Modulation of adipose tissue derived stem cells encapsulated in injectable multi-functional hydrogels

Objective : The cellular microenvironment plays an important role in controlling the cellular behavior. Therefore, in Tissue Engineering strategies, systems have been designed so that by combining cells, signaling molecules and engineered substrates, one can mimic as closely as possible the native microenvironment of the extracellular matrix. In this context, injectable hydrogels have been developed that allow controlling the cellular spatial distribution and that provide a 3D support. However, many of these systems fail to replicate the mechanical properties of tissues and more significantly to provide a cell-friendly environment. Therefore, the aim of this study is to evaluate the cellular response of human adipose stem cells (hACS) within a growth factor-enriched injectable hydrogel. Methods : Hydrogels were formed by combining platelet lysates (PLs) with a methacrylated gellan gum (MeGG) solution at different ratios. The hydrogels were further stabilized by photopolymerization. The parameters of photocrosslinking were varied and the dynamical mechanical properties evaluated for all the conditions. Total protein content released from the hydrogels was quantified for all the conditions using micro-BCA assay. Human ASCs were both seeded on the surface of the hydrogels for 7 days and encapsulated within the materials for 14 days. Results and discussion : Hydrogels with tunable mechanical properties were fabricated by changing the volume ratio of PLs and MeGG. The highest elastic modulus (nearly 500kPa) was achieved for the condition with the lowest volume of PLs (2MeGG:1PLs), being significantly more elastic than MeGG alone. The rate of release of proteins present in the PLs from the PLs-MeGG hydrogels was higher for the condition with equal volume of MeGG and PLs (1MeGG:1PLs), as a result of the lower crosslinked polymer network. Human ASCs cultured onto the engineered surfaces showed a good metabolic activity and proliferation. Immunostaining revealed that MeGG:PL combinations fostered the attachment and spreading of cells. A strikingly improved cellular behavior was observed for the formulations with PLs, when compared to MeGG alone. This behavior was further confirmed at a 3D scale, demonstrated by a significantly higher cellular metabolic activity on the hydrogels with PLs.