Engineering of volume-stable adipose tissues

Adipogenesis of bioabsorbable implants under irradiation in a rodent model

Background

Breast cancer is the most common cancer among women. Partial mastectomy is an alternative to mastectomy in early-stage breast cancer to restore a poor quality of life (QOL). However, the aesthetic satisfaction with this procedure is inadequate. The standard methods for breast reconstruction have certain limitations. We developed bioabsorbable implants consisting of an outer mesh composed of poly L-lactic acid (PLLA) and an inner component filled with a collagen sponge (CS). These implants were designed to promote and sustain adipogenesis in vivo, without the addition of exogenous cells or growth factors. In this study, we used PLLA mesh implants to investigate the effects of irradiation on fat formation, which is important in partial mastectomy.

Methods

The implants were inserted into both the inguinal regions of the rats. One month after the implantation, a dose of 13 Gy was delivered to the left-side implants. We compared adipose tissue formation in the non-irradiated and irradiated groups at 6 and 12 months after irradiation.

Results

Irradiation of implants did not lead to malignant tumor formation. The newly formed tissues and adipose tissue were not significantly different between the two groups at 6 and 12 months after irradiation.

Conclusions

PLLA mesh implants containing CS are desirable bioabsorbable implants that can be replaced with autologous adipose tissue after in vivo implantation under irradiation. These implants serve as an effective material for partial mastectomy and have the potential to improve the QOL of patients after mastectomy.

Long term observation of de novo adipogenesis using novel bioabsorbable implants with larger size in a porcine model

Introduction

The regeneration of adipose tissue in patients after breast cancer surgery would be desirable without the use of growth factors or cells to avoid potential recurrence and metastasis. We reported that prolate spheroidal-shaped poly-L-lactic acid (PLLA) mesh implants of approximately 18-mm polar diameter and 7.5-mm greatest equatorial diameter containing collagen sponge (CS) would be replaced by regenerated adipose tissue after implantation, thereby suggesting an innovative method for breast reconstruction. Our study aimed to evaluate the adipose tissue regeneration ability of implant aggregates in a porcine model.

Methods

We prepared implant aggregates consisting of thirty PLLA mesh implants containing CS packed in a woven poly (glycolic acid) bag. The implant aggregates were inserted under the mammary glands in the porcine abdomen for a year. Single and double groups were classified by inserting either one or two implant aggregates on each side of the abdomen, respectively.

Results

In both groups, the volume of the implant aggregates decreased over time, and the formation of adipose tissue peaked between 6 and 9 months. Histologically, the formation of adipose tissue was confirmed in the area that was in contact with native adipose tissue.

Conclusions

Our implant aggregates could induce the autologous adipose tissue after long term implantation in vivo, without the use of any growth factor or cell treatment, presenting a potential novel method of breast reconstruction.

Biofabrication of vascularized adipose tissues and their biomedical applications

Recent advances in adipose tissue engineering and cell biology have led to the development of innovative therapeutic strategies in regenerative medicine for adipose tissue reconstruction. To date, the many in vitro and in vivo models developed for vascularized adipose tissue engineering cover a wide range of research areas, including studies with cells of various origins and types, polymeric scaffolds of natural and synthetic derivation, models presented using decellularized tissues, and scaffold-free approaches. In this review, studies on adipose tissue types with different functions, characteristics and body locations have been summarized with 3D in vitro fabrication approaches. The reason for the particular focus on vascularized adipose tissue models is that current liposuction and fat transplantation methods are unsuitable for adipose tissue reconstruction as the lack of blood vessels results in inadequate nutrient and oxygen delivery, leading to necrosis in situ. In the first part of this paper, current studies and applications of white and brown adipose tissues are presented according to the polymeric materials used, focusing on the studies which could show vasculature in vitro and after in vivo implantation, and then the research on adipose tissue fabrication and applications are explained.

Cell-free biomimetic polyurethane-based scaffold for breast reconstruction following non-malignant lesion resection. A first-in-human study

BACKGROUND

Based on the volume of tissue removed, conservative surgery (BCS) cannot always guarantee satisfactory cosmetic results, unless resorting to more complex oncoplastic approaches. Investigating an alternative to optimize aesthetic outcomes minimizing surgical complexity, was the purpose of this study. We assessed an innovative surgical procedure based on the use of a biomimetic polyurethane-based scaffold intended for regenerating soft-tissue resembling fat, in patients undergoing BCS for non-malignant breast lesions. Safety and performance of the scaffold, and safety and feasibility of the entire implant procedure were evaluated.

METHODS

A volunteer sample of 15 female patients underwent lumpectomy with immediate device positioning, performing seven study visits with six-month follow-up. We evaluated incidence of adverse events (AEs), changes in breast appearance (using photographs and anthropomorphic measurements), interference with ultrasound and MRI (assessed by two independent investigators), investigator's satisfaction (through a VAS scale), patient's pain (through a VAS scale) and quality of life (QoL) (using the BREAST-Q© questionnaire). Data reported are the results of the interim analysis on the first 5 patients.

RESULTS

No AEs were device related nor serious. Breast appearance was unaltered and the device did not interference with imaging. High investigator's satisfaction, minimal post-operative pain and positive impact on QoL were also detected.

CONCLUSIONS

Albeit on a limited number of patients, data showed positive outcomes both in terms of safety and performance, paving the way to an innovative breast reconstructive approach with a potential remarkable impact on clinical application of tissue engineering.

TRIAL REGISTRATION

ClinicalTrials.gov (NCT04131972, October 18, 2019).

Preliminary report of de novo adipogenesis using novel bioabsorbable implants and image evaluation using a porcine model

Our bioabsorbable poly-l-lactic acid (PLLA) mesh implants containing collagen sponge are replaced with adipose tissue after implantation, and this is an innovative method for breast reconstruction. In this preliminary study, we investigated the formation of adipose tissue and evaluated the process via multimodal images in a porcine model using an implant aggregate to generate the larger adipose tissue. The implant aggregate consists of PLLA mesh implants containing collagen sponge and a poly-glycolic acid woven bag covering them. We inserted the implant aggregates under the porcine mammary glands. Magnetic resonance imaging (MRI), ultrasonography (USG), and 3-dimensional (3D) surface imaging and histological evaluations were performed to evaluate the formation of adipose tissue over time. The volume of the implant aggregate and the formed adipose tissue inside the implant aggregate could be evaluated over time via MRI. The space within the implant aggregate was not confirmed on USG due to the acoustic shadow of the PLLA threads. The change in volume was not confirmed precisely using 3D surface imaging. Histologically, the newly formed adipose tissue was confirmed on the skin side of the implant aggregate. This implant aggregate has the ability to regenerate adipose tissue, and MRI is an appropriate method for the evaluation of the volume of the implant aggregation and the formation of adipose tissue.

Understanding of how the properties of medical grade lactide based copolymer scaffolds influence adipose tissue regeneration: Sterilization and a systematic in vitro assessment

Aliphatic polyesters are the synthetic polymers most commonly used in the development of resorbable medical implants/devices. Various three-dimensional (3D) scaffolds have been fabricated from these polymers and used in adipose tissue engineering. However, their systematic evaluation altogether lacks, which makes it difficult to select a suitable degradable polymer to design 3D resorbable implants and/or devices able to effectively mimic the properties of adipose tissue. Additionally, the impact of sterilization methods on the medical devices, if any, must be taken into account. We evaluate and compare five different medical-grade resorbable polyesters with l-lactide content ranging from 50 to 100 mol% and exhibiting different physiochemical properties depending on the comonomer (d-lactide, ε-caprolactone, glycolide, and trimethylene carbonate). The salt-leaching technique was used to prepare 3D microporous scaffolds. A comprehensive assessment of physical, chemical, and mechanical properties of the scaffolds was carried out in PBS at 37 °C. The cell-material interactions and the ability of the scaffolds to promote adipogenesis of human adipose tissue-derived stem cells were assessed in vitro. The diverse physical and mechanical properties of the scaffolds, due to the different composition of the copolymers, influenced human adipose tissue-derived stem cells proliferation and differentiation. Scaffolds made from polymers which were above their glass transition temperature and with low degree of crystallinity showed better proliferation and adipogenic differentiation of stem cells. The effect of sterilization techniques (electron beam and ethylene oxide) on the polymer properties was also evaluated. Results showed that scaffolds sterilized with the ethylene oxide method better retained their physical and chemical properties. Overall, the presented research provides (i) a detailed understanding to select a degradable polymer that has relevant properties to augment adipose tissue regeneration and can be further used to fabricate medical devices/implants; (ii) directions to prefer a sterilization method that does not change polymer properties.

Enhanced Regeneration of Vascularized Adipose Tissue with Dual 3D-Printed Elastic Polymer/dECM Hydrogel Complex

A flexible and bioactive scaffold for adipose tissue engineering was fabricated and evaluated by dual nozzle three-dimensional printing. A highly elastic poly (L-lactide-co-ε-caprolactone) (PLCL) copolymer, which acted as the main scaffolding, and human adipose tissue derived decellularized extracellular matrix (dECM) hydrogels were used as the printing inks to form the scaffolds. To prepare the three-dimensional (3D) scaffolds, the PLCL co-polymer was printed with a hot melting extruder system while retaining its physical character, similar to adipose tissue, which is beneficial for regeneration. Moreover, to promote adipogenic differentiation and angiogenesis, adipose tissue-derived dECM was used. To optimize the printability of the hydrogel inks, a mixture of collagen type I and dECM hydrogels was used. Furthermore, we examined the adipose tissue formation and angiogenesis of the PLCL/dECM complex scaffold. From in vivo experiments, it was observed that the matured adipose-like tissue structures were abundant, and the number of matured capillaries was remarkably higher in the hydrogel–PLCL group than in the PLCL-only group. Moreover, a higher expression of M2 macrophages, which are known to be involved in the remodeling and regeneration of tissues, was detected in the hydrogel–PLCL group by immunofluorescence analysis. Based on these results, we suggest that our PLCL/dECM fabricated by a dual 3D printing system will be useful for the treatment of large volume fat tissue regeneration.

Differences of embedding adipose-derived stromal cells in natural and synthetic scaffolds for dermal and subcutaneous delivery

Background

In recent years, adipose-derived stromal cells (ASCs) have been heavily studied for soft tissue regeneration, augmentation, and dermal wound healing.

Methods

In this review, we investigated the trends in injectable scaffolds for ASC delivery in the dermis, and injectable or implantable scaffolds for ASC delivery in the subcutis. A total of 547 articles were screened across three databases; of these, 22 studies were found to be eligible and were included. The scaffolds were subdivided and analyzed based on their tissue placement (dermis or subcutis), delivery method (injected or implanted), and by the origin of the materials (natural, synthetic, and combinatory).

Results

ASCs embedded in scaffolds generally showed improved viability. Neovascularization in the transplanted tissue was greater when undifferentiated ASCs were embedded in a combinatory scaffold or if differentiated ASCs were embedded in a natural scaffold. ASCs embedded in natural materials underwent more adipogenic differentiation than ASCs embedded in synthetic scaffolds, indicating an etiologically unknown difference that has yet to be described. Increased mechanical strength of the scaffold material correlated with improved outcome measurements in the investigated studies. Wound healing studies reported reduced healing time in all except one article due to contraction of the control wounds.

Conclusions

In future clinical trials, we recommend embedding ASCs in injectable and implantable scaffolds for enhanced protection, retained viability, and improved therapeutic effects.

Trial registration

This review was registered with PROSPERO: ID=CRD42020171534.

Graphical abstract

The use of scaffolds as a vehicle for ASC delivery generally improved cell viability, angiogenesis, and wound healing in vivo compared to utilizing ASCs alone. ASCs embedded in natural materials induced more adipogenesis than ASCs embedded in synthetic materials. Adipogenic-induced ASCs further increased this effect. The included studies indicate that the seeded scaffold material influences the differentiation of ASCs in vivo. All studies investigating the mechanical strength of ASC scaffolds reported improved outcome measurements with improved mechanical strength. The results suggest that scaffolds, in general, are favorable for ASC delivery. We recommend initiating clinical studies using scaffolds based on mechanical properties and tunability to improve ASC viability. For fat regeneration, natural scaffolds are recommended.

Breast Reconstruction with a Tissue Engineering and Regenerative Medicine Approach (Systematic Review)

Current techniques for breast reconstruction include an autologous-tissue flap or an implant-based procedure, although both can impose further morbidity. This systematic review aims to explore the existing literature on breast reconstruction using a tissue engineering approach; conducted with the databases Medline and Embase. A total of 28 articles were included, mainly comprising of level-5 evidence with in vitro and animal studies focusing on utilizing scaffolds to support the migration and growth of new tissue; scaffolds can be either biological or synthetic. Biological scaffolds were composed of collagen or a decellularized tissue matrix scaffold. Synthetic scaffolds were primarily composed of polymers with customisable designs, adjusting the internal morphology and pore size. Implanting cells, including adipose-derived stem cells, with combined use of basic fibroblast growth factor has been studied in an attempt to enhance tissue regeneration. Lately, a level-4 evidence human case series was reported; successfully regenerating 210 mL of tissue using an arterio-venous pedicled fat flap within a tissue engineering chamber implanted on the chest wall. Further research is required to evaluate whether the use of cells and other growth factors could adjust the composition of regenerated tissue and improve vascularity; the latter a major limiting factor for creating larger volumes of tissue.

Tissue-mimicking gelatin scaffolds by alginate sacrificial templates for adipose tissue engineering

When adipose tissue (AT) is impaired by trauma or disease, AT engineering could provide a shelf-ready structural and functional restoration as alternative to current clinical treatments, which mainly aim at aesthetic replacement. Yet, the lack of an efficient vascular network within the scaffolds represents a major limitation to their translation application in patients. Here, we propose the use of microstructured crosslinked gelatin hydrogels with an embedded prevascular channel as scaffolding materials for AT engineering. The scaffolds are fabricated using - simultaneously - alginate-based microbeads and 3D printed filaments as sacrificial material encapsulated in gelatin at the point of material fabrication and removed post-crosslinking. This method yields the formation of microstructures that resemble the micro-architecture of physiological human fat tissue and of microvessels that can facilitate vascularization through anastomosis with patients' own blood vessels. The cytocompatible method used to prepare the gelatin scaffolds showed structural stability over time while allowing for cell infiltration and protease-based remodeling/degradation. Scaffolds' mechanical properties were also designed to mimic the one of natural breast adipose tissue, a key parameter for AT regeneration. Scaffold's embedded channel (∅ = 300-400 µm) allowed for cell infiltration and enabled blood flow in vitro when an anastomosis with a rat blood artery was performed using surgical glue. In vitro tests with human mesenchymal stem cells (hMSC) showed colonization of the porous structure of the gelatin hydrogels, differentiation into adipocytes and accumulation of lipid droplets, as shown by Oil Red O staining. STATEMENT OF SIGNIFICANCE: The potential clinical use of scaffolds for adipose tissue (AT) regeneration is currently limited by an unmet simultaneous achievement of adequate structural/morphological properties together with a promoted scaffold vascularization. Sacrificial materials, currently used either to obtain a tissue-mimicking structure or hollow channels to promote scaffold' vascularization, are powerful versatile tools for the fabrication of scaffolds with desired features. However, an integrated approach by means of sacrificial templates aiming at simultaneously achieving an adequate AT-mimicking structure and hollow channels for vascularization is missing. Here, we prove the suitability of crosslinked gelatin scaffolds obtained by using sacrificial alginate microbeads and 3D printed strands to achieve proper features and hollow channels useful for scaffolds vascularization.

Cosmetic reconstruction in breast cancer patients: Opportunities for nanocomposite materials

The most common malignancy in women, breast cancer remains a major medical challenge that affects the life of thousands of patients every year. With recognized benefits to body image and self-esteem, the use of synthetic mammary implants for elective cosmetic augmentation and post-mastectomy reconstruction continues to increase. Higher breast implant use leads to an increased occurrence of implant-related complications associated with implant leakage and rupture, capsular contracture, necrosis and infections, which include delayed healing, pain, poor aesthetic outcomes and the need for revision surgeries. Along with the health status of the implant recipient and the skill of the surgeon, the properties of the implant determine the likelihood of implant-related complications and, in doing so, specific patient outcomes. This paper will review the challenges associated with the use of silicone, saline and "gummy bear" implants in view of their application in patients recovering from breast cancer-related mastectomy, and investigate the opportunities presented by advanced functional nanomaterials in meeting these challenges and potentially opening new dimensions for breast reconstruction. STATEMENT OF SIGNIFICANCE: Breast cancer is a significant cause of morbidity and mortality in women worldwide, which is difficult to prevent or predict, and its treatment carries long-term physiological and psychological consequences. Post-mastectomy breast reconstruction addresses the cosmetic aspect of cancer treatment. Yet, drawbacks of current implants contribute to the development of implant-associated complications, which may lead to prolonged patient care, pain and loss of function. Nanomaterials can help resolve the intrinsic biomechanical mismatch between implant and tissues, enhance mechanical properties of soft implantable materials, and provide an alternative avenue for controlled drug delivery. Here, we explore advances in the use of functionalized nanomaterials to enhance the properties of breast implants, with representative examples that highlight the utility of nanomaterials in addressing key challenges associated with breast reconstruction.

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.

Delivered adipose-derived stromal cells improve host-derived adipose tissue formation in composite constructs in vivo

OBJECTIVES/HYPOTHESIS

Adipose tissue engineering aims to provide functional tissue surrogates for the restoration of soft tissue defects and contour deformities in the face. Many studies involve the delivery of cells; however, the impact and the exact role of the implanted cells is not yet fully elucidated.

STUDY DESIGN

Animal research.

METHODS

In this study, we used a mouse model for the development of volume-stable adipose tissue using polyurethane scaffolds combined with a long-term stable fibrin gel and adipose-derived stromal cells to investigate the influence of cell delivery on tissue development.

RESULTS

After 12 weeks in vivo, the emerging tissue in these constructs was shown to be exclusively of host origin by human-specific vimentin staining. Comparison of unseeded versus seeded scaffolds revealed a significant effect of the delivered cells on adipose tissue development as shown by histological staining and histomorphometric quantification of adipocytes, whereas blood vessel formation was not affected by delivery of adipose-derived stromal cells at this time point.

CONCLUSIONS

This is evidence for an indirect action of the implanted cells, providing a proadipogenic microenvironment within constructs, which was further boosted by adipogenic precultivation of the seeded constructs. Especially in peripheral areas of the constructs, the number of adipocytes was significantly elevated in seeded scaffolds compared to nonseeded controls, suggesting that the implanted cells likely triggered the invasion and differentiation of host cells. This is supported by the fact that the provision of a fat rich environment (by coverage of the constructs with a fat flap upon implantation) additionally stimulated adipose tissue formation.

LEVEL OF EVIDENCE

NA. Laryngoscope, 127:E428-E436, 2017.

Native extracellular matrix/fibroin hydrogels for adipose tissue engineering with enhanced vascularization

Adipose tissue engineering is a promising field for regeneration of soft tissue defects. However, vascularization is needed since nutrients and oxygen cannot reach cells in thick implants by diffusion. Obtaining a biocompatible scaffold with good mechanical properties is another problem. In this study, we aimed to develop thick and vascularized adipose tissue constructs supporting cell viability and adipose tissue regeneration. Hydrogels were prepared by mixing rat decellularized adipose tissue (DAT) and silk fibroin (Fib) at different v/v ratios (3:1, 1:1 and 1:3) and vortexing. Gelation times decreased with increasing fibroin ratio Among hydrogel groups 1:3-DAT:Fib ratio group showed similar mechanical properties with adipose tissue. Both pre-adipocytes and pre-endothelial cells, pre-differentiated from adipose derived stem cells (ASCs), were encapsulated in hydrogels at a 1: 3 ratio. In vitro analyses showed that hydrogels with 1:3 (v/v) DAT:Fib ratio supported better cell viability. Pre-adipocytes had lipid vesicles, and pre-endothelial cells formed tubular structures inside hydrogels only after 3 days in vitro. When endothelial and adipogenic pre-differentiated ASCs (for 7 days before encapsulation) were encapsulated together into 1:3-DAT:Fib hydrogels both cell types continued to differentiate into the committed cell lineage. Vascularization process in the hydrogels implanted with adipogenic and endothelial pre-differentiated ASCs took place between the first and second week after implantation which was faster than observed in the empty hydrogels. ASCs pre-differentiated towards adipogenic lineage inside hydrogels had begun to accumulate lipid vesicles after 1 week of subcutaneous implantation Based on these results, we suggest that 1:3-DAT:Fib hydrogels with enhanced vascularization hold promise for adipose tissue engineering.

Breast Augmentation and Reconstruction from a Regenerative Medicine Point of View: State of the Art and Future Perspectives

Breast reconstruction and augmentation are very common procedures, yet the prevailing current methods utilize silicone implants that may have significant local complications requiring reoperation. Lipofillling is increasingly used to contour and is considered safe, however, its utility is limited by significant volume loss. A new approach could offer an alternative and increase the scope of patient choice. A small number of teams around the world are investigating a breast tissue engineering (TE) paradigm. Conventional breast TE concepts are based on seeding a scaffold with the patients' own stem cells. However, the clinical viability of many of these approaches is limited by their costs in relevant volumes. In this article the state of the art of tissue-engineered breast reconstruction is reviewed and future perspectives are presented and discussed.

Human Adipose Tissue Derived Extracellular Matrix and Methylcellulose Hydrogels Augments and Regenerates the Paralyzed Vocal Fold

Vocal fold paralysis results from various etiologies and can induce voice changes, swallowing complications, and issues with aspiration. Vocal fold paralysis is typically managed using injection laryngoplasty with fat or synthetic polymers. Injection with autologous fat has shown excellent biocompatibility. However, it has several disadvantages such as unpredictable resorption rate, morbidities associated with liposuction procedure which has to be done in operating room under general anesthesia. Human adipose-derived extracellular matrix (ECM) grafts have been reported to form new adipose tissue and have greater biostability than autologous fat graft. Here, we present an injectable hydrogel that is constructed from adipose tissue derived soluble extracellular matrix (sECM) and methylcellulose (MC) for use in vocal fold augmentation. Human sECM derived from adipose tissue was extracted using two major steps—ECM was isolated from human adipose tissue and was subsequently solubilized. Injectable sECM/MC hydrogels were prepared by blending of sECM and MC. Sustained vocal fold augmentation and symmetric vocal fold vibration were accomplished by the sECM/MC hydrogel in paralyzed vocal fold which were confirmed by laryngoscope, histology and a high-speed imaging system. There were increased number of collagen fibers and fatty granules at the injection site without significant inflammation or fibrosis. Overall, these results indicate that the sECM/MC hydrogel can enhance vocal function in paralyzed vocal folds without early resorption and has potential as a promising material for injection laryngoplasty for stable vocal fold augmentation which can overcome the shortcomings of autologous fat such as unpredictable duration and morbidity associated with the fat harvest.

Strategies for bioengineered scaffolds that support adipose stem cells in regenerative therapies

Regenerative medicine possesses the potential to ameliorate damage to tissue that results from a vast range of conditions, including traumatic injury, tumor resection and inherited tissue defects. Adult stem cells, while more limited in their potential than pluripotent stem cells, are still capable of differentiating into numerous lineages and provide feasible allogeneic and autologous treatment options for many conditions. Adipose stem cells are one of the most abundant types of stem cell in the adult human. Here, we review recent advances in the development of synthetic scaffolding systems used in concert with adipose stem cells and assess their potential use for clinical applications.

Biologically and mechanically driven design of an RGD-mimetic macroporous foam for adipose tissue engineering applications

Despite clinical treatments for adipose tissue defects, in particular breast tissue reconstruction, have certain grades of efficacy, many drawbacks are still affecting the long-term survival of new formed fat tissue. To overcome this problem, in the last decades, several scaffolding materials have been investigated in the field of adipose tissue engineering. However, a strategy able to recapitulate a suitable environment for adipose tissue reconstruction and maintenance is still missing. To address this need, we adopted a biologically and mechanically driven design to fabricate an RGD-mimetic poly(amidoamine) oligomer macroporous foam (OPAAF) for adipose tissue reconstruction. The scaffold was designed to fulfil three fundamental criteria: capability to induce cell adhesion and proliferation, support of in vivo vascularization and match of native tissue mechanical properties. Poly(amidoamine) oligomers were formed into soft scaffolds with hierarchical porosity through a combined free radical polymerization and foaming reaction. OPAAF is characterized by a high water uptake capacity, progressive degradation kinetics and ideal mechanical properties for adipose tissue reconstruction. OPAAF's ability to support cell adhesion, proliferation and adipogenesis was assessed in vitro using epithelial, fibroblast and endothelial cells (MDCK, 3T3L1 and HUVEC respectively). In addition, in vivo subcutaneous implantation in murine model highlighted OPAAF potential to support both adipogenesis and vessels infiltration. Overall, the reported results support the use of OPAAF as a scaffold for engineered adipose tissue construct.

Application of Hydrogel in Reconstruction Surgery: Hydrogel/Fat Graft Complex Filler for Volume Reconstruction in Critical Sized Muscle Defects

Autogenic fat graft usually suffers from degeneration and volume shrinkage in volume reconstruction applications. How to maintain graft viability and graft volume is an essential consideration in reconstruction therapies. In this presented investigation, a new fat graft transplantation method was developed aiming to improve long term graft viability and volume reconstruction effect by incorporation of hydrogel. The harvested fat graft is dissociated into small fragments and incorporated into a collagen based hydrogel to form a hydrogel/fat graft complex for volume reconstruction purpose. In vitro results indicate that the collagen based hydrogel can significantly improve the survivability of cells inside isolated graft. In a 6-month investigation on artificial created defect model, this hydrogel/fat graft complex filler has demonstrated the ability of promoting fat pad formation inside the targeted defect area. The newly generated fat pad can cover the whole defect and restore its original dimension in 6-month time point. Compared to simple fat transplantation, this hydrogel/fat graft complex system provides much improvement on long term volume restoration effect against degeneration and volume shrinkage. One notable effect is that there is continuous proliferation of adipose tissue throughout the 6-month period. In summary, the hydrogel/fat graft system presented in this investigation demonstrated a better and more significant effect on volume reconstruction in large sized volume defect than simple fat transplantation.

In vitro and in vivo biocompatibility, bioavailability and tolerance of an injectable vehicle for adipose-derived stem/stromal cells for plastic surgery indications

Soft tissue reconstruction is a challenge in plastic surgery, when replacing lost materials and correcting contour defects. Many permanent and temporary fillers have been used to restore the volume of these lesions, but often with poor results and even complications. Adipose-derived stem/stromal cells (ASCs) and adipose tissue engineering have been suggested as valuable alternatives. In order to inject these cultured cells, it was essential to find a suitable vehicle. The purpose of this study was to evaluate Cytocare(®), an injectable medical device, composed of hyaluronic acid plus amino acids, vitamins and mineral salts. First, ASC viability and bioavailability in the 3 different available Cytocare(®) formulations using the MTT test were assessed; then an animal experiment, testing the tolerance after intradermal injections of both Cytocare(®) alone and with ASCs was carried out. Our in vitro results demonstrate a high biocompatibility of Cytocare(®) resulting in a better viability of ASCs when cultured in Cytocare(®) compared to culture medium (p < 0.05, Mann and Whitney). Cytocare(®) also permits their bioavailability and proliferation, making it a potential transfer vehicle that can retain the cells before their integration around the recipient site. Finally, our animal experiment shows that the ASC + Cytocare(®) combination is well tolerated. In conclusion, Cytocare(®) can be used as a biocompatible scaffold for cultured ASCs in therapeutic treatments, ensuring ASC bioavailability, as well as evidence of excellent tolerance in nude mice.

Human Adipose Stem Cells: From Bench to Bedside

Stem cell-based therapies for repair and regeneration of different tissues are becoming more important in the treatment of several diseases. Adult stem cells currently symbolize the most available source of cell progenitors for tissue engineering and repair and can be harvested using minimally invasive procedures. Moreover, mesenchymal stem cells (MSCs), the most widely used stem cells in stem cell-based therapies, are multipotent progenitors, with capability to differentiate into cartilage, bone, connective, muscle, and adipose tissue. So far, bone marrow has been regarded as the main source of MSCs. To date, human adult adipose tissue may be the best suitable alternative source of MSCs. Adipose stem cells (ASCs) can be largely extracted from subcutaneous human adult adipose tissue. A large number of studies show that adipose tissue contains a biologically and clinically interesting heterogeneous cell population called stromal vascular fraction (SVF). The SVF may be employed directly or cultured for selection and expansion of an adherent population, so called adipose-derived stem cells (ASCs). In recent years, literature based on data related to SVF cells and ASCs has augmented considerably: These studies have demonstrated the efficacy and safety of SVF cells and ASCs in vivo in animal models. On the basis of these observations, in several countries, various clinical trials involving SVF cells and ASCs have been permitted. This review aims at summarizing data regarding either ASCs cellular biology or ASCs-based clinical trials and at discussing the possible future clinical translation of ASCs and their potentiality in cell-based tissue engineering.

Methacrylated gelatin and mature adipocytes are promising components for adipose tissue engineering

In vitro engineering of autologous fatty tissue constructs is still a major challenge for the treatment of congenital deformities, tumor resections or high-graded burns. In this study, we evaluated the suitability of photo-crosslinkable methacrylated gelatin (GM) and mature adipocytes as components for the composition of three-dimensional fatty tissue constructs. Cytocompatibility evaluations of the GM and the photoinitiator Lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) showed no cytotoxicity in the relevant range of concentrations. Matrix stiffness of cell-laden hydrogels was adjusted to native fatty tissue by tuning the degree of crosslinking and was shown to be comparable to that of native fatty tissue. Mature adipocytes were then cultured for 14 days within the GM resulting in a fatty tissue construct loaded with viable cells expressing cell markers perilipin A and laminin. This work demonstrates that mature adipocytes are a highly valuable cell source for the composition of fatty tissue equivalents in vitro. Photo-crosslinkable methacrylated gelatin is an excellent tissue scaffold and a promising bioink for new printing techniques due to its biocompatibility and tunable properties.

Engineering vascularized adipose tissue using the stromal-vascular fraction and fibrin hydrogels

The development of vascularized and functional adipose tissue substitutes is required to improve soft tissue augmentation. In this study, vascularized adipose tissue constructs were generated using uncultured cells from the stromal-vascular fraction (SVF) of adipose tissue as an alternative cell source to adipose-derived stem cells. SVF cell behavior and tissue formation were compared in a stable fibrin formulation developed by our group and a commercial fibrin sealant (TissuCol; Baxter) upon direct subcutaneous implantation in a nude mouse model. Further, the effect of in vitro adipogenic induction on SVF cell development was investigated by implanting stable fibrin constructs after 1 week of precultivation (adipogenic vs. noninduced control). Constructs were thoroughly analyzed before implantation regarding adipogenic differentiation status, cell viability, and distribution as well as the presence of endothelial cells. Before implantation, in vitro precultivation strongly promoted adipogenesis (under adipogenic conditions) and the formation of CD31(+) prevascular structures by SVF cells (under nonadipogenic conditions). Tissue development in vivo was determined after 4 weeks by histology (hematoxylin and eosin, human vimentin) and quantified histomorphometrically. In stable fibrin gels, adipogenic precultivation was superior to noninduced conditions, resulting in mature adipocytes and the formation of distinct vascular structures of human origin in vivo. Strong neovascularization by the implanted cells predominated in noninduced constructs. Without pretreatment, the SVF in stable fibrin gels displayed only a weak differentiation capability. In contrast, TissuCol gels strongly supported the formation of coherent and well-vascularized adipose tissue of human origin, displaying large unilocular adipocytes. The developed native-like tissue architecture was highlighted by a whole mount staining technique. Taken together, SVF cells from human adipose tissue were shown to successfully lead to adipose tissue formation in fibrin hydrogels in vivo. The results render the SVF a promising cell source for subsequent studies both in vitro and in vivo with the aim of engineering clinically applicable soft tissue substitutes.

Global Inactivation of the Pla2g6 Gene in Mice Does Not Cause Dyslipidemia under Chow or High-fat Diet Conditions

Background:

Genome-wide association studies suggest that plasma triacylglyceride (TAG) in humans was associated with variation in the PLA2G6 locus, a gene that encodes calcium-independent phospholipase A₂ (iPLA₂β). The objective of the present study is to understand the impact of genetic inactivation of iPLA₂β on hepatic TAG metabolism in C57BL/6 mice.

Methods:

Male iPLA₂β^+/− mice were backcrossed with female iPLA₂β^−/− mice for up to 10 generations prior to experiments. Lipid and lipoprotein metabolism from plasma, hepatocytes, thigh subcutaneous adipose and thigh skeletal muscle tissues of the mice were determined under various experimental conditions.

Results:

The iPLA₂β^−/− mice, either male or female as compared with iPLA₂β^+/+ littermates, showed no change in fasted or postprandial plasma TAG or total cholesterol at young (12–15 weeks) or old (40–44 weeks) ages under chow diet or high-fat diet (HFD) conditions. However, fractionation of plasma lipoproteins showed that under HFD conditions, there was a significant increase (by 40%) in apoB-100 association with VLDL₁ fractions in iPLA₂β^−/− mice as compared with iPLA₂β^+/+ littermates. There was no significant difference in triglyceride or cholesterol contents in the liver, muscle, or adipose tissue between iPLA₂β^−/− and iPLA₂β^+/+ littermates. Metabolic labeling experiments with cultured primary hepatocytes isolated from iPLA₂β^−/− mice also showed 2-fold increase in the secretion of [³⁵S]methionine-labeled apoB-100 in VLDL₁ fractions as compared with that from iPLA₂β^+/+ hepatocytes. Likewise, secretion of [³H]palmitate-labeled TAG from the iPLA₂β^−/− hepatocytes was increased by 2-fold.

Conclusions:

Although iPLA₂β may play a role in TAG-rich VLDL₁ production from cultured hepatocytes, there is no evidence that inactivation of iPLA₂β would lead to dyslipidemia in mice in vivo.

Clinical implication of allogenic implantation of adipogenic differentiated adipose-derived stem cells

We recently reported that autologous adipogenic differentiated adipose-derived stem cells (ASCs) can potentially be used as an effective and safe therapy for soft-tissue regeneration. In the present study, we investigated whether adipogenic differentiated ASCs can be used for allogenic applications to enlarge their therapeutic use. The allogenic immune response of adipogenic differentiated ASCs was investigated by flow cytometry and mixed lymphocyte culture. To determine whether adipogenic differentiated ASCs can form new adipose tissue without immune rejection, these cells were implanted subcutaneously into allo- or xenogenic recipient mice. In addition, the safety of the allogenic implantation of adipogenic differentiated ASCs was explored in a phase I clinical study. Adipogenic differentiated ASCs do not express major histocompatibility complex (MHC) class II molecules and costimulatory molecules, and the expression levels of MHC class I decreased after differentiation. In addition, these cells do not elicit an immune response against MHC-mismatched allogenic lymphocytes and formed new adipose tissue without immune rejection in the subcutaneous region of MHC-mismatched mice. Moreover, these cells did not induce clinically significant local and systemic immune responses or adverse events in the subcutaneous region of donor-independent healthy subjects. These results suggest that adipogenic differentiated ASCs can be used as a "universal donor" for soft-tissue engineering in MHC-mismatched recipients.

Adipose-derived stromal cells for osteoarticular repair: trophic function versus stem cell activity

The identification of multipotent adipose-derived stromal cells (ASC) has raised hope that tissue regeneration approaches established with bone-marrow-derived stromal cells (BMSC) can be reproduced with a cell-type that is far more accessible in large quantities. Recent detailed comparisons, however, revealed subtle functional differences between ASC and BMSC, stressing the concept of a common mesenchymal progenitor existing in a perivascular niche across all tissues. Focussing on bone and cartilage repair, this review summarises recent in vitro and in vivo studies aiming towards tissue regeneration with ASC. Advantages of good accessibility, high yield and superior growth properties are counterbalanced by an inferiority of ASC to form ectopic bone and stimulate long-bone healing along with their less pronounced osteogenic and angiogenic gene expression signature. Hence, particular emphasis is placed on establishing whether stem cell activity of ASC is so far proven and relevant for successful osteochondral regeneration, or whether trophic activity may largely determine therapeutic outcome.

Biomaterials for adipose tissue engineering

There is high clinical need for an adequate reconstruction of soft tissue defects as found after tumor resections, deep burns or severe trauma. A promising solution for these defects is adipose tissue engineering, with adult stem cells of the adipose tissue, implanted on 3D biomaterials. These adipogenic precursor cells survive ischemia better than mature adipocytes and have the potency to proliferate and differentiate into fat cells after transplantation. They can be yielded from excised adipose tissue or liposuction material. When preadipocytes are seeded on carriers for the generation of adipose tissue, chemical composition, mechanical stability and 3D architecture of the construct are crucial factors. They ensure cellular penetration into the construct, sufficient proliferation on the material and full differentiation inside the construct after transplantation. In hydrogels, it is especially the use and combination of growth factors that determine the overall outcome of the applied biopolymer. Over recent years, in vivo trials in particular have allowed significant insights into the potential, the perspectives, but also the current difficulties and draw-backs in adipose tissue engineering. This review focuses on the main strategies in adipose tissue regeneration, compares the various materials that have been used as carrier matrices so far and considers them in light of the challenges they have yet to meet.

Development of volume-stable adipose tissue constructs using polycaprolactone-based polyurethane scaffolds and fibrin hydrogels

Adipose tissue engineering aims at the restoration of soft tissue defects and the correction of contour deformities. It is therefore crucial to provide functional adipose tissue implants with appropriate volume stability. Here, we investigate two different fibrin formulations, alone or in combination with biodegradable polyurethane (PU) scaffolds as additional support structures, with regard to their suitability to generate volume-stable adipose tissue constructs. Human adipose-derived stem cells (ASCs) were incorporated in a commercially available fibrin sealant as well as a stable fibrin hydrogel previously developed by our group. The composite constructs made from the commercially available fibrin and porous poly(ε-caprolactone)-based polyurethane scaffolds exhibited increased volume stability as compared to fibrin gels alone; however, only constructs using the stable fibrin gels completely maintained their size and weight for 21 days. Adipogenesis of ASCs was not impaired by the additional PU scaffold. After induction with a common hormonal cocktail, for constructs with either fibrin formulation, strong adipogenic differentiation of ASCs was observed after 21 days in vitro. Furthermore, upregulation of adipogenic marker genes was demonstrated at mRNA (PPARγ, C/EBPα, GLUT4 and aP2; qRT-PCR) and protein (leptin; ELISA) levels. Stable fibrin/PU constructs were further evaluated in a pilot in vivo study, resulting in areas of well-vascularized adipose tissue within the implants after only 5 weeks. Copyright © 2013 John Wiley & Sons, Ltd.

Volume-stable adipose tissue formation by implantation of human adipose-derived stromal cells using solid free-form fabrication-based polymer scaffolds

Regeneration of volume-stable adipose tissue is required for treatment of soft-tissue loss due to cancer, trauma, burns and for correctional cosmetic surgery. In this study, we hypothesized that transplantation of human adipose-derived stromal cells (hADSCs) using polycaprolactone (PCL) scaffolds fabricated with a solid free-form fabrication method would better maintain the volume of regenerated adipose tissues, as compared with the use of fibrin gel. Six weeks after implantation into the dorsal subcutaneous pockets of athymic mice, the volumes and adipose tissue areas of hADSC-PCL scaffold implants were significantly larger than those of hADSC-fibrin implants. In addition, the mRNA expression of adipogenic genes was more extensive in the hADSC-PCL scaffold implants.

Subcutaneous fat tissue engineering using autologous adipose-derived stem cells seeded onto a collagen scaffold

BACKGROUND

This pilot study examined the efficacy of 5-bromo-2-deoxyuridine-labeled autologous adipose-derived stem cells seeded onto collagen scaffolds to augment and/or regenerate the fat-enriched hypodermal tissue in an acute porcine wound model.

METHODS

Porcine autologous adipose-derived stem cells were isolated and cultured. At passage 2, the cells were labeled with 5-bromo-2-deoxyuridine, seeded onto a three-dimensional collagen scaffold, and cultured for 10 days. Scaffolds were implanted subcutaneously in adult pigs with two adipose-derived stem cell scaffolds and two control scaffolds. Animals were euthanized at 2, 4, 8, and 12 weeks; all scaffold conditions were explanted for histology and immunohistochemistry analyses.

RESULTS

For all time points, adipose-derived stem cell scaffolds had increased connective tissue matrix within the subcutaneous tissue compared with scaffold alone and untreated porcine skin (p < 0.01). The neosynthesized connective tissue was vascularized and composed of small cells within an abundant extracellular matrix organized in layers. 5-Bromo-2-deoxyuridine cells were detectable only up to 4 weeks and mature adipocytes were absent. Levels of collagen types I, III, and VI differed among the experimental groups, with increased extracellular matrix associated with the presence of adipose-derived stem cells.

CONCLUSIONS

The authors' data clearly show the efficacy of adipose-derived stem cells for soft-tissue repair and skin aging because it induces a significant increase of the dermis thickness. Moreover, the authors' results demonstrate the interest of their acute wound model and allowed them to show the skin thickness variation over time of the experiment, which is one of the challenges with which clinicians struggle in fat grafting.

Intrinsic dynamics of the fat graft: in vitro interactions between the main cell actors

BACKGROUND

Successful soft-tissue reconstruction requires autologous tissue transfer in respect to the increasingly important "replace like-with-like" principle. Autologous lipoaspirate material for fat grafting can easily be obtained in large amounts without substantial donor-site morbidity. The exact nature and fate of the different cells in the transplanted fat graft and their contribution to tissue reconstruction, however, remain largely unknown.

METHODS

Adipose tissue was harvested from healthy female patients. CD34+ adipose-derived stem cells were isolated through magnetic-activated cell sorting and brought into co-culture with mature adipocytes in various culture medium conditions. Proliferation and differentiation of the adipose-derived stem cells were examined through histology, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays, and polymerase chain reaction assays.

RESULTS

This study demonstrates that adipose-derived stem cells from fresh adipose tissue can be isolated within a few hours via magnetic-activated cell sorting with selection for CD34+ cells. All unpassaged adipose-derived stem cells in fresh adipose tissue are CD34+. Subsets include CD34+ CD31+ and CD34+ CD271+. No CD34+ CD45+ cells were present. Histological staining, polymerase chain reaction, and MTT assays confirm that purified mature adipose cells incite adipose-derived stem cells proliferation and adipose differentiation in vitro.

CONCLUSIONS

This in vitro study demonstrates important interactions between the main actors in the adipose graft, the adipose-derived stem cells and the mature adipocytes. Although the eventual fate of these cells in a clinically implemented fat graft is still largely unknown, the results of this study support the theory that lipofilling can be conceived as an in vivo tissue engineering approach in which the mature adipocytes within fat grafts support proliferation and differentiation in the co-grafted stromal cell population.

Decellularized omentum as novel biologic scaffold for reconstructive surgery and regenerative medicine

Homologous tissues, such as adipose tissue, may be an interesting source of acellular scaffolds, maintaining a complex physiological three-dimensional (3D) structure, to be recellularized with autologous cells. The aim of the present work is to evaluate the possibility of obtaining homologous acellular scaffolds from decellularization of the omentum, which is known to have a complex vascular network. Adult rat and human omenta were treated with an adapted decellularization protocol involving mechanical rupture (freeze-thaw cycles), enzymatic digestion (trypsin, lipase, deoxyribonuclease, ribonuclease) and lipid extraction (2-propanol). Histological staining confirmed the effectiveness of decellularization, resulting in cell-free scaffolds with no residual cells in the matrix. The complex 3D networks of collagen (azan-Mallory), elastic fibers (Van Gieson), reticular fibers and glycosaminoglycans (PAS) were maintained, whereas Oil Red and Sudan stains showed the loss of lipids in the decellularized tissue. The vascular structures in the tissue were still visible, with preservation of collagen and elastic wall components and loss of endothelial (anti-CD31 and -CD34 immunohistochemistry) and smooth muscle (anti-alpha smooth muscle actin) cells. Fat-rich and well vascularized omental tissue may be decellularized to obtain complex 3D scaffolds preserving tissue architecture potentially suitable for recellularization. Further analyses are necessary to verify the possibility of recolonization of the scaffold by adipose-derived stem cells in vitro and then in vivo after re implantation, as already known for homologus implants in regenerative processes.

Simple and longstanding adipose tissue engineering in rabbits

Adipose tissue engineering for breast reconstruction can be performed for patients who have undergone breast surgery. We have previously confirmed adipogenesis in mice implanted with type I collagen sponge with controlled release of fibroblast growth factor 2 (FGF2) and human adipose tissue-derived stem cells. However, in order to use this approach to treat breast cancer patients, a large amount of adipose tissue is needed, and FGF2 is not readily available. Thus, we aimed to regenerate large amounts of adipose tissue without FGF2 for a long period. Under general anesthesia, cages made of polypropylene mesh were implanted into the rabbits' bilateral fat pads. Each cage was 10 mm in radius and 10 mm in height. Minced type I collagen sponge was injected as a scaffold into the cage. Regenerated tissue in the cage was examined with ultrasonography, and the cages were harvested 3, 6, and 12 months after the implantation. Ultrasonography revealed a gradually increasing homogeneous high-echo area in the cage. Histology of the specimen was assessed with hematoxylin and eosin staining. The percentages of regenerated adipose tissue area were 76.2 ± 13.0 and 92.8 ± 6.6 % at 6 and 12 months after the implantation, respectively. Our results showed de novo adipogenesis 12 months after the implantation of only type I collagen sponge inside the space. Ultrasonography is a noninvasive and useful method of assessing the growth of the tissue inside the cage. This simple method could be a promising clinical modality in breast reconstruction.

Adipose tissue engineering with human adipose tissue-derived adult stem cells and a novel porous scaffold

We investigated the effect of a novel porous scaffold composed with water-soluble poly(L-glutamic acid) (PLGA) and chitosan (CS) on the attachment, proliferation, and adipogenic differentiation of human adipose tissue-derived adult stem cells (ADSCs) in vitro and in vivo. Scanning electron microscope and fluorescent Dil labeling were used to reveal the attachment and growth of ADSCs on scaffolds; cell proliferation was detected by DNA assay. The adipogenic differentiation potential of ADSCs on the scaffolds was assayed by Oil-red O staining and further confirmed by reverse transcriptase polymerase chain reaction (RT-PCR) for adipogenic gene markers (peroxisome proliferator-activated receptor γ2, lipoprotein lipase, fatty acid-binding protein, adiponectin). Cell-seeded constructs exposed to adipogenic medium for 2 weeks in vitro were implanted in severe combined immunodeficient (SCID) mice for 6 weeks. It was shown that ADSCs attached and spread well on scaffolds with good proliferation behaviors and abundance of extracellular matrix deposition. Oil-red O staining and RT-PCR showed adipogenic differentiation potential of ADSCs on scaffolds. Newly formed adipose-like tissue was confirmed in vivo in SCID mice by Oil-red O staining. PLGA/CS porous scaffolds exhibit good compatibility to ADSCs and can be promising biomaterials for adipose tissue engineering.

Adipose tissue engineering with cells in engineered matrices

Tissue engineering has shown promise for the development of constructs to facilitate large volume soft tissue augmentation in reconstructive and cosmetic plastic surgery. This article reviews the key progress to date in the field of adipose tissue engineering. In order to effectively design a soft tissue substitute, it is critical to understand the native tissue environment and function. As such, the basic physiology of adipose tissue is described and the process of adipogenesis is discussed. In this article, we have focused on tissue engineering using a cell-seeded scaffold approach, where engineered extracellular matrix substitutes are seeded with exogenous cells that may contribute to the regenerative response. The strengths and limitations of each of the possible cell sources for adipose tissue engineering, including adipose-derived stem cells, are detailed. We briefly highlight some of the results from the major studies to date, involving a range of synthetic and naturally derived scaffolds. While these studies have shown that adipose tissue regeneration is possible, more research is required to develop optimized constructs that will facilitate safe, predictable and long-term augmentation in clinical applications.

An injectable adipose matrix for soft-tissue reconstruction

BACKGROUND

Soft-tissue repair is currently limited by the availability of autologous tissue sources and the absence of an ideal soft-tissue replacement comparable to native adipose tissue. Extracellular matrix-based biomaterials have demonstrated great potential as instructive scaffolds for regenerative medicine, mechanically and biochemically defined by the tissue of origin. As such, the distinctive high lipid content of adipose tissue requires unique processing conditions to generate a biocompatible scaffold for soft-tissue repair.

METHODS

Human adipose tissue was decellularized to obtain a matrix devoid of lipids and cells while preserving extracellular matrix architecture and bioactivity. To control degradation and volume persistence, the scaffold was cross-linked using hexamethylene diisocyanate and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide. In vitro studies with human adipose-derived stem cells were used to assess cell viability and adipogenic differentiation on the biomaterial. In vivo biocompatibility and volume persistence were evaluated by subcutaneous implantation over 12 weeks in a small-animal model.

RESULTS

The scaffold provided a biocompatible matrix supporting the growth and differentiation of adipose-derived stem cells in vitro. Cross-linking the matrix increased its resistance to enzymatic degradation. Subcutaneous implantation of the acellular adipose matrix in Sprague-Dawley rats showed minimal inflammatory reaction. Adipose tissue development and vascularization were observed in the implant, with host cells migrating into the matrix indicating the instructive potential of the matrix for guiding tissue remodeling and regeneration.

CONCLUSIONS

With its unique biological and mechanical properties, decellularized adipose extracellular matrix is a promising biomaterial scaffold that can potentially be used allogenically for the correction of soft-tissue defects.

Comparing scaffold-free and fibrin-based adipose-derived stromal cell constructs for adipose tissue engineering: an in vitro and in vivo study

Success of adipose tissue engineering for soft tissue repair has been limited by insufficient adipogenic differentiation, an unfavorable host response, and insufficient vascularization. In this study, we examined how scaffold-free spheroid and fibrin-based environments impact these parameters in human adipose-derived stromal cell (ASC)-based adipose constructs. ASCs were differentiated in spheroids or fibrin-based constructs. After 7 days, conditioned medium was collected and spheroids/fibrin-based constructs were either harvested or implanted subcutaneously in athymic mice. Following 7 days of implantation, the number of blood vessels in fibrin-based constructs was significantly higher than in spheroids (93±45 vs. 23±11 vessels/mm(2)), and the inflammatory response to fibrin-based constructs was less severe. The reasons for these results were investigated further in vitro. We found that ASCs in fibrin-based constructs secreted significantly higher levels of the angiogenic factors VEGF and HGF and lower levels of the inflammatory cytokine IL-8. Furthermore, ASCs in fibrin-based constructs secreted significantly higher levels of leptin and showed a 2.5-fold upregulation of the adipogenic transcription factor PPARG and a fourfold to fivefold upregulation of the adipocyte-specific markers FABP4, perilipin, and leptin. These results indicate that fibrin-based ASC constructs are potentially more suitable for ASC-based adipose tissue reconstruction than scaffold-free spheroids.

The adjuvant use of stromal vascular fraction and platelet-rich fibrin for autologous adipose tissue transplantation

Autologous adipose transplantation is rapidly gaining popularity for the restoration of soft tissue defects and lipoatrophy as well as for aesthetic improvements (e.g., facial reconstruction and rejuvenation). However, the current technique is crude that suffers from serious demerits, particularly the long-term unpredictability of volume maintenance due to resorption of the grafted adipose tissue and limited adipogenesis. We hypothesized that the adjuvant use of patient-derived adipose stromal vascular fraction (SVF) and platelet-rich fibrin (PRF) may enhance the overall outcome of autologous fat grafting in plastic and reconstructive surgery. Autologous SVF, with a mean cell number of (4.8±3.79)×10⁷ cells/mL and a mean cell viability of 71.8%, and autologous PRF, with sustained release of multiple angiogenic growth factors, were created before surgical use. The following adipose tissue implants were injected subcutaneously into a rabbit ear's auricula according to the following study design: 2 mL adipose granules and 0.2 mL normal saline solution (AG+NS group), 2 mL adipose granules and 0.2 mL SVF (AG+SVF group), 2 mL adipose granules and 0.2 mL PRF (AG+PRF group), or 2 mL adipose granules combined with 0.1 mL SVF and 0.1 mL PRF (AG+SVF+PRF group). Histological examinations showed that the implanted adipose granules were well engrafted in the AG+SVF+PRF group, with a higher microvessel density 4 weeks postimplantation compared with the other three groups (p<0.01). Twenty-four weeks postimplantation, the resorption rates of implanted tissue in each group were 49.39%±9.47%, 27.25%±4.37%, 36.41%±8.47%, and 17.37%±6.22%, respectively, and were significantly different (p<0.01). The results demonstrated that the efficacy of adipose tissue implantation can be enhanced by using autologous PRF and SVF as therapeutic adjuvants, offering a clinically translatable strategy for soft tissue augmentation and reconstruction.