Morphological and functional changes in RAW 264 macrophage‐like cells in response to a hydrated layer of carbonate‐substituted hydroxyapatite

The polycaprolactone/silk fibroin/carbonate hydroxyapatite electrospun scaffold promotes bone reconstruction by regulating the polarization of macrophages

Macrophages are known to modulate the osteogenic environment of bone regeneration elicited by biological bone grafts. Alteration in certain chemical components tends to affect macrophages polarization. Comparatively to hydroxyapatite (HAp), carbonate hydroxyapatite (CHA) consists of 7.4 (wt%) carbonate ions and more closely resembles the mineral content of bone. It remains unknown whether CHA scaffolds or HA scaffolds have better osteogenic properties. In this study, we fabricated PCL/SF scaffold, PCL/SF/HAp scaffold and PCL/SF/CHA scaffold using the electrospinning technique. Despite comparable mechanical properties, the PCL/SF/CHA scaffold exhibited better osteogenic properties than the PCL/SF/HAp scaffold. Although no significant differences were observed between the two scaffolds for promoting osteoblast differentiation in vitro, the PCL/SF/CHA group appeared to be more effective at promoting bone regeneration in cranial defects in vivo. The PCL/SF/CHA scaffold was found to promote macrophage polarization toward M2 via activating the JAK/STAT5 pathway which caused a pro-osteogenic microenvironment to facilitate osteoblast differentiation. The results of this study indicated a higher potential of CHA to substitute HAp in the production of bone scaffolds for better bone regeneration.

Immunomodulatory Properties: The Accelerant of Hydroxyapatite-Based Materials for Bone Regeneration

The immunoinflammatory response is the prerequisite step for wound healing and tissue regeneration, and the immunomodulatory effects of biomaterials have attracted increasing attention. Hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂] (HAp), a common calcium phosphate ceramic, due to its structural and functional similarity to the inorganic constituent of natural bones, has been developed for different application purposes such as bone substitutes, tissue engineering scaffolds, and implant coatings. Recently, the interaction between HAp-based materials and the immune system (various immune cells), and the immunomodulatory effects of HAp-based materials on bone tissue regeneration have been explored extensively. Macrophages-mediated regenerative effect by HAp stimulation occupies the mainstream status of immunomodulatory strategies. The immunomodulation of HAp can be manipulated by tuning the physical, chemical, and biological cues such as surface functionalization (physical or chemical modifications), structural and textural characteristics (size, shape, and surface topography), and the incorporation of bioactive substances (cytokines, rare-earth elements, and bioactive ions). Therefore, HAp ceramic materials can contribute to bone regeneration by creating a favorable osteoimmune microenvironment, which would provide a more comprehensive theoretical basis for their further clinical applications. Considering the rapidly developed HAp-based materials as well as their excellent biological performances in the field of regenerative medicine, this review discusses the recent advances concerning the immunomodulatory methods for HAp-based biomaterials and their roles in bone tissue regeneration.

Inflammation and biomaterials: role of the immune response in bone regeneration by inorganic scaffolds

The regulatory role of the immune system in maintaining bone homeostasis and restoring its functionality, when disturbed due to trauma or injury, has become evident in recent years. The polarization of macrophages, one of the main constituents of the immune system, into the pro-inflammatory or anti-inflammatory phenotype has great repercussions for cellular crosstalk and the subsequent processes needed for proper bone regeneration such as angiogenesis and osteogenesis. In certain scenarios, the damaged osseous tissue requires the placement of synthetic bone grafts to facilitate the healing process. Inorganic biomaterials such as bioceramics or bioactive glasses are the most widely used due to their resemblance to the mineral phase of bone and superior osteogenic properties. The immune response of the host to the inorganic biomaterial, which is of an exogenous nature, might determine its fate, leading either to active bone regeneration or its failure. Therefore, various strategies have been employed, like the modification of structural/chemical features or the incorporation of bioactive molecules, to tune the interplay with the immune cells. Understanding how these particular modifications impact the polarization of macrophages and further osteogenic and osteoclastogenic events is of great interest in view of designing a new generation of osteoimmunomodulatory materials that support the regeneration of osseous tissue during all stages of bone healing.

Antibacterial graphene-based hydroxyapatite/chitosan coating with gentamicin for potential applications in bone tissue engineering

Electrophoretic deposition process (EPD) was successfully used for obtaining graphene (Gr)-reinforced composite coating based on hydroxyapatite (HAP), chitosan (CS), and antibiotic gentamicin (Gent), from aqueous suspension. The deposition process was performed as a single step process at a constant voltage (5 V, deposition time 12 min) on pure titanium foils. The influence of graphene was examined through detailed physicochemical and biological characterization. Fourier transform infrared spectroscopy, field emission scanning electron microscopy, thermogravimetric analysis, X-ray diffraction, Raman, and X-ray photoelectron analyses confirmed the formation of composite HAP/CS/Gr and HAP/CS/Gr/Gent coatings on Ti. Obtained coatings had porous, uniform, fracture-free surfaces, suggesting strong interfacial interaction between HAP, CS, and Gr. Large specific area of graphene enabled strong bonding with chitosan, acting as nanofiller throughout the polymer matrix. Gentamicin addition strongly improved the antibacterial activity of HAP/CS/Gr/Gent coating that was confirmed by antibacterial activity kinetics in suspension and agar diffusion testing, while results indicated more pronounced antibacterial effect against Staphylococcus aureus (bactericidal, viable cells number reduction >3 logarithmic units) compared to Escherichia coli (bacteriostatic, <3 logarithmic units). MTT assay indicated low cytotoxicity (75% cell viability) against MRC-5 and L929 (70% cell viability) tested cell lines, indicating good biocompatibility of HAP/CS/Gr/Gent coating. Therefore, electrodeposited HAP/CS/Gr/Gent coating on Ti can be considered as a prospective material for bone tissue engineering as a hard tissue implant.

Improved osteogenesis of boron incorporated calcium silicate coatings via immunomodulatory effects

Osteoimmunology has revealed the importance of a favorable immune response for successful biomaterial-mediated osteogenesis. Boron-incorporated calcium silicate (Ca₁₁ Si₄ B₂ O₂₂ , B-CS) coating has been reported as a potential candidate for improving osteogenesis in orthopedic applications in vitro. However, relatively little is known about its effects on the immune response and subsequent osteogenesis. In this work, the immunomodulatory properties of the B-CS coating and its specific mechanism of action were explored. We found that the B-CS coating decreased M1 polarization and converted macrophages to the M2 phenotype via restraining the toll-like receptor signaling pathway, thus inducing a significant reduction in pro-inflammatory cytokines and an increase in anti-inflammatory cytokines. Moreover, the B-CS coating inhibited osteoclastogenesis and osteoclastic activities by downregulating osteoclastogenic genes and inhibiting the RANKL/RANK system. BMP2 and VEGF were also significantly upregulated by macrophages and bone mesenchymal stem cells, leading to activation of the BMP2 signaling pathway and subsequent upregulation of osteogenesis-associated genes, finally promoting osteogenic differentiation. These findings show that the B-CS coating could be a promising coating material for hip and knee implants. Furthermore, incorporation of the element boron into bioceramic coatings could be a good strategy in the design of bone biomaterials with beneficial immune responses. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 12-24, 2019.

The effect of glucose modification of hydroxyapatite nanoparticles on gene delivery

Surface modification techniques have been employed for the use of biocompatible and bioresorbable hydroxyapatite (HAp) nanoparticles in cell biology and medicine for the delivery of bioactive molecules. We demonstrated the effects of glucose modification of HAp (GlcHAp) on the transfection efficiency in endothelial cells. After preparing homogeneous HAp nanoparticles with a microemulsion technique, the particles with or without glucose modification and plasmid DNA (pDNA) complexes were transfected into endothelial cells. The transfection efficiency of GlcHAp/pDNA was higher than that of HAp/pDNA. To elucidate the mechanism underlying the improvement in the transfection efficiency following glucose modification, the uptake route into the cells and the inhibition of DNA degradation were investigated. GlcHAp/pDNA enhanced the transfection efficiency after interacting with the glucose transporter 1, as observed by the selective inhibitor assay. In addition, GlcHAp/pDNA was more stable than HAp/pDNA in the DNA degradation assay. Our results suggest that the glucose modification could promote the uptake of HAp nanoparticles by cells and protect the internalized DNA; properties essential for non-viral transfection carriers. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 61-66, 2019.

[Effect of human tooth bone graft materials on proliferation and differentiation of mice mononuclear macrophage RAW264.7]

Objective

To investigate the effect of human tooth bone graft materials on the proliferation, differentiation, and morphology of macrophages, and to understand the biocompatibility and cytotoxicity of human tooth bone graft materials.

Methods

Fresh human teeth were collected to prepare human tooth bone graft materials, the adhesion of mouse mononuclear macrophages RAW264.7 to human bone graft materials was observed under confocal microscopy. Scanning electron microscopy was used to observe the morphology of human tooth bone graft materials, OSTEONⅡ synthetic highly resorbable bone grafting materials, and untreated tooth powder (dental particles without preparation reagents). Different components of the extract were prepared in 4 groups: group A (DMEM medium containing 10% fetal bovine serum), group B (human tooth bone graft materials), group C (OSTEONⅡ synthetic highly resorbable bone grafting materials), group D (untreated tooth powder without preparation reagents). The 4 groups of extracts were co-cultured with the cells, and the cytotoxicity was qualitatively determined by observing the cell morphological changes by inverted microscope. The cell proliferation and differentiation results and cell relative proliferation rate were determined by MTT method to quantitatively determine cytotoxicity. The cell viability was detected by trypanosoma blue staining, and tumor necrosis factor α (TNF-α ) and interleukin 6 (IL-6) expressions were detected by ELISA.

Results

Scanning electron microscopy showed that the surface of the human tooth bone graft material and the OSTEONⅡ synthetic highly resorbable bone grafting materials had a uniform pore structure, while the untreated tooth particle collagen fiber structure and the demineralized dentin layer collapsed without specific structure. Confocal microscopy showed that the cells grew well on human tooth bone graft materials. After co-culture with the extract, the morphology and quantity of cells in groups A, B, and C were normal, and the toxic reaction grades were all grade 0, while group D was grade 3 reaction. MTT test showed that the cytotoxicity of groups B and C was grade 0 or 1 at each time point, indicating that the materials were qualified. The cytotoxicity was grade 2 in group D at 1 day after culture, and was grade 4 at 3, 5, and 7 days. Combined with cell morphology analysis, the materials were unqualified. The trypanosoma blue staining showed that the number of cells in groups A, B, and C was significantly higher than that in group D at each time point ( P<0.05), but no significant difference was found among groups A, B, and C ( P<0.05). ELISA test showed that the levels of TNF-α and IL-6 in groups A, B, and C were significantly lower than those in group D ( P<0.05), but no significant difference was found among groups A, B, and C ( P<0.05).

Conclusion

The human tooth bone graft materials is co-cultured with mice mononuclear macrophages without cytotoxicity. The extract has no significant effect on cell proliferation and differentiation, does not increase the expression of inflammatory factors, has good biocompatibility, and is expected to be used for clinical bone defect repair.