Structural Guidance in 3D Microgel-in-Hydrogel Systems to Improve Chondrogenesis.

Anisotropic biomaterials are broadly studied in regenerative medicine as they aim to mimic the hierarchical structures of native tissue. The Anisogel, an anisotropic microgel-in-hydrogel system, involves two key factors for tissue engineering: guidance cues-magnetically aligned rod-shape structures-and a surrounding matrix-polyethylene glycol-vinylsulfone (PEG-VS) with a degradable peptide crosslinker. This research shows the potential of using a PEG-VS- based Anisogel to allow for guided ingrowth and chondrogenic differentiation of human mesenchymal stromal cells (hMSCs) modulated by the alignment and size of anisometric microgels. The properties of the surrounding matrix are optimized for the availability of anchoring peptides (RGD concentration) and matrix density (hydrogel precursor concentration). The microgels of highest tested dimensions (10 × 10 × 100 µm3) lead to a donor-independent significant upregulation of chondrogenic markers (SOX 9, ACAN and COL2A1) and a decrease of hypertrophic chondrogenic markers (RUNX 2, COL10A1), compared to unaligned and smaller microgel sizes. As a proof of concept, the Anisogel is tested in a semi-orthotopic mouse model where the effect of microgel alignment on cell infiltration and osteochondral tissue formation is evaluated.