Effects of phosphatidylserine-containing supported lipid bilayers on the polarization of macrophages

Latest advances: Improving the anti-inflammatory and immunomodulatory properties of PEEK materials

Excellent biocompatibility, mechanical properties, chemical stability, and elastic modulus close to bone tissue make polyetheretherketone (PEEK) a promising orthopedic implant material. However, biological inertness has hindered the clinical applications of PEEK. The immune responses and inflammatory reactions after implantation would interfere with the osteogenic process. Eventually, the proliferation of fibrous tissue and the formation of fibrous capsules would result in a loose connection between PEEK and bone, leading to implantation failure. Previous studies focused on improving the osteogenic properties and antibacterial ability of PEEK with various modification techniques. However, few studies have been conducted on the immunomodulatory capacity of PEEK. New clinical applications and advances in processing technology, research, and reports on the immunomodulatory capacity of PEEK have received increasing attention in recent years. Researchers have designed numerous modification techniques, including drug delivery systems, surface chemical modifications, and surface porous treatments, to modulate the post-implantation immune response to address the regulatory factors of the mechanism. These studies provide essential ideas and technical preconditions for the development and research of the next generation of PEEK biological implant materials. This paper summarizes the mechanism by which the immune response after PEEK implantation leads to fibrous capsule formation; it also focuses on modification techniques to improve the anti-inflammatory and immunomodulatory abilities of PEEK. We also discuss the limitations of the existing modification techniques and present the corresponding future perspectives.

Synergistic effects of arginine-glycine-aspartic acid and phosphatidylserine on the surface immunomodulation and osseointegration of titanium implants

The control of macrophage polarization is important in bone tissue regeneration such as osseointegration. In this study, a coating method was developed to improve the osseointegration of titanium (Ti) implants by generating an immunomodulatory effect. The surface of the Ti discs was coated with a poly(lactide-co-glycolide)(PLGA) polymer, phosphatidylserine (PS), and arginine-glycine-aspartic acid (RGD) peptide conjugated phospholipid. In in vitro assay using mouse bone marrow-derived macrophages (BMDMs), the most significant expression of the M2 marker genes (Arg-1, YM-1, FIZZ1) and CD206, an M2 surface marker, was obtained with coatings containing 6 mol% RGD conjugates and phospholipids consisting of 50 mol% PS. The M2-inducing effect of RGD and PS was also verified in rat femurs where coated Ti rods were implanted. The RGD and PS coating significantly enhanced the osseointegration of the Ti implants. Moreover, a biomechanical push-out test showed that the RGD and PS coating increased the interfacial binding force between the bone and implants. These results indicate that PS and RGD can be applied to the solid surface of implantable biomedical devices to improve immunomodulation and tissue regeneration.

Blocking antibody-mediated phosphatidylserine enhances cancer immunotherapy

Cancer immunotherapy is a major breakthrough in tumor therapy and has been used in monotherapy or combination therapy. However, it has been associated with poor immune tolerance in some patients or immune-related adverse events. Therefore, ideal and reliable tumor elimination strategies are urgently needed to overcome these shortcomings. Phosphatidylserine (PS) is a negatively charged phospholipid, usually present in the inner lobules of eukaryotic cell membranes. Under certain physiological or pathological conditions, PS may be exposed on the outer leaflets of apoptotic cells serving as recognition signals by phagocytes and modulating the immune response. On the contrary, increased exposure of PS in the tumor microenvironment can significantly antagonize the body's anti-tumor immunity, thereby promoting tumor growth and metastasis. During radiotherapy and chemotherapy, PS-mediated immunosuppression increases the PS levels in necrotic tissue in the tumor microenvironment, further suppressing tumor immunity. PS-targeted therapy is a promising strategy in cancer immunotherapy. It inhibits tumor growth and improves the anti-tumor activity of immune checkpoint inhibitors. A comprehensive understanding of the mechanism of PS-targeted therapy opens up a new perspective for future cancer immunotherapies.

Modulation of Macrophage Polarization by Phospholipids on the Surface of Titanium

Macrophage polarization has become increasingly important for the improvement of the biocompatibility of biomaterials. In this study, we coated Ti discs with phospholipids (phosphatidylserine/phosphatidylcholine [4:1 mole/mole]) by evaporating the solvent under vacuum, and observed the polarization of RAW 264.7 cells cultured on the discs. The coated discs were hydrated before cell culture was added. The shape of the hydrated phospholipids varied with the concentration of loaded phospholipids: a perforated layer (0.1 mM), tubules and spheres (1 mM), and spheres (10 mM). RAW 264.7 cells exhibited different morphologies, depending on the concentration of phospholipids. On the coated discs, the gene expression and protein release of TGF-β1, VEGF, Arg-1, and TNF-α were downregulated, especially with 10 mM phospholipids. The stimulation of mRNA expression and the protein release of those genes by IL-4 and LPS were also disturbed on the phospholipid-coated discs. In conclusion, the polarization of RAW 264.7 cells was prevented by hydrated phospholipids on Ti discs.

Dopamine-Mediated Zwitterionic Polyelectrolyte-Coated Polypropylene Hernia Mesh with Synergistic Anti-inflammation Effects

Over 20 million ventral hernia repairs are performed worldwide annually and only a minority (<10%) of cases are not mesh-based. However, even polypropylene (PP), endorsed as the "gold standard" of all prosthetic materials used in this field, is still subject to many complications caused by the foreign body reaction (FBR). Here, we describe the buildup of dopamine-mediated zwitterionic poly(sulfobetaine methacrylate) (PSBMA) coatings to inhibit nonspecific protein adsorption. Based on the universal adhesive ability of polydopamine (PDA), PSBMA has been coated on the PP mesh surface via two strategies: sequential deposition (PSBMA-PDA-PP) and co-deposition (PSBMA@PDA-PP). The presence of PSBMA shows great contribution to obviously decreased hydrophobicity of the PP surface (WCA_co = 36.3° and WCA_seq = 30.7°) as well as improved protein resistance (Reduction_co = 74% and Reduction_seq = 82%). Notably, as the intermedia between PP and PSBMA, PDA can endow the PP mesh with antioxidant activity, further featuring synergistic anti-inflammation therapeutic effect when coupled with PSBMA. With almost equal surface content of PSBMA, PSBMA-PDA-PP exhibited a more superior ability against macrophage adhesion and proliferation and showed more significantly decreased releases of TNF-α and IL-6 (p < 0.05) than those of PSBMA@PDA-PP, fundamentally attributed to its more neutral surface potential and the protection for polyphenols of PDA from oxidation with PSBMA as the outer layer. Furthermore, the coating layers demonstrated good stability and no sacrifice of the pristine mechanical property. The proposed dopamine-mediated PSBMA coatings possess high potential in biomedical implant areas for attenuating the FBR.

The observed difference of macrophage phenotype on different surface roughness of mineralized collagen

Biomaterials regulate macrophages and promote regeneration function, which is a new hot pot in tissue engineering and regenerative medicine. The research based on macrophage materials biology has appeared happy future, but related research on regulating macrophages and promoting tissue regeneration is still in its infancy. The surface roughness of biomaterials is one of the important factors affecting macrophage behavior. Previous study also found that the surface roughness of many biomaterials regulating macrophage polarization, but not including mineralized collagen (MC). In this study, we designed and fabricated MC with different roughness and investigated the influence of MC with different roughness on macrophages. In the study, we found that on the rough surface of MC, macrophages exhibited M1 phenotype-amoeboid morphology and high-level secretory of inflammatory factor (tumor necrosis factor-α and interleukin-6), while smoother surface exhibited M2 phenotype. These data will be beneficial to understand the mechanism deeply and enrich biomaterials tissue regeneration theory, provide a new train of thought biomaterials inducing tissue regeneration and repair and guide the optimum design of new biomaterials, development and reasonable applications.

Nanotubular TiO2 regulates macrophage M2 polarization and increases macrophage secretion of VEGF to accelerate endothelialization via the ERK1/2 and PI3K/AKT pathways

Background

Macrophages play important roles in the immune response to, and successful implantation of, biomaterials. Titanium nanotubes are considered promising heart valve stent materials owing to their effects on modulation of macrophage behavior. However, the effects of nanotube-regulated macrophages on endothelial cells, which are essential for stent endothelialization, are unknown. Therefore, in this study we evaluated the inflammatory responses of endothelial cells to titanium nanotubes prepared at different voltages.

Methods and results

In this study we used three different voltages (20, 40, and 60 V) to produce titania nanotubes with three different diameters by anodic oxidation. The state of macrophages on the samples was assessed, and the supernatants were collected as conditioned media (CM) to stimulate human umbilical vein endothelial cells (HUVECs), with pure titanium as a control group. The results indicated that titanium dioxide (TiO2) nanotubes induced macrophage polarization toward the anti-inflammatory M2 state and increased the expression of arginase-1, mannose receptor, and interleukin 10. Further mechanistic analysis revealed that M2 macrophage polarization controlled by the TiO2 nanotube surface activated the phosphatidylinositol 3-kinase/AKT and extracellular signal-regulated kinase 1/2 pathways through release of vascular endothelial growth factor to influence endothelialization.

Conclusion

Our findings expanded our understanding of the complex influence of nanotubes in implants and the macrophage inflammatory response. Furthermore, CM generated from culture on the TiO2 nanotube surface may represent an integrated research model for studying the interactions of two different cell types and may be a promising approach for accelerating stent endothelialization through immunoregulation.