Macrophages are a cell type with a critical function in the regulation of bone healing, able to instruct bone regeneration upon biomaterials implantation. During the regeneration process, macrophages undergo a phenotypic switch from a pro-inflammatory type (M1) to an anti-inflammatory profile (M2) able to promote osteogenesis. This process called polarization can be induced by cytokines as interleukin 4 (IL-4), apart from other factors. Magnetic iron oxide nanoparticles (NPs) have been widely studied as magnetic contrast agents, hyperthermia agents and magnetic vectors. These NPs allow the uploading of therapeutic molecules (IL-4) over the shell for inducing macrophage polarization towards M2 [1].

In this work, two different systems consisting of single-core and multi-core citrate coated iron oxide NPs, hereafter SC and MC respectively, loaded with IL-4 were prepared. SC and MC were characterized by electron transmission micrography (TEM), infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). The loading efficiency of IL-4 on the NPs was determined by Micro BCA™ Protein Assay Kit.

The IL-4 loaded NPs were internalized by M1 macrophages through passive transfection and magnetotransfection. Their effect on polarization towards M2 phenotype was studied through the analysis of the secretion of pro-inflammatory and anti-inflammatory cytokines. With passive transfection, both SC and MC showed anti-inflammatory response, which was greater in the case of SC. In the case of magnetotransfection, SC triggered an anti-inflammatory response, while MC provoked a strong pro-inflammatory response.

[1] V. M. T. Bart, R. J. Pickering, P. R. Taylor, N. Ipseiz, Immunology, 2021, 163, 128.