Jürgen Kopp

Tissue Engineering of Cultured Skin Substitutes

Skin replacement has been a challenging task for surgeons ever since the introduction of skin grafts by Reverdin in 1871. Recently, skin grafting has evolved from the initial autograft and allograft preparations to biosynthetic and tissue‐engineered living skin replacements. This has been fostered by the dramatically improved survival rates of major burns where the availability of autologous normal skin for grafting has become one of the limiting factors. The ideal properties of a temporary and a permanent skin substitute have been well defined. Tissue‐engineered skin replacements: cultured autologous keratinocyte grafts, cultured allogeneic keratinocyte grafts, autologous/allogeneic composites, acellular biological matrices, and cellular matrices including such biological substances as fibrin sealant and various types of collagen, hyaluronic acid etc. have opened new horizons to deal with such massive skin loss. In extensive burns it has been shown that skin substitution with cultured grafts can be a life‐saving measure where few alternatives exist. Future research will aim to create skin substitutes with cultured epidermis that under appropriate circumstances may provide a wound cover that could be just as durable and esthetically acceptable as conventional split‐thickness skin grafts. Genetic manipulation may in addition enhance the performance of such cultured skin substitutes. If cell science, molecular biology, genetic engineering, material science and clinical expertise join their efforts to develop optimized cell culture techniques and synthetic or biological matrices then further technical advances might well lead to the production of almost skin like new tissue‐engineered human skin products resembling natural human skin.

Applied tissue engineering in the closure of severe burns and chronic wounds using cultured human autologous keratinocytes in a natural fibrin matrix

Whereas in severe burns cultured human epithelial cells may well serve as a life saving method, the true value of tissue-engineered skin products in chronic wound care has yet to be clearly defined. Among other well-known clinical problems, the engraftment rate of commercially available multilayered “sheet grafts” has been shown to vary extremely. Adherence of transplanted cells to the wound bed — especially in the presence of potential wound contamination — is one of the crucial aspects of this technique. Keratinocyte suspensions in a natural fibrin sealant matrix can potentially treat a variety of skin defects. In acute burn wounds, as well as in chronic wounds the clinical application of this type of tissue-engineered skin substitute demonstrates the capacity of cultured human autologous keratinocytes in a fibrin sealant matrix to adhere to wound beds, attach and spread over the wound resulting in reepithelialization of both acute and chronic wounds. In full thickness burns the combination of this new tool with allogenic dermis is a promising option to achieve complete dermal—epidermal reconstitution by means of tissue engineering and guided tissue repair. When transferring this technique into the treatment of chronic wounds we found an optimal preparation of such recipient wound beds to be crucial to the success. The additional application of continuous negative pressure (vacuum therapy) and preliminary chip skin grafting to optimally prepare the recipient site may be helpful tools to achieve such well-prepared and graftable surfaces. Prospective controlled comparative studies should be designed to further assess the clinical efficacy of this technique.

The versatility of the distally based peroneus brevis muscle flap in reconstructive surgery of the foot and lower leg

Soft tissue and bone defects of the lower leg, ankle, and heel region often require coverage by local or distant flaps. The authors successfully used the distally based peroneus brevis muscle flap for the treatment of 15 patients with osteomyelitis (n = 5), melanoma (n = 1), Achilles tendon defects (n = 6), posttraumatic bone defects (n = 2), and chronic diabetic heel ulcer (n = 1). The size of the defects ranged from 6 to 60 cm2. All defects were covered successfully without major complications by the muscle flap. The distally based peroneus brevis muscle represents a very reliable flap for coverage of small and moderate defects of the medial and lateral malleolus, the Achilles tendon, and the heel area. This flap offers a convincing alternative for covering defects in the distal leg region and is often preferable to the use of free flaps because the surgery is rapidly performed and does not require microsurgical expertise.

Intrinsic axial vascularization of an osteoconductive bone matrix by means of an arteriovenous vascular bundle.

Background: The purpose of this study was to generate an autonomously vascularized hard-tissue construct suitable for microsurgical transfer. The effector of vascularization was an arteriovenous bundle inserted into a specially designed channel in the matrix. The authors also evaluated corrosion cast and intravital magnetic resonance angiography as methods for monitoring and quantifying the angiogenic response. Methods: Thirty inbred male Lewis rats were divided into two groups. In both groups (n = 15), a disk of processed bovine cancellous bone matrix was placed into an isolation chamber. In group A, a ligated arteriovenous bundle was inserted into the biogenic matrix as a vascular carrier. In group B, there was no vascular carrier. At 2, 4, and 8 weeks after implantation, four constructs per group were evaluated by means of histology and histomorphometry and one by scanning electron microscopy of vascular corrosion casts. Micro-magnetic resonance angiography was used for intravital evaluation of the vascularized matrices. Results: Vascular density was higher in group A. The capillary network in group A displayed a higher degree of maturation, with organization into vessels of different orders. Both the sprouting and intussusceptive modes of angiogenesis could be documented. Micro-magnetic resonance angiography showed a patency rate of approximately 75 percent in the bundle. Conclusions: The authors zeroed in on the issue of vascularization. The results might provide a basis for further investigations on induction of bone formation in axially prevascularized matrices. Axially vascularized bone substitutes might solve issues of availability in mass and form and provide perfusion autonomy in sites of impaired circulation.

Vacuum application increases therapeutic safety and allows intensified local radiation treatment of malignant soft-tissue tumors

Purpose:In order to simplify and improve outcome of radiation therapy and final defect coverage in patients suffering from invasive soft-tissue tumors, brachytherapy and application of V.A.C.uum-assisted closure (V.A.C.®) were combined with delaying flap incision.Patients and Methods:Two patients were excised as radically as possible and brachytherapy tubes were implanted directly on the tumor bed. At the same time, flaps for later defect coverage were preconditioned by circumcision. Brachytherapy and external- beam irradiation were performed directly on the vacuum sponge followed by subsequent defect coverage with the preconditioned flaps.Results:Excision significantly reduced tumor masses in both patients; in one case sensible and motor function of the involved extremity was clearly improved. V.A.C.® coverage allowed repeated brachytherapy and external-beam applications following exact placing of plastic tubes and FLABs on the tumor bed. Sequential irradiation had no effect on neighboring flap tissues, which healed without impairment following transposition.Conclusion:Combination of V.A.C.® and brachytherapy can effectively replace circumstantial and laborious IORT (intraoperative radiotherapy) procedures. Exact placement of tubes on the tumor bed without subsequent tissue coverage is conserving preconditioned flap tissues, which are transposed for final defect coverage at the end of radiotherapy. However, by circumventing radiation exposure of these tissues, a possible later irradiation sequence can be performed without endangering defect-covering flaps.Ziel:Zur Vereinfachung und Verbesserung radiotherapeutischer Strategien bei der Behandlung invasiv wachsender Weichgewebetumoren wurde die gemeinsame Anwendung von Brachytherapie und Vakuumversiegelung (V.A.C.®) mit der Technik der chirurgischen Lappenpräkonditionierung kombiniert.Patienten und Methodik:Bei zwei Patienten wurde so radikal wie möglich reseziert. Nachfolgend wurden Brachytherapieröhren direkt auf das Tumorbett implantiert und mit einem V.A.C.®-Schwamm vakuumversiegelt. Gleichzeitig erfolgte die Umschneidung eines benachbarten Weichgewebeareals zur Präkonditionierung und späteren Defektdeckung. Brachytherapie und externe Bestrahlung wurden direkt unter oder auf dem schwammgedeckten Areal appliziert. Anschließend erfolgte die Defektdeckung mit den präkonditionierten Weichgewebelappen.Ergebnisse:Die Exzisionen reduzierten die jeweilige Tumormasse erheblich und resultierten in einem Fall in einer deutlichen Verbesserung von Motorik und Sensibilität an der betroffenen Extremität. Die Vakuumversiegelung erlaubte wiederholte Brachytherapien und externe Bestrahlungen nach exakter Platzierung der Röhren und FLABs auf dem jeweiligen Tumorbett. Die wiederholte Radiatio hatte keinen Effekt auf die benachbarten, präkonditionierten Lappengewebe, welche nach Einschwenken in den jeweiligen Defekt ohne Störung einheilten.Schlussfolgerung:Die Kombination von Vakuum- und Brachytherapie kann die umständliche und aufwendige Anwendung einer intraoperativen Bestrahlung (IORT) effektiv ersetzen. Die exakte Platzierung der Bestrahlungsröhren ohne nachfolgende Defektdeckung schont das präkonditionierte Lappengewebe, welches am Ende der Radiotherapie zur Defektdeckung in den Tumordefekt eingeschwenkt wird. Da eine Strahlenexposition dieser Gewebe umgangen wird, kann eine später erforderliche Bestrahlung durchgeführt werden, ohne die Lappengewebe dabei zu gefährden.

The versatility of the free osteocutaneous fibula flap in the reconstruction of extremities after sarcoma resection.

BackgroundAn understanding of the biology of bone and soft-tissue sarcomas, knowledge of adjuvant therapies and refinement in techniques of reconstructive surgery have allowed limb-sparing and limb salvage surgery to become a reality in the management of malignant tumors of the extremities. Functional limb salvage following radical resection has become a possibility in many resectable tumors by the use of alloplastic prostheses, homograft or autogenous bone for skeletal reconstitution combined with vascularized soft tissue coverage. Although the free fibula flap has been well described for reconstructions of the mandible and oral cavity, it has not been widely presented as an ideal tool to preserve extremities and to circumvent amputation.Patients and methodsWe describe the complex surgical reconstruction in four patients with primary sarcomas of the extremities. The sarcomas (Ewings sarcoma, osteosarcoma and epitheloid sarcoma) were resected radically and the massive bone and soft tissue defect was replaced by vascularized free fibula transfer.ResultsWe present our experience with versatility of this osteocutaneous flap to allow reconstruction and salvage of extremitity sarcomas. There were no operative or postoperative complication and all the four patients had good limb function. The flap was found to be versatile as it could be used for either upper limb or lower limb and for large defects. The results were better in upper limb than in lower limb.ConclusionsFree fibular graft was found to be effective for salvaging limb function where a massive bone defect resulted from wide tumor resection in the extremities.

Intrinsic versus extrinsic vascularization in tissue engineering.

In-vitro culture of tissues can be regulated by controlled medium administration whereas ex-vivo bioreactors are designed with the capability of providing tissue engineered devices with continuous nutrient support. When these materials or cellular constructs are transferred in vivo they have to rely on processes like interstitial fluid diffusion and blood perfusion. Here recites a core limitation for transfer of tissue engineering models from the in vitro to the in vivo environment. Diffusion is the initial process involved but it can only provide for cell support within a maximum range of 200 μm into the matrix.1, 2, 3, 4

Cologne Burn Centre experiences with glycerol-preserved allogeneic skin: Part I: Clinical experiences and histological findings (overgraft and sandwich technique)

In an effort to improve the take of finely meshed autografts a modification of the sandwich technique, as first published by Alexander et al. (1981), was developed. In contrast to the techniques described by other authors, the wound bed is sealed with fibrin glue spray after excision of the burns. Widely meshed autografts are then covered with non-meshed (only scarcely sliced) glycerolized allograft sheets, being fixed with staples. Patients are placed on fluidized beds and are exposed without dressings from the fifth day onwards. Histologically and clinically, it can be assumed that part of the glycerolized allodermis is incorporated. During the weeks after transplantation, a creeping substitution of the allodermis by autologous tissue takes place. This would suggest a co-existence between glycerol-preserved hypo-allergenic allografts and auto-epidermis. Research on the definitive fate of allodermis in cases of sandwich grafting is continuing.

MRSA—retrospective analysis of an outbreak in the burn centre Aachen

The growing interest in methicillin-resistant Staphylococcus aureus (MRSA) has been caused by its increased appearance in hospital and community populations. In our burn centre, an outbreak of MRSA was noticed during an 8-month period. We were able to isolate MRSA in eight patients. DNA analysis by pulsed-field gel electrophoresis (PFGE) demonstrated the development of five different strains during this period. Only two patients developed an infection caused by MRSA colonisation. The infections were proven by positive blood culture or catheter colonisation. One patient developed a clinical vancomycin-resistant sepsis which was treated successfully with the additional application of Quinupristin/Dalfopristin. THIS ANALYSIS SHOWS THAT: (1) the development of MRSA in a burn unit is often created in a single patient by long-term antibiotic therapy and not a result of cross-infection, (2) manifest MRSA infection seldom occurs even in colonised burn patients, and (3) a clinically vancomycin-resistant MRSA infection in burn patients can be treated sufficiently with Quinupristin/Dalfopristin.

Ancient traditional Chinese medicine in burn treatment: a historical review.

Burn treatment in traditional Chinese medicine (TCM) has a long and remarkable history. This article provides a review of its philosophy and knowledge, basic principles and treatment strategies as well as their modifications during 1300 years of medical development. The specific features presented are still influencing modern traditional Chinese medicine practitioners as well as modern Chinese burn treatment with considerable benefit for the treatment of burn victims.