Modulating diseased skin with tissue engineering: actinic purpura treated with Apligraf

Engineered Vascularized Muscle Flap

One of the main factors limiting the thickness of a tissue construct and its consequential viability and applicability in vivo, is the control of oxygen supply to the cell microenvironment, as passive diffusion is limited to a very thin layer. Although various materials have been described to restore the integrity of full-thickness defects of the abdominal wall, no material has yet proved to be optimal, due to low graft vascularization, tissue rejection, infection, or inadequate mechanical properties. This protocol describes a means of engineering a fully vascularized flap, with a thickness relevant for muscle tissue reconstruction. Cell-embedded poly L-lactic acid/poly lactic-co-glycolic acid constructs are implanted around the mouse femoral artery and vein and maintained in vivo for a period of one or two weeks. The vascularized graft is then transferred as a flap towards a full thickness defect made in the abdomen. This technique replaces the need for autologous tissue sacrifications and may enable the use of in vitro engineered vascularized flaps in many surgical applications.

An engineered muscle flap for reconstruction of large soft tissue defects

Large soft tissue defects involve significant tissue loss, requiring surgical reconstruction. Autologous flaps are occasionally scant, demand prolonged transfer surgery, and induce donor site morbidity. The present work set out to fabricate an engineered muscle flap bearing its own functional vascular pedicle for repair of a large soft tissue defect in mice. Full-thickness abdominal wall defect was reconstructed using this engineered vascular muscle flap. A 3D engineered tissue constructed of a porous, biodegradable polymer scaffold embedded with endothelial cells, fibroblasts, and/or myoblasts was cultured in vitro and then implanted around the femoral artery and veins before being transferred, as an axial flap, with its vascular pedicle to reconstruct a full-thickness abdominal wall defect in the same mouse. Within 1 wk of implantation, scaffolds showed extensive functional vascular density and perfusion and anastomosis with host vessels. At 1 wk posttransfer, the engineered muscle flaps were highly vascularized, were well-integrated within the surrounding tissue, and featured sufficient mechanical strength to support the abdominal viscera. Thus, the described engineered muscle flap, equipped with an autologous vascular pedicle, constitutes an effective tool for reconstruction of large defects, thereby circumventing the need for both harvesting autologous flaps and postoperative scarification.

A review of a bi-layered living cell treatment (Apligraf) in the treatment of venous leg ulcers and diabetic foot ulcers

Apligraf^® (Organogenesis, Canton, MA) is a bi-layered bioengineered skin substitute and was the first engineered skin US Food and Drug Administration (FDA)-approved to promote the healing of ulcers that have failed standard wound care. Constructed by culturing human foreskin-derived neonatal fibroblasts in a bovine type I collagen matrix over which human foreskin-derived neonatal epidermal keratinocytes are then cultured and allowed to stratify, Apligraf provides both cells and matrix for the nonhealing wound. Its exact mechanism of action is not known, but it is known to produce cytokines and growth factors similar to healthy human skin. Initially approved by the FDA in 1998 for the treatment of venous ulcers greater than one-month duration that have not adequately responded to conventional therapy, Apligraf later received approval in 2000 for treatment of diabetic foot ulcers of greater than three weeks duration. Herein, we review the use of Apligraf in the treatment of chronic venous leg ulcers and diabetic foot ulcers. Our goal is to provide a working understanding of appropriate patient selection and proper use of the product for any physician treating this segment of the aging population.

Update on tissue-engineered biological dressings

Tissue-engineered biological dressings offer promise in the treatment of burns, chronic ulcers, donor site and other surgical wounds, and a variety of blistering and desquamating dermatologic conditions. For example, the prevalence of diabetic foot ulcers ranges from 4.4% to 10.5% of diabetics, resulting in 82,000 lower extremity amputations annually; venous leg ulcers affect 0.18% to 1.35% of the population; and pressure ulcers are found in 5.0% to 8.8% of institutionalized patients and 14.8% of patients in acute care facilities. Despite the large number of potential beneficiaries, cellular tissue-engineered products have suffered setbacks in recent years and have garnered considerably lower market share than commercial promoters anticipated. The mechanism of action of these products is not universally agreed upon, but delivery of growth factors and extracellular matrix components to the wound is thought to be important; graft "take" is not usually considered to occur. These "engineered" products do not specifically match a treatment modality to an underlying pathology. Clinical effect is often modest, and sometimes not justi- fiable from a cost-benefit perspective. Nevertheless, clinical reports in the literature of uses of tissueengineered biological dressings continue to mount, indicating that these products are finding niche applications where clinical utility is high and the cost can be defended. Despite commercial setbacks, the first-approved products, Dermagraft, Apligraf, and Cultured Epidermal Autograft (Epicel) are still being marketed, and new ones, such as OrCel, continue to be developed. The major indications for these products are summarized and a brief review of the available clinical literature is offered.