Bone formation on rough, but not polished, subcutaneously implanted Ti surfaces is preceded by macrophage accumulation

A Mapping Review of the Pathogenesis of Peri-Implantitis: The Biofilm-Mediated Inflammation and Bone Dysregulation (BIND) Hypothesis

This mapping review highlights the need for a new paradigm in the understanding of peri-implantitis pathogenesis. The biofilm-mediated inflammation and bone dysregulation (BIND) hypothesis is proposed, focusing on the relationship between biofilm, inflammation, and bone biology. The close interactions between immune and bone cells are discussed, with multiple stable states likely existing between clinically observable definitions of peri-implant health and peri-implantitis. The framework presented aims to explain the transition from health to disease as a staged and incremental process, where multiple factors contribute to distinct steps towards a tipping point where disease is manifested clinically. These steps might be reached in different ways in different patients and may constitute highly individualised paths. Notably, factors affecting the underlying biology are identified in the pathogenesis of peri-implantitis, highlighting that disruptions to the host-microbe homeostasis at the implant-mucosa interface may not be the sole factor. An improved understanding of disease pathogenesis will allow for intervention on multiple levels and a personalised treatment approach. Further research areas are identified, such as the use of novel biomarkers to detect changes in macrophage polarisation and activation status, and bone turnover.

Recent advances in nanomedicines for regulation of macrophages in wound healing

Macrophages are essential immune cells and play a major role in the immune response as pro-inflammatory or anti-inflammatory agents depending on their plasticity and functions. Infiltration and activation of macrophages are usually involved in wound healing. Herein, we first described macrophage polarization and their critical functions in wound healing process. It is addressed how macrophages collaborate with other immune cells in the wound microenvironment. Targeting macrophages by manipulating or re-educating macrophages in inflammation using nanomedicines is a novel and feasible strategy for wound management. We discussed the design and physicochemical properties of nanomaterials and their functions for macrophages activation and anti-inflammatory signaling during wound therapy. The mechanism of action of the strategies and appropriate examples are also summarized to highlight the pros and cons of those approaches. Finally, the potential of nanomedicines to modulate macrophage polarization for skin regeneration is discussed.

Nanostructured Zirconia Surfaces Regulate Human Gingival Fibroblasts Behavior Through Differential Modulation of Macrophage Polarization

Zirconia exhibits excellent biocompatibility and is widely used as dental implant materials in prosthodontics. Over the past years, research and development of dental implant biomaterials has focused on osseointegration, but few reports exist regarding the role of the immune environment on cellular responses to these materials. The present study investigates the effect of different nanostructured zirconia surface topographies on macrophage phenotypes and their influence on gingival fibroblast behavior. Three different nanostructured zirconia surfaces are characterized using scanning electron microscopy, atomic force microscopy, and water contact angle. Blank-machined zirconia (BMZ) surfaces were superior to RAW264.7 cell proliferation and adhesion. RAW264.7 seeded on all nanostructured zirconia surfaces polarized toward both inflammatory M1 and anti-inflammatory M2 macrophages with more M2 macrophage phenotype on BMZ surfaces. Meanwhile, conditioned media (CM) from RAW264.7 culture on three nanostructured zirconia surfaces inhibited cell apoptosis to human gingival fibroblasts (HGFs) but promoted HGF proliferation and secretion. Under modulation of RAW264.7 culture, HGFs cultured on BMZ surfaces significantly secreted more extracellular matrix with a higher expression of collagen-I (COL-I), vinculin (VCL), and fibronectin (FN) than those coated on self-glazed zirconia (CSGZ) and self-glazed zirconia (SGZ) surfaces. After being coated with a nano zirconia film, CSGZ surfaces showed certain changes in cell proliferation, adhesion, and protein production compared with SGZ surfaces. These findings will provide an overview of manipulating surface topography to modulate macrophage phenotypes in order to create an effective macrophage immune response and reinforce soft tissue integration.

Immunological Aspects of Dental Implant Rejection

Nowadays, dental implants are a prominent therapeutic approach among dentists for replacing missing teeth. Failure in dental implants is a severe challenge recently. The factors which lead to dental implant failure are known. These factors can be categorized into different groups. In this article, we discussed the immunological aspects of implant failure as one of these groups. Cytokines and immune cells have extensive and various functions in peri-implantitis. The equilibrium between pro and anti-inflammatory cytokines and cells, which involve in this orchestra, has a crucial role in implant prognosis. In conclusion, immune cells, especially macrophages and dendritic cells, almost increased in the patients with implant failure. Also, proinflammatory cytokines were proposed as diagnostic factors according to their higher levels in dental implant rejection.

In Vitro and In Vivo Biocompatibility Studies of a Cast and Coated Titanium Alloy

The biocompatibility of a cast porous and with a calcium titanate reaction layer functionalized titanium alloy (Ti-6Al-7Nb) was tested by means of cell culture, and a small (rat) and large animal (sheep) model. The uncoated titanium material served as a control. In-vitro tests included the validation of osteoblast-like cells attached to the surface of the material with scanning electron microscopy and immunofluorescence of cytoskeletal actin as well as their osteogenic development, the ability to mineralize, and their vitality. Following the in-vitro tests a small animal (rat) and big animal (sheep) model were accomplished by inserting a cylindrical titanium implant into a drill hole defect in the femoral condyle. After 7, 14, and 30 days (rat) and 6 months (sheep) the condyles were studied regarding histological and histomorphometrical characteristics. Uncoated and coated material showed a good biocompatibility both in cell culture and animal models. While the defect area in the rat is well consolidated after 30 days, the sheep show only little bone inside the implant after 6 months, possibly due to stress shielding. None of the executed methods indicated a statistically significant difference between coated and uncoated material.

The role of macrophages in osseointegration of dental implants: An experimental study in vivo

To investigate the role of macrophages in the osseointegration of dental implants through induced macrophage reduction in a murine model. Fifty-four Sprague-Dawley rats with bilateral maxillary first molars replaced by titanium implants were randomly assigned into three groups. For the test group, macrophages were depleted by tail-vein injection of clodronate liposome (20 mg/kg) 3 days before implantation and reinjection every 3 days until the sacrifice of the rats (10 mg/kg). Animals treated with Phosphate Buffer saline (PBS) alone or empty liposome were included as controls. Samples contained implants were retrieved after 3, 7, 14, and 28 days, and the alterations of macrophages (CD68) and osteoblasts (Osterix) were evaluated using histology and immunohistochemistry technique. Histological analysis showed that new bone gradually formed within the lateral chamber regions in both the Control group and the Lip group, whereas bone healing was delayed at the first 2-weeks despite of pronounced newly formed peri-implant bone at 4 weeks in the Lipclod group. The bone-to-implant contact was significantly higher in the Lip and Control group than in the Lipclod group after 2 weeks. Immunohistochemical analysis showed that CD68+ cells were present both in the central region and in direct contact with implant surface throughout the healing period. Macrophages depletion reduced osteoblast amounts and new bone formation around implants in the first 2 weeks, and have no adverse impacts on the final formation of osseointegration. Macrophages play a dual role in both regulating the bone healing process and immune response to implant installation during the early stages.

Laser Polishing of Ti6Al4V Fabricated by Selective Laser Melting

Selective laser melting (SLM) is emerging as a promising 3D printing method for orthopedic and dental applications. However, SLM-based Ti6Al4V components frequently exhibit high roughness values and partial surface defects. Laser polishing (LP) is a newly developed technology to improve the surface quality of metals. In this research, LP is applied to improve the surface finish of components. The results show that the laser beam can neatly ablate the aggregates of metallic globules and repair cracks and pores on the surface, resulting in a smooth surface with nanocomposites. Overall, the results indicate that using LP optimizes surface morphology to favor fatigue behavior and osteoblastic differentiation. These findings provide foundational data to improve the surface roughness of a laser-polished implant and pave the way for optimized mechanical behavior and biocompatibility via the laser process.

Nanostructural Surfaces with Different Elastic Moduli Regulate the Immune Response by Stretching Macrophages

A proper immune response is key for the successful implantation of biomaterials, and designing and fabricating biomaterials to regulate immune responses is the future trend. In this work, three different nanostructures were constructed on the surface of titanium using a hydrothermal method, and through a series of in vitro and in vivo experiments, we found that the aspect ratio of nanostructures can affect the elastic modulus of a material surface and further regulate immune cell behaviors. This work demonstrates that nanostructures with a higher aspect ratio can endow a material surface with a lower elastic modulus, which was confirmed by experiments and theoretical analyses. The deflection of nanostructures under the cell adsorption force is a substantial factor in stretching macrophages to enhance cell adhesion and spreading, further inducing macrophage polarization toward the M1 phenotype and leading to intense immune responses. In contrast, a nanostructure with a lower aspect ratio on a material surface leads to a higher surface elastic modulus, making deflection of the material difficult and creating a surface that is not conducive to macrophage adhesion and spreading, thus reducing the immune response. Moreover, molecular biology experiments indicated that regulation of the immune response by the elastic modulus is primarily related to the NF-κB signaling pathway. These findings suggest that the immune response can be regulated by constructing nanostructural surfaces with the proper elastic modulus through their influence on cell adhesion and spreading, which provides new insights into the surface design of biomaterials.

In vitro response of macrophages to ceramic scaffolds used for bone regeneration

Macrophages, the primary cells of the inflammatory response, are major regulators of healing, and mediate both bone fracture healing and the inflammatory response to implanted biomaterials. However, their phenotypic contributions to biomaterial-mediated bone repair are incompletely understood. Therefore, we used gene expression and protein secretion analysis to investigate the interactions in vitro between primary human monocyte-derived macrophages and ceramic scaffolds that have been shown to have varying degrees of success in promoting bone regeneration in vivo Specifically, baghdadite (Ca3ZrSi2O9) and strontium-hardystonite-gahnite (Sr-Ca2ZnSi2O7-ZnAl2O4) scaffolds were chosen as two materials that enhanced bone regeneration in vivo in large defects under load compared with clinically used tricalcium phosphate-hydroxyapatite (TCP-HA). Principal component analysis revealed that the scaffolds differentially regulated macrophage phenotype. Temporal changes in gene expression included shifts in markers of pro-inflammatory M1, anti-inflammatory M2a and pro-remodelling M2c macrophage phenotypes. Of note, TCP-HA scaffolds promoted upregulation of many M1-related genes and downregulation of many M2a- and M2c-related genes. Effects of the scaffolds on macrophages were attributed primarily to direct cell-scaffold interactions because of only minor changes observed in transwell culture. Ultimately, elucidating macrophage-biomaterial interactions will facilitate the design of immunomodulatory biomaterials for bone repair.

Genomic analyses of early peri-implant bone healing in humans: a systematic review

Objective

The objective of the study was to systematically review the literature for studies reporting gene expression analyses (GEA) of the biological processes involved in early human peri-implant bone healing.

Methods

Electronic databases (MEDLINE, EMBASE) were searched in duplicate. Controlled and uncontrolled studies reporting GEA of human peri-implant tissues - including ≥5 patients and ≥2 time points - during the first 4 weeks of healing were eligible for inclusion. Methodological quality and risk of bias were also assessed.

Results

Four exploratory studies were included in reporting GEA of either tissues attached to SLA or SLActive implants after 4 to 14 days or cells attached to TiOBlast or Osseospeed implants after 3 to 7 days. A total of 111 implants from 43 patients were analyzed using validated array methods; however, considerable heterogeneity and risk of bias were detected. A consistent overall pattern of gene expression was observed; genes representing an immuno-inflammatory response were overexpressed at days 3 to 4, followed by genes representing osteogenic processes at day 7. Genes representing bone remodeling, angiogenesis, and neurogenesis were expressed concomitantly with osteogenesis. Several regulators of these processes, such as cytokines, growth factors, transcription factors, and signaling pathways, were identified. Implant surface properties seemed to influence the healing processes at various stages via differential gene expression.

Conclusion

Limited evidence from gene expression studies in humans indicates that osteogenic processes commence within the first post-operative week and they appear influenced at various stages by implant surface properties.

Composition and Modifications of Dental Implant Surfaces

Since Brånemark discovered the favorable effects of titanium in bone healing in 1965, titanium has emerged as the gold standard bulk material for present-time dental implantology. In the course of years researchers aimed for improvement of the implants performance in bone even at compromised implant sites and multiple factors were investigated influencing osseointegration. This review summarizes and clarifies the four factors that are currently recognized being relevant to influence the tissue-implant contact ratio: bulk materials and coatings, topography, surface energy, and biofunctionalization. The macrodesigns of bulk materials (e.g., titanium, zirconium, stainless steel, tantalum, and magnesium) provide the mechanical stability and their influence on bone cells can be additionally improved by surface treatment with various materials (calcium phosphates, strontium, bioglasses, diamond-like carbon, and diamond). Surface topography can be modified via different techniques to increase the bone-implant contact, for example, plasma-spraying, grit-blasting, acid-etching, and microarc oxidation. Surface energy (e.g., wettability and polarity) showed a strong effect on cell behavior and cell adhesion. Functionalization with bioactive molecules (via physisorption, covalent binding, or carrier systems) targets enhanced osseointegration. Despite the satisfying clinical results of presently used dental implant materials, further research on innovative implant surfaces is inevitable to pursuit perfection in soft and hard tissue performance.

Sequential delivery of immunomodulatory cytokines to facilitate the M1-to-M2 transition of macrophages and enhance vascularization of bone scaffolds

In normal tissue repair, macrophages exhibit a pro-inflammatory phenotype (M1) at early stages and a pro-healing phenotype (M2) at later stages. We have previously shown that M1 macrophages initiate angiogenesis while M2 macrophages promote vessel maturation. Therefore, we reasoned that scaffolds that promote sequential M1 and M2 polarization of infiltrating macrophages should result in enhanced angiogenesis and healing. To this end, we first analyzed the in vitro kinetics of macrophage phenotype switch using flow cytometry, gene expression, and cytokine secretion analysis. Then, we designed scaffolds for bone regeneration based on modifications of decellularized bone for a short release of interferon-gamma (IFNg) to promote the M1 phenotype, followed by a more sustained release of interleukin-4 (IL4) to promote the M2 phenotype. To achieve this sequential release profile, IFNg was physically adsorbed onto the scaffolds, while IL4 was attached via biotin-streptavidin binding. Interestingly, despite the strong interactions between biotin and streptavidin, release studies showed that biotinylated IL4 was released over 6 days. These scaffolds promoted sequential M1 and M2 polarization of primary human macrophages as measured by gene expression of ten M1 and M2 markers and secretion of four cytokines, although the overlapping phases of IFNg and IL4 release tempered polarization to some extent. Murine subcutaneous implantation model showed increased vascularization in scaffolds releasing IFNg compared to controls. This study demonstrates that scaffolds for tissue engineering can be designed to harness the angiogenic behavior of host macrophages towards scaffold vascularization.

Manipulating the intersection of angiogenesis and inflammation

There exists a critical need to develop strategies that promote blood vessel formation (neovascularization) in virtually all tissue engineering and regenerative medicine efforts. While research typically focuses on understanding and exploiting the role of angiogenic factors and vascular cells on new blood vessel formation, the activity of the immune system is being increasingly recognized to impact vascular formation and adaptation. This review will provide both an overview of the intersection of angiogenesis and the immune system, and how biomaterials may be designed to promote favorable interactions between these two systems to promote effective vascularization.

Effects of TiO2 nanotube layers on RAW 264.7 macrophage behaviour and bone morphogenetic protein-2 expression

OBJECTIVES

To investigate behaviour and osteogenic cytokine expression of RAW264.7 macrophages grown on TiO2 nanotube layers.

MATERIALS AND METHODS

The murine macrophage cell line RAW 264.7 was cultured on TiO2 nanotubes of varying diameter; macrophage morphology was examined using scanning electron microscopy. Cell adhesion and viability were assessed with the aid of the MTT method and BMP-2 and TGF-β gene expression were examined by RT-PCR analysis. Levels of BMP-2, TGF-β1 and ICAM-1 proteins secreted into the supernatant were measured by ELISA assay.

RESULTS

Macrophages cultured on nanotube layers had spread out morphology, the largest (120 nm) nanotube layer eliciting an elongation by 24 h. Macrophages adhered significantly less to 120 nm TiO2 nanotubes than to control discs at 4 h after application; after 24 h incubation, macrophages were sufficiently viable (P < 0.05) on 30 and 70 nm nanotube layers. Increasing nanotube diameter led to increased BMP-2 protein secretion and increased BMP-2 mRNA expression.

CONCLUSION

These results demonstrate that nanoscale topography of TiO2 nanotube layers can affect macrophage morphology, adhesion, viability and BMP-2 expression. Macrophages grown on layers of large nanotubes had the highest potential to enhance bone formation during bone healing.

Surface modification of biomedical and dental implants and the processes of inflammation, wound healing and bone formation

Bone adaptation or integration of an implant is characterized by a series of biological reactions that start with bone turnover at the interface (a process of localized necrosis), followed by rapid repair. The wound healing response is guided by a complex activation of macrophages leading to tissue turnover and new osteoblast differentiation on the implant surface. The complex role of implant surface topography and impact on healing response plays a role in biological criteria that can guide the design and development of future tissue-implant surface interfaces.