Engineering naturally-derived human connective tissues for clinical applications using a serum-free production system

Abstract

The increasing need for tissue substitutes in reconstructive surgery spurs the development of engineering methods suited for clinical applications. Cell culture and tissue production traditionally require the use of fetal bovine serum (FBS) which is associated with various complications especially from a translational perspective. Using the self-assembly approach of tissue engineering, we hypothesized that all important parameters of tissue reconstruction can be maintained in a production system devoid of FBS from cell extraction to tissue reconstruction. We studied two commercially available serum-free medium (SFM) and xenogen-free serum-free medium (XSFM) for their impact on tissue reconstruction using human adipose-derived stem/stromal cells (ASCs) in comparison to serum-containing medium. Both media allowed higher ASC proliferation rates in primary cultures over five passages compared with 10% FBS supplemented medium while maintaining high expression of mesenchymal cell markers. For both media, we evaluated extracellular matrix production and deposition necessary to engineer manipulatable tissues using the self-assembly approach. Tissues produced in SFM exhibited a significantly increased thickness (up to 6.8-fold) compared with XSFM and FBS-containing medium. A detailed characterization of tissues produced under SFM conditions showed a substantial 50% reduction of production time without compromising key tissue features such as thickness, mechanical resistance and pro-angiogenic secretory capacities (plasminogen activator inhibitor 1, hepatocyte growth factor, vascular endothelial growth factor, angiopoietin-1) when compared to tissues produced in the control FBS-containing medium. Furthermore, we compared ASCs to the frequently used human dermal fibroblasts (DFs) in the SFM culture system. ASC-derived tissues displayed a 2.4-fold increased thickness compared to their DFs counterparts. In summary, we developed all-natural human substitutes using a production system compatible with clinical requirements. Under culture conditions devoid of bovine serum, the resulting engineered tissues displayed similar and even superior structural and functional properties over the classic FBS-containing culture conditions with a considerable 50% shortening of production time.

Keywords: adipose tissue; mechanical properties; mesenchymal cells; pro-angiogenic factors; serum-free medium; tissue engineering; xenogen-free.