Comparative Analysis of Hydrogels From Porcine Extracellular Matrix for 3D Bioprinting of Adipose Tissue

The extracellular matrix (ECM) is the natural scaffold of all soft tissues in tissue engineering. Of special interest is the use of ECM as a hydrogel, which can be used to enclose cells and to be molded into any form by 3D bioprinting. Protocols for the preparation of ECM vary in the use of physical and chemical processing steps, the use of different detergents for decellularization, and the removal of DNA and RNA residues and show a different use of solvents and wash buffers. We have, therefore, compared seven different variations for the decellularization of a primary porcine isolate to manufacture decellularized adipose tissue (DAT) for their use in adipose tissue engineering and as a hydrogel in particular. Decellularization efficacy was assessed by DNA quantification while retention of ECM components was evaluated by measuring the content of hydroxyproline and glycosaminoglycan (GAGs). Depending on the decellularization protocol, the composition and DNA content of the resulting DAT were different. All DAT samples were processed into hydrogels to assess their mechanical properties as well as their influence on cellular metabolic activity and cell differentiation. The different compositions of the DAT and the resulting hydrogels had an effect on the stability and printability of the gels. Some DAT that were digested with hydrochloric acid (HCl) were more stable than those that were digested with acetic acid (AA). In addition, depending on the protocol, there was a clear effect on adipose-derived stem cells (ASC), endothelial cells and fibroblasts, cultured with the hydrogels. The differentiation of ASC to adipocytes could be achieved on most of the hydrogels. Human dermal microvascular endothelial cells (HDMEC) showed significantly better metabolic activity on hydrogels digested with HCl than digested with AA. HDMEC cultured on hydrogel #2 digested with HCl showed a 40% higher metabolic activity compared to collagen as a positive control, whereas culturing HDMEC on hydrogel #2 digested with AA resulted in a cellular metabolic activity loss of 60%. In a triculture of all three cell types, the formation of first tubular networks by HDMEC was achieved depending on the hydrogel used.