The substrate-dependent regeneration capacity of mesenchymal stem cell spheroids derived on various biomaterial surfaces.

Mesenchymal stem cells (MSCs) are widely used for their self-renewal and multipotent abilities, which can be further enhanced by growing MSCs as three-dimensional (3D) cellular spheroids on certain substrates. Although various surfaces have been used to generate 3D MSC spheroids, the answer to whether all these spheroids have similar in vitro and in vivo properties remains unclear. In this study, adipose-derived adult stem cells (ADSCs) were cultured on a non-adherent Petri dish, polyvinyl alcohol, chitosan (CS), or chitosan-hyaluronan (CS-HA) to form 3D spheroids. The expression of the cell adhesion molecule, N-cadherin, was analyzed by qRT-PCR and Western blotting. The functional migration ability was tested using the transwell assay. The capacity for chondral regeneration of various ADSC spheroids was further evaluated in a rabbit model. We demonstrated that ADSC spheroids derived on the CS or CS-HA surface had the greater expression of N-cadherin and better migration ability. The latter was consistent with the higher expression levels of chemokine/receptor SDF-1/CXCR4 for the spheroids derived on CS or CS-HA. Animal studies also revealed significantly better cartilage repair in defects loaded with CS- or CS-HA-derived spheroids. In particular, CS-HA-derived spheroids gave rise to the best regeneration when combined with a 3D printed scaffold. This study suggested that MSC spheroids derived on different surfaces may have distinct in vitro and in vivo properties, which appeared to be associated with the surface-bound calcium as well as the calcium-dependent N-cadherin and CXCR4 signaling. The substrate-dependent properties may eventually lead to different regeneration capacities of various MSC spheroids in vivo.