Rat models of skin wound healing: a review

Ultrafine Silver Nanoparticles Embedded in Cyclodextrin Metal-Organic Frameworks with GRGDS Functionalization to Promote Antibacterial and Wound Healing Application

The challenge of bacterial infection increases the risk of mortality and morbidity in acute and chronic wound healing. Silver nanoparticles (Ag NPs) are a promising new version of conventional antibacterial nanosystem to fight against the bacterial resistance in concern of the drug discovery void. However, there are several challenges in controlling the size and colloidal stability of Ag NPs, which readily aggregate or coalesce in both solid and aqueous state. In this study, a template-guided synthesis of ultrafine Ag NPs of around 2 nm using water-soluble and biocompatible γ-cyclodextrin metal-organic frameworks (CD-MOFs) is reported. The CD-MOF based synthetic strategy integrates AgNO₃ reduction and Ag NPs immobilization in one pot achieving dual functions of reduced particle size and enhanced stability. Meanwhile, the synthesized Ag NPs are easily dispersible in aqueous media and exhibit effective bacterial inhibition. The surface modification of cross-linked CD-MOF particles with GRGDS peptide boosts the hemostatic effect that further enhances wound healing in synergy with the antibacterial effect. Hence, the strategy of ultrafine Ag NPs synthesis and immobilization in CD-MOFs together with GRGDS modification holds promising potential for the rational design of effective wound healing devices.

The role of Iranian medicinal plants in experimental surgical skin wound healing: An integrative review

OBJECTIVES

Wounds are physical injuries that cause a disturbance in the normal skin anatomy and function. Also, it has a severe impact on the cost of health care. Wound healing in human and mammalian species is similar and contains a complex and dynamic process consisting of four phases for restoring skin cellular structures and tissue layers. Today, therapeutic approaches using herbal medicine have been considered. Although the benefits of herbal medicine are vast, some medicinal plants have been shown to have wound healing effects in different experimental studies. Therefore, the current review highlights information about the potency of herbal medicine in the experimental surgical skin wound healing.

MATERIALS AND METHODS

Electronic database such as PubMed, Google Scholar, Scopus, and Medscape were searched for Iranian medicinal plants with healing activity in experimental surgical skin wounds. In this area, some of the most important papers were included.

RESULTS

There are numerous Iranian medicinal plants with skin wound healing activity, but clinical application and manufacturing are very low in comparison to the research volume.

CONCLUSION

In normal instances, the human/animal body usually can repair tissue damage precisely and completely; therefore, the utilization of herbs is limited to special conditions or in order to accelerate the healing process.

Lupeol, a Dietary Triterpene, Enhances Wound Healing in Streptozotocin-Induced Hyperglycemic Rats with Modulatory Effects on Inflammation, Oxidative Stress, and Angiogenesis

Impaired wound healing is a debilitating complication of diabetes that leads to significant morbidity, particularly foot ulcers. Natural products have shown to be effective in treating skin wounds. Lupeol is known to stimulate angiogenesis, fibroblast proliferation, and expressions of cytokines and growth factors involved in wound healing. The study is performed to evaluate the wound healing activity of lupeol in streptozotocin-induced hyperglycemic rats by macroscopical, histological, immunohistochemical, immunoenzymatic, and molecular methods. Percentage of wound closure and contraction was increased in the lupeol-treated group when compared to the Lanette group. Histopathological observation revealed decreased inflammatory cell infiltration and increased proliferation of fibroblasts, vascularization, and deposition of collagen fibers after lupeol treatment. Immunohistochemical analyses showed decreased intensity of NF-κB and increased intensity of FGF-2, TGF-β1, and collagen III. ELISA results revealed downregulated IL-6 levels and upregulated IL-10 levels in response to lupeol. The mRNA expression levels of Hif-1α, Sod-2, and Ho-1 were significantly increased in response to lupeol as compared to Lanette whereas Nf-κb and Vegf-A levels were decreased in relation to insulin and lupeol treatment. These findings indicate that lupeol possesses wound healing potential in hyperglycemic conditions and may be useful as a treatment for chronic wounds in diabetic patients.

Short time insulin treatment post burn improves elastic-collagen rearrangement and reepithelization

Extensive burn may cause acute resistance to insulin, which accentuates hypermetabolism, impairs glucose metabolism, immune dysfunction and risks of sepsis. To minimize these effects, insulin is used as a treatment. The purpose was to analyze the collagen-elastic arrangement effects of insulin on the burned skin. Wistar rats were assigned in groups: control (C); control with insulin (C + I); scald burn injury (SBI); and SBI with insulin (SBI+ I). SBI were submitted to 45% total body surface area burn and the insulin-treated groups received insulin (5 UI/Kg/day) for 4 or 14 days (d). Insulin levels, glucose tolerance test and HOMA index were determined. The skin sections were analyzed for histophatological and morphoquantitative data. Histopathological findings showed increased reepithelization of SBI+ I and formation of a new muscle layer after 14 days. In the collagen-elastic arrangement, insulin for 4 days increased the volume fraction (Vv) of thin collagen and elastic fibers. After 14 days, independently of injury, insulin decreased the elastic fibers. Insulin was able to reverse damages in the collagen-elastic rearrangement and stimulate reepithelization after 4 days. Untreated scald-burned animals showed higher Vv of thick collagen after 4 days, while those treated had a higher Vv of thin collagen. The Vv of elastic fibers was increased in SBI+ I for 4 days. In conclusion, insulin treatment was able to stimulate reepithelization. It also reversed the damages to the collagen-elastic arrangement in the scald-burned group, improving the organization of thin collagen and increasing the Vv of elastic fibers in the injured group treated with insulin for a short time, that is, for 4 days.

Effects of subcutaneous injection of ozone during wound healing in rats

Fibroblast growth factor 2 (FGF2) regulates the wound repair process and it is secreted by inflammatory and endothelial cells, and by myofibroblasts. This study aimed to establish the expression patterns of FGF2 and myofibroblastic differentiation during wound healing in rats treated with subcutaneous ozone injection. We created full-thickness excisional wounds in rats, and the healing process was analyzed through morphometric analyses and digital quantification of immunoreactivity of smooth muscle actin and FGF2. Ozone therapy-treated wounds presented granulation tissue with a reduced number of inflammatory cells and greater dermal cellularity, and intense collagen deposition. FGF2 immunoreactivity, microvessel density, and amount of myofibroblasts were significantly higher in treated wounds compared to controls. In conclusion, it was demonstrated that subcutaneous injections of ozone accelerate and ameliorate wound repairing process. Moreover, injectable ozone therapy's action mechanism may be associated with FGF2 overexpression.

Metabolite profiling and wound-healing activity of Boerhavia diffusa leaf extracts using in vitro and in vivo models

Boerhavia diffusa is a perennial herb belonging to the Nyctaginaceae family. This plant has been widely used in Indian traditional medicinal system to cure several human ailments. However, traditional use of this plant in the treatment and management of wounds has not been validated by any comprehensive scientific study. The present study was aimed to explore the in vitro and in vivo wound healing potential of methanol extract (ME) and chloroform extract (CE) from B. diffusa leaf and subsequent identification of the bioactive metabolites, which might be responsible for enhancement of wound healing property of the extracts.

The study included in vitro cell viability and wound scratch assays as well as in vivo excision wound assays in rat models. Both ME and CE were analysed for their antioxidant properties and phenolics content. The gas chromatography-mass spectrometry analyses were performed for identification of bioactive metabolites present in the ME and CE. ME of B. diffusa leaf significantly enhanced viability and migration of human keratinocyte cells (HaCaT) as compared to the untreated and CE-treated groups. The topical application of ME of B. diffusa leaf in excision wound model significantly decreased the wound area by the 14th day (91%) as compared to control (22%) (p < 0.05). The GC-MS analysis revealed the presence of caffeic acid, ferulic acid and D-pinitol as the major bioactive metabolites in ME. These results suggest that ME of B. diffusa possesses significant wound healing potential, where D-pinitol and caffeic acid served as the lead constituent metabolites responsible for the healing.

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Reporting wound healing potential of Boerhavia diffusa leaf extracts.

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GC-MS analyses of B. diffusa leaf extracts to identify bioactive wound healing metabolites.

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D-Pinitol and caffeic acid were identified as lead metabolites triggering wound healing.

Characterisation of impaired wound healing in a preclinical model of induced diabetes using wide-field imaging and conventional immunohistochemistry assays

Major complications of diabetes lead to inflammation and oxidative stress, delayed wound healing, and persistent ulcers. The high morbidity, mortality rate, and associated costs of management suggest a need for non-invasive methods that will enable the early detection of at-risk tissue. We have compared the wound-healing process that occurs in streptozotocin (STZ)-treated diabetic rats with non-diabetic controls using contrast changes in colour photography (ie, Weber Contrast) and the non-invasive optical method Spatial Frequency Domain Imaging (SFDI). This technology can be used to quantify the structural and metabolic properties of in-vivo tissue by measuring oxyhaemoglobin concentration (HbO2 ), deoxyhaemoglobin concentration (Hb), and oxygen saturation (StO2 ) within the visible boundaries of each wound. We also evaluated the changes in inducible nitric oxide synthase (iNOS) in the dermis using immunohistochemistry. Contrast changes in colour photographs showed that diabetic rats healed at a slower rate in comparison with non-diabetic control, with the most significant change occurring at 7 days after the punch biopsy. We observed lower HbO2 , StO2 , and elevated Hb concentrations in the diabetic wounds. The iNOS level was higher in the dermis of the diabetic rats compared with the non-diabetic rats. Our results showed that, in diabetes, there is higher level of iNOS that can lead to an observed reduction in HbO2 levels. iNOS is linked to increased inflammation, leading to prolonged wound healing. Our results suggest that SFDI has potential as a non-invasive assessment of markers of wound-healing impairment.

Nano-silver modified porcine small intestinal submucosa for the treatment of infected partial-thickness burn wounds

BACKGROUND AND AIM

Silver has been widely used as a topical antimicrobial agent in burn wound care. In a previous study, we demonstrated the introduction of nano-silver particles to porcine small intestinal submucosa (NS-PSIS) led to significant enhancement in antibacterial property in repairing contaminated abdominal defect. In this study, we explored the efficacy of NS-PSIS in the treatment of Pseudomonas aeruginosa-infected partial-thickness burn wounds.

METHODS

48 male Sprague-Dawley rats were divided into four groups of equal number. Standardized and reproducible Pseudomonas aeruginosa-infected partial-thickness thermal burns wound model were created using these rats. NS-PSIS, PSIS (porcine small intestinal submucosa) or lipido-colloid dressingss (Urgotul™) were tested for 14days to assess their ability to heal the rats' burn wounds. Control group was without any treatment after the establishment of infected burn-wound. The wound contraction rate, animal body weight change, histological examination, and the quantification of IL-6 and C-reactive protein (CRP) were measured to evaluate the healing effects.

RESULTS

NS-PSIS significantly promoted wound healing and recovered the normal growth of rats. There were significantly lower expression levels of pro-inflammatory cytokine (IL-6) and CRP in NS-PSIS group as compared with the PSIS or Urgotul group in the treatment of infected partial-thickness burn wounds. Histological exams revealed significant less inflammatory cells infiltrating, more re-epithelization and neovascularization in NS-PSIS group. There were also less inflammatory cells infiltrations in the major organs in NS-PSIS group.

CONCLUSIONS

Nano-silver modified porcine small intestinal submucosa (NS-PSIS) can be used as a biological derivative dressing for the treatment of infected partial-thickness burn wounds.

Macrophage functions in wound healing

Macrophages play a crucial role in regeneration and consecutive phases of wound healing. In this review, we summarise current knowledge on the ontogeny, origin, phenotypical heterogeneity, and functional exchangeability of macrophages participating in these processes. We also describe the genetic, pharmacologic, and bioengineering methods for manipulation of macrophage phenotype and functions and their potential for development of the novel, clinically applicable therapies.

PEG-Plasma Hydrogels Increase Epithelialization Using a Human Ex Vivo Skin Model

In vitro cell culture methods are used extensively to study cellular migration, proliferation, and differentiation, which play major roles in wound healing but the results often do not translate to the in vivo environment. One alternative would be to establish an ex vivo model utilizing human discarded skin to evaluate therapies in a more natural setting. The purpose of this study was to institute such a model by creating ‘wounds’ in the center of a piece of discarded skin and treating them with three different biomaterials: collagen, polyethylene glycol (PEG)-fibrin, or PEG-platelet free plasma (PFP). Explants were cultured for 14 days with supernatant and microscopy images collected every 3 days to assess cytotoxicity and epithelialization. After 14 days, the explants were fixed, sectioned, and stained for cytokeratin-10 (CK-10), alpha-smooth muscle actin (α-SMA), and wheat germ (WG). Compared to controls, similar levels of cytotoxicity were detected for 12 days which decreased slightly at day 14. The PEG-PFP hydrogel-treated wounds epithelialized faster than other treatments at days 6 to 14. A 6-8 cell layer thick CK-10+ stratified epidermis had developed over the PEG-PFP hydrogel and cells co-stained by WG and α-SMA were observed within the hydrogel. An ex vivo model was established that can be used practically to screen different therapies exploring wound healing.

Review: Multimodal bioactive material approaches for wound healing

Wound healing is a highly complex process of tissue repair that relies on the synergistic effect of a number of different cells, cytokines, enzymes, and growth factors. A deregulation in this process can lead to the formation of a non-healing chronic ulcer. Current treatment options, such as collagen wound dressings, are unable to meet the demand set by the wound environment. Therefore, a multifaceted bioactive dressing is needed to elicit a targeted affect. Wound healing strategies seek to develop a targeted effect through the delivery of a bioactive molecule to the wound by a hydrogel or a polymeric scaffold. This review examines current biomaterial and small molecule-based approaches that seek to develop a bioactive material for targeted wound therapy and accepted wound healing models for testing material efficacy.

A Gelatin Hydrogel-Containing Nano-Organic PEI⁻Ppy with a Photothermal Responsive Effect for Tissue Engineering Applications

The introduction and designing of functional thermoresponsive hydrogels have been recommended as recent potential therapeutic approaches for biomedical applications. The development of bioactive materials such as thermosensitive gelatin-incorporated nano-organic materials with a porous structure and photothermally triggerable and cell adhesion properties may potentially achieve this goal. This novel class of photothermal hydrogels can provide an advantage of hyperthermia together with a reversibly transformable hydrogel for tissue engineering. Polypyrrole (Ppy) is a bioorganic conducting polymeric substance and has long been used in biomedical applications owing to its brilliant stability, electrically conductive features, and excellent absorbance around the near-infrared (NIR) region. In this study, a cationic photothermal triggerable/guidable gelatin hydrogel containing a polyethylenimine (PEI)⁻Ppy nanocomplex with a porous microstructure was established, and its physicochemical characteristics were studied through dynamic light scattering, scanning electronic microscopy, transmission electron microscopy, an FTIR; and cellular interaction behaviors towards fibroblasts incubated with a test sample were examined via MTT assay and fluorescence microscopy. Photothermal performance was evaluated. Furthermore, the in vivo study was performed on male Wistar rat full thickness excisions model for checking the safety and efficacy of the designed gelatin⁻PEI⁻Ppy nanohydrogel system in wound healing and for other biomedical uses in future. This photothermally sensitive hydrogel system has an NIR-triggerable property that provides local hyperthermic temperature by PEI⁻Ppy nanoparticles for tissue engineering applications. Features of the designed hydrogel may fill other niches, such as being an antibacterial agent, generation of free radicals to further improve wound healing, and remodeling of the promising photothermal therapy for future tissue engineering applications.

Development of tensile strength methodology for murine skin wound healing

In this study, a methodology was evaluated and improved to quickly measure the tensile strength of murine skin in a biomechanical assay for an incisional wound healing model. The aim was to streamline and enhance the wound model, skin specimen preparation, and tensile test so that large numbers of fresh tissue could be tested reliably and rapidly. Linear incisions of 25-mm length were made in the dorsal skin of mice along the spine and metallic staples were used to close the wound. After 20 days, the mice were sacrificed, and a square-shaped section of skin containing the linear incision was excised. Two metallic punches were fabricated and used to punch 15-mm long strips of skin of 2 mm width whose length was orthogonal to the direction of incision. The tensiometer configuration was modified to expedite tensile measurements on fresh skin, and load-to-failure was measured for each strip of skin from the cephalad to the caudal region. We evaluated sources of error in the animal model and the testing protocol and developed procedures to maximize speed and reproducibility in tensile strength measurements. This report provides guidance for efficient and reproducible tensile strength measurement of large numbers of skin specimens from freshly sacrificed animals.

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Tattoo placement to identify the two ends of the healing incisional wound assisted in decreasing error in the position and orientation of tensile strips.

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Custom-made punches to prepare skin strips for tensile testing helped conduct tensile tests of fresh tissue rapidly.

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Alteration of the manual grips of the tensile tester enabled specimens to be gripped rapidly to significantly accelerate testing for each skin strip.

Adipose-derived stem cells improve full-thickness skin grafts in a rat model

To investigate the effects of heterologous adipose-derived stem cells (ADSCs) on autologous full-thickness skin grafts, we designed a first-intention healing model using Wistar rats. We harvested and sutured two full-thickness skin grafts in the dorsal recipient beds of 15 rats, randomized into three groups. In the treatment group, 1 × 10⁶ ADSCs resuspended in saline solution (200 μL) were administered subcutaneously to the skin graft. The control group received only saline solution subcutaneously, whereas the negative control group did not receive any treatment. Compressive dressings were maintained until postoperative day 5. The grafts were assessed by two observers, who checked for the presence of epidermolysis on day 14. Planimetry showed the relative areas of normal skin, redness, ulceration, and contraction. Graft samples were obtained on day 14 and stained with hematoxylin and eosin and Masson's trichrome. Epidermal analysis evaluated thickening, keratosis, acanthosis, hydropic degeneration, and inflammatory infiltrate. Dermal evaluation investigated the absence of hair follicles, granulation tissue formation, presence of inflammatory infiltrate, and collagen deposition. Immunohistochemistry was performed for dermal anti-VEGF and epidermal anti-Ki-67 staining. The ADSC group presented better macroscopic aspects, lower incidence of epidermolysis, and less loss of hair follicles. In addition, the ADSC group presented the lowest frequency of histopathological changes in the dermis and epidermis, as well as the largest subcutaneous and granulation tissue VEGF averages and the weakest Ki-67 staining of the epidermal basal layer. Subcutaneous administration of ADSCs may improve the integration of skin grafts, reducing the deleterious effects of ischemia and reperfusion injury.

Comparative regenerative mechanisms across different mammalian tissues

Stimulating regeneration of complex tissues and organs after injury to effect complete structural and functional repair, is an attractive therapeutic option that would revolutionize clinical medicine. Compared to many metazoan phyla that show extraordinary regenerative capacity, which in some instances persists throughout life, regeneration in mammalians, particularly humans, is limited or absent. Here we consider recent insights in the elucidation of molecular mechanisms of regeneration that have come from studies of tissue homeostasis and injury repair in mammalian tissues that span the spectrum from little or no self-renewal, to those showing active cell turnover throughout life. These studies highlight the diversity of factors that constrain regeneration, including immune responses, extracellular matrix composition, age, injury type, physiological adaptation, and angiogenic and neurogenic capacity. Despite these constraints, much progress has been made in elucidating key molecular mechanisms that may provide therapeutic targets for the development of future regenerative therapies, as well as previously unidentified developmental paradigms and windows-of-opportunity for improved regenerative repair.

Comparative in vivo evaluation of novel formulations based on alginate and silver nanoparticles for wound treatments

In the present study, possibilities for using novel nanocomposites based on alginate and silver nanoparticles for wound treatment were investigated in a second-degree thermal burn model in Wistar rats. Silver nanoparticles (AgNPs) were electrochemically synthesized in alginate solutions that were further utilized to obtain the Ag/alginate solution and microfibers for subsequent in vivo studies. Daily applications of the Ag/alginate colloid solution, containing AgNPs, alginate and ascorbic acid (G3), wet Ag/alginate microfibers containing AgNPs (G5) and dry Ag/alginate microfibers containing AgNPs (G6) were compared to treatments with a commercial cream containing silver sulfadiazine (G2) and a commercial Ca-alginate wound dressing containing silver ions (G4), as well as to the untreated controls (G1). Results of the in vivo study have shown faster healing in treated wounds, which completely healed on day 19 (G4, G5 and G6) and 21 (G2 and G3) after the thermal injury, while the period for complete reepitelization of untreated wounds (G1) was 25 days. The macroscopic analysis has shown that scabs fell off between day 10 and 12 after the thermal injury induction in treated groups, whereas between day 15 and 16 in the control group. These macroscopic findings were supported by the results of histopathological analyses, which have shown enhanced granulation and reepithelization, reduced inflammation and improved organization of the extracellular matrix in treated groups without adverse effects. Among the treated groups, dressings based on Ca-alginate (G4-G6) induced enhanced healing as compared to the other two groups (G2, G3), which could be attributed to additional stimuli of released Ca²⁺. The obtained results indicated potentials of novel nanocomposites based on alginate and AgNPs for therapeutic applications in wound treatments.

3D printing of hydrogel composite systems: Recent advances in technology for tissue engineering

Three-dimensional (3D) printing of hydrogels is now an attractive area of research due to its capability to fabricate intricate, complex and highly customizable scaffold structures that can support cell adhesion and promote cell infiltration for tissue engineering. However, pure hydrogels alone lack the necessary mechanical stability and are too easily degraded to be used as printing ink. To overcome this problem, significant progress has been made in the 3D printing of hydrogel composites with improved mechanical performance and biofunctionality. Herein, we provide a brief overview of existing hydrogel composite 3D printing techniques including laser based-3D printing, nozzle based-3D printing, and inkjet printer based-3D printing systems. Based on the type of additives, we will discuss four main hydrogel composite systems in this review: polymer- or hydrogel-hydrogel composites, particle-reinforced hydrogel composites, fiber-reinforced hydrogel composites, and anisotropic filler-reinforced hydrogel composites. Additionally, several emerging potential applications of hydrogel composites in the field of tissue engineering and their accompanying challenges are discussed in parallel.

The mechanical fingerprint of murine excisional wounds

A multiscale mechanics approach to the characterization of murine excisional wounds subjected to uniaxial tensile loading is presented. Local strain analysis at a physiological level of tension uncovers the presence of two distinct regions within the wound: i) a very compliant peripheral cushion and ii) a core area undergoing modest deformation. Microstructural visualizations of stretched wound specimens show negligible engagement of the collagen located in the center of a 7-day old wound; fibers remain coiled despite the applied tension, confirming the existence of a mechanically isolated wound core. The compliant cushion located at the wound periphery appears to protect the newly-formed tissue from excessive deformation during the phase of new tissue formation. The early remodeling phase (day 14) is characterized by a restored mechanical connection between far field and wound center. The latter remains less deformable, a characteristic possibly required for cell activities during tissue remodeling. The distribution of fibrillary collagens at these two time points corresponds well to the identified heterogeneity of mechanical properties of the wound region. This novel approach provides new insight into the mechanical properties of wounded skin and will be applicable to the analysis of compound-treated wounds or wounds in genetically modified tissue.

STATEMENT OF SIGNIFICANCE

Biophysical characterization of healing wounds is crucial to assess the recovery of the skin barrier function and the associated mechanobiological processes. For the first time, we performed highly resolved local deformation analysis to identify mechanical characteristics of the wound and its periphery. Our results reveal the presence of a compliant cushion surrounding a stiffer wound core; we refer to this heterogeneous mechanical behavior as "mechanical fingerprint" of the wound. The mechanical response is shown to progress towards that of the intact skin as healing takes place. Histology and multiphoton microscopy suggest that wounded skin recovers its mechanical function via progressive reconnection of the newly-deposited collagen fibers with the surrounding intact matrix.

Topical use and systemic action of green and roasted coffee oils and ground oils in a cutaneous incision model in rats (Rattus norvegicus albinus)

Introduction

Wounds are a common health problem. Coffee is widely consumed and its oil contains essential fatty acids. We evaluated the local (skin) and systemic effects associated with the topical use of coffee oils in rats.

Methods

Punch skin wounds (6 mm) incisions were generated on the backs of 75 rats. Saline (SS), mineral oil (MO), green coffee oil (GCO), roasted coffee oil (RCO), green coffee ground oil (GCGO) or roasted coffee ground oil (RCGO) were topically applied to the wounds. Healing was evaluated by visual and histological/morphometric optical microscopy examination; second harmonics generation (SHG) microscopy, wound tissue q-PCR (values in fold-change) and blood serum (ELISA, values in pg/mL).

Results

RCO treated animals presented faster wound healing (0.986 vs. 0.422), higher mRNA expression of IGF-1 (2.78 vs. 1.00, p = 0.01), IL-6 (10.72 vs. 1.00, p = 0.001) and IL-23 (4.10 vs. 1.2, p = 0.05) in early stages of wound healing; higher IL-12 (3.32 vs. 1.00, p = 0.05) in the later stages; and lower serum levels of IFN-γ (11.97 vs. 196.45, p = 0.01). GCO treatment led to higher mRNA expression of IL-6 (day 2: 7.94 vs. 1.00, p = 0.001 and day 4: 6.90 vs. 1.00, p = 0.01) and IL-23 (7.93 vs. 1.20, p = 0.001) in the early stages. The RCO treatment also produced higher serum IFN-α levels throughout the experiment (day 2: 52.53 vs. 21.20; day 4: 46.98 vs.21.56; day 10: 83.61 vs. 25.69, p = 0.05) and lower levels of IL-4 (day 4: 0.9 vs.13.36, p = 0.01), adiponectin (day 10: 8,367.47 vs. 16,526.38, p = 0.001) and IFN-γ (day 4: 43.03 vs.196.45, p = 0.05). The SHG analysis showed a higher collagen density in the RCO and GCO treatments (p = 0.05).

Conclusion

Topical treatment with coffee oils led to systemic actions and faster wound healing in rats. Further studies should be performed are necessary to assess the safety of topical vegetal oil use for skin lesions.

Design and Testing of an Experimental Steam-Induced Burn Model in Rats

Background

Most of the current models for experimental burns pose difficulties in ensuring consistency and standardization.

Aim of Study

We aimed to develop an automated, reproducible technique for experimental burns using steam-based heat transfer.

Methods

The system developed for steam exposure was based on a novel, integrated, computer-controlled design. Three groups of rats were exposed to steam for 1, 3, and 7 seconds. The lesions were evaluated after 20 minutes, 48 hours, and 72 hours after burn induction.

Results

One-second steam application produced a superficial second-degree burn; three-second application induced deep second-degree burn; and seven-second application led to a third-degree burn.

Conclusion

The high level of automation of our integrated, computer-controlled system makes the difference between our system and other models, by ensuring the control of the duration of exposure, temperature, and pressure and eliminating as many potential human generated errors as possible. The automated system can accurately reproduce specific types of burns, according to histological assessment. This model could generate the reproducible data needed in the study of burn pathology and in order to assess new treatments.

Enhanced wound-healing performance of a phyto-polysaccharide-enriched dressing - a preclinical small and large animal study

Alginate is a natural rich anionic polysaccharide (APS), commonly available as calcium alginate (CAPS). It can maintain a physiologically moist microenvironment, which minimises bacterial infection and facilitates wound healing at a wound site. Patients with burn injuries suffer from pain and an inflammatory response. In this study, we evaluated the CAPS dressing and traditional dressing containing carboxymethyl cellulose (CMC) for wound healing and scar tissue formation in a burn model of rat and swine. In our pilot study of a burn rat model to evaluate inflammatory response and wound healing, we found that the monocyte chemoattractant protein (MCP)-1 and transforming growth factor (TGF)-β were up-regulated in the CAPS treatment group. Next, the burn swine models tested positive for MCP-1 in a Gram-positive bacterial infection, and there was overproduction of TGF-β during the burn wound healing process. Rats were monitored daily for 1 week for cytokine assay and sacrificed on day 28 post-burn injury. The swine were monitored over 6 weeks. We further examined the pain and related factors and inflammatory cytokine expression in a rodent burns model monitored everyday for 7 days post-burn. Our results revealed that the efficacy of the dressing containing CAPS for wound repair post-burn was better than the CMC dressing with respect to natural wound healing and scar formation. The polysaccharide-enriched dressing exerted an antimicrobial effect on burn wounds, regulated the inflammatory response and stimulated anti-inflammatory cytokine release. However, one pain assessment method showed no significant difference in the reduction in levels of adenosine triphosphate in serum of rats after wound dressing in either the CAPS or CMC group. In conclusion, a polysaccharide-enriched dressing outperformed a traditional dressing in reducing wound size, minimising hypertrophic scar formation, regulating cytokines and maximising antimicrobial effects.

Minocycline modulates NFκB phosphorylation and enhances antimicrobial activity against Staphylococcus aureus in mesenchymal stromal/stem cells

Background

Mesenchymal stromal/stem cells (MSCs) have demonstrated pro-healing properties due to their anti-inflammatory, angiogenic, and even antibacterial properties. We have shown previously that minocycline enhances the wound healing phenotype of MSCs, and MSCs encapsulated in poly(ethylene glycol) and gelatin-based hydrogels with minocycline have antibacterial properties against Staphylococcus aureus (SA). Here, we investigated the signaling pathway that minocycline modulates in MSCs which results in their enhanced wound healing phenotype and determined whether preconditioning MSCs with minocycline has an effect on antimicrobial activity. We further investigated the in-vivo antimicrobial efficacy of MSC and antibiotic-loaded hydrogels in inoculated full-thickness cutaneous wounds.

Methods

Modulation of cell signaling pathways in MSCs with minocycline was analyzed via western blot, immunofluorescence, and ELISA. Antimicrobial efficacy of MSCs pretreated with minocycline was determined by direct and transwell coculture with SA. MSC viability after SA coculture was determined via a LIVE/DEAD® stain. Internalization of SA by MSCs pretreated with minocycline was determined via confocal imaging. All protein and cytokine analysis was done via ELISA. The in-vivo antimicrobial efficacy of MSC and antibiotic-loaded hydrogels was determined in Sprague–Dawley rats inoculated with SA. Two-way ANOVA for multiple comparisons was used with Bonferroni test assessment and an unpaired two-tailed Student’s t test was used to determine p values for all assays with multiple or two conditions, respectively.

Results

Minocycline leads to the phosphorylation of transcriptional nuclear factor-κB (NFκB), but not c-Jun NH₂-terminal kinase (JNK) or mitogen-activated protein kinase (ERK). Inhibition of NFκB activation prevented the minocycline-induced increase in VEGF secretion. Preconditioning of MSCs with minocycline led to a reduced production of the antimicrobial peptide LL-37, but enhanced antimicrobial activity against SA via an increased production of IL-6 and SA internalization. MSC and antibiotic-loaded hydrogels reduced SA bioburden in inoculated wounds over 3 days and accelerated reepithelialization.

Conclusions

Minocycline modulates the NFκB pathway in MSCs that leads to an enhanced production of IL-6 and internalization of SA. This mechanism may have contributed to the in-vivo antibacterial efficacy of MSC and antibiotic-loaded hydrogels.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0623-1) contains supplementary material, which is available to authorized users.

Laboratory Models for the Study of Normal and Pathologic Wound Healing

Current knowledge of wound healing is based on studies using various in vitro and in vivo wound models. In vitro models allow for biological examination of specific cell types involved in wound healing. In vivo models generally provide the full spectrum of biological responses required for wound healing, including inflammation and angiogenesis, and provide cell-cell interactions not seen in vitro. In this review, the authors aim to delineate the most relevant wound healing models currently available and to discuss their strengths and limitations in their approximation of the human wound healing processes to aid scientists in choosing the most appropriate wound healing models for designing, testing, and validating their experiments.

The effect of color type on early wound healing in farmed mink (Neovison vison)

BACKGROUND

Individual differences of mink, including color type, are speculated to affect the course of wound healing, thereby impacting wound assessment and management on the farms, as well as the assessment of wounds in forensic cases. In this study, we examined the effect of color type on early wound healing in farmed mink. Full thickness excisional wounds (2 × 2 cm) were made on the back in 18 mink of the color types Brown, Silverblue and Blue Iris. Gross and microscopic pathology of the wounds was evaluated 2 days post-wounding together with degree of wound size reduction, presence of bacteria and blood analyses.

RESULTS

Pathological examination on day 2 showed the greatest mean wound size reduction in Brown mink (11.0%) followed by Blue Iris (7.9%) and Silverblue (1.6%). Bacteria were cultured from all wounds, and predominantly Staphylococcus species were recovered in mixed or pure culture. Histopathology from day 2 wounds showed a scab overlying necrotic wound edges, which were separated from underlying vital tissue by a demarcation zone rich in polymorphonuclear leukocytes. Fibroblasts and plump endothelial cells were more numerous in the deeper tissues. Complete blood count parameters were within normal ranges in most cases, however, the mink showed mildly to markedly decreased hematocrit and six mink of the color types Silverblue and Blue Iris showed moderately elevated numbers of circulating segmented neutrophils on day 2. There was a marked increase in concentration of serum amyloid A from day 0 to day 2 in all color types.

CONCLUSIONS

We have described differences in early wound healing between mink of the color types Brown, Silverblue and Blue Iris by use of an experimental wound model in farmed mink. The most pronounced difference pertained to the degree of wound size reduction which was greatest in Brown mink, followed by Blue Iris and Silverblue, respectively.

A review of the evidence for threshold of burn injury

INTRODUCTION

Burn injury is common and depth is one measure of severity. Although the depth of burn injury is determined by many factors, the relationship between the temperature of the injurious agent and exposure duration, known as the time-temperature relationship, is widely accepted as one of the cornerstones of burn research. Moritz and Henriques first proposed this relationship in 1947 and their seminal work has been cited extensively. However, over the years, readers have misinterpreted their findings and incorporated misleading information about the time-temperature relationship into a wide range of industrial standards, burn prevention literature and medicolegal opinion.

AIM

The purpose of this paper is to present a critical review of the evidence that relates temperature and time to cell death and the depth of burn injury. These concepts are used by researchers, burn prevention strategists, burn care teams and child protection professionals involved in ascertaining how the mechanism of burning relates to the injury pattern and whether the injury is consistent with the history.

REVIEW METHODS

This review explores the robustness of the currently available evidence. The paper summarises the research from burn damage experimental work as well as bioheat transfer models and discusses the merits and limitations of these approaches.

REVIEW FINDINGS

There is broad agreement between in vitro and in vivo studies for superficial burns. There is clear evidence that the perception of pain in adult human skin occurs just above 43°C. When the basal layer of the epidermis reaches 44°C, burn injury occurs. For superficial dermal burns, the rate of tissue damage increases logarithmically with a linear increase in temperature. Beyond 70°C, rate of damage is so rapid that interpretation can be difficult. Depth of injury is also influenced by skin thickness, blood flow and cooling after injury. There is less clinical evidence for a time-temperature relationship for deep or subdermal burns. Bioheat transfer models are useful in research and becoming increasingly sophisticated but currently have limited practical use. Time-temperature relationships have not been established for burns in children's skin, although standards for domestic hot water suggest that the maximum temperature should be revised downward by 3-4°C to provide adequate burn protection for children.

CONCLUSION

Time-temperature relationships established for pain and superficial dermal burns in adult human skin have an extensive experimental modeling basis and reasonable clinical validation. However, time-temperature relationships for subdermal burns, full thickness burns and burn injury in children have limited clinical validation, being extrapolated from other data, and should be used with caution, particularly if presented during expert evidence.

The characterization of a full-thickness excision open foot wound model in n5-streptozotocin (STZ)-induced type 2 diabetic rats that mimics diabetic foot ulcer in terms of reduced blood circulation, higher C-reactive protein, elevated inflammation, and reduced cell proliferation

Delayed foot wound healing is a major complication attributed to hyperglycemia in type 2 diabetes mellitus (DM) patients, and these wounds may develop into foot ulcers. There are at least two types of DM wound models used in rodents to study delayed wound healing. However, clinically relevant animal models are not common. Most models use type 1 DM rodents or wounds created on the back rather than on the foot. An open full-thickness excision wound on the footpad of type 2 DM rats is more clinically relevant, but such a model has not yet been characterized systematically. The objective of this study was to investigate and characterize how DM affected a full-thickness excision open foot wound in n5-streptozotocin (n5-STZ)-induced type 2 DM rats. We hypothesized that elevated inflammation, reduced blood circulation, and cell proliferation due to hyperglycemia could delay the wound healing of DM rats. The wounds of DM rats were compared with those of non-DM rats (Ctrl) at Days 1 and 8 post wounding. The wound healing process of the DM rats was significantly delayed compared with that of the Ctrl rats. The DM rats also had higher C-reactive protein (CRP) and lower blood circulation and proliferating cell nuclear antigen (PCNA) in DM wounds. This confirmed that elevated inflammation and reduced blood flow and cell proliferation delayed foot wound healing in the n5-STZ rats. Hence, this open foot wound animal model provides a good approach to study the process of delayed wound healing.

Xenogeneic transplantation of human adipose-derived stem cell sheets accelerate angiogenesis and the healing of skin wounds in a Zucker Diabetic Fatty rat model of obese diabetes

Introduction

Diabetic patients with foot ulcers often suffer impaired wound healing due to diabetic neuropathy and blood flow disturbances. Direct injection of human adipose-derived stem cells (hASCs) effectively accelerates wound healing, although hASCs are relatively unstable.

Methods

We developed an optimized protocol to engineer hASC sheets using temperature-responsive culture dishes to enhance the function and stability of transplanted cells used for regenerative medicine. Here, we evaluated the efficacy of hASC sheets for enhancing wound healing. For this purpose, we used a xenogeneic model of obese type 2 diabetes, the Zucker Diabetic Fatty rat (ZDF rat), which displays full-thickness skin defects. We isolated hASCs from five donors, created hASC sheets, and transplanted the hASC sheets along with artificial skin into full-thickness, large skin defects (15-mm diameter) of ZDF rats.

Results

The hASC sheets secreted angiogenic growth factors. Transplantation of the hASC sheets combined with artificial skin increased blood vessel density and dermal thickness, thus accelerating wound healing compared with that in the controls. Immunohistochemical analysis revealed significantly more frequent neovascularization in xenografted rats of the transplantation group, and the transplanted hASCs were localized to the periphery of new blood vessels.

Conclusion

This xenograft model may contribute to the use of human cell tissue-based products (hCTPs) and the identification of factors produced by hCTPs that accelerate wound healing.

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We established a protocol for human adipose-derived stem cells (hASC) sheets.

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The hASC sheets secreted angiogenic growth factors.

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Xenogeneic hASC sheet transplantation accelerated wound healing in diabetic rats.

Terahertz Imaging of Cutaneous Edema: Correlation With Magnetic Resonance Imaging in Burn Wounds

OBJECTIVE

In vivo visualization and quantification of edema, or 'tissue swelling' following injury, remains a clinical challenge. Herein, we investigate the ability of reflective terahertz (THz) imaging to track changes in tissue water content (TWC)-the direct indicator of edema-by comparison to depth-resolved magnetic resonance imaging (MRI) in a burn-induced model of edema.

METHODS

A partial thickness and full thickness burns were induced in an in vivo rat model to elicit unique TWC perturbations corresponding to burn severity. Concomitant THz surface maps and MRI images of both burn models were acquired with a previously reported THz imaging system and T₂-weighted MRI, respectively, over 270 min. Reflectivity was analyzed for the burn contact area in THz images, while proton density (i.e., mobile TWC) was analyzed for the same region at incrementally increasing tissue depths in companion, transverse MRI images. A normalized cross correlation of THz and depth-dependent MRI measurements was performed as a function of time in histologically verified burn wounds.

RESULTS

For both burn types, strong positive correlations were evident between THz reflectivity and MRI data analyzed at greater tissue depths (>258 μm). MRI and THz results also revealed biphasic trends consistent with burn edema pathogenesis.

CONCLUSION

This paper offers the first in vivo correlative assessment of mobile TWC-based contrast and the sensing depth of THz imaging.

SIGNIFICANCE

The ability to implement THz imaging immediately following injury, combined with TWC sensing capabilities that compare to MRI, further support THz sensing as an emerging tool to track fluid in tissue.

A Model of Free Tissue Transfer: The Rat Epigastric Free Flap

Free tissue transfer has been increasingly used in clinical practice since the 1970s, allowing reconstruction of complex and otherwise untreatable defects resulting from tumor extirpation, trauma, infections, malformations or burns. Free flaps are particularly useful for reconstructing highly complex anatomical regions, like those of the head and neck, the hand, the foot and the perineum. Moreover, basic and translational research in the area of free tissue transfer is of great clinical potential. Notwithstanding, surgical trainees and researchers are frequently deterred from using microsurgical models of tissue transfer, due to lack of information regarding the technical aspects involved in the operative procedures. The aim of this paper is to present the steps required to transfer a fasciocutaneous epigastric free flap to the neck in the rat.

This flap is based on the superficial epigastric artery and vein, which originates from and drain into the femoral artery and vein, respectively. On average the caliber of the superficial epigastric vein is 0.6 to 0.8 mm, contrasting with the 0.3 to 0.5 mm of the superficial epigastric artery. Histologically, the flap is a composite block of tissues, containing skin (epidermis and dermis), a layer of fat tissue (panniculus adiposus), a layer of striated muscle (panniculus carnosus), and a layer of loose areolar tissue.

Succinctly, the epigastric flap is raised on its pedicle vessels that are then anastomosed to the external jugular vein and to the carotid artery on the ventral surface of the rat's neck. According to our experience, this model guarantees the complete survival of approximately 70 to 80% of epigastric flaps transferred to the neck region. The flap can be evaluated whenever needed by visual inspection. Hence, the authors believe this is a good experimental model for microsurgical research and training.

John MA, Grundfest WS, Taylor ZD. Non-invasive terahertz imaging of tissue water content for flap viability assessment

Accurate and early prediction of tissue viability is the most significant determinant of tissue flap survival in reconstructive surgery. Perturbation in tissue water content (TWC) is a generic component of the tissue response to such surgeries, and, therefore, may be an important diagnostic target for assessing the extent of flap viability in vivo. We have previously shown that reflective terahertz (THz) imaging, a non-ionizing technique, can generate spatially resolved maps of TWC in superficial soft tissues, such as cornea and wounds, on the order of minutes. Herein, we report the first in vivo pilot study to investigate the utility of reflective THz TWC imaging for early assessment of skin flap viability. We obtained longitudinal visible and reflective THz imagery comparing 3 bipedicled flaps (i.e. survival model) and 3 fully excised flaps (i.e. failure model) in the dorsal skin of rats over a postoperative period of 7 days. While visual differences between both models manifested 48 hr after surgery, statistically significant (p < 0.05, independent t-test) local differences in TWC contrast were evident in THz flap image sets as early as 24 hr. Excised flaps, histologically confirmed as necrotic, demonstrated a significant, yet localized, reduction in TWC in the flap region compared to non-traumatized skin. In contrast, bipedicled flaps, histologically verified as viable, displayed mostly uniform, unperturbed TWC across the flap tissue. These results indicate the practical potential of THz TWC sensing to accurately predict flap failure 24 hours earlier than clinical examination.

Antioxidant and wound healing activity of Lavandula aspic L. ointment

Lavandula aspic L. is a strongly aromatic shrub plant of the Lamiaceae family and traditionally used in herbal medicine for the treatment of several skin disorders, including wounds, burns, and ulcers. The present study aimed to investigate the composition and in vitro antioxidant activity of lavender essential oil. In addition, it aimed to evaluate the excision wound healing activity and antioxidant property of a Lavandula aspic L. essential oil formulated in ointment using a rat model. The rats were divided into five groups of six animals each. The test groups were topically treated with the vehicle, lavender ointment (4%) and a reference drug, while the control group was left untreated. Wound healing efficiency was determined by monitoring morphological and biochemical parameters and skin histological analysis. Wound contraction and protein synthesis were also determined. Antioxidant activity was assessed by the determination of MDA rates and antioxidant enzymes (GPx, catalase and superoxide dismutase). The treatment with lavender ointment was noted to significantly enhance wound contraction rate (98%) and protein synthesis. Overall, the results provided strong support for the effective wound healing activity of lavender ointment, making it a promising candidate for future application as a therapeutic agent in tissue repairing processes associated with skin injuries.

Comparison of the effects of gabapentin and pregabalin on wound healing in rats

Gabapentinoids are effective adjunct drugs for reducing postoperative pain. However, the effects of gabapentinoids on wound healing have not been evaluated yet. In this study we evaluated their effects on wound healing. A total of 17 male Wistar-Albino rats, 250-350 g, were divided into three groups randomly: control group (n = 5, 2 ml saline), gabapentin group (n = 6, 20 mg/kg gabapentin) and pregabalin group (n = 6, 20 mg/kg pregabalin). Until day 13 inflammation scores were significantly lower (P < 0·05) and wound healing was significantly better in the control group when compared with gabapentin and pregabalin groups (P < 0·001). Inflammation scores were significantly lower in pregabalin group when compared with gabapentin group until day 13. But wound healing was significantly better in gabapentin group than in pregabalin group between days 13 and 21. In conclusion when gabapentin and pregabalin were compared, although pregabalin decreases inflammation scores, gabapentin has better results in wound healing.

Titanium wound chambers for wound healing research

Standardized and reproducible animal models are crucial in medical research. Rodents are commonly used in wound healing studies since, they are easily available, affordable and simple to handle and house. However, the most significant limitation of rodent models is that the wounds heal by contraction while in humans the primary mechanisms of healing are reepithelialization and granulation tissue formation. The robust contraction results in faster wound closure that complicates the reproducibility of rodent studies in clinical trials. We have developed a titanium wound chamber for rodent wound healing research. The chamber is engineered from two pieces of titanium and is placed transcutaneously on the dorsum of a rodent. The chamber inhibits wound contraction and provides a means for controlled monitoring and sampling of the wound environment in vivo with minimal foreign body reaction. This technical report introduces two modalities utilizing the titanium chambers in rats: (1) Wound in a skin island model and, (2) Wound without skin model. Here, we demonstrate in rats how the "wound in a skin island model" slows down wound contraction and how the "wound without skin" model completely prevents the closure. The titanium wound chamber provides a reproducible standardized models for wound healing research in rodents.

Transparent crosslinked ultrashort peptide hydrogel dressing with high shape-fidelity accelerates healing of full-thickness excision wounds

Wound healing is a major burden of healthcare systems worldwide and hydrogel dressings offer a moist environment conducive to healing. We describe cysteine-containing ultrashort peptides that self-assemble spontaneously into hydrogels. After disulfide crosslinking, the optically-transparent hydrogels became significantly stiffer and exhibited high shape fidelity. The peptide sequence (LIVAGKC or LK₆C) was then chosen for evaluation on mice with full-thickness excision wounds. Crosslinked LK₆C hydrogels are handled easily with forceps during surgical procedures and offer an improvement over our earlier study of a non-crosslinked peptide hydrogel for burn wounds. LK₆C showed low allergenic potential and failed to provoke any sensitivity when administered to guinea pigs in the Magnusson-Kligman maximization test. When applied topically as a dressing, the medium-infused LK₆C hydrogel accelerated re-epithelialization compared to controls. The peptide hydrogel is thus safe for topical application and promotes a superior rate and quality of wound healing.

Cutaneous wound healing in aging small mammals: a systematic review

As the elderly population grows, so do the clinical and socioeconomic burdens of nonhealing cutaneous wounds, the majority of which are seen among persons over 60 years of age. Human studies on how aging effects wound healing will always be the gold standard, but studies have ethical and practical hurdles. Choosing an animal model is dictated by costs and animal lifespan that preclude large animal use. Here, we review the current literature on how aging effects cutaneous wound healing in small animal models and, when possible, compare healing across studies. Using a literature search of MEDLINE/PubMed databases, studies were limited to those that utilized full-thickness wounds and compared the wound-healing parameters of wound closure, reepithelialization, granulation tissue fill, and tensile strength between young and aged cohorts. Overall, wound closure, reepithelialization, and granulation tissue fill were delayed or decreased with aging across different strains of mice and rats. Aging in mice was associated with lower tensile strength early in the wound healing process, but greater tensile strength later in the wound healing process. Similarly, aging in rats was associated with lower tensile strength early in the wound healing process, but no significant tensile strength difference between young and old rats later in healing wounds. From studies in New Zealand White rabbits, we found that reepithelialization and granulation tissue fill were delayed or decreased overall with aging. While similarities and differences in key wound healing parameters were noted between different strains and species, the comparability across the studies was highly questionable, highlighted by wide variability in experimental design and reporting. In future studies, standardized experimental design and reporting would help to establish comparable study groups, and advance the overall knowledge base, facilitating the translatability of animal data to the human clinical condition.