Citing the literature, enhanced sterility and ease of use, this author says human acellular dermal matrices are an effective option for wound care.
By Howard Kimmel, DPM
In today’s wound care market, the clinician has many choices of products. Both human acellular dermis and fibroblast-derived dermal substitutes require the patient to have adequate vascularity and be free of clinical signs of infection.
Fibroblast-derived dermal substitutes have become very popular over the past few years. Even though these products have a high level of evidence to show that they work, they have some disadvantages and limitations. For instance, one can apply fibroblast-derived dermal substitutes on ulcers that extend into the dermis but not through it. Also, in patients who have a Charcot deformity with a midfoot ulcer, fibroblast-derived dermal substitutes have not been tested. If there are any sinus tracts present, one cannot use a dermal substitute. Fibroblast-derived dermal substitutes are also contraindicated for patients who have sensitivity to bovine products while such patients can use human acellular dermis.
In spite of good wound care by means such as offloading, debridement, control of infection and maintaining a moist wound environment, there are instances in which exposed musculoskeletal structures prohibit the use of fibroblast-derived dermal substitutes.
There is also a limitation to when one can apply fibroblast-derived dermal substitutes. Depending on the product, the FDA requires that the wound be present for four to six weeks for one to use fibroblast-derived dermal substitutes.1 Lavery and colleagues published a study showing that wounds open greater than 30 days have a 4.7 greater risk of infection.2
In contrast, there is no limitation as to when one can apply human acellular dermis.
Key Insights On The Advantages Of Human Acellular Dermis
Human acellular dermis has been safely in use for over 20 years. The initial indication for the product was for burns. Physicians have not only used the technology in diabetic foot ulcers and venous leg ulcers but have also used it in plastic and reconstructive surgery, as tendon reinforcement, and in abdominal wall reconstruction. Human acellular dermis has shown promise in graft integration, host cell infiltration and revascularization of the acellular dermis. Depending on the Medicare local coverage determination, one application of human acellular dermis can occur in the office.
Human acelluar demis is harvested from heavily screened donors. The tissue processing is in accordance with the American Association of Tissue Banks under FDA requirements. The current guidelines published in 2000 deal with implementing a program of “Current Good Tissue Practice.”3 Specifically, section 1271.230b states that “sterility should be based on a validated process.”
The Association for the Advancement of Medical Instrumentation, a standards-setting organization for the medical industry, defines the sterility assurance level (SAL) as the probability of an item being non-sterile after it has been exposed to a validated sterilization process to achieve a SAL of 10-6, meaning that there is less than a 1 in 1,000,000 possibility of a contaminating organism surviving the treatment.4 The process of sterilization differentiates the human allograft products. It is important to look for products that use the highest level of sterilization. Products that are aseptically processed do not achieve this level of sterility.
Graft Applications And Healing: What The Research Reveals
There is level 2 evidence on both fibroblast-derived dermal substitutes and human acellular dermis. There are a total of seven studies published on fibroblast-derived dermal substitutes. Marston and coworkers published a study that was based on a multicenter randomized controlled trial, which enrolled a total of 245 patients.5 The study compared a fibroblast-derived dermal substitute to a control of wet-to-dry dressings along with proper wound treatment with a primary endpoint of 12 weeks. In this trial, the results show an increased incidence of complete ulcer healing of 30 percent in the fibroblast-derived dermal substitutes versus 18.3 percent in the control group. The authors noted a faster time to closure for the fibroblast-derived dermal substitute. This study did not list the average number of grafts needed for closure but the study authors stated that researchers used up to eight grafts.
Veves and colleagues looked at a bilayered, fibroblast-derived dermal substitute.6 This trial enrolled a total of 208 randomized patients in a multicenter study. The results showed a significant benefit for bilayered, fibroblast-derived dermal substitutes in complete ulcer healing at 12 weeks: 56 percent versus 38 percent for the control group and a median time to closure of 65 days versus 90 days for control. The authors noted one could use up to five grafts per patient but they used an average of 3.9 grafts per patient.
Iorio and coworkers did a systemic review of human acellular dermal matrices utlilizing both Medline and the Cocharane Database.7 They found a total of five papers published with a total of 299 patients enrolled in studies. A total of three papers had either level 1 or 2 evidence.
In 2004, Brigido and coworkers performed a single center prospective study on 40 patients with full thickness wounds.8 These patients were randomized to receive either human acellular dermal matrix or sharp debridement and wound gel. The endpoint was evaluation of wound reduction at four weeks. In the human acellular dermal matrix group, there was a 73.1 percent wound reduction in comparison to 25 percent in the control group.
In their next study, Brigido and colleagues performed a randomized prospective single center study on patients with a total of 28 full-thickness diabetic ulcers that had a duration of longer than six weeks without any epidermal coverage.9 The randomization was the same as the authors’ previous study. There was offloading for plantar ulcers in both groups. The wound gel group had weekly dressing changes while the human acellular dermal group only had one application and interval dressing changes. The results at 16 weeks demonstrated complete wound healing in 86 percent of the human acellular dermal group and 29 percent in the control group.
Reyzelman and coworkers published the most significant paper on acellular dermal regenerative tissue matrix in 2009.10 The authors conducted a prospective, randomized, controlled multicenter trial over a 12-week period on a total of 86 patients. All had sharp debridement and offloading when needed. Forty-one patients randomized to the human acellular dermal matrix group completed the trial with 70 percent progressing to complete healing at an average of approximately six weeks. There were 37 patients in the control group with 46 percent progressing to complete healing at an average of seven weeks. The odds ratio for the patients to heal was 2.7 times higher than the control group. In all three studies, researchers used only one application of human acellular dermis.
In my opinion, both products have their role in wound care. There is evidence to show that these products work. It comes down to the number of applications, cost of the product, the strength of the evidence and ease of use. In this case, human acellular dermal matrix has the advantage.
Dr. Kimmel is a Diplomate of the American Board of Podiatric Surgery. He is the Director of Residency Training at the Department of Veterans Affairs in Cleveland, Ohio. Dr. Kimmel is the Senior Clinical Instructor in the Department of Surgery at Case Western Reserve University School of Medicine in Cleveland.
1. Available at www.apligraf.com .
2. Lavery LA, Armstrong DG, Wunderlich RP, et al. Risk factors for foot infections in individuals with diabetes. Diabetes Care 2006;29(6):1288-1293.
3. FDA docket No. 97-484P. Available at http://www.fda.gov/ohrms/dockets/dailys/01/May01/050901/97n_484p-c000024... .
4. Association for the Advancement of Medical Instrumentation. Sterilization of health care products – general requirements for characterization of a sterilizing agent and the development, validation, and routine control of a sterilization process for medical devices. Standard 14937. 2000. Available at http://marketplace.aami.org/eseries/scriptcontent/docs/Preview Files/14937preview.pdf .
5. Marston WA, Hanft J, Norwood P, Pollak R, Dermagraft Diabetic Foot Ulcer Study Group. 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.
6. Veves A, Falanga V, Armstrong DG, Sabolinski ML, Apligraf Diabetic Foot Ulcer Study. Graftskin, a human skin equivalent, is effective in the management of noninfected neuropathic diabetic foot ulcers: a prospective randomized multicenter clinical trial. Diabetes Care. 2001;24(2):290-5.
7. Iorio ML, Shuck J, Attinger CE. Wound healing in the upper and lower extremities: a systematic review on the use of acellular dermal matrices. Plast Reconstr Surg. 2012; 130(5):232S–241S.
8. Brigido SA, Boc SF, Lopez RC. Effective management of major lower extremity wounds using an acellular regenerative tissue matrix: a pilot study. Orthopedics 2004; 27(Suppl 1):s145–49.
9. Brigido SA. The use of an acellular dermal regenerative tissue matrix in the treatment of lower extremity wounds: a prospective 16-week pilot study. Int Wound J 2006; 3(3):181–7.
10. Reyzelman A, Crews RT, Moore JC, et al. Clinical effectiveness of an acellular dermal regenerative tissue matrix compared to standard wound management in healing diabetic foot ulcers: a prospective, randomised, multicentre study. Int Wound J. 2009;6(3):196-208.
This author says the role that fibroblasts play in facilitating the healing of chronic wounds is well established whereas questions abound for acellular dermal matrices, which lack high-quality supporting evidence.
By Alexander Reyzelman, DPM
The field of bioengineered tissue has significantly expanded during the last decade. In addition to living skin substitutes, we now have access to many acellular dermal matrices. It is becoming more and more important to have a better understanding of the role these wound healing modalities play in our treatment armamentarium.
The success of fibroblast-derived dermal substitutes is based on the premise that there are living dermal fibroblasts seeded on to a scaffold, which one then applies to the wound. These living dermal fibroblasts are able to secrete growth factors, deposit matrix proteins and facilitate epithelial cell migration.
There are multiple reasons for the failure of the wound healing process but in order to understand how fibroblast-derived dermal substitutes may help, it is important to understand the role that fibroblasts play in the non-healed wound.
Several studies have shown that fibroblasts taken from chronic ulcers demonstrate low proliferative capacity and what is referred to as senescence. It is postulated that the ulcer environment is responsible for the senescence.1
Studies performed on venous ulcer fibroblasts demonstrated that growth factors released from the fibroblasts could stimulate proliferation.1 It stands to reason that providing young/live allogeneic human cells to the chronic wound can improve the healing potential of the chronic wound. These cells are then able to secrete growth factors that are necessary to stimulate wound repair. Researchers have demonstrated that these cells stay within the wound environment for up to six months.2
The importance of growth factors in wound healing has been well established. The number of growth factors and their receptors in chronic ulcers is known to decrease. Experiments have shown that acute wound fluid that is full of various growth factors stimulates proliferation and wound fluid from chronic wounds inhibits proliferation.3,4
Therefore, the number of growth factors found in chronic wounds is less than that found in the acute wounds. The addition of any one single growth factor has not been effective in vivo except for platelet-derived growth factor beta (PDGF-beta).5
However, fibroblast-derived dermal substitutes have multiple growth factors, which allow a greater likelihood of aiding in the induction of angiogenesis, enhancing the formation of granulation tissue, stimulating epithelialization and modulating the inflammatory response.
Inflammation has been implicated as another important factor in the maintenance of the chronic wound. Chronic wounds are typically heavily colonized and have an intense inflammatory infiltrate. Fibroblast-derived dermal substitutes have inflammatory cytokines interleukin-6 (IL-6), interleukin-8 (IL-8) and granulocyte colony-stimulating factor (G-CSF). These cytokines in appropriate concentrations have the potential to modulate the inflammatory process within the chronic wound site.
A Few Considerations About Acellular Dermal Matrices
Acellular dermal matrices are biologically active materials that mimic the skin’s natural dermal extracellular matrix by providing growth factors that stimulate host cell proliferation and serve as a scaffold for their migration during wound healing. Acellular dermal matrices are manufactured by purifying human cadaveric or animal skin to remove all cells that could potentially initiate immune rejection of the graft material or serve as vehicles for disease transmission. All xenogeneic acellular dermal matrices that are currently on the market are of either bovine or porcine origin. This is probably due to the lower costs and wider commercial availability. It is important to note that neither the cows nor pigs are considered to be immunologically similar to humans.
Purification techniques have a significant influence on the properties of each acellular dermal matrix and vary depending on the product. Some contain basement membranes and some do not. I have found that some people in the industry believe that acellular dermal matrices with a preserved basement membrane demonstrate better adherence, outgrowth and differentiation of keratinocytes due to the presence of laminin and collagen type IV, which are absent in acellular dermal matrices that undergo more aggressive sterilization.
Another variable affecting the success of acellular dermal matrices is the crosslinking. Chemical crosslinking is a technique employed in the manufacturing of acellular dermal matrices that improves the matrix’s stability and longevity at the wound site. Crosslinking lowers the chances of immune rejection by the host tissue. However, recent research indicates that crosslinking may also result in disruption of the wound healing process by inducing foreign body response and production of toxic degradation products that have a detrimental effect on host cell survival and proliferation.6,7
The above paragraphs demonstrate the effect that fibroblast-derived dermal substitutes have on a chronic wound. However, to a wound care practitioner, successful clinical outcomes are much more important. We learn to practice evidence-based medicine when treating our patients. Based on the level of evidence pyramid, randomized controlled trials are considered to be the best level of evidence.
At this time, when one compares the level of high quality clinical evidence between acellular dermal matrices and fibroblast-derived dermal substitutes, the pendulum swings to the fibroblast-derived dermal substitutes.
There are only three wound care products that have received premarket approval for diabetic foot ulcerations and two of these are skin substitutes. There are many acellular dermal matrices on the market and unfortunately high quality clinical trial data in chronic lower extremity wounds does not yet exist for the majority of the acellular dermal matrices.
Dr. Reyzelman is an Associate Professor in the Department of Medicine at California School of Podiatric Medicine at Samuel Merritt University in Oakland, Calif. He is the Co-Director of the University of California, San Francisco Center for Limb Preservation.
1. Stanley AC, Park, HY, Phillips TJ, Russakovsky V, Menzonian JO. Reduced growth of dermal fibroblasts from chronic venous ulcers can be stimulated with growth factors. J Vasc Surg 1997; 26(6):994-1001.
2. Mansbridge J, Liu K, Pinney E, et al. Growth factors secreted by fibroblasts: a role in healing diabetic foot ulcers. Diabetes Obes Metab 1999; 1(5):265-79.
3. Chen WY, Rogers AA, Lydon MJ. Characterization of biological properties of wound fluid collected during early stages of wound healing. J Invest Dermatol 1992; 99(5):559-64.
4. Falanga VF, Grinnel B, Gilchrest Y, Maddox T, Moshelle A. Experimental approaches to chronic wounds. Wound Repair Regen 1995; 3(2):132-40.
5. Data on file, Regranex, Healthpoint Biotherapeutics.
6. Van der Veen VC, van der Wal MB, van Leeuwen MC, Ulrich MM, Middelkoop E. Biological background of dermal substitutes. Burns. 2010; 36(3):305-321.
7. De Vries HJ, Mekkes JR, Middelkoop E, Hinrichs WL, Wildevuur CR, Westerhof W. Dermal substitutes for full-thickness wounds in a one-stage grafting model. Wound Repair Regen. 1993; 1(4):244-252.