Fate of Free Fat Grafts with or without Adipogenic Adjuncts to Enhance Graft Outcomes:

Effects of nanographene oxide on adipose-derived stem cell cryopreservation

Cryoinjury mitigation is key in cell cryopreservation. Here, we aimed to assess the effectiveness of nanographene oxide (nano-GO) for improving cryoprotectant agents (CPAs) in human adipose stem cell (hADSC) cryopreservation. For in vitro experiments, nano-GO (5 μg/mL) was added to the CPAs in the control, and passage (P) 2 hADSCs were collected and cryopreserved for around two weeks. We compared cytotoxicity, cell viability, immunophenotypes, proliferation, cell apoptosis, and tri-lineage differentiation. In vivo, studies used lipoaspirate to create non-enriched or hADSC-enriched fat tissues by combining it with PBS or hADSCs cryopreserved with the aforementioned CPAs. Each nude mouse received a 0.3 mL subcutaneous injection of the graft. At 12 weeks, the grafts were harvested. Histology, adipocyte-associated genes and protein, vascular density and angiogenic cytokines, macrophage infiltration, and inflammatory cytokines were analyzed. Nano-GO CPA contributed to increased cell viability, improved cell recovery, and lowered levels of early apoptosis. Nano GO at concentrations of 0.01-100 μg/mL caused no cytotoxicity to hADSCs. The absence of nano GOs in the intracellular compartments of the cells was confirmed by transmission electron microscopy. The fat grafts from the CPA-GO group showed more viable adipocytes and significantly increased angiogenesis compared to the PBS and CPA-C groups. Adding hADSCs from the CPA-GO group to the graft reduced macrophage infiltration and MCP-1 expression. Nano-GO plays an anti-apoptotic role in the cryopreservation of hADSCs, which could improve the survival of transplanted fat tissues, possibly via improved angiogenesis and lower inflammatory response in the transplanted adipose tissue.

Establishment of Early Blood Perfusion Promotes CXCL12 Expression and Recruits Monocytes/Macrophages in Damaged Adipose Tissue in Mice Model

BACKGROUND

Blood perfusion in the recipient site is important for adipose tissue repair after fat grafting. It delivers host-derived macrophages derived from monocytes in bone marrow to initiate inflammatory reactions and regenerative responses. According to the ability of CXCL12, a stromal cell-derived factor, to recruit monocytes/macrophages, we studied its effect on adipose tissue repair and regeneration under ischemic and normal conditions.

METHODS

Each inguinal fat pad was crushed for 30 seconds with a clamp in mice (n = 35). The left inguinal vessels were divided and cut off (ischemic group), while the right inguinal vessels were kept patent (control group). Seven animals were sacrificed at 1, 3, 7, 14, and 30 days after surgery, and macrophages (Mac2 and CD206) and adipocytes (perilipin) were assessed. Levels of inflammatory factors (interleukin (IL)-1β, IL-6, and tumor necrosis factor-α) and CXCL12 were measured by quantitative PCR.

RESULTS

The number of macrophages was higher in the control group than in the ischemic group at day 3 (10.33 ± 2.40 vs. 1.33 ± 0.33, p = 0.021). The percentage of M2 macrophages was higher in the control group than in the ischemic group at day 7 (p<0.05). The levels of inflammatory factors and CXCL12 were higher in the control group than in the ischemic group at the early stage (p = 0.038).

CONCLUSIONS

Established blood perfusion leads to up-regulation of CXCL12 during adipose tissue repair and regeneration, which may increase recruitment of monocytes to damaged adipose tissue. These findings increase understanding of the cellular events involved in fat graft survival after grafting.

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Clinical Applicability of Visible Light-Mediated Cross-linking for Structural Soft Tissue Reconstruction

Visible light-mediated cross-linking has utility for enhancing the structural capacity and shape fidelity of laboratory-based polymers. With increased light penetration and cross-linking speed, there is opportunity to extend future applications into clinical spheres. This study evaluated the utility of a ruthenium/sodium persulfate photocross-linking system for increasing structural control in heterogeneous living tissues as an example, focusing on unmodified patient-derived lipoaspirate for soft tissue reconstruction. Freshly-isolated tissue is photocross-linked, then the molar abundance of dityrosine bonds is measured using liquid chromatography tandem mass spectrometry and the resulting structural integrity assessed. The cell function and tissue survival of photocross-linked grafts is evaluated ex vivo and in vivo, with tissue integration and vascularization assessed using histology and microcomputed tomography. The photocross-linking strategy is tailorable, allowing progressive increases in the structural fidelity of lipoaspirate, as measured by a stepwise reduction in fiber diameter, increased graft porosity and reduced variation in graft resorption. There is an increase in dityrosine bond formation with increasing photoinitiator concentration, and tissue homeostasis is achieved ex vivo, with vascular cell infiltration and vessel formation in vivo. These data demonstrate the capability and applicability of photocrosslinking strategies for improving structural control in clinically-relevant settings, potentially achieving more desirable patient outcomes using minimal manipulation in surgical procedures.

Pyramidal multiple-theory (multi-type, multi-method and multi-layer) for facial fat grafting

BACKGROUND

Age-related changes to the face pertinent anatomy and important aspects of autologous fat grafting have been widely applied in facial rejuvenation. Various types of autologous fat products (Macrofat, Microfat, SEFF, nanofat, and SVF-gel) with different properties and applicabilities have been introduced and available for surgeons.

METHODS

Key differences between common techniques for fat processing and infiltration. Develop a plan for patients based on site-specific facial anatomical zones, we suggested a pyramidal multiple-theory (multi-type, multi-method and multi-layer) for facial fat grafting. Based on the complicated mechanism of the face decrepitude in different layers of facial soft tissue, autologous fat products with various particle sizes and components into different layers.

RESULTS

Fifty-eight patients underwent this facial fat grafting strategy from June 2020 to Jan 2022. All achieved cosmetic improvements, with higher patients' satisfaction, and minor complications. Our facial fat grafting strategy takes advantage of different fat products and is able to address the physiological tissue changes during aging, more properly and targetedly, than the traditional facial fat grafting.

CONCLUSIONS

Fat grafting to the face aids in volume restoration and rejuvenation, thereby addressing soft-tissue atrophy associated with the aging face, acquired conditions, or congenital malformations. The technique described as "lipo-tumescence" has been successfully used in the breast and other regions of the body that have radiation damage and is discussed in this article specifically for the face and neck.

The Importance of Protecting the Structure and Viability of Adipose Tissue for Fat Grafting

BACKGROUND

Fat grafting is widely used for soft-tissue augmentation; however, the related clinical outcome remains variable and technique-dependent. The mechanisms underlying fat graft survival are not fully understood, particularly regarding the contributions of different cell types, such as functional adipocytes. This study evaluated the importance of adipose tissue structure and viability in fat grafting and, to some extent, revealed the effect of adipocytes in fat grafting.

METHODS

Human lipoaspirate was harvested using suction-assisted liposuction and processed using three separate methods: cotton-pad filtration, soft centrifugation (400 g for 1 minute), and Coleman centrifugation (1200 g for 3 minutes). Then all samples were subjected to second cotton-pad concentration. Adipose tissue structure and viability, the numbers of adipose-derived stem cells, and their proliferation and multilineage differentiation abilities were compared in vitro. The volume retention rate and fat graft quality were evaluated in vivo.

RESULTS

Cell structure destruction and viability decline were more evident in the Coleman centrifugation group compared to the cotton-pad filtration group and the soft centrifugation group. However, no intergroup differences were observed in the numbers, proliferation, or multilineage differentiation abilities of adipose-derived stem cells. After transplantation, the volume retention rates were similar in the three groups. However, greater structural and functional damage was associated with poorer graft quality, including decreased levels of graft viability, vessel density, and vascular endothelial growth factor secretion and increased levels of vacuoles, necrotic areas, fibrosis, and inflammation.

CONCLUSIONS

Protecting adipose tissue structure and viability is crucial for improving fat grafting outcomes.

CLINICAL RELEVANCE STATEMENT

The protection of the structure and viability of adipose tissue should be ensured throughout the whole process of fat grafting to reduce complications and improve graft quality.

Overcoming functional challenges in autologous and engineered fat grafting trends

Autologous fat grafting offers significant promise for the repair of soft tissue deformities; however, high resorption rates indicate that engineered solutions are required to improve adipose tissue (AT) survival. Advances in material development and biofabrication have laid the foundation for the generation of functional AT constructs; however, a balance needs to be struck between clinically feasible delivery and improved structural integrity of the grafts. A new approach combining the objectives from both the clinical and research communities will assist in developing morphologically and genetically mature AT constructs, with controlled spatial arrangement and increased potential for neovascularization. In a rapidly progressing field, this review addresses research in both the preclinical and bioengineering domains and assesses their ability to resolve functional challenges.

Phenotypic and Cellular Characteristics of a Stromal Vascular Fraction/Extracellular Matrix Gel Prepared Using Mechanical Shear Force on Human Fat

The retention of fat-derived grafts remains a challenge for regenerative medicine. Fat aspirates from patients undergoing liposuction were prepared into standard Coleman fat grafts or further isolated using mechanical shear force to prepare a stromal vascular fraction (SVF)/extracellular matrix (ECM) gel. The retention rate of the SVF/ECM gel was significantly higher than that of the Coleman fat at 3, 14, 28, and 60 days following transplantation on the backs of nude mice. The viscosity of the fat was directly proportional to the shearing force. Although the mechanical isolation did not affect the total number of cells, it significantly decreased the number of living cells. Flow cytometry showed a greater number of mesenchymal stem cells, supra-adventitial (SA)-adipose stromal cells (ASCs), and adipose-derived stem cells but a lower number of endothelial progenitor cells in the SVF/ECM gel than in the Coleman fat. Thus, mechanical isolation of fat can increase the pluripotency of adipocytes, which can improve graft retention in cell therapy.

Blood Impairs Viability of Fat Grafts and Adipose Stem Cells: Importance of Washing in Fat Processing

BACKGROUND

Fat processing plays a pivotal role in graft survival. Each component of the blood in lipoaspirate affects fat survival in different ways, but the mechanisms are not clear.

OBJECTIVES

The aim of this study was to investigate, by various experimental methods, the effect of blood on the viability of fat grafts and adipose stem cells (ASCs).

METHODS

Blood and fat samples were obtained from 6 female patients undergoing aesthetic liposuction. For the in vivo experiment, we compared fat mixed with normal saline or various ratios of blood in nude mice. The samples were explanted at 2 and 8 weeks to evaluate the gross volume retention and histologic and immunohistochemical characteristics. For in vitro experiments, ASCs were pretreated with hemoglobin at different concentrations and for different times. We then assessed the proliferation, migration, adipogenesis, and reactive oxygen species production of ASCs.

RESULTS

Blood in the graft led to a decrease in graft viability, as evaluated by general observation and histologic and immunohistochemical morphology in vivo. In vitro experiments showed inhibited proliferation, migration, and adipogenesis, and increased reactive oxygen species production in ACSs, after hemoglobin treatment, suggesting impaired ASC viability.

CONCLUSIONS

This study suggests that blood impairs the viability of fat grafts and ASCs and provides evidence that washing to remove blood is important in fat processing.

Introduction of ligated vessels promote the retention and regeneration of free fat: constructing a fat flap in tissue engineering chamber

Background: Breast reconstruction with fat grafting has an unstable retention rate due to insufficient revascularization. Tissue Engineering Chamber (TEC) model can promote tissue regeneration in the chamber by introducing ligated vessels around the tissue. We introduced ligated vessels with free fat graft to investigate the retention rate and revascularization of grafted fat that in TEC model.

Methods: SD rats (n=24) was divided into 3 groups randomly. Group A: Standard TEC model was constructed; Group B: the epigastric vessel bundles were dissected from the fat flap and ligated, fat flap was cut into granules and planted into the chamber; Group C: Free fat was planted in the chamber. At week 6, samples in the chamber were harvested.

Results: Significant volume increase was observed in group A and B, while the volume decreased in group C (P<0.05). Regeneration morphology could be found according to the histological observation in A and B. Micro CT results showed the ligated vessels into grafted fat sprouting robustly, coordinated with volume changes.

Conclusion: Fat grafts in TEC model could not only survive but also regenerate. The combination of fat graft and TEC could fabricate a vascularized fat flap, which was a promising method in breast reconstruction.

Abbreviations: VOI: Volumes of Interest; TEC: Tissue Engineering Chamber; CAL: Cell Assisted Lipotransfer.

In vivo tissue engineering of an adipose tissue flap using fat grafts and Adipogel

For decades, plastic surgeons have spent considerable effort exploring anatomical regions for free flap design. More recently, tissue-engineering approaches have been utilised in an attempt to grow transplantable tissue flaps in vivo. The aim of this study was to engineer a fat flap with a vascular pedicle by combining autologous fat grafts and a novel acellular hydrogel (Adipogel) in an established tissue-engineering model comprising a chamber and blood vessel loop. An arteriovenous loop was created in the rat groin from the femoral vessels and positioned inside a perforated polycarbonate chamber. In Group 1, the chamber contained minced, centrifuged autologous fat; in Group 2, Adipogel was added to the graft; and in Group 3, Adipogel alone was used. Constructs were histologically examined at 6 and 12 weeks. In all groups, new tissue was generated. Adipocytes, although appearing viable in the graft at the time of insertion, were predominantly nonviable at 6 weeks. However, by 12 weeks, new fat had formed in all groups and was significantly greater in the combined fat/Adipogel group. No significant difference was seen in final construct total volume or construct neovascularisation between the groups. This study demonstrated that a pedicled adipose flap can be generated in rats by combining a blood vessel loop, an adipogenic hydrogel, and a lipoaspirate equivalent. Success appears to be based on adipogenesis rather than on adipocyte survival, and consistent with our previous work, this adipogenesis occurred subsequent to graft death and remodelling. The regenerative process was significantly enhanced in the presence of Adipogel.

Effectiveness of the combination of fat grafting and injection on radiation ulcer healing

Fat injections aid in the healing of radiation-induced skin damage. We hypothesized that the direct application of fat grafts to the surfaces of radiation-induced ulcers is also effective. Here, we aimed to evaluate the effectiveness of a combination treatment comprising fat injections around ulcers and fat grafts on ulcer surfaces. The dorsal skin of inbred rats was irradiated at a single dose of 20 Gy before producing ulcers. After the inguinal fat was harvested using the Coleman technique, the rats were divided into four groups: Group 1, ulcer wounds were covered using dressing materials and staples only; Group 2, fat was injected around the ulcers using a cannula; Group 3, fat was grafted onto ulcer surfaces; and Group 4, a combination of fat injection around the ulcers and fat grafts onto ulcer surfaces was employed. The mean healing time (± standard deviation) of each group was as follows: Group 1, 16.0 ± 2.2 days; Group 2, 14.5 ± 2.0 days; Group 3, 15.2 ± 1.7 days; and Group 4, 13.4 ± 1.0 days. The healing time of Group 4 was significantly shorter than that of Group 1 (p = .0005) and Group 3 (p = .023). In both groups that received fat grafts, fat tissue was observed in the dermis on hematoxylin-eosin-stained slides at 4 and 8 weeks after the ulcers were created. In conclusion, the combination treatment of fat grafted onto ulcer surfaces and injected around ulcers was effective in accelerating the epithelization of radiation-induced ulcers.