Human adipose-derived stem cells promote vascularization of collagen-based scaffolds transplanted into nude mice

Combination therapy of placenta-derived mesenchymal stem cells and artificial dermal scaffold promotes full-thickness skin defects vascularization in rat animal model

PURPOSE

Recently, placenta-derived mesenchymal stem cells (PMSCs) have garnered considerable attention in tissue repair and regeneration. The present study was conducted to evaluate the effect of PMSCs on artificial dermal scaffold (ADS) angiogenesis and their combination therapy on wound closure.

MATERIAL AND METHODS

Herein, the growth and survival of PMSCs in ADS were explored. CCK8, scratch wound, and tubule formation assays were employed to investigate the effects of ADS conditioned medium (CM) and ADS-PMSCs CM on human umbilical vein endothelial cells (HUVECs). The effect of ADS-PMSCs on full-thickness skin defects healing was evaluated based on a rat model. Wound healing progresses was meticulously investigated through hematoxylin and eosin (HE), Masson's trichrome, and immunohistochemical staining analyses.

RESULTS

In vitro cell culture results demonstrated the proliferation of PMSCs in ADS. The ADS-PMSCs CM notably stimulated the proliferation, migration, and tube formation of HUVECs compared to the ADS CM group. In the rat full-thickness skin defect model, the ADS-PMSCs treatment significantly accelerated the vascularization area of ADS after 2 weeks. Besides, HE and Masson's trichrome staining results indicated that ADS-PMSCs treatment significantly enhanced fibroblast proliferation and collagen fiber 2 weeks after surgical procedure. Compared to the ADS group, collagen fiber arrangement was thicker in the ADS-PMSCs group. Immunohistochemical staining reinforced this finding, illustrating a substantial increase in CD31 expression within the ADS-PMSCs group.

CONCLUSIONS

The results suggest that the combination of ADS with PMSCs accelerates ADS vascularization by fostering granulation tissue development and boosting the formation of new blood vessels.

Human Dental Pulp Mesenchymal Stem Cell-Derived Soluble Factors Combined with a Nanostructured Scaffold Support the Generation of a Vascular Network In Vivo

Among all strategies directed at developing new tools to support re-vascularization of damaged tissues, the use of pro-angiogenic soluble factors, derived from mesenchymal stem cells (MSCs), appears a promising approach for regenerative medicine. Here, we compared the feasibility of two devices, generated by coupling soluble factors of human dental pulp mesenchymal stem cells (DPSCs), with a nanostructured scaffold, to support angiogenesis once transplanted in mice. DPSCs were obtained from impacted wisdom tooth removal, usually considered surgical waste material. After 28 days, we verified the presence of active blood vessels inside the scaffold through optical and scansion electron microscopy. The mRNA expression of surface antigens related to macrophage polarization (CD68, CD80, CD86, CD163, CD206), as well as pro-angiogenic markers (CD31, CD34, CD105, Angpt1, Angpt2, CDH5) was evaluated by real-time PCR. Our results demonstrate the capability of DPSC-scaffold and DPSC soluble factors-scaffold to support angiogenesis, similarly to adipose stem cells, whereas the absence of blood vessels was found in the scaffold grafted alone. Our results provide evidence that DPSC-conditioned medium can be proposed as a cell-free preparation able to support angiogenesis, thus, providing a relevant tool to overcome the issues and restrictions associated with the use of cells.

Mesenchymal Stem/Stromal Cells for Therapeutic Angiogenesis

Mesenchymal stem/stromal cells (MSCs) are known to possess medicinal properties to facilitate vascular regeneration. Recent advances in the understanding of the utilities of MSCs in physiological/pathological tissue repair and technologies in isolation, expansion, and enhancement strategies have led to the use of MSCs for vascular disease-related treatments. Various conditions, including chronic arterial occlusive disease, diabetic ulcers, and chronic wounds, cause significant morbidity in patients. Therapeutic angiogenesis by cell therapy has led to the possibilities of treatment options in promoting angiogenesis, treating chronic wounds, and improving amputation-free survival. Current perspectives on the options for the use of MSCs for therapeutic angiogenesis in vascular research and in medicine, either as a monotherapy or in combination with conventional interventions, for treating patients with peripheral artery diseases are discussed in this review.

Adipose mesenchymal stem cell-derived soluble factors, produced under hypoxic condition, efficiently support in vivo angiogenesis

Tissue regeneration or healing both require efficient vascularization within a tissue-damaged area. Based on this concept, a remarkable number of strategies, aimed at developing new tools to support re-vascularization of damaged tissue have emerged. Among the strategies proposed, the use of pro-angiogenic soluble factors, as a cell-free tool, appears as a promising approach, able to overcome the issues concerning the direct use of cells for regenerative medicine therapy. Here, we compared the effectiveness of adipose mesenchymal stem cells (ASCs), use as cell suspension, ASC protein extract or ASC-conditioned-medium (i.e., soluble factors), combined with collagenic scaffold, in supporting in vivo angiogenesis. We also tested the capability of hypoxia in increasing the efficiency of ASC to promote angiogenesis, via soluble factors, both in vivo and in vitro. In vivo studies were performed using the Integra® Flowable Wound Matrix, and the Ultimatrix in sponge assay. Flow cytometry was used to characterize the scaffold- and sponge-infiltrating cells. Real-time PCR was used to evaluate the expression of pro-angiogenic factors by stimulating Human Umbilical-Vein Endothelial Cells with ASC-conditioned media, obtained in hypoxic and normoxic conditions. We found that, in vivo, ACS-conditioned media can support angiogenesis similar to ASCs and ASC protein extract. Also, we observed that hypoxia increases the pro-angiogenic activities of ASC-conditioned media, compared to normoxia, by generating a secretome enriched in pro-angiogenic soluble factors, with bFGF, Adiponectine, ENA78, GRO, GRO-a, and ICAM1-3, as most regulated factors. Finally, ASC-conditioned media, produced in hypoxic condition, induce the expression of pro-angiogenic molecules in HUVECs. Our results provide evidence that ASC-conditioned-medium can be proposed as a cell-free preparation able to support angiogenesis, thus providing a relevant tool to overcome the issues and restrictions associated with the use of cells.

Bladder Acellular Matrix Prepared by a Self-Designed Perfusion System and Adipose-Derived Stem Cells to Promote Bladder Tissue Regeneration

The bladder patch constructed with the bladder acellular matrix (BAM) and adipose-derived stem cells (ASCs) was incubated with the omentum for bladder reconstruction in a rat model of bladder augmentation cystoplasty. A self-designed perfusion system and five different decellularization protocols were used to prepare the BAM. Finally, an optimal protocol (group C) was screened out by comparing the cell nucleus residue, collagen structure preservation and biologically active components retention of the prepared BAM. ASCs-seeded (BAM-ASCs group) and unseeded BAM (BAM group) were incubated with the omentum for 7 days to promote neovascularization and then perform bladder reconstruction. Hematoxylin and eosin and Masson’s trichrome staining indicated that the bladder patches in the BAM-ASCs group could better regenerate the bladder wall structure compared to the BAM group. Moreover, immunofluorescence analyses demonstrated that the ASCs could promote the regeneration of smooth muscle, neurons and blood vessels, and the physiological function (maximal bladder capacity, max pressure prior to voiding and bladder compliance) restoration in the BAM-ASCs group. The results demonstrated that the self-designed perfusion system could quickly and efficiently prepare the whole bladder scaffold and confirmed that the prepared BAM could be used as the scaffold material for functional bladder tissue engineering applications.

Human Adipose-Derived Stem Cell-Conditioned Medium Promotes Vascularization of Nanostructured Scaffold Transplanted into Nude Mice

Several studies have been conducted on the interaction between three-dimensional scaffolds and mesenchymal stem cells for the regeneration of damaged tissues. Considering that stem cells do not survive for sufficient time to directly sustain tissue regeneration, it is essential to develop cell-free systems to be applied in regenerative medicine. In this work, by in vivo experiments, we established that a collagen-nanostructured scaffold, loaded with a culture medium conditioned with mesenchymal stem cells derived from adipose tissue (hASC-CM), exerts a synergic positive effect on angiogenesis, fundamental in tissue regeneration. To this aim, we engrafted athymic BALB-C nude mice with four different combinations: scaffold alone; scaffold with hASCs; scaffold with hASC crude protein extract; scaffold with hASC-CM. After their removal, we verified the presence of blood vessels by optical microscopy and confirmed the vascularization evaluating, by real-time PCR, several vascular growth factors: CD31, CD34, CD105, ANGPT1, ANGPT2, and CDH5. Our results showed that blood vessels were absent in the scaffold grafted alone, while all the other systems appeared vascularized, a finding supported by the over-expression of CD31 and CDH5 mRNA. In conclusion, our data sustain the capability of hASC-CM to be used as a therapeutic cell-free approach for damaged tissue regeneration.

Human Spheroids from Adipose-Derived Stem Cells Induce Calvarial Bone Production in a Xenogeneic Rabbit Model

ABSTRACT

Calvarial defects can result from several causes. Tissue engineering hold the potential to restore native form and protective function. We have recently shown that stemness and differentiation ability of spheroids from adipose-derived stem cells (S-ASCs) promotes osteoblasts growth within Integra in a small vertebral lesion. In our study, we aimed to test osteogenic potential of S-ASCs in aiding regeneration of a calvarial defect. Groups containing Integra showed increased bone regeneration at the calvarial defect-Integra interface compared with the control group. In particular, S-ASC-derived osteoblasts group showed a superior calvarial remodeling than undifferentiated S-ASCs group. Clusters of ossification were observed in these both groups with enhanced microvasculature density and fibrosis. In conclusion, seeding of S-ASCs in dermal regeneration templates enhanced bone healing in a rabbit calvarial defect model. These findings could prompt the elective use of S-ASCs with enhanced multilineage differentiation potential for tissue engineering purposes.

Bilayer Scaffolds for Interface Tissue Engineering and Regenerative Medicine: A Systematic Reviews

PURPOSE

This systematic review focus on the application of bilayer scaffolds as an engaging structure for the engineering of multilayered tissues, including vascular and osteochondral tissues, skin, nerve, and urinary bladder. This article provides a concise literature review of different types of bilayer scaffolds to understand their efficacy in targeted tissue engineering.

METHODS

To this aim, electronic search in the English language was performed in PMC, NBCI, and PubMed from April 2008 to December 2019 based on the PRISMA guidelines. Animal studies, including the "bilayer scaffold" and at least one of the following items were examined: osteochondral tissue, bone, skin, neural tissue, urinary bladder, vascular system. The articles which didn't include "tissue engineering" and just in vitro studies were excluded.

RESULTS

Totally, 600 articles were evaluated; related articles were 145, and 35 full-text English articles met all the criteria. Fifteen articles in soft tissue engineering and twenty items in hard tissue engineering were the results of this exploration. Based on selected papers, it was revealed that the bilayer scaffolds were used in the regeneration of the multilayered tissues. The highest multilayered tissue regeneration has been achieved when bilayer scaffolds were used with mesenchymal stem cells and differentiation medium before implanting. Among the studies being reported in this review, bone marrow mesenchymal stem cells are the most studied mesenchymal stem cells. Among different kinds of multilayer tissue, the bilayer scaffold has been most used in osteochondral tissue engineering in which collagen and PLGA have been the most frequently used biomaterials. After osteochondral tissue engineering, bilayer scaffolds were widely used in skin tissue engineering.

CONCLUSION

The current review aimed to manifest the researcher and surgeons to use a more sophisticated bilayer scaffold in combinations of appropriate stem cells, and different can improve multilayer tissue regeneration. This systematic review can pave a way to design a suitable bilayer scaffold for a specific target tissue and conjunction with proper stem cells.

Paracrine effect of human adipose-derived stem cells on lymphatic endothelial cells

Aim: The proposal of this study was to evaluate, in vitro, the potential paracrine effect of human adipose-derived stem cells (hASCs) to promote lymphangiogenesis in lymphatic endothelial cells isolated from rat diaphragmatic lymphatic vessels. Materials & methods: ELISA on VEGFA, VEGFC and IL6 in hASC-conditioned medium; LYVE1 immunostaining; and gene expression of PROX1, VEGFR3, VEGFC, VEGFA and IL6 were the methods used. Results: In 2D culture, hASC-conditioned medium was able to promote lymphatic endothelial cell survival, maintenance of endothelial cobblestone morphology and induction to form a vessel-like structure. Conclusion: The authors' results represent in vitro evidence of the paracrine effect of hASCs on lymphatic endothelial cells, suggesting the possible role of hASC-conditioned medium in developing new therapeutic approaches for lymphatic system-related dysfunction such as secondary lymphedema.

Effect of Nanostructured Scaffold on Human Adipose-Derived Stem Cells: Outcome of In Vitro Experiments

This work is addressed to provide, by in vitro experiments, results on the repercussion that a nanostructured scaffold could have on viability, differentiation and secretion of bioactive factors of human adipose-derived stem cells (hASCs) when used in association to promote angiogenesis, a crucial condition to favour tissue regeneration. To achieve this aim, we evaluated cell viability and morphology by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay and microscopy analysis, respectively. We also investigated the expression of some of those genes involved in angiogenesis and differentiation processes utilizing quantitative polymerase chain reaction (qPCR), whereas the amounts of Vascular Endothelial Growth Factor A, Interleukin 6 and Fatty Acid-Binding Protein 4 secreted in the culture medium, were quantified by enzyme-linked immunosorbent assay (ELISA). Results suggested that, in the presence of the scaffold, cell proliferation and the exocytosis of factors involved in the angiogenesis process are reduced; by contrast, the expression of those genes involved in hASC differentiation appeared enhanced. To guarantee cell survival, the construct dimensions are, generally, smaller than clinically required. Furthermore, being the paracrine event the primary mechanism exerting the beneficial effects on injured tissues, the use of conditioned culture medium instead of cells may be convenient.

Combination product of dermal matrix, human mesenchymal stem cells, and timolol promotes diabetic wound healing in mice

Diabetic foot ulcers are a major health care concern with limited effective therapies. Mesenchymal stem cell (MSC)-based therapies are promising treatment options due to their beneficial effects of immunomodulation, angiogenesis, and other paracrine effects. We investigated whether a bioengineered scaffold device containing hypoxia-preconditioned, allogeneic human MSCs combined with the beta-adrenergic antagonist timolol could improve impaired wound healing in diabetic mice. Different iterations were tested to optimize the primary wound outcome, which was percent of wound epithelialization. MSC preconditioned in 1 μM timolol at 1% oxygen (hypoxia) seeded at a density of 2.5 × 10⁵  cells/cm² on Integra Matrix Wound Scaffold (MSC/T/H/S) applied to wounds and combined with daily topical timolol applications at 2.9 mM resulted in optimal wound epithelialization 65.6% (24.9% ± 13.0% with MSC/T/H/S vs 41.2% ± 20.1%, in control). Systemic absorption of timolol was below the HPLC limit of quantification, suggesting that with the 7-day treatment, accumulative steady-state timolol concentration is minimal. In the early inflammation stage of healing, the MSC/T/H/S treatment increased CCL2 expression, lowered the pro-inflammatory cytokines IL-1B and IL6 levels, decreased neutrophils by 44.8%, and shifted the macrophage ratio of M2/M1 to 1.9 in the wound, demonstrating an anti-inflammatory benefit. Importantly, expression of the endothelial marker CD31 was increased by 2.5-fold with this treatment. Overall, the combination device successfully improved wound healing and reduced the wound inflammatory response in the diabetic mouse model, suggesting that it could be translated to a therapy for patients with diabetic chronic wounds.

Adipose-Derived Stromal Cells Seeded on Integra® Dermal Regeneration Template Improve Post-Burn Wound Reconstruction

Fibrosis of burn-related wounds remains an unresolved clinical issue that leads to patient disability. The aim of this study was to assess the efficacy of the transplantation of adipose-derived stromal cells seeded onto a collagen-based matrix in the reconstruction of burn-related scars. Here, we characterized an in vitro interaction between adipose-derived stromal cells and a collagen-based matrix, Integra^®DRT. Our results show that transcription of pro-angiogenic, remodeling, and immunomodulatory factors was more significant in adipose-derived stromal cells than in fibroblasts. Transcription of metalloproteinases 2 and 9 is positively correlated with the collagenolytic activity of the adipose-derived stromal cells seeded onto Integra^®DRT. The increase in the enzymatic activity corresponds to the decrease in the elasticity of the whole construct. Finally, we validated the treatment of a post-excision wound using adipose-derived stromal cells and an Integra^®DRT construct in a 25-year-old woman suffering from burn-related scars. Scarless healing was observed in the area treated by adipose-derived stromal cells and the Integra^®DRT construct but not in the reference area where Integra^®DRT was applied without cells. This clinical observation may be explained by in vitro findings: Enhanced transcription of the vascular endothelial growth factor as well as remodeling of the collagen-based matrix decreased mechanical stress. Our experimental treatment demonstrated that the adipose-derived stromal cells seeded onto Integra^®DRT exhibit valuable properties that may improve post-excision wound healing and facilitate skin regeneration without scars.

Vascularization Strategies for Porous Polyethylene Implants

Porous polyethylene (pPE) is a frequently implanted biomaterial in craniofacial reconstructive surgery. Its rapid vascularization and tissue incorporation are major prerequisites to prevent complications, such as material infection, migration, and extrusion. To achieve this, several sophisticated strategies have been introduced and evaluated during the last 20 years. These include (i) the angiogenic stimulation of the host tissue with epidermal growth factor, basic fibroblast growth factor or macrophage-activating lipopeptide-2, (ii) material modifications, such as increase of surface roughness and incorporation of bioactive glass particles, (iii) surface coatings with growth factors, glycoproteins, acrylic acid, arginine/glycine/aspartic acid peptide as well as components of the plasminogen activation system and autologous clotted blood or serum, and (iv) the seeding with fibroblasts, chondrocytes, stem cells, or adipose-tissue-derived microvascular fragments. The majority of these approaches showed promising results in experimental studies and, thus, may be capable of improving the success rates after pPE implantation in future clinical practice.

Recovery ability of human adipose stem cells exposed to cobalt nanoparticles: outcome of dissolution

Aim: To demonstrate that cobalt nanoparticles doses are safe for use in humans and to understand the consequences of the particulate effects, which may persist inside the cells. Materials & methods: Human adipose stem cells were used. We evaluated cell recovery by viability test, morphology and ultrastructure using electronic and optical microscopy, while gene expression was assessed utilizing real-time PCR. Results: After exposure, most stem cells recovered their normal function. Co₃O₄-nanoparticles remained inside the cell for the entirety of the considered time. A slight modification of gene expression was observed in the exposed cells. Conclusion: After exposure to 100 M cobalt nanoparticles, most cells returned to normal function. Nanoparticle toxicity was due to ions released by dissolution as well as from the nanoparticles themselves.

The Role of Adipose-Derived Stem Cells, Dermal Regenerative Templates, and Platelet-Rich Plasma in Tissue Engineering-Based Treatments of Chronic Skin Wounds

The continuous improvements in the field of both regenerative medicine and tissue engineering have allowed the design of new and more efficacious strategies for the treatment of chronic or hard-to-heal skin wounds, which represent heavy burden, from a medical and economic point of view. These novel approaches are based on the usage of three key methodologies: stem cells, growth factors, and biomimetic scaffolds. These days, the adipose tissue can be considered the main source of multipotent mesenchymal stem cells, especially adipose-derived stem cells (ASCs). ASCs are easily accessible from various fat depots and show an intrinsic plasticity in giving rise to cell types involved in wound healing and angiogenesis. ASCs can be found in fat grafts, historically used in the treatment of chronic wounds, and have been evaluated as such in both animal models and human trials, to exploit their capability of accelerating wound closure and inducing a correct remodeling of the newly formed fibrovascular tissue. Since survival and fitness of ASCs need to be improved, they are now employed in conjunction with advanced wound dressings, together with dermal regenerative templates and platelet-rich plasma (as a source of growth and healing factors). In this work, we provide an overview of the current knowledge on the topic, based on existing studies and on our own experience.

Vascularization strategies for skin tissue engineering

Lack of proper vascularization after skin trauma causes delayed wound healing. This has sparked the development of various tissue engineering strategies to improve vascularization.

An electrochemically deposited collagen wound matrix combined with adipose-derived stem cells improves cutaneous wound healing in a mouse model of type 2 diabetes

Chronic wounds complicated by diabetes are a significant clinical issue, and their occurrence is expected to continue to rise due to an increased prevalence of diabetes mellitus, especially type 2 diabetes. Diabetic wounds frequently lead to nonhealing ulcers, and often eventually result in limb amputation due to the high risk of infection of the chronic wound. Here, we present a tissue-engineered treatment that combines a novel electrochemically deposited collagen wound matrix and human adipose-derived stem cells. The matrix fabrication process is optimized for voltage and time, and the final collagen biomaterial is thoroughly characterized. This collagen material possesses high tensile strength, high porosity, and excellent biocompatibility and cellular proliferation capabilities. Human adipose-derived stem cells were seeded onto the collagen wound matrix and this construct is investigated in a full thickness excisional wound in a mouse model of type 2 diabetes. This novel treatment is shown to stimulate excellent healing and tissue regeneration, resulting in increased granulation tissue formation, epidermal thickness, and overall higher quality tissue reformation. Both the collagen wound matrix alone and collagen wound matrix in combination with adipose derived stem cells appeared to be excellent treatments for diabetic skin wounds, and in the future can also be optimized to treat other injuries such as burns, blast injuries, surgical incisions, and other traumatic injuries.

Hybrid nanocomposite as a chest wall graft with improved integration by adipose-derived stem cells

Surgery of the chest wall is potentially required to cover large defects after  removal of malignant tumours. Usually, inert and non-degradable Gore-Tex serves to replace the missing tissue. However, novel biodegradable materials combined with stem cells are available that stimulate the healing. Based on poly-lactic-co-glycolic acid and amorphous calcium phosphate nanoparticles (PLGA/aCaP) and pure PLGA, a dual layer biodegradable hybrid nanocomposite was generated. Mouse adipose-derived stem cells were cultered on electrospun disks (ASCs of C57BL/6), and biomechanical tests were performed. The cell-seeded scaffolds were engrafted in C57BL/LY5.1 mice to serve as a chest wall substitute. Cell invasion into the bi-layered material, extent of CD45⁺ cells, inflammatory response, neo-vascularization and ECM composition were determined at 1 and 2 months post-surgery, respectively. The bi-layered hybrid nanocomposite was stable after a 2-week in vitro culture, in contrast to PLGA/aCaP without a PLGA layer. There was a complete biointegration and good vascularization in vivo. The presence of ASCs attracted more CD45⁺ cells (hematopoietic origin) compared to cell-free scaffolds. Inflammatory reaction was similar for both groups (±ASCs) at 8 weeks. A bi-layered hybrid nanocomposite fabricated of electrospun PLGA/aCaP and a reinforcing layer of pristine PLGA is an ideal scaffold for chest wall reconstruction. It is stable and allows a proper host tissue integration. If ASCs are seeded, they attract more CD45⁺ cells, supporting the regeneration process.

Collagen-Based Tissue Engineering Strategies for Vascular Medicine

Cardiovascular diseases (CVDs) account for the 31% of total death per year, making them the first cause of death in the world. Atherosclerosis is at the root of the most life-threatening CVDs. Vascular bypass/replacement surgery is the primary therapy for patients with atherosclerosis. The use of polymeric grafts for this application is still burdened by high-rate failure, mostly caused by thrombosis and neointima hyperplasia at the implantation site. As a solution for these problems, the fast re-establishment of a functional endothelial cell (EC) layer has been proposed, representing a strategy of crucial importance to reduce these adverse outcomes. Implant modifications using molecules and growth factors with the aim of speeding up the re-endothelialization process has been proposed over the last years. Collagen, by virtue of several favorable properties, has been widely studied for its application in vascular graft enrichment, mainly as a coating for vascular graft luminal surface and as a drug delivery system for the release of pro-endothelialization factors. Collagen coatings provide receptor-ligand binding sites for ECs on the graft surface and, at the same time, act as biological sealants, effectively reducing graft porosity. The development of collagen-based drug delivery systems, in which small-molecule and protein-based drugs are immobilized within a collagen scaffold in order to control their release for biomedical applications, has been widely explored. These systems help in protecting the biological activity of the loaded molecules while slowing their diffusion from collagen scaffolds, providing optimal effects on the targeted vascular cells. Moreover, collagen-based vascular tissue engineering substitutes, despite not showing yet optimal mechanical properties for their use in the therapy, have shown a high potential as physiologically relevant models for the study of cardiovascular therapeutic drugs and diseases. In this review, the current state of the art about the use of collagen-based strategies, mainly as a coating material for the functionalization of vascular graft luminal surface, as a drug delivery system for the release of pro-endothelialization factors, and as physiologically relevant in vitro vascular models, and the future trend in this field of research will be presented and discussed.

Advanced drug delivery systems and artificial skin grafts for skin wound healing

Cutaneous injuries, especially chronic wounds, burns, and skin wound infection, require painstakingly long-term treatment with an immense financial burden to healthcare systems worldwide. However, clinical management of chronic wounds remains unsatisfactory in many cases. Various strategies including growth factor and gene delivery as well as cell therapy have been used to enhance the healing of non-healing wounds. Drug delivery systems across the nano, micro, and macroscales can extend half-life, improve bioavailability, optimize pharmacokinetics, and decrease dosing frequency of drugs and genes. Replacement of the damaged skin tissue with substitutes comprising cell-laden scaffold can also restore the barrier and regulatory functions of skin at the wound site. This review covers comprehensively the advanced treatment strategies to improve the quality of wound healing.

Sufficient therapeutic effect of cryopreserved frozen adipose-derived regenerative cells on burn wounds

Introduction

The purpose of this study was to evaluate whether cryopreserved (frozen) adipose-derived regenerative cells (ADRCs) have a therapeutic effect on burn wound healing as well as freshly isolated (fresh) ADRCs.

Methods

Full thickness burns were created on dorsum of nude mice and burn wound was excised. The wound was covered by artificial dermis with; (i) fresh ADRCs, (ii) frozen ADRCs, and (iii) PBS (control). The assessment for wound healing was performed by morphological, histopathological and immunohistochemical analyses.

Results

In vivo analyses exhibited the significant therapeutic effect of frozen ADRCs on burn wound healing up to the similar or higher level of fresh ADRCs. There were significant differences of wound closure, epithelized tissue thickness, and neovascularization between the treatment groups and control group. Although there was no significant difference of therapeutic efficacy between fresh ADRC group and frozen ADRC group, frozen ADRCs improved burn wound healing process in dermal regeneration with increased great type I collagen synthesis compared with fresh ADRCs.

Conclusions

These findings indicate that frozen ADRCs allow us to apply not only quickly but also for multiple times, and the cryopreserved ADRCs could therefore be useful for the treatment of burn wounds in clinical settings.

•

Frozen ADRCs had a therapeutic effect on burn wounds as well as fresh ADRCs.

•

Frozen ADRCs promoted tissue regeneration by paracrine factors.

•

Frozen ADRCs could be useful for the treatment of burn wounds in clinical setting.

Adipose-derived mesenchymal stem cells accelerate diabetic wound healing in a similar fashion as bone marrow-derived cells

We have previously shown that bone marrow-derived mesenchymal stem cells (BMSC) accelerate wound healing in a diabetic mouse model. In this study, we hypothesized that adipose tissue-derived stem cells (ADSC), cells of greater translational potential to human therapy, improve diabetic wound healing to a similar extent as BMSC. In vitro, the characterization and function of murine ADSC and BMSC as well as human diabetic and nondiabetic ADSC were evaluated by flow cytometry, cell viability, and VEGF expression. In vivo, biomimetic collagen scaffolds containing murine ADSC or BMSC were used to treat splinted full-thickness excisional back wounds on diabetic C57BL/6 mice, and human healthy and diabetic ADSC were used to treat back wounds on nude mice. Wound healing was evaluated by wound area, local VEGF-A expression, and count of CD31-positive cells. Delivery of murine ADSC or BMSC accelerated wound healing in diabetic mice to a similar extent, compared with acellular controls ( P < 0.0001). Histological analysis showed similarly increased cellular proliferation ( P < 0.0001), VEGF-A expression ( P = 0.0002), endothelial cell density ( P < 0.0001), numbers of macrophages ( P < 0.0001), and smooth muscle cells ( P < 0.0001) with ADSC and BMSC treatment, compared with controls. Cell survival and migration of ADSC and BMSC within the scaffolds were similar ( P = 0.781). Notch signaling was upregulated to a similar degree by both ADSC and BMSC. Diabetic and nondiabetic human ADSC expressed similar levels of VEGF-A ( P = 0.836) in vitro, as well as in scaffolds ( P = 1.000). Delivery of human diabetic and nondiabetic ADSC enhanced wound healing to a similar extent in a nude mouse wound model. Murine ADSC and BMSC delivered in a biomimetic-collagen scaffold are equivalent at enhancing diabetic wound healing. Human diabetic ADSC are not inferior to nondiabetic ADSC at accelerating wound healing in a nude mouse model. This data suggests that ADSC are a reasonable choice to evaluate for translational therapy in the treatment of human diabetic wounds.

Current Therapeutic Strategies for Adipose Tissue Defects/Repair Using Engineered Biomaterials and Biomolecule Formulations

Tissue engineered scaffolds for adipose restoration/repair has significantly evolved in recent years. Patients requiring soft tissue reconstruction, caused by defects or pathology, require biomaterials that will restore void volume with new functional tissue. The gold standard of autologous fat grafting (AFG) is not a reliable option. This review focuses on the latest therapeutic strategies for the treatment of adipose tissue defects using biomolecule formulations and delivery, and specifically engineered biomaterials. Additionally, the clinical need for reliable off-the-shelf therapies, animal models, and challenges facing current technologies are discussed.

Effects of Metal Micro and Nano-Particles on hASCs: An In Vitro Model

As the knowledge about the interferences of nanomaterials on human staminal cells are scarce and contradictory, we undertook a comparative multidisciplinary study based on the size effect of zero-valent iron, cobalt, and nickel microparticles (MPs) and nanoparticles (NPs) using human adipose stem cells (hASCs) as a model, and evaluating cytotoxicity, morphology, cellular uptake, and gene expression. Our results suggested that the medium did not influence the cell sensitivity but, surprisingly, the iron microparticles (FeMPs) resulted in being toxic. These data were supported by modifications in mRNA expression of some genes implicated in the inflammatory response. Microscopic analysis confirmed that NPs, mainly internalized by endocytosis, persist in the vesicles without any apparent cell damage. Conversely, MPs are not internalized, and the effects on hASCs have to be ascribed to the release of ions in the culture medium, or to the reduced oxygen and nutrient exchange efficiency due to the presence of MP agglomerating around the cells. Notwithstanding the results depicting a heterogeneous scene that does not allow drawing a general conclusion, this work reiterates the importance of comparative investigations on MPs, NPs, and corresponding ions, and the need to continue the thorough verification of NP and MP innocuousness to ensure unaffected stem cell physiology and differentiation.

Use of human fat grafting in the prevention of perineural adherence: Experimental study in athymic mouse

Perineural adherences represent a problem after surgery involving peripheral neural system. Fat-grafting with adipose derived stem cells (ASCs) with their pro-regenerative characteristics can be important to prevent the neural damage or to facilitate the neural regeneration. Our idea was to use the fat-grafting as an anti-adherence device and test its efficacy on a postsurgical scar animal model and comparing to an antiadhesive gel. 32 athymic mice were operated under magnification, we exposed both sciatic nerves. We randomly divided all sciatic nerves into four experimental groups: burning (1), burning + carboxy-methylcellulose and poly- ethylene oxide (CMC-PEO) (2) + human adipose fat tissue (3), control group (4). Bio-mechanical evaluation was performed to measure the peak force required to pull out the nerve from the muscular bed. Results: in the CMC-PEO group the peak pull out force was 0.37 Newton. In the fat grafted group we registered a peak pull out force of 0.35 N (t Student 0.913). In burning group the force necessary to tear the nerve apart was markedly superior (0.46 N). In control group, we reported the minimal strength (0.31 N) to slide the nerve from the tissue. Histologically, in the group treated with fat-grating, a thinner scar layer was highlighted. Considering the results of this study we can support the efficacy in animal experimental model of fat graft as an anti-adherence device in peripheral nerve surgery.

Identification of reference genes for qPCR analysis during hASC long culture maintenance

Up to now quantitative PCR based assay is the most common method for characterizing or confirming gene expression patterns and comparing mRNA levels in different sample populations. Since this technique is relative easy and low cost compared to other methods of characterization, e.g. flow cytometry, we used it to typify human adipose-derived stem cells (hASCs). hASCs possess several characteristics that make them attractive for scientific research and clinical applications. Accurate normalization of gene expression relies on good selection of reference genes and the best way to choose them appropriately is to follow the common rule of the “Best 3”, at least three reference genes, three different validation software and three sample replicates. Analysis was performed on hASCs cultivated until the eleventh cell confluence using twelve candidate reference genes, initially selected from literature, whose stability was evaluated by the algorithms NormFinder, BestKeeper, RefFinder and IdealRef, a home-made version of GeNorm. The best gene panel (RPL13A, RPS18, GAPDH, B2M, PPIA and ACTB), determined in one patient by IdealRef calculation, was then investigated in other four donors. Although patients demonstrated a certain gene expression variability, we can assert that ACTB is the most unreliable gene whereas ribosomal proteins (RPL13A and RPS18) show minor inconstancy in their mRNA expression. This work underlines the importance of validating reference genes before conducting each experiment and proposes a free software as alternative to those existing.

Sandwich Fascial Anterolateral Thigh Flap in Head and Neck Reconstruction: Evolution or Revolution?

Supplemental Digital Content is available in the text.

Introduction:

The anterolateral thigh perforator flap (ALT) represents the workhorse for most reconstructive efforts in the head and neck regions. The main advantages of this flap are its versatility, the length of the pedicle, and the low morbidity of the donor site. The major drawback is the bulkiness of this flap with the frequent need for secondary revisions. To overcome this, we have developed a novel way to harvest and inset the ALT, called the sandwich fascial ALT flap (SALT).

Methods:

All patients undergoing head and neck reconstruction using the SALT flap from January 2013 to March 2016 were included in this retrospective analysis. The SALT flap was harvested as a composite flap including the superficial fascia, the subscarpal fat, and the deep fascia. At the recipient site, the flap was inset with the deep fascia facing out. A split thickness skin graft (± dermal substitute) was used to cover the deep fascia and the pedicle.

Results:

Eleven patients were included: 8 cases of orbital exenteration, 1 case of forehead reconstruction, and 2 cases of palatal reconstruction after radical maxillectomy. Flap survival was 100%. One patient required an early take back for venous thrombosis. The reconstruction was effective in all cases, allowing a prosthetic rehabilitation when required. Donor-site morbidity was minimal.

Conclusions:

The reconstruction of head and neck defects with a bulky fasciocutaneous ALT flap might not be the best option in every case. The SALT flap could represent a valid alternative for selected cases, with encouraging functional and cosmetic outcomes.