Development of an experimental model of infected skin ulcer

Establishment and characterization of a rat model of scalp-cranial composite defect for multilayered tissue engineering

Composite cranial defects have individual functional and aesthetic ramifications, as well as societal burden, while posing significant challenges for reconstructive surgeons. Single-stage composite reconstruction of these deformities entail complex surgeries that bear many short- and long-term risks and complications. Current research on composite scalp-cranial defects is sparse and one-dimensional, often focusing solely on bone or skin. Thus, there is an unmet need for a simple, clinically relevant composite defect model in rodents, where there is a challenge in averting healing of the skin component via secondary intention. By utilizing a customizable (3D-printed) wound obturator, the scalp wound can be rendered non-healing for a long period (more than 6 weeks), with the cranial defect patent. The wound obturator shows minimal biotoxicity and will not cause severe endocranium-granulation adhesion. This composite defect model effectively slowed the scalp healing process and preserved the cranial defect, embodying the characteristics of a "chronic composite defect". In parallel, an autologous reconstruction model was established as the positive control. This positive control exhibited reproducible healing of the skin within 3 weeks with variable degrees of osseointegration, consistent with clinical practice. Both models provide a stable platform for subsequent research not only for composite tissue engineering and scaffold design but also for mechanistic studies of composite tissue healing.

Maltodextrin/ascorbic acid stimulates wound closure by increasing collagen turnover and TGF-β1 expression in vitro and changing the stage of inflammation from chronic to acute in vivo

It has been reported that carbohydrates confer physicochemical properties to the wound environment that improves tissue repair. We evaluated in vitro and in vivo wound healing during maltodextrin/ascorbic acid treatment. In a fibroblast monolayer scratch assay, we demonstrated that maltodextrin/ascorbic acid stimulated monolayer repair by increasing collagen turnover coordinately with TGF-β1 expression (rising TGF-β1 and MMP-1 expression, as well as gelatinase activity, while TIMP-1 was diminished), similar to in vivo trends. On the other hand, we observed that venous leg ulcers treated with maltodextrin/ascorbic acid diminished microorganism population and improved wound repair during a 12 week period. When maltodextrin/ascorbic acid treatment was compared with zinc oxide, almost four fold wound closure was evidenced. Tissue architecture and granulation were improved after the carbohydrate treatment also, since patients that received maltodextrin/ascorbic acid showed lower type I collagen fiber levels and increased extracellular alkaline phosphatase activity and blood vessels than those treated with zinc oxide. We hypothesize that maltodextrin/ascorbic acid treatment stimulated tissue repair of chronic wounds by changing the stage of inflammation and modifying collagen turnover directly through fibroblast response.

Novel models for bacterial colonization and infection of full-thickness wounds in rats

An animal model is needed to study the pathophysiology of wound infections; however, an animal model that is reproducible and clinically relevant has not previously been available. In addition, an animal model of wound colonization generated in a manner similar to the wound infection model would be useful. Here, we describe new animal models of the wound infection continuum for the characterization of essential host-pathogen relationships. We determined the conditions needed to establish rat models of stable wound colonization and infection, without the use of disturbing factors (e.g., foreign bodies or induction of diabetes mellitus). We found that the age of the rats, bacterial inoculum size, and wound location were important elements in generating reproducible, obvious, spreading wound infections. We inoculated approximately 6-month-old rats with 2.06 × 10(9) or 4.12 × 10(9) colony-forming units of Pseudomonas aeruginosa to generate the wound colonization and wound infection models, respectively. Wounds were made 2 cm cranial to the greater trochanter. These clinically relevant and highly reproducible animal models can be used to investigate the mechanisms of wound infection and monitor the effect of therapeutic agents in vivo.

Mixture of sugar and povidone-iodine stimulates healing of MRSA-infected skin ulcers on db/db mice

The topical application of a mixture of sugar and povidone-iodine (PI) has been reported to accelerate the healing of cutaneous wounds and ulcers by promoting reepithelialization and granulation tissue formation, as well as by having an anti-microbial effect. In order to clarify the efficacy of a 70% sugar and 3% PI paste (U-PASTA(SP) on infectious skin ulcers, we made a bacterial infection model using methicillin-resistant Staphylococcus aureus (MRSA) on the skin of diabetic db/db mice, and investigated the effect of the paste on the healing process of wounds. Full-thickness wounds were made on the backs of female diabetic mice, (C57BL/ksJ db/db) and inoculated with S. aureus. SP was applied to the closed wounds for 8 days. The degree of repair was evaluated using three histological parameters: The degree of reepithelialization was given a percentage value of 0-100%; the amount of granulation tissue was quantified by measuring the area of granulation (mm(2)); and the number of capillary lumens in the granulation tissue was counted in the complete wound cross-section at 100x magnification. In addition, the colony-forming units (CFU) of MRSA on the wounds were counted. Continuous MRSA infection in the wounds of db/db mice was demonstrated with macroscopic and histopathological images. Wounding and infection caused by MRSA on the back of the diabetic mice significantly induced delayed reepithelialization, granulation tissue formation with inflammatory cell infiltrate and increased CFU on wounds (P < 0.01, respectively) compared to those of the MRSA-infected normal mice. Application of SP significantly accelerated reepithelialization (P < 0.01) and decreased CFU (P < 0.05) of the ulcers in the MRSA-infected wounds, compared to the non-treated group. Histopathological evaluation and CFU on this animal model revealed no significant difference between Methicilin-sensitive Staphylococcus aureus and MRSA infection. These results indicate that wounding on db/db mice provides a useful animal model of bacterial skin infections, and that SP is an effective topical agent for the treatment of diabetic skin ulcers.

The effect of a silver-containing Hydrofiber dressing on superficial wound bed and bacterial balance of chronic wounds

The treatment of chronic wounds represents a major cost to society and has a profound effect on the participant's quality of life. Chronic wounds may have an increased bacterial burden that can impair healing without all the clinical signs of infection. Silver dressings may provide an alternative topical method to control bacterial burden. The primary aim of this study was to evaluate the clinical improvement in chronic wounds through the effect on wound size, maceration, resolution of surface slough and conversion to healthy granulation during a 4-week application of the silver-containing Hydrofiber dressing. This was a single centre, open-label case series study which included a total of 30 evaluable participants: four with diabetic neuropathic foot ulcers, 13 venous stasis ulcers, four pressure ulcers and nine miscellaneous wounds that did not fit any of the previous categories. All participants had adequate vascular supply, indicating the potential to heal. The wounds were stalled or had the signs and symptoms consistent with critical colonisation. The underlying cause of the ulceration was identified and corrected, or the symptoms and signs were treated. This was followed by the application of silver-containing Hydrofiber dressings for a period of 4 weeks. The majority of wounds treated decreased in size (70%) with decreased exudate, decreased purulence and resolution of surface slough (75%). There was an increased quality and quantity of healthy granulation tissue. Unlike some silver dressings, the Hydrofiber and silver combination dressing was unlikely to cause burning and stinging on application. Peri-wound maceration was present in 54% of participants at baseline, and 85% of these resolved with this dressing. A desloughing action was seen in those patients with pre-existing slough at baseline and its removal will lower the bacterial burden of the wound.

Comparison of bacteria-retaining ability of absorbent wound dressings

Fibrous materials in some modern absorbent wound dressings have the ability to sequester and retain bacteria; however, this ability varies according to the nature of the fibres. We studied the bacterial retention capacity of alginate and carboxymethylcellulose dressings, using an infected skin ulcer model on the backs of rats. Wound surfaces were inoculated with either Staphylococcus aureus or Pseudomonas aeruginosa at a concentration of 1.5 x 10(6) colony-forming units per wound. AQUACEL; Hydrofiber;, Kaltostat; or Sorbsan; were applied to the contaminated wounds for 12 h. Each dressing was then divided into two pieces. Total viable bacterial count within the dressing was calculated using one piece, and bacterial count released from the dressing into physiological saline was determined using the other piece, enabling bacterial retention rate to be calculated. Bacterial counts in tissue were also determined. Each dressing was tested on each of 10 wounds contaminated with each bacterium. Statistical analyses were performed using one-way analysis of variance (ANOVA) for replicated measures combined with Duncan's multiple comparison test. AQUACEL; Hydrofiber; dressing was most effective in its ability to retain both Staphylococcus aureus and Pseudomonas aeruginosa (p < 0.05). Bacterial counts in tissue showed no significant change with respect to pathogen or the type of dressing used. It can be concluded that the bacterial retaining ability of AQUACEL; Hydrofiber; dressing was found to be significantly higher than that of alginate dressings in an infected animal wound model.