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Uncertainties in thermal-optical measurements of black carbon: Insights from source and ambient samples
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Current Available Cellular and Tissue-Based Products for Treatment of Skin Defects Yukun Liu, MD; Adriana C. Panayi, MD; Lauren R. Bayer, PA-C; and Dennis P. Orgill, MD, PhD regeneration of viable tissue. Scaffolds can be natural, synthetic, or composite, as well as biodegradable or permanent. Growth factors, secreted by cells via signaling pathways, also play a crucial part in processes related to tissue regeneration and wound healing.2 Regenerative medicine replaces or regenerates human cells, tissues, or organs to restore or establish normal function.3 This broader approach has been particularly effective in the treatment of hematologic malignancies with the use of bone marrow transplants and does not necessarily rely on scaffolds. With the rapid development of tissue engineering and regenerative medicine, innovative strategies such as stem cellYbased therapy, gene therapy, nanomedicine, and three-dimensional bioprinting techniques are largely in preclinical testing, but also in some cases have been translated into human clinical use.4 Recently, for example, a patient with epidermolysis bullosa was treated with gene-edited skin, showing great promise for these techniques.5 Despite tissue engineering approaches being extensively applied in multiple fields such as skin substitution, organ replacement, tissue repair, and disease modulation, many problems still exist. Limitations for routine practice include the immunogenic rejection of allogeneic cells, concerns about malignancy, the challenges of harvesting adequate stem cells, the manufacturing costs, and the complexity of clinical studies needed for regulatory approval. Establishment of adequate vascular perfusion of the underlying tissue is important in effective use of these products as well as in wound healing, although peripheral arterial disease is a limiting factor. It has been reported that peripheral arterial disease is 10 times more prevalent in developed countries where these products are also more readily available.5Y7 A simple ankle-to-brachial systolic blood pressure index can be used to predict the likelihood of successful wound management with these products to avoid impaired healing or poor outcomes. This article focuses on selected cellular and tissue-based products (CTPs) that are available for sale in the US and used for diabetic foot ulcers (DFUs), venous leg ulcers (VLUs), and burns. The FDA approval levels to be discussed include 510(k); premarket approval (PMA); human cells, tissue, tissue-based products (HCT/ Ps); and humanitarian device exemption (HDE; Figure 1).
ABSTRACT Downloaded from http://journals.lww.com/aswcjournal by BhDMf5ePHKbH4TTImqenVLTWxlDBt+9A5zZyDMqnnNF2FON5AJgxtPEDStC3Pl4v on 01/17/2019
The occurrence of diabetic foot ulcers and venous leg ulcers is increasing because of aging population trends as well as increases in the number of people with diabetes and obesity. New technologies have been developed to treat these conditions, whereas other technologies previously designed for burns and traumatic wounds have been adapted. This article reviews the development of selected skin replacement technologies, particularly cellular and tissue-based products, highlighting their effectiveness on diabetic foot ulcers, venous leg ulcers, and burns. KEYWORDS: cellular and tissue-based products, diabetic foot ulcers, skin replacement, skin substitutes, tissue engineering, venous leg ulcers, wound healing ADV SKIN WOUND CARE 2019;32:19Y25.
INTRODUCTION Organ and tissue replacements are common goals of many surgical procedures. Autogenous tissues work well but are often in short supply and can leave scars or deform the donor site. Allogeneic tissues often result in immunologic rejection, whereas permanent biomaterials can lead to infection and capsular contracture (immune response to foreign materials). The field of tissue engineering (the use of a combination of cells, engineering materials, and suitable biochemical factors to improve or replace biologic functions1) was established in an attempt to reduce these complications. The term tissue engineering has also been used to define the integration of cells with acellular matrices or synthetic biomaterials. Cells provide both structural proteins and biochemical signaling molecules critical in tissue engineering constructs. Autologous, allogeneic, or xenogeneic tissues have all been used. The ability of stem cells to differentiate has made them a logical cell source, but their applicability is limited by availability, safety concerns, and regulatory hurdles. Scaffolds are materials that provide a three-dimensional structure for cells and blood vessels to populate, allowing growth and
At Brigham and Women’s Hospital in Boston, Massachusetts, Yukun Liu, MD, was a Research Fellow at the time this manuscript was written; Adriana C. Panayi, MD, is a Research Fellow; Lauren R. Bayer, PA-C, is Clinical Director of the Wound Care Center; and Dennis P. Orgill MD, PhD is Director of the Wound Care Center, Department of Surgery, Brigham and Women’s Hospital; and Professor of Surgery, Harvard Medical School. Acknowledgment: Dr Orgill is a consultant and/or receives research funding from Integra LifeSciences Corporation, the Musculoskeletal Research Foundation, Geistlich Corporation, Acell Corporation, and Professional Education and Research Incorporated. The authors have disclosed no other financial relationships related to this article. Submitted May 18, 2018; accepted June 29, 2018. WWW.WOUNDCAREJOURNAL.COM
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on volunteers with variable-depth surgical incisions and no comorbidities, Dunkin et al10 determined that skin injuries less than 0.57 mm do not result in scar formation. Interestingly, this value corresponds to the junction of the papillary and reticular dermis. In addition, the skin separates with deeper wounds because of loss of tension. Given that full-thickness wounds do not have direct access to the keratinocytes found in epidermal appendages, they must rely on keratinocyte migration from the wound edge for wound closure. Consequently, in large surface area wounds, autologous skin grafts or flaps are necessary for repair.11 The limited skin graft donor sites for large defects spawned the development of tissue engineering approaches that are now being applied to smaller defects. The ideal engineered skin replacements would provide a scaffold that closely mimics the structure and biologic function of native skin.8 Autologous or allogeneic cells have been combined in vitro with biologic or synthetic materials to generate tissue-engineered skin replacements. In addition, epidermal cell suspensions and cell sheets have been used, as well as semisynthetic and decellularized scaffolds. Previous research has summarized the essential properties for skin replacements:12Y14 1. nontoxic 2. nonantigenic 3. cost effective 4. easy to handle and apply 5. long shelf life 6. provide a barrier against contamination 7. result in minimal inflammatory reaction 8. improve wound healing 9. appropriate resistance to mechanical forces Unfortunately, there is currently no skin replacement technology that completely satisfies all of these criteria.
Figure 1. CLASSIFICATION BASED ON FDA APPROVAL
SKIN REPLACEMENT CONCEPTS Skin is the largest human organ and consists of three layers: the epidermis, dermis, and hypodermis (subcutaneous fat). The epidermis, which provides a barrier function, is populated with keratinocytes, melanocytes, and Langerhans cells. The dermis, which provides structural integrity, is composed of fibroblasts and the extracellular matrix (ECM), and contains important macromolecules including collagen, elastin, and glycosaminoglycans. Finally, the hypodermis, which protects the body from mechanical stresses and assists in thermoregulation, is composed of fat and connective tissues that provide a rich source of stem cells. Further, the skin confers UV radiation protection, is an important site for vitamin D metabolism, and provides visual signals critical for aesthetics.8 Damage to the skin that occurs in DFUs, VLUs, burns, and other skin conditions leads to wound formation. Wounds can be classified according to the depth of injury: epidermal wounds (superficial erosions), partial dermal wounds (partial-thickness wounds or shallow ulcers), and wounds spanning the entire dermis (full-thickness wounds or deep dermal ulcers).9 Superficial and partial-thickness dermal injuries, if treated properly, tend to heal without surgical intervention. Full-thickness wounds can also heal but result in the formation of scar tissue. In a study ADVANCES IN SKIN & WOUND CARE & VOL. 32 NO. 1
FROM CONCEPT TO CREATION The process of developing and approving a skin substitute follows a series of procedures. First, the concept of a new skin replacement is proposed and designed according to set criteria.15 This is followed by development and testing during preclinical studies, both in vitro and in vivo. The initial proposed product, as well as its components, needs to be tested for safety based on good laboratory practices. Animal testing is often used to test efficacy and clarify the mechanism of action. Next, optimal manufacturing requires optimizing the inventory, product storage, shipping, and shelf life. Further, products need to be approved by the FDA. When a product is FDA approved, it is assessed for reimbursement, a process by which the interests among individuals, insurance companies, and the developer are balanced. The Centers for Medicare & Medicaid 20
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Services produces the Healthcare Common Procedure Coding System codes, integral to reimbursement for medical devices (Table).16 Some products never reach mass production because of failure to receive reimbursement from third-party payers.
Figure 2. LOWER LEG VENOUS STASIS ULCER
Premarket Approval Premarket approval is required by the FDA when no similar product exists on the market or when a substantial change has been made to a preexisting product. The process requires adequate and well-controlled clinical studies in order for the product to be approved. Products and devices that go through the PMA process eventually receive approval from the FDA, and the approval serves as a patent for the company. A clinical case using a PMA-approved product is shown in Figure 2. Integra Dermal Regeneration Template (IDRT; Integra LifeSciences Corporation, Plainsboro, New Jersey). Developed by Burke and Yannas in 1980, the IDRT was first reported in a small clinical trial by Burke17 and later in a multicenter postapproval clinical trial.18 It was subsequently manufactured by Integra LifeSciences Corporation and approved by the FDA in 1996. The IDRT is an artificial bilayer material in which the lower layer is composed of a highly porous collagen and chondroitin-6sulfate copolymer that is covered with a semipermeable silicone elastomer that provides a moisture and bacterial barrier. The lower layer is optimized for pore size, degradation rate, and the percentage of glycosaminoglycan present to reduce wound contraction. The silicone layer is replaced by split-thickness skin graft after 2 to 3 weeks or for smaller wounds closed by epidermal migration from the wound margins.19 It is approved for the treatment of second- and third-degree burns and since 2002 for scar reconstruction.20 The effectiveness and safety of IDRT treating burns were evaluated in a multicenter postapproval clinical trial with 216 burn injury patients. These patients were treated with IDRT followed with a thin skin graft on the surface. The results showed Table.
HEALTHCARE COMMON PROCEDURE CODING SYSTEM FOR SKIN SUBSTITUTES Q4100 Q4101 Q4102 Q4104 Q4105 Q4106 Q4107 Q4108 Q4110 Q4116 Q4128
Skin substitute, not otherwise specified Apligraf, per square centimeter Oasis wound matrix, per square centimeter Integra bilayer matrix wound dressing, per square centimeter Integra dermal regeneration template or Integra Omnigraft dermal regeneration matrix, per square centimeter Dermagraft, per square centimeter GRAFTJACKET, per square centimeter Integra matrix, per square centimeter PriMatrix, per square centimeter AlloDerm, per square centimeter FlexHD, AllopatchHD, or MatrixHD, per square centimeter
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This is a 65-year-old woman with a left lower leg venous stasis ulcer. Debridement of the wound was performed first, and then Apligraf (Organogenesis) was applied to the wound twice with a month between applications.
a lower infection and higher uptake rate. These results highlight the use of IDRT as a safe and effective treatment for burn patients.21 A clinical case using the dermal matrix is shown in Figure 3. Currently, this product has been used for treating DFUs as an additional indication under the name Omnigraft Dermal Regeneration Matrix. A multicenter, randomized, controlled, parallelgroup clinical trial on 307 subjects with DFUs was conducted 21
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Figure 3. TREATMENT OF PG WITH DERMAL MATRIX
Above (left), patient developed PG after sternotomy. Preoperative view, final debridement. Above (center), after debridement. Above (right), Integra and Acticoat were placed on day 9 after debridement. Below (left), 4-week appearance after Integra placement. Silicone layer is starting to peel off. Below (center), 11 weeks after Integra placement. The wound is completely granulated. Below (right), 28 weeks after Integra implanting, the wound is nearly healed. Reprinted from Climov M, Bayer LR, Moscoso AV, Matsumine H, Orgill DP. The role of dermal matrices in treating inflammatory and diabetic wounds. Plast Reconstr Surg 2016;138 (3 Suppl):148S-57S.
treatment of life-threatening third-degree burns, especially when the donor site is not sufficient. These clinical studies investigated the effectiveness of IDRTrelated products; they indicated that it is safe and effective and demonstrates improved graft take properties. However, the risk of infection and scar formation is not negligible, as well as the need for a second operation that increases the length of hospital stay. In addition, the high cost of IDRT products limits widespread application.21,22 Dermagraft (Organogenesis, Canton, Massachusetts). Dermagraft is a unilayer cultured skin replacement (UCSR) that uses a provisional, tear-resistant, bioresorbable polyglactin mesh seeded with cultured fibroblasts that require cryopreservation. Over time, this mesh is replaced by ECM produced by the
under an Investigational Device Exemption. The experimental group (154 patients) was treated with IDRT, and the control group was treated with sodium chloride gel. The treatment lasted for at least 16 weeks and was followed up for 12 weeks. The results documented successful DFU closure during the treatment phase; these rates were significantly higher with IDRT treatment (51%) than with the control treatment (32%; P = .001) at week 16. There was complete DFU closure at 43 days in comparison to 78 days for patients treated with standard of care alone.22 The clinical trial laid the foundation for Omnigraft approval for the treatment of partial- and full-thickness neuropathic DFUs that are longer than 6 weeks in duration, with no capsule and tendon or bone exposed. The skin substitute must be used in conjunction with standard care. In addition, it is approved for the ADVANCES IN SKIN & WOUND CARE & VOL. 32 NO. 1
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replacement fibroblasts.23 Following application, the cells continue to secrete growth factors and ECM components until the mesh resorbs in about 3 to 4 weeks.24 Although initial success was reported in a prelinical experiment, it was not until 2001 that the product was approved by the FDA for the treatment of chronic wounds including DFUs.25,26 A randomized, controlled, multicenter study of 314 patients with a DFU was conducted in the US to evaluate complete wound closure using UCSR or regular treatment for 12 weeks. The results determined that 30% of UCSR patients healed versus 18.3% of control patients,27 demonstrating that UCSR is an effective treatment for chronic DFUs. The effectiveness of UCSR in treating VLUs has also been confirmed and approved for marketing in the US.25 In a prospective, multicenter, randomized, controlled study, 186 patients with VLUs were treated with UCSR plus compression therapy, and 180 patients were treated with compression therapy alone and followed up for 12 weeks. In ulcers with less than 12 months’ duration, 52% of patients in the UCSR group versus 37% of patients in the control group healed at 12 weeks. This was statistically significant (P = .029). This study suggested that the earlier use of UCSR as an adjuvant therapy would be beneficial to patients.28 Although there are no actual FDA-approved indications for UCSR on burn injuries, there are published studies.29 A multicenter clinical trial compared UCSR with cryopreserved human cadaver skin for temporary coverage on 66 patients with burn wounds. In this study, UCSR led to clinical improvement with no epidermal slough and less bleeding.30
grafting (4.5%), and hypertrophic scars (3.3%).34 Another retrospective medical record review of 164 burn patients in a pediatric burn center indicated that porcine xenograft can be used to provide useful wound coverage with pain relief and reduced need for dressing changes. Oasis Wound Matrix (Cook Biotech Inc, West Lafayette, Indiana). Oasis Wound Matrix is a xenogeneic collagen scaffold derived from porcine small intestinal mucosa. As a threedimensional collagenous ECM, it allows molecular adhesion, cell growth, and cytokine secretion.35 The natural ECM of this product provides a scaffold for tissue repair and wound healing. It has a long shelf life and can be stored at room temperature. In 2000, it was cleared by the FDA for the management of partial- and fullthickness wounds.20 At least one study has demonstrated its effect in DFUs.36 A prospective, randomized, controlled multicenter trial of 120 patients with VLUs treated by OASIS Wound Matrix combined with compression therapy demonstrated improved results compared with compression therapy alone.37
Human Cells, Tissues, and Cellular and Tissue-Based Products Although these products are considered part of human tissue banks, these products are not strictly regulated by the FDA. Manufacturers of HCT/Ps are, however, required to list their products with the FDA’s Center for Biologics Evaluation and Research as well as ensure they appropriately establish donor eligibility and follow good tissue practices and other procedures to prevent the introduction, transmission, and spread of communicable diseases. Allopatch (Musculoskeletal Transplant Foundation, Edison, New Jersey). AlloPatch is an aseptically processed human reticular acellular dermal matrix (HR-ADM) that contains cytokines and growth factors. Because it is derived from the deeper, reticular layer of dermis, it retains its inherent mechanical and biologic properties. With a more open and uniform structure, it facilitates vascular in-growth and cellular integration.38 Two advantages of HR-ADM are its readiness for use in wound care and its ability to be stored at room temperature.39 As banked human tissue, it has been approved by the FDA as an adjunct therapy in the treatment of chronic, uninfected, full-thickness DFUs.20 One prospective randomized controlled trial compared HR-ADM with standard wound care on nonhealing DFUs. At 12 weeks, the proportion of 20 DFUs treated with HR-ADM that healed was 80%, compared with 20% of DFUs that received standard care alone, a difference reported to be statistically significant.40 The study concluded that HR-ADM was both superior and more cost-effective than standard therapy.
510(k) Clearance A 510(k) is a premarket submission made to the FDA to demonstrate that a product to be marketed is at least as safe and effective, or “substantially equivalent,” to a legally marketed device. Substantial equivalence refers to similarity in construction, design, use, safety, effectiveness, and so on. Once the device or product is determined to be substantially equivalent, it can be marketed in the US. EZ Derm (Brennen Medical, Inc; St Paul, Minnesota). Because of its similarity to human skin, porcine skin has been used for wound coverage since 1960s.31 EZ Derm is a porcinederived xenograft temporary wound dressing. Previous studies have stated its properties include ready availability, easy handling, adherence to the wound surface, reduced pain, and prevention of water loss from wound.32,33 It has 510(k) clearance for the treatment of partial-thickness burns, venous ulcers, diabetic neurotrophic foot ulcers, and pressure injuries. A 4-year retrospective review study was conducted for 157 burn patients treated by EZ Derm, and researchers concluded that it is an effective and durable wound dressing with low rates of complications such as infection (3.0%), the need for additional excision and WWW.WOUNDCAREJOURNAL.COM
Humanitarian Device Exception In order to qualify for HDE approval, a product or device must aid in the treatment or cure of a disease or condition that 23
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difficult to transport. Allogeneic cell-based skin replacements are at risk of graft rejection and disease transmission.48 Biosynthetic and animal-based skin replacements can be applied only as temporary dressings, whereas xenogeneic matrices may result in immunogenic rejection. Further, infection and scar formation are usually unavoidable.49 Like allogeneic cell-based skin replacements, nonliving tissue skin replacements can, in some cases, result in disease transmission. The use of amniotic membrane substitutes, which preserve the native skin properties better than other skin replacement therapies, is limited to temporary wound dressings or in combination with other materials because of their antigenic potential, risk of spreading infection, and fast degradation rates.12 Future experiments should focus on enhancing the ability of CTPs to promote wound healing. Past research has established the role of stem cells in wound healing and laid the foundation for developing stem cells with tissue engineering.50,51 In recent years, researchers have focused on inducing stem cells to differentiate into specific types of cells, including keratinocytes and fibroblasts, and then incorporating them into biomaterial scaffolds.52 Hair follicles contain epithelial stem cells capable of forming skin tissue that may be used in wound healing in the near future.53,54 In terms of scaffolding, materials are still being optimized to create better-quality engineered skin. Vascularization is necessary for wound healing, and prevascularized skin grafts are being studied in order to develop blood vessel networks using cellular strategies or growth factor delivery systems.55,56 There is high level of interest in creating three-dimensional models that better imitate the properties and functions of mature skin. Advanced techniques, including three-dimensional bioprinting, have been used in the creation of the next generation of scaffolding models.57,58 The regeneration of skin components, including sweat glands and hair follicles, has been achieved in animal models but not yet in humans.59,60 Other innovative strategies include the combination of nanotechnology and regenerative medicine; gene therapy strategies are also currently in development.44,61 These strategies are not, however, completely understood. Overall, the need for further research and clinical trials is imperative before widespread clinical application of CTPs can occur.
affects a population of no more than 8,000 per year. The applicant must first obtain humanitarian use device designation from the FDA’s Office of Orphaned Products Development and then submit an HDE to the appropriate FDA premarket review center. Similar to premarket approval, the device or product cannot be comparable to a device that is already legally marketed for the same intended use. Further, HDE approval does not require demonstration of effectiveness. The company must not profit from the sale of the product or device. Epicel (Genzyme Biosurgery, Cambridge, Massachusetts). Cultured epithelial autografts (CEAs) have been a major conceptual development in the care of burn victims. Keratinocytes produce the skin barrier by going through a sequential maturation and senescence process that eventually results in a flexible, semipermeable membrane (stratum corneum). Many investigators have stressed that the reestablishment of the critical barrier structure is a fundamental goal in the treatment of patients with large surface area thermal injuries. This need has led to the development of numerous constructs.41 In 1975, Rheinwald and Green42 pioneered keratinocyte cell culturing. This was subsequently commercialized into Epicel, which can be derived from a small skin biopsy and expanded in a commercial facility over 2 to 3 weeks.43 As a permanent wound covering, it decreases the requirement for donor skin harvesting. Epicel is approved by the FDA under the HDE in the treatment of deep dermal or full-thickness burns, including a burn surface area of greater than 30%.20 It can be used alone or in combination with allogeneic or autologous split-thickness skin grafts, especially when there is a lack of donor site skin. A 5-year prospective controlled trial carried out in 1996 compared the use of cultured keratinocytes with conventional therapy on the treatment of massive burns. There was a significant reduction in mortality in the CEA group versus the control group.44 The results reported a beneficial effect of CEAs in the management of severe burn patients with a total surface burn area greater than 60%.45 However, the fragility, long cultivation time, and susceptibility to infection of autologous cells remain to be addressed.30 Most clinicians use CEAs in combination with allografts, where the epidermis is removed prior to grafting with CEAs. In addition, it has been used in the treatment of VLUs and corneal replacement.46 An earlier multicenter study was conducted on 30 patients evaluating the effectiveness of cryopreserved allogeneic cultured epithelium VLU patients. Results showed 66.6% of the patients healed completely within 12 weeks.47
&
REFERENCES 1. Langer R, Vacanti JP. Tissue engineering. Science 1993;260(5110):920-6. 2. Martino MM, Tortelli F, Mochizuki M, et al. Engineering the growth factor microenvironment with fibronectin domains to promote wound and bone tissue healing. Sci Transl Med 2011; 3(100):100ra189. 3. Mason C, Dunnill P. A brief definition of regenerative medicine. Regen Med 2008;3(1):1-5. 4. Salgado AJ, Oliveira JM, Martins A, et al. Tissue engineering and regenerative medicine: past, present, and future. Int Rev Neurobiol 2013;108:1-33.
QUESTIONS AND FUTURE PROSPECTS Although promising, widespread use of CTPs is currently hindered by limitations. Skin replacements composed of living cells require a long cell culture period, have a short shelf life, and are ADVANCES IN SKIN & WOUND CARE & VOL. 32 NO. 1
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33. Chiu T, Shah M. Porcine xenograft dressing for facial burns: beware of the mesh imprint. Burns 2002;28(3):279-82. 34. Troy J, Karlnoski R, Downes K, et al. The use of EZ Derm in partial-thickness burns: an institutional review of 157 patients. Eplasty 2013;13:e14. 35. Shi L, Ronfard V. Biochemical and biomechanical characterization of porcine small intestinal submucosa (SIS): a mini review. Int J Burns Trauma 2013;3(4):173-9. 36. Hodde JP, Ernst DM, Hiles MC. An investigation of the long-term bioactivity of endogenous growth factor in OASIS Wound Matrix. J Wound Care 2005;14(1):23-5. 37. Mostow EN, Haraway GD, Dalsing M, Hodde JP, King D. Effectiveness of an extracellular matrix graft (OASIS Wound Matrix) in the treatment of chronic leg ulcers: a randomized clinical trial. J Vasc Surg 2005;41(5):837-43. 38. Dasgupta A, Orgill D, Galiano RD, et al. A novel reticular dermal graft leverages architectural and biological properties to support wound repair. Plast Reconstr Surg 2016;4(10):e1065. 39. Zelen CM, Kaufman J, Lang A. Use of AlloPatch Pliable, a human acellular dermal matrix, as an adjunctive therapy for chronic non-healing diabetic foot ulcers: case studies and clinical review. MTF Wound Care. 2017. www.mtfbiologics.org/docs/default-source/clinical/allopatchpliable-case-studies-final-10-28-15.pdf. Last accessed September 20, 2018. 40. Zelen CM, Orgill DP, Serena T, et al. A prospective, randomised, controlled, multicentre clinical trial examining healing rates, safety and cost to closure of an acellular reticular allogenic human dermis versus standard of care in the treatment of chronic diabetic foot ulcers. Int Wound J 2017;14(2):307-15. 41. Hancock K, Leigh IM. Cultured keratinocytes and keratinocyte grafts. BMJ 1989;299(6709): 1179-80. 42. Rheinwald JG, Green H. Serial cultivation of strains of human epidermal keratinocytes: the formation of keratinizing colonies from single cells. Cell 1975;6(3):331-43. 43. Cerqueira MT, Pirraco RP, Martins AR, Santos TC, Reis RL, Marques AP. Cell sheet technology-driven re-epithelialization and neovascularization of skin wounds. Acta Biomater 2014;10(7):3145-55. 44. Bleiziffer O, Eriksson E, Yao F, Horch RE, Kneser U. Gene transfer strategies in tissue engineering. J Cell Mol Med 2007;11(2):206-23. 45. Blot SI, Monstrey SJ, Hoste EA, Carsin H, et al. Cultured epithelial autografts in extensive burn coverage of severely traumatized patients: a five year single-center experience with 30 patients. Burns 2001;27(4):418-9. 46. Pellegrini G, Traverso CE, Franzi AT, Zingirian M, Cancedda R, de Luca M. Long-term restoration of damaged corneal surfaces with autologous cultivated corneal epithelium. Lancet 1997;349(9057):990-3. 47. De Luca M, Albanese E, Cancedda R, et al. Treatment of leg ulcers with cryopreserved allogeneic cultured epithelium. A multicenter study. Arch Dermatol 1992;128(5):633-8. 48. Matthews RN. Transmission of HIV infection by amniotic membrane dressing. Burns 1990;16(4):313. 49. Catalano E, Cochis A, Varoni E, Rimondini L, Azzimonti B. Tissue-engineered skin substitutes: an overview. J Artif Organs 2013;16(4):397-403. 50. Hassan WU, Greiser U, Wang W. Role of adipose-derived stem cells in wound healing. Wound Repair Regen 2014;22(3):313-25. 51. Gauglitz GG, Jeschke MG. Combined gene and stem cell therapy for cutaneous wound healing. Mol Pharm 2011;8(5):1471-9. 52. Han SK, Yoon TH, Lee DG, Lee MA, Kim WK. Potential of human bone marrow stromal cells to accelerate wound healing in vitro. Ann Plast Surg 2005;55(4):414-9. 53. Tumbar T. Epithelial skin stem cells. Methods Enzymol 2006;419:73-99. 54. Zheng Y, Du X, Wang W, Boucher M, Parimoo S, Stenn K. Organogenesis from dissociated cells: generation of mature cycling hair follicles from skin-derived cells. J Invest Dermatol 2005;124(5):867-76. 55. Costa-Almeida R, Gomez-Lazaro M, Ramalho C, Granja PL, Soares R, Guerreiro SG. Fibroblastendothelial partners for vascularization strategies in tissue engineering. Tissue Eng Part A 2015;21(5-6):1055-65. 56. Costa-Almeida R, Granja PL, Soares R, Guerreiro SG. Cellular strategies to promote vascularisation in tissue engineering applications. Eur Cell Mater 2014;28:51-66. 57. Bhardwaj N, Chouhan D, Mandal BB. Tissue engineered skin and wound healing: current strategies and future directions. Curr Pharm Des 2017;23(24):3455-82. 58. Chua CK, Yeong WY, An J. Special issue: 3D printing for biomedical engineering. Materials (Basel) 2017;10(3). 59. Takagi R, Ishimaru J, Sugawara A, et al. Bioengineering a 3D integumentary organ system from iPS cells using an in vivo transplantation model. Sci Adv 2016;2(4):e1500887. 60. Blanpain C, Horsley V, Fuchs E. Epithelial stem cells: turning over new leaves. Cell 2007; 128(3):445-58. 61. Bhardwaj N, Kundu SC. Electrospinning: a fascinating fiber fabrication technique. Biotechnol Adv 2010;28(3):325-47.
5. Hirsch T, Rothoeft T, Teig N, et al. Regeneration of the entire human epidermis using transgenic stem cells. Nature 2017;551(7680):327-32. 6. Jockenho¨fer F, Gollnick H, Herberger K, et al. Aetiology, comorbidities and cofactors of chronic leg ulcers: retrospective evaluation of 1 000 patients from 10 specialised dermatological wound care centers in Germany. Int Wound J. 2016;13(5):821-8. 7. Sampson UK, Fowkes FG, McDermott MM, et al. Global and regional burden of death and disability from peripheral artery disease: 21 world regions, 1990 to 2010. Glob Heart 2014;9(1):145-158.e21. 8. Lei P, You H, Andreadis ST. Bioengineered skin substitutes. Methods Mol Biol 2013;1001: 267-78. 9. Papini R. Management of burn injuries of various depths. BMJ 2004;329(7458):158-60. 10. Dunkin CS, Pleat JM, Gillespie PH, Tyler MP, Roberts AH, McGrouther DA. Scarring occurs at a critical depth of skin injury: precise measurement in a graduated dermal scratch in human volunteers. Plast Reconstr Surg 2007;119(6):1722-32. 11. Stanton RA, Billmire DA. Skin resurfacing for the burned patient. Clin Plast Surg 2002; 29(1):29-51. 12. Haddad AG, Giatsidis G, Orgill DP, Halvorson EG. Skin substitutes and bioscaffolds: temporary and permanent coverage. Clin Plast Surg 2017;44(3):627-34. 13. Nyame TT, Chiang HA, Orgill DP. Clinical applications of skin substitutes. Surg Clin North Am 2014;94(4):839-50. 14. Metcalfe AD, Ferguson MW. Tissue engineering of replacement skin: the crossroads of biomaterials, wound healing, embryonic development, stem cells and regeneration. J R Soc Interface 2007;4(14):413-37. 15. Nicholas MN, Jeschke MG, Amini-Nik S. Methodologies in creating skin substitutes. Cell Mol Life Sci 2016;73(18):3453-72. 16. Nusgart M. HCPCS coding: an integral part of your reimbursement strategy. Adv Wound Care 2013;2(10):576-82. 17. Burke JF, Yannas IV, Quinby WC Jr, Bondoc CC, Jung WK. Successful use of a physiologically acceptable artificial skin in the treatment of extensive burn injury. Ann Surg 1981;194(4): 413-28. 18. Heimbach D, Luterman A, Burke J, et al. Artificial dermis for major burns. A multi-center randomized clinical trial. Ann Surg 1988;208(3):313-20. 19. Yannas IV, Burke JF. Design of an artificial skin. I. Basic design principles. J Biomed Mat Res 1980;14(1):65-81. 20. BlueShield of Northeastern New York. Protocol: Bioengineered Skin and Soft Tissue Substitutes. 2012. https://securews.bsneny.com/web/content/dam/BSNENY/Provider/Protocols/B/prov_ prot_701113.pdf. Last accessed September 28, 2018. 21. Driver VR, Lavery LA, Reyzelman AM, et al. A clinical trial of Integra Template for diabetic foot ulcer treatment. Wound Repair Regen 2015;23(6):891-900. 22. Heimbach DM, Warden GD, Luterman A, et al. Multicenter postapproval clinical trial of Integra dermal regeneration template for burn treatment. J Burn Care Rehabil 2003;24(1): 42-8. 23. Cooper ML, Hansbrough JF, Spielvogel RL, Cohen R, Bartel RL, Naughton G. In vivo optimization of a living dermal substitute employing cultured human fibroblasts on a biodegradable polyglycolic acid or polyglactin mesh. Biomater 1991;12(2):243-8. 24. Debels H, Hamdi M, Abberton K, Morrison W. Dermal matrices and bioengineered skin substitutes: a critical review of current options. Plast Reconstr Surg 2015;3(1):e284. 25. Hart CE, Loewen-Rodriguez A, Lessem J. Dermagraft: use in the treatment of chronic wounds. Adv Wound Care 2012;1(3):138-41. 26. Stark HJ, Willhauck MJ, Mirancea N, et al. Authentic fibroblast matrix in dermal equivalents normalises epidermal histogenesis and dermoepidermal junction in organotypic co-culture. Eur J Cell Biol 2004;83(11-12):631-45. 27. Marston WA, Hanft J, Norwood P, Pollak R. The efficacy and safety of Dermagraft in improving the healing of chronic diabetic foot ulcers: results of a prospective randomized trial. Diabetes Care 2003;26(6):1701-5. 28. Harding K, Sumner M, Cardinal M. A prospective, multicentre, randomised controlled study of human fibroblast-derived dermal substitute (Dermagraft) in patients with venous leg ulcers. Int Wound J 2013;10(2):132-7. 29. Pham C, Greenwood J, Cleland H, Woodruff P, Maddern G. Bioengineered skin substitutes for the management of burns: a systematic review. Burns 2007;33(8):946-57. 30. Hefton JM, Caldwell D, Biozes DG, Balin AK, Carter DM. Grafting of skin ulcers with cultured autologous epidermal cells. J Am Acad Dermatol 1986;14(3):399-405. 31. Bromberg BE, Song IC, Mohn MP. The use of pig skin as a temporary biological dressing. Plast Reconstr Surg 1965;36:80-90. 32. Lawin PB, Silverstein P, Still JM Jr. E-Z Derm a porcine heterograft material. Am J Clin Dermatol 2002;3(7):507. WWW.WOUNDCAREJOURNAL.COM
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Current Available Cellular and Tissue-Based Products for Treatment of Skin Defects Yukun Liu, MD; Adriana C. Panayi, MD; Lauren R. Bayer, PA-C; and Dennis P. Orgill, MD, PhD regeneration of viable tissue. Scaffolds can be natural, synthetic, or composite, as well as biodegradable or permanent. Growth factors, secreted by cells via signaling pathways, also play a crucial part in processes related to tissue regeneration and wound healing.2 Regenerative medicine replaces or regenerates human cells, tissues, or organs to restore or establish normal function.3 This broader approach has been particularly effective in the treatment of hematologic malignancies with the use of bone marrow transplants and does not necessarily rely on scaffolds. With the rapid development of tissue engineering and regenerative medicine, innovative strategies such as stem cellYbased therapy, gene therapy, nanomedicine, and three-dimensional bioprinting techniques are largely in preclinical testing, but also in some cases have been translated into human clinical use.4 Recently, for example, a patient with epidermolysis bullosa was treated with gene-edited skin, showing great promise for these techniques.5 Despite tissue engineering approaches being extensively applied in multiple fields such as skin substitution, organ replacement, tissue repair, and disease modulation, many problems still exist. Limitations for routine practice include the immunogenic rejection of allogeneic cells, concerns about malignancy, the challenges of harvesting adequate stem cells, the manufacturing costs, and the complexity of clinical studies needed for regulatory approval. Establishment of adequate vascular perfusion of the underlying tissue is important in effective use of these products as well as in wound healing, although peripheral arterial disease is a limiting factor. It has been reported that peripheral arterial disease is 10 times more prevalent in developed countries where these products are also more readily available.5Y7 A simple ankle-to-brachial systolic blood pressure index can be used to predict the likelihood of successful wound management with these products to avoid impaired healing or poor outcomes. This article focuses on selected cellular and tissue-based products (CTPs) that are available for sale in the US and used for diabetic foot ulcers (DFUs), venous leg ulcers (VLUs), and burns. The FDA approval levels to be discussed include 510(k); premarket approval (PMA); human cells, tissue, tissue-based products (HCT/ Ps); and humanitarian device exemption (HDE; Figure 1).
ABSTRACT Downloaded from http://journals.lww.com/aswcjournal by BhDMf5ePHKbH4TTImqenVLTWxlDBt+9A5zZyDMqnnNF2FON5AJgxtPEDStC3Pl4v on 01/17/2019
The occurrence of diabetic foot ulcers and venous leg ulcers is increasing because of aging population trends as well as increases in the number of people with diabetes and obesity. New technologies have been developed to treat these conditions, whereas other technologies previously designed for burns and traumatic wounds have been adapted. This article reviews the development of selected skin replacement technologies, particularly cellular and tissue-based products, highlighting their effectiveness on diabetic foot ulcers, venous leg ulcers, and burns. KEYWORDS: cellular and tissue-based products, diabetic foot ulcers, skin replacement, skin substitutes, tissue engineering, venous leg ulcers, wound healing ADV SKIN WOUND CARE 2019;32:19Y25.
INTRODUCTION Organ and tissue replacements are common goals of many surgical procedures. Autogenous tissues work well but are often in short supply and can leave scars or deform the donor site. Allogeneic tissues often result in immunologic rejection, whereas permanent biomaterials can lead to infection and capsular contracture (immune response to foreign materials). The field of tissue engineering (the use of a combination of cells, engineering materials, and suitable biochemical factors to improve or replace biologic functions1) was established in an attempt to reduce these complications. The term tissue engineering has also been used to define the integration of cells with acellular matrices or synthetic biomaterials. Cells provide both structural proteins and biochemical signaling molecules critical in tissue engineering constructs. Autologous, allogeneic, or xenogeneic tissues have all been used. The ability of stem cells to differentiate has made them a logical cell source, but their applicability is limited by availability, safety concerns, and regulatory hurdles. Scaffolds are materials that provide a three-dimensional structure for cells and blood vessels to populate, allowing growth and
At Brigham and Women’s Hospital in Boston, Massachusetts, Yukun Liu, MD, was a Research Fellow at the time this manuscript was written; Adriana C. Panayi, MD, is a Research Fellow; Lauren R. Bayer, PA-C, is Clinical Director of the Wound Care Center; and Dennis P. Orgill MD, PhD is Director of the Wound Care Center, Department of Surgery, Brigham and Women’s Hospital; and Professor of Surgery, Harvard Medical School. Acknowledgment: Dr Orgill is a consultant and/or receives research funding from Integra LifeSciences Corporation, the Musculoskeletal Research Foundation, Geistlich Corporation, Acell Corporation, and Professional Education and Research Incorporated. The authors have disclosed no other financial relationships related to this article. Submitted May 18, 2018; accepted June 29, 2018. WWW.WOUNDCAREJOURNAL.COM
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on volunteers with variable-depth surgical incisions and no comorbidities, Dunkin et al10 determined that skin injuries less than 0.57 mm do not result in scar formation. Interestingly, this value corresponds to the junction of the papillary and reticular dermis. In addition, the skin separates with deeper wounds because of loss of tension. Given that full-thickness wounds do not have direct access to the keratinocytes found in epidermal appendages, they must rely on keratinocyte migration from the wound edge for wound closure. Consequently, in large surface area wounds, autologous skin grafts or flaps are necessary for repair.11 The limited skin graft donor sites for large defects spawned the development of tissue engineering approaches that are now being applied to smaller defects. The ideal engineered skin replacements would provide a scaffold that closely mimics the structure and biologic function of native skin.8 Autologous or allogeneic cells have been combined in vitro with biologic or synthetic materials to generate tissue-engineered skin replacements. In addition, epidermal cell suspensions and cell sheets have been used, as well as semisynthetic and decellularized scaffolds. Previous research has summarized the essential properties for skin replacements:12Y14 1. nontoxic 2. nonantigenic 3. cost effective 4. easy to handle and apply 5. long shelf life 6. provide a barrier against contamination 7. result in minimal inflammatory reaction 8. improve wound healing 9. appropriate resistance to mechanical forces Unfortunately, there is currently no skin replacement technology that completely satisfies all of these criteria.
Figure 1. CLASSIFICATION BASED ON FDA APPROVAL
SKIN REPLACEMENT CONCEPTS Skin is the largest human organ and consists of three layers: the epidermis, dermis, and hypodermis (subcutaneous fat). The epidermis, which provides a barrier function, is populated with keratinocytes, melanocytes, and Langerhans cells. The dermis, which provides structural integrity, is composed of fibroblasts and the extracellular matrix (ECM), and contains important macromolecules including collagen, elastin, and glycosaminoglycans. Finally, the hypodermis, which protects the body from mechanical stresses and assists in thermoregulation, is composed of fat and connective tissues that provide a rich source of stem cells. Further, the skin confers UV radiation protection, is an important site for vitamin D metabolism, and provides visual signals critical for aesthetics.8 Damage to the skin that occurs in DFUs, VLUs, burns, and other skin conditions leads to wound formation. Wounds can be classified according to the depth of injury: epidermal wounds (superficial erosions), partial dermal wounds (partial-thickness wounds or shallow ulcers), and wounds spanning the entire dermis (full-thickness wounds or deep dermal ulcers).9 Superficial and partial-thickness dermal injuries, if treated properly, tend to heal without surgical intervention. Full-thickness wounds can also heal but result in the formation of scar tissue. In a study ADVANCES IN SKIN & WOUND CARE & VOL. 32 NO. 1
FROM CONCEPT TO CREATION The process of developing and approving a skin substitute follows a series of procedures. First, the concept of a new skin replacement is proposed and designed according to set criteria.15 This is followed by development and testing during preclinical studies, both in vitro and in vivo. The initial proposed product, as well as its components, needs to be tested for safety based on good laboratory practices. Animal testing is often used to test efficacy and clarify the mechanism of action. Next, optimal manufacturing requires optimizing the inventory, product storage, shipping, and shelf life. Further, products need to be approved by the FDA. When a product is FDA approved, it is assessed for reimbursement, a process by which the interests among individuals, insurance companies, and the developer are balanced. The Centers for Medicare & Medicaid 20
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Services produces the Healthcare Common Procedure Coding System codes, integral to reimbursement for medical devices (Table).16 Some products never reach mass production because of failure to receive reimbursement from third-party payers.
Figure 2. LOWER LEG VENOUS STASIS ULCER
Premarket Approval Premarket approval is required by the FDA when no similar product exists on the market or when a substantial change has been made to a preexisting product. The process requires adequate and well-controlled clinical studies in order for the product to be approved. Products and devices that go through the PMA process eventually receive approval from the FDA, and the approval serves as a patent for the company. A clinical case using a PMA-approved product is shown in Figure 2. Integra Dermal Regeneration Template (IDRT; Integra LifeSciences Corporation, Plainsboro, New Jersey). Developed by Burke and Yannas in 1980, the IDRT was first reported in a small clinical trial by Burke17 and later in a multicenter postapproval clinical trial.18 It was subsequently manufactured by Integra LifeSciences Corporation and approved by the FDA in 1996. The IDRT is an artificial bilayer material in which the lower layer is composed of a highly porous collagen and chondroitin-6sulfate copolymer that is covered with a semipermeable silicone elastomer that provides a moisture and bacterial barrier. The lower layer is optimized for pore size, degradation rate, and the percentage of glycosaminoglycan present to reduce wound contraction. The silicone layer is replaced by split-thickness skin graft after 2 to 3 weeks or for smaller wounds closed by epidermal migration from the wound margins.19 It is approved for the treatment of second- and third-degree burns and since 2002 for scar reconstruction.20 The effectiveness and safety of IDRT treating burns were evaluated in a multicenter postapproval clinical trial with 216 burn injury patients. These patients were treated with IDRT followed with a thin skin graft on the surface. The results showed Table.
HEALTHCARE COMMON PROCEDURE CODING SYSTEM FOR SKIN SUBSTITUTES Q4100 Q4101 Q4102 Q4104 Q4105 Q4106 Q4107 Q4108 Q4110 Q4116 Q4128
Skin substitute, not otherwise specified Apligraf, per square centimeter Oasis wound matrix, per square centimeter Integra bilayer matrix wound dressing, per square centimeter Integra dermal regeneration template or Integra Omnigraft dermal regeneration matrix, per square centimeter Dermagraft, per square centimeter GRAFTJACKET, per square centimeter Integra matrix, per square centimeter PriMatrix, per square centimeter AlloDerm, per square centimeter FlexHD, AllopatchHD, or MatrixHD, per square centimeter
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This is a 65-year-old woman with a left lower leg venous stasis ulcer. Debridement of the wound was performed first, and then Apligraf (Organogenesis) was applied to the wound twice with a month between applications.
a lower infection and higher uptake rate. These results highlight the use of IDRT as a safe and effective treatment for burn patients.21 A clinical case using the dermal matrix is shown in Figure 3. Currently, this product has been used for treating DFUs as an additional indication under the name Omnigraft Dermal Regeneration Matrix. A multicenter, randomized, controlled, parallelgroup clinical trial on 307 subjects with DFUs was conducted 21
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Figure 3. TREATMENT OF PG WITH DERMAL MATRIX
Above (left), patient developed PG after sternotomy. Preoperative view, final debridement. Above (center), after debridement. Above (right), Integra and Acticoat were placed on day 9 after debridement. Below (left), 4-week appearance after Integra placement. Silicone layer is starting to peel off. Below (center), 11 weeks after Integra placement. The wound is completely granulated. Below (right), 28 weeks after Integra implanting, the wound is nearly healed. Reprinted from Climov M, Bayer LR, Moscoso AV, Matsumine H, Orgill DP. The role of dermal matrices in treating inflammatory and diabetic wounds. Plast Reconstr Surg 2016;138 (3 Suppl):148S-57S.
treatment of life-threatening third-degree burns, especially when the donor site is not sufficient. These clinical studies investigated the effectiveness of IDRTrelated products; they indicated that it is safe and effective and demonstrates improved graft take properties. However, the risk of infection and scar formation is not negligible, as well as the need for a second operation that increases the length of hospital stay. In addition, the high cost of IDRT products limits widespread application.21,22 Dermagraft (Organogenesis, Canton, Massachusetts). Dermagraft is a unilayer cultured skin replacement (UCSR) that uses a provisional, tear-resistant, bioresorbable polyglactin mesh seeded with cultured fibroblasts that require cryopreservation. Over time, this mesh is replaced by ECM produced by the
under an Investigational Device Exemption. The experimental group (154 patients) was treated with IDRT, and the control group was treated with sodium chloride gel. The treatment lasted for at least 16 weeks and was followed up for 12 weeks. The results documented successful DFU closure during the treatment phase; these rates were significantly higher with IDRT treatment (51%) than with the control treatment (32%; P = .001) at week 16. There was complete DFU closure at 43 days in comparison to 78 days for patients treated with standard of care alone.22 The clinical trial laid the foundation for Omnigraft approval for the treatment of partial- and full-thickness neuropathic DFUs that are longer than 6 weeks in duration, with no capsule and tendon or bone exposed. The skin substitute must be used in conjunction with standard care. In addition, it is approved for the ADVANCES IN SKIN & WOUND CARE & VOL. 32 NO. 1
22
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replacement fibroblasts.23 Following application, the cells continue to secrete growth factors and ECM components until the mesh resorbs in about 3 to 4 weeks.24 Although initial success was reported in a prelinical experiment, it was not until 2001 that the product was approved by the FDA for the treatment of chronic wounds including DFUs.25,26 A randomized, controlled, multicenter study of 314 patients with a DFU was conducted in the US to evaluate complete wound closure using UCSR or regular treatment for 12 weeks. The results determined that 30% of UCSR patients healed versus 18.3% of control patients,27 demonstrating that UCSR is an effective treatment for chronic DFUs. The effectiveness of UCSR in treating VLUs has also been confirmed and approved for marketing in the US.25 In a prospective, multicenter, randomized, controlled study, 186 patients with VLUs were treated with UCSR plus compression therapy, and 180 patients were treated with compression therapy alone and followed up for 12 weeks. In ulcers with less than 12 months’ duration, 52% of patients in the UCSR group versus 37% of patients in the control group healed at 12 weeks. This was statistically significant (P = .029). This study suggested that the earlier use of UCSR as an adjuvant therapy would be beneficial to patients.28 Although there are no actual FDA-approved indications for UCSR on burn injuries, there are published studies.29 A multicenter clinical trial compared UCSR with cryopreserved human cadaver skin for temporary coverage on 66 patients with burn wounds. In this study, UCSR led to clinical improvement with no epidermal slough and less bleeding.30
grafting (4.5%), and hypertrophic scars (3.3%).34 Another retrospective medical record review of 164 burn patients in a pediatric burn center indicated that porcine xenograft can be used to provide useful wound coverage with pain relief and reduced need for dressing changes. Oasis Wound Matrix (Cook Biotech Inc, West Lafayette, Indiana). Oasis Wound Matrix is a xenogeneic collagen scaffold derived from porcine small intestinal mucosa. As a threedimensional collagenous ECM, it allows molecular adhesion, cell growth, and cytokine secretion.35 The natural ECM of this product provides a scaffold for tissue repair and wound healing. It has a long shelf life and can be stored at room temperature. In 2000, it was cleared by the FDA for the management of partial- and fullthickness wounds.20 At least one study has demonstrated its effect in DFUs.36 A prospective, randomized, controlled multicenter trial of 120 patients with VLUs treated by OASIS Wound Matrix combined with compression therapy demonstrated improved results compared with compression therapy alone.37
Human Cells, Tissues, and Cellular and Tissue-Based Products Although these products are considered part of human tissue banks, these products are not strictly regulated by the FDA. Manufacturers of HCT/Ps are, however, required to list their products with the FDA’s Center for Biologics Evaluation and Research as well as ensure they appropriately establish donor eligibility and follow good tissue practices and other procedures to prevent the introduction, transmission, and spread of communicable diseases. Allopatch (Musculoskeletal Transplant Foundation, Edison, New Jersey). AlloPatch is an aseptically processed human reticular acellular dermal matrix (HR-ADM) that contains cytokines and growth factors. Because it is derived from the deeper, reticular layer of dermis, it retains its inherent mechanical and biologic properties. With a more open and uniform structure, it facilitates vascular in-growth and cellular integration.38 Two advantages of HR-ADM are its readiness for use in wound care and its ability to be stored at room temperature.39 As banked human tissue, it has been approved by the FDA as an adjunct therapy in the treatment of chronic, uninfected, full-thickness DFUs.20 One prospective randomized controlled trial compared HR-ADM with standard wound care on nonhealing DFUs. At 12 weeks, the proportion of 20 DFUs treated with HR-ADM that healed was 80%, compared with 20% of DFUs that received standard care alone, a difference reported to be statistically significant.40 The study concluded that HR-ADM was both superior and more cost-effective than standard therapy.
510(k) Clearance A 510(k) is a premarket submission made to the FDA to demonstrate that a product to be marketed is at least as safe and effective, or “substantially equivalent,” to a legally marketed device. Substantial equivalence refers to similarity in construction, design, use, safety, effectiveness, and so on. Once the device or product is determined to be substantially equivalent, it can be marketed in the US. EZ Derm (Brennen Medical, Inc; St Paul, Minnesota). Because of its similarity to human skin, porcine skin has been used for wound coverage since 1960s.31 EZ Derm is a porcinederived xenograft temporary wound dressing. Previous studies have stated its properties include ready availability, easy handling, adherence to the wound surface, reduced pain, and prevention of water loss from wound.32,33 It has 510(k) clearance for the treatment of partial-thickness burns, venous ulcers, diabetic neurotrophic foot ulcers, and pressure injuries. A 4-year retrospective review study was conducted for 157 burn patients treated by EZ Derm, and researchers concluded that it is an effective and durable wound dressing with low rates of complications such as infection (3.0%), the need for additional excision and WWW.WOUNDCAREJOURNAL.COM
Humanitarian Device Exception In order to qualify for HDE approval, a product or device must aid in the treatment or cure of a disease or condition that 23
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difficult to transport. Allogeneic cell-based skin replacements are at risk of graft rejection and disease transmission.48 Biosynthetic and animal-based skin replacements can be applied only as temporary dressings, whereas xenogeneic matrices may result in immunogenic rejection. Further, infection and scar formation are usually unavoidable.49 Like allogeneic cell-based skin replacements, nonliving tissue skin replacements can, in some cases, result in disease transmission. The use of amniotic membrane substitutes, which preserve the native skin properties better than other skin replacement therapies, is limited to temporary wound dressings or in combination with other materials because of their antigenic potential, risk of spreading infection, and fast degradation rates.12 Future experiments should focus on enhancing the ability of CTPs to promote wound healing. Past research has established the role of stem cells in wound healing and laid the foundation for developing stem cells with tissue engineering.50,51 In recent years, researchers have focused on inducing stem cells to differentiate into specific types of cells, including keratinocytes and fibroblasts, and then incorporating them into biomaterial scaffolds.52 Hair follicles contain epithelial stem cells capable of forming skin tissue that may be used in wound healing in the near future.53,54 In terms of scaffolding, materials are still being optimized to create better-quality engineered skin. Vascularization is necessary for wound healing, and prevascularized skin grafts are being studied in order to develop blood vessel networks using cellular strategies or growth factor delivery systems.55,56 There is high level of interest in creating three-dimensional models that better imitate the properties and functions of mature skin. Advanced techniques, including three-dimensional bioprinting, have been used in the creation of the next generation of scaffolding models.57,58 The regeneration of skin components, including sweat glands and hair follicles, has been achieved in animal models but not yet in humans.59,60 Other innovative strategies include the combination of nanotechnology and regenerative medicine; gene therapy strategies are also currently in development.44,61 These strategies are not, however, completely understood. Overall, the need for further research and clinical trials is imperative before widespread clinical application of CTPs can occur.
affects a population of no more than 8,000 per year. The applicant must first obtain humanitarian use device designation from the FDA’s Office of Orphaned Products Development and then submit an HDE to the appropriate FDA premarket review center. Similar to premarket approval, the device or product cannot be comparable to a device that is already legally marketed for the same intended use. Further, HDE approval does not require demonstration of effectiveness. The company must not profit from the sale of the product or device. Epicel (Genzyme Biosurgery, Cambridge, Massachusetts). Cultured epithelial autografts (CEAs) have been a major conceptual development in the care of burn victims. Keratinocytes produce the skin barrier by going through a sequential maturation and senescence process that eventually results in a flexible, semipermeable membrane (stratum corneum). Many investigators have stressed that the reestablishment of the critical barrier structure is a fundamental goal in the treatment of patients with large surface area thermal injuries. This need has led to the development of numerous constructs.41 In 1975, Rheinwald and Green42 pioneered keratinocyte cell culturing. This was subsequently commercialized into Epicel, which can be derived from a small skin biopsy and expanded in a commercial facility over 2 to 3 weeks.43 As a permanent wound covering, it decreases the requirement for donor skin harvesting. Epicel is approved by the FDA under the HDE in the treatment of deep dermal or full-thickness burns, including a burn surface area of greater than 30%.20 It can be used alone or in combination with allogeneic or autologous split-thickness skin grafts, especially when there is a lack of donor site skin. A 5-year prospective controlled trial carried out in 1996 compared the use of cultured keratinocytes with conventional therapy on the treatment of massive burns. There was a significant reduction in mortality in the CEA group versus the control group.44 The results reported a beneficial effect of CEAs in the management of severe burn patients with a total surface burn area greater than 60%.45 However, the fragility, long cultivation time, and susceptibility to infection of autologous cells remain to be addressed.30 Most clinicians use CEAs in combination with allografts, where the epidermis is removed prior to grafting with CEAs. In addition, it has been used in the treatment of VLUs and corneal replacement.46 An earlier multicenter study was conducted on 30 patients evaluating the effectiveness of cryopreserved allogeneic cultured epithelium VLU patients. Results showed 66.6% of the patients healed completely within 12 weeks.47
&
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QUESTIONS AND FUTURE PROSPECTS Although promising, widespread use of CTPs is currently hindered by limitations. Skin replacements composed of living cells require a long cell culture period, have a short shelf life, and are ADVANCES IN SKIN & WOUND CARE & VOL. 32 NO. 1
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