Sequentially activating macrophages M1 and M2 phenotypes by lipopolysaccharide-containing Mg-Fe layered double hydroxides coating on the Ti substrate

As cells of innate immunity, macrophages are a class of innate immune cells existing in almost all tissues and play a crucial role in bone repair. However, it remains a challenge to modulate the sequential activation of the deferent phenotypes in macrophage when designing the titanium (Ti) implants. In this study, the Mg-Fe layered double hydroxides (LDHs) was coated on Ti substrate through hydrothermal treatment. Further on lipopolysaccharide (LPS) was introduced onto the LDHs through adsorption and ions exchange. The adsorption efficiency of the coating on LPS reached 72.8% in 24 h due to the anion exchange and electrostatic interactions between the LPS and the LDH layers in deionized water. The LDHs-LPS coating released a large amount of LPS in the early stage, which induced macrophages into M1 phenotype via activating TLR-4 → MyD88 and TLR-4 → Ticam-1/2 signal pathways. Subsequently, the M1 macrophages were transformed into M2 phenotype by regulating the integrin α5β1 of cells by the nanostructures, wetting angle and Mg²⁺ of the coating. The LDHs-LPS coating endows Ti with the ability of stage immunomodulation, indicating the positive osteoimmunomodulatory property.

Sequential activation of M1 and M2 phenotypes in macrophages by Mg degradation from Ti-Mg alloy for enhanced osteogenesis

BACKGROUND

Even though the modulatory effects of Magnisum (Mg) and its alloys on bone-healing cells have been widely investigated during the last two decades, relatively limited attention has been paid on their inflammation-modulatory properties. Understanding the activation process of macrophages in response to the dynamic degradation process of Mg as well as the relationship between macrophage phenotypes and their osteogenic potential is critical for the design and development of advanced Mg-based or Mg-incorporated biomaterials.

METHODS

In this work, a Ti-0.625 Mg (wt.%) alloy fabricated by mechanical alloying (MA) and subsequent spark plasma sintering (SPS) was employed as a material model to explore the inflammatory response and osteogenic performance in vitro and in vivo by taking pure Ti as the control. The data analysis was performed following Student's t-test.

RESULTS

The results revealed that the macrophages grown on the Ti-0.625 Mg alloy underwent sequential activation of M1 and M2 phenotypes during a culture period of 5 days. The initially increased environmental pH (~ 8.03) was responsible for the activation of M1 macrophages, while accumulated Mg²⁺ within cells contributed to the lateral M2 phenotype activation. Both M1 and M2 macrophages promoted osteoblast-like SaOS-2 cell maturation. In vivo experiment further showed the better anti-inflammatory response, regenerative potentiality and thinner fibrous tissue layer for the Ti-0.625 Mg alloy than pure Ti.

CONCLUSION

The results highlighted the roles of Mg degradation in the Ti-0.625 Mg alloy on the sequential activation of macrophage phenotypes and the importance of modulating M1-to-M2 transition in macrophage phenotypes for the design and development of inflammation-modulatory biomaterials.

Cholesterol-like Condensing Effect of Perfluoroalkyl Substances on a Phospholipid Bilayer

To understand the potential cytotoxicity of perfluoroalkyl substances (PFAS), we study their interactions with a model phospholipid bilayer membrane using molecular dynamics (MD) simulations. Four typical PFAS molecules are investigated, including perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorooctanesulfonic acid (PFOS), and perfluorohexane sulfonate (PFHxS). All of these PFAS molecules are found to spontaneously penetrate the lipid bilayer within a short simulation time (a few nanoseconds). During the penetration process, further free-energy analysis reveals that a PFAS molecule encounters an energy barrier at the bilayer/water interface. To overcome this free-energy barrier, the PFAS molecule flips itself at the interface. We further investigate the influence of embedded PFAS molecules on the membrane properties. All of the embedded PFAS molecules are found to produce a cholesterol-like condensing effect on the lipid bilayer, which includes increases of the order parameters of lipid tails and the thickness of the lipid bilayer and a decrease of area per lipid. Moreover, the PFAS molecules are found to form hydrogen bonds with oxygen atoms at three different positions of a lipid molecule. Our work reveals the penetration pathway of PFAS molecules entering into a lipid bilayer. In addition, the cholesterol-like condensing effect induced by embedded PFAS molecules on model membranes is systematically investigated and discussed. Our simulations can help understand the physical mechanisms of PFAS cytotoxicity.