Abstract: Venous ulceration, a relative common manifestation of chronic venous insufficiency and venous hypertension, is often difficult to treat. Successful treatment begins with the management of the underlying pathology and wound bed preparation. This article reports the authors’ experience with a novel wound dressing produced from microbial cellulose synthesized by an acid-producing bacterium, Acetobacter xylinium. Twenty-four patients with chronic venous insufficiency and lower-leg ulceration were treated with either biocellulose wound dressing (BWD) plus a two-layer compression bandage or standard care. Standard care consisted of a nonadherent primary wound dressing plus a two-layer compression bandage. Evaluations were performed weekly to measure wound pain, nonviable tissue reduction, degree of wound granulation, and wound healing (reduction in wound size and surface area). BWD was significantly more effective than standard care for autolytic debridement (reduction in the amount of nonviable tissue [p=0.0094]). The mean number of days to >75-percent granulation was 43 days for the BWD treated group and 71 for the standard care group. Mean percent reduction in wound area was also greater for the BWD treated group at Week 6 (39% vs. 19%) and at Week 12 (74% vs. 49%). When compared to patients treated with standard care, the group treated with BWD reported less wound pain at each evaluation point. Significant differences in wound pain scores between the two treatments were noted at Week 3, 6 (p=0.039), and 8 (p=0.043).

Disclosures: This study was supported by a research grant from Xylos Corporation, Langhorne, Pennsylvania. The sponsors of the study had no role in study protocol preparation, study design, and data collection. Dr. Alvarez is a member of the Xylos Speakers Bureau. This data has not been reported previously.

Introduction

Normally, calf muscle contraction promotes venous return by squeezing blood in deep veins; this pressure is prevented from reaching the superficial circulatory system by one-way valves within the perforating veins. In some individuals, however, venous pressure builds up in the superficial veins and is transmitted to the capillaries of the skin.[1] Many patients develop venous incompetence subsequent to thrombophilia (a clotting disorder causing recurrent thrombosis), which often damages valves.[2] Several hypotheses have been advanced to explain how venous insufficiency leads to ulceration. The fibrin-cuff hypothesis proposes that distension of capillary beds from increased venous pressure causes fibrinogen extravasation through endothelial gap junctions, resulting in a pericapillary cuff that acts as a diffusion barrier to oxygen and other nutrients in the blood contributing to ulceration.[3] The white cell entrapment (sticky leukocyte) hypothesis proposes that leukocytes trapped in the diseased circulation by reduced shear stress become activated on the endothelial surface. These leukocytes release inflammatory mediators, leading to inflammatory tissue destruction, or blockage of small capillaries causing localized ischemia.[4] The “trap” hypothesis proposes that fibrinogen and other blood-borne materials leak into the dermis from the vasculature where they trap growth factors and prevent them from reaching the epidermis, resulting in ulceration and abnormal wound healing.[5]

Therapies for venous ulcers. Therapies for venous ulcers are directed at lowering venous hypertension, increasing fibrinolytic activity in the wound, and enhancing tissue vascularization/oxygenation from the blood.[6] Compression, a long-time standard treatment for venous ulcers, pushes leaked fluid back into circulation. Inelastic and elastic compression provided by the modified Unna’s boot provides a rigid structure for the calf muscle to press against during ambulation, improving the muscle’s pumping action and aiding venous return.[7] Proper compression will also prevent further leakage of fibrinogen.[8] Although compression of 20–40mmHg seems sufficient to improve central venous insufficiency and improve the healing process, how much compression is optimal is not known. Two-layer bandage systems (2LB) generally provide between 20–30mmHg counter compression above the ankle, while four-layer bandage systems (4LB) provide greater compression (30–40mmHg).[9,10] Over a 12-week period, consistent treatment with 4LB results in a greater proportion of healed ulcers when compared to 2LB.9 However, over a 24-week period, the incidence of healing was not statistically different between 2LB and 4LB.[10] Compression stockings, if properly fitted, could provide 20–40mmHg above the ankle and have been shown to be beneficial to ulcer healing when compared to dressings alone.[11]

Skin grafts, human skin equivalents, and dressings. Skin grafts may heal ulcers by serving both as tissue replacements and as pharmacologic delivery systems.[12] However, autologous split-thickness grafting techniques require a donor site, are not reliably vascularized, and may slough off and become necrotic[13] if the venous hypertension (localized tissue ischemia) is not adequately controlled. In a large, multicenter, clinical study, the human skin equivalent (Apligraf®, Organogenesis Inc., Canton, Massachusetts) was shown to be significantly more effective than standard care for chronic venous ulcer healing.[14] Occlusive dressings maintain wound moisture and modify the wound environment. Occlusion also provides autolytic debridement, accelerates epithelization, and reduces wound pain.[15]

The chronic (nonhealing) venous ulcer. Although there are a number of alternatives for the management of uncomplicated venous ulcers, progress in the treatment for the complicated chronic venous wound has been disappointing. The key to encouraging chronic venous ulcers to heal more quickly is the rapid correction of venous insufficiency/venous hypertension together with adequate preparation of the wound bed. In general, the healing process in a chronic wound is hindered if the underlying pathology is not addressed along with local barriers to repair.[16–18] Understanding and removing the barriers to healing will help to produce a wound bed with healthy granulation tissue that is ready for the next phase of the healing process.[18,19]

Preparing the venous ulcer wound for healing. It is believed that the principal barriers to healing a chronic wound are nonviable tissue, bacterial burden, proteolytic imbalance, and altered composition/amount of wound fluid (exudates).

Biocellulose wound dressing for wound bed preparation. The majority of clinical studies to evaluate venous ulcer treatments have been designed to measure endpoints linked with wound closure. Normally, proportion of wounds healed in unit time or healing rates (decrease in wound surface area) are the primary endpoints of these clinical trials. The authors’ goal was to concentrate on endpoints associated with the preparation of the chronic venous ulcer wound bed. Therefore, this study was designed to measure the dressings’ effect on autolytic debridement (natural removal of nonviable tissue), time to complete granulation, exudate (type and volume), and local wound pain (as a measure of inflammation). Wound healing (rate and incidence of wound closure) was a secondary endpoint for this trial.

Materials and Methods

Primary dressings. Biocellulose wound dressing (BWD; XCell®, Xylos Corporation, Langhorne, Pennsylvania) is a biosynthetic matrix that is hydrophilic and has excellent tensile strength. BWD is unique in that it has the ability to either donate or remove (absorb) moisture (Figure 1). It is synthesized by Acetobacter xylinum and processed into a matrix material that is biocompatible, pyrogen free, and nontoxic. The dressing is provided sterile in sealed foil pouches and available in four sizes (3x3, 5.5x8, 6x7, 8.5x0.75 inches). Application and appearance of BWD in venous ulcer treatment are shown in Figure 2. BWD was provided by the study sponsor, Xylos Corporation, Langhorne, Pennsylvania (lot number NB031902) for the purpose of clinical evaluation.

Figure 1

Absorption donation profiles of several wound dressings.

Figures 2A–C

Figure 2. A) Photograph of BWD prior to application; B) within one week, BWD forms a blister roof-like seal over the ulcer; C) venous ulcer immediately after the removal of BWD. Note the exposed edges and the migrating epithelium along the wound margins.

The primary dressing used as the control was a nonadherent petrolatum emulsion impregnated cellulose acetate gauze (Adaptic®, Johnson & Johnson, Inc., Fort Worth, Texas). It is sterile and packaged in a plastic pouch.

Sustained compression therapy. A modified Unna’s boot was used to treat the venous insufficiency in all of the patients. The modified Unna’s boot consists of inelastic and elastic compression. The inelastic component of the compression bandage is the Unna’s paste boot (Viscopaste® Boot, Smith & Nephew Inc., Largo, Florida) and the elastic component is a cohesive elastic bandage (Coban®, 3M Inc., Minneapolis, Minnesota). The modified Unna’s boot provides between 20 and 35mmHg compression above the ankle depending on leg circumference. The modified Unna’s boot is accepted as standard care in the treatment of lower leg ulcers secondary to chronic venous insufficiency.[20]

All study supplies were purchased by the sponsor from Suburban Ostomy/Invacare, Holliston, Massachusetts.

Study design. The study was a prospective, parallel-group, comparative, open trial. Eligible patients between the ages of 18 and 90 were randomly assigned to receive either BWD plus a modified Unna’s boot or standard care consisting of a nonadherent wound dressing plus a modified Unna’s boot (Control). The patients were followed for 12 weeks or until healing for analysis of efficacy endpoints prospectively set at one-week intervals. Healing was defined as a wound that had fully (100%) re-epithelized with the absence of drainage and not needing a dressing.

Screening. To enroll the patient, the target ulcer had to be secondary to chronic venous insufficiency (having the signs of venous disease). Minimum ulcer duration was set at two months with no upper limit. The wound, in the opinion of the investigator, had to require debridement (more than 50% of the surface area covered with nonviable tissue fibrin). Appropriate vascular studies (ankle to brachial index [ABI] of >0.75 or a normal pulse volume recording [PVR]) were obtained in order to exclude peripheral arterial occlusive disease. Exclusion criteria were as follows: clinical signs of infection, cellulitis, osteomyelitis, inadequate nutrition, uncontrolled diabetes, and other clinically significant conditions that would impair wound healing inclusive of renal, hepatic, hematologic, neurologic, or immunological disease. Patients receiving corticosteroids, immunosuppressive agents, radiation, or chemotherapy within one month prior to entry into the study were also excluded. If the patient had more than one venous ulcer that satisfied the criteria for enrollment, the ulcer of longest duration was designated the target ulcer. If two or more ulcers were present for the same period of time, the ulcer with the largest surface area became the target ulcer. Patients were entered into the study after an institutional review-board informed consent was obtained. Patients were assigned treatment according to a computer-generated randomization schedule.

This report summarizes the data obtained from one clinical center as part of an ongoing multi-center trial.

Patient population. Twenty-four patients were randomized and received treatment. Patient demographics and wound characteristics of the two treatment groups are presented in Table 1. There were 12 evaluable patients in each treatment group. Ten out of the 12 patients (83.3%) assigned to BWD completed the study without protocol violations. Two patients missed two or more clinic visits for evaluation but completed the 12-week period. In the Control group, all patients completed the study, but there were five patients with protocol violations (missed visits [3], infection [1], stasis dermatitis [1]).

Table 1

Treatment protocol and follow up. Wound cleansing was performed with normal saline without the use of forceful irrigation. Surgical, mechanical, enzymatic, or chemical debridement was not allowed at any point throughout the study, and topical wound treatments were not allowed. Manufacturer suggestions for dressing application were followed in accordance to the package inserts whenever possible. Treatment with the test agents was performed at the initial (baseline) visit and once weekly until healing or 12 weeks. If the patient was unable to come to the clinic every week, a visiting nurse was provided to change the dressing and apply the compression bandages at home.

Study evaluations. All evaluations were performed at the same outpatient clinical center by the same investigator or study coordinator. Patients were evaluated prior to the initial treatment (baseline visit, day 0) and once weekly thereafter immediately after wound cleansing. At each evaluation, the nonviable tissue type was described as follows: fibrin slough, eschar (solid crust covering the ulcer), or a combination of fibrin and eschar. Nonviable tissue amount covering the ulcer was clinically estimated using the following scale: 5=none, 4=<25 percent, 3=25–49 percent, 2=50–74 percent, and 1=75–100 percent. The amount of granulation tissue was also graded clinically using a five-point scoring scale (5=100% complete granulation, 4=>75%, 3=50–74%, 2=25–49%, and 1=<25%). Local wound pain was evaluated using a clinically validated visual graded categorical analog scale from 0 (no pain) to 10 (extreme pain). Wound size was determined by measurement (maximal length and width) as well as by computerized planimetry of wound tracings. Other clinical assessments included wound exudates, wound odor, signs of infection, interstitial (lower leg) edema, and adverse events.

Statistical analysis. Data analysis was performed using Statistical Analysis System software (SAS Institute Inc., Cary, North Carolina). Fisher’s exact test was computed to compare autolytic debridement, exudate amount, and wound pain between treatment groups. A survival analysis was performed to compare the amount of nonviable tissue, time to granulation, and time to 50 percent re-epithelization between treatments using the Kaplan Meier method and the log rank chi-square test. Due to heavy censoring (missing data points), it was not possible to compare survival curves when the outcome of interest was 100-percent (complete) granulation or healing. Therefore, time to 75-percent granulation and time to 50-percent re-epithelization were compared between treatment groups. The Mann-Whitney U test was employed to compare nonparametric data, such as wound measurements and other clinical assessment parameters.

Results

Patient demographics (gender and age) were similar between the BWD and Control treatment groups. No significant differences were found between the two groups with respect to baseline ulcer size and amount of nonviable tissue. However, mean wound duration (history of nonhealing) was nearly two times greater (1.857) in the BWD treatment arm (p<0.05). Treatment with both primary dressings was easy and convenient. The application of either BWD or control dressings was not associated with any pain or discomfort.

Autolytic debridement was significantly (p=0.0094) greater in the BWD treatment group (Table 2). Ninety-two percent (11/12) of the patients treated with BWD had greater than 75-percent reduction in nonviable tissue (fibrin) compared to 33-percent (4/12) in the Control group. Wound pain was studied by comparing the categorical analog scores from individual patients in each group.

Tables 2 and 3

The effect of BWD on wound pain is summarized in Figure 3. At each evaluation point (Weeks 1–12), when compared with Control, a greater proportion of patients treated with BWD reported no pain (score of 0) or mild pain (score of 1–3). Differences were statistically significant at Weeks 3, 6 (p=0.0391), and 8 (p=0.043).

Figure 3

Effect of BWD on wound pain*. *p=0.031 at Weeks 3 and 6; p=0.043 at Week 8.

The mean percent reduction in wound size for the two treatment groups is presented in Table 3. Although wounds treated with BWD had a greater reduction in wound area than wounds treated with Control, the differences were not statistically significant.

The mean number of days to reach >75-percent healthy granulation was 43 days for the BWD treatment group compared to 71 days for the standard care group. However, this difference was not statistically significant (c2 [1] = 0.592, p=0.442). Survival analysis (Kaplan Meier and log rank chi-square) was also performed to compare the time to 50-percent re-epithelization in each treatment arm. The time to 50-percent re-epithelization was 57 days for the group treated with BWD and 85 days for Control. As was the case with the other survival analysis (time to granulation), time to attaining 50-percent reduction in wound size did not differ significantly (c2 [1] = 2.120,
p=0.141). Kaplan Meier plots for time to >75-percent granulation and 50-percent re-epithelization are presented in Figure 4.

Figures 4A and B

Figure 4. Kaplan Meier plot for granulation (A) and reepithelization (B). CTR = standard care control; XCL = biocellulose wound dressing; o = censored observations

There were no marked differences noted between the two treatment groups in several secondary endpoints evaluated (leg edema, wound exudates, wound odor, maceration, pain upon dressing removal or wound re-injury), and thus, the data is not presented. Representative photographs of venous ulcers treated with BWD are shown in Figure 5.

Figure 5

Representative photographs of a venous ulcer treated with BWD.

Discussion

Successful standard care for patients with chronic venous ulcers combines local wound care to cleanse, protect, and facilitate healing and ambulatory hemodynamic support to control the venous hypertension and insufficiency.[21] It has been documented[1,8,9,15,21] that the occlusive, moist, hypoxic environment created by the combination of dressings and compression bandages assists to dissolve necrotic debris painlessly (autolytic debridement). In addition, such occlusive environments improve the development of healthy granulation tissue and accelerate re-epithelization.[22] It is also known that once the fibrin has dissolved and healthy granulation tissue fills the venous ulcer bed, healing progresses in a slow but consistent manner.[23] With the exception of human skin equivalent (cell therapy [Apligraf]), there has been little development to improve the treatment of these difficult wounds.[14]

This study was undertaken to evaluate a new primary dressing designed to assist in chronic wound bed preparation. Therefore, the trial was designed to have autolytic debridement and time to granulation as its primary outcome measures.

The authors found that BWD creates a protective, hypoxic, moist environment similar to an undisturbed wound protected by its own blister roof. Because this dressing can donate or absorb moisture, it conforms to wounded and intact skin differently. The perimeter of BWD (in contact with intact skin) desiccates forming a thin cellophane-like sheet that adheres to the stratum corneum without re-injury, while the center of the dressing (in contact with the wound) remains moist but insulated from the exterior environment (Figure 2B and C).

The authors’ findings show that treatment with BWD plus compression consisting of inelastic and elastic bandages (modified Unna’s boot) provided more effective dissolution of nonviable fibrin when compared to standard care (nonadherent primary dressing plus a modified Unna’s boot). It is likely that the improved fibrinolysis is the result of the occlusive environment formed by BWD. Previous studies have shown that wounds covered with occlusive dressings have greater macrophage activity,[24] improved fibrinolysis,[25] greater angiogenesis,[26] and accelerated epidermal resurfacing[27] than wounds allowed to dry. It appears that the degree of occlusiveness may be important, since the environment under a modified Unna’s boot is already quite hypoxic and moist, yet applying BWD accelerated autolysis. Hydrocolloid dressings under compression bandages have also been found to provide an environment that favors removal of fibrin and necrotic tissue.[28] It is hypothesized by the authors that the hydrocolloid-induced autolytic debridement arises from the combination of the slightly acidic environment, improved inflammatory cell infiltration, and the proteolytic milieu created by the wound fluid. Further studies are needed to test how the blister roof enclosure created by BWD modifies the wound bed and wound fluid.

This study also demonstrated that the combination of BWD with 2LB compression significantly reduced venous ulcer pain. Prior reports have already suggested the usefulness of occlusive dressings to reduce wound pain.[29] To the authors’ knowledge, this is the first report of venous ulcer pain reduction by a primary wound dressing utilizing a clinically validated categorical analog pain scale. The reduction in local wound pain observed is probably due to the insulating properties of BWD providing a seal and protecting the wound with its synthetic blister roof. Such a seal protects the sensitive nerve endings while preventing major shifts in wound temperature. It is important to note that patients treated with the control regimen also noted a reduction in wound pain after compression therapy was initiated. Pain relief in the control group was lasting provided that compression therapy continued. Therefore, pain relief with BWD was additional and complimentary to the pain relief associated to compression alone.

Time to >75-percent granulation and time to 50-percent re-epithelization were shorter in the BWD group than in the control group. Although the differences were not statistically significant, it should be pointed out that the mean duration of the ulcers (history of nonhealing) in the BWD-treated group was nearly double (13 months vs. 7 months) compared to Control. In randomized trials of venous ulcer healing, wound duration was a significant indicator of wound chronicity and nonhealing.[14,30] Small sample sizes also accounted for the lack of statistical proof of difference. It will be interesting to see if greater power (larger sampling) resulting from the pooled data of the multicenter study provides additional ulcer healing support.

The balance to either deliver or absorb moisture by BWD can be influenced by the secondary dressing used. Depending on the moisture vapor transmission rate (MVTR) of the secondary dressing, the balance of moisture can be shifted to absorb or deliver. For example, if a polyurethane film dressing is used as a secondary dressing, the BWD will serve to deliver moisture. Conversely, if gauze or another absorbent material is used as a secondary dressing, BWD will absorb moisture. In this study, the authors used a combination of impregnated gauze (Unna’s paste bandage) as the secondary dressing. The MVTR of Unna’s paste bandage is somewhere in the middle between a polyurethane film and gauze. Depending on the exudative characteristics of the wound, the proper secondary dressing should be selected so that a blister-like appearance over the wound is achieved.

Standard venous ulcer treatment generally consists of a dressing over the wound and compression provided with either 2LB or a 4LB. In most cases, after five to six days, the patients will complain of malodor emitting from the boot. The authors inform patients that this is commonplace and is to be expected until the wound cleanses itself (fibrin replaced with granulation tissue). All of the patients in this study were considered to have chronic venous ulcers (ulcer duration >2 months) and, therefore, had experienced the effect of compression bandages previously.

At times, the authors noticed a characteristic odor (somewhat like wet cardboard) with the use of BWD. The odor was more prevalent with heavily exudating wounds during the early stages of use (Weeks 1–4). The odor is mild and not offensive. Although the exact cause of this odor is unknown, it may be caused by anaerobic bacteria (cultures not performed) from the wound adherent to BWD. The odor disappears when the dressing is removed. Unlike the odor experienced with hydrocolloid dressings, this odor is not due to the breakdown of the dressing (cellulose can only be broken down by certain cellulases that are only found in ruminant digestion). Patients in both groups complained about odor equally (most complaints were during initial treatment with resolution after 4 weeks).

In studies with a relatively small patient population, strong scientific conclusions cannot be made with confidence. However, small controlled clinical trials, such as this one, can provide meaningful outcomes to assist clinicians in decision-making. In summary, this study has demonstrated BWD’s effectiveness in the treatment of chronic venous ulcers. Significant improvements over standard care were noted in autolytic debridement (fibrinolysis) and pain reduction. Shorter times to granulation and re-epithelialization were also noted but did not differ statistically due to the small sample size.

Acknowledgment

The authors contracted Ingenix Inc., Salt Lake City, Utah, to monitor the study and perform data analysis. The authors would like to thank Stephanie Majors (study monitor) and Andre DeChamplain, PhD, (statistician) for their
assistance.