Dynamic Rheology for the Prediction of Surgical Outcomes in Autologous Fat Grafting

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.

Comparison of the Rheological Properties and Structure of Fat Derivatives Generated via Different Mechanical Processing Techniques: Coleman Fat, Nanofat, and Stromal Vascular Fraction-Gel

Importance: Coleman fat, nanofat, and stromal vascular fraction-gel (SVF-gel) are three widely used fat derivatives. However, their rheological properties and structure remain unknown. Objectives: To disclose the rheological properties and structure of three different fat derivatives. Design, Settings, and Participants: Fat tissues obtained from eight different donors were processed into three separate groups: Coleman fat, nanofat, and SVF-gel (n = 8); their viscoelastic properties and structure were determined. Intervention: Oscillation measurements were performed in the context of serrated 25-mm parallel-plate geometry with a 1.2-mm gap at 25°C. In addition, fat samples were fixed using a patented protocol and observed under scanning electron microscopy. Main Outcomes and Measures: Comparison of the viscoelastic properties, microstructure, and particle size. Results: At 0.77 Hz, the elastic modulus of SVF-gel, Coleman fat, and nanofat was 201.6 ± 0.74, 69.94 ± 15.61, and 34.89 ± 3.484 Pa, respectively; their viscosity was 44.06 ± 3.038, 15.37 ± 2.0380, and 7.516 ± 0.7250 mPa, respectively. The particle size of SVF-gel, Coleman fat, and nanofat was 106.0 ± 4.796, 86.93 ± 3.597, and 12.61 ± 7.603 μm, respectively. Conclusion and Relevance: Mechanical processing may impact graft efficacy. The characterization of the rheological properties and structure of different fat derivatives in this study may help surgeons select the better type of tissue for a given intervention; however, further studies are still required.

Surgical Decision Making in Autologous Fat Grafting: An Evidence-Based Review of Techniques to Maximize Fat Survival

Autologous fat grafting is an important tool in plastic surgery and is widely used for a variety of applications, both aesthetic and reconstructive. Despite an ever-increasing list of indications and extensive research over many years into improving outcomes, fat grafting remains plagued by incomplete and often unpredictable graft survival. Decisions made at each stage of surgery can potentially contribute to ultimate success, including donor site selection and preparation, fat harvest, processing, and purification of lipoaspirate, recipient site preparation, and delivery of harvested fat to the recipient site. In this review, we examine the evidence for and against proposed techniques at each stage of fat grafting. Areas of consensus identified include use of larger harvesting and grafting cannulas and slow injection speeds to limit cell damage due to shearing forces, grafting techniques emphasizing dispersion of fat throughout the tissue with avoidance of graft pooling, and minimizing exposure of the lipoaspirate to the environment during processing. Safety considerations include use of blunt-tipped needles or cannulas to avoid inadvertent intravascular injection as well as awareness of cannula position and avoidance of danger zones such as the subgluteal venous plexus. We believe that using the evidence to guide surgical decision-making is the key to maximizing fat grafting success. Level of Evidence: 4.

Viscoelastic characterization of diabetic and non-diabetic human adipose tissue

BACKGROUND

Obesity-induced chronic inflammation and fibrosis in adipose tissue contributes to the progression of type 2 diabetes mellitus (DM). While fibrosis is known to induce mechanical stiffening of numerous tissue types, it is unknown whether DM is associated with alterations in adipose tissue mechanical properties.

OBJECTIVE

The purpose of this study was to investigate whether DM is associated with differences in bulk viscoelastic properties of adipose tissue from diabetic (DM) and non-diabetic (NDM) obese subjects.

METHODS

Bulk shear rheology was performed on visceral (VAT) and subcutaneous (SAT) adipose tissue, collected from obese subjects undergoing elective bariatric surgery. Rheology was also performed on the remaining extracellular matrix (ECM) from decellularized VAT (VAT ECM). Linear mixed models were used to assess whether correlations existed between adipose tissue mechanical properties and DM status, sex, age, and body mass index (BMI).

RESULTS

DM was not associated with significant differences in adipose tissue viscoelastic properties for any of the tissue types investigated. Tissue type dependent differences were however detected, with VAT having significantly lower shear storage and loss moduli than SAT and VAT ECM independent of DM status.

CONCLUSION

Although DM is typically associated with adipose tissue fibrosis, it is not associated with differences in macroscopic adipose tissue mechanical properties.

Platelet-Rich Fibrin Improves Fat Graft Survival Possibly by Promoting Angiogenesis and Adipogenesis, Inhibiting Apoptosis, and Regulating Collagen Production

BACKGROUND

Platelet-rich fibrin (PRF) can promote fat graft survival, but limited data are currently available, and the underlying mechanism of this effect has not yet been explained.

OBJECTIVES

The aim of this study was to explore the mechanism by which PRF promotes fat graft survival, from the aspects of angiogenesis, adipogenesis, cellular apoptosis, and collagen production.

METHODS

Nude mice were randomly assigned to a PRF group (subcutaneously injected with PRF and fat in the ratio of 1:5 by volume) and a control group (subcutaneously injected with normal saline and fat in the ratio of 1:5 by volume). On days 0, 3, 7, 14, 21, and 28 after transplantation, graft samples (n = 12) were obtained for quantification of target growth factors. In weeks 1, 2, 3, and 4 after transplantation, graft samples (n = 12) were obtained for the following evaluations. The volume and weight retention rates were calculated; gene and protein expression of vascular endothelial growth factor A (VEGF-A), peroxisome proliferator-activated receptor γ (PPAR-γ), COL1-A1, and BAX were evaluated; hematoxylin & eosin staining, Masson's trichrome staining, α smooth muscle actin staining, and perilipin-1 staining were performed to evaluate graft survival.

RESULTS

After transplantation, the concentrations of growth factors produced by the fat increased to varying degrees, and the addition of PRF made these concentration changes ever greater. Compared with the control group, the PRF group had a higher volume and weight retention rate, a higher expression level of VEGF-A and PPAR-γ, a lower expression level of COL1-A1 and BAX, a higher vessel density, less fibrosis, and more viable adipocytes.

CONCLUSIONS

PRF can promote autocrine function of the grafted fat to produce more growth factors. It greatly increased fat retention rate, possibly by promoting vascularization and adipogenic differentiation, inhibiting cellular apoptosis, and regulating collagen production.

Recipient-Site Preconditioning with Deferoxamine Increases Fat Graft Survival by Inducing VEGF and Neovascularization in a Rat Model

BACKGROUND

The authors hypothesize that ischemic preconditioning of the recipient site with deferoxamine will increase fat graft survival by enhancing angiogenesis in a rat model.

METHODS

Cell viability, tube formation, and mRNA expression were measured in human umbilical vein endothelial cells treated with deferoxamine. A total of 36 rats were then used for an in vivo study. A dose of 100 mg/kg of deferoxamine was injected subcutaneously into the rat scalp every other day for five treatments. On the day after the final injection, the scalp skin was harvested from half the animals to evaluate the effects of deferoxamine on the recipient site. In the remaining animals, inguinal fat tissue was transplanted to the scalp. Eight weeks after transplantation, the grafts were harvested to evaluate the effects of deferoxamine preconditioning on fat graft survival.

RESULTS

In human umbilical vein endothelial cells, treatment with a deferoxamine concentration higher than 400 μM decreased cell viability compared with the control (p = 0.002). Treatment with 100 and 200 μM deferoxamine increased endothelial tube formation (p = 0.001) and mRNA levels of angiogenesis-related factors (p = 0.02). Rat scalps treated with deferoxamine exhibited increased capillary neoformation (p = 0.001) and vascular endothelial growth factor protein expression (p = 0.024) compared with controls. Fat graft volume retention, capillary density (p < 0.001), and adipocyte viability (p < 0.001) in the grafted fat increased when the recipient site was preconditioned with deferoxamine.

CONCLUSION

This study demonstrated that recipient site preconditioning with deferoxamine increases fat graft survival by inducing vascular endothelial growth factor and neovascularization.

The Effect of Liposuction Cannula Diameter on Fat Retention-Based on a Rheological Simulation

Supplemental Digital Content is available in the text.

Background:

Autologous fat is considered as an ideal material for soft-tissue augmentation in plastic and reconstructive surgery. The primary drawback of autologous fat grafting is the high absorption rate, thus fat retention is considered as an essential indicator. There are several researches about the factors that can influence fat retention, including centrifugation and cannula size. However, rheological models of cannula during liposuction are limited. This research focuses on the effects of cannulas with diameters of 2 mm and 2.5 mm on fat retention, which is based on a rheological simulation of inlet pressure and maximum velocity. Experiments on mice were also conducted to confirm the result from the simulation.

Methods:

A simulation was conducted with the physical parameters of the adipose tissue. Human lipoaspirate samples were obtained from patients by liposuction through cannulas of different diameters and were transferred into subcutaneous tissue of nude mice, a part of which were used in viscosity and density measurement. Graft retention was measured and fat quality was assessed through histologic analysis after 6 months.

Results:

Viscosity and density of the fat tissue had significant effects on fat retention. The 2.5 mm diameter cannula had significantly lower inlet pressure and maximum velocity and thus led to higher graft retention, but oil cystic nodules appeared meanwhile.

Conclusions:

Cannulas with larger diameters have lower inlet pressure and maximum velocity during the liposuction process, which further influences the viability of adipocytes and adipose stem cells and thus has larger fat graft retention. This research built a mathematical model with less bias than in vivo experiments and provides a general way for analyzing the outcome of a liposuction precisely, which adds to the data for cannula optimization.