Experimental In-Vivo Models Used in Fat Grafting Research for Volume Augmentation in Soft Tissue Reconstruction

Investigation of the Effect of Mobile and Immobile Regions on Fat Graft Viability: An Experimental Study in a New Model

BACKGROUND

Fat grafts are widely used in plastic, aesthetic and reconstructive surgery. Their unpredictable resorption is their main disadvantage. A review of the literature shows that there is a lack of research on the effect of mobile and immobile regions on fat graft survival in fat graft applications.

OBJECTIVE

Our aim was to investigate the relationship of fat graft survival with mobile and immobile region in a new experimental model.

METHODS

Twenty-four male Wistar albino rats were randomly divided into two groups (n=12). Fat grafts were harvested from the right inguinal region of the rat. In Group 1, the fat graft was placed in the subcutaneous pouch formed in the scalp region of the rat. In Group 2, fat grafts were placed in the pouch formed in the posterior cervical region of the rat. At the end of 6 weeks, the weights and histopathology of the fat grafts were evaluated. Histopathological examinations were performed in a blinded fashion.

RESULTS

The weights of the fat grafts were found to be higher in Group 1. At the same time, histopathological examinations showed that vascular density was higher in Group 1. There was no statistically significant difference in other histopathological examinations.

CONCLUSION

The mobile and immobile areas may have different effects on the survival of transplanted fat grafts. Sliding movement between muscle and skin in the mobile zone puts stress on the fat graft. In our study, the mobile site was shown to have a negative effect on the vascularity of the fat graft. It was observed that the vascular density was higher in the fat graft placed in the immobilised area. Further studies on the increase in vascularity can be carried out using the new experimental model we have created.

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Subcutaneous Transplantation of White Adipose Tissue

In the research setting, white adipose tissue (WAT) transplantation, also known as fat transplantation, is often used to understand the physiological function of adipocytes or associated stromal vascular cells such as macrophages in the context of local and systemic metabolism. The mouse is the most common animal model used where WAT from a donor is transferred either to a subcutaneous site of the same organism or to a subcutaneous region of a recipient. Here, we describe in detail the procedure for heterologous fat transplantation, and, given the need for survival surgery, peri- and postoperative care and subsequent histological confirmation of fat grafts will also be discussed.

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.

Histological analysis of the effect of nanofat grafting in scar rejuvenation

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Short-term post-implantation dynamics of in vitro engineered human microvascularized adipose tissues

Engineered adipose tissues are developed for their use as substitutes for tissue replacement in reconstructive surgery. To ensure a timely perfusion of the grafted substitutes, different strategies can be used such as the incorporation of an endothelial component. In this study, we engineered human adipose tissue substitutes comprising of functional adipocytes as well as a natural extracellular matrix using the self-assembly approach, without the use of exogenous scaffolding elements. Human microvascular endothelial cells (hMVECs) were incorporated during tissue production in vitro and we hypothesized that their presence would favor the early connection with the host vascular network translating into functional enhancement after implantation into nude mice in comparison to the substitutes that were not enriched in hMVECs. In vitro, no significant differences were observed between the substitutes in terms of histological aspects. After implantation, both groups presented numerous adipocytes and an abundant matrix in addition to the presence of host capillaries within the grafts. The substitutes thickness and volume were not significantly different between groups over the short-term time course of 14 days (d). For the microvascularized adipose tissues, human CD31 staining revealed a human capillary network connecting with the host microvasculature as early as 3 d after grafting. The detection of murine red blood cells within human CD31+ structures confirmed the functionality of the human capillary network. By analyzing the extent of the global vascularization achieved, a tendency towards increased total capillary network surface and volume was revealed for prevascularized tissues over 14 d. Therefore, applying this strategy on thicker reconstructed adipose tissues with rate-limiting oxygen diffusion might procure added benefits and prove useful to provide voluminous substitutes for patients suffering from adipose tissue loss or defects.