Fluorinated hydroxyapatite conditions a favorable osteo-immune microenvironment via triggering metabolic shift from glycolysis to oxidative phosphorylation

BACKGROUND

Biological-derived hydroxyapatite is widely used as a bone substitute for addressing bone defects, but its limited osteoconductive properties necessitate further improvement. The osteo-immunomodulatory properties hold crucial promise in maintaining bone homeostasis, and precise modulation of macrophage polarization is essential in this process. Metabolism serves as a guiding force for immunity, and fluoride modification represents a promising strategy for modulating the osteoimmunological environment by regulating immunometabolism. In this context, we synthesized fluorinated porcine hydroxyapatite (FPHA), and has demonstrated its enhanced biological properties and osteogenic capacity. However, it remains unknown whether and how FPHA affects the immune microenvironment of the bone defects.

METHODS

FPHA was synthesized and its composition and structural properties were confirmed. Macrophages were cultured with FPHA extract to investigate the effects of FPHA on their polarization and the related osteo-immune microenvironment. Furthermore, total RNA of these macrophages was extracted, and RNA-seq analysis was performed to explore the underlying mechanisms associated with the observed changes in macrophages. The metabolic states were evaluated with a Seahorse analyzer. Additionally, immunohistochemical staining was performed to evaluate the macrophages response after implantation of the novel bone substitutes in critical size calvarial defects in SD rats.

RESULTS

The incorporation of fluoride ions in FPHA was validated. FPHA promoted macrophage proliferation and enhanced the expression of M2 markers while suppressing the expression of M1 markers. Additionally, FPHA inhibited the expression of inflammatory factors and upregulated the expression of osteogenic factors, thereby enhancing the osteogenic differentiation capacity of the rBMSCs. RNA-seq analysis suggested that the polarization-regulating function of FPHA may be related to changes in cellular metabolism. Further experiments confirmed that FPHA enhanced mitochondrial function and promoted the metabolic shift of macrophages from glycolysis to oxidative phosphorylation. Moreover, in vivo experiments validated the above results in the calvarial defect model in SD rats.

CONCLUSION

In summary, our study reveals that FPHA induces a metabolic shift in macrophages from glycolysis to oxidative phosphorylation. This shift leads to an increased tendency toward M2 polarization in macrophages, consequently creating a favorable osteo-immune microenvironment. These findings provide valuable insights into the impact of incorporating an appropriate concentration of fluoride on immunometabolism and macrophage mitochondrial function, which have important implications for the development of fluoride-modified immunometabolism-based bone regenerative biomaterials and the clinical application of FPHA or other fluoride-containing materials.

Nanosized Silk-Magnesium Complexes for Promotion of Angiogenic and Osteogenic Activities

Injectable hydrogels with osteogenic and angiogenetic properties are of interest in bone tissue engineering. Since the bioactivity of ions is concentration-dependent, nanosized silk-magnesium (Mg) complexes were previously developed and assembled into hydrogels with angiogenic capabilities but failed to control both osteogenic and angiogenetic activities effectively. Here, nanosized silk particles with different sizes were obtained by using ultrasonic treatment to control silk-Mg coordination and particle formation, resulting in silk-Mg hydrogels with different types of bioactivity. Fourier transform infrared and X-ray diffraction results revealed that different coordination intensities were present in the different complexes as a basis for the differences in activities. Slow Mg ion release was controlled by these nanosized silk-Mg complexes through degradation. With the same amount of Mg ions, the different silk-Mg complexes exhibited different angiogenic and osteogenic capacities. Complexes with both angiogenic and osteogenic capacities were developed by optimizing the sizes of the silk particles, resulting in faster and improved quality of bone formed in vivo than complexes with the same composition of silk and Mg but only angiogenic or osteogenic capacities. The biological selectivity of silk-Mg complexes should facilitate applications in tissue regeneration.

Regulating Blood Clot Fibrin Films to Manipulate Biomaterial-Mediated Foreign Body Responses

The clinical efficacy of implanted biomaterials is often compromised by host immune recognition and subsequent foreign body responses (FBRs). During the implantation, biomaterials inevitably come into direct contact with the blood, absorbing blood protein and forming blood clot. Many studies have been carried out to regulate protein adsorption, thus manipulating FBR. However, the role of clot surface fibrin films formed by clotting shrinkage in host reactions and FBR is often ignored. Because of the principle of fibrin film formation being relevant to fibrinogen or clotting factor absorption, it is feasible to manipulate the fibrin film formation via tuning the absorption of fibrinogen and clotting factor. As biological hydroxyapatite reserved bone architecture and microporous structure, the smaller particle size may expose more microporous structures and adsorb more fibrinogen or clotting factor. Therefore, we set up 3 sizes (small, <0.2 mm; medium, 1 to 2 mm; large, 3 to 4 mm) of biological hydroxyapatite (porcine bone-derived hydroxyapatite) with different microporous structures to investigate the absorption of blood protein, the formation of clot surface fibrin films, and the subsequent FBR. We found that small group adsorbed more clotting factors because of more microporous structures and formed the thinnest and sparsest fibrin films. These thinnest and sparsest fibrin films increased inflammation and profibrosis of macrophages through a potential signaling pathway of cell adhesion-cytoskeleton-autophagy, leading to the stronger FBR. Large group adsorbed lesser clotting factors, forming the thickest and densest fibrin films, easing inflammation and profibrosis of macrophages, and finally mitigating FBR. Thus, this study deepens the understanding of the role of fibrin films in host recognition and FBR and demonstrates the feasibility of a strategy to regulate FBR by modulating fibrin films via tuning the absorption of blood proteins.

Optimized osteogenesis of porcine bone-derived xenograft through surface coating of magnesium-doped nanohydroxyapatite

As one of the key factors influencing the outcome of guided bone regeneration, the currently used xenografts possess insufficient capability in osteogenesis. With the aim of improving the osteogenic performance of xenografts, porcine bone-derived hydroxyapatite (PHA) was prepared and subsequently coated by magnesium-doped nano hydroxyapatite (nMgHA, 10%, 20%, and 30% of Mg/Ca + Mg) through a straightforward and cost-efficient approach. The physiochemical and biological properties of nMgHA/PHAs were examinedin vitroandin vivo. The inherent three-dimensional (3D) porous framework with the average pore size of 300 μm was well preserved in nMgHA/PHAs. Meanwhile, excess magnesium released from the so-called 'surface pool' of PHA was verified. In contrast, slower release of magnesium at lower concentrations was detected for nMgHA/PHAs. Significantly more newly-formed bone and microvessels were observed in 20%nMgHA/PHA than the other specimens. With the limitations of the present study, it could be concluded that PHA coated by 20%nMgHA may have the optimized osteogenic performance due to the elimination of the excess magnesium from the 'surface pool', the preservation of the inherent 3D porous framework with the favorable pore size, and the release of magnesium at an appropriate concentration that possessed osteoimmunomodulatory effects on macrophages.

Functional role of circRNAs in osteogenesis: A review

The extracellular matrixes (ECM), as well as the microenvironmental signals, play an essential role in osteogenesis by regulating intercellular pathways. Recently, it has been demonstrated that a newly identified RNA, circular RNA, contributes to the osteogenesis process. Circular RNA (circRNA), the most recently identified RNA, is involved in the regulation of gene expression at transcription to translation levels. The dysregulation of circRNAs has been observed in several tumors and diseases. Also, various studies have shown that circRNAs expression is changed during osteogenic differentiation of progenitor cells. Therefore, understanding the role of circRNAs in osteogenesis might help the diagnosis as well as treatment of bone diseases such as bone defects and osteoporosis. In this review, circRNA functions and the related pathways in osteogenesis have been discussed.

Optimized osteogenesis of biological hydroxyapatite-based bone grafting materials by ion doping and osteoimmunomodulation

BACKGROUND: Biological hydroxyapatite (BHA)-based bone grafting materials have been widely used for bone regeneration in implant surgery. Much effort has been made in the improvement of their osteogenic property as it remains unsatisfactory for clinical use. Osteoimmunomodulation plays a significant role in bone regeneration, which is highly related to active inorganic ions. Therefore, attempts have been made to obtain osteoimmunomodulatory BHA-based bone grafting materials with optimized osteogenic property by ion doping. OBJECTIVE: To summarize and discuss the active inorganic ions doped into BHA and their effects on BHA-based bone grafting materials. METHOD: A literature search was performed in databases including Google Scholar, Web of Science and PubMed, with the elementary keywords of “ion doped” and “biological hydroxyapatite”, as well as several supplementary keywords. All document types were included in this search. The searching period and language were not limited and kept updated to 2022. RESULTS: A total of 32 articles were finally included, of which 32 discussed the physiochemical properties of BHA-based biomaterials, while 12 investigated their biological features in vitro, and only three examined their biological performance in vivo. Various ions were doped into BHA, including fluoride, zinc, magnesium and lithium. Such ions improved the biological performance of BHA-based biomaterials, which was attributed to their osteoimmunomodulatory effect. CONCLUSION: The doping of active inorganic ions is a reliable strategy to endow BHA-based biomaterials with osteoimmunomodulatory property and promote bone regeneration. Further studies are still in need to explore more ions and their effects in the crosstalk between the skeletal and immune systems.

Histomorphometric assessment of implant coated with mixture of nano-alumina and fluorapatite in rabbits

Background

The application of nanoscale surface modification was found to be useful in the improvement of osseointegration of endosseous dental implants. The fluorapatite (FA)/alumina (Al₂O₃) mixture is recognized for its outstanding bioinertia and can significantly increase the biocompatibility and bioactivity of biomaterials.

Objective

The aim of the present work was to evaluate the bone response to nano-alumina- and fluorapatite-coated dental implants using rabbit tibiae.

Material and Methods

The coating was performed using the dip-coating method. Commercially pure titanium screw-type implants were used as a control group. The coated implants were the experimental group. Each group consisted of 12 screws that were surgically implanted in 6 healthy New Zealand rabbits. Histological and histomorphometric evaluations were performed at the bone to implant contact (BIC) interface, bone fraction area occupancy (BAFO) and fibrous tissue at 2 and 6 weeks of healing.

Results

This analysis showed that the coated implants had more rapid osseointegration than the control group, with a significant difference after 2 and 6 weeks of healing for both groups. The histomorphometric evaluation demonstrated higher values for BIC% and BAFO% and lower values of fibrous tissue in the mixture-coated Ti implants than in the control group.

Conclusion

The current study suggested that the nano-alumina and fluorapatite mixture coating is a favourable candidate for rapid osseointegration over uncoated implants.

Tantalum oxide submicro-particles into microporous coating on polyimide possessing antibacterial property and inducing cellular response for orthopedic application

Surface characteristics of the biomaterials have significant effects on response of osteoblast and formation of new bone tissue. In this study, to improve the bio-performance of polyimide (PI) as an implantable material for bone substitute, concentrated sulfuric acid suspension with tantalum (V) oxide (vTO) submicro-particles of 10w% (PIST10) and 15w% (PIST15) was utilized to modify PI surface. After sulfonation, microporous coatings including vTO particles were created on PI (PIST10 and PIST15) while microporous coating without vTO particles was also created on PI (PIS). Results showed that surface roughness, hydrophilicity and protein adsorption of PIST15 was remarkably higher than PIST10 and PIS. Furthermore, after soaking into simulated body fluid (SBF), no apatite mineralization on PIS was found, while PIST15 with high vTO content exhibited better apatite mineralization compared with PIST10. Moreover, PIS showed low antibacterial property, while PIST15 with high vTO content revealed better antibacterial property compared with PIST10. In addition, cellular response (such as adhesion, proliferation and alkaline phosphatase activity) of bone marrow stromal cells (BMSC) of rat to PIST15 was higher than PIST10 and PIS. In conclusion, the microporous coating of PIST15 including vTO submicro-particles possessed good antibacterial property and bioactivity, which significantly promoted the responses of BMSC. Therefore, PIST15 has potential application prospects for bone substitute.

Sequential activation of heterogeneous macrophage phenotypes is essential for biomaterials-induced bone regeneration

Macrophage has been gradually recognized as a central regulator in tissue regeneration, and the study of how macrophage mediates biomaterials-induced bone regeneration through immunomodulatory pathway becomes popular. However, the current understanding on the roles of different macrophage phenotypes in regulating bone tissue regeneration remains controversial. In this study, we demonstrate that sequential infiltration of heterogeneous phenotypes of macrophages triggered by bio-metal ions effectively facilitates bone healing in bone defect. Indeed, M1 macrophages promote the recruitment and early commitment of osteogenic and angiogenic progenitors, while M2 macrophages and osteoclasts support the deposition and mineralization of the bone matrix, as well as the maturation of blood vessels. Moreover, we have identified a group of bone biomaterial-related multinucleated cells that behave similarly to M2 macrophages with wound-healing features rather than participate in the bone resorption cascade similarly to osteoclasts. Our study shows how sequential activation of macrophage-osteoclast lineage contribute to a highly orchestrated immune response in the bone tissue microenvironment around biomaterials to regulate the complex biological process of bone healing. Therefore, we believe that the temporal activation pattern of heterogeneous macrophage phenotypes should be considered when the next generation of biomaterials for bone regeneration is engineered.

Pretreatment by recyclable Fe3O4@Mg/Al-CO3-LDH magnetic nano-adsorbent to dephosphorize for the determination of trace F- and Cl- in phosphorus-rich solutions

The magnetic nano-adsorbent Fe₃O₄@Mg/Al-CO₃-LDH (Mg/Al-type layered double hydroxide) with a CO₃²⁻ interlayer anion has been synthesized successfully on Fe₃O₄ nanoparticles via a urea hydrothermal method. It is confirmed that the nano-adsorbent can adsorb PO₄³⁻ rapidly and efficiently in multi-ion solutions; meanwhile, it did not adsorb any F⁻ and Cl⁻, even with a high amount of the nano-adsorbent or a longer adsorption time. This behaviour is beneficial for applications to remove PO₄³⁻ in phosphorus-rich solutions, and especially can be utilized to determine trace F⁻ and Cl⁻ anions in phosphorus-rich solutions by physical and chemical analysis methods including ion chromatography without serious interference from PO₄³⁻ for trace determinations. Herein, the hydrothermally synthesized Fe₃O₄@Mg/Al-CO₃-LDH was characterized via SEM, TEM, SAED, XRD, FTIR, magnetic hysteresis loop analysis and adsorption–desorption isotherm analysis. The structure and stability, adsorption mechanism, magnetic saturation value, specific surface area, total pore volume, phosphate adsorption capacity and recyclability are discussed. Using the optimized pretreatment conditions, Fe₃O₄@Mg/Al-CO₃-LDH was utilized successfully to adsorb PO₄³⁻ in real samples and determine trace F⁻ and Cl⁻ accurately by ion chromatography; this would be very beneficial for continuous analysis and on-line tests by physical and chemical analysis methods without interference from PO₄³⁻ in phosphorus-rich samples, leaving F⁻ and Cl⁻ even if in a trace content.

Synthesized recyclable Fe₃O₄@Mg/Al-CO₃-LDH magnetic nano-adsorbent is utilized to dephosphorize phosphorous-rich solutions but leave F⁻ and Cl⁻ to be detected chromatographically.

Bioinorganic supplementation of calcium phosphate-based bone substitutes to improve in vivo performance: a systematic review and meta-analysis of animal studies

Supplementation of CaP-based bone graft substitutes with bioinorganics such as strontium, zinc or silicon is an interesting approach to increase the biological performance in terms of bone regenerative potential of calcium phosphate (CaP)-based bone substitutes. However, the in vivo efficacy of this approach has not been systematically analyzed, yet. Consequently, we performed a systematic review using the available literature regarding the effect of bioinorganic supplementation in CaP-based biomaterials on new bone formation and material degradation in preclinical animal bone defect models and studied this effect quantitatively by performing a meta-analysis. Additional subgroup analyses were used to study the effect of different bioinorganics, animal model, or phase category of CaP-based biomaterial on bone formation or material degradation. Results show that bioinorganic supplementation increases new bone formation (standardized mean difference [SMD]: 1.43 SD, confidence interval [CI]: 1.13-1.73). Additional subgroup analysis showed that strontium, magnesium and silica significantly enhanced bone formation, while zinc did not have any effect. This effect of bioinorganic supplementation on new bone formation was stronger for DCPD or β-TCP and biphasic CaPs than for HA or α-TCP (p < 0.001). In general, material degradation was slightly hindered by bioinorganic supplementation (mean difference [MD]: 0.84%, CI: 0.01-1.66), with the exception of strontium that significantly enhanced degradation. Overall, bioinorganic supplementation represents an effective approach to enhance the biological performance of CaP-based bone substitutes.

Therapeutic Metallic Ions in Bone Tissue Engineering: A Systematic Review of The Literature

An important field of bone tissue engineering (BTE) concerns the design and fabrication of smart scaffolds capable of inducing cellular interactions and differentiation of osteo-progenitor cells. One of these additives that has gained growing attention is metallic ions as therapeutic agents (MITAs). The specific biological advantage that these ions bring to scaffolds as well as other potential mechanical, and antimicrobial enhancements may vary depending on the ion entity, fabrication method, and biomaterials used. Therefore, this article provides an overview on current status of In-vivo application of MITAs in BTE and the remaining challenges in the field. Electronic databases, including PubMed, Scopus, Science direct and Cochrane library were searched for studies on MITAs treatments for BTE. We searched for articles in English from January-2000 to October-2019. Abstracts, letters, conference papers and reviews, In-vitro studies, studies on alloys and studies investigating effects other than enhancement of new bone formation (NBF) were excluded. A detailed summary of relevant metallic ions with specific scaffold material and design, cell type, animal model and defect type, the implantation period, measured parameters and obtained qualitative and quantitative results is presented. No ideal material or fabrication method suited to deliver MITAs can yet be agreed upon, but an investigation into various systems and their drawbacks or potential advantages can lead the future research. A tendency to enhance NBF with MITAs can be observed in the studies. However, this needs to be validated with further studies comparing various ions with each other in the same animal model using critical-sized defects.

Bone Xenografts in Trauma and Orthopaedics (Analytical Review)

Purpose of the analytical review — to evaluate the application experience of bone xenografts in trauma and orthopaedics surgery. Methods. Data search was performed in the electronic databases of PubMed and eLIBRARY with depth of 20 years. Results. The authors identified 13 papers which described the application experience of bone xenografts in trauma surgery and orthopaedics. The highest efficiency (from 92 to 100%) was reported for cases of xenografts use to replace defects in intraarticular fractures and revision arthroplasty. Unsatisfactory outcomes were related to cases with no integration and graft rejection. The least efficiency (from 41,9 to 46,1%) was reported in reconstructive foot surgery. No effect of bone xenografts was observed for replacement of defects in cases of pseudoarthrosis. The most frequent complication was graft material infection. The summarized literature data provided the calculated share of complications following xenograft use of 7,53% (18 out of 239 cases, CI 5-95%, 4,53-11,21). Two areas were identified for improvement of technical and biological properties of bone xenografts: 1. Modification of original xeno-matrix (enhancement of purification technique, alteration of structure of chemical composition of the bone matrix); 2. Augmentation of matrix volume by additional elements (biologically active agents, stem cells). It’s noted that demand for xenografts in traumatology and orthopaedics can increase after refining and expanding the indications for clinical use. Conclusion. Bone xenografts used in the modern trauma surgery and orthopaedics to replace bone defects in revision arthroplasty as well as in certain fracture types. Such material is relatively safe and its ability to be modified allows to improve its biological properties.

Commercially available bone graft substitutes: the impact of origin and processing on graft functionality

Development of effective and cost-efficient bone tissue engineering grafts has been the key area of research for regenerative medicine, yet an ideal grafting material has remained elusive due in large part to the highly dynamic nature of bone. A wide array of materials, both natural and synthetic, have been implemented as potential candidates for commercially available products, yet the gold standard for grafting material still remains autogenous bone. We review currently commercially available bone graft materials and relevant graft characteristics that impact the effectiveness of tissue repair, emphasizing the advantages and disadvantages of materials based on composition and origin. Examined materials were selected through a web-based search for readily accessible and clinically applicable graft materials. Grafts were then categorized according to material source to examine advantages and disadvantages associated with allogenic, xenogeneic, synthetic materials. Lastly, the application of bioactive molecules onto these basal grafts is explored to illustrate the enhancement and regulative capacity of these additives on traditional osteobiologic materials.

Current Stage of Marine Ceramic Grafts for 3D Bone Tissue Regeneration

Bioceramic scaffolds are crucial in tissue engineering for bone regeneration. They usually provide hierarchical porosity, bioactivity, and mechanical support supplying osteoconductive properties and allowing for 3D cell culture. In the case of age-related diseases such as osteoarthritis and osteoporosis, or other bone alterations as alveolar bone resorption or spinal fractures, functional tissue recovery usually requires the use of grafts. These bone grafts or bone void fillers are usually based on porous calcium phosphate grains which, once disposed into the bone defect, act as scaffolds by incorporating, to their own porosity, the intergranular one. Despite their routine use in traumatology and dental applications, specific graft requirements such as osteoinductivity or balanced dissolution rate are still not completely fulfilled. Marine origin bioceramics research opens the possibility to find new sources of bone grafts given the wide diversity of marine materials still largely unexplored. The interest in this field has also been urged by the limitations of synthetic or mammalian-derived grafts already in use and broadly investigated. The present review covers the current stage of major marine origin bioceramic grafts for bone tissue regeneration and their promising properties. Both products already available on the market and those in preclinical phases are included. To understand their clear contribution to the field, the main clinical requirements and the current available biological-derived ceramic grafts with their advantages and limitations have been collected.