Healing of full-thickness wounds in pigs: effects of occlusive and non-occlusive dressings associated with a gel vehicle

Comparative study of fibroblast growth factor 2 and ofloxacin ear drops for repairing large traumatic perforations: A randomized controlled study

OBJECTIVE

The objective of this study was to compare the healing outcome of fibroblast growth factor 2 (FGF2), ofloxacin ear drops (OFLX) and spontaneous healing for repairing large traumatic tympanic membrane (TM) perforations.

MATERIAL AND METHODS

A total of 75 traumatic large perforations with >1/4 of TM were randomly divided into FGF2 (n = 25), OFLX (n = 25), and spontaneous healing (n = 25) groups. The closure rates, closure times, and hearing gains were compared at 3 months.

RESULTS

At 2 weeks after treatment, the closure rate was 95.8 % in the FGF2 group, 96.0 % in the ofloxacin ear drops group, and 14.3 % in the spontaneous healing group (P < 0.01), respectively. At 3 months after treatment, the closure rate was 100 % in the FGF2 group, 100 % in the OFLX group, and 85.7 % in the spontaneous healing group, no among-group differences were significant (P > 0.05). The mean closure time was 9.69 ± 2.46 days in the FGF2 group, 9.45 ± 2.32 days in the OFLX group, and 30.94 ± 8.95 days in the spontaneous healing group (P < 0.01). The mean ABG was 10.37 ± 2.51 dB for the FGF2 group, 11.01 ± 1.31 dB for the OFLX group, and 10.86 ± 1.94 dB for the spontaneous healing group, no significant difference was found among three groups (P > 0.05).

CONCLUSIONS

This study suggested that both FGF2 and OFLX significantly shortened the mean closure time and improved the closure rate compared with spontaneous healing for repairing large traumatic perforations, while the healing outcome wasn't significantly different among FGF2 and OFLX groups.

Sling Training with Positive Reinforcement to Facilitate Porcine Wound Studies

Domestic swine have become important large animal models for dermatologic and wound studies owing to the similarity of their skin architecture to that of human skin. To improve on current porcine wound protocols and accomplish postoperational daily wound care or treatment in a welfare-centered, low-stress setting, we developed a unique sling-training program using a commercially available Panepinto-like sling in combination with positive reinforcement of desired behaviors. Training using these methods is initiated during the acclimation period of 7-10 days before the initial surgical manipulation and continued throughout project-specific treatments for the duration of the study. Using this protocol, daily treatments can be administered without additional anesthesia while the animals rest in the sling with the administration of simultaneous nutritional enrichment. This low-stress handling program successfully facilitates the postoperational treatments and wound care without the use of potentially confounding anesthesia or sedation. It has a wide range of potential applications in translational medicine and in data acquisition from a resting state where baseline readouts of unstressed animals can be achieved.

Protecting the skin-implant interface with transcutaneous silver-coated skin-and-bone-integrated pylon in pig and rabbit dorsum models

Implant-associated soft tissue infections at the skin-implant interface represent the most frequent complications in reconstructive surgery and lead to implant failures and revisions. Titanium implants with deep porosity, called skin-and-bone-integrated-pylons (SBIP), allow for skin ingrowth in the morphologically natural direction, thus restoring a reliable dermal barrier and reducing the risk of infection. Silver coating of the SBIP implant surface using physical vapor deposition technique offers the possibility of preventing biofilm formation and exerting a direct antimicrobial effect during the wound healing phase. In vivo studies employing pig and rabbit dorsum models for assessment of skin ingrowth into the pores of the pylon demonstrated the safety of transcutaneous implantation of the SBIP system. No postoperative complications were reported at the end of the follow-up period of 6 months. Histological analysis proved skin ingrowth in the minipig model without signs of silver toxicity. Analysis of silver release (using energy dispersive X-ray spectroscopy) in the model of intramedullary-inserted silver-coated SBIP in New Zealand rabbits demonstrated trace amounts of silver after 3 months of in-bone implantation. In conclusion, selected temporary silver coating of the SBIP implant surface is powerful at preventing the periprosthetic infections without imparing skin ingrowth and can be considered for clinical application.

The Effect of a Hydrocolloid Dressing on Second Intention Wound Healing in Cats

The objective of the present study was to evaluate the effect of a hydrocolloid dressing on second intention wound healing in cats. Two full-thickness skin wounds, measuring 2 × 2 cm, were created on both sides of the dorsal midline of 10 cats; bilaterally, one randomly selected wound was bandaged with a hydrocolloid dressing and the second one (control) with a semiocclusive pad. Subjective clinical evaluation of granulation tissue formation, of the quantity and nature of wound exudate, and planimetry were performed on the right-side wounds, and histological examination on the left. No significant differences in subjective clinical evaluation or in planimetry were observed between the hydrocolloid-treated wounds and controls. Most wounds had serous or absence of exudate (41.25% and 25%, respectively), whereas purulent exudate was observed in 7.5% of wounds. Edema was significantly increased in the hydrocolloid-treated wounds compared with controls on day 7 but no significant differences in the other histological variables were observed.

Effects of two occlusive, hydrocolloid dressings on healing of full-thickness skin wounds in cats

OBJECTIVES

To determine the effects of two occlusive, hydrocolloid dressings on second intention wound healing in cats.

METHODS

Three 2×2 cm full-thickness skin wounds were created on each side of the trunk of 10 cats. Two bilateral wounds were bandaged using different hydrocolloid dressings, namely Hydrocoll and DuoDerm while a semi-occlusive pad (Melolin) was applied to the third bilateral wound (control group). Wound planimetry, subjective evaluation of wound healing, and qualitative bacterial cultures were performed on the right-sided wounds, whereas left-sided wounds were subjected to histological examination.

RESULTS

Subjective evaluation revealed accelerated (p <0.01) granulation tissue formation in hydrocolloid-treated wounds. The amount of wound exudate was initially greater (p <0.01) in these wounds. Seventeen out of 120 evaluated wounds (14.2%) produced purulent exudate, 11 of which showed Staphylococcus aureus growth. Fewer control wounds (3/17) emitted purulent exudate, but all of them yielded moderate bacterial growth as compared to hydrocolloid-treated wounds (8/17) which had a low incidence of bacterial growth. The only significant difference in histological variables was increased cellular infiltration noted on day 7 in Hydrocoll-treated wounds compared to controls. No significant differences in planimetry variables were found between groups.

CLINICAL SIGNIFICANCE

Despite the initially increased amount of wound exudate and the low growth of Staphylococcus aureus, hydrocolloid dressings accelerate granulation tissue formation and can hence be suggested for second intention wound healing in cats.

Reduction of diabetic foot ulcer healing times through use of advanced treatment modalities

Diabetic wounds are a major health care problem associated with delayed healing and high amputation rates. This review systematically evaluated newer wound care therapies for the treatment of diabetic wounds. More recent means of approaching diabetic foot ulcers include various dressings, off-loading shoes, and bioengineered skin constructs and growth factors. Electrical stimulation, phototherapy, electromagnetic fields, and shockwave therapy have been further proposed as potential treatments. A brief overview of these treatments is presented using peer-reviewed evidenced-based literature. A review of the literature demonstrated that treatment of diabetic wounds has focused on either prevention of the wounds in the form of off-loading shoes or adequate protective dressings or on direct treatment of wounds with bioengineered skin constructs, growth factors, or medical devices that accelerate wound healing. The authors' conclusion, following extensive literature review, is that although excellent national and international guidelines exist regarding suggested approaches to the treatment of the diabetic foot ulcer, there is no definitive or universal consensus on the choice of specific treatment modalities. The importance of optimizing comorbidities and the disease state, hemodynamics, local and peripheral skin and wound care, and metabolic challenges while reducing biological and bacterial burden and minimizing trauma remain the primary approach, followed by choice of the most appropriate treatment material or product.

Novel microstructured sildenafil dosage forms as wound healing promoters

PURPOSE

Study the possible benefit of combining biodegradable polymers with sildenafil citrate (SC) in wound healing.

METHOD

Biodegradable micronized powdered formulations of SC were prepared by spray drying using chitosan (P₁) or chitosan/gum Arabic (P₂). Powders were characterized by differential scanning calorimetry, Scanning electron microscope, particle size analysis, flow and swelling behavior. The powders were also incorporated into microstructured gels and in vitro SC release from powders and gels was tested. In vivo wound healing acceleration was tested by measuring area contraction of excision wounds and histologically. Post-healing tensile strength (TS) for incision wounds in rats receiving powder formulations was tested.

RESULTS

The powders were in the micron-size range showing no SC-polymers interaction. Powders had poor flow with angle of repose (θ) of 41 - 48°, and high moisture uptake reaching 107% for placebo powder P₁. Good excision wound healing was seen with P1 and G1 formulations showing 98.4 and 98.5% reduction in wound area, respectively, compared with 83% for the control. Incision wounds were improved with P1 showing TS value of 6.9 compared with 3.7 kg/cm² for control. Histological examinations supported.

CONCLUSION

Spray-dried chitosan/SC powder (P₁) and its gel form (G₁) could be promising wound healing promoters as supported by the histological examinations.

Hairless descendants of Mexican hairless dogs: an experimental model for studying hypertrophic scars

BACKGROUND/OBJECTIVE

In previous studies, the author noticed hypertrophic scar formation in hairless dogs. The purpose of this study was to evaluate both grossly and histopathologically hypertrophic scars in hairless dogs to explore any similarities with hypertrophic scars in humans and to introduce these dogs as an appropriate model for further investigation on hypertrophic scarring.

METHODS

Full-thickness wounds were made on the dorsolumbar skin of hairless dogs. Hypertrophic scarring was examined with three methods: clinical observations, dihydroxyphenylalanine (DOPA)-positive melanocytes, and skin histopathology.

RESULTS

Hairless dogs clinically developed the formation of hyperpigmented and hypertrophic scars that did not extend beyond the original wound margins. In hypertrophic scars of hairless dogs, the split epidermal sheet showed an increased number of DOPA-positive melanocytes with well-developed dendrites exhibiting activated melanocytes. There were very few DOPA-positive melanocytes in the repaired skin of haired dogs. Histopathologic examinations demonstrated that hypertrophic scars were fully reepithelialized and granulation tissue formation was accompanied by inflammatory cell infiltration. There was remodeling of thick collagens and fine elastic fibers in the course of hypertrophic scar formation.

CONCLUSION

Experimental hypertrophic scars produced in hairless dogs have morphologic properties similar to those of human hypertrophic scars.

Development of chitosan-collagen hydrogel incorporated with lysostaphin (CCHL) burn dressing with anti-methicillin-resistant Staphylococcus aureus and promotion wound healing properties

Methicillin-resistant Staphylococcus aureus (MRSA) have become increasingly prevalent as nosocomial pathogens, especially in burn patients, which is the leading cause of their death. A drug delivery system of chitosan-collagen hydrogel incorporated with lysostaphin (CCHL) based on the lysostaphin gauze was developed for MRSA infected burn wounds. CCHL scaffold consisted of numerous interconnected sphericles and tubular bodies with an average diameter of 100-200 µm, 20-60-fold swelling, high water retention capacity, and cell proliferation properties. The minimal inhibitory concentration of CCHL was 0.053 U/mL. By the second week after its application on MRSA infected third-degree burn wounds, no bacteria could be detected and the burn wounds had started healing. Therefore, CCHL should be studied further as a promising candidate of burn treatment dressing against MRSA infections for clinics.

Preparation and function of composite asymmetric chitosan/CM-chitosan membrane

A novel composite asymmetric chitosan/CM-chitosan membrane (C-P-C) was prepared, the top-layer was chitosan (CS), the intermediate was PVA, and the substrate was carboxymethyl chitosan (CM-CS). C-P-C membrane had capability in mechanical strength, light transparence, vapor permeability, and wound skin joining. The CS and CM-CS in C-P-C membrane were selected by series independent experiments, respectively. CS (MW 90,000 Da) had the highest antibacterial activity for E.coli. CM-CS had biocompatibility, no cytotoxicity, and had the activity of promoting growth of human skin fibroblast and inhibiting the growth of keloid fibroblast. The normal skin fibroblast can growth on the CM-CS surface of C-P-C, and have no conglomeration in higher cell density, and the keloid fibroblast could not growth on CM-CS surface of C-P-C. The animal experiment demonstrated that wound, covered with the C-P-C membrane, was hemostatic, healing quickly and had histocompatibility. The results indicated that the C-P-C membrane could be used as dressing of skin repair, and had the potential in promoting wound healing and inhibiting the keloid formation.

Artificial Barrier Repair in Wounds by Semi-Occlusive Foils Reduced Wound Contraction and Enhanced Cell Migration and Reepithelization in Mouse Skin

The repair of the permeability barrier to prevent the entry of harmful substances into the body is a goal in wound healing. Semi-occlusive foils, which provide an artificial barrier, are commonly used for the treatment of wounds. We examined the effects of foils on wound contraction, cell migration, and reepithelization. Full-thickness skin wounds in mice were covered with occlusive latex foils or semi-occlusive water vapor-permeable hydrocolloid foils for either the entire, the first half, or the second half of the wound-healing period. We found that application of foils for the entire healing period initially reduced wound healing during the first week of treatment, whereas healing was enhanced during the second week. Foils were found to reduce wound contraction, but enhanced reepithelization during the second week of wound healing because of increased proliferation and migration of keratinocytes. These effects were also noted when the hydrocolloid foils were applied for the second part of the healing period, only. The fully occlusive latex foil led to irritation of the skin, whereas less irritation occurred under semi-occlusive conditions. In summary, we found that artificial barrier repair with semi-occlusive foils in wounds reduced wound contraction and enhanced cell migration and reepithelization without irritation.

Validation of a model for the study of multiple wounds in the diabetic mouse (db/db)

The genetically diabetic db/db mouse exhibits symptoms that resemble human type 2 diabetes mellitus, demonstrates delayed wound healing, and has been used extensively as a model to study the role of therapeutic topical reagents in wound healing. The purpose of the authors' study was to validate an excisional wound model using a 6-mm biopsy punch to create four full-thickness dorsal wounds on a single db/db mouse. Factors considered in developing the db/db wound model include reproducibility of size and shape of wounds, the effect of semiocclusive dressings, comparison with littermate controls (db/-), clinical versus histologic evidence of wound closure, and cross-contamination of wounds with topically applied reagents. The size of wounds was larger, with less variation in the db/db mice (31.11 +/- 3.76 mm2) versus db/- mice (23.64 +/- 4.78 mm2). Wounds on db/db mice that were covered with a semiocclusive dressing healed significantly more slowly (mean, 27.75 days) than wounds not covered with the dressing (mean, 13 days; p < 0.001), suggesting the dressings may splint the wounds open. As expected, wounds healed more slowly on db/db mice than db/- mice (covered wounds, 27.75 days versus 11.86 days, p < 0.001; wounds not covered, 13 days versus 11.75 days, p = 0.39). Covered wounds, thought to be closed by clinical examination, were confirmed closed by histology only 62 percent of the time in the db/db and 100 percent of the time in the db/- mice. Topical application of blue histologic dye or soluble biotinylated laminin 5 to one of the four wounds did not spread locally and contaminate adjacent wounds. Multiple, uniform, 6-mm wounds in db/db mice heal in a relatively short time, decrease the number of animals needed for each study, and allow each animal to serve as its own control. The db/db diabetic mouse appears to be an excellent model of delayed wound healing, particularly for studying factors related to epithelial migration.

Glycosaminoglycan Hydrogels as Supplemental Wound Dressings for Donor Sites

Chemically crosslinked glycosaminoglycan (GAG) hydrogel films were evaluated as biointeractive dressings in a porcine model for donor-site autograft wounds. Multiple 5 x 5 x 0.03 cm wounds were created on the dorsum of pigs. Half of the wounds were treated with a GAG film plus an occlusive dressing (Tegaderm), whereas the other half were treated with Tegaderm alone. At 3, 5, or 7 days after surgery, the partially healed wounds were excised and evaluated histologically for three animals at each time point. By day 3, epithelial cells had proliferated and migrated from wound edges and from epithelial islands associated with residual hair follicles to begin to cover the wound bed. A statistically significant increase in coverage was observed for GAG + Tegaderm-dressed wounds than for those with Tegaderm alone at day 3 and day 5 post-surgery. By day 7, all treatment groups were completely healed. Thus, GAG hydrogels accelerated wound healing by enhancing re-epithelialization.

Incorporation of drugs in an amorphous state into electrospun nanofibers composed of a water-insoluble, nonbiodegradable polymer

Electrostatic spinning was applied to the preparation of drug-laden nonbiodegradable nanofiber for potential use in topical drug administration and wound healing. The specific aim of these studies was to assess whether these systems might be of interest as delivery systems for poorly water-soluble drugs. Itraconazole and ketanserin were selected as model compounds while a segmented polyurethane (PU) was selected as the nonbiodegradable polymer. For both itraconazole and ketanserin, an amorphous nanodispersion with PU was obtained when the drug/polymer solutions were electrospun from dimethylformide (DMF) and dimethylacetamide (DMAc), respectively. The collected nonwoven fabrics were shown to release the drugs at various rates and profiles based on the nanofiber morphology and drug content. Data were generated using a specially designed release apparatus based around a rotating cylinder. At low drug loading, itraconazole was released from the nanofibers as a linear function of the square root of time suggesting Fickian kinetics. No initial drug burst was observed. A biphasic release pattern was observed for ketanserin in which two sequential linear components were noted. These release phases may be temporally correlated with (1) drug diffusion through the polymer and (2) drug diffusion through formed aqueous pores.

THE PIG AS A MODEL FOR HUMAN WOUND HEALING

The medical literature describes numerous in vitro and in vivo wound-healing models. The selection of an animal model depends on a number of factors including availability, cost, ease of handling, investigator familiarity, and anatomical/functional similarity to humans. Small mammals are frequently used for wound healing studies, however, these mammals differ from humans in a number of anatomical and physiological ways. Anatomically and physiologically, pig skin is more similar to human skin. The many similarities between man and pig would lead one to believe that the pig should make an excellent animal model for human wound healing. The purpose of this paper is to review the existing literature for evidence of this supposition and determine how well the various models correlate to human wound healing. Studies of wound dressings, topical antimicrobials, and growth factors are examined. Over 180 articles were utilized for this comparative review. Our conclusion is that the porcine model is an excellent tool for the evaluation of therapeutic agents destined for use in human wounds.

Comparative trial of octyl-cyanoacrylate and silver sulfadiazine for the treatment of full-thickness skin wounds

A prospective, randomized, blinded, controlled experimental trial was performed in pigs to compare the rates of reepithelialization of 126 full-thickness cutaneous 4-mm punches treated with an octyl-cyanoacrylate spray, silver sulfadiazine, or a dry gauze (controls). Full thickness biopsies were taken 7, 14, or 30 days later for histopathological evaluation of hematoxylin and eosin stained tissue sections by a dermatopathologist. The primary outcome measure was the proportion of wounds completely re-epithelialized at days 7 and 14. Secondary outcomes were the rates of infection, foreign body reactions, and the depth of any resulting cutaneous dells measured with a micrometer. Between-group comparisons were performed with ANOVA or Chi-square tests. Octyl-cyanoacrylate treated wounds re-epithelialized more slowly, as fewer wounds treated with octyl-cyanoacrylate were re-epithelialized at day 7 in comparison with silver sulfadiazine or control wounds (50% vs. 90% vs. 100%, p < 0.001). There were no infections or foreign body type reactions. Amounts of granulation tissue were similar among groups. Octyl-cyanoacrylate wounds were more depressed than silver sulfadiazine wounds at days 7 and 14 yet had similar histopathological characteristics at day 30. We conclude that treatment of small, full thickness cutaneous wounds with octyl-cyanoacrylate results in delayed re-epithelialization and dermal repair in comparison with silver sulfadiazine, yet it does not result in any foreign body-type reaction. However, by 30 days, histopathological wound characteristics were similar in all groups.