Reduced Time to Skin Grafting in Chronic Wounds Using an Esterified Hyaluronic Acid Matrix and Negative Pressure Wound Therapy

Soft tissue wound healing and management of LEWs such as chronic ulcers has routinely comprised surgical, mechanical, or chemical debridement; prevention of primary infection; nutrition balance; and wet-to-moist dressing application.^1,2 The soft tissue wound healing process has 4 phases: hemostasis, inflammation, proliferative, and remodeling.² During the acute wound remodeling phase, the extracellular matrix within the granulation tissue increases in mechanical strength, usually beginning around day 3 and continuing until week 2.^2,3 Granulation tissue is considered to be completely formed when a continuous layer extends across the entire wound gap and the layer of granulation fills the entire wound depth.⁴

The use of biomaterials to create and modify the wound microenvironment and promote cell migration has become a powerful tool to stimulate wound healing. Several biomaterials have been designed to reduce cost; these use in situ tissue regeneration to promote increased cell migration, promote release of wound signaling molecules, and accelerate wound healing.⁵ In the past 2 decades, biological regenerative matrices have gained acceptance for the treatment of chronic wounds.^6,7 Derivatives of HA have been extensively studied, and several forms are now available (eg, cream, gel, scaffold, HA-embedded membrane).⁸ For example, HA-based creams and gel formulations have been shown to be effective in the treatment of inflammatory and joint diseases.⁹

Several HA wound products have been used since their introduction in the management of burn wounds, as well as for the treatment of partial- or full-thickness wounds.¹⁰ In particular, the benzyl ester form of HA (ie, eHAM) has been studied for its safety and efficacy in the management of chronic LEWs.^11-13 The dermal regenerative matrix wound product eHAM has been studied as a 3-dimensional scaffold for providing a temporary matrix and coverage of partial- or full-thickness wounds.^12,13 The tissue regeneration mechanisms of eHAM include enhancement of angiogenesis, regulation and organization of collagen deposition, promotion of cell migration, and scavenging of free radicals.^7,12,14

HA is a natural component of the skin; however, the half-life of HA in the skin is less than 1 day.¹⁵ Esterified HA can provide the necessary extracellular matrix with a prolonged half-life to facilitate wound healing.¹⁵ Upon application at the wound site, the eHAM reverts to HA following nonspecific de-esterification of the ester groups in eHAM. During this process, eHAM acts as a bioabsorbable scaffold to support cellular infiltration and vascularization. The esterification process results in a highly hydrophobic polymer that can be used to form a 3-dimensional matrix for cell growth and colonization of fibroblast.¹⁶ A silicone layer atop the HA matrix helps maintain moisture at the wound site; this layer is subsequently removed (usually around 21 days) following incorporation of the eHAM during the wound healing process.¹³ The silicone film also serves as a barrier, reducing vapor loss, reducing bacterial infection, and allowing for monitoring of the wound repair process during reconstruction of the dermal tissue.

NPWT devices used in conjunction with FTSG and STSG have been shown to be effective in the reconstruction of open tibiofibular fractures with exposed bone and tendon.^17,18 NPWT is also used for wound closure and limb salvage in patients with DFU.^19-21 Armstrong et al¹⁹ reported a 90% wound healing rate at an average of 8.1 weeks ± 5.5 standard deviation in 31 patients with DFU treated with surgical debridement followed by NPWT. A different study showed repeated surgical debridement and NPWT to be effective for lower limb salvage in 21 patients with exposed bone and tendon.²² In all 21 patients, the exposed tendons and bones were covered without the need for free flap transfer. In patients with comorbidities including diabetes, peripheral artery disease, and sepsis, lower extremity amputation was considered, but was avoided allowing for improved mobility and quality of life.²²

In a prospective randomized controlled trial published in 2006, treatment of chronic leg ulcers with a proprietary NPWT device (V.A.C. Therapy; 3M Health Care) was compared with conventional wound care.²³ Sixty patients were enrolled and randomized to receive either NPWT at 125 mm Hg (NPWT group) or compression therapy with commercially available wound dressings (control group). The median time to complete healing was 29 days for the NPWT group versus 45 days for the control group (P =.0001). The total wound care cost was 25% to 30% lower for the NPWT group (P =.005). The increased cost in the control group was due to higher personnel costs and longer hospitalization required for wound healing (median, 7 days for NPWT vs 17 days for control).²³ A more recent review reports that between 1999 and 2014 the average wound care cost per day for institutionalized NPWT use was $131.29, including dressing changes and labor costs.²⁴

Most clinical studies have reported staged surgical debridement of devitalized or necrotic tissue prior to or during staged reconstruction and application of eHAM. In a prospective case series, 12 patients with serious surgical wounds received eHAM treatment following extensive debridement, including removal of osteomyelitic bone and necrotic soft tissue (including tendons).²⁵ Those authors observed that the combination of debridement and application of eHAM resulted in enhanced wound bed granulation, with rapid and complete reepithelialization. Of the 12 patients, 9 (75%) received an STSG and 3 (25%) achieved healing by secondary intention. Ten patients (83%) required only 1 application of eHAM, 1 patient (8%) required 2 applications, and 1 patient (8%) required 4 applications. The average time to reepithelialization was 6 weeks for lesions that healed by secondary intention (n = 3) and 5.4 weeks for wounds that received STSG (n = 9). All lesions achieved complete healing within 5 to 8 weeks with no incidence of graft failure.²⁵

The current study is a retrospective case series evaluating the effect of NPWT and eHAM on soft tissue wound healing in 10 patients. The objective was to determine if NPWT with eHAM would result in decreased time to skin grafting and decreased time to wound closure compared with NPWT without eHAM. All patients were treated in an outpatient clinic setting.

A total of 10 patients ranging in age from 48 years to 81 years were evaluated (8 males, 2 females). Patients provided written consent for use of their images. All patients were treated in an outpatient clinic setting at the McLaren Bay Region Wound Care Center and Hyperbaric Medicine in Bay City, Michigan. All patients were treated for LEWs associated with various comorbidities, including insulin- and non-insulin-dependent diabetes, peripheral neuropathies, respiratory disorders, hypertension, obesity, coronary artery disease, and hyperlipidemia. Patients were selected based on similarity of wounds and NPWT treatment with or without eHAM. Patients received treatment from July 2017 through January 2020. All 10 patients in this study received NPWT. The follow-up period was 5 to 31 weeks. Patients underwent wound debridement and ultrasound prior to wound treatment. Noncontact, low-frequency ultrasound performed 3 times per week has been shown to significantly reduce wound size when compared with standard of care (debridement, offloading, and moist wound care).^26,27

A dermal regenerative template had previously been used for wound care without success in the study authors’ clinic. In the current study, the authors used an eHAM (Hyalomatrix; Medline Industries) that was applied to wounds following wide surgical debridement and wound bed preparation. The silicone layer of the eHAM, which provides a barrier that mimics the epidermis to achieve wound coverage, reduce bioburden, and avoid vapor loss,¹³ was removed prior to applying the NPWT sponge. NPWT was applied at −125 mm Hg pressure with continuous suction (V.A.C. Veraflo; 3M Health Care). The first dressing changes were done 3 to 4 days after surgery. For wounds with moderate exudate the dressings were changed 2 times per week, and for wounds with copious exudate the dressings were changed 3 times per week.

Five patients were treated with NPWT and eHAM (group 1), and 5 patients were treated with NPWT without eHAM (group 2). All patients received at least 1 autologous skin graft (STSG or FTSG) during the course of treatment. Grafts were applied in a surgical suite under local anesthesia. Skin grafts were covered with a layered bolster dressing comprising (from bottom to top) a silicone contact layer, polymeric membrane dressing, antimicrobial gauze, and/or self-adherent compression wrap that was secured with staples at the edges. For wounds that were not healing or improving, vascular status was determined at venous reflex or arterial Doppler ultrasound. Some patients required vascular surgical intervention to repair damaged blood vessels.

Wound measurements for determining area (cm²) and volume (cm³) were taken following wound debridement at the beginning of treatment and then every 1 to 2 weeks until the time of wound healing. Initial wound size was measured at the time of initial treatment for both groups. Wound area was also determined at the time of skin grafting for both groups. Photographs were taken at various time points to document wound status and healing. Wound area and volume were typically measured weekly. The change in area and change in volume at the time of skin grafting and wound closure were determined by subtracting the initial wound area or volume from each respective weekly measurement. The rate was calculated as the change divided by the number of weeks to wound closure. To calculate the rate of change in weeks to skin graft, the change was similarly calculated as change prior to skin graft divided by the number of weeks at skin graft. Wound closure was defined as the week of outpatient discharge or the time at which there was no measurable change in area or volume compared with the week prior.

The authors performed a statistical analysis comparing group 1 and group 2, taking into consideration the initial wound area. All data were imported into Stata 17 (StataCorp. 2021; Statistical Software: Release 17), and all analyses were conducted with 95% confidence. T tests with unequal variance were used to determine whether statistically significant differences existed between group 1 and group 2 in number of weeks to wound closure, rate of wound closure, number of weeks to skin graft, and rate of skin graft. However, owing to the small patient sample size and large variability in wound sizes, comparison of wound healing parameters including weeks to wound healing and weeks to STSG yielded no detectable significant difference between the 2 groups. Therefore, clinical results and differences are reported herein as observed.

Patient demographics and wound characteristics are listed in Table 1. Seven patients had type 2 diabetes, and 7 had exposed bone or tendon. Patient 1 had exposed bone and fixator hardware.

Representative images from patients in group 1 following NPWT and eHAM treatment and a representative graph showing percentage wound closure by week in 1 patient in group 1 are shown in Figures 1 and 2 (patient 1), Figure 3 (patient 4), and Figure 4 (patient 5). Patient 1 had a prior wound history and had previously undergone external fixation of the left tibia followed by NPWT to manage left trimalleolar fracture and fracture of the left tibia and fibula. NPWT was discontinued after 3 weeks owing to failure of wound closure and intraoperative edema. After an additional 2 weeks, the patient presented to the authors of the current study with a full-thickness, nonhealing surgical wound (Figure 1A). At the start of the second round of treatment, the patient underwent wide excisional debridement of the left lower extremity, 1 application of eHAM, and NPWT at −125 mm Hg of pressure.

A wound area of 86 cm² and wound volume of 112 cm³ remained visible at 3 weeks of treatment, with no signs of granulation (Figure 1B). The wound bed was prepared using noncontact ultrasound twice weekly. At 5 weeks after the start of the second round of treatment, a second eHAM with an area of 25 cm² was applied to the wound with an area of 80.8 cm², along with continuous NPWT (Figure 1C, D). Within 10 days, granulation tissue completely covered the wound site, including the fixator hardware (Figure 1E). FTSG was applied 12 days later, at 8 weeks (Figure 2). At week 13 of treatment, the wound area measured 10.3 cm² and the volume measured 2.1 cm³ (Figure 1F). This represented a percentage wound area closure and percentage wound volume closure from 1 to 13 weeks of 88% and 98%, respectively (Figure 2).

As noted previously, Figure 2 shows percentage wound closure (percentage area change and percentage volume change) following treatment with NPWT and eHAM in patient 1. Patients in group 1 received their first eHAM application at 1 week to 9 weeks (average, 3.2 weeks ± 1.9) and their second eHAM application at 3 to 13 weeks (average, 8.0 weeks ± 3.2). Patient 5 did not require a second eHAM application. Skin grafts were applied within 2 to 3 weeks (average, 2.6 weeks ± 0.5) following the second eHAM application. In group 1, there was no difference regarding the week of the final eHAM application and the week of skin grafting. However, clinical evidence from this study shows that eHAM can promote wound site granulation within 2 to 3 weeks, thus allowing for rapid skin grafting and subsequent wound closure.

Patient 4 presented with trauma to the right lower extremity owing to a fall that resulted in injury to the right femoral vein along the posterior thigh (Figure 3). The patient underwent emergency surgery with debridement and exploration owing to excess bleeding. The right femoral vein was transected, and vascular surgery was required to repair the vein. The wound was evaluated after 1 week of NPWT (Figure 3A). At 3 weeks, eHAM was applied (Figure 3B) which helped to level out the wound deficit and prepare the wound site for STSG. Good granulation of the wound site was evident at week 5, at which time STSG was applied (Figure 3C). Photographs showing progression of wound healing were obtained at week 7 (2 weeks after STSG) (Figure 3D) and week 11 (Figure 3E).

Patient 5 presented to the emergency department 3 days prior to the wound clinic with fever, swelling, erythema, and a necrotizing diabetic soft tissue infection of the right foot. At that time, the patient underwent wide excisional debridement and amputation of the right second toe and the distal metatarsal shaft. The resulting wound size following debridement and surgery was 9.0 cm (length) × 6.0 cm (width) × 2.5 cm (depth), with an area of 54.0 cm² and volume of 135 cm³. After 1 week of NPWT, the wound size had decreased to 8.4 cm × 5.7 cm × 1.8 cm, with an area of 47.9 cm² and volume of 86.2 cm³ (Figure 4A). NPWT was continued for another week, resulting in an 18% decrease in wound area and volume, to 39.5 cm² and 71.1 cm³, respectively. At week 2, eHAM was applied to the wound with continuous NPWT at the beginning of week 2 (Figure 4B). At week 5 during NPWT with eHAM (ie, after 1 week of NPWT without eHAM followed by 5 weeks of eHAM plus NPWT), the wound size decreased to an area of 32.0 cm² (a 19% decrease) and a volume of 6.4 cm³ (a 91% decrease) (Figure 4C). The wound site was suitable for STSG at week 5. At week 6 (1 week after STSG) and week 8 (3 weeks after STSG), good STSG take and wound healing were seen (Figure 4D, E).

The initial wound area following surgery and/or debridement for all 10 patients in this study ranged from 38 cm² to 305 cm² (Table 2). The average initial wound area for patients in group 1 (NPWT with eHAM) was twice that of patients in group 2 (NPWT without eHAM), at 132 cm² ± 69 and 64 cm² ± 17, respectively. Of note, 2 patients in group 1 (patients 3 and 4) had the largest initial wound area of any of the patients treated.

Four patients in group 1 received 2 eHAM applications during treatment, but patient 5 required only 1 eHAM application prior to skin grafting. Patients in group 2 did not receive eHAM. All patients in group 1 received skin grafts within 2 to 3 weeks (average, 2.6 weeks ± 0.5) after the second eHAM application. As shown in Table 2, patients in group 1 and group 2 had a similar average time to skin graft (9.6 weeks ± 3.9 and 9.6 weeks ± 4.7, respectively) despite the nearly twofold difference in the average initial wound area.

The average number of weeks to wound closure was similar, at 15.2 weeks ± 4.5 for group 1 and 14.6 weeks ± 7.9 for group 2. However, the average overall rate of area wound closure at discharge was 9.0 cm² ± 3.4 per week for group 1 and 6.8 cm² ± 4.1 per week for group 2 (Figure 5). The average number of weeks to skin grafting was 9.6 weeks ± 3.9 for group 1 and 9.6 weeks ± 4.7 for group 2, and the average rate of change in wound area per week prior to skin grafting was 4.5 cm² ± 1.7 for group 1 and 3.8 cm² ± 2.5 for group 2 (Figure 5).

The rate of change in wound volume per week prior to skin grafting was 25.9 cm³ ± 9.4 for group 1 and 4.1 cm³ ± 2.1 for group 2 (Figure 5). The overall rate of change in wound volume per week at discharge was 12.3 cm³ ± 3.5 for group 1 and 5.4 cm³ ± 4.2 for group 2 (Figure 5). One patient in group 2 (patient 8) had an extremely large wound depth of 7 cm and was excluded from the volume rate change analysis. The other 4 patients in group 2 were included in the volume rate analysis. As a result, the rate of volume change at skin graft and overall rate of volume change at discharge were greater for group 1. This larger change in wound volume in group 1 but not in group 2 suggests that eHAM has an effect on wound depth.

The current case series shows that eHAM and NPWT can be used in combination to prepare a wound site in 2 to 3 weeks for receiving skin grafting. In addition, improved wound granulation and reepithelialization was observed in patients treated with NPWT and 1 to 2 eHAM applications, allowing for improved skin grafting compared with patients treated with NPWT without eHAM. The average number of weeks to wound closure was similar between group 1 and group 2 (15.2 weeks ± 4.5 and 14.6 weeks ± 7.9, respectively) even though the initial wound area differed substantially (average of 132 cm² ± 69 and 64 cm² ± 17, respectively).

Despite the twofold difference in initial wound size, the rate of closure at skin grafting was improved from 3.8 cm² ± 2.5 per week (group 2) to 4.5 cm² ± 1.7 per week (group 1). In addition, the rate of area wound closure was improved from 6.8 cm² ± 4.1 per week (group 2) to 9.0 cm² ± 3.4 per week (group 1), which indicates that eHAM was working synergistically with NPWT in reducing the time to skin graft and wound closure. This study has clinical significance because it shows that skin grafts can be applied within 2 to 3 weeks (average, 2.6 weeks ± 0.5) following a second eHAM application.

A comparison of wound healing in similar DFUs in 2 patients who were not part of the current study is shown in Figure 6. Both patients’ DFUs are shown at 1 week of NPWT and following treatment at 18 weeks for 1 patient and 12 weeks for the other patient. Both patients required several selective debridements prior to treatment, and both received treatment with eHAM and NPWT throughout the course of treatment. However, the first patient (Figures 6A, B) did not receive an STSG, but the second patient (Figures 6C, D) did receive an STSG during the course of treatment (at 8 weeks). The patient treated with eHAM, NPWT, and STSG had improved wound healing compared with the patient who did not receive an STSG and was treated only with NPWT and eHAM.

Dermal regenerative matrices can achieve wound coverage by providing a local environment favorable to wound reepithelialization.²⁸ In the experience of the authors of the current study, eHAM is superior to other dermal regenerative matrices. Other case studies have reported on eHAM with NPWT and STSG.^11,25,29 One study reported on 15 patients with wounds of various etiologies, including 5 wounds with exposed bone and 5 with exposed tendon.²⁹ Three wounds closed by secondary intention with eHAM and NPWT without the need for STSG, while the remaining 12 wounds were ready for STSG at an average of 3 weeks after eHAM application. In a prospective case series, 12 patients received eHAM treatment following extensive debridement.²⁵ For 11 patients (92%), 1 to 2 eHAM applications were sufficient for wound bed preparation. For 9 patients, treatment included NPWT and eHAM for an average of 3 weeks prior to grafting. There were no incidents of graft failure in that study.

A different case series reported on 16 patients with venous leg ulcers (average area, 153 cm²) treated with eHAM alone without NPWT.¹³ Wound bed preparation with reepithelialization was achieved at an average of 21 days and autologous skin grafting was required in 12 patients. At 6- to 12-month follow-up, results were good in 12 patients, fair in 3, and poor in 1. In the current study, patients that received eHAM alone without NPWT were not evaluated.

In the authors’ experience, wound bed preparation and 1 to 2 applications of eHAM along with NPWT is a reliable approach for the treatment of chronic LEWs in patients with multiple medical comorbidities who may be at risk for limb loss. A study of a single case evaluated the combination of NPWT and eHAM for an 18-year-old patient with an exposed proximal phalanx of the right great toe who was facing amputation.¹¹ The wound size had decreased at 21 days, and nearly complete healing was achieved at 3 months.

The current study emphasizes the importance of eHAM with NPWT to hasten time to skin grafting, promote wound healing, and reduce the risk of limb amputation. In addition, eHAM and NPWT treatment were found to promote wound granulation and wound healing for patients with various comorbidities, chronic wound sizes, and wound etiologies. The current study shows that skin grafts can be applied within 2 to 3 weeks (average, 2.6 weeks ± 0.5) following a second eHAM application.

Two limitations of this case series include the small number of patients and the large difference in initial wound size between the treatment groups. There were also several differences in comorbidities; however, the findings suggest that the combination of eHAM and NPWT is effective for a wide range of wound etiologies resulting from various comorbidities.

Despite the twofold difference in initial wound area between treatment groups in this case series, the number of weeks to wound closure was similar; however, the overall rate of wound closure per week (area and volume) was better in patients who received NPWT with eHAM. In addition, although the number of weeks to skin grafting was similar for both groups, the overall rate of wound closure per week at skin grafting was better in group 1 in both area and volume. The improved wound site granulation for patients in group 1 enabled skin grafting within 2 to 3 weeks following the second eHAM application. The findings of the current study suggest that eHAM has a synergistic effect when used in combination with NPWT; in addition, this treatment was shown to be effective for patients with chronic wounds with exposed bone and tendon.