Introduction. Chronic wounds are physically debilitating and painful and are responsible for the addition of more than $25 billion annually in health care costs in the United States. Extracellular matrix (ECM) replacements have been demonstrated to aid in wound healing by providing an optimal environment to facilitate the healing process. Objective. This study examines the healing rates of stage 4 pressure ulcers using combination of a commercially available porcine-based wound matrix dressing alongside negative pressure wound therapy (NPWT) versus using NPWT alone. Materials and Methods. Patients were randomized to receive either the matrix plus NPWT (study) or NPWT alone (control) for stage 4 sacral pressure ulcer treatment. Wounds were photographed and measured weekly. The experimental group had their ECM dressings changed every other week and their NPWT changed twice weekly. Results. A total of 16 patients, 8 study and 8 control, completed this study. After the 12-week study period, the average control patient healing rate was 45.79% as compared with the 89.98% healing rate in the study group (P < .01). The difference in healing rate between control and study patients was optimal by 12 weeks. Conclusions. These studies suggest that ECM dressings may be a promising adjunctive treatment option for stage 4 pressure ulcers.

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Wound healing is a sophisticated, interactive process during which tissue repairs itself.^1,2 The wound healing process occurs through a series of 4 stages: hemostasis, inflammation, proliferation, and remolding. Through this process, the interaction between inflammatory mediators, local cells, and the extracellular matrix (ECM) actively contributes to the aforementioned stages of healing.³ Chronic wounds are defined as wounds that fail to heal within a period of 3 months.¹ These nonhealing wounds represent a significant health care issue affecting more than 1% of the western population.⁴ Chronic wounds also impose an enormous financial burden on the health care system, resulting in costs of more than $25 billion annually in the United States alone.¹ 

According to the National Pressure Ulcer Advisory Panel (NPUAP), “a pressure injury/ulcer is localized damage to the skin and underlying soft tissue usually over a bony prominence or related to a medical or other device.”^5,6 Pressure ulcers present first as unbroken skin and then frequently progress to an open ulcer that may be painful. The wound develops due to a combination of pressure and shear stress. Soft tissue may exhibit different tolerance to pressure and shear due to variance in tissue perfusion, microclimate, nutritional status of the patients, comorbidities, and the condition of the tissue.⁴

Ulcers classified as chronic wounds are thought to be stuck in the inflammatory phase of wound healing. This current concept suggests that a local increase in the level of proteases, such as matrix metallopeptidases, in the wound bed leads to a stalled wound healing process. The hypoxic microenvironment breaks down important growth factors and thus prevents the wound from continuing to the next phase of repair (proliferative phase) to form granulation tissue and a new provisional matrix for remodeling and healing.⁷

Collagen is the most abundant protein in the human body, and it is a fundamental component in the ECM.⁸ It is also an obligatory protein in all stages of the wound healing cascade. Fibroblasts secrete collagen in the proliferative phase to direct keratinocyte migration to areas of the injured epidermis. A collagen-rich dressing induces localized production and assembly of collagen.⁹ Furthermore, it helps create an ideal environment for wound healing through recruiting repair cells such as fibroblasts and macrophages. In addition, this type of dressing is convenient to apply and remove and provides an absorptive, moist environment to promote healing. Oasis Ultra (small intestinal submucosa extracellular matrix [SIS-ECM]; Smith & Nephew, Fort Worth, TX) is a porcine-based, triple-layered ECM wound wrap that contains different types of glycosaminoglycans such as heparan sulfate, hyaluronic acid, and chondroitin sulfate.¹⁰ In addition, it contains adhesion molecules such as fibronectin and laminin along with various growth factors such as transforming growth factor, basic fibroblast growth factor, and vascular endothelial growth factor (VEGF).³ Collagen-rich biomaterial is often synthesized from avian, bovine, and porcine collagen.

The SIS-ECM is made from porcine small intestinal submucosa. This product has been previously reported to produce a dressing that inactivates the tissue metalloproteases, thereby preventing destruction of the provisional ECM.⁷ Its composition stimulates cell migration, reduces inflammation, and provides moisture to the wound bed; SIS-ECM also grants structural support and enhances cellular proliferation and attachments. The SIS-ECM has been employed for a variety of wounds including chronic vascular, venous, and diabetic ulcers; partial-thickness burns; donor sites and skin graft preparation; and partial- and full-thickness, surgical, and traumatic wounds.⁷

Closed suction drainage systems are used to enable mass transport of fluid from the body as an adjunct to surgical procedures. For instance, a chest tube using this system can evacuate air from the pleural cavity. Moreover, closed suction is also used to drain stomach contents, which facilitates small intestinal obstruction treatment. High suction can even remove tissue from the body, similar to liposuction. In 1997, Morykwas et al¹¹ faced a significant number of complicated wounds and tried to come up with a better approach to treatment. Their first idea was to develop a way to apply suction on the wound to pull the wound edges together. Based on this idea, they designed several prototypes that expedited wound healing.¹¹ The prototype that has had significant success in treating wounds contains an open pore polyethylene foam positioned in the wound, shielded by a semi-adhesive dressing, and linked by tube to a suction source. They named this technique negative pressure wound therapy (NPWT). An alternative description that more precisely defines the physics of the method is microdeformational wound therapy. This device by Morykwas et al¹¹ has changed the course of treatment for many patients with complex wounds even to this day and has become the standard of care used to heal complex wounds in the United States.¹² According to Orgill and Bayer,⁹ NPWT’s mechanisms of action are divided into primary and secondary effects that affect the process of wound healing. 

The primary effects of NPWT include tissue macrodeformation, in which the wound edges are pulled together by the open pore foam; however, that effect depends on the mobility of the tissue surrounding the wound. Furthermore, microscopic deformation at the wound surface stretches the cells and enhances cell proliferation and division.¹³ In addition, NPWT has the ability to eliminate large amounts of extracellular fluid and affords an isolated moist environment for the wound to heal. The secondary effect includes promoting granulation tissue via upregulation of the hypoxia-inducible factor 1-alpha-VEGF pathway through the microdeformation effect, which promotes localized hypoxia close to the wound surface.⁹ Negative pressure wound therapy also modulates inflammation, induces cellular proliferation, and changes the bacterial levels in the wound. It is indicated for various types of wounds, including acute, subacute, chronic, traumatic, or dehisced wounds; NPWT also is indicated for partial-thickness burns; ulcers, including diabetic, pressure, or venous insufficiency; and flaps and grafts. Negative pressure wound therapy is contraindicated in malignancy (since proliferation is induced by NPWT and may enhance malignant growth), untreated osteomyelitis, nonenteric and unexplored fistulas, necrotic tissue with eschar, and sensitivity to silver (GranuFoam Silver [KCI, an Acelity Company, San Antonio, TX] dressing only).⁹

The present study tested the hypothesis that combining SIS-ECM with NPWT would increase wound healing over NPWT alone in chronic pressure ulcers; the authors suggest that this combination could have added benefit in the population of patients with difficult-to-treat stage 4 pressure ulcers.  

Experimental design
This 12-week study was a prospective, multicentered, randomized, controlled, single-blinded clinical trial permitted by the Ethics Committee of the Copernicus Independent Review Board from August 2014 to June 2016. Written, informed consent was attained from all patients. The treating physician discussed and answered patient and caregiver concerns before obtaining consent. Wound fluid samples were obtained from 16 patients with stage 4 pressure ulcers (14 sacral, 1 gluteal, and 1 ischial; Table). Patients were divided randomly in 2 groups of 8 each: a control group that received NPWT (V.A.C. Therapy; KCI, an Acelity Company) alone or a study group with NPWT plus SIS-ECM. The primary endpoint of the study was the healing percentage of wound surface at the beginning and end of the study period.

Patient selection
Potential candidates were evaluated by the study principal investigator for inclusion and exclusion criteria. The majority of the participants were enrolled at the Wound Center at Sycamore Medical Center (Miamisburg, OH); the remaining patients were enrolled at other participating sites (LifeCare Hospital, LTAC at Sycamore Hospital, Miamisburg, OH).

Patients who met inclusion criteria for this study were adults between the ages of 18 to 89 years who exhibited stage 3 or 4 pelvis pressure ulcers with no signs of infection, a hemoglobin A_1C (HbA_1C) < 8 (if the patient had diabetes), and with adequate nutrition, indicated by an albumin level ≥ 2.0 g/dL and a prealbumin level ≥ 12.5 mg/dL. Exclusion criteria for this study included wounds that cannot have a NPWT device properly applied due to location (eg, too close to anus and no colostomy), diarrhea, or periwound skin issues; patients with infected wounds; patients with an HbA_1C > 8 or uncontrolled diabetes; patients with malnourishment, immunodeficiency, or an immunocompromised state; patients who have a religious or ethical aversion or any allergy to porcine products; and patients who indicated do not resuscitate and/or do not intubate. In addition, patients who were at high risk of bleeding were excluded, including patients who have weakened or friable blood vessels or organs in or around the wound as result of, but not limited to, suturing of the blood vessel (native anastomoses or grafts) and organ; patients without adequate wound hemostasis; patients who have been administered anticoagulants or platelet aggregation inhibitors; and patients who do not have adequate tissue coverage over vascular structures.

Patient medical records were examined for all inclusion and exclusion criteria. Laboratory results for albumin and prealbumin up to 30 days prior to enrollment and HbA_1C results up to 100 days prior to enrollment were considered for eligibility.

Treatment protocol 
The control group had NPWT changed twice weekly, and the wound bed was covered with ADAPTIC Non-Adhering Silicone Dressing (KCI, an Acelity Company) before applying the black foam of the NPWT device. The study group received the matrix that was changed every other week. In addition, the nonadherent dressing was applied over the matrix and below the black foam. Negative pressure wound therapy was set at -125 mm Hg and continuous fashion. Pressure reduction beds and repositioning methods were employed throughout the study as part of patient standard of care.

Patient wounds were photographed and measured using a paper ruler weekly. The SIS-ECM dressings were changed every other week. 

At about weeks 4, 8, and 12, wound specimen canisters from the NPWT devices of both groups were collected and taken to the laboratory at Wright State University (WSU) Department of Pharmacology and Toxicology (Dayton, OH) for analysis of the drained fluids from all wounds. Specimen canisters were secured in biohazard bags and transported to WSU by a member of the study team within 24 hours of collection. 

To maintain blinding for the assessment laboratory personnel, specimen canisters and stored specimens were identified by a coded label. 

Statistical analyses
Analyses were performed using Graph Pad Prism 7 (GraphPad Software, Inc, La Jolla, CA), Excel 2016 (Microsoft Corporation, Redmond, WA), and SPSS version 13 (SPSS Inc, Chicago, IL) software. Statistical comparisons were expressed as mean ± standard error of the mean for continuous variables of experiments conducted at least 3 times, where n is the patient. The differences between the groups were done by multiple comparisons and analyzed by either analysis of variance (ANOVA), paired t test, or nonpaired t test. In all cases, P ≤ .05 was considered statistically significant. 

During the study period (August 2014–June 2016), the total number of patients screened for inclusion/exclusion criteria was 94 patients. Of this, 39 patients met requirements and were consented, 19 were withdrawn from the study for reasons determined by the primary investigator (significant wound infections, worsening of diabetes, etc), and 16 participants finished the study successfully (Table). 

Effect of SIS-ECM on the study group’s healing percentage
Healing rate was studied over a 12-week period with wound measurements recorded every week. Control wounds that received NPWT only showed an increase in healing rate at the beginning of the study with a peak at 8 weeks, after which the healing rate declined for the remainder of the study period (Figure 1). However, the healing rate of the wounds receiving SIS-ECM in addition to NPWT showed a steady increase over time until the end of the study period (Figure 1). 

The difference in healing between the 2 groups was analyzed by 1-way ANOVA. The differences between the mean percentages ± standard deviation (SD) of control (45.8% ± 38.7%) versus SIS-ECM-treated (90.0% ± 9.5%) wounds was found to be significant at P < .01 at 12 weeks. Using these results, a box and whisker plot was created to show the average of overall healing percentage after 12 weeks in both groups (Figure 2). 

The average healing percentage in the 2 groups at 4, 8, and 12 weeks was compared using 1-way ANOVA. There was no significant difference in the healing percentage between the 2 groups at 4 weeks (P = .09), and at 8 weeks, the control had a higher rate of healing (P = .03). However, at 12 weeks, there was a significant difference between the 2 groups (P < .01), with the study group having a higher healing rate than the control. Figure 1 shows that in week 12, the wounds treated with SIS-ECM continued to show increased healing, while the wounds treated with NPWT alone peaked in healing at week 8 and then declined. These findings suggest SIS-ECM may be superior to NPWT alone in facilitating the progression of wound healing.  

The differences in healing percentage between the 4- and 12-week time points in the study group were calculated by performing 1-way ANOVA; the difference was significant (P < .05; Figure 3). In contrast, the difference in healing percentage between the same 2 time points in the control group was not significant. Figure 4 and Figure 5 depict 2 examples of clinical wound healing associated with the combination of SIS-ECM and NPWT.

Wound healing is a dynamic process that involves a system of complex coordination among a variety of resident cells within a suitable extracellular environment.¹⁰ The wound healing process is initiated by tightly coordinated, interactive, and overlapping time-dependent stages. These stages include the hemostatic, inflammatory, proliferative, and remodeling phases, wherein resident cells, inflammatory mediators, and the ECM actively participate in each phase of healing.^3,14

The main objective of this project was to determine if wound healing of chronic pressure ulcers could be enhanced by the addition of a specific type of wound dressing as an ECM replacement, the SIS-ECM, in conjunction with NPWT as compared with NPWT alone as the standard of care. The results clearly show SIS-ECM did, in fact, significantly enhance wound healing in this clinical setting, as measured by healing rate. 

It is of interest to note that the positive effects of SIS-ECM were delayed in comparison with standard therapy. It is unclear the exact mechanism(s) by which SIS-ECM is exerting its positive effects. The SIS-ECM has been reported to exert a mechanism similar to other collagen wound wraps: it is a stimulator of cell migration and induces the proliferation of cells in the ECM, mainly fibroblasts that produce collagen^12-14 and facilitate wound healing. Extracellular matrix dressings such as SIS-ECM also provide a scaffold for these cells and proteins to adhere to, which can further facilitate the healing process.^12,15 It also has been shown that chronic wounds are deficient in ECM,¹² which may explain the advantage of use of the SIS-ECM dressing over NPWT alone in treating these wounds because NPWT dressings do not contain collagen or other ECM proteins. It is possible that the delayed effect associated with the SIS-ECM and NPWT combination is due to the natural lag that occurs in the body when responding to chemotactic factors by deploying cytokines, inducing cellular proliferation, and creating and secreting ECM products. In other words, the body is mounting a natural wound-healing response that needs time to take effect. Promotion of angiogenesis, trapping autologous growth factors and reducing metalloproteases in the wound are all other potential effects of the matrix.

The limitations of this study include the relatively small sample size that was able to finish the study. Also, the population of patients who experience chronic stage 4 pressure ulcers are usually very debilitated and have multiple other comorbidities affecting healing rates. 

Although the findings in this pilot study show significant improvement in wound healing with the use of SIS-ECM as adjunctive therapy to NPWT, the authors propose that a larger study would provide more definitive findings. Moreover, the exact mechanism of action of this combination therapy for chronic pressure ulcers should be a future area of investigation.

This study is the first to compare the use of SIS-ECM in combination with NPWT versus NPWT alone for chronic stage 4 pressure ulcers. The data suggest SIS-ECM could be a valuable adjunct to standard therapy for chronic pressure ulcers. Given that this type of ulcer is notoriously difficult to treat and not all patients are good candidates for flap closure, the present study can provide rationale for use of this combination for recalcitrant chronic pressure ulcers. 

Authors: Walid Mari, MD, MS; Sara Younes, MD, MS; Jaree Naqvi, BA; Abdelfatah Abu Issa, MD, MS; Terry L. Oroszi, EdD; David R Cool, PhD; Jeffrey B. Travers, MD, PhD; and Richard Simman, MD, FACS, FACCWS

Affiliation: Department of Pharmacology and Toxicology, Boonshoft School of Medicine, Wright State University, Dayton, OH

Correspondence: Richard Simman, MD, FACS, FACCWS, Plastic and Reconstructive Surgery, Clinical Professor, ProMedica Toledo Hospital, Jobst Vascular Institute, 2109 Hughes Drive, Suite 400, Toledo, OH 43606; richard.simmanmd@promedica.org

Disclosure: This study was sponsored by an unrestricted educational grant from Smith & Nephew (Fort Worth, TX). The authors disclose no financial or other conflicts of interest.