Strategies for Human Adipose Tissue Repair and Regeneration:

Adipose tissue is an extremely vascularized connective tissue in the human body. It is responsible for energy storage and release of a number of adipokines that may act in an endocrine or paracrine manner. It is also a highly plastic tissue than can increase energy depots by hypertrophic growth and hyperplasic expansion of adipose stromal cells (ASCs). It contains many cell types including adipocytes, endothelial cells (ECs), fibroblasts, macrophages and leukocytes. The human adipose tissue can be found either in the white adipose tissue (WAT) or the brown adipose tissue (BAT) form.

Tissue engineering is the interdisciplinary field where materials, cells, growth factors and other bioactive molecules are combined together to make transplantable constructs, the final goal being to promote repair and regeneration of damaged tissue . Loss or damage of adipose tissue needs repair and regenerative approaches not only for the cosmetically impact of absent tissue but also for the well-being of the patients.

Adipose Tissue Engineering

Adipose tissue engineering is significant importance due to the increasing need for clinical soft tissue filler procedures and the known impact of ASCs and their secretions in wound healing. Currently, most adipose tissue engineering approaches include two different strategies: in situ adipogenesis for small volume loss, and 3D in vitro tissue engineering for large adipose tissue defects. Both strategies usually imply the use of living cells, biomolecules and biocompatible scaffolds. One of the barriers that hampered the in vitro fat tissue development was the impossibility to maintain the long term culture of mature adipocytes ex vivo. Mature adipocytes are prone to mechanical damage during fat tissue manipulation and also highly susceptible to ischemic death. Moreover, they are terminally differentiated and thus unable to proliferate. These characteristics make them unsuitable for regenerative purposes. Recently developed a new culture method for adipocytes using a plasma hydrogel scaffold.

The ideal hard scaffolds have a long list of selection criteria:

1) It should support cell attachment, migration, cell-cell interactions, cell proliferation and differentiation

2) It must be biocompatible

 3) It should also be biodegradable at a controlled rate -ideally one to match the rate of neotissue growth to facilitate the integration of engineered tissue into the surrounding host tissue

4) It must provide structural support for cells and neotissue formed in the scaffold during the initial stages post-implantation

5) It should present interconnected pores to facilitate vessel growth and nutrient transport

 6) They should have versatile processing options to alter structure and morphology related to defect-specific needs.

 Synthetic materials possess several drawbacks when compared to natural ones, such as the absence of intrinsic surface ligands for cell attachment and a potential impact of their degradation products on cell function .Scaffold prevascularization strategies offer great promise to the field of adipose tissue engineering. Prevascularization of matrices with the co-culture of endothelial cells and fibroblasts increased the ability of the constructs to create anastomoses with the host vasculature. Once the capillary network was developed in vitro, the graft was implanted into the recipient. Natural scaffolding materials have extensively been used in the vascularisation of tissue engineering constructs including collagen, chitosan , decellularized extracellular matrix, and silk fibroin-fibrin. The two most commonly used synthetic materials used for vascularization are PEG and PLGA. Soft Scaffolds for in Situ Neoadipogenesis Soft scaffolds permit the in situ generation of new adipose tissue.

Tissue engineering strategies thus hold great promise to hopefully offer a permanent solution for adipose tissue repair and regeneration in  future.