Macrophage proinflammatory response to the titanium alloy equipment in dental implantation

Titanium Surface Characteristics Induce the Specific Reprogramming of Toll-like Receptor Signaling in Macrophages

Most of the research on titanium-based dental implants (Ti-discs) is focused on how they are able to stimulate the formation of new tissue and/or cytotoxic studies, with very scarce data on their effects on functional responses by immunocompetent cells. In particular, the link between the rewiring of innate immune responses and surface biomaterials properties is poorly understood. To address this, we characterize the functional response of macrophage cultures to four different dental titanium surfaces (MA: mechanical abrasion; SB + AE: sandblasting plus etching; SB: sandblasting; AE: acid etching). We use different Toll-like receptor (TLR) ligands towards cell surface receptors (bacterial lipopolysaccharide LPS for TLR4; imiquimod for TLR7; synthetic bacterial triacylated lipoprotein for TLR2/TLR1) and endosomal membrane receptor (poly I:C for TLR3) to simulate bacterial (cell wall bacterial components) or viral infections (dsRNA and ssRNA). The extracellular and total LDH levels indicate that exposure to the different Ti-surfaces is not cytotoxic for macrophages under resting or TLR-stimulated conditions, although there is a tendency towards an impairment in macrophage proliferation, viability or adhesion under TLR4, TLR3 and TLR2/1 stimulations in SB discs cultures. The secreted IL-6 and IL-10 levels are not modified upon resting macrophage exposure to the Ti-surfaces studied as well as steady state levels of iNos or ArgI mRNA. However, macrophage exposure to MA Ti-surface do display an enhanced immune response to TLR4, TLR7 or TLR2/1 compared to other Ti-surfaces in terms of soluble immune mediators secreted and M1/M2 gene expression profiling. This change of characteristics in cellular phenotype might be related to changes in cellular morphology. Remarkably, the gene expression of Tlr3 is the only TLR that is differentially affected by distinct Ti-surface exposure. These results highlight the relevance of patterned substrates in dental implants to achieve a smart manipulation of the immune responses in the context of personalized medicine, cell-based therapies, preferential lineage commitment of precursor cells or control of tissue architecture in oral biology.

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.

Wnt signaling modulates macrophage polarization and is regulated by biomaterial surface properties

Macrophages are among the first cells to interact with biomaterials and ultimately determine their integrative fate. Biomaterial surface characteristics like roughness and hydrophilicity can activate macrophages to an anti-inflammatory phenotype. Wnt signaling, a key cell proliferation and differentiation pathway, has been associated with dysregulated macrophage activity in disease. However, the role Wnt signaling plays in macrophage activation and response to biomaterials is unknown. The aim of this study was to characterize the regulation of Wnt signaling in macrophages during classical pro- and anti-inflammatory polarization and in their response to smooth, rough, and rough-hydrophilic titanium (Ti) surfaces. Peri-implant Wnt signaling in macrophage-ablated (MaFIA) mice instrumented with intramedullary Ti rods was significantly attenuated compared to untreated controls. Wnt ligand mRNA were upregulated in a surface modification-dependent manner in macrophages isolated from the surface of Ti implanted in C57Bl/6 mice. In vitro, Wnt mRNAs were regulated in primary murine bone-marrow-derived macrophages cultured on Ti in a surface modification-dependent manner. When macrophageal Wnt secretion was inhibited, macrophage sensitivity to both physical and biological stimuli was abrogated. Loss of macrophage-derived Wnts also impaired recruitment of mesenchymal stem cells and T-cells to Ti implants in vivo. Finally, inhibition of integrin signaling decreased surface-dependent upregulation of Wnt genes. These results suggest that Wnt signaling regulates macrophage response to biomaterials and that macrophages are an important source of Wnt ligands during inflammation and healing.

Quantifying the Adhesion of Silicate Glass-Ceramic Coatings onto Alumina for Biomedical Applications

Deposition of bioactive glass or ceramic coatings on the outer surface of joint prostheses is a valuable strategy to improve the osteointegration of implants and is typically produced using biocompatible but non-bioactive materials. Quantifying the coating–implant adhesion in terms of bonding strength and toughness is still a challenge to biomaterials scientists. In this work, wollastonite (CaSiO₃)-containing glass–ceramic coatings were manufactured on alumina tiles by sinter-crystallization of SiO₂–CaO–Na₂O–Al₂O₃ glass powder, and it was observed that the bonding strength decreased from 34 to 10 MPa as the coating thickness increased from 50 to 300 µm. From the viewpoint of bonding strength, the coatings with thickness below 250 µm were considered suitable for biomedical applications according to current international standards. A mechanical model based on quantized fracture mechanics allowed estimating the fracture toughness of the coating on the basis of the experimental data from tensile tests. The critical strain energy release rate was also found to decrease from 1.86 to 0.10 J/m² with the increase of coating thickness, which therefore plays a key role in determining the mechanical properties of the materials.

A critical review of multifunctional titanium surfaces: New frontiers for improving osseointegration and host response, avoiding bacteria contamination

Evolution of metal implants progressively shifted the focus from adequate mechanical strength to improved biocompatibility and absence of toxicity and, finally, to fast osseointegration. Recently, new frontiers and challenges of Ti implants have been addressed to improvement of bioactivity, fighting of bacterial infection and biofilm formation, as well as modulation of inflammation. This is closely related to the clinical demand of multifunctional implants able to simultaneously have a number of specific responses with respect to body fluids, cells (osteoblasts, fibroblasts, macrophages) and pathogenic agents (bacteria, viruses). This complex system of multiple biological stimuli and surface responses is a major arena of the current research on biomaterials and biosurfaces. This review covers the strategies explored to this purpose since 2010 in the case of Ti and Ti alloys, considering that the number of related papers doubled about in the last seven years and no review has comprehensively covered this engaging research area yet. The different approaches followed for producing multifunctional Ti-based surfaces involve the use of thick and thin inorganic coatings, chemical surface treatments, and functionalization strategies coupled with organic coatings.

STATEMENT OF SIGNIFICANCE

According to the clinical demand of multifunctional implants able to simultaneously have a number of specific responses with respect to body fluids, cells and pathogenic agents, new frontiers of Ti implants have been addressed to improvement of bioactivity, fighting of bacterial infection and biofilm formation, as well as modulation of inflammation. Literature since 2010 is here reviewed. Several strategies for getting bioactive and antibacterial actions on Ti surfaces have been suggested, but they still need to be optimized with respect to several concerns. A further step will be to combine on the same surface a proven ability of modulation of inflammatory response. The achievement of multifunctional surfaces able to modulate inflammation and to promote osteogenesis is a grand challenge.

In Vitro Effect of 3D Plates Used for Surgical Treatment of Condylar Fractures on Prostaglandin E₂ (PGE₂) and Thromboxane B₂ (TXB₂) Concentration in THP-1 Macrophages

Recent studies have shown promising results concerning the effectiveness of 3D plates in terms of stabilization of condylar fractures. Despite the use of new techniques and new materials, we can still observe certain side effects, including the immune reaction of the body, which may lead to the excessive inflammation. The aim of this paper was to determine how the production of prostaglandin E₂ (PGE₂) and thromboxane B₂ (TXB₂) in THP-1 monocytes/macrophages is influenced by the titanium 3D plates and dedicated screws. The experiments were conducted on THP-1 monocytic cell line and macrophages derived from a THP-1cells. The concentrations of PGE₂ and TXB₂ released were measured by using immunoassay kit. Verification of plate-induced activation of THP-1 monocytes and macrophages and initiation of inflammatory reaction was conducted by flow cytometry. Despite some differences in the content of the implant devices our results showed that these plates did not statistically significantly increase the production of these prostanoids. Osteosynthesis of condylar fractures using 3D titanium mini-plates seems to be a good alternative to traditional plates due to their lack of stimulating the cyclooxygenase-dependent production of prostanoids; limiting the development of inflammatory reactions.

M2 macrophages contribute to osteogenesis and angiogenesis on nanotubular TiO2 surfaces

The monocyte/macrophage system plays an essential role in the host response and the fate of endosseous implanted materials. Macrophage behavior was thought to be regulated by nanostructured titanium which has been considered as a very promising candidate for dental implants. However, there is little known for subsequent effects of these activated macrophages on osteogenesis and angiogenesis which were essential for bone integration. Here we presented two different dimensions of titanium nanotubes generated by anodic oxidation at 10 V (NT 10) and 20 V (NT 20), respectively. The behavior of macrophages on the surfaces was evaluated, and their conditioned medium (CM) was collected to stimulate MC3T3 and HUVECs, with commercially pure titanium (cp Ti) as control. We found that NT 20 induced macrophage activation similar to the anti-inflammatory M2 macrophage state with the enhanced expression of IL-10 and ARG, while NT 10 was associated with M1 macrophage phenotype characterized by high levels of IL-1β, iNOS and TNF-α. Furthermore, the osteogenic capacity of MC3T3 in CM from NT 20 was enhanced (NT 20 > NT 10 ≈ cp Ti) and the tube formation capacity of HUVECs was promoted in CM from nanotubular surfaces with increasing tube dimensions (NT 20 > NT 10 > cp Ti). Our data suggest that dental implants with the large nanotube dimension surface could result in a favorable osteoimmunomodulatory microenvironment for the establishment of osseointegration.