich granulation tissue. The mechanism(s) underlying keratinocyte movement in this precise pathway has not been previously addressed. Here we demonstrate that cultured human keratinocytes do not express functional fibrinogen/fibrin receptors, specifically alpha v beta 3. Biologic modifiers known to induce integrin expression or activation did not induce adhesion to fibrin, fibrinogen, or its fragments. Epidermal explant outgrowth and single epidermal cell migration failed to occur on either fibrin or fibrinogen. Surprisingly, fibrin and fibrinogen mixed at physiologic molar ratios with fibronectin abrogated keratinocyte attachment to fibronectin. Keratinocytes transduced with the beta 3 integrin subunit cDNA, expressed alpha v beta 3 on their surface and attached to and spread on fibrinogen and fibrin. beta-gal cDNA-transduced keratinocytes did not demonstrate this activity. Furthermore, beta 3 cDNA-transduced keratinocyte adhesion to fibrin was inhibited by LM609 monoclonal antibody to alpha v beta 3 in a concentration-dependent fashion. From these data, we conclude that normal human keratinocytes cannot interact with fibrinogen and its derivatives due to the lack of alpha v beta 3. Thus, fibrinogen and fibrin are authentic anti-adhesive for keratinocytes. This may be a fundamental reason why the migrating epidermis dissects the fibrin eschar from wounds.

The use of fibrin glue in skin grafts and tissue-engineered skin replacements: a review

Fibrin glue has been widely used as an adhesive in plastic and reconstructive surgery. This article reviews the advantages and disadvantages of its use with skin grafts and tissue-engineered skin substitutes. Fibrin glue has been shown to improve the percentage of skin graft take, especially when associated with difficult grafting sites or sites associated with unavoidable movement. Evidence also suggests improved hemostasis and a protective effect resulting in reduced bacterial infection. Fibrin, associated with fibronectin, has been shown to support keratinocyte and fibroblast growth both in vitro and in vivo, and may enhance cellular motility in the wound. When used as a delivery system for cultured keratinocytes and fibroblasts, fibrin glue may provide similar advantages to those proven with conventional skin grafts. Fibrin glue has also been shown to be a suitable delivery vehicle for exogenous growth factors that may in the future be used to accelerate wound healing.

Cutaneous wound healing: an update

Our understanding of wound-healing mechanisms has progressed over the past decade. Wound healing is traditionally divided into three phases--the inflammatory phase, the proliferation phase, and the remodeling phase--and involves a well-orchestrated interaction among blood vessels (platelets, macrophages, neutrophils, endothelial cells, and smooth muscle cells), epidermis (keratinocytes, melanocytes, and Langerhans cells), adnexal structures (outer root sheath cells and hair dermal papilla cells), dermis (fibroblasts and myofibroblasts), nervous system (neurons), and subcutaneous fatty layers (adipocytes). We review recent discoveries of basic and clinical aspects of wound healing including several revolutions that occurred in wound management: occlusive dressing therapy, use of living skin equivalents, and topical administration of growth factors. As we previously proposed, the use of tissue substitutes and autologous epidermal sheets led to a new concept of skin grafting through the keratinocyte activation phase in the graft healing mechanism. In this review, we also discuss a representative patient who presented with plantar wounds caused by calcaneal osteomyelitis and healed by the coverage of epidermal grafting.