OsteoMacs: Key players around bone biomaterials

Biosynthesized Bandages Carrying Magnesium Oxide Nanoparticles Induce Cortical Bone Formation by Modulating Endogenous Periosteal Cells

Bone grafting is frequently conducted to treat bone defects caused by trauma and tumor removal, yet with significant medical and socioeconomic burdens. Space-occupying bone substitutes remain challenging in the control of osteointegration, and meanwhile activation of endogenous periosteal cells by using non-space-occupying implants to promote new bone formation becomes another therapeutic strategy. Here, we fabricated a magnesium-based artificial bandage with optimal micropatterns for activating periosteum-associated biomineralization. Collagen was self-assembled on the surface of magnesium oxide nanoparticles embedded electrospun fibrous membranes as a hierarchical bandage structure to facilitate the integration with periosteum in situ. After the implantation on the surface of cortical bone in vivo, magnesium ions were released to generate a pro-osteogenic immune microenvironment by activating the endogenous periosteal macrophages into M2 phenotype and, meanwhile, promote blood vessel formation and neurite outgrowth. In a cortical bone defect model, magnesium-based artificial bandage guided the surrounding newly formed bone tissue to cover the defected area. Taken together, our study suggests that the strategy of stimulating bone formation can be achieved with magnesium delivery to periosteum in situ and the proposed periosteal bandages act as a bioactive media for accelerating bone healing.

The crosstalk between macrophages and bone marrow mesenchymal stem cells in bone healing

Bone injury plagues millions of patients worldwide every year, and it demands a heavy portion of expense from the public medical insurance system. At present, orthopedists think that autologous bone transplantation is the gold standard for treating large-scale bone defects. However, this method has significant limitations, which means that parts of patients cannot obtain a satisfactory prognosis. Therefore, a basic study on new therapeutic methods is urgently needed. The in-depth research on crosstalk between macrophages (Mϕs) and bone marrow mesenchymal stem cells (BMSCs) suggests that there is a close relationship between inflammation and regeneration. The in-depth understanding of the crosstalk between Mϕs and BMSCs is helpful to amplify the efficacy of stem cell-based treatment for bone injury. Only in the suitable inflammatory microenvironment can the damaged tissues containing stem cells obtain satisfactory healing outcomes. The excessive tissue inflammation and lack of stem cells make the transplantation of biomaterials necessary. We can expect that the crosstalk between Mϕs and BMSCs and biomaterials will become the mainstream to explore new methods for bone injury in the future. This review mainly summarizes the research on the crosstalk between Mϕs and BMSCs and also briefly describes the effects of biomaterials and aging on cell transplantation therapy.

Biocompatibility and degradation comparisons of four biodegradable copolymeric osteosynthesis systems used in maxillofacial surgery: A goat model with four years follow-up

Applying biodegradable osteosyntheses avoids the disadvantages of titanium osteosyntheses. However, foreign-body reactions remain a major concern and evidence of complete resorption is lacking. This study compared the physico-chemical properties, histological response and radiographs of four copolymeric biodegradable osteosynthesis systems in a goat model with 48-months follow-up. The systems were implanted subperiosteally in both tibia and radius of 12 Dutch White goats. The BioSorb FX [poly(70LLA-co-30DLLA)], Inion CPS [poly([70–78.5]LLA-co-[16–24]DLLA-co-4TMC)], SonicWeld Rx [poly(DLLA)], LactoSorb [poly(82LLA-co-18GA)] systems and a negative control were randomly implanted in each extremity. Samples were assessed at 6-, 12-, 18-, 24-, 36-, and 48-month follow-up. Surface topography was performed using scanning electron microscopy (SEM). Differential scanning calorimetry and gel permeation chromatography were performed on initial and explanted samples. Histological sections were systematically assessed by two blinded researchers using (polarized) light microscopy, SEM and energy-dispersive X-ray analysis. The SonicWeld Rx system was amorphous while the others were semi-crystalline. Foreign-body reactions were not observed during the complete follow-up. The SonicWeld Rx and LactoSorb systems reached bone percentages of negative controls after 18 months while the BioSorb Fx and Inion CPS systems reached these levels after 36 months. The SonicWeld Rx system showed the most predictable degradation profile. All the biodegradable systems were safe to use and well-tolerated (i.e., complete implant replacement by bone, no clinical or histological foreign body reactions, no [sterile] abscess formation, no re-interventions needed), but nanoscale residual polymeric fragments were observed at every system's assessment.

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Foreign-body reactions are a major concern of biodegradable osteosyntheses.

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Amorphous poly(DLLA) showed the most predictable degradation profile.

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Nanoscale residual polymeric fragments could still be observed after 4 years.

Regulation of Macrophage Polarization Through Periodic Photo-Thermal Treatment to Facilitate Osteogenesis

The richened reactive oxygen species (ROS) and their derived excessive inflammation at bone injured sites hinder osteogenesis of endosseous Ti-based implants. Herein, anti-oxidized polydopamine (PDA) is deposited on hydrothermal growth formed hydroxyapatite (HA) nanorods on Ti to form a core-shell structural nanorod-like array with HA as a core and PDA as an amorphous shell (PDA@HA), showing not only ROS scavenging ability but also near-infrared (NIR) light derived photo-thermal effects. PDA@HA suppresses inflammation based on its ROS scavenging ability to a certain extent, while periodic photo-thermal treatment (PTT) at a mild temperature (41 ± 1 °C) further accelerates the transition of the macrophages (MΦs) adhered to PDA@HA from the pro-inflammatory (M1) phenotype to the anti-inflammatory (M2) phenotype in vitro and in vivo. Transcriptomic analysis reveals that the activation of the PI3K-Akt1 signaling pathway is responsible for the periodic PTT induced acceleration of the M1-to-M2 transition of MΦs. Acting on mesenchymal stem cells (MSCs) with paracrine cytokines of M2 macrophages, PDA@HA with mild PTT greatly promote the osteogenetic functions of MSCs and thus osteogenesis. This work paves a way of employing mildly periodic PTT to induce a favorable immunomodulatory microenvironment for osteogenesis and provides insights into its underlying immunomodulation mechanism.

Nervous System-Driven Osseointegration

Implants are essential therapeutic tools for treating bone fractures and joint replacements. Despite the in-depth study of osseointegration for more than fifty years, poor osseointegration caused by aseptic loosening remains one of the leading causes of late implant failures. Osseointegration is a highly sophisticated and spatiotemporal process in vivo involving the immune response, angiogenesis, and osteogenesis. It has been unraveled that the nervous system plays a pivotal role in skeletal health via manipulating neurotrophins, neuropeptides, and nerve cells. Herein, the research related to nervous system-driven osseointegration was systematically analyzed and reviewed, aiming to demonstrate the prominent role of neuromodulation in osseointegration. Additionally, it is indicated that the implant design considering the role of neuromodulation might be a promising way to prevent aseptic loosening.

Treatment methods toward improving the anti-infection ability of poly(etheretherketone) implants for medical applications

Due to its favorable chemical stability, biocompatibility, and mechanical properties, Poly(etheretherketone) (PEEK) is a promising material for repairing bone and dental hard tissue defects. However, there are critical disadvantages: PEEK is biologically and chemically inert, which influences osseointegration of implants and bonding strength of prostheses, and its mechanical properties still cannot meet the requirements for some medical applications. Furthermore, bacterial infections and inflammatory reactions often accompany bone defects caused by trauma or inflammation or teeth loss caused by periodontitis. Previous studies mainly focused on enhancing PEEK's bioactivity and mechanical performance, but PEEK also lacks effective anti-infection ability. Thus, it is necessary to improve its anti-infection ability, and this is considered in this paper from two aspects. The first is to inhibit the attachment and growth of bacteria on the material, and the second is to endow the material with immunoregulatory ability, which means mobilizing the host immune system to protect tissue from inflammation. In this review, we analyze and discuss the existing treatment methods to improve the antibacterial and immunomodulatory abilities of PEEK addressing their limitations, relevant future challenges, and required research efforts.

Photo-thermic mineralized collagen coatings and their modulation of macrophages polarization

Macrophages polarization in bone immune microenvironment is crucial in bone regeneration. In this work, mineralized collagen (MC) coatings with photo-thermal effect were prepared through incorporation of polydopamine (PDA). MC coatings with different thicknesses were deposited on titanium substrate through electrochemical deposition. PDA preformed on the substrate, acting as a photo-thermal agent. The effects of light illumination, i.e., different thermal effects, on the polarization of mouse bone marrow-derived macrophages were explored. It was found that heat can promote the M1 polarization of macrophages and inhibit the M2 polarization. Also, gene expression results revealed that such photo illumination based macrophage modulation is effective and safe. It provides a possible way for the design of functional materials to regulate the bone immune microenvironment.

Comparison of Different Fixation Methods for Combined Histological and Biomolecular Analysis of Fixed and Decalcified Bone Samples

The combination of histological and biomolecular analyses provides deep understanding of different biological processes and is of high interest for basic and applied research. However, the available analytical methods are still limited, especially when considering bone samples. This study compared different fixation media to identify a sufficient analytical method for the combination of histological, immuno-histological and biomolecular analyses of the same fixed, processed and paraffin embedded bone sample. Bone core biopsies of rats’ femurs were fixed in different media (RNAlater + formaldehyde (R + FFPE), methacarn (MFPE) or formaldehyde (FFPE)) for 1 week prior to decalcification by EDTA and further histological processing and paraffin embedding. Snap freezing (unfixed frozen tissue, UFT) and incubation in RNAlater were used as additional controls. After gaining the paraffin sections for histological and immunohistological analysis, the samples were deparaffined and RNA was isolated by a modified TRIZOL protocol. Subsequently, gene expression was evaluated using RT-qPCR. Comparable histo-morphological and immuno-histological results were evident in all paraffin embedded samples of MFPE, FFPE and R + FFPE. The isolated RNA in the group of MFPE showed a high concentration and high purity, which was comparable to the UFT and RNAlater groups. However, in the groups of FFPE and R + FFPE, the RNA quality and quantity were statistically significantly lower when compared to MFPE, UFT and RNAlater. RT-qPCR results showed a comparable outcome in the group of MFPE and UFT, whereas the groups of FFPE and R + FFPE did not result in a correctly amplified gene product. Sample fixation by means of methacarn is of high interest for clinical samples to allow a combination of histological, immunohistological and biomolecular analysis. The implementation of such evaluation method in clinical research may allow a deeper understanding of the processes of bone formation and regeneration.

Titania nanospikes activate macrophage phagocytosis by ligand-independent contact stimulation

Macrophage phagocytosis is an important research target to combat various inflammatory or autoimmune diseases; however, the phenomenon has never been controlled by artificial means. Titania nanospikes created by alkaline etching treatment can tune macrophage polarization toward a M1-like type and might regulate macrophage phagocytosis. This in vitro study aimed to determine whether the two-dimensional titania nanosurfaces created by alkaline etching treatment activated the macrophage phagocytosis by nanospike-mediated contact stimulation. On two-dimensional pure titanium sheets, alkaline etching treatments with different protocols created superhydrophilic nanosurfaces with hydroxyl function groups and moderate or dense nanospikes. Both types of titania nanosurfaces promoted the phagocytic activity of the mouse macrophage-like cell line, J774A.1, through upregulation of M1 polarization markers and phagocytosis-related receptors, such as toll-like receptors (TLR2 and 4). In contrast, the hydrophobic smooth or micro-roughened titanium surfaces did not activate macrophage phagocytosis or the expression of related receptors. These phenomena remained unchanged even under the antibody blockade of macrophage TLR2 but were either suppressed or augmented for each surface excited by ultraviolet irradiation. Titania nanospikes induced paxillin expression and provided physical stimuli to macrophages, the extent of which was positively correlated with TLR expression levels. Ligand stimulation with lipopolysaccharide did not upregulate macrophage TLR expression but further enhanced M1 marker expression by titania nanosurfaces. These results showed that the two-dimensional titania nanosurfaces activated macrophage phagocytosis by enhancing expression of phagocytosis-related receptors through nanospike-mediated contact stimulation, in assistance with physical surface properties, in a ligand-independent manner.

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.

Macrophages Characterization in an Injured Bone Tissue

Biomaterial use is a promising approach to facilitate wound healing of the bone tissue. Biomaterials induce the formation of membrane capsules and the recruitment of different types of macrophages. Macrophages are immune cells that produce diverse combinations of cytokines playing an important role in bone healing and regeneration, but the exact mechanism remains to be studied. Our work aimed to identify in vivo macrophages in the Masquelet induced membrane in a rat model. Most of the macrophages in the damaged area were M2-like, with smaller numbers of M1-like macrophages. In addition, high expression of IL-1β and IL-6 cytokines were detected in the membrane region by RT-qPCR. Using an innovative combination of two hybridization techniques (in situ hybridization and in situ hybridization chain reaction (in situ HCR)), M2b-like macrophages were identified for the first time in cryosections of non-decalcified bone. Our work has also demonstrated that microspectroscopical analysis is essential for macrophage characterization, as it allows the discrimination of fluorescence and autofluorescence. Finally, this work has revealed the limitations of immunolabelling and the potential of in situ HCR to provide valuable information for in vivo characterization of macrophages.

Sustained local ionic homeostatic imbalance caused by calcification modulates inflammation to trigger heterotopic ossification

Heterotopic ossification (HO) is a condition triggered by an injury leading to the formation of mature lamellar bone in extraskeletal soft tissues. Despite being a frequent complication of orthopedic and trauma surgery, brain and spinal injury, the etiology of HO is poorly understood. The aim of this study is to evaluate the hypothesis that a sustained local ionic homeostatic imbalance (SLIHI) created by mineral formation during tissue calcification modulates inflammation to trigger HO. This evaluation also considers the role SLIHI could play for the design of cell-free, drug-free osteoinductive bone graft substitutes. The evaluation contains five main sections. The first section defines relevant concepts in the context of HO and provides a summary of proposed causes of HO. The second section starts with a detailed analysis of the occurrence and involvement of calcification in HO. It is followed by an explanation of the causes of calcification and its consequences. This allows to speculate on the potential chemical modulators of inflammation and triggers of HO. The end of this second section is devoted to in vitro mineralization tests used to predict the ectopic potential of materials. The third section reviews the biological cascade of events occurring during pathological and material-induced HO, and attempts to propose a quantitative timeline of HO formation. The fourth section looks at potential ways to control HO formation, either acting on SLIHI or on inflammation. Chemical, physical, and drug-based approaches are considered. Finally, the evaluation finishes with a critical assessment of the definition of osteoinduction. STATEMENT OF SIGNIFICANCE: The ability to regenerate bone in a spatially controlled and reproducible manner is an essential prerequisite for the treatment of large bone defects. As such, understanding the mechanism leading to heterotopic ossification (HO), a condition triggered by an injury leading to the formation of mature lamellar bone in extraskeletal soft tissues, would be very useful. Unfortunately, the mechanism(s) behind HO is(are) poorly understood. The present study reviews the literature on HO and based on it, proposes that HO can be caused by a combination of inflammation and calcification. This mechanism helps to better understand current strategies to prevent and treat HO. It also shows new opportunities to improve the treatment of bone defects in orthopedic and dental procedures.

From hurdle to springboard: The macrophage as target in biomaterial-based bone regeneration strategies

The past decade has seen a growing appreciation for the role of the innate immune response in mediating repair and biomaterial directed tissue regeneration. The long-held view of the host immune/inflammatory response as an obstacle limiting stem cell regenerative activity, has given way to a fresh appreciation of the pivotal role the macrophage plays in orchestrating the resolution of inflammation and launching the process of remodelling and repair. In the context of bone, work over the past decade has established an essential coordinating role for macrophages in supporting bone repair and sustaining biomaterial driven osteogenesis. In this review evidence for the role of the macrophage in bone regeneration and repair is surveyed before discussing recent biomaterial and drug-delivery based approaches that target macrophage modulation with the goal of accelerating and enhancing bone tissue regeneration.

The Osteoinductivity of Calcium Phosphate-Based Biomaterials: A Tight Interaction With Bone Healing

Calcium phosphate (CaP)-based bioceramics are the most widely used synthetic biomaterials for reconstructing damaged bone. Accompanied by bone healing process, implanted materials are gradually degraded while bone ultimately returns to its original geometry and function. In this progress report, we reviewed the complex and tight relationship between the bone healing response and CaP-based biomaterials, with the emphasis on the in vivo degradation mechanisms of such material and their osteoinductive properties mediated by immune responses, osteoclastogenesis and osteoblasts. A deep understanding of the interaction between biological healing process and biomaterials will optimize the design of CaP-based biomaterials, and further translate into effective strategies for biomaterials customization.

Immunomodulation of Telmisartan-Loaded PCL/PVP Scaffolds on Macrophages Promotes Endogenous Bone Regeneration

Biomaterial-immune system interactions play an important role in postimplantation osseointegration to retain the functionality of healthy and intact bones. Therefore, appropriate osteoimmunomodulation of implants has been considered and validated as an efficient strategy to alleviate inflammation and enhance new bone formation. Here, we fabricated a nanostructured PCL/PVP (polycaprolactone/polyvinylpyrrolidone) electrospinning scaffold for cell adhesion, tissue ingrowth, and bone defect padding. In addition, telmisartan, an angiotensin 2 receptor blocker with distinct immune bioactivity, was doped into PCL-/PVP-electrospun scaffolds at different proportions [1% (TPP-1), 5% (TPP-5), and 10% (TPP-10)] to investigate its immunomodulatory effects and osteoinductivity/conductivity. Telmisartan-loaded scaffolds displayed in vitro anti-inflammatory bioactivity on lipopolysaccharide-induced M1 macrophages by polarizing them to an M2-like phenotype and exhibited pro-osteogenic properties on bone marrow-derived mesenchymal stem cells (BMSCs). Histological analysis and micro-CT results of a rat skull defect model also showed that the telmisartan-loaded scaffolds induced a higher M2/M1 ratio, less inflammatory infiltration, and better bone regenerative patterns. Furthermore, activation of the BMP2 (bone morphogenetic protein-2)-Smad signaling pathway was found to be dominant in telmisartan-loaded scaffold-mediated macrophage-BMSC interactions. These findings indicate that telmisartan incorporation with PCL/PVP nanofibrous scaffolds is a potential therapeutic strategy for promoting bone healing by modulating M1 macrophages to a more M2 phenotype at early stages of postimplantation.

Regulating Macrophage Polarization in High Glucose Microenvironment Using Lithium-Modified Bioglass-Hydrogel for Diabetic Bone Regeneration

Diabetes mellitus is a chronic metabolic disease with a proinflammatory microenvironment, causing poor vascularization and bone regeneration. Due to the lack of effective therapy and one-sided focus on the direct angiogenic properties of biomaterials and osteogenesis stimulation, the treatment of diabetic bone defect remains challenging and complex. In this study, using gelatin methacryloyl (GelMA) as a template, a lithium (Li) -modified bioglass-hydrogel for diabetic bone regeneration is developed. It exhibits a sustained ion release for better bone regeneration under diabetic microenvironment. The hydrogel is shown to be mechanically adaptable to the complex shape of the defect. In vitro, Li-modified bioglass-hydrogel promoted cell proliferation, direct osteogenesis, and regulated macrophages in high glucose (HG) microenvironment, with the secretion of bone morphogenetic protein-2 and vascular endothelial growth factor to stimulate osteogenesis and neovascularization indirectly. In vivo, composite hydrogels containing GelMA and Li-MBG (GM/M-Li) release Li ions to relieve inflammation, providing an anti-inflammatory microenvironment for osteogenesis and angiogenesis. Applying Li-modified bioglass-hydrogel, significantly enhances bone regeneration in a diabetic rat bone defect. Together, both remarkable in vitro and in vivo outcomes in this study present an opportunity for diabetic bone regeneration on the basis of HG microenvironment.

Effects of Dicationic Imidazolium-Based Ionic Liquid Coatings on Oral Osseointegration of Titanium Implants: A Biocompatibility Study in Multiple Rat Demographics

Dicationic imidazolium-based ionic liquids with amino acid anions, such as IonL-phenylalanine (IonL-Phe), have been proposed as a multifunctional coating for titanium (Ti) dental implants. However, there has been no evaluation of the biocompatibility of these Ti coatings in the oral environment. This study aims to evaluate the effects of IonL-Phe on early healing and osseointegration of Ti in multiple rat demographics. IonL-Phe-coated and uncoated Ti screws were implanted into four demographic groups of rats to represent biological variations that could affect healing: young males (YMs) and females (YFs), ovariectomized (OVXFs) females, and old males (OMs). Samples underwent histopathological and histomorphometric analysis to evaluate healing at 7 and 30 days around IonL-coated and uncoated Ti. The real-time quantitative polymerase chain reaction was also conducted at the 2- and 7-day YM groups to evaluate molecular dynamics of healing while the IonL-Phe was present on the surface. IonL-coated and uncoated implants demonstrated similar histological signs of healing, while coated samples’ differential gene expression of immunological and bone markers was compared with uncoated implants at 2 and 7 days in YMs. While YMs presented suitable osseointegration for both uncoated and IonL-Phe-coated groups, decreased success rate in other demographics resulted from lack of supporting bone in YFs and poor bone quality in OVXFs and OMs. Overall, it was found that IonL-coated samples had increased bone-to-implant contact across all demographic groups. IonL-Phe coating led to successful osseointegration across all animal demographics and presented the potential to prevent failures in scenarios known to be challenged by bacteria.

Site-Directed Immobilization of an Engineered Bone Morphogenetic Protein 2 (BMP2) Variant to Collagen-Based Microspheres Induces Bone Formation In Vivo

For the treatment of large bone defects, the commonly used technique of autologous bone grafting presents several drawbacks and limitations. With the discovery of the bone-inducing capabilities of bone morphogenetic protein 2 (BMP2), several delivery techniques were developed and translated to clinical applications. Implantation of scaffolds containing adsorbed BMP2 showed promising results. However, off-label use of this protein-scaffold combination caused severe complications due to an uncontrolled release of the growth factor, which has to be applied in supraphysiological doses in order to induce bone formation. Here, we propose an alternative strategy that focuses on the covalent immobilization of an engineered BMP2 variant to biocompatible scaffolds. The new BMP2 variant harbors an artificial amino acid with a specific functional group, allowing a site-directed covalent scaffold functionalization. The introduced artificial amino acid does not alter BMP2′s bioactivity in vitro. When applied in vivo, the covalently coupled BMP2 variant induces the formation of bone tissue characterized by a structurally different morphology compared to that induced by the same scaffold containing ab-/adsorbed wild-type BMP2. Our results clearly show that this innovative technique comprises translational potential for the development of novel osteoinductive materials, improving safety for patients and reducing costs.

Macrophage-like Cells Are Responsive to Titania Nanotube Intertube Spacing-An In Vitro Study

With the introduction of a new interdisciplinary field, osteoimmunology, today, it is well acknowledged that biomaterial-induced inflammation is modulated by immune cells, primarily macrophages, and can be controlled by nanotopographical cues. Recent studies have investigated the effect of surface properties in modulating the immune reaction, and literature data indicate that various surface cues can dictate both the immune response and bone tissue repair. In this context, the purpose of the present study was to investigate the effects of titanium dioxide nanotube (TNT) interspacing on the response of the macrophage-like cell line RAW 264.7. The cells were maintained in contact with the surfaces of flat titanium (Ti) and anodic TNTs with an intertube spacing of 20 nm (TNT20) and 80 nm (TNT80), under standard or pro-inflammatory conditions. The results revealed that nanotube interspacing can influence macrophage response in terms of cell survival and proliferation, cellular morphology and polarization, cytokine/chemokine expression, and foreign body reaction. While the nanostructured topography did not tune the macrophages' differentiation into osteoclasts, this behavior was significantly reduced as compared to flat Ti surface. Overall, this study provides a new insight into how nanotubes' morphological features, particularly intertube spacing, could affect macrophage behavior.

Multiple ways for the same destination: bone regeneration

The regeneration of the bone is a challenging topic for maxillofacial plastic and reconstructive surgeons. For successful bone regeneration, timely providing of essential components is prerequisite. They are cellular components (osteoblasts, osteoclasts, and immune cells), extracellular matrix, and inorganic components (calcium and phosphate). Any deficient component can be provided from outside as a graft. Accordingly, there are many ways for successful bone regeneration. Selection of appropriate methods in an individualized situation is important.

Enhanced Bone Remodeling After Fracture Priming

The immune system is an active component of bone repair. Mast cells influence the recruitment of macrophages, osteoclasts and blood vessels into the repair tissue. We hypothesized that if mast cells and other immune cells are sensitized to recognize broken bone, they will mount an increased response to subsequent fractures that may be translated into enhanced healing. To test this, we created a bone defect on the left leg of anesthetized mice and 2 weeks later, a second one on the right leg. Bone repair in the right legs was then compared to control mice that underwent the creation of bilateral window bone defects at the same time. Mice were euthanized at 14 and 56 days. Mineralized tissue quantity and morphometric parameters were assessed using micro-CT and histology. The activity of osteoblasts, osteoclasts, vascular endothelial cells, mast cells, and macrophages was evaluated using histochemistry. Our main findings were (1) no significant differences in the amount of bone produced at 14- or 56 days post-operative between groups; (2) mice exposed to subsequent fractures showed significantly better bone morphometric parameters after 56 days post-operative; and (3) significant increases in the content of blood vessels, osteoclasts, and the number of macrophages in the subsequent fracture group. Our results provide strong evidence that a transient increase in the inflammatory state of a healing injury promotes faster bone remodelling and increased neo-angiogenesis. This phenomenon is also characterized by changes in mast cell and macrophage content that translate into more active recruitment of mesenchymal stromal cells.

Guiding bone formation using semi-onlay calcium phosphate implants in an ovine calvarial model

The restoration of cranio‐maxillofacial deformities often requires complex reconstructive surgery in a challenging anatomical region, with abnormal soft tissue structures and bony deficits. In this proof‐of‐concept, the possibility of vertical bone augmentation was explored by suspending hemispherically shaped titanium‐reinforced porous calcium phosphate (CaP) implants (n = 12) over the frontal bone in a sheep model (n = 6). The animals were euthanized after week 13 and the specimens were subject to micro‐computed tomography (μCT) and comprehensive histological analysis. Histology showed that the space between implant and the recipient bone was filled with a higher percentage of newly formed bone (NFB) versus soft tissue with a median of 53% and 47%, respectively. Similar results were obtained from the μ‐CT analysis, with a median of 56% NFB and 44% soft tissue filling the void. Noteworthy, significantly higher bone‐implant contact was found for the CaP (78%, range 14%–94%) versus the Titanium (29%, range 0%–75%) portion of the implant exposed to the surrounding bone. The histological analysis indicates that the CaP replacement by bone is driven by macrophages over time, emphasized by material‐filled macrophages found in close vicinity to the CaP with only a small number of single osteoclasts found actively remodeling the NFB. This study shows that CaP based implants can be assembled with the help of additive manufacturing to guide vertical bone formation without decortification or administration of growth factors. Furthermore, it highlights the potential disadvantage of a seamless fit between the implant and the recipient's bone.

In Situ Gene Expression in Native Cryofixed Bone Tissue

Bone is a very complex tissue that is constantly changing throughout the lifespan. The precise mechanism of bone regeneration remains poorly understood. Large bone defects can be caused by gunshot injury, trauma, accidents, congenital anomalies and tissue resection due to cancer. Therefore, understanding bone homeostasis and regeneration has considerable clinical and scientific importance in the development of bone therapy. Macrophages are well known innate immune cells secreting different combinations of cytokines and their role in bone regeneration during bone healing is essential. Here, we present a method to identify mRNA transcripts in cryosections of non-decalcified rat bone using in situ hybridization and hybridization chain reaction to explore gene expression in situ for better understanding the gene expression of the bone tissues.

CD301b+ macrophages mediate angiogenesis of calcium phosphate bioceramics by CaN/NFATc1/VEGF axis

Calcium phosphate (CaP) bioceramics are important for tissue regeneration and immune response, yet how CaP bioceramics influence these biological processes remains unclear. Recently, the role of immune cells in biomaterial-mediated regeneration, especially macrophages, has been well concerned. CD301b⁺ macrophages were a new subset of macrophages we have discovered, which were required for bioceramics-mediated bone regeneration. Nevertheless, the impact of CD301b⁺ macrophages on angiogenesis, which is a vital prerequisite to bone formation is yet indistinct. Herein, we found that CD301b⁺ macrophages were closely correlated to angiogenesis of CaP bioceramics. Additionally, depletion of CD301b⁺ macrophages led to the failure of angiogenesis. We showed that store-operated Ca²⁺ entry and calcineurin signals regulated the VEGF expression of CD301b⁺ macrophages via the NFATc1/VEGF axis. Inhibition of calcineurin effectively impaired angiogenesis via decreasing the infiltration of CD301b⁺ macrophages. These findings provided a potential immunomodulatory strategy to optimize the integration of angiogenesis and bone tissue engineering scaffold materials.

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BCP bioceramics need the involvement of CD301b⁺ macrophages to promote angiogenesis.

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Surrounding BCP, CD301b⁺ macrophages are controlled by CaN and SOCE to express VEGF.

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BCP bioceramics direct CD301b⁺ macrophages' infiltration partly through calcineurin.

Finding the Perfect Membrane: Current Knowledge on Barrier Membranes in Regenerative Procedures: A Descriptive Review

Guided tissue regeneration (GTR) and guided bone regeneration (GBR) became common procedures in the corrective phase of periodontal treatment. In order to obtain good quality tissue neo-formation, most techniques require the use of a membrane that will act as a barrier, having as a main purpose the blocking of cell invasion from the gingival epithelium and connective tissue into the newly formed bone structure. Different techniques and materials have been developed, aiming to obtain the perfect barrier membrane. The membranes can be divided according to the biodegradability of the base material into absorbable membranes and non-absorbable membranes. The use of absorbable membranes is extremely widespread due to their advantages, but in clinical situations of significant tissue loss, the use of non-absorbable membranes is often still preferred. This descriptive review presents a synthesis of the types of barrier membranes available and their characteristics, as well as future trends in the development of barrier membranes along with some allergological aspects of membrane use.

Finding the Perfect Membrane: Current Knowledge on Barrier Membranes in Regenerative Procedures: A Descriptive Review

Guided tissue regeneration (GTR) and guided bone regeneration (GBR) became common procedures in the corrective phase of periodontal treatment. In order to obtain good quality tissue neo-formation, most techniques require the use of a membrane that will act as a barrier, having as a main purpose the blocking of cell invasion from the gingival epithelium and connective tissue into the newly formed bone structure. Different techniques and materials have been developed, aiming to obtain the perfect barrier membrane. The membranes can be divided according to the biodegradability of the base material into absorbable membranes and non-absorbable membranes. The use of absorbable membranes is extremely widespread due to their advantages, but in clinical situations of significant tissue loss, the use of non-absorbable membranes is often still preferred. This descriptive review presents a synthesis of the types of barrier membranes available and their characteristics, as well as future trends in the development of barrier membranes along with some allergological aspects of membrane use.

Titanium surface with nanospikes tunes macrophage polarization to produce inhibitory factors for osteoclastogenesis through nanotopographic cues

Definitive prevention of inflammatory osteolysis around peri-implant bone tissue remains unestablished. M1 macrophages play a key role in the host defense against inflammatory osteolysis, and their polarization depends on cell shape. Macrophage polarization is controlled by environmental stimuli, particularly physicochemical cues and hence titanium nanosurface might tune macrophage polarization and function. This study determined whether titanium nanosurfaces with anisotropically patterned nanospikes regulates macrophage polarization for inhibiting osteoclast differentiation of osteoclast precursors. Alkaline-etching treatment with different protocols created two types of titanium nanosurfaces that had anisotropically patterned nanospikes with high or low distribution density, together with superhydrophilicity and the presence of hydroxyl groups. J774A.1 cells (mouse macrophage-like cell line), cultured on both titanium nanosurfaces, exhibited truly circulated shapes and highly expressed M1, but less M2, markers, without loss of viability. M1-like polarization of macrophages on both titanium nanosurfaces was independent of protein-mediated ligand stimulation or titanium surface hydrophilic or chemical status. In contrast, other smooth or micro-roughened titanium surfaces with little or no nanospikes did not activate macrophages under any culture conditions. Macrophage culture supernatants on both titanium nanosurfaces inhibited osteoclast differentiation of RAW264.7 cells (mouse osteoclast precursor cell line), even when co-incubated with osteoclast differentiation factors. The inhibitory effects on osteoclast differentiation tended to be higher in macrophages cultured on titanium nanosurfaces with denser nanospikes. These results showed that titanium nanosurfaces with anisotropically patterned nanospikes tune macrophage polarization for inhibiting osteoclast differentiation of osteoclast precursors, with nanotopographic cues rather than other physicochemical properties. STATEMENT OF SIGNIFICANCE: Peri-implant inflammatory osteolysis is one of the serious issues for dental and orthopedic implants. Macrophage polarization and function are key for prevention of peri-implant inflammatory osteolysis. Macrophage polarization can be regulated by the biomaterial's surface physicochemical properties such as hydrophilicity or topography. However, there was no titanium surface modification to prevent inflammatory osteolysis through immunomodulation. The present study showed for the first time that the titanium nanosurfaces with anisotropically patterned nanospikes, created by the simple alkali-etching treatment polarized macrophages into M1-like type producing the inhibitory factor on osteoclast differentiation. This phenomenon attributed to nanotopographic cues, but not hydrophilicity on the titanium nanosurfaces. This nanotechnology might pave the way to develop the smart implant surface preventing peri-implant inflammatory osteolysis through immunomodulation.

Role of Macrophages and Plasminogen Activator Inhibitor-1 in Delayed Bone Repair Induced by Glucocorticoids in Mice

Glucocorticoids delay fracture healing and induce osteoporosis. However, the mechanisms by which glucocorticoids delay bone repair have yet to be clarified. Plasminogen activator inhibitor-1 (PAI-1) is the principal inhibitor of plasminogen activators and an adipocytokine that regulates metabolism. We herein investigated the roles of macrophages in glucocorticoid-induced delays in bone repair after femoral bone injury using PAI-1-deficient female mice intraperitoneally administered with dexamethasone (Dex). Dex significantly decreased the number of F4/80-positive macrophages at the damaged site two days after femoral bone injury. It also attenuated bone injury-induced decreases in the number of hematopoietic stem cells in bone marrow in wild-type and PAI-1-deficient mice. PAI-1 deficiency significantly weakened Dex-induced decreases in macrophage number and macrophage colony-stimulating factor (M-CSF) mRNA levels at the damaged site two days after bone injury. It also significantly ameliorated the Dex-induced inhibition of macrophage phagocytosis at the damaged site. In conclusion, we herein demonstrated that Dex decreased the number of macrophages at the damaged site during early bone repair after femoral bone injury partly through PAI-1 and M-CSF in mice.

Anti-Inflammatory and Prochondrogenic In Situ-Formed Injectable Hydrogel Crosslinked by Strontium-Doped Bioglass for Cartilage Regeneration

Directed differentiation of bone marrow mesenchymal stem cells (BMSCs) toward chondrogenesis plays a predominant role in cartilage repair. However, the uncontrolled inflammatory response to implants is found to impair the stability of scaffolds and the cartilage regeneration outcome. Herein, we fabricated an injectable hydrogel crosslinked by strontium-doped bioglass (SrBG) to modulate both human BMSC (hBMSC) differentiation and the inflammatory response. The results revealed that the introduction of Sr ions could simultaneously enhance the proliferation of hBMSCs, upregulate cartilage-specific gene expression, and improve the secretion of glycosaminoglycan. Moreover, after cultured with SA/SrBG extracts in vitro, a majority of macrophages were polarized toward the M2 phenotype and subsequently facilitated the chondrogenic differentiation of hBMSCs. Furthermore, after the composite hydrogel was injected into a cartilage defect model, neonatal cartilage-like tissues with a smooth surface and tight integration with original tissues could be found. This study suggests that the synergistic strategy based on an enhanced differentiation ability and a regulated inflammatory response is promising and may lead the way to new anti-inflammatory biomaterials.

Cell-based therapeutics for the treatment of hematologic diseases inside the bone marrow

Cell-based therapies could overcome the limitations of traditional drugs for the treatment of refractory diseases. Cell exchange between the bone marrow and blood is bidirectional. Several kinds of cells in the blood have the capability to enter the bone marrow by interacting with sinusoidal cells under specific physiological or pathological conditions. These cells are the potential living therapeutics or delivery vehicles to treat or prevent bone marrow-related hematologic diseases. In this review, we summarized the in vivo molecular mechanisms and kinetics of these cells in entering the bone marrow. The advances in the fabrication of living cell drugs and the strategies to design cell-based carriers into the bone marrow were discussed. The latest studies on how to use blood cells as living drugs or as drug carriers to improve therapeutic outcomes of hematologic diseases inside the bone marrow were highlighted.

Structure, Barrier Function, and Bioactivity of Platelet-Rich Fibrin Following Thermal Processing

Platelet-rich fibrin (PRF) has been utilized as a substitute for resorbable membranes during guided bone regeneration therapy as it is a more bioactive biomaterial with living cells and growth factors than resorbable membranes. Nevertheless, PRF poses obvious disadvantages in its mechanical strength since its rapid degradability has been shown to typically resorb within a 2-week time period. In the present study, the barrier function and biological and mechanical properties of PRF were investigated both as standard therapy and after thermal processing. Two heating processes were applied: both single-side heating and double-side heating at 90°C for 10 s using a metal plate heater. The appearance and weight of PRF membranes were documented after heating, along with their morphological and mechanical properties evaluated by scanning electron microscope and tensile strength tests. The viability of cells found within PRF membranes was also evaluated using live/dead cell viability and CCK-8 (cell counting kit-8) assays. To comprehensively evaluate the barrier function of PRF membranes, Hoechst staining of human gingival fibroblasts, which can be distinguished from cells within the PRF membrane by emitting blue light at an excitation wavelength of 488 nm, was seeded onto the surface of PRF membranes. Furthermore, osteoblasts were cultured with extracts from different PRF groups to evaluate the biocompatibility of PRF membranes. The degradation rate of PRF membranes was examined by digestion assay. Compared with the nonheated PRF control, the size and weight of PRF membranes led to a significant decrease with a denser PRF microstructure following heating. In summary, the double-sided heating of PRF membranes not only demonstrated an improvement in mechanical and degradation properties but also led to a decrease in cell viability and proliferation.

Lateral Ridge Augmentation with Guided Bone Regeneration Using Particulate Bone Substitutes and Injectable Platelet-Rich Fibrin in a Digital Workflow: 6 Month Results of a Prospective Cohort Study Based on Cone-Beam Computed Tomography Data

This study aimed to test whether or not a digital workflow for GBR with particulate bone substitutes and injectable platelet-rich fibrin improved the thickness of the hard tissue compared to the conventional workflow. 26 patients in need of lateral bone augmentation were enrolled. GBR with particulate bone substitutes and injectable platelet-rich fibrin was performed in all patients. Patients were divided into two groups: control (conventional workflow; n = 14) and test (digital workflow; n = 12). CBCT scans were performed before surgery, immediately after wound closure, and 6 months post-surgery, and the labial thickness of the hard tissue (LT) was assessed at 0–5 mm apical to the implant shoulder (LT₀–LT₅) at each time point. A total of 26 patients were included in this study. After wound closure, the test group showed significantly greater thickness in LT₀–LT₂ than the control group (LT₀: test: 4.31 ± 0.73 mm, control: 2.99 ± 1.02 mm; LT₁: test: 4.55 ± 0.69 mm, control: 3.60 ± 0.96 mm; LT₂: test: 4.76 ± 0.54 mm, control: 4.05 ± 1.01 mm; p < 0.05). At 6 months, significant differences in LT₀–LT₁ were detected between the groups (LT₀: test: 1.88 ± 0.57 mm, control: 1.08 ± 0.60 mm; LT₁: test: 2.36 ± 0.66 mm, control: 1.69 ± 0.58 mm; p < 0.05). Within the limitations of this study, the use of digital workflow in GBR with particulate bone substitutes and i-PRF exerted a positive effect on the labial thickness of hard tissue in the coronal portion of the implant after wound closure and at 6 months.

Immunomodulatory bioactive glasses for tissue regeneration

The regulatory functions of the immune response in tissue healing, repair, and regeneration have been evidenced in the last decade. Immune cells play central roles in immune responses toward inducing favorable tissue regenerative processes. Modulating and controlling the immune cell responses (particularly macrophages) is an emerging approach to enhance tissue regeneration. Bioactive glasses (BGs) are multifunctional materials exhibiting osteogenic, angiogenic, and antibacterial properties, being increasingly investigated for various tissue regeneration scenarios, including bone regeneration and wound healing. On the other hand, the immunomodulatory effects of BGs in relation to regenerating tissues have started to be understood, and key knowledge is emerging. This is the first review article summarizing the immunomodulatory effects of BGs for tissue repair and regeneration. The immune response to BGs is firstly introduced, discussing potential mechanisms regarding the immunomodulation effects induced by BGs. Moreover, the interactions between the immune cells involved in the immunomodulation process and BGs (dissolution products) are summarized in detail. Particularly, a well-regulated and timely switch of macrophage phenotype from pro-inflammatory to anti-inflammatory is crucial to constructive tissue regeneration through modulating osteogenesis, osteoclastogenesis, and angiogenesis. The influence of BG characteristics on macrophage responses is discussed. We highlight the strategies employed to harness macrophage responses for enhanced tissue regeneration, including the incorporation of active ions, surface functionalization, and controlled release of immunomodulatory molecules. Finally, we conclude with our perspectives on future research challenges and directions in the emerging field of immunomodulatory BGs for tissue regeneration. STATEMENT OF SIGNIFICANCE: Immunomodulatory effects of bioactive glasses (BGs) in relation to bone regeneration and wound healing have started to be understood. We summarize those studies which have focused on immunomodulatory BGs for tissue regeneration. We first introduce the potential mechanisms of the immunomodulation effects induced by BGs. Interactions between the cells involved in immunomodulation processes and BGs (and their dissolution products, biologically active ions) are elaborated. We highlight the strategies employed to modulate macrophage responses for enhancing tissue regeneration, including incorporation of active ions, surface functionalization, and controlled release of immunomodulatory agents. This is the first review article summarizing and outlining the immunomodulatory effects of BGs for tissue regeneration. We anticipate that increasing research efforts will start to emerge in the area of immunomodulatory BGs.

Targeted ToF-SIMS Analysis of Macrophage Content from a Human Cranial Triphasic Calcium Phosphate Implant

Macrophages play a key role in determining the fate of implanted biomaterials, especially for biomaterials such as calcium phosphates (CaPs) where these cells play a vital role in material resorption and osteogenesis, as shown in different models, including clinical samples. Although substantial consideration is given to the design and validation of different CaPs, relatively little is known about their material-cell interaction. Specifically, the intracellular content of different CaP phases remains to be assessed, even though CaP-filled macrophages have been observed in several studies. In this study, 2D/3D ToF-SIMS imaging and multivariate analysis were directly applied on the histology samples of an explant to reveal the content of macrophages. The cellular content of the macrophages was analyzed to distinguish three CaP phases, monetite, beta-tricalcium phosphate, and pyrophosphate, which are all part of the monetite-based CaP implant composition under study. ToF-SIMS combined with histology revealed that the content of the identified macrophages was most similar to that of the pyrophosphate phase. This study is the first to uncover distinct CaP phases in macrophages from a human multiphasic CaP explant by targeted direct cell content analysis. The uncovering of pyrophosphate as the main phase found inside the macrophages is of great importance to understand the impact of the selected material in the process of biomaterial-instructed osteogenesis.

The role of autophagy in the process of osseointegration around titanium implants with micro-nano topography promoted by osteoimmunity

Osteoimmunity plays an important role in the process of implant osseointegration. Autophagy is a conservative metabolic pathway of eukaryotic cells, but whether the interaction between autophagy and osteoimmunity plays a key role in osseointegration remains unclear. In this study, we prepared smooth titanium disks and micro-nano topography titanium disks, to study the immune microenvironment of RAW264.7 cells, and prepared the conditioned medium to study the effect of immune microenvironment on the osteogenesis and autophagy of MC3T3-E1 cells. Autophagy inhibitor 3-MA was used to inhibit autophagy to observe the change of expression of osteogenic markers. The results showed that the micro-nano topography titanium disks could stimulate RAW264.7 cells to differentiate into M2 type, forming an anti-inflammatory immune microenvironment; compared with the control group, the anti-inflammatory immune microenvironment promoted the proliferation and differentiation of osteoblasts better. The anti-inflammatory immune environment activated the autophagy level of osteoblasts, while the expression of osteogenic markers was down-regulated after inhibition of autophagy. These results indicate that anti-inflammatory immune microenvironment can promote cell proliferation and osteogenic differentiation, autophagy plays an important role in this process. This study further explains the mechanism of implant osseointegration in osteoimmune microenvironment, and provides reference for improving implant osseointegration.

Regulation of an Antimicrobial Peptide GL13K-Modified Titanium Surface on Osteogenesis, Osteoclastogenesis, and Angiogenesis Base on Osteoimmunology

Creating a pro-regenerative immune microenvironment around implant biomaterial surfaces is significant to osseointegration. Immune cells, especially macrophages that participate in the osseointegration, including osteogenesis, osteoclastogenesis, and angiogenesis, should be considered when testing biomaterials. In this study, we immobilized an antimicrobial peptide GL13K with immunomodulatory properties onto a titanium surface via silanization. The modified surfaces show good biocompatibility with bone mesenchymal stromal cells (BMSCs), human umbilical vein endothelial cells (HUVECs), and RAW264.7. By co-culturing BMSCs with RAW264.7, we found that the GL13K-coated titanium surfaces could promote late-stage osteogenesis as demonstrated by the upregulated expression of recombinant collagen type I alpha 1 (COL-1α1) and more extracellular matrix mineralization, while the early phase remained unchanged. The surfaces inhibited the osteoclastogenic differentiation of RAW264.7 cells by restraining nuclear factor-activated T cells, cytoplasmic 1 (NFATc1), the main factor of the receptor activator of nuclear factor-κ B, and the receptor activator of the nuclear factor-κ B ligand signaling pathway, from entering the nucleus and further reduced the expression of the activating osteoclastogenic tartrate-resistant acid phosphatase gene. Moreover, the GL13K-coated titanium surface demonstrated significant promotion of angiogenesis differentiation of HUVECs as indicated by the upregulated expression of essential angiogenesis function genes, including hypoxia-inducible factor-1α, endothelial nitric oxide synthase, kinase insert domain receptor, and vascular endothelial growth factor A (HIF-1α, eNOS, KDR, and VEGF-A). Taken together, these results demonstrated that the GL13K coating had properties of osteogenesis, angiogenesis, and anti-osteoclastogenesis via its immunomodulatory potential.

A novel delivery nanobiotechnology: engineered miR-181b exosomes improved osteointegration by regulating macrophage polarization

Background

Many patients suffer from implant loosening after the implantation of titanium alloy caused by immune response to the foreign bodies and this could inhibit the following osteogenesis, which could possibly give rise to aseptic loosening and poor osteointegration while there is currently no appropriate solution in clinical practice. Exosome (Exo) carrying miRNA has been proven to be a suitable nanocarrier for solving this problem. In this study, we explored whether exosomes overexpressing miR-181b (Exo-181b) could exert beneficial effect on promoting M2 macrophage polarization, thus inhibiting inflammation as well as promoting osteogenesis and elaborated the underlying mechanism in vitro. Furthermore, we aimed to find whether Exo-181b could enhance osteointegration.

Results

In vitro, we firstly verified that Exo-181b significantly enhanced M2 polarization and inhibited inflammation by suppressing PRKCD and activating p-AKT. Then, in vivo, we verified that Exo-181b enhanced M2 polarization, reduced the inflammatory response and enhanced osteointegration. Also, we verified that the enhanced M2 polarization could indirectly promote the migration and osteogenic differentiation by secreting VEGF and BMP-2 in vitro.

Conclusions

Exo-181b could suppress inflammatory response by promoting M2 polarization via activating PRKCD/AKT signaling pathway, which further promoting osteogenesis in vitro and promote osteointegration in vivo.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-01015-y.

Titanium dioxide nanotubes promote M2 polarization by inhibiting macrophage glycolysis and ultimately accelerate endothelialization

Titanium has been widely used in prosthetic valves, but they are associated with serious defects in titanium-based prosthetic valves, such as thrombosis, calcification, and decay. Therefore, it is very important to biofunctionalize titanium-based valves to reduce inflammation and accelerate endothelialization of stents and antithrombosis. The titanium dioxide nanotubes were prepared from pure titanium (Ti) by anodic oxidation method in this study. The effects of titanium dioxide nanotubes on the metabolism of macrophages and the inflammatory reaction as implants were studied in vitro. The polarization state of macrophages and the ability to accelerate endothelialization were analyzed. The results demonstrated that titanium nanotubes promote M2 polarization of macrophages by inhibiting glycolysis and activating the Adenosine monophosphate-activated protein kinase (AMPK) signaling pathway. In general, biofunctionalization titanium with nanotube could inhibit macrophage glycolysis, reduce inflammatory factor release and promote M2 polarization by activating the AMPK signaling pathway. And endothelialization was accelerated in vitro. Our result demonstrated that titanium nanotube could act as a potential approach to biofunctionlize titanium-based prosthetic valves for endothelialization.

Targeting thymidine phosphorylase as a potential therapy for bone loss associated with periprosthetic osteolysis

Macrophages are generally thought to play a key role in the pathogenesis of aseptic loosening through initiating periprosthetic inflammation and pathological bone resorption. The aim of this study was to identify macrophage-derived factors that promote osteoclast differentiation and periprosthetic bone destruction. To achieve this, we examined the effects of 12 macrophage-derived factors that were identified by RNA-seq analysis of stimulated macrophages on osteoclast differentiation. Surprisingly, thymidine phosphorylase (TYMP) was found to trigger significant number of osteoclasts that exhibited resorbing activities on dentine slices. Functionally, TYMP knockdown reduced the number of osteoclasts in macrophages that had been stimulated with polyethylene debris. TYMP were detected in serum and synovial tissues of patients that had been diagnosed with aseptic loosening. Moreover, the administration of TYMP onto calvariae of mice induced pathological bone resorption that was accompanied by an excessive infiltration of inflammatory cells and osteoclasts. The RNA-seq for TYMP-induced-osteoclasts was then performed in an effort to understand action mode of TYMP. TYMP stimulation appeared to activate the tyrosine kinase FYN signaling associated with osteoclast formation. Oral administration of saracatinib, a FYN kinase inhibitor, significantly suppressed formation of bone osteolytic lesions in a polyethylene debris-induced osteolysis model. Our findings highlight a novel molecular target for therapeutic intervention in periprosthetic osteolysis.

A practical guide for evaluating the osteoimmunomodulatory properties of biomaterials

Biomaterials offer a promising approach to repair bone defects. Whereas traditional studies predominantly focused on optimizing the osteogenic capacity of biomaterials, less focus has been on the immune response elicited by them. However, the immune and skeletal systems extensively interact, a concept which is referred to as 'osteoimmunology'. This realization has fuelled the development of biomaterials with favourable osteoimmunomodulatory (OIM) properties, aiming to modulate the immune response and to support bone regeneration, thereby affecting the success of an implant. Given the plethora of in vitro assays used to evaluate the OIM properties of biomaterials, it may be challenging to select the right methods to produce conclusive results. In this review, we aim to provide a comprehensive and practical guide for researchers interested in studying the OIM properties of biomaterials in vitro. After a concise overview of the concept of osteoimmunology, emphasis is put on the methodologies that are regularly used to evaluate the OIM properties of biomaterials. First, a description of the most commonly used cell types and cell culture media is provided. Second, typical experimental set-ups and their relevant characteristics are discussed. Third, a detailed overview of the generally used methodologies and readouts, including cell type-specific markers and time points of analysis, is given. Finally, we highlight the promise of advanced approaches, namely microarrays, bioreactors and microfluidic-based systems, and the potential that these may offer to the osteoimmunology field. STATEMENT OF SIGNIFICANCE: Osteoimmunology focuses on the connection and communication between the skeletal and immune systems. This interaction has been recognized to play an important role in the clinical success of biomaterials, which has resulted in an increasing amount of research on the osteoimmunomodulatory (OIM) properties of biomaterials. However, the amount of literature makes it challenging to extract the information needed to design experiments from beginning to end, and to compare obtained results to existing work. This article intends to serve as a guide for those aiming to learn more about the commonly used experimental approaches in the field. We cover early-stage choices, such as cell types and experimental set-ups, but also discuss specific assays, including cell markers and time points of analysis.

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.

In Vivo Biological Evaluation of Biodegradable Nanofibrous Membranes Incorporated with Antibiofilm Compounds

Guided bone regeneration involves excluding non-osteogenic cells from the surrounding soft tissues and allowing osteogenic cells originating from native bone to inhabit the defect. The aim of this work was to fabricate, analyze antibiofilm activity and evaluate in vivo biological response of poly (lactic-co-glycolic acid) (PLGA) electrospun membranes incorporated with tea tree oil and furan-2(5H)-one. Samples were exposed to Streptococcus mutans culture and after 48 h incubation, biofilm was evaluated by colony forming units (CFU/mL) followed by scanning electron microscopy. Additionally, seventy-five Balb-C mice were divided into five experimental groups for subcutaneous implantation: tea tree oil loaded PLGA electrospun fiber membrane, furanone loaded PLGA electrospun fiber membrane, neat PLGA electrospun fiber membrane, a commercially available PLGA membrane –Pratix^® and Sham (no-membrane implantation). Post implantation period of each experimental group (1, 3 and 9 weeks), samples were collected and processed for by histological descriptive and semiquantitative evaluation. Results showed a significant reduction of bacterial attachment on tea tree oil and furan-2(5H)-one incorporated membranes. Macrophage counts were significant found in all the materials implanted, although giant cells were predominantly associated with electrospun fiber membranes. The incorporation of antibiofilm compounds in nanofibers membranes did not incite inflammatory response significantly different in comparison with pure PLGA electrospun membranes, indicating its potential for development of novel functionalized membranes targeting the inhibition of bacterial biofilms on membrane-grafting materials.

Mechanism of Exosomes Involved in Osteoimmunity Promoting Osseointegration Around Titanium Implants With Small-Scale Topography

Exosomes are nanoscale extracellular vesicles. Several studies have shown that exosomes participate in intercellular communication and play a key role in osseointegration. However, it is unclear whether exosomes and their contents participate in the communication between the immune and skeletal systems in the process of osseointegration. In this study, we obtained smooth titanium disks by polishing and small-scale topography titanium disks by sandblasted large-grit acid-etched (SLA) technology combined with alkali thermal reaction. After stimulating mouse RAW264.7 cells with these two kinds of titanium disks, we co-cultured the MC3T3-E1 cells and the RAW264.7 cells, obtained and identified the exosomes derived from RAW264.7 cells, and studied the effect of the osteoimmune microenvironment and the exosomes on the osseointegration of mouse MC3T3-E1 cells. Cell counting kit-8 (CCK-8), real time quantitative PCR, western blotting, alizarin red staining, and quantitative and confocal fluorescence microscopy were used to study the effects of exosomes on MC3T3-E1 cells; RNA sequencing and correlation analysis were performed. We found that the osteoimmune microenvironment could promote the osseointegration of MC3T3-E1 cells. We successfully isolated exosomes and found that RAW264.7 cell-derived exosomes can promote osteogenic differentiation and mineralization of MC3T3-E1 cells. Through RNA sequencing and gene analysis, we found differentially expressed microRNAs that targeted the signal pathways that may be related, such as mTOR, AMPK, Wnt, etc., and thus provide a reference for the mechanism of osteoimmunue regulation of implant osseointegration. The study further elucidated the mechanism of implant osseointegration and provided new insights into the effect of exosomes on implant osseointegration, and provided reference for clinical improvement of implant osseointegration and implant success rate.

Sustained calcium ion release from bioceramics promotes CaSR-mediated M2 macrophage polarization for osteoinduction

Innate immune cells, especially macrophages, play a dual role in tissue repair and the defense against foreign bodies. Although biphasic calcium phosphate (BCP) ceramics have been confirmed as an excellent osteoimmunoregulatory biomaterial, it is unclear whether the ions release of BCP directly affects macrophage polarization and the mechanism by which the ions release is involved in osteoimmunomodulation. Herein, we verified the superior osteoinductive capacity of BCP in wild-type mice and showed its inability to promote this process in macrophage-deficient (LysM^-/- ) mice. Moreover, scanning electron microscopy, ion release curve, and calcein AM-staining results confirmed that BCP-released Ca²⁺ in a sustained manner, thereby maintaining the long-term induction of M2 macrophage polarization and promoting the differentiation of mesenchymal stem cells into osteoblasts during osteogenesis. Furthermore, Ca²⁺ targeted the Wnt/β-catenin signaling pathway and activated Arg1 and IL-10 (M2 marker genes) transcription through the calcium-sensing receptor (CaSR) in macrophages. Under treatment with a CaSR antagonist, macrophages cultured with the BCP fluid extract exhibited lower Ca²⁺ intake and weaker M2 macrophage polarization. These findings underscore the critical role of macrophages in bone regeneration and clarify the molecular mechanisms of Ca²⁺ -mediated osteoinduction by biomaterials, which is of great significance for the future design of biomaterial-oriented tissue regeneration engineering.

Cellular and Molecular Dynamics during Early Oral Osseointegration: A Comprehensive Characterization in the Lewis Rat

OBJECTIVE

There is a need to improve the predictability of osseointegration in implant dentistry. Current literature uses a variety of in vivo titanium (Ti) implantation models to investigate failure modes and test new materials and surfaces. However, these models produce a variety of results, making comparison across studies difficult. The purpose of this study is to validate an oral osseointegration in the Lewis rat to provide a reproducible baseline to track the inflammatory response and healing of Ti implants.

METHODS

Ti screws (0.76 mm Ø × 2 mm length) were implanted into the maxillary diastema of 52 adult male Lewis rats. Peri-implant tissues were evaluated 2, 7, 14, and 30 days after implantation (n = 13). Seven of the 13 samples underwent microtomographic analysis, histology, histomorphometry, and immunohistochemistry to track healing parameters. The remaining six samples underwent quantitative polymerase chain reaction (qPCR) to evaluate gene expression of inflammation and bone remodeling markers over time.

RESULTS

This model achieved a 78.5% success rate. Successful implants had a bone to implant contact (BIC)% of 68.86 ± 3.15 at 30 days on average. Histologically, healing was similar to other rodent models: hematoma and acute inflammation at 2 days, initial bone formation at 7, advanced bone formation and remodeling at 14, and bone maturation at 30. qPCR indicated the highest expression of bone remodeling and inflammatory markers 2-7 days, before slowly declining to nonsurgery control levels at 14-30 days.

CONCLUSION

This model combines cost-effectiveness and simplicity of a rodent model, while maximizing BIC, making it an excellent candidate for evaluation of new surfaces.

Amorphous Carbon Coatings for Total Knee Replacements-Part II: Tribological Behavior

Diamond-like carbon coatings may decrease implant wear, therefore, they are helping to reduce aseptic loosening and increase service life of total knee arthroplasties (TKAs). This two-part study addresses the development of such coatings for ultrahigh molecular weight polyethylene (UHMWPE) tibial inlays as well as cobalt-chromium-molybdenum (CoCr) and titanium (Ti64) alloy femoral components. While the deposition of a pure (a-C:H) and tungsten-doped hydrogen-containing amorphous carbon coating (a-C:H:W) as well as the detailed characterization of mechanical and adhesion properties were the subject of Part I, the tribological behavior is studied in Part II. Pin-on-disk tests are performed under artificial synovial fluid lubrication. Numerical elastohydrodynamic lubrication modeling is used to show the representability of contact conditions for TKAs and to assess the influence of coatings on lubrication conditions. The wear behavior is characterized by means of light and laser scanning microscopy, Raman spectroscopy, scanning electron microscopy and particle analyses. Although the coating leads to an increase in friction due to the considerably higher roughness, especially the UHMWPE wear is significantly reduced up to a factor of 49% (CoCr) and 77% (Ti64). Thereby, the coating shows continuous wear and no sudden failure or spallation of larger wear particles. This demonstrated the great potential of amorphous carbon coatings for knee replacements.