Micro-computed tomography evaluation of human fat grafts in nude mice

The efficiency of human fat products in wound healing: A systematic review and meta-analysis

Wound development and healing involve intricate genetic and molecular processes, posing significant clinical management challenges. The objective of this study was to assess commonly used fat extracts' efficacy and safety (autologous fat, stromal vascular fraction and adipose-derived stem cells) in wound healing, particularly for refractory wounds, with the goal of providing evidence in clinical use. After a systematic review, 21 randomised controlled trials were included in our study. Based on the classification of human fat products, our meta-analysis revealed that the use of human fat products could speed healing rate, shorten healing time and achieve more complete healing, with statistically significant differences in outcome indicators when compared to conventional treatments. The analysis of histological findings across various studies indicated that fat extracts can promote epithelialization, collagen deposition and vascularization, thereby facilitating tissue regeneration and reducing inflammatory reactions. There were potential benefits to reducing patient pain levels after using adipose extracts. Furthermore, we analysed and summarised adverse events indicating the safe and effective clinical use of human fat products in wound treatment. Our research findings supported the efficiency of human fat products and demonstrated a high degree of safety in the clinical practice of wound management.

In Vivo MRI Tracking of Degradable Polyurethane Hydrogel Degradation In Situ Using a Manganese Porphyrin Contrast Agent

BACKGROUND

A noninvasive method to track implanted biomaterials is desirable for real-time monitoring of material interactions with host tissues and assessment of efficacy and safety.

PURPOSE

To explore quantitative in vivo tracking of polyurethane implants using a manganese porphyrin (MnP) contrast agent containing a covalent binding site for pairing to polymers.

STUDY TYPE

Prospective, longitudinal.

ANIMAL MODEL

Rodent model of dorsal subcutaneous implants (10 female Sprague Dawley rats).

FIELD STRENGTH/SEQUENCE

A 3-T; two-dimensional (2D) T1-weighted spin-echo (SE), T2-weighted turbo SE, three-dimensional (3D) spoiled gradient-echo T1 mapping with variable flip angles.

ASSESSMENT

A new MnP-vinyl contrast agent to covalently label polyurethane hydrogels was synthesized and chemically characterized. Stability of binding was assessed in vitro. MRI was performed in vitro on unlabeled hydrogels and hydrogels labeled at different concentrations, and in vivo on rats with unlabeled and labeled hydrogels implanted dorsally. In vivo MRI was performed at 1, 3, 5, and 7 weeks postimplantation. Implants were easily identified on T1-weighted SE, and fluid accumulation from inflammation was distinguished on T2-weighted turbo SE. Implants were segmented on contiguous T1-weighted SPGR slices using a threshold of 1.8 times the background muscle signal intensity; implant volume and mean T1 values were then calculated at each timepoint. Histopathology was performed on implants in the same plane as MRI and compared to imaging results.

STATISTICAL TESTS

Unpaired t-tests and one-way analysis of variance (ANOVA) were used for comparisons. A P value <0.05 was considered to be statistically significant.

RESULTS

Hydrogel labeling with MnP resulted in a significant T1 reduction in vitro (T1 = 517 ± 36 msec vs. 879 ± 147 msec unlabeled). Mean T1 values of labeled implants in rats increased significantly by 23% over time, from 1 to 7 weeks postimplantation (651 ± 49 msec to 801 ± 72 msec), indicating decreasing implant density.

DATA CONCLUSION

Polymer-binding MnP enables in vivo tracking of vinyl-group coupling polymers.

EVIDENCE LEVEL

1.

TECHNICAL EFFICACY

Stage 1.

Decellularized Adipose Matrices Can Alleviate Radiation-Induced Skin Fibrosis

Objective: Radiation therapy is commonplace for cancer treatment but often results in fibrosis and atrophy of surrounding soft tissue. Decellularized adipose matrices (DAMs) have been reported to improve these soft tissue defects through the promotion of adipogenesis. These matrices are decellularized by a combination of physical, chemical, and enzymatic methods to minimize their immunologic effects while promoting their regenerative effects. In this study, we aimed at exploring the regenerative ability of a DAM (renuva®; MTF biologics, Edison, NJ) in radiation-induced soft tissue injury. Approach: Fresh human lipoaspirate or DAM was injected into the irradiated scalp of CD-1 nude mice, and volume retention was monitored radiographically over 8 weeks. Explanted grafts were histologically assessed, and overlying skin was examined histologically and biomechanically. Irradiated human skin was also evaluated from patients after fat grafting or DAM injection. However, integrating data between murine and human skin in all cohorts is limited given the genetic variability between the two species. Results: Volume retention was found to be greater with fat grafts, though DAM retention was, nonetheless, appreciated at irradiated sites. Improvement in both mouse and human irradiated skin overlying fat and DAM grafts was observed in terms of biomechanical stiffness, dermal thickness, collagen density, collagen fiber networks, and skin vascularity. Innovation: This is the first demonstration of the use of DAMs for augmenting the regenerative potential of irradiated mouse and human skin. Conclusions: These findings support the use of DAMs to address soft tissue atrophy after radiation therapy. Morphological characteristics of the irradiated skin can also be improved with DAM grafting.

Fat Grafts Augmented With Vitamin E Improve Volume Retention and Radiation-Induced Fibrosis

BACKGROUND

Treatments for radiation-induced fibrosis range from vitamin E and pentoxifylline systemically to deferoxamine and fat grafting locally. Regarding fat grafting, volume retention hinders its long-term functionality and is affected by two factors: inflammation and necrosis secondary to hypovascularity.

OBJECTIVE

We aimed to simultaneously improve fat graft retention and radiation-induced fibrosis by integrating vitamin E and pentoxifylline into fat grafts locally.

METHODS

Forty adult CD-1 nude male mice at 6 weeks of age underwent scalp irradiation and recovered for four weeks to allow for the development of fibrosis. Mice received 200μL of donor human fat graft to the scalp. Mice were separated into 4 conditions: no grafting, fat graft without treatment, graft treated with pentoxifylline, and graft treated with vitamin E. Fat graft volume retention was monitored in-vivo using microCT scans at weeks 0, 1, 2, 4, 6, and 8 after grafting. Histological and cytokine analysis of the scalp skin and fat grafts were also performed.

RESULTS

Vitamin E (VE) treated grafts had significant improvement in dermal thickness and collagen density of overlying skin compared to all other groups. VE decreased 8-isoprostane and increased CD31 + staining compared to the other grafted groups. Cytokine analysis revealed decreased inflammatory and increased angiogenic markers in both the fat graft and overlying skin of the vitamin E group. Fat graft volume retention was significantly improved in the vitamin E group starting at 1 week post grafting.

CONCLUSION

Radiation-induced fibrosis and fat graft volume retention are both simultaneously improved with local administration of vitamin E.

In Vivo Evaluation of Mechanically Processed Stromal Vascular Fraction in a Chamber Vascularized by an Arteriovenous Shunt

Mechanically processed stromal vascular fraction (mSVF) is a promising source for regenerative purposes. To study the in vivo fate of the mSVF, we herein used a vascularized tissue engineering chamber that insulates the target mSVF from the surrounding environment. In contrast to previous models, we propose an arteriovenous (AV) shunt between saphenous vessels in rats without a venous graft. Mechanical SVF was processed from the fat pads of male Sprague Dawley rats, mixed with a fibrin hydrogel and implanted into an inguinal tissue engineering chamber. An arteriovenous shunt was established between saphenous artery and vein. On the contralateral side, an mSVF-fibrin hydrogel mix without vascular axis served as a non-vascularized control. After two and six weeks, rats were sacrificed for further analysis. Mechanical SVF showed significant numbers of mesenchymal stromal cells. Vascularized mSVF explants gained weight over time. Perilipin and CD31 expression were significantly higher in the mSVF explants after six weeks while no difference in DAPI positive cells, collagen deposition and FABP4 expression was observed. Morphologically, no differentiated adipocytes but a dense cell-rich tissue with perilipin-positive cells was found after six weeks. The phosphorylation of ERK1/2 was significantly enhanced after six weeks while Akt activation remained unaltered. Finally, mSVF explants stably expressed and released VEGF, bFGF and TGFb. Vascularized mSVF is able to proliferate and express adipocyte-specific markers. The AV shunt model is a valuable refinement of currently existing AV loop models in the rat which contributes to the fundamental 3R principles of animal research.

Angiogenic CD34+CD146+ adipose-derived stromal cells augment recovery of soft tissue after radiotherapy

Radiation therapy is effective for cancer treatment but may also result in collateral soft tissue contracture, contour deformities, and non-healing wounds. Autologous fat transfer has been described to improve tissue architecture and function of radiation-induced fibrosis and these effects may be augmented by enrichment with specific adipose-derived stromal cells (ASCs) with enhanced angiogenic potential. CD34+CD146+, CD34+CD146-, or CD34+ unfractionated human ASCs were isolated by flow cytometry and used to supplement human lipoaspirate placed beneath the scalp of irradiated mice. Volume retention was followed radiographically and fat grafts as well as overlying soft tissue were harvested after eight weeks for histologic and biomechanical analyses. Radiographic evaluation revealed the highest volume retention in fat grafts supplemented with CD34+CD146+ ASCs, and these grafts were also found to have greater histologic integrity than other groups. Irradiated skin overlying CD34+CD146+ ASC-enriched grafts was significantly more vascularized than other treatment groups, had significantly less dermal thickness and collagen deposition, and the greatest improvement in fibrillin staining and return of elasticity. Radiation therapy obliterates vascularity and contributes to scarring and loss of tissue function. ASC-enrichment of fat grafts with CD34+CD146+ ASCs not only enhances fat graft vascularization and retention, but also significantly promotes improvement in overlying radiation-injured soft tissue. This regenerative effect on skin is highly promising for patients with impaired wound healing and deformities following radiotherapy.

Perilipin2 is an Earlier Marker Than Perilipin1 for Identifying Adipocyte Regeneration in Fat Grafts

BACKGROUND

Both perilipin1 (Plin1) and perilipin2 (Plin2) play a crucial role in regulating lipid droplet (LD) formation in fat cells. Plin2 is expressed early in the adipocyte differentiation process but is replaced by Plin1 after cell maturation. In free fat grafts, only a small number of adipocytes remain alive or are replaced by newly regenerated fat cells. It is known that Plin1-positive adipocytes participate in regeneration, but the characteristics of Plin2 expression during this process are still poorly understood.

OBJECTIVES

The aim of this study was to investigate whether Plin2 is a more precise early marker for detecting adipocyte regeneration in fat grafts than Plin1.

METHODS

Autologous fat tissue (120 mg) harvested from inguinal fat pads was injected under the scalps of C57 mice. Samples were explanted at days 3, 7, 15, and 30 after transplantation. Changes in sample size and weight were evaluated. Hematoxylin-eosin staining, real-time polymerase chain reaction, and immunostaining of Plin1 and Plin2 expression were performed.

RESULTS

Plin1, but not Plin2, expression was detected in the freshly harvested fat, but the latter was activated after grafting. Newly regenerated Plin2-positive adipocytes increased from day 3 to day 7 and then declined, whereas the number of Plin1-positive fat cells decreased first and began to increase after day 15. The expression levels of Plin1 and Plin2 mRNA demonstrated similar changes over time. At day 30, adipocytes lost Plin2 expression and were positive for Plin1 again.

CONCLUSIONS

Our experiments showed convincing evidence that Plin2 expression could be used to detect early adipocyte regeneration in grafted fat tissue.

Human ESC-derived MSCs enhance fat engraftment by promoting adipocyte reaggregation, secreting CCL2 and mobilizing macrophages

Mesenchymal stem cells (MSCs) derived from somatic tissues have been used to promote lipotransfer, a common practice in cosmetic surgery. However, the effect of lipotransfer varies, and the mechanism of action remains vague. To address these questions, we differentiated human embryonic stem cells, a stable and unlimited source, into MSCs (EMSCs). Then we subcutaneously transplanted human fat aspirates together with EMSCs or PBS as a control into the back of nude mice. Within 24 h of transplantation, EMSCs promoted aggregation and encapsulation of injected fat tissues. Afterward, all grafts gradually shrank. However, EMSC-containing grafts were larger, heavier and had fewer dark areas on the surface than the control grafts. Histologically, more live adipocytes, vascular cells, and macrophages and less fibrosis were observed in EMSC-containing grafts than in the controls. Some EMSCs differentiated into vascular cells and adipocytes in the EMSC-containing grafts. RNA sequencing revealed that human RNA was shown to decline rapidly, while mouse RNA increased in the grafts; further, human genes related to extracellular matrix remodeling, adipogenesis, and chemokine (including CCL2) signaling were expressed at higher levels in the EMSC-containing grafts than they were in the controls. CCL2 knockout reduced macrophage migration towards EMSCs in vitro and early macrophage recruitment to the grafts and the pro-engraftment effect of EMSCs in vivo. Treating mice with a macrophage inhibitor abolished the EMSC effects and converted the grafts to heavy masses of cell debris. Together, these data demonstrate that EMSCs promote fat engraftment via enhanced tissue reconstitution and encapsulation of implanted tissues, which was followed by increased angiogenesis and adipocyte survival and reduced fibrosis, in which stimulated CCL2 signaling and mobilized macrophages play pivotal roles.

[The influence of harvesting and processing on the regenerative potential in fat grafting]

The autologous lipotransfer represents an established method in the field of Plastic Surgery. As a reliable and safe method for breast reconstruction and breast augmentation it offers an alternative to established methods such as implants and flap surgery.Survival rate of adipose derived stromal cells limits success or failure of fat grafting. Slight changes in the fat grafting process can lead to huge changes in ADSC-survival rate.This review wants to optimize the fat-grafting process to ensure best outcomes.

The antifibrotic adipose-derived stromal cell: Grafted fat enriched with CD74+ adipose-derived stromal cells reduces chronic radiation-induced skin fibrosis

Fat grafting can reduce radiation‐induced fibrosis. Improved outcomes are found when fat grafts are enriched with adipose‐derived stromal cells (ASCs), implicating ASCs as key drivers of soft tissue regeneration. We have identified a subpopulation of ASCs positive for CD74 with enhanced antifibrotic effects. Compared to CD74− and unsorted (US) ASCs, CD74+ ASCs have increased expression of hepatocyte growth factor, fibroblast growth factor 2, and transforming growth factor β3 (TGF‐β3) and decreased levels of TGF‐β1. Dermal fibroblasts incubated with conditioned media from CD74+ ASCs produced less collagen upon stimulation, compared to fibroblasts incubated with media from CD74− or US ASCs. Upon transplantation, fat grafts enriched with CD74+ ASCs reduced the stiffness, dermal thickness, and collagen content of overlying skin, and decreased the relative proportions of more fibrotic dermal fibroblasts. Improvements in several extracellular matrix components were also appreciated on immunofluorescent staining. Together these findings indicate CD74+ ASCs have antifibrotic qualities and may play an important role in future strategies to address fibrotic remodeling following radiation‐induced fibrosis.

CD34+CD146+ adipose-derived stromal cells enhance engraftment of transplanted fat

Fat grafting is a surgical technique able to reconstruct and regenerate soft tissue. The adipose‐derived stromal cells (ASCs) within the stromal vascular fraction are believed to drive these beneficial effects. ASCs are increasingly recognized to be a heterogeneous group, comprised of multiple stem and progenitor subpopulations with distinct functions. We hypothesized the existence of an ASC subpopulation with enhanced angiogenic potential. Human ASCs that were CD34+CD146+, CD34+CD146−, or CD34+ unfractionated (UF) were isolated by flow cytometry for comparison of expression of proangiogenic factors and endothelial tube‐forming potential. Next, lipoaspirate was enriched with either CD34+CD146+, CD34+CD146−, CD34+ UF ASCs, or was not enriched, and grafted beneath the scalp skin of immunodeficient CD‐1 Nude mice (10 000 cells/200 μL/graft). Fat retention was monitored radiographically more than 8 weeks and fat grafts were harvested for histological assessment of quality and vascularization. The CD34+CD146+ subpopulation comprised ~30% of ASCs, and exhibited increased expression of vascular endothelial growth factor and angiopoietin‐1 compared to CD34+CD146− and CD34+ UF ASCs, and increased expression of fibroblast growth factor‐2 compared to CD34+CD146− ASCs. The CD34+CD146+ subpopulation exhibited enhanced induction of tube‐formation compared to CD34+CD146− ASCs. Upon transplantation, fat enriched CD34+CD146+ ASCs underwent less resorption and had improved histologic quality and vascularization. We have identified a subpopulation of CD34+ ASCs with enhanced angiogenic effects in vitro and in vivo, likely mediated by increased expression of potent proangiogenic factors. These findings suggest that enriching lipoaspirate with CD34+CD146+ ASCs may enhance fat graft vascularization and retention in the clinical setting.

Transplanted fat adapts to the environment of the recipient: An animal study using a murine model to investigate the suitability of recipient obesity mismatch in face transplantation

INTRODUCTION

Face transplantation can offer patients with severe facial deformities a better quality of life, but questions of donor suitability remain unanswered. The aim of this study is to determine how an obesity mismatch between donor and recipient affects facial fat graft retention and cellular properties, potentially increasing the donor pool substantially. We hypothesized that facial fat would respond to the microenvironment of the recipient and developed an animal model to evaluate this hypothesis.

METHODS

This study utilized 30 C57BL/6J wild-type (WT) and 30 diet-induced obese (DIO), immunologically identical mice. One hundred seventy-five micrograms of perigonadal fat was harvested from 10 mice from each group and transplanted to the subcutaneous scalp of the remaining mice. Ten DIO mice were implanted with DIO donor fat and 10 with WT donor fat. The 10 WT mice were implanted with DIO fat and 10 with WT fat. Recipients underwent micro-CT scans at 2 days and 2, 4, 6, 8, 10, and 12 weeks postoperation. Scans were 3D-reconstructed to assess transplanted fat volume. At 12 weeks, the transplanted fat was analyzed by hematoxylin-eosin staining.

RESULTS

Volume retention of the transplanted fat depended on recipient phenotype, which was confirmed through ANOVA and Student-Newman-Keuls test. Graft volume with a DIO recipient increased with both a DIO (25.6%) and a WT (24.4%) donor from 2 days to 12 weeks postoperation. In a WT recipient, graft volume decreased when the donor was WT (54.0%) and DIO (53.0%). Average cellular volume was also dependent on the recipient phenotype.

CONCLUSION

This study demonstrates that fat transplanted to the facial region responds to the surrounding microenvironment both macroscopically and microscopically. This study has large implications in donor suitability in face transplant, as it indicates that a donor-recipient obesity mismatch may be acceptable.

Three-Dimensional Ultrasound Versus Computerized Tomography in Fat Graft Volumetric Analysis

Studies evaluating fat grafting in mice have frequently used micro-computed tomography (micro-CT) as an accurate radiographic tool to measure longitudinal volume retention without killing the animal. Over the past decade, however, microultrasonography has emerged as an equally powerful preclinical imaging tool. Given their respective strengths in 3-dimensional reconstruction, there is no study to our knowledge that directly compares micro-CT with microultrasound in volumetric analysis. In this study, we compared the performance of micro-CT with microultrasound in the evaluation of adipose tissue graft volume in a murine model. Fifteen immunodeficient mice were given 200 μL of adipose tissue grafts. In vivo volumetric analysis of the grafts by micro-CT and microultrasound was conducted at discrete time points up to postoperative day 105. Three mice were killed at multiple time points, and explanted grafts were reimaged by CT and ultrasound, as mentioned previously. Analysis revealed that in vivo graft volumes measured by micro-CT do not differ significantly from those of microultrasound. Furthermore, both micro-CT and microultrasound were capable of accurately measuring fat grafts as in vivo volumes closely correlated with explanted volumes. Finally, ultrasound was found to yield improved soft tissue contrast compared with micro-CT. Therefore, either modality may be used, depending on experimental needs.

Fat Grafting into Younger Recipients Improves Volume Retention in an Animal Model

BACKGROUND

Soft-tissue deficits associated with various craniofacial anomalies can be addressed by fat grafting, although outcomes remain unpredictable. Furthermore, consensus does not exist for timing of these procedures. Whereas some advocate approaching soft-tissue reconstruction after the underlying skeletal foundation has been corrected, other studies have suggested that earlier grafting may exploit a younger recipient niche that is more conducive to fat graft survival. As there is a dearth of research investigating effects of recipient age on fat graft volume retention, this study compared the effectiveness of fat grafting in younger versus older animals through a longitudinal, in vivo analysis.

METHODS

Human lipoaspirate from three healthy female donors was grafted subcutaneously over the calvaria of immunocompromised mice. Volume retention over 8 weeks was evaluated using micro-computed tomography at three experimental ages: 3 weeks, 6 months, and 1 year. Histologic examination was performed on explanted grafts to evaluate graft health and vascularity. Recipient-site vascularity was also evaluated by confocal microscopy.

RESULTS

The greatest retention of fat graft volume was noted in the youngest group compared with both older groups (p < 0.05) at 6 and 8 weeks after grafting. Histologic and immunohistochemical analyses revealed that improved retention in younger groups was associated with greater fat graft integrity and more robust vascularization.

CONCLUSION

The authors' study provides evidence that grafting fat into a younger recipient site correlates with improved volume retention over time, suggesting that beginning soft-tissue reconstruction with fat grafting in patients at an earlier age may be preferable to late correction.

Generation of Functional Human Adipose Tissue in Mice from Primed Progenitor Cells

Adipose tissue (AT) is used extensively in reconstructive and regenerative therapies, but transplanted fat often undergoes cell death, leading to inflammation, calcification, and requirement for further revision surgery. Previously, we have found that mesenchymal progenitor cells within human AT can proliferate in three-dimensional culture under proangiogenic conditions. These cells (primed ADipose progenitor cells, PADS) robustly differentiate into adipocytes in vitro (ad-PADS). The goal of this study is to determine whether ad-PADS can form structured AT in vivo, with potential for use in surgical applications. Grafts formed from ad-PADS were compared to grafts formed from AT obtained by liposuction after implantation into nude mice. Graft volume was measured by microcomputed tomography scanning, and the functionality of cells within the graft was assessed by quantifying circulating human adiponectin. The degree of graft vascularization by donor or host vessels and the content of human or mouse adipocytes within the graft were measured using species-specific endothelial and adipocyte-specific quantitative real time polymerase chain reaction probes, and histochemistry with mouse and human-specific lectins. Our results show that ad-PADS grafted subcutaneously into nude mice induce robust vascularization from the host, continue to increase in volume over time, express the human adipocyte marker PLIN1 at levels comparable to human AT, and secrete increasing amounts of human adiponectin into the mouse circulation. In contrast, grafts composed of AT fragments obtained by liposuction become less vascularized, develop regions of calcification and decreased content of PLIN1, and secrete lower amounts of adiponectin per unit volume. Enrichment of liposuction tissue with ad-PADS improves vascularization, indicating that ad-PADS may be proangiogenic. Mechanistically, ad-PADS express an extracellular matrix gene signature that includes elements previously associated with small vessel development (COL4A1). Thus, through the formation of a proangiogenic environment, ad-PADS can form functional AT with capacity for long-term survival, and can potentially be used to improve outcomes in reconstructive and regenerative medicine.

Deferoxamine Preconditioning of Irradiated Tissue Improves Perfusion and Fat Graft Retention

BACKGROUND

Radiation therapy is a mainstay in the treatment of many malignancies, but collateral damage to surrounding tissue, with resultant hypovascularity, fibrosis, and atrophy, can be difficult to reconstruct. Fat grafting has been shown to improve the quality of irradiated skin, but volume retention of the graft is significantly decreased. Deferoxamine is a U.S. Food and Drug Administration-approved iron-chelating medication for acute iron intoxication and chronic iron overload that has also been shown to increase angiogenesis. The present study evaluates the effects of deferoxamine treatment on irradiated skin and subsequent fat graft volume retention.

METHODS

Mice underwent irradiation to the scalp followed by treatment with deferoxamine or saline and perfusion and were analyzed using laser Doppler analysis. Human fat grafts were then placed beneath the scalp and retention was also followed up to 8 weeks radiographically. Finally, histologic evaluation of overlying skin was performed to evaluate the effects of deferoxamine preconditioning.

RESULTS

Treatment with deferoxamine resulted in significantly increased perfusion, as demonstrated by laser Doppler analysis and CD31 immunofluorescent staining (p < 0.05). Increased dermal thickness and collagen content secondary to irradiation, however, were not affected by deferoxamine (p > 0.05). Importantly, fat graft volume retention was significantly increased when the irradiated recipient site was preconditioned with deferoxamine (p < 0.05).

CONCLUSIONS

The authors' results demonstrated increased perfusion with deferoxamine treatment, which was also associated with improved fat graft volume retention. Preconditioning with deferoxamine may thus enhance fat graft outcomes for soft-tissue reconstruction following radiation therapy.

Cell-Based Soft Tissue Reconstruction in a Hydrogel Scaffold

BACKGROUND

Renevia is a hyaluronin-gelatin crosslinked matrix scaffold that has been studied as an alternative to adipose transfer in soft tissue reconstruction. It is designed to emulate the native extracellular matrix environment by supporting stromal vascular fraction (SVF) cell attachment, survival, and proliferation, thus promoting cell-based volume restoration. However, the concentration of incorporated cells for a clinically relevant result has yet to be determined.

METHODS

Five experimental groups of seven CD-1 nude immunodeficient mice were given 250 μL grafts of the following composition: 1 million human SVF cells per mL of Renevia scaffold, 6 million human SVF cells per mL scaffold, 12 million human SVF cells per mL scaffold, Renevia scaffold-alone or human adipose tissue-alone. Volumetric analysis was conducted at discrete time points over 16 weeks using 3-dimensional ultrasound, after which time the grafts were explanted for histologic analysis.

RESULTS

At the conclusion of the study at week 16, the Renevia scaffold group incorporating the highest concentration of human SVF cells (12 million cells per mL scaffold) had significantly greater volume retention compared with the 2 lower concentrations, scaffold-alone and fat-alone groups. Histology of the 12 million scaffold group revealed abundant adipocyte formation within the scaffold, exceeding that observed in the 6 million, 1 million, and scaffold-alone groups. The 12 million group also demonstrated significantly increased vascularity per CD31 staining.

CONCLUSIONS

Stromal vascular fraction cells coupled with Renevia hydrogel scaffold can enhance soft tissue volume reconstruction. In this study, we observed the greatest effect with 12 million cells per mL. From the perspective of volume retention, incorporation of higher concentrations of SVF cells with Renevia may be an alternative to conventional adipose tissue grafting.

Is Centrifugation Necessary for Processing Lipoaspirate Harvested via Water-Jet Force Assisted Technique before Grafting? Evidence of Lipoaspirate Concentration With Enhanced Fat Graft Survival

BACKGROUND

Although water-jet force-assisted liposuction technique (WAL) was demonstrated to have favorable effects on fat grafting, controversy continues concerning the application of centrifugation for lipoaspirate harvested via WAL. As a controversial technique, plastic surgeons often get perplexed to the necessity of using centrifugation during fat grafting procedure. In the present study, we adopted the recommended centrifugal intensity (1200g, 3 minutes) to process lipoaspirate and focused on the influence of centrifugation on the fate of lipoaspirate harvested with WAL technique.

METHODS

Lipoaspirate was obtained from 10 healthy Chinese female patients who underwent cosmetic liposuction. The harvested lipoaspirate was either not centrifuged (group A) or centrifuged at 1200g for 3 minutes (group B). Lipoaspirate from each group was compared in the in vitro and in vivo experiments. The influence of centrifugation on lipoaspirate viability and lipoaspirate survival after grafting were evaluated.

RESULTS

The viability of the lipoaspirates was similar between equally volumetric uncentrifugal and centrifugal lipoaspirate. However, centrifugation at 1200g for 3 minutes concentrated stromal vascular fraction cells and adipose-derived stem cells in lipoaspirate; greater angiogenesis and weight retention rates were observed in centrifugal lipoaspirate after grafting than those uncentrifugal lipoaspirate.

CONCLUSIONS

Centrifugation at 1200g for 3 minutes enhanced the survival of lipoaspirate harvested via WAL technique after grafting. Centrifugation at 1200g for 3 minutes was recommended to process lipoaspirate harvested with water-jet force assistance before grafting.

* Microcomputed Tomography Technique for In Vivo Three-Dimensional Fat Tissue Volume Evaluation After Polymer Injection

Tissue engineering technologies are new and promising techniques in fat tissue reconstruction. However, to assess their efficacy before any clinical application, in vivo experiments are mandatory. This study assesses whether microcomputed tomography (CT) scan imaging is suitable to analyze in vivo the behavior of injected engineered polymer and changes in fat tissue. The volume of mice inguinal fat pads and the resorption rate of different polymers were analyzed by CT scan for up to 3 months. Different biomaterials were used, including our innovative microspheres loaded with oleic acid. We were able to follow in vivo the polymer and the fat volume of the same animals during a long-term follow-up of 90 days. Semiautomatic three-dimensional quantification allowed to determine the fat volume enhancement after injection, as well as the resorption rate of our product compared to other biomaterials (i.e., polylactic and hyaluronic acid) until 90 days. Our results demonstrate the encouraging proof-of-principle evidence for the application of micro-CT scan technology to follow in vivo biodegradable polymers in a fat tissue engineering approach. This noninvasive technique offers the advantages of the long-term follow-up of fat tissue and synthetic materials in the same animals, which allows both a scientific evaluation of the measurements and the reduction of the number of animals used in in vivo protocols in accordance with the 3 "R" principles governing the use of animals in science.

Purified Adipose-Derived Stromal Cells Provide Superior Fat Graft Retention Compared with Unenriched Stromal Vascular Fraction

Cell-assisted lipotransfer has shown much promise as a technique to improve fat graft retention in both mouse and human studies. However, the literature varies as to whether fresh stromal vascular fraction or culture-expanded adipose-derived stromal cells are used to augment volume retention. The authors' study sought to determine whether there was a significant advantage to using adipose-derived stromal cells over unpurified stromal vascular fraction cells in a mouse model of cell-assisted lipotransfer.

A Novel Method of Human Adipose-Derived Stem Cell Isolation with Resultant Increased Cell Yield

BACKGROUND

The authors have developed a novel protocol for isolating adipose-derived stem cells from human lipoaspirate. In this study, they compare their new method to a previously published standard protocol.

METHODS

Human adipose-derived stem cell isolation was performed using two methods to compare cell yield, cell viability, cell proliferation, and regenerative potential. The new and conventional isolation methods differ in two key areas: the collagenase digestion buffer constituents and the use of an orbital shaker. The osteogenic and adipogenic potential of adipose-derived stem cells isolated using both protocols was assessed in vitro, and gene expression analysis was performed. To assess the ability of the isolated cells to generate bone in vivo, the authors created critical-size calvarial defects in mice, which were treated with adipose-derived stem cells loaded onto hydroxyapatite-coated poly(lactic-co-glycolic acid) scaffolds. To test the ability of the isolated cells to enhance adipogenesis, the cells were added to lipoaspirate and placed beneath the scalp of immunocompromised mice. Fat graft volume retention was subsequently assessed by serial computed tomographic volumetric scanning.

RESULTS

The new method resulted in a 10-fold increased yield of adipose-derived stem cells compared with the conventional method. Cells harvested using the new method demonstrated significantly increased cell viability and proliferation in vitro (p < 0.05). New method cells also demonstrated significantly enhanced osteogenic and adipogenic differentiation capacity in vitro (p < 0.05) in comparison with the conventional method cells. Both cell groups demonstrated equivalent osteogenic and adipogenic regenerative potential in mice.

CONCLUSIONS

The authors have developed a protocol that maximizes the yield of adipose-derived stem cells derived from lipoaspirate. The new method cells have increased osteogenic and adipogenic potential in vitro and are not inferior to conventional method cells in terms of their ability to generate bone and fat in vivo.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, V.

Magnetic Nanoparticle-Based Upregulation of B-Cell Lymphoma 2 Enhances Bone Regeneration

Clinical translation of cell-based strategies for tissue regeneration remains challenging because survival of implanted cells within hostile, hypoxic wound environments is uncertain. Overexpression of B-cell lymphoma 2 (Bcl-2) has been shown to inhibit apoptosis in implanted cells. The present study describes an "off the shelf" prefabricated scaffold integrated with magnetic nanoparticles (MNPs) used to upregulate Bcl-2 expression in implanted adipose-derived stromal cells for bone regeneration. Iron oxide cores were sequentially coated with branched polyethyleneimine, minicircle plasmid encoding green fluorescent protein and Bcl-2, and poly-β-amino ester. Through in vitro assays, increased osteogenic potential and biological resilience were demonstrated in the magnetofected group over control and nucleofected groups. Similarly, our in vivo calvarial defect study showed that magnetofection had an efficiency rate of 30%, which in turn resulted in significantly more healing compared with control group and nucleofected group. Our novel, prefabricated MNP-integrated scaffold allows for in situ postimplant temporospatial control of cell transfection to augment bone regeneration. Stem Cells Translational Medicine 2017;6:151-160.

Quantification of adipose transfer viability using a novel, bioluminescent murine model

Fat grafting has highly variable long-term results. Research efforts to improve the reliability of fat grafting are limited by inefficient methods for evaluation of fat engraftment. In this work, we describe a novel animal model for the quantitative evaluation of fat grafting using in vivo bioluminescence of adipocytes from luciferase-expressing mice. Subcutaneous adipose tissue from GFP and luciferase-expressing FVB mice were obtained. The samples were homogenized, decanted, and injected into the dorsal skin folds of wild-type FVB mice. Viability of the transferred tissue was examined over a 28-day time period with quantitative bioluminescence after luciferin injection. All animals demonstrated viable adipose transfer with bioluminescence detectable on days 0, 1, 7, 14, and 28. This animal model may be used for noninvasive, longitudinal studies for quantification of the fat engraftment process.

Characterization of human adipose tissue-derived stem cells with enhanced angiogenic and adipogenic properties

Autologous fat grafting is a popular method for soft tissue reconstructions but graft survival remains highly unpredictable. Supplementation of the graft with the stromal vascular fraction (SVF) or cultured adipose tissue-derived stem cells (ASCs) can enhance graft viability. In this study we have examined the phenotypic properties of a selected population of cells isolated from ASCs, with a view to determining their suitability for transplantation into grafts. ASCs were isolated from the SVF of human abdominal fat (n = 8 female patients) and CD146⁺ cells were selected using immunomagnetic beads. The angiogenic and adipogenic properties of the positively selected cells were compared with the negative fraction. CD146⁺ cells expressed the immunophenotypic characteristics of pericytes. With prolonged in vitro expansion, CD146^- cells exhibited increased population doubling times and morphological signs of senescence, whereas CD146⁺ cells did not. CD146⁺ cells expressed higher levels of the angiogenic molecules VEGF-A, angiopoietin-1 and FGF-1. Conditioned medium taken from CD146⁺ cells significantly increased formation of in vitro endothelial cell tube networks, whereas CD146^- cells did not. CD146⁺ cells could be differentiated into adipocytes in greater numbers than CD146^- cells. Consistent with this, differentiated CD146⁺ cells expressed higher levels of the adipocyte markers adiponectin and leptin. These results suggest that CD146⁺ cells selected from a heterogeneous mix of ASCs have more favourable angiogenic and adipogenic properties, which might provide significant benefits for reconstructive and tissue-engineering applications. Copyright © 2016 John Wiley & Sons, Ltd.

Cell-Assisted Lipotransfer Improves Volume Retention in Irradiated Recipient Sites and Rescues Radiation-Induced Skin Changes

Radiation therapy is not only a mainstay in the treatment of many malignancies but also results in collateral obliteration of microvasculature and dermal/subcutaneous fibrosis. Soft tissue reconstruction of hypovascular, irradiated recipient sites through fat grafting remains challenging; however, a coincident improvement in surrounding skin quality has been noted. Cell-assisted lipotransfer (CAL), the enrichment of fat with additional adipose-derived stem cells (ASCs) from the stromal vascular fraction, has been shown to improve fat volume retention, and enhanced outcomes may also be achieved with CAL at irradiated sites. Supplementing fat grafts with additional ASCs may also augment the regenerative effect on radiation-damaged skin. In this study, we demonstrate the ability for CAL to enhance fat graft volume retention when placed beneath the irradiated scalps of immunocompromised mice. Histologic metrics of fat graft survival were also appreciated, with improved structural qualities and vascularity. Finally, rehabilitation of radiation-induced soft tissue changes were also noted, as enhanced amelioration of dermal thickness, collagen content, skin vascularity, and biomechanical measures were all observed with CAL compared to unsupplemented fat grafts. Supplementation of fat grafts with ASCs therefore shows promise for reconstruction of complex soft tissue defects following adjuvant radiotherapy.

In search of the optimal processing technique for fat grafting

OBJECTIVE

Unpredictability in graft retention remains a significant drawback of fat grafting. Processing of fat grafts has been the focus of several studies to improve graft survival. The objective of this study was to systematically review the outcomes of different fat graft processing techniques with the goal of (1) deriving clinically oriented insights and (2) identifying gaps in knowledge to stimulate future research.

METHODS

PubMed, EMBASE, and Cochrane Databases were searched to identify studies that compared different fat graft processing techniques. Outcome measures of interest were any subjective or objective measures of fat graft survival or reports of adverse events.

RESULTS

A total of 2056 abstracts were generated from the literature searches; 13 studies met the criteria for data extraction and analysis. Processing methods assessed included decantation, washing, gauze filtration, and centrifugation. Each processing method was found to be better than other methods, depending on the outcome measure used to study graft survival. As well, several studies found statistical equipoise in the outcome measures when analyzing the results of the different techniques. Adverse events were rarely reported and did not correlate with any processing method in particular.

CONCLUSIONS

No firm concluding recommendation can be made to deem 1 processing technique superior to the others. However, it would seem that techniques, which use a combination of gentle washing and centrifugation, strike the optimal balance of preserving adipocyte viability while removing bulk of the contaminants.

Studies in Fat Grafting: Part V. Cell-Assisted Lipotransfer to Enhance Fat Graft Retention Is Dose Dependent

BACKGROUND

Cell-assisted lipotransfer has shown much promise as a technique for improving fat graft take. However, the concentration of stromal vascular fraction cells required to optimally enhance fat graft retention remains unknown.

METHODS

Human lipoaspirate was processed for both fat transfer and harvest of stromal vascular fraction cells. Cells were then mixed back with fat at varying concentrations ranging from 10,000 to 10 million cells per 200 μl of fat. Fat graft volume retention was assessed by means of computed tomographic scanning over 8 weeks, and then fat grafts were explanted and compared histologically for overall architecture and vascularity.

RESULTS

Maximum fat graft retention was seen at a concentration of 10,000 cells per 200 μl of fat. The addition of higher number of cells negatively impacted fat graft retention, with supplementation of 10 million cells producing the lowest final volumes, lower than fat alone. Interestingly, fat grafts supplemented with 10,000 cells showed significantly increased vascularity and decreased inflammation, whereas fat grafts supplemented with 10 million cells showed significant lipodegeneration compared with fat alone

CONCLUSIONS

: The authors' study demonstrates dose dependence in the number of stromal vascular fraction cells that can be added to a fat graft to enhance retention. Although cell-assisted lipotransfer may help promote graft survival, this effect may need to be balanced with the increased metabolic load of added cells that may compete with adipocytes for nutrients during the postgraft period.

Opportunities and challenges in three-dimensional brown adipogenesis of stem cells

The formation of brown adipose tissue (BAT) via brown adipogenesis has become a notable process due to its ability to expend energy as heat with implications in the treatment of metabolic disorders and obesity. With the advent of complexity within white adipose tissue (WAT) along with inducible brown adipocytes (also known as brite and beige), there has been a surge in deciphering adipocyte biology as well as in vivo adipogenic microenvironments. A therapeutic outcome would benefit from understanding early events in brown adipogenesis, which can be accomplished by studying cellular differentiation. Pluripotent stem cells are an efficient model for differentiation and have been directed towards both white adipogenic and brown adipogenic lineages. The stem cell microenvironment greatly contributes to terminal cell fate and as such, has been mimicked extensively by various polymers including those that can form 3D hydrogel constructs capable of biochemical and/or mechanical modifications and modulations. Using bioengineering approaches towards the creation of 3D cell culture arrangements is more beneficial than traditional 2D culture in that it better recapitulates the native tissue biochemically and biomechanically. In addition, such an approach could potentially protect the tissue formed from necrosis and allow for more efficient implantation. In this review, we highlight the promise of brown adipocytes with a focus on brown adipogenic differentiation of stem cells using bioengineering approaches, along with potential challenges and opportunities that arise when considering the energy expenditure of BAT for prospective therapeutics.

Studies in fat grafting: Part IV. Adipose-derived stromal cell gene expression in cell-assisted lipotransfer

BACKGROUND

Fat graft volume retention remains highly unpredictable, but addition of adipose-derived stromal cells to fat grafts has been shown to improve retention. The present study aimed to investigate the mechanisms involved in adipose-derived stromal cell enhancement of fat grafting.

METHODS

Adipose-derived stromal cells isolated from human lipoaspirate were labeled with green fluorescent protein and luciferase. Fat grafts enhanced with adipose-derived stromal cells were injected into the scalp and bioluminescent imaging was performed to follow retention of adipose-derived stromal cells within the fat graft. Fat grafts were also explanted at days 1, 5, and 10 after grafting for adipose-derived stromal cell extraction and single-cell gene analysis. Finally, CD31 immunohistochemical staining was performed on fat grafts enriched with adipose-derived stromal cells.

RESULTS

Bioluminescent imaging demonstrated significant reduction in luciferase-positive adipose-derived stromal cells within fat grafts at 5 days after grafting. A similar reduction in viable green fluorescent protein-positive adipose-derived stromal cells retrieved from explanted grafts was also noted. Single-cell analysis revealed expression of multiple genes/markers related to cell survival and angiogenesis, including BMPR2, CD90, CD105, FGF2, CD248, TGFß1, and VEGFA. Genes involved in adipogenesis were not expressed by adipose-derived stromal cells. Finally, CD31 staining revealed significantly higher vascular density in fat grafts explanted at day 10 after grafting.

CONCLUSIONS

Although adipose-derived stromal cell survival in the hypoxic graft environment decreases significantly over time, these cells provide multiple angiogenic growth factors. Therefore, improved fat graft volume retention with adipose-derived stromal cell enrichment may be attributable to improved graft vascularization.

Targeted protection of donor graft vasculature using a phosphodiesterase inhibitor increases survival and predictability of autologous fat grafts

BACKGROUND

Fat grafting is limited by unpredictable long-term graft retention. The authors postulate that injury to the donor-derived microvasculature during harvest and subsequent ischemia may account for this clinical variability. They examined the use of the U.S. Food and Drug Administration-approved phosphodiesterase-5 inhibitor sildenafil citrate to protect graft microvasculature and its role in revascularization and survival.

METHODS

Inguinal fat of donor Tie2/LacZ mice was infiltrated with sildenafil or saline, harvested, and transplanted onto the dorsa of recipient FVB mice. Additional donor mice were perfused with intraarterial trypsin to inactivate the fat graft microvasculature before harvest and transplantation. Differences in graft revascularization, perfusion, volume of retention, and biochemical changes were assessed.

RESULTS

Surviving fat grafts were characterized by exclusively donor-derived vasculature inosculating with the recipient circulation at the graft periphery. Inactivation of donor-derived microvasculature decreased early graft perfusion and led to nearly total graft loss by 8 weeks. Sildenafil attenuated vascular ischemic injury, consistent with reductions in VCAM-1 and SDF1α expression at 48 hours and 4-fold increases in microvasculature survival by 2 weeks over controls. Compared with controls, targeted sildenafil treatment improved early graft perfusion, doubled graft retention at 12 weeks (83 percent versus 39 percent; p < 0.05), ultimately retaining 64 percent of the original graft volume by 24 weeks (compared to 4 percent; p < 0.05) with superior histologic features.

CONCLUSIONS

Fat graft vascularization is critically dependent on maintenance of the donor microvasculature. Sildenafil protects the donor microvasculature during transfer and revascularization, increasing long-term volume retention. These data demonstrate a rapidly translatable method of increasing predictability and durability of fat grafting in clinical practice.

Alternatively activated M2 macrophages improve autologous Fat Graft survival in a mouse model through induction of angiogenesis

BACKGROUND

Variability in graft retention with subsequent undercorrection remains a significant limitation of autologous fat grafting. The authors evaluated whether graft retention in a mouse model could be improved via graft supplementation with alternatively activated M2 macrophages, cells known to play a critical role in tissue repair.

METHODS

Grafts from C57BL/6 mouse inguinal fat pads were supplemented with M2 macrophages generated by intraperitoneal Brewer's thioglycollate injection and in vitro culture. Grafts with saline or M2 macrophages were injected under recipient mouse scalps and assessed by serial micro-computed tomographic analysis. Explanted grafts underwent immunohistochemical and flow cytometric analyses. M2 culture supernatants were added to stromal vascular fraction adipose-derived stem cells to assess adipogenic gene expression induction.

RESULTS

One month after graft injection, no significant difference was noted between M2 macrophage-supplemented (105 ± 7.0 mm) and control graft volumes (72 ± 22 mm). By 3 months after injection, M2 macrophage-supplemented grafts remained stable, whereas controls experienced further volume loss (103 ± 8 mm versus 39.4 ± 15 mm; p = 0.015). Presence of macrophages in supplemented grafts was confirmed by flow cytometry. M2 macrophage-supplemented grafts exhibited a 157 percent increase in vascular density compared with controls (p < 0.05). Induction of adipogenic C/EBPα gene expression was observed with M2 supernatants addition to stromal vascular fraction adipose-derived stem cells.

CONCLUSIONS

M2 macrophages improve autologous fat graft volume retention by stimulating angiogenesis. These findings provide proof-of-principle for development of fat grafting techniques that harness reparative properties of M2 macrophages.

Magnetic Resonance Imaging of Human Tissue-Engineered Adipose Substitutes

Adipose tissue (AT) substitutes are being developed to answer the strong demand in reconstructive surgery. To facilitate the validation of their functional performance in vivo, and to avoid resorting to excessive number of animals, it is crucial at this stage to develop biomedical imaging methodologies, enabling the follow-up of reconstructed AT substitutes. Until now, biomedical imaging of AT substitutes has scarcely been reported in the literature. Therefore, the optimal parameters enabling good resolution, appropriate contrast, and graft delineation, as well as blood perfusion validation, must be studied and reported. In this study, human adipose substitutes produced from adipose-derived stem/stromal cells using the self-assembly approach of tissue engineering were implanted into athymic mice. The fate of the reconstructed AT substitutes implanted in vivo was successfully followed by magnetic resonance imaging (MRI), which is the imaging modality of choice for visualizing soft ATs. T1-weighted images allowed clear delineation of the grafts, followed by volume integration. The magnetic resonance (MR) signal of reconstructed AT was studied in vitro by proton nuclear magnetic resonance ((1)H-NMR). This confirmed the presence of a strong triglyceride peak of short longitudinal proton relaxation time (T1) values (200 ± 53 ms) in reconstructed AT substitutes (total T1=813 ± 76 ms), which establishes a clear signal difference between adjacent muscle, connective tissue, and native fat (total T1 ~300 ms). Graft volume retention was followed up to 6 weeks after implantation, revealing a gradual resorption rate averaging at 44% of initial substitute's volume. In addition, vascular perfusion measured by dynamic contrast-enhanced-MRI confirmed the graft's vascularization postimplantation (14 and 21 days after grafting). Histological analysis of the grafted tissues revealed the persistence of numerous adipocytes without evidence of cysts or tissue necrosis. This study describes the in vivo grafting of human adipose substitutes devoid of exogenous matrix components, and for the first time, the optimal parameters necessary to achieve efficient MRI visualization of grafted tissue-engineered adipose substitutes.

Assessment of viability of human fat injection into nude mice with micro-computed tomography

Lipotransfer is a vital tool in the surgeon's armamentarium for the treatment of soft tissue deficits of throughout the body. Fat is the ideal soft tissue filler as it is readily available, easily obtained, inexpensive, and inherently biocompatible.(1) However, despite its burgeoning popularity, fat grafting is hampered by unpredictable results and variable graft survival, with published retention rates ranging anywhere from 10-80%. (1-3) To facilitate investigations on fat grafting, we have therefore developed an animal model that allows for real-time analysis of injected fat volume retention. Briefly, a small cut is made in the scalp of a CD-1 nude mouse and 200-400 µl of processed lipoaspirate is placed over the skull. The scalp is chosen as the recipient site because of its absence of native subcutaneous fat, and because of the excellent background contrast provided by the calvarium, which aids in the analysis process. Micro-computed tomography (micro-CT) is used to scan the graft at baseline and every two weeks thereafter. The CT images are reconstructed, and an imaging software is used to quantify graft volumes. Traditionally, techniques to assess fat graft volume have necessitated euthanizing the study animal to provide just a single assessment of graft weight and volume by physical measurement ex vivo. Biochemical and histological comparisons have likewise required the study animal to be euthanized. This described imaging technique offers the advantage of visualizing and objectively quantifying volume at multiple time points after initial grafting without having to sacrifice the study animal. The technique is limited by the size of the graft able to be injected as larger grafts risk skin and fat necrosis. This method has utility for all studies evaluating fat graft viability and volume retention. It is particularly well-suited to providing a visual representation of fat grafts and following changes in volume over time.

Studies in fat grafting: Part III. Fat grafting irradiated tissue--improved skin quality and decreased fat graft retention

BACKGROUND

Following radiation therapy, skin becomes fibrotic and can present a difficult problem for reconstructive surgeons. There is an increasing belief that fat grafting under irradiated skin can reverse the damage caused by radiation. The present study evaluated the effect of fat grafting on irradiated skin, along with fat graft quality and retention rates in irradiated tissue.

METHODS

Nine adult Crl:NU-Foxn1 CD-1 mice underwent 30-Gy external beam irradiation of the scalp. Four weeks after irradiation, scalp skin from irradiated and nonirradiated mice was harvested and compared histologically for dermal thickness, collagen content, and vascular density. Human fat grafts were then injected in the subcutaneous plane of the scalp. Skin assessment was performed in the irradiated group at 2 and 8 weeks after grafting, and fat graft retention was measured at baseline and every 2 weeks up to 8 weeks after grafting using micro-computed tomography. Finally, fat graft samples were explanted at 8 weeks, and quality scoring was performed.

RESULTS

Fat grafting resulted in decreased dermal thickness, decreased collagen content, and increased vascular density in irradiated skin. Computed tomographic analysis revealed significantly decreased fat graft survival in the irradiated group compared with the nonirradiated group. Histologic scoring of explanted fat grafts demonstrated no difference in quality between the irradiated and nonirradiated groups.

CONCLUSIONS

Fat grafting attenuates dermal collagen deposition and vessel depletion characteristic of radiation fibrosis. Although fat graft retention rates are significantly lower in irradiated than in nonirradiated tissue, the quality of retained fat between the groups is similar.

Studies in fat grafting: Part I. Effects of injection technique on in vitro fat viability and in vivo volume retention

BACKGROUND

Fat grafting has become increasingly popular for the correction of soft-tissue deficits at many sites throughout the body. Long-term outcomes, however, depend on delivery of fat in the least traumatic fashion to optimize viability of the transplanted tissue. In this study, the authors compare the biological properties of fat following injection using two methods.

METHODS

Lipoaspiration samples were obtained from five female donors, and cellular viability, proliferation, and lipolysis were evaluated following injection using either a modified Coleman technique or an automated, low-shear device. Comparisons were made to minimally processed, uninjected fat. Volume retention was also measured over 12 weeks after injection of fat under the scalp of immunodeficient mice using either the modified Coleman technique or the Adipose Tissue Injector. Finally, fat grafts were analyzed histologically.

RESULTS

Fat viability and cellular proliferation were both significantly greater with the Adipose Tissue Injector relative to injection with the modified Coleman technique. In contrast, significantly less lipolysis was noted using the automated device. In vivo fat volume retention was significantly greater than with the modified Coleman technique at the 4-, 6-, 8-, and 12-week time points. This corresponded to significantly greater histologic scores for healthy fat and lower scores for injury following injection with the device.

CONCLUSION

Biological properties of injected tissues reflect how disruptive and harmful techniques for placement of fat may be, and the authors' in vitro and in vivo data both support the use of the automated, low-shear devices compared with the modified Coleman technique.

Autologous Fat Transfer: The Progenitor Cell Response to Different Recipient Environments

BACKGROUND

Autologous fat transfer is a common procedure; however, results are variable and unpredictable.

OBJECTIVES

Stem cell responses to hypoxic environments need to be elucidated to determine which cell types contribute to graft survival.

METHODS

Acellular dermal matrix (ADM) envelopes were implanted in the subcutaneous tissues of 4 swine. In each swine, 2 envelopes were inserted as controls (ADM group), and 2 were placed and injected with 5 mL of autologous fat (ADM/fat group). Two additional envelopes were inserted and filled with 5 mL of fat and an omental pedicle (A/F/O group). Animals were sacrificed and the envelopes excised at 1, 2, 4, and 16 weeks. Specimens were analyzed histologically and/or with flow cytometry.

RESULTS

Fat was retained in ADM envelopes with and without a pedicle blood supply, although the percentage of volume retention was greater in the pedicled group. The peak number of mesenchymal progenitor cells within the ADM/fat group was significantly greater than the peak in the A/F/O group (P =.044), whereas endothelial progenitor cells in the ADM/fat group showed a prolonged increase through 4 weeks (P =.015 vs the A/F/O group at week 4). At 16 weeks, the interior surface of the matrix in the ADM/fat group had significantly more blood vessels than that of the ADM or A/F/O group (P = .0021 and .0036, respectively).

CONCLUSIONS

Injecting fat into hypoxic environments significantly increases the mesenchymal and endothelial progenitor cell responses and enhances the formation of blood vessels.

A clinical scalable cryopreservation method of adipose tissue for reconstructive surgery assessed by stromal vascular fraction and mice studies

BACKGROUND

Adipose tissue is widely used in plastic surgery. The main obstacle is that it can be used only immediately after liposuction, while reconstruction often requires several procedures to achieve optimal results. This study aimed to develop a cryopreservation protocol directly applicable to clinical situations, allowing repetitive procedures without multiple tissue harvests.

METHODS

The authors first tested scalable bags suitable for therapeutic uses. All subsequent experiments were performed in those bags. The authors evaluated in vitro, on the basis of cell viability, cell number, phenotype, and stromal cell proliferation, the efficacy of six cryopreservation media composed of an external cryoprotectant (human albumin or hydroxylethyl starch) with or without an internal cryoprotectant (dimethyl sulfoxide). Two storage temperatures (-196°C and -80°C) were tested in vitro and in vivo (subcutaneous graft in 30 nude mice) with the selected medium.

RESULTS

The combination of 5% dimethyl sulfoxide and 95% hydroxylethyl yielded in vitro results that were good and the most consistent. With this cryoprotective solution, the authors observed no significant difference in vitro for a storage period of 7 days. When the storage was extended to 1 month, the cell viability was decreased by 10 percent for both storage temperatures. The in vivo experiments assessed the superiority of cryopreservation at -80°C with less graft resorption (60 percent and 70 percent, respectively, for -80°C and -196°C) and less fibrosis.

CONCLUSION

The study's protocol with a chemically defined cryoprotective solution, specific scalable bags constrained in an aluminum holder, and a storage temperature of -80°C is promising for long-term adipose tissue cryopreservation.

Adipogenic differentiation potential of rat adipose tissue-derived subpopulations of stromal cells

Adipose-derived stromal cells (ASCs) are mostly isolated by enzymatic digestion, centrifugation and adherent growth resulting in a very heterogeneous cell population. Therefore, other cell types in the cell culture can comprise the differentiation and proliferation potential of the ASC population. Recent studies indicated that an antibody-aided isolation of distinct ASC subpopulations provides advantages over the conventional method of ASC isolation. The aim of this study was to investigate the adipogenic differentiation potential of CD29-, CD71-, CD73- and CD90-selected ASCs in vitro. The stromal vascular fraction (SVF) was obtained from rat adipose tissue by enzymatic digestion and centrifugation. Subsequently, CD29(+)-, CD71(+)-, CD73(+)- and CD90(+) cells were isolated by magnetic activated cell sorting (MACS), seeded into culture plates and differentiated into the adipogenic lineage. ASCs isolated by adherent growth only served as controls. Adipogenic differentiation was assessed by Oil Red O staining and quantification of the adiponectin and leptin concentrations in the cell culture supernatants. Statistical analysis was carried out using one-way analysis of variance (ANOVA) followed by the Scheffe's post hoc procedure. The results showed that different subpopulations with different adipogenic differentiation potentials can be isolated by the MACS procedure. The highest adipogenic differentiation potential was determined in the CD29-selected ASC population followed by the unsorted ASC population. The CD71-, CD73- and CD90-selected cells exhibited significantly the lowest adipogenic differentiation potential. In conclusion, the CD29-selected ASCs and the unsorted ASCs exhibited a similar adipogenic differentiation potential. Therefore, we do not see a clear advantage in the application of an anti-CD29-based isolation of ASCs over the conventional technique using adherent growth. However, the research on isolation/purification methods of adipogenic ASCs should continue in order to make this stem cell source even more attractive for future adipose tissue engineering applications.

Combining decellularized human adipose tissue extracellular matrix and adipose-derived stem cells for adipose tissue engineering

Repair of soft tissue defects resulting from lumpectomy or mastectomy has become an important rehabilitation process for breast cancer patients. This study aimed to provide an adipose tissue engineering platform for soft tissue defect repair by combining decellularized human adipose tissue extracellular matrix (hDAM) and human adipose-derived stem cells (hASCs). To derive hDAM incised human adipose tissues underwent a decellularization process. Effective cell removal and lipid removal were proved by immunohistochemical analysis and DNA quantification. Scanning electron microscopic examination showed a three-dimensional nanofibrous architecture in hDAM. The hDAM included collagen, sulfated glycosaminoglycan, and vascular endothelial growth factor, but lacked major histocompatibility complex antigen I. hASC viability and proliferation on hDAM were proven in vitro. hDAM implanted subcutaneously in Fischer rats did not cause an immunogenic response, and it underwent remodeling, as indicated by host cell infiltration, neovascularization, and adipose tissue formation. Fresh fat grafts (Coleman technique) and engineered fat grafts (hDAM combined with hASCs) were implanted subcutaneously in nude rats. The implanted engineered fat grafts maintained their volume for 8 weeks, and the hASCs contributed to adipose tissue formation. In summary, the combination of hDAM and hASCs provides not only a clinically translatable platform for adipose tissue engineering, but also a vehicle for elucidating fat grafting mechanisms.