Modulation of MNC Phenotype and Macrophage Differentiation by the Matrix Elasticity in the Foreign Body Reaction

Biomaterial-induced multinucleated cells (MNC) have been observed within the material implantation sites, but their subtypes and roles in tissue repair and wound healing remain unclear. Herein, we present using an elastic gradient of the gelatin-based 3D matrix (Col-Tgel), as compared to cytokine, to induce MNCs in the in vitro and in vivo models. The 3D embedded Raw264.7 cells and rat bone marrow-derived monocytes (BMDMs), with or without cytokines such as IL-4 and RANKL, were characterized in terms of their MNCs morphologies and subtypes by in situ immunocytochemistry and flow cytometry. The macrophage polarization or osteoclasts differentiation markers such as NO production, arginase, and tartrate-resistant acid phosphatase activities assays were conducted to compare matrix specific effects. 3D matrix-induced MNCs expressed the same phenotypic heterogeneity as the IL-4 and RANK treated ones. The high elastic matrix (1006.48±92.29 Pa) induced high proinflammatory and osteoclast-like MNCs populations, but pro-, anti-inflammatory, and osteoclast-like macrophage differentiation and gene expression were highly active in the low elastic matrix (38.61±7.56 Pa). The matrix elasticity also altered the effect of IL-4 and RANKL on macrophage-derived MSC polarization. In the in vivo subcutaneous implantation model, higher CD86+ and RANK+ MNCs populations displayed in the medium to high elastic matrices while relatively high CD206+ MNCs population presented in the low elastic matrix. Results suggested that the matrix elasticity modulated macrophage differentiation and MNCs phenotype. The low elastic matrix may favor anti-inflammatory MNCs and macrophage differentiation for subcutaneous implantation.