Whisker of biphasic calcium phosphate ceramics: Osteo-immunomodulatory behaviors

Immune systems play a critical role in the regulation of bone formation and homeostasis, which arouses a growing interest in the development of biomaterials that can modulate both immune response and osteogenesis. In this study, biphasic calcium phosphate (BCP) ceramics were modified with different whiskered surface, and their effects on macrophage polarization and functional status were investigated. The results showed that compared to BCP-W ceramics with long and solid whiskers, BCP-HW ceramics with short and hollow whiskers surface were conducive to protein adsorption and macrophage elongation. Furthermore, BCP-HW ceramics down-regulated the expression of M1 macrophage markers (Il1β, Tnfα, and iNos), promoted the expression of M2 macrophage markers (Il10 and Arg) and growth factors (Tgfβ1 and Bmp2), which might be attributed to the differential integrin expression regulated by different whisker structures. The conditioned medium derived from the supernatant of macrophage/whiskered ceramic co-culture was further used to culture MC3T3-E1 pre-osteoblasts to evaluate the effects of whiskered ceramic-mediated macrophage secretion on osteogenesis in vitro. Compared with BCP-W ones, the secretion pattern induced by BCP-HW ceramics could promote the expression of bone markers in pre-osteoblasts, which might due to the activation of intracellular signaling cascades like BMP/Smad and TGF-β/Smad signaling pathways. A murine intramuscular implantation model suggested that after implantation for 1, 2, and 3 weeks, BCP-HW ceramics drove the switch of macrophages to ARG⁺ wound-healing M2 phenotype, while BCP-W ceramics increased the proportion of iNOS⁺ M1 inflammatory macrophages. At 2 months, only BCP-HW could induce ectopic bone formation. Taken together, these results indicated that BCP ceramics with hollow whiskers were capable of creating a proper inflammatory microenvironment to induce bone formation. These whiskered BCP ceramics with good osteo-immunomodulatory capacity hold promise in serving as bone grafts to achieve desired bone repair and regeneration.