Speaker
Description
Introduction. Despite considerable developments in the field of orthopedic implants, complications including poor bone ingrowth and implant-associated infections (IAI) persist. Macrophages have recently been acknowledged to be essential for the implant success in the body, partly through intimate crosstalk with mesenchymal stem cells (MSCs) in the process of new bone formation [1]. However, the behavior of these immune cells is known to be affected by environmental cues, including the implant surface properties. Additive manufacturing (AM), surface biofunctionalization, and silver nanoparticles incorporation are promising techniques to achieve orthopedic implants with osteogenic, immunomodulatory, and antibacterial biofunctionalities [2–4]. The osteoimmunomodulatory properties of such implants are, however, not yet well understood. We, therefore, investigated the effects of human macrophages on the human mesenchymal stem cells (hMSCs) when co-cultured in vitro with AM titanium implants biofunctionalized via plasma electrolytic oxidation (PEO) and incorporated with silver nanoparticles (AgNPs).
Methodology. AM generated Ti-6Al-4V implants were biofunctionalized via PEO with/without AgNPs. Surface characterization was performed with a scanning electron microscope (SEM) and silver ion release was measured. The effects of the incorporation of AgNPs at different concentrations on human macrophages and bacterial cells were assessed by evaluating the viability of human macrophages and performing an isothermal microcalorimetry assay where bacterial metabolic activity was measured. The response of human macrophages and hMSCs monocultures to the PEO-treated Ti-6Al-4V implants were subsequently evaluated by measuring mineralization, protein, and gene expression. Finally, an indirect co-culture of macrophage-hMSCs was performed to study the effects of the macrophage response induced by the implants on the hMSCs osteogenic differentiation.
Results. The PEO modification of the AM implants created TiO₂ surfaces with micro- and nano-porosities. AgNPs were successfully incorporated into the TiO₂ layer. A concentration of 0.3 g/L AgNPs was found to be optimal to maintain the viability of human macrophages while imparting sufficient antibacterial properties to prevent bacterial growth on their surfaces. The expression of tissue repair related factors decreased in the specimens containing 0.3 g/L AgNPs as compared to the PEO-treated specimens not incorporating AgNPs. The same trend was observed for the macrophages co-cultured with hMSCs. However, this did not affect the osteogenic differentiation of hMSCs. Both co- and single-cultured hMSCs could osteogenically differentiate without any adverse effects caused by the presence of macrophages that were exposed to the either surface.
Conclusions. Based on the findings of this study, the incorporation of AgNPs into the PEO layers does not compromise the osteogenic differentiation and mineralization of hMSCs when co-cultured with human macrophages, while adding antibacterial functionalities to AM surfaces. Further evaluation of these promising implants in a bony in vivo environment with and without infection is, thus, recommended, and may prove them worthy of further development for potential clinical use.
References:
[1] Chen, Z. et al., Mater. Today 19, 304–321 (2016)
[2] Taniguchi, N. et al., Mater. Sci. Eng. 59, 690–701 (2016)
[3] Van Hengel, I. A. J. et al., Mater. Today Bio. 7, 1–12 (2020)
[4] F. Razzi et al., Biomed Mater. 15, 035017 (2020)
52354545528
