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Background: External volume expansion devices are effective for adipose tissue regeneration. However, the detailed mechanisms by which external volume expansion devices induce adipose tissue regeneration remain unclear., Methods: An external volume expansion device was used to construct expanded prefabricated adipose tissue in a rat model. CXCL12 levels in local exudate and serum were measured by enzyme-linked immunosorbent assay, and CXCL12 expression in adipose tissue was assessed immunohistochemically. Fluorescent dye (CM-DiI)-labeled bone marrow-derived mesenchymal stromal cells and labeled mesenchymal stromal cells pretreated with the CXCR4 antagonist AMD3100 were transplanted into rats and tracked in vivo by fluorescence imaging., Results: CXCL12 levels in local exudate and serum peaked 2 and 7 days, respectively, after external volume expansion device application. CXCL12 cell counts were significantly higher in the external volume expansion than in the control group. These CXCL12 cells were mainly columnar or cuboidal and began to express peroxisome proliferator-activated receptor γ on day 9. CM-DiI-labeled mesenchymal stromal cells were successfully recruited to the expanded prefabricated adipose tissue, a process partly inhibited by the CXCR4 antagonist AMD3100. These recruited CM-DiI-labeled mesenchymal stromal cells were found among the CXCL12 columnar cells., Conclusions: External volume expansion devices enhance CXCL12 expression levels, especially in columnar and cuboidal cells. The CXCL12/CXCR4 pathway is involved in recruiting circulating mesenchymal stromal cells to participate in adipose regeneration. These findings may reveal the mechanism underlying external volume expansion and provide insights into the refinement of these devices.

Background: Fat grafting has variable and sometimes poor outcomes, and therefore new methods are needed. Multiple studies have demonstrated the excellent performance of external volume expansion and focused only on preexpansion with emphasis on the recipient., Methods: Two mouse models (a suction model and a fat-exchange transplantation model) were established to investigate changes in the origins and biological behaviors of regeneration-related cells in grafted fat under daily suction provided by external volume expansion., Results: Blood supply increased from new host-derived capillaries or macrophage infiltration under suction. CD34-positive cells showed increased migration from the host into the grafts under suction. At week 12, nearly half of the mature adipocytes regenerated in the grafts in the suction group were derived from the host. Peroxisome proliferator-activated receptor γ expression of the suction group was significantly higher than that of controls at weeks 2 and 4 during adipogenesis. The normalized sample weight of the grafted fat was significantly greater than that of controls at 1 (0.081 ± 0.001 versus 0.072 ± 0.005; p < 0.001), 4 (0.060 ± 0.002 versus 0.048 ± 0.001; p = 0.002), 8 (0.060 ± 0.001 versus 0.046 ± 0.001; p < 0.001), and 12 weeks (0.060 ± 0.001 versus 0.046 ± 0.001; p = 0.002)., Conclusions: The mechanical effect of daily suction provided by external volume expansion favors the regeneration of grafted fat and improves retention by promoting the migration of regeneration-related cells and the differentiation of adipocytes. Thus, more mature fat tissue with a well-organized structure was formed under suction.

In plastic and reconstructive surgery, adipose tissue is widely used as effective filler for tissue defects. Strategies for treating soft tissue deficiency, which include free adipose tissue grafts, use of hyaluronic acid, collagen injections, and implantation of synthetic materials, have several clinical limitations. With the aim of overcoming these limitations, researchers have recently utilized tissue engineering chambers to produce large volumes of engineered vascularized fat tissue. However, the process of growing fat tissue in a chamber is still relatively limited, and can result in unpredictable or dissatisfactory final tissue volumes. Therefore, detailed understanding of the process is both necessary and urgent. Many studies have shown that mechanical force can change the function of cells via mechanotransduction. Here, we hypothesized that, besides the inflammatory response, one of the key factors to control the regeneration of vascularized fat flap inside a tissue engineering chamber might be the balance of mechanical forces. To test our hypothesis, we intend to change the balance of forces by means of measures in order to make the equilibrium point in favor of the direction of regeneration. If those measures proved to be feasible, they could be applied in clinical practice to engineer vascularized adipose tissue of predictable size and shape, which would in turn help in the advancement of tissue engineering., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Advances in structural fat transplantation technology have significantly improved the survival rate and stability of grafts. This study investigated the importance of the spatial structural integrity of adipose tissue for adipose regeneration after fat transplantation. We sought to enhance understanding of structural fat transplantation and optimize procedures used for the clinical acquisition, purification, and transplantation of adipose tissue. In an inactivated structuration adipose tissue model established by freezing at -20 °C for 3 days, nearly all cells were dead but the structure was intact. We transplanted this adipose tissue model (group A) or non-treated adipose tissue (group B) into GFP-expressing mice. Group B showed a higher graft survival percentage and less fibrosis than group A. The macrophage infiltration (F4/80) peak period was longer in group A than in group B. The change in vessel density (CD31) was similar in the two groups: it peaked at 4 weeks after transplantation and decreased thereafter. In both groups, the number of Ki67+ cells showed a similar trend. In comparison to group B, group A had more Ki67+ cells at 4-8 weeks after transplantation, but fewer of these cells at 12 weeks after transplantation. The intact spatial structure of adipose tissue, which is supported by adipocytes and extracellular matrix, provides a niche for adipogenesis and angiogenesis after fat transplantation.

Our objective was to explore the mechanism of cell-assisted adipose transplantation by using freshly isolated human stromal vascular fraction (SVF) cells and to observe the dynamic changes of the graft after transplantation. The SVF was isolated from human liposuction aspirates, and 0.5 ml adipose tissue was mixed with 1 × 10(6) SVF cells or culture medium then injected to nude mice subcutaneously. At 1, 4, 7, 14, 30, 60, and 90 days after transplantation, samples were harvested for 1) general observation and retention rate; 2) whole-mount stain; 3) H&E stain; 4) immunohistochemical staining for S100, CD68, and CD34; 5) ELISA for VEGF and bFGF; 6) peroxisome proliferator-activated receptor-γ (PPARγ) fluorescence in situ hybridization. The retention rate in the experiment group was markedly higher than that in the control group. Whole-mount stain shows most of the cells in the center of the graft could not survive the ischemia until day 14. Histology showed new vessels on the surface of the graft at 3 days. However, in the control group, fewer newly formed vessels were detected until day 7. In the late stage of transplantation, gradual fibrosis was found in the graft, and the tissue was divided into a grid-like structure. A large number of round neonatal adipocytes with big nuclei in the center were found surrounding the new vessels, which were S100 and CD34 positive and CD68 negative. In the late stage of transplantation, most of the neonatal adipocytes were human PPARγ positive. Moreover, the SVF group showed a higher level of VEGF and bFGF. SVF assisting adipose transplantation could increase the retention rate of the graft through promoting adipose tissue regeneration via secretion of growth factors, promotion of angiogenesis, and increasing the density of mesenchymal stem cells.

Liposuction aspirates separate into fatty and fluid portions. Cells isolated from the fatty portion are termed processed lipoaspirate (PLA) cells and isolated from the fluid portion termed liposuction aspirate fluid (LAF) cells, both of which contain adipose-derived stromal cells (ASCs). Here, we examined the biological differences between PLA and LAF cells and then tested the differentiation capacity of LAF cells in vivo. The cell surface marker and the multiple differentiation ability of fresh isolated PLA and LAF cells and which from passaged 3-5 were examined in vitro. LAF cells were then incubated in adipogenic medium, stained with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine (DiI), mixed with fibrin glue then injected to nude mice; fibrin glue without cells was as a control. Three months later, the transplants were subjected to macroscopic observation and histological analysis. PLA and LAF cells were similar in growth kinetics, morphology, capacity for differentiation, and surface marker profiles. After plating, both PLA and LAF cells showed increased expression of CD29, CD44, CD133 and HLA DR and decreased expression of CD34. In vivo differentiation assay showed the mixture of LAF cells and fibrin glue formed adipose tissue which contained red fluorescent DiI-positive adipocytes. LAF cells can be harvested more easily than PLA cells. The in vivo adipogenic capacity suggested LAF cells would be useful and valuable for cell-based therapies and soft tissue reconstruction., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Inflammatory responses mediated by macrophages play a role in tissue repair. However, it is unclear whether the repair in the donor site after liposuction would have any effects on fat graft retention in the recipient site. This study is designed to evaluate the effects of a macrophage‐mediated inflammatory response in donor sites on long‐term retention of fat grafting. In this study, mice were randomly divided into two groups. One underwent simulated liposuction, called the fat procurement plus grafting (Pro‐Grafting) group, and the other underwent sham surgery, called the fat grafting only (Grafting Only) group. The prepared fat (0.3 ml each) was engrafted and cellular events over a 90‐day period were assessed. We found macrophages were infiltrated into adipose tissue at the recipient site in the Grafting Only group within 7 days and the repair essentially completed within 30 days. By contrast, few macrophages infiltrated the recipient site in the Pro‐Grafting group within 7 days and the entire remodeling process took 30 days longer in the Pro‐Grafting than the Grafting Only group. Moreover, C‐reactive protein levels were immediately upregulated after surgery, and the inflammatory factors' expression was higher at the donor rather than the recipient site. However, the repair processes and the long‐term retention rate became normal when the adipose tissue was grafted after the donor site did not require macrophages for repair. Therefore, we suggest higher inflammatory factors promote macrophage infiltration and the adipose tissue regeneration process at the donor site. This process is delayed at the recipient site, which may affect long‐term retention of fat grafts. [ABSTRACT FROM AUTHOR]