Efficacy of a Nanofabricated Electrospun Wound Matrix in Treating Full-thickness Cutaneous Wounds in a Porcine Model

Objective. This study aims to evaluate the comparative performance of a resorbable nanofiber wound matrix (Restrata Wound Matrix; Acera Surgical Inc, St Louis, MO) and a bilayered collagen xenograft (Integra Bilayer Matrix Wound Dressing; Integra, Plainsboro, NJ) in healing critical full-thickness cutaneous wounds in a preclinical porcine model. Materials and Methods. Full-thickness cutaneous wounds were created in Yucatan miniature swine and treated with either the nanofiber wound matrix or xenograft. Wound area was measured and inflammation and healing were assessed until euthanasia at day 15 or 30, at which time tissue samples were harvested for histopathology. Results. Wounds treated with the nanofiber wound matrix demonstrated significantly faster wound areal reduction, less inflammation, greater neovascularization, more collagen maturation, and superior quality of healing compared with wounds treated with the xenograft. Conclusions. The nanofiber wound matrix is an effective wound healing material that may offer a unique alternative in the treatment of challenging refractory wounds.

Cutaneous wounds resulting from disease or trauma place a major burden on the health care system. A significant need exists for new technologies capable of treating these wounds, specifically those refractory to existing therapies. Clinical solutions include the use of wound matrices, which ideally provide a barrier for protection and prevention of dehydration while promoting wound healing.^1-3 However, current solutions present significant limitations. Autografts are limited in availability and create donor site morbidity, while allograft and xenografts are associated with risks of disease transmission, excessive inflammatory reaction, and transplant rejection. 

Synthetic materials are therefore of particular interest given their ability to minimize risks presented by biologic matrices while promoting complete healing.⁴ Recently, a novel, fully synthetic, nanofabricated wound matrix was developed for the local management of critical cutaneous wounds (Restrata Wound Matrix; Acera Surgical Inc., St Louis, MO). This electrospun nanofiber wound matrix is a conformable, nonfriable, nonwoven, resorbable scaffold composed of 2 synthetic polymers: polygalactin 910 poly (lactic-co-glycolic acid; PLGA; 10:90) and polydioxanone, materials that are biocompatible and commonly found in existing medical products (eg, resorbable sutures). These resorbable polymers are processed utilizing a novel electrospinning technique to create a matrix of nanoscale fibers that are similar in structure and architecture to a native extracellular matrix.² The diameter of the electrospun fibers were specifically engineered within a range that has been shown to support important cellular activity, including cell migration, retention, and proliferation.^5-7 The nanofabricated wound matrix has high porosity that is positioned to fall within the range shown to permit critical biologic activities, including tissue ingrowth and neovascularization.^7-9 In addition, the resorption rate of the nanofiber wound matrix is tailored to match the rate of new tissue formation and provide a stable and persistent scaffold capable of supporting wound healing prior to complete dissolution via hydrolysis.^10,11 The nanofabricated matrix also provides excellent handling properties suitable for withstanding clinical manipulation, suture/staple application, and application in challenging anatomical locations (eg, plantar surface of the foot). The synthetic construction of the nanofabricated wound matrix enables these unique mechanical properties. For example, electrospun PLGA can possess a tensile modulus similar to that of native skin.⁵

The purpose of this study is to investigate the use of the nanofabricated wound matrix in treating full-thickness cutaneous wounds in a porcine model and to compare its performance to a commercially available xenograft collagen matrix.

This study was approved by the Institutional Animal Care and Use Committee (Sinclair Research Center, Animal Care and Use Committee, Auxvasse, MO; Protocol #: D14119). Six full-thickness cutaneous wounds (each 3 cm in diameter) were created 3 cm apart along the dorsum of 2 Yucatan miniature swine. Nanofabricated matrices were prepared and applied directly to the wounds on the right side of the dorsum, ensuring complete contact along the bottom and sides of each wound site. Control matrices composed of cross-linked bovine collagen (Integra Bilayer Matrix Wound Dressing; Integra LifeSciences, Plainsboro, NJ) were prepared and applied on the left side of the dorsum. Barrier dressings were then used to cover the wounds and were changed 2 to 3 times weekly. Wounds were photographed and measurements were taken 1 to 2 times per week at dressing changes until euthanasia at day 15 or day 30 (390 mg pentobarbital sodium/50 mg phenytoin sodium). At euthanasia, the wound sites were harvested, embedded in paraffin, and sectioned and stained with hematoxylin and eosin (Figure 1).

Analysis included gross and histopathological evaluation of the wound sites to assess healing and inflammation. Planimetric analysis of the wound photographs was performed using Adobe Photoshop CS6 (Adobe Systems, San Jose, CA) to measure wound area and score wound edges, exudate quality, exudate quantity, granulation tissue, and epithelialization. Each category was scored using a modified Bates-Jensen scoring system. Histological analysis of the paraffin-embedded wound tissue sections consisted of semiquantitative grading of inflammation, granulation tissue, collagen maturation, vascularization, and epithelialization. 

Student’s t tests were used for between-group comparison of wound area over time. Statistical significance was defined as P < .05. 

Gross evaluation of the wound sites (Figure 2) revealed that both the nanofabricated matrix and the control supported wound healing and were resorbed over the course of the study. No adverse reactions were observed. 

Planimetric analysis showed that the average surface area of wounds treated with the nanofabricated wound matrix was statistically reduced compared with wounds treated with the control for all time points after day 5 (Figure 2A; P < .05). Compared with day 5 planimetric measurements, wounds treated with the nanofabricated wound matrix decreased by 98% in wound area (on average) by day 30, while wounds treated with the control xenograft only decreased in area by 64%. Of note, the wound area of 2 nanofiber-treated sites reached 0 cm² (fully healed) by day 30. The Bates-Jensen wound score (Figure 2B) decreased over time and was lower for the nanofabricated wound matrix compared with the control at both time points. A 46% and a 19% difference in average scores were found in favor of nanofiber-treated wounds at days 15 and 30, respectively. 

Histopathological analysis and scoring (Figures 3, 4) revealed differences between wounds treated with the nanofabricated wound matrix and the control matrix. Nanofiber-treated wounds were found to exhibit moderate inflammation at day 15 and minimal inflammation at day 30 compared with the control-treated wounds, which showed more significant inflammation at both time points as well as areas of hemorrhaging, necrosis, and seroma. Compared with the controls at day 15, nanofiber-treated wounds were observed to have more mature collagen in the wound beds, a greater amount of granulation tissue coverage (20–50% vs. 100% ingrowth, respectively), and a greater degree of vascularization. Treatment with the nanofabricated wound matrix also resulted in greater epithelialization of the wounds at both days 15 and 30 compared with treatment with the control matrices. Wounds treated with the nanofabricated wound matrix were fully reepithelialized at day 30, unlike the wounds treated with the control.

The synthetic nanofabricated matrix significantly improved the speed and quality of wound healing compared with the control (xenograft). The nanofabricated wound matrix accelerated the rate of granulation tissue ingrowth, collagen maturation, and neovascularization; elicited less inflammation; and facilitated faster and more complete wound closure and reepithelialization in porcine full-thickness cutaneous wounds. Several of the nanofiber-treated wound sites were fully healed by day 30. In contrast, all of the wounds treated with the control matrix had not yet closed at the same time point. 

While the porcine model is well accepted for the examination of wound healing interventions, animal models are not always indicative of human clinical results. Preliminary clinical experience with the nanofabricated wound matrix appears to confirm the advantages of the fully synthetic wound matrix, yet additional clinical evidence is needed in order to identify optimal methods and scenarios for clinical use.

The nanofabricated wound matrix is a unique and effective alternative to existing wound matrices capable of supporting the natural wound healing process. This experimental wound matrix demonstrated superior performance compared with a cross-linked bovine collagen xenograft, including earlier vascularization and deposition of granulation tissue and mature collagen, and resulted in accelerated and improved wound closure and healing with reduced inflammation compared with the xenograft control. This nanofabricated matrix may offer significant benefits for the treatment of wounds refractory to existing wound care modalities, including partial- and full-thickness wounds, chronic wounds (eg, diabetic, venous, or pressure ulcers), and severe wounds caused by trauma or surgery. 

Affiliations: Acera Surgical, Inc, St Louis, MO; Telos Partners, LLC, Denver, CO; and Sinclair Research Center, Auxvasse, MO

Correspondence: Matthew R. MacEwan, PhD, President/Chief Science Officer, Acera Surgical, Inc, 10880 Baur Blvd, St Louis, MO 63132;
macewan@acera-surgical.com

Disclosure: This study was funded by Acera Surgical, Inc. The nanofabricated wound matrix (Restrata Wound Matrix; Acera Surgical, Inc.) examined in this study is currently patent pending under US Application number 20130197663 A1.