Novel skin chamber for rat ischemic flap studies in regenerative wound repair

The rat as an animal model in chronic wound research: An update

The increasing global prevalence of chronic wounds underscores the growing importance of developing effective animal models for their study. This review offers a critical evaluation of the strengths and limitations of rat models frequently employed in chronic wound research and proposes potential improvements. It explores these models in the context of key comorbidities, including diabetes, venous and arterial insufficiency, pressure-induced blood flow obstruction, and infections. Additionally, the review examines important wound factors including age, sex, smoking, and the impact of anesthetic and analgesic drugs, acknowledging their substantial effects on research outcomes. A thorough understanding of these variables is crucial for refining animal models and can provide valuable insights for future research endeavors.

A Model to Study Wound Healing Over Exposed Avascular Structures in Rodents With a 3D-Printed Wound Frame

BACKGROUND

Soft tissue defects with exposed avascular structures require reconstruction with well-vascularized tissues. Extensive research is ongoing to explore tissue engineered products that provide durable coverage. However, there is a lack of controlled and affordable testbeds in the preclinical setting to reflect this challenging clinical scenario. We aimed to address this gap in the literature and develop a feasible and easily reproducible model in rodents that reflects an avascular structure in the wound bed.

METHODS

We created 20 × 20 mm full thickness wounds on the dorsal skin of Lewis rats and secured 0.5-mm-thick silicone sheets of varying sizes to the wound bed. A 3D-printed wound frame was designed to isolate the wound environment. Skin graft and free flap survival along with exposure of the underlying silicone was assessed. Rats were followed for 4 weeks with weekly dressing changes and photography. Samples were retrieved at the endpoint for tissue viability and histologic analysis.

RESULTS

The total wound surface area was constant throughout the duration of the experiment in all groups and the wound frames were well tolerated. The portion of the skin graft without underlying silicone demonstrated integration with the underlying fascia and a histologically intact epidermis. Gradual necrosis of the portion of the skin graft overlying the silicone sheet was observed with varying sizes of the silicone sheet. When the size of the silicone sheet was reduced from 50% of the wound surface area, the portion surviving over the silicone sheet increased at the 4-week timepoint. The free flap provided complete coverage over the silicone sheet.

CONCLUSION

We developed a novel model of rodent wound healing to maintain the same wound size and isolate the wound environment for up to 4 weeks. This model is clinically relevant to a complex wound with an avascular structure in the wound bed. Skin grafts failed to completely cover increasing sizes of the avascular structure, whereas the free flap was able to provide viable coverage. This cost-effective model will establish an easily reproducible platform to evaluate more complex bioengineered wound coverage solutions.

In Situ Monitoring and Assessment of Ischemic Skin Flap by High-Frequency Ultrasound and Quantitative Parameters

Skin flap surgery is a critical procedure for treating severe skin injury in which post-surgery lesions must well monitored and cared for noninvasively. In the present study, attempts using high-frequency ultrasound imaging, quantitative parameters, and statistical analysis were made to extensively assess variations in the skin flap. Experiments were arranged by incising the dorsal skin of rats to create a skin flap using the chamber model. Measurements, including photographs, 30 MHz ultrasound B-mode images, skin thickness, echogenicity, Nakagami statistics, and histological analysis of post-surgery skin flap, were performed. Photograph results showed that color variations in different parts of the skin flap may readily correspond to ischemic states of local tissues. Compared to post-surgery skin flap on day 7, both integrated backscatter (IB) and Nakagami parameter (m) of the distal part of tissues were increased, and those of the skin thickness were decreased. Overall, relative skin thickness, IB, and m of the distal part of post-surgery skin flap varied from 100 to 67%, -66 to -61 dB, and 0.48 to 0.36, respectively. These results demonstrate that this modality and quantitative parameters can be feasibly applied for long-term and in situ assessment of skin flap tissues.

Vascularization of cutaneous wounds by stem cells

Differentiated skin cells have limited self-renewal capacity; thus, the application of stem/progenitor cells, adult or induced stem cells, has attracted much attention for wound healing applications. Upon skin injury, vascularization, known as a highly dynamic process, occurs with the contribution of cells, the extracellular matrix, and relevant growth factors. Considering the importance of this process in tissue regeneration, several strategies have been proposed to enhance angiogenesis and accelerate wound healing. Previous studies report the effectiveness of stem/progenitor cells in skin wound healing by facilitating the vascularization process. This chapter reviews and highlights some of the key and recent investigations on application of stem/progenitor cells to induce skin revascularization after trauma.

Fibroblast Growth Factor 9 Inhibited Apoptosis in Random Flap via the ERK1/2-Nrf2 Pathway to Improve Tissue Survival

BACKGROUND

The application of random pattern skin flaps is limited in plastic surgery reconstruction due to necrosis. Fibroblast growth factor 9 (FGF9) was reported to exert a protective effect against myocardial damage and cerebral ischemia injury, but the impact of FGF9 in random flap survival is still unclear. In this study, we used a mouse model of random flaps to verify that FGF9 can directly increase flap survival area and blood flow intensity by promoting angiogenesis.

MATERIALS AND METHODS

In total, 84 male C57BL/6 mice weighing between 22 and 25 g were randomly divided into three groups (n = 28 each group). After skin flap operation, one group served as a control, a treatment group received FGF9, and a treatment group received FGF9+U0126. All flap samples were incised on postoperative day 7.

RESULTS

Our results showed that flap survival was significantly increased in the FGF9 group compared with that in the control group. This protective function was restrained by U0126. The results of histopathology, laser Doppler, and fluorescent staining all showed significant increases in capillary count, collagen deposition, and angiogenesis. FGF9 also significantly increased the expression of antioxidant stress proteins SOD1, eNOS, HO-1, vascular marker proteins CD31, VE cadherin, and pericyte marker protein PDGFRβ. Western blot showed that the phosphorylation degree of ERK1/2 increased after FGF9 treatment, and the expression of Nrf2, a downstream factor, was u-regulated. Western blot and immunofluorescence results of apoptosis-related proteins cleaved caspase-3, BAX, and Bcl2 showed that FGF9 inhibited apoptosis. ERK inhibitor U01926 reduced the beneficial effects of FGF9 on skin flap survival, including promoting angiogenesis, and showing antiapoptosis and antioxidative stress activities.

CONCLUSIONS

Exogenous FGF9 stimulates angiogenesis of random flap and survival of tissue. the impact of FGF9 is closely linked to the prevention of oxidative stress mediated by ERK1/2-Nrf2. In the function of FGF9 in promoting effective angiogenesis, there may be a close interaction in the FGF9-FGFR-PDGFR-ERK-VE cadherin pathway. In particular, PDGFR and VE cadherin may interact.

Challenges faced in developing an ideal chronic wound model

INTRODUCTION

Chronic wounds are a major drain on healthcare resources and can lead to substantial reductions in quality of life for those affected. Moreover, they often precede serious events such as limb amputations and premature death. In the long run, this burden is likely to escalate with an ageing population and lifestyle diseases such as obesity. Thus far, the identification of beneficial therapeutics against chronic wounds have been hindered by the lack of an ideal chronic wound animal model. Although animal models of delayed healing have been developed, none of these models fully recapitulate the complexity of the human chronic wound condition. Furthermore, most animals do not develop chronic wounds. Only the thoroughbred racehorse develops chronic ulcers.

AREAS COVERED

In this review, the different characteristics of chronic wounds that highlight its complexity are described. In addition, currently available models reflecting different aspects of chronic wound pathology and their relevance to human chronic wounds are discussed. This article concludes by listing relevant features representative of an ideal chronic wound model. Additionally, alternative approaches for the development of chronic wound models are discussed.

EXPERT OPINION

Delayed models of healing, including the streptozotocin diabetic model, skin flap model and magnet-induced IR models have emerged. While these models have been widely adopted for preclinical therapeutic testing, their relevance towards human chronic wounds remains debatable. In particular, current delayed healing models often fail to fully incorporate the key characteristics of chronic ulcers. Ultimately, more representative models are required to expedite the advancement of novel therapeutics to the clinic.

Skin Mast Cell Promotion in Random Skin Flaps in Rats using Bone Marrow Mesenchymal Stem Cells and Amniotic Membrane

Background

Skin flap procedures are employed in plastic surgery, but failure can lead to necrosis of the flap. Studies have used bone marrow mesenchymal stem cells (BM-MSCs) to improve flap viability. BM-MSCs and acellular amniotic membrane (AAM) have been introduced as alternatives. The objective of this study was to evaluate the effect of BM-MSCs and AAM on mast cells of random skin flaps (RSF) in rats.

Methods

RSFs (80 × 30 mm) were created on 40 rats that were randomly assigned to one of four groups, including (I) AAM, (II) BM-MSCs, (III) BM-MSCs/AAM, and (IV) saline (control). Transplantation was carried out during the procedure (zero day). Flap necrosis was observed on day 7, and skin samples were collected from the transition line of the flap to evaluate the total number and types of mast cells. The development and the total number of mast cells were related to the development of capillaries.

Results

The results of one-way ANOVA indicated that there was no statistically significant difference between the mean numbers of mast cell types for different study groups. However, the difference between the total number of mast cells in the study groups was statistically significant (p = 0.001).

Conclusion

The present study suggests that the use of AAM/BM-MSCs can improve the total number of mast cells and accelerate the growth of capillaries at the transient site in RSFs in rats.

Endothelial differentiation of bone marrow mesenchyme stem cells applicable to hypoxia and increased migration through Akt and NFκB signals

BACKGROUND

Bone marrow mesenchymal stem cells (MSCs) and endothelial progenitor cells (EPCs) are used to repair hypoxic or ischemic tissue. However, the underlining mechanism of resistance in the hypoxic microenvironment and the efficacy of migration to the injured tissue are still unknown. The current study aims to understand the hypoxia resistance and migration ability of MSCs during differentiation toward endothelial lineages by biochemical and mechanical stimuli.

METHOD

MSCs were harvested from the bone marrow of 6-8-week-old Sprague-Dawley rats. The endothelial growth medium (EGM) was added to MSCs for 3 days to initiate endothelial differentiation. Laminar shear stress was used as the fluid mechanical stimulation.

RESULTS

Application of EGM facilitated the early endothelial lineage cells (eELCs) to express EPC markers. When treating the hypoxic mimetic desferrioxamine, both MSCs and eELCs showed resistance to hypoxia as compared with the occurrence of apoptosis in rat fibroblasts. The eELCs under hypoxia increased the wound closure and C-X-C chemokine receptor type 4 (CXCR4) gene expression. Although the shear stress promoted eELC maturation and aligned cells parallel to the flow direction, their migration ability was not superior to that of eELCs either under normoxia or hypoxia. The eELCs showed higher protein expressions of CXCR4, phosphorylated Akt (pAkt), and endogenous NFκB and IκBα than MSCs under both normoxia and hypoxia conditions. The potential migratory signals were discovered by inhibiting either Akt or NFκB using specific inhibitors and revealed decreases of wound closure and transmigration ability in eELCs.

CONCLUSION

The Akt and NFκB pathways are important to regulate the early endothelial differentiation and its migratory ability under a hypoxic microenvironment.