Autologous skin transplantation: comparison of minced skin to other techniques

Novel Techniques in Fractional Skin Replacement

The gold standards for coverage of wounds that cannot be primarily closed are full thickness skin grafts (FTSGs) and split thickness skins graft (STSGs). FTSGs harvest sites generally require primary closure, which limits availability, especially when treating larger wounds. STSGs have many shortcomings, including donor site morbidity. Fractional autologous skin replacement can be utilized in conjunction with or in lieu of STSGs to both improve graft outcomes of large wounds and to decrease donor site morbidity. Skin can be mechanically or chemically fractionated. Fractionated skin can be advantageous, as adnexal structures provide additional functionality without donor site morbidity. In this review, we will discuss current and emerging techniques in fractional skin replacement.

Skin Grafting

Significance: Although skin grafting is a basic surgical procedure, there are many sophisticated innovations that are used only by experienced surgeons. In-depth knowledge of new and old methods gives the opportunity to select the most appropriate technique in each case. Recent Advances: Most methods have been invented long ago, but some of them have been rediscovered and further refined. An improved understanding of wound healing and basic skin grafting techniques enable the development of new solutions. Critical Issues: Clinical randomized controlled trials in wound research are time consuming, expensive, and difficult to perform. This has given rise to many techniques that are not well proven. Recent strict regulations concerning all forms of cell therapy have further hindered the development of promising new ideas. Future Directions: Cell therapies to enhance epithelialization and promote wound healing are already available but far from everyday practice. Very strict regulations have halted many promising projects. An alternative approach to circumvent some of these regulatory hurdles is the grafting of uncultured, autologous cells or very small pieces of skin, which also offer very large expansion of the graft. The development and adoption of new bilayered skin substitutes are expected to be the most significant development in the near future, although they face similar regulatory challenges as cell therapies.

Minced skin grafts for chronic wounds compared to conventional mesh grafts

Background and Aims

Skin grafting is the single most effective method to close a chronic wound. The current standard of care is to use meshed split thickness skin grafts. This entails the use of surgical instruments that need to be autoclaved and to have a power source, which usually requires an OR facility. The minced skin technique uses single use, presterilized instruments and the procedure can be done under local anesthesia, by a wound care practitioner, in a wound clinic, a physician's office or even at the bedside. The current study was designed to determine if the results from micrografting were non inferior to conventional mesh grafting.

Methods

In a prospective non inferiority study, 26 chronic ulcers were treated with micrografting (MSG) and 24 with conventional mesh grafts 1:3 (control group-CG) in a total of 21 patients, 10 male and 11 female. The donor site areas in the MSG group were predetermined to 2.5 × 5 cm and the mesh grafts expansion was set at 1:3.

Results

In the first weeks postoperatively, micrograft healing initially lagged behind the conventional mesh grafts but at 60 days after grafting, all MSG wounds were healed. The MSG wounds had better pigmentation, less itching, and less scarring. The micrografting procedure was easy to learn and expeditious to perform. The MSG mean expansion was 9.1 compared to three times (CG).

Conclusion

The MSG procedure is not inferior to conventional mesh grafting, requires smaller donor sites, and can be done with single use instruments, under local anesthesia, with early discharge.

Electrospun Nanofibers for Wound Management

Electrospun nanofibers show great potential in biomedical applications. This mini review article traces the recent advances in electrospun nanofibers for wound management via various approaches. Initially, we provide a short note on the four phases of wound healing, including hemostasis, inflammation, proliferation, and remodeling. Then, we state how the nanofiber dressings can stop bleeding and reduce the pain. Following that, we discuss the delivery of therapeutics and cells using different types of nanofibers for enhancing cell migration, angiogenesis, and re-epithelialization, resulting in the promotion of wound healing. Finally, we present the conclusions and future perspectives regarding the use of electrospun nanofibers for wound management.

Use of Minced Residual Skin Grafts to Improve Donor Site Healing in Split-Thickness Skin Grafting

Background

The morbidity of the donor site in split-thickness skin graft (STSG) may include abnormal pigmentation, delayed healing, and unfavorable scarring. Studies are usually focused on improving the healing of the recipient site, so donor site management becomes a secondary consideration. An optimal solution should be sought for donor site management to improve healing and minimize morbidity.

Methods

In this study, we used minced residual skin grafts over half of the donor site (cases) and compared the healing duration and scar quality with the other half (control). Healing duration was measured in days and the scar quality was assessed by the Patient and Observer Scar Assessment Scale (POSAS) at 90 days, 180 days, and 360 days.

Results

The healing time was reduced with the application of minced residual skin grafts on the donor site. The scar quality was significantly better in the case group as compared to the control group at 90 days, 180 days, and 360 days (p<0.05).

Conclusion

Mincing residual skin grafts and replacing them back to the donor site reduces the healing time and improves the quality of the scar.

Pixel Grafting: A Novel Skin Graft Expansion Technique

Skin grafting is the transplantation of skin, a routinely performed procedure to cover the loss of skin. Skin is the largest organ of the body, which falls short of availability in extensive injuries, especially burns. In such a situation, pixel grafting, a novel expansion technique helps to cover a large area with less skin harvest. The objective of the study was to test fast, minimally invasive, easy to use minced split-thickness skin graft to cover large wounds and to reflect on the advantages of pixel graft. It is a pilot study of patients admitted with severe burns. We conclude that with this technique of pixel or minced grafting, large areas can be grafted with minimal donor-site requirement, and the techniques of preparation provide adequate size graft for pixel grafting.

Optimal structural pattern for maximal compliance using topology optimization based on phasefields: Application to improve skin graft meshing efficiency

This article focuses on the problem of maximal compliance design of a hyper-elastic solid with the optimal design of human skin grafts as the application in mind. The solution method is a phasefield-based topology optimization method that supposes multiple local phasefields and a minimum distance constraint in order to prevent the phasefields from merging. Consequently, structurally disintegrating solutions such as by the coalescence of voids can be prevented. The method is used to find an optimal graft meshing pattern for a sample that is subjected to a biaxial extension of up to 150%, which corresponds to an expansion ratio of 1 : 2.25. Three prospective unitcell solutions that exhibit meta-material behavior are proposed for a periodic graft pattern. The results are a step toward improving the skin graft meshing efficiency. This work does not cover experimental validation.

A Multicentre Study: The Use of Micrografts in the Reconstruction of Full-Thickness Posttraumatic Skin Defects of the Limbs-A Whole Innovative Concept in Regenerative Surgery

The skin graft is a surgical technique commonly used in the reconstructive surgery of the limbs, in order to repair skin loss, as well as to repair the donor area of the flaps and cover the dermal substitutes after engraftment. The unavoidable side effect of this technique consists of unaesthetic scars. In order to achieve the healing of posttraumatic ulcers by means of tissue regeneration and to avoid excessive scarring, a new innovative technology based on the application of autologous micrografts, obtained by Rigenera technology, was reported. This technology was able to induce tissue repair by highly viable skin micrografts of 80 micron size achieved by a mechanical disaggregation method. The specific cell population of these micrografts includes progenitor cells, which in association with the fragment of the Extracellular Matrix (ECM) and growth factors derived by patients' own tissue initiate biological processes of regeneration enhancing the wound healing process. We have used this technique in 70 cases of traumatic wounds of the lower and upper limbs, characterized by extensive loss of skin substance and soft tissue. In all cases, we have applied the Rigenera protocol using skin micrografts, achieving in 69 cases the complete healing of wounds in a period between 35 and 84 days. For each patient, the reconstructive outcome was evaluated weekly to assess the efficacy of this technique and any arising complication. A visual analogue scale (VAS) was administered to assess the amount of pain felt after the micrografts' application, whereas we evaluated the scars according to the Vancouver scale and the wound prognosis according to Wound Bed Score. We have thus been able to demonstrate that Rigenera procedure is very effective in stimulating skin regeneration, while reducing the outcome scar.

The Effect of Enzymatic Digestion on Cultured Epithelial Autografts

Severe burns are often treated by means of autologous skin grafts, preferably following early excision of the burnt tissue. In the case of, for example, a large surface trauma, autologous skin cells can be expanded in vitro prior to transplantation to facilitate the treatment when insufficient uninjured skin is a limitation. In this study we have analyzed the impact of the enzyme (trypsin or accutase) used for cell dissociation and the incubation time on cell viability and expansion potential, as well as expression of cell surface markers indicative of stemness. Skin was collected from five individuals undergoing abdominal reduction surgery and the epidermal compartment was digested in either trypsin or accutase. Trypsin generally generated more cells than accutase and with higher viability; however, after 7 days of subsequent culture, accutase-digested samples tended to have a higher cell count than trypsin, although the differences were not significant. No significant difference was found between the enzymes in median fluorescence intensity of the analyzed stem cell markers; however, accutase digestion generated significantly higher levels of CD117- and CD49f-positive cells, but only in the 5 h digestion group. In conclusion, digestion time appeared to affect the isolated cells more than the choice of enzyme.

Evaluation of Donor Site Pain After Fractional Autologous Full-Thickness Skin Grafting

Background: Despite the development of numerous wound treatment alternatives, 25% to 50% of leg ulcers and >30% of foot ulcers are not fully healed after 6 months of treatment. Autologous skin grafting is a time-tested therapy for these wounds; however, the creation of a new wound in the donor area yields a considerable limitation to this procedure.

Innovation: Fractional autologous full-thickness skin grafting (FFTSG) is a technique wherein multiple small full-thickness skin grafts (FTSGs) are harvested with possibly minor donor-site comorbidities. The first device used to harvest FFTSG (ART™ system, Medline, Northfield, IL) is a device capable of harvesting >300 small FTSGs and transferring them to a target wound.

Objective: To better evaluate patients' clinical experience, we sought to evaluate pain at the donor site associated with this procedure.

Approach: Pain was assessed with numeric visual analog pain scales at days 1, 2, 4, and 7. Nine subjects underwent this procedure with only six of them reporting any level of pain on day 1, and none disclosing pain after day 2.

Conclusion: In this study, we evidenced that this device manages to harvest FTSGs with minimal associated pain. Future research will need to evaluate other aspects of the procedure as well as long-term outcomes at the donor and recipient areas.

The Benefit of Microskin in Combination With Autologous Keratinocyte Suspension to Treat Full Skin Loss In Vivo

Patients with extensive deep burns often lack enough autologous skin to cover the wounds. This study explores a new method using microskin in combination with autologous keratinocytes in the treatment of extensive deep burn. Wounds in the combination group were treated with automicroskin at an area expansion ratio of 20:1 (wound area to automicroskin area) and autologous keratinocyte suspension, which were compared with the following treatments: no autotransplant, only allografts (control group); autologous keratinocyte suspension only (keratinocyte only group); automicroskin at an area expansion ratio of 20:1 (20:1 group); and automicroskin at an area expansion ratio of 10:1 (10:1 group, positive control). The authors used epithelialization rate (epithelialized area on day 21 divided by original wound area), hematoxylin and eosin staining, laminin, and type IV collagen immunohistochemistry to assess wound healing. The epithelialization rate of combination group (74.2% ± 8.0%) was similar to that of 10: 1 group (84.3% ± 11.9%, P = .085) and significantly (P < .05) higher than that of 20:1 group (59.2% ± 10.8%), keratinocyte only group (53.8% ± 11.5%), and control group (22.7% ± 5.5%). The hematoxylin and eosin staining and immunohistochemistry showed the epithelialization in the combination group was better than that in the keratinocyte only group and control group. Microskin in combination with autologous keratinocyte suspension can promote the reepithelialization of full-thickness wounds and reduce the requirements for automircoskin, and it is a useful option in the treatment of extensive deep burns.

Pathophysiologic Mechanisms and Current Treatments for Cutaneous Sequelae of Burn Wounds

Burn injuries are a pervasive clinical problem. Extensive thermal trauma can be life-threatening or result in long-lasting complications, generating a significant impact on quality of life for patients as well as a cost burden to the healthcare system. The importance of addressing global or systemic issues such as resuscitation and management of inhalation injuries is not disputed but is beyond the scope of this review, which focuses on cutaneous pathophysiologic mechanisms for current treatments, both in the acute and long-term settings. Pathophysiological mechanisms of burn progression and wound healing are mediated by highly complex cascades of cellular and biochemical events, which become dysregulated in slow-healing wounds such as burns. Burns can result in fibroproliferative scarring, skin contractures, or chronic wounds that take weeks or months to heal. Burn injuries are highly individualized owing to wound-specific differences such as burn depth and surface area, in addition to patient-specific factors including genetics, immune competency, and age. Other extrinsic complications such as microbial infection can complicate wound healing, resulting in prolonged inflammation and delayed re-epithelialization. Although mortality is decreasing with advancements in burn care, morbidity from postburn deformities continues to be a challenge. Optimizing specialized acute care and late burn outcome intervention on a patient-by-patient basis is critical for successful management of burn wounds and the associated pathological scar outcome. Understanding the fundamentals of integument physiology and the cellular processes involved in wound healing is essential for designing effective treatment strategies for burn wound care as well as development of future therapies. Published 2018. Compr Physiol 8:371-405, 2018.

Expansion of Submucosal Bladder Wall Tissue In Vitro and In Vivo

In order to develop autologous tissue engineering of the whole wall in the urinary excretory system, we studied the regenerative capacity of the muscular bladder wall. Smooth muscle cell expansion on minced detrusor muscle in vitro and in vivo with or without urothelial tissue was studied. Porcine minced detrusor muscle and urothelium were cultured in vitro under standard culture conditions for evaluation of the explant technique and in collagen for tissue sectioning and histology. Autografts of minced detrusor muscle with or without minced urothelium were expanded on 3D cylinder moulds by grafting into the subcutaneous fat of the pig abdominal wall. Moulds without autografts were used as controls. Tissue harvesting, mincing, and transplantation were performed as a one-step procedure. Cells from minced detrusor muscle specimens migrated and expanded in vitro on culture plastic and in collagen. In vivo studies with minced detrusor autografts demonstrated expansion and regeneration in all specimens. Minced urothelium autografts showed multilayered transitional urothelium when transplanted alone but not in cotransplantation with detrusor muscle; thus, minced bladder mucosa was not favored by cografting with minced detrusor. No regeneration of smooth muscle or epithelium was seen in controls.

Minced Tissue in Compressed Collagen: A Cell-containing Biotransplant for Single-staged Reconstructive Repair

Conventional techniques for cell expansion and transplantation of autologous cells for tissue engineering purposes can take place in specially equipped human cell culture facilities. These methods include isolation of cells in single cell suspension and several laborious and time-consuming events before transplantation back to the patient. Previous studies suggest that the body itself could be used as a bioreactor for cell expansion and regeneration of tissue in order to minimize ex vivo manipulations of tissues and cells before transplanting to the patient. The aim of this study was to demonstrate a method for tissue harvesting, isolation of continuous epithelium, mincing of the epithelium into small pieces and incorporating them into a three-layered biomaterial. The three-layered biomaterial then served as a delivery vehicle, to allow surgical handling, exchange of nutrition across the transplant, and a controlled degradation. The biomaterial consisted of two outer layers of collagen and a core of a mechanically stable and slowly degradable polymer. The minced epithelium was incorporated into one of the collagen layers before transplantation. By mincing the epithelial tissue into small pieces, the pieces could be spread and thereby the propagation of cells was stimulated. After the initial take of the transplants, cell expansion and reorganization would take place and extracellular matrix mature to allow ingrowth of capillaries and nerves and further maturation of the extracellular matrix. The technique minimizes ex vivo manipulations and allow cell harvesting, preparation of autograft, and transplantation to the patient as a simple one-stage intervention. In the future, tissue expansion could be initiated around a 3D mold inside the body itself, according to the specific needs of the patient. Additionally, the technique could be performed in an ordinary surgical setting without the need for sophisticated cell culturing facilities.

Challenging the Conventional Therapy: Emerging Skin Graft Techniques for Wound Healing

BACKGROUND

Split-thickness skin grafting is the current gold standard for treatment of major traumatic skin loss. However, split-thickness skin grafting is limited by donor-skin availability, especially in large burns. In addition, the donor-site wound is associated with pain and scarring. Multiple techniques have been developed in the past to overcome these limitations but have been unable to achieve clinical relevance. In this study, the authors examine the novel emerging skin grafting techniques, aiming to improve the utility of split-thickness skin grafting.

METHODS

An extensive literature review was conducted on PubMed, MEDLINE, and Google Scholar to look for new skin grafting techniques. Special focus was given to techniques with potential for large expansion ratio and decreased donor-site pain.

RESULTS

The new modalities of modified skin grafting technique, discussed in this article, include (1) Xpansion Micrografting System, (2) fractional skin harvesting, (3) epidermal suction blister grafting, and (4) ReCell technology. These techniques are able to achieve significantly increased expansion ratios compared with conventional split-thickness skin grafting and also have decreased donor-site morbidity.

CONCLUSIONS

These techniques can be used separately or in conjunction with split-thickness skin grafting to overcome the associated pitfalls. Further studies and clinical trials are needed to define the utility of these procedures and where they fit into routine clinical practice.

Transplantation of autologous minced bladder mucosa for a one-step reconstruction of a tissue engineered bladder conduit

Surgical intervention is sometimes needed to create a conduit from the abdominal wall to the bladder for self-catheterization. We developed a method for tissue engineering a conduit for bladder emptying without in vitro cell culturing as a one-step procedure. In a porcine animal model bladder, wall tissue was excised and the mucosa was minced to small particles. The particles were attached to a tube in a 1 : 3 expansion rate with fibrin glue and transplanted back by attaching the tube to the bladder and through the abdominal wall. Sham served as controls. After 4-5 weeks, conduits were assessed in respect to macroscopic and microscopic appearance in 6 pigs. Two pigs underwent radiology before termination. Gross examination revealed a patent conduit with an opening to the bladder. Histology and immunostaining showed a multilayered transitional uroepithelium in all cases. Up to 89% of the luminal surface area was neoepithelialized but with a loose attachment to the submucosa. No epithelium was found in control animals. CT imaging revealed a patent channel that could be used for filling and emptying the bladder. Animals that experienced surgical complications did not form conduits. Minced autologous bladder mucosa can be transplanted around a tubular mold to create a conduit to the urinary bladder without in vitro culturing.

Fractional Skin Harvesting: Autologous Skin Grafting without Donor-site Morbidity

Background:

Conventional autologous skin grafts are associated with significant donor-site morbidity. This study was conducted to determine feasibility, safety, and efficacy of a new strategy for skin grafting based on harvesting small columns of full-thickness skin with minimal donor-site morbidity.

Methods:

The swine model was used for this study. Hundreds of full-thickness columns of skin tissue (~700 µm diameter) were harvested using a custom-made harvesting device, and then applied directly to excisional skin wounds. Healing in donor and graft sites was evaluated over 3 months by digital photographic measurement of wound size and blinded, computer-aided evaluation of histological features and compared with control wounds that healed by secondary intention or with conventional split-thickness skin grafts (STSG).

Results:

After harvesting hundreds of skin columns, the donor sites healed rapidly without scarring. These sites reepithelialized within days and were grossly and histologically indistinguishable from normal skin within 7 weeks. By contrast, STSG donor sites required 2 weeks for reepithelialization and retained scar-like characteristics in epidermal and dermal architecture throughout the experiment. Wounds grafted with skin columns resulted in accelerated reepithelialization compared with ungrafted wounds while avoiding the “fish-net” patterning caused by STSG.

Conclusion:

Full-thickness columns of skin can be harvested in large quantities with negligible long-term donor-site morbidity, and these columns can be applied directly to skin wounds to enhance wound healing.

Selective release of cytokines, chemokines, and growth factors by minced skin in vitro supports the effectiveness of autologous minced micrografts technique for chronic ulcer repair

A new effective surgical procedure to repair chronic ulcers called minced micrografts technique has been recently reported. The technique consists in spreading a finely minced skin sample upon the wound bed. In this study, we investigate the in vitro release of cytokines (interleukin-6, tumor necrosis factor-α, interleukin-1α, and granulocyte-colony stimulating factor), chemokines (monocyte chemoattractant protein-1 and growth-related oncogene-α), and growth factors (platelet-derived growth factor, basic fibroblast growth factor, vascular endothelial growth factor, hepatocyte growth factor, and nerve growth factor) by minced (referred to as the minced sample) vs. not minced (referred to as the whole sample) human skin biopsy samples from the same donor. Factor release in the culture medium at different time points was detected using a multiplexed protein assay. The minced sample, which could behave like the skin fragments used in vivo in the autologous minced micrografts technique, expressed higher levels of tumor necrosis factor-α, interleukin-1α, platelet-derived growth factor, and basic fibroblast growth factor, and lower levels of interleukin-6, monocyte chemoattractant protein-1, growth related oncogene-α, and vascular endothelial growth factor compared with the whole sample. In conclusion, mincing of healthy skin may allow appropriate regulation of the inflammatory phase of wound healing and could induce overexpression of some growth factors, which facilitates the proliferative phase of healing.

Comparison of healing parameters in porcine full-thickness wounds transplanted with skin micrografts, split-thickness skin grafts, and cultured keratinocytes

BACKGROUND

Transplantation of skin micrografts (MGs), split-thickness skin grafts (STSGs), or cultured autologous keratinocytes (CKs) enhances the healing of large full-thickness wounds. This study compares these methods in a porcine wound model, investigating the utility of micrograft transplantation in skin restoration.

STUDY DESIGN

Full-thickness wounds were created on Yorkshire pigs and assigned to one of the following treatment groups: MGs, STSGs, CKs, wet nontransplanted, or dry nontransplanted. Dry wounds were covered with gauze and the other groups' wounds were enclosed in a polyurethane chamber containing saline. Biopsies were collected 6, 12, and 18 days after wounding. Quantitative and qualitative wound healing parameters including macroscopic scar appearance, wound contraction, neoepidermal maturation, rete ridge formation, granulation tissue thickness and width, and scar tissue formation were studied.

RESULTS

Transplanted wounds scored lower on the Vancouver Scar Scale compared with nontransplanted wounds, indicating a better healing outcome. All transplanted wounds exhibited significantly lower contraction compared with nontransplanted wounds. Wounds transplanted with either MGs, STSGs, or CKs showed a significant increase in re-epithelialization compared with nontransplanted wounds. Wounds transplanted with MGs or STSGs exhibited improved epidermal healing compared with nongrafted wounds. Furthermore, transplantation with STSGs or MGs led to less scar tissue formation compared with the nontransplanted wounds. No significant impact on scar formation was observed after transplantation of CKs.

CONCLUSIONS

Qualitative and quantitative measurements collected from full-thickness porcine wounds show that transplantation of MGs improve wound healing parameters and is comparable to treatment with STSGs.

A new technique of ex vivo gene delivery of VEGF to wounds using genetically modified skin particles promotes wound angiogenesis

BACKGROUND

Transplantation of genetically modified keratinocytes has been shown to accelerate wound healing. However, this method is labor-intensive and time-consuming. We have developed a new technique of intraoperative gene delivery to wounds that involves transplantation of transfected minced skin particles (MSPs) derived from harvested partial-thickness skin.

STUDY DESIGN

MSPs measuring 0.8 × 0.8 × 0.35 mm were created from a split-thickness skin graft of a pig. In vitro transfection was carried out with adenoviral LacZ (Ad-LacZ) for qualitative and adenoviral vascular endothelial growth factor (Ad-VEGF) for quantitative analysis. Transfected MSPs were transplanted to each of 2.5 × 2.5 cm full-thickness wounds on the dorsum of the pig. Nontransfected MSPs served as controls. Wound chambers were applied and injected with saline to create a wet environment.

RESULTS

LacZ expression was detected in migrating cells originating from MSPs both in vitro and in vivo. VEGF expression in the wound fluid of Ad-VEGF-MSP-transplanted wounds on each of days 2 to 4 (mean ± SEM 6.74 ± 1.89 ng/mL, day 2; 9.88 ± 2.27 ng/mL, day 3; 9.87 ± 1.28 ng/mL, day 4) was significantly higher (p < 0.0001) compared with wounds transplanted with either untransfected MSPs, Ad-LacZ-MSPs, or untransplanted controls. In vitro VEGF expression was significantly higher (p < 0.0001) in Ad-VEGF 1 × 10(10) transfected MSPs compared with either Ad-VEGF 1 × 10(9) transfected MSPs or untransfected MSPs. Wounds transplanted with Ad-VEGF-MSPs showed significantly higher (p < 0.0001) numbers of newly formed blood vessels (12.6 ± 0.9 vessels/high power field [HPF]) compared with wounds transplanted with either Ad-LacZ-MSPs (4.4 ± 0.5 vessels/HPF) or untransfected MSPs (5.2 ± 0.7 vessels/HPF). All MSP-transplanted wounds (Ad-VEGF-MSPs, untransfected MSPs, Ad-LacZ-MSPs) showed significantly higher re-epithelialization compared with untransplanted wounds on days 10 and 14 (p < 0.0001).

CONCLUSIONS

We demonstrated successful transfection of MSPs that can be transplanted to wounds as a source of gene-expressing cells. This technique can be used to deliver growth-modulating genes in wound healing.

The micrograft concept for wound healing: strategies and applications

The standard of care for wound coverage is to use an autologous skin graft. However, large or chronic wounds become an exceptionally challenging problem especially when donor sites are limited. It is important that the clinician be aware of various treatment modalities for wound care and incorporate those methods appropriately in the proper clinical context. This report reviews an alternative to traditional meshed skin grafting for wound coverage: micrografting. The physiological concept of micrografting, along with historical context, and the evolution of the technique are discussed, as well as studies needed for micrograft characterization and future applications of the technique.

Meshed skin grafts placed upside down can take if desiccation is prevented

BACKGROUND

The role of the wet environment in wound healing has been investigated in various studies. The current study explores the role of the wet wound environment in promoting healing of skin grafts. The authors hypothesized that the survival of skin grafts is dependent not only on the orientation of transplantation but also on the environment into which the skin is transplanted.

METHODS

This study included 72 full-thickness (2.5 x 2.5-cm) wounds in six Yorkshire pigs. The wounds were grafted with autologous split-thickness skin grafts (meshed or sheet), placed either regularly (dermal side down) or inverted (dermal side up), and treated in a wet or a dry environment. Behavior of the skin grafts and healing were analyzed in histologic specimens collected on days 4, 6, 9, and 12 after wounding. Wound contraction was quantified by photoplanimetry.

RESULTS

In the wet environment, not only did inverted meshed skin grafts survive, but also they proliferated to accelerate reepithelialization. In this environment, wounds transplanted with inverted and regular meshed grafts showed no significant difference in reepithelialization rate and contraction. In contrast, in the dry environment, wounds transplanted with inverted meshed grafts showed a significantly lower reepithelialization rate and a higher contraction rate than wounds transplanted with regular grafts. Inverted meshed grafts in a dry environment and inverted sheet grafts did not survive.

CONCLUSION

The wound environment has an important role in the survival and proliferation of skin grafts, as demonstrated by survival of inverted meshed grafts in the wet environment and their contribution to accelerated reepithelialization, equal to the regularly placed grafts.

Minced skin for tissue engineering of epithelialized subcutaneous tunnels

We used minced, autologous skin for neoepithelialization of surgically created subcutaneous tunnels in a large animal model. Partial-thickness skin grafts were harvested from the back region of five 50-60 kg Yorkshire pigs. The skin was minced to 0.8 x 0.8 x 0.3 mm particles. Silicone-latex tubes were covered with fibrin, rolled in minced skin, and placed in subcutaneous tunnels created in the abdominal area. For comparison, single cell suspensions of keratinocytes and fibroblasts in fibrin or fibrin only were transplanted on tubes. Tunnels were extracted after 14, 21, and 28 days for microscopic evaluation. All tubes transplanted with minced skin particles showed neoepithelialization. The epithelium was stratified and differentiated after 2 weeks in vivo, and the stratum corneum was directed toward the implanted tube. No epithelium formed from tubes transplanted with single cell suspensions, and only sparse keratinocytes could be detected by serial sectioning and immunostaining on day 14, but not later. No epithelial lining was found in tunnels with fibrin-only-coated tubes. Epithelial cysts could be found the first 2 weeks after transplantation in the minced skin group but not later. In conclusion, a minced skin technique could serve as a potential source for tissue engineering of tubular conduits for reconstructive purposes of the urethra and for cutaneous stomas for bladder catheterization, or intestinal irrigations. The method would have the advantage of being simple and expeditious and not requiring in vitro culturing.

General handling and anesthesia for experimental surgery in pigs

The pig is a common large animal for experimental settings in many fields of surgery. In experimental surgery, there is a need for different narcotic procedures depending on the complexity of the surgical investigation. Narcotic procedures have to be safe, easy to handle, and should not influence the experimental results. We hereby present important aspects of handling and narcotic procedures for pigs. The aim of this publication is to supply an introduction for young surgical investigators who are planning or already have started investigations using pigs as an experimental animal. This publication is based on our institutional experience of narcotic and surgical procedures in more than 400 cases.