The primary role of the interface material in wound healing is to provide optimal wound healing conditions. In general practice, polyurethane foam or moistened gauze is used as wound filler material.34-38 Many experimental and clinical studies have sought to determine which interface material is more effective in difficult-to-heal wounds and whether interface materials affect changes in wound characteristics such as depth, size, and exudate.16,17,20,21,38 Different indications provide some guidance on using negative pressure with foam or gauze and depend on types of wounds, patients, and anatomical location.38 Malmsjö et al’s experimental studies16,17 showed that gauze and foam are equally effective at delivering negative pressure and creating mechanical deformation of the wound. According to a large review of the literature,16-20 no differences in the degree of blood flow or wound contraction in small wounds was observed with either foam or gauze, although polyurethane foam was found to result in more contraction than gauze in large wounds. In the current study, wound diameter was 9 cm2. Thus, wounds were small and created on rabbits, where it is known wounds heal faster than in larger animals or humans.
Current study results regarding the control, gauze, and foam correlate with the literature on wound contraction, granulation, and neovascularization. The use of loofah sponge, a natural product similar in form to foam or gauze, was found to have the same results. It has been shown in a literature review39 and an in vivo study40 that the open-pore wound filler plays a crucial role in suction device-induced wound healing. Foam porosity is a critical parameter that can affect cellular activities such as binding, migration, proliferation, morphology, and ingrowth into biomaterials.20 O’Brien et al21 suggested pore sizes between 20 and 120 µm were optimal and that pores should be large enough to allow cell migration but small enough to allow cell adhesion. Heit et al’s41 similar experimental study utilized polyurethane foam in large (300 µm), medium (130 µm), and small (70 µm) pore size diameters to treat full-thickness wounds in diabetic mice. In that study, the thickest granulation tissue was obtained after large pore size treatment compared with medium and small pore size treatments. Angiogenesis was induced only in small and medium pore size groups. Small and medium pore size-treated wounds showed a greater number of proliferating cells compared with large pore size-treated wounds. In addition, tissue ingrowth into small pore size polyurethane foam was much lower than that of medium and large pore size. According to Klinge et al’s in vivo study,42 the pore size of an interface material appears to be an important parameter in tissue integration. In that study, the authors concluded that small diameters theoretically will lead to increased flow resistance and to impaired passive exchange of the soluble components, particularly if the surface tension of the tissue liquids is considered. Thus, it can be speculated that tiny pores may markedly inhibit fluid transport through the interface material. Per experimental studies,43-45 cellular ingrowth within a sponge depends on the porosity and the presence of fibrous structure. In an experimental study,46 larger pores were shown to increase wound surface strain, tissue ingrowth, and transformation of contractile cells. The medium and small pore size can be superior to large pore size to enable the reorganization and clustering of the cells in a granulating wound. In the current study, loofah sponge (736 µm) stimulated granulation tissue formation and neovascularization by days 6 and 9 as well as gauze (912 µm) and foam (415 µm), with no difference among study groups.
Granulation tissue formation was observed to be more coarse in the control and smooth in the study groups. Wound biopsies showed similar surface undulations and small tissue blebs, which is the result of pulling effect of NPWT into the pores of the wound filler in all study groups. These mechanical effects (microdeformations) are thought to result in shearing forces of the wound dressing materials with NPWT, which affects the cytoskeleton and stimulation of angiogenesis and leads to promotion of granulation tissue formation and accelerated wound healing.47 Thus, loofah sponge exacted the same end result as available wound fillers on the market today.
In humans, NPWT helps decrease wound volume through active contraction and generation of granulation tissue; in rabbits, where the skin is loose, the primary mode for wound closure is contraction and epithelialization, even though some granulation tissue formation occurs, usually after about 4 to 6 days.48 In animal studies with NPWT, the time to complete closure is between 8 to 12 days depending on the size of the wound.49 In the present study, the optimum follow-up period was 9 days. At that time, the surface area of the wounds in the study groups was significantly smaller than that of control group, and no differences between the study groups were seen.
Several techniques have been developed to process synthetic and natural scaffold materials into porous structures.50 These conventional fabrication techniques are defined herein as processes that create scaffolds having a continuous, uninterrupted pore structure that lacks any long-range channeling microarchitecture. The fibrous network of loofah sponge is mainly comprised of cellulose (60%), hemicelluloses (30%), and lignin (10%).26,27 The tensile strength of the fibers is due to cellulose and its compression strength to lignin.51 The netting-like, fibrovascular loofah sponge has approximately 800 µm macropores, created by rough and indented fibers with continuous hollow microchannels.52 Cellulose, as a bioaffinity carrier, exhibits good chemical stability, recoverability, reproducibility, and mechanical strength.53 In plant cell walls, lignins are closely related with hydrophilic polysaccharides; they are amorphous, hydrophobic heteropolymers. Because of their hydrophobic character, lignins make plant cells impermeable to water.53 The presence of lignin in the cell walls or between the fibers is known to hinder the chemical reactions of cellulose and hemicelluloses as it prevents the permeation of water across the cell walls. Thus, loofah sponge may be a suitable biostructure for cell immobilization and bioprocess activities. The sponge structure follows the “tensegrity” principle — ie, an architectonical system in which structures stabilize themselves owing to equilibrium between opposite forces of traction and compression.54 The surface of the fibers is rough, due to the presence of small longitudinal and transverse stripes. In longitudinal section, the sponge appears like a network of fibers of different diameters, more or less close together.55
The fibrous and porous network of loofah sponge is similar to gauze and foam. It is similar to gauze in hydrophilic character, and its absorption capacity has been found to be 13.6 g/g.56
NPWT has been used for many difficult-to-heal wounds during the last decade; however, it is still an expensive treatment modality. Wounds present a substantial cost to patients as well as the healthcare system. The most important determinant of cost appears to be wound complications that require hospitalization or delay hospital discharge. Reducing costs requires a systematic focus on effective and timely diagnosis, on planning an appropriate wound treatment, and on taking measures to prevent complications and wound-related hospitalization.57 According to Albert et al’s prospective comparison,58 gauze- and foam-based NPWT systems both can provide comparable wound healing; nurse perceptions of ease of dressing changes when working with these devices and direct costs associated with the use of the devices (dressings and chargeable equipment) did not significantly differ. The total cost of interface materials in the present study was $1,580 for polyurethane foam, $1,000 for cotton gauze, and $20 for loofah sponge. Because it was the same for all three interface materials, the cost of the canister (collection unit) was not taken into consideration. The price advantage of using loofah is derived from its more basic route of supply — ie, a local store. Manufactured products cost more, and loofah sponge can be prepared locally for use as an interface material. It should be noted that raw material costs of gauze or foam dressings are probably relatively a small fraction of their commercial price after manufacturing. Even though the business costs account for a significant portion of the final price, it can be concluded that loofah sponge can be an inexpensive interface material option as compared to foam and gauze. In addition, because it dissolves easily, it has organic (“green”) implications.