Bioactive potential of silica coatings and its effect on the adhesion of proteins to titanium implants

Proteomics as a tool to study the osteoimmunomodulatory role of metallic ions in a sol-gel coating

The success of bone implants depends on the osteoimmunomodulatory (OIM) activity of the biomaterials in the interactions with the periimplantary tissues. Many in vitro tests have been conducted to evaluate the osteoimmunology effects of biomaterials. However, results of these tests have often been inconclusive. This study examines the properties of newly developed sol-gel coatings doped with two metal ions associated with bone regeneration, Ca and Zn. The study uses both proteomic methods and traditional in vitro assays. The results demonstrate that proteomics is an effective tool to scrutinize the OIM properties of the materials. Moreover, sol-gel coatings offer excellent base materials to evaluate the effects of metal ions on these properties. The obtained data highlight the highly tunable nature of sol-gel materials; studying the materials with different doping levels supplies valuable information on the interactions between the immune and bone-forming processes.

Insight into the antibacterial mechanism of Cu-enriched sol-gel coatings employing proteomics

Advanced antibacterial biomaterials can help reduce the severe consequences of infections. Using copper compounds is an excellent option to achieve this goal; they offer a combination of regenerative and antimicrobial functions. In this study, new CuCl₂-doped sol-gel coatings were developed and physicochemically characterised. Their osteogenic and inflammatory responses were tested in vitro using human osteoblasts and THP-1 macrophages. Their antibacterial effect was evaluated using Escherichia coli and Staphylococcus aureus. The Cu influence on the adsorption of human serum proteins was analysed employing proteomics. The materials released Cu²⁺ and were not cytotoxic. The osteoblasts in contact with these materials showed an increased ALP, BMP2 and OCN gene expression. THP-1 showed an increase in pro-inflammatory markers related to M1 polarization. Moreover, Cu-doped coatings displayed a potent antibacterial behaviour against E. coli and S. aureus. The copper ions affected the adsorption of proteins related to immunity, coagulation, angiogenesis, fibrinolysis, and osteogenesis. Interestingly, the coatings had increased affinity to proteins with antibacterial functions and proteins linked to the complement system activation that can lead to direct bacterial killing via large pore-forming complexes. These results contribute to our understanding of the antibacterial mechanisms of Cu-biomaterials and their interaction with biological systems.

Proteomic evaluation of human osteoblast responses to titanium implants over time

Titanium is widely used in bone prostheses due to its excellent biocompatibility and osseointegration capacity. To understand the effect of sandblasted acid-etched (SAE) Ti implants on the biological responses of human osteoblast (HOb), their proteomic profiles were analyzed using nLC-MS/MS. The cells were cultured with the implant materials, and 2544 distinct proteins were detected in samples taken after 1, 3, and 7 days. Comparative analyses of proteomic data were performed using Perseus software. The expression of proteins related to EIF2, mTOR, insulin-secretion and IGF pathways showed marked differences in cells grown with SAE-Ti in comparison with cells cultured without Ti. Moreover, the proteomic profiles obtained with SAE-Ti were compared over time. The affected proteins were related to adhesion, immunity, oxidative stress, coagulation, angiogenesis, osteogenesis, and extracellular matrix formation functions. The proliferation, mineralization and osteogenic gene expression in HObs cultured with SAE-Ti were characterized in vitro. The results showed that the osteoblasts exposed to this material increase their mineralization rate and expression of COLI, RUNX2, SP7, CTNNB1, CAD13, IGF2, MAPK2, and mTOR. Overall, the observed proteomic profiles can explain the SAE-Ti osteogenic properties, widening our knowledge of key signaling pathways taking part in the early stages of the osseointegration process in this type of implantations.

Dental implant material related changes in molecular signatures in peri-implantitis - A systematic review and integrative analysis of omics in-vitro studies

OBJECTIVE

Since peri-implantitis differs clinically and histopathologically from periodontitis, implant wear debris is considered to play a role in the destructive processes. This work aims to systematically review if titanium particles affect oral-related cells through changes in molecular signatures (e.g., transcriptome, proteome, epigenome), thereby promoting peri-implantitis.

METHODS

Leveraging three literature databases (Medline, Embase, Cochrane) a systematic search based on a priori defined PICOs was conducted: '-omics' studies examining titanium exposure in oral-related cells. After risk of bias assessments, lists of differentially expressed genes, proteins, and results of functional enrichment analyses were compiled. The significance of overlapping genes across multiple studies was assessed via Monte Carlo simulation and their ranking was verified using rank aggregation.

RESULTS

Out of 2104 screened articles we found 12 eligible publications. A significant overlap of gene expression in oral-related cells exposed to titanium particles was found in four studies. Furthermore, changes in biological processes like immune/inflammatory or stress response as well as toll-like receptor (TLR) and mitogen-activated protein kinase (MAPK) signaling pathways were linked to titanium in transcriptome and proteome studies. Epigenetic changes caused by titanium were detected but inconsistent.

CONCLUSION

An influence of titanium implant wear debris on the development and progression of peri-implantitis is plausible but needs to be proven in further studies. Limitations arise from small sample sizes of included studies and insufficient publication of re-analyzable data.

Bioactive Coatings Based on Nanostructured TiO2 Modified with Noble Metal Nanoparticles and Lysozyme for Ti Dental Implants

This work presents the synthesis of nanostructured TiO₂ modified with noble metal nanoparticles (Au, Ag) and lysozyme and coated on titanium foil. Moreover, the specific structural and functional properties of the resulting inorganic and hybrid materials were explored. The purpose of this study was to identify the key parameters for developing engineered coatings on titanium foil appropriate for efficient dental implants with intrinsic antibacterial activity. TiO₂ nanoparticles obtained using the sol-gel method were deposited on Ti foil and modified with Au/Ag nanoparticles. Morphological and structural investigations (scanning electron and atomic force microscopies, X-ray diffraction, photoluminescence, and UV-Vis spectroscopies) were carried out for the characterization of the resulting inorganic coatings. In order to modify their antibacterial activity, which is essential for safe dental implants, the following aspects were investigated: (a) singlet oxygen (¹O₂) generation by inorganic coatings exposed to visible light irradiation; (b) the antibacterial behavior emphasized by titania-based coatings deposited on titanium foil (TiO₂/Ti foil; Au-TiO₂/Ti foil, Ag-TiO₂/Ti foil); (c) the lysozyme bioactivity on the microbial substrate (Micrococcus lysodeicticus) after its adsorption on inorganic surfaces (Lys/TiO₂/Ti foil; Lys/Au-TiO₂/Ti foil, Lys/Ag-TiO₂/Ti foil); (d) the enzymatic activity of the above-mentioned hybrids materials for the hydrolysis reaction of a synthetic organic substrate usually used for monitoring the lysozyme biocatalytic activity, namely, 4-Methylumbelliferyl β-D-N,N',N″-triacetylchitotrioside [4-MU-β- (GlcNAc)₃]. This was evaluated by identifying the presence of a fluorescent reaction product, 7-hydroxy-4-metyl coumarin (4-methylumbelliferone).

The effect of calcium-magnesium mixtures in sol-gel coatings on bone tissue regeneration

Calcium and magnesium are two elements essential for bone structure and metabolism. However, their synergistic or competitive effects on bone regeneration are often overlooked during biomaterial development. We examined the interactions between Ca and Mg in sol-gel coatings doped with mixtures of CaCl₂ (0.5%) and MgCl₂ (0.5, 1, and 1.5%). After physicochemical characterisation, the materials were incubated in vitro with MC3T3-E1 osteoblastic cells and RAW264.7 macrophages, and the protein adsorption was analysed using nLC-MS/MS. The incorporation of the ions did not lead to the formation of crystalline structures and did not affect the sol-gel network cross-linking. The release of the ions did not cause cytotoxic effects at any tested concentration. The proteomic analysis showed that adding the Ca and Mg ions elevated the adsorption of proteins associated with inflammatory response regulation (e.g., ALBU, CLUS, HPT, HPTR, A1AG1 and A1AG2) but decreased the adsorption of immunoglobulins. The CaMg coatings had reduced affinity to proteins associated with coagulation (e.g., FA9, FA10, FA11, FA12) but increased the adsorption of proteins involved in cell adhesion (DSG1, DESP, FBLN1, ZA2G). In vitro assays revealed that the cellular response was affected by changing the concentration of Mg. Moreover, our results show that these differences reflect the changes in the concentrations of both ions in the mix but are not a simple additive effect.

Cross-kingdom microbial interactions in dental implant-related infections: is Candida albicans a new villain?

Candida albicans, an oral fungal opportunistic pathogen, has shown the ability to colonize implant surfaces and has been frequently isolated from biofilms associated with dental implant-related infections, possibly due to its synergistic interactions with certain oral bacteria. Moreover, evidence suggests that this cross-kingdom interaction on implant can encourage bacterial growth, leading to increased fungal virulence and mucosal damage. However, the role of Candida in implant-related infections has been overlooked and not widely explored or even considered by most microbiological analyses and therapeutic approaches. Thus, we summarized the scientific evidence regarding the ability of C. albicans to colonize implant surfaces, interact in implant-related polymicrobial biofilms, and its possible role in peri-implant infections as far as biologic plausibility. Next, a systematic review of preclinical and clinical studies was conducted to identify the relevance and the gap in the existing literature regarding the role of C. albicans in the pathogenesis of peri-implant infections.

Characterization of magnesium doped sol-gel biomaterial for bone tissue regeneration: The effect of Mg ion in protein adsorption

Magnesium is the fourth most abundant element in the human body with a wide battery of functions in the maintenance of normal cell homeostasis. In the bone, this element incorporates in the hydroxyapatite structure and it takes part in mineral metabolism and regulates osteoclast functions. In this study, sol-gel materials with increasing concentrations of MgCl₂ (0.5, 1, and 1.5%) were synthesized and applied onto Ti surfaces as coatings. The materials were first physicochemically characterized. In vitro responses were examined using the MC3T3-E1 osteoblastic cells and RAW264.7 macrophages. Human serum protein adsorption was evaluated employing nLC-MS/MS. The incorporation of Mg did not affect the crosslinking of the sol-gel network, and a controlled release of Mg was observed; it was not cytotoxic at any of the tested concentrations. The cytoskeleton arrangement of MC3T3-E1 cells cultured on the Mg-doped materials changed in comparison with controls; the cells became more elongated, with protruded lamellipodia and increased cell surface. The expression of integrins (ITGA5 and ITGB1) was boosted by Mg-coatings. The ALP activity and expression of TGF-β, OSX and RUNX2 genes were also increased. In RAW264.7 cells, TNF-α secretion was reduced, while TGF-β and IL-4 expression rose. These changes correlated with the altered protein adsorption patterns. The Mg-doped coatings showed increased adsorption of anti-inflammatory (CLUS, IC1, CFAH, and VTNC), cell adhesion (DSG1, FILA2, and DESP) and tissue regeneration (VTNC and CYTA) proteins. This integrated approach to biomaterial characterization revealed the potential of Mg in bone tissue regeneration.

Evaluation of the inflammatory responses to sol-gel coatings with distinct biocompatibility levels

The immune system plays a crucial role in determining the implantation outcome, and macrophages are in the frontline of the inflammatory processes. Further, cellular oxidative stress resulting from the material recognition can influence how cell responses develop. Considering this, the aim of this study was to study oxidative stress and macrophages phenotypes in response to sol-gel materials with distinct in vivo outcomes. Four materials were selected (70M30T and 35M35G30T, with high biocompatibility, and 50M50G and 50V50G, with low biocompatibility). Gene expression, immunocytochemistry and cytokine secretion profiles for M1 and M2 markers were determined. Moreover, oxidative stress markers were studied. Immunocytochemistry and ELISA showed that 50M50G and 50V50G lead to a higher differentiation to M1 phenotype, while 70M30T and 35M35G30T promoted M2 differentiation. In oxidative stress, no differences were found. These results show that the balance between M1 and M2, more than individual quantification of each phenotype, determines a biomaterial outcome.

Bioactive zinc-doped sol-gel coating modulates protein adsorption patterns and in vitro cell responses

Zinc is an essential element with an important role in stimulating the osteogenesis and mineralization and suppressing osteoclast differentiation. In this study, new bioactive ZnCl₂-doped sol-gel materials were designed to be applied as coatings onto titanium. The biomaterials were physicochemically characterized and the cellular responses evaluated in vitro using MC3T3-E1 osteoblasts and RAW264.7 macrophages. The effect of Zn on the adsorption of human serum proteins onto the material surface was evaluated through nLC-MS/MS. The incorporation of Zn did not affect the crosslinking of the sol-gel network. A controlled Zn²⁺ release was obtained, reaching values below 10 ppm after 21 days. The materials were no cytotoxic and lead to increased gene expression of ALP, TGF-β, and RUNX2 in the osteoblasts. In macrophages, an increase of IL-1β, TGF-β, and IL-4 gene expression was accompanied by a reduced TNF-α liberation. Proteomic results showed changes in the adsorption patterns of proteins associated with immunological, coagulative, and regenerative functions, in a Zn dose-dependent manner. The variations in protein adsorption might lead to the downregulation of the NF-κB pathway, thus explain the observed biological effects of Zn incorporation into biomaterials. Overall, these coatings demonstrated their potential to promote bone tissue regeneration.

Hydroxyapatite Formation on Coated Titanium Implants Submerged in Simulated Body Fluid

Titanium implants are commonly used in the field of dentistry for prosthetics such as crowns, bridges, and dentures. For successful therapy, an implant must bind to the surrounding bone in a process known as osseointegration. The objective for this ongoing study is to determine the potential of different implant surface coatings in providing the formation of hydroxyapatite (HA). The coatings include titanium nitride (TiN), silicon dioxide (SiO₂), and quaternized titanium nitride (QTiN). The controls were a sodium hydroxide treated group, which functioned as a positive control, and an uncoated titanium group. Each coated disc was submerged in simulated body fluid (SBF), replenished every 48 h, over a period of 28 days. Each coating successfully developed a layer of HA, which was calculated through mass comparisons and observed using scanning electron microscopy (SEM) and energy dispersive analysis x-rays (EDX). Among these coatings, the quaternized titanium nitride coating seemed to have a better yield of HA. Further studies to expand the data concerning this experiment are underway.

Surface Modification Techniques of Titanium and its Alloys to Functionally Optimize Their Biomedical Properties: Thematic Review

Depending on the requirements of specific applications, implanted materials including metals, ceramics, and polymers have been used in various disciplines of medicine. Titanium and its alloys as implant materials play a critical role in the orthopedic and dental procedures. However, they still require the utilization of surface modification technologies to not only achieve the robust osteointegration but also to increase the antibacterial properties, which can avoid the implant-related infections. This article aims to provide a summary of the latest advances in surface modification techniques, of titanium and its alloys, specifically in biomedical applications. These surface techniques include plasma spray, physical vapor deposition, sol-gel, micro-arc oxidation, etc. Moreover, the microstructure evolution is comprehensively discussed, which is followed by enhanced mechanical properties, osseointegration, antibacterial properties, and clinical outcomes. Future researches should focus on the combination of multiple methods or improving the structure and composition of the composite coating to further enhance the coating performance.

Bioactive Surfaces vs. Conventional Surfaces in Titanium Dental Implants: A Comparative Systematic Review

Animal studies and the scarce clinical trials available that have been conducted suggest that bioactive surfaces on dental implants could improve the osseointegration of such implants. The purpose of this systematic review was to compare the effectiveness of osseointegration of titanium (Ti) dental implants using bioactive surfaces with that of Ti implants using conventional surfaces such as sandblasted large-grit acid-etched (SLA) or similar surfaces. Applying the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) statement, the MEDLINE, PubMed Central and Web of Science databases were searched for scientific articles in April 2020. The keywords used were “dental implants”, “bioactive surfaces”, “biofunctionalized surfaces”, and “osseointegration”, according to the question: “Do bioactive dental implant surfaces have greater osseointegration capacity compared with conventional implant surfaces?” Risk of bias was assessed using the Cochrane Collaboration tool. 128 studies were identified, of which only 30 met the inclusion criteria: 3 clinical trials and 27 animal studies. The average STROBE (STrengthening the Reporting of OBservational studies in Epidemiology) and ARRIVE (Animal Research: Reporting of In Vivo Experiments) scores were 15.13 ± 2.08 and 17.7±1.4, respectively. Implant stability quotient (ISQ) was reported in 3 studies; removal torque test (RTT)—in 1 study; intraoral periapical X-ray and microcomputed tomography radiological evaluation (RE)—in 4 studies; shear force (SF)—in 1 study; bone-to-implant contact (BIC)—in 12 studies; and BIC and bone area (BA) jointly—in 5 studies. All animal studies reported better bone-to-implant contact surface for bioactive surfaces as compared to control implants with a statistical significance of p < 0.05. Regarding the bioactive surfaces investigated, the best results were yielded by the one where mechanical and chemical treatment methods of the Ti surfaces were combined. Hydroxyapatite (HA) and calcium–phosphate (Ca–Ph) were the most frequently used bioactive surfaces. According to the results of this systematic review, certain bioactive surfaces have a positive effect on osseointegration, although certain coating biomolecules seem to influence early peri-implant bone formation. Further and more in-depth research in this field is required to reduce the time needed for osseointegration of dental implants.

Mechanism of lysozyme adsorption onto gold surface determined by quartz crystal microbalance and surface plasmon resonance

In this study, the physicochemical characterization of lysozyme adsorbed on gold was investigated. Through the use of MP-SPR it was possible to establish that the orientation of molecules changes from side-on to between or end-on with increasing surface coverage. The data confirms that the process of adsorption is driven primarily by electrostatic interactions but also by hydrophobic forces. MP-SPR data was compared with the Random Sequential Adsorption model for a molecule with an ellipsoidal shape. Contact angle measurements showed that higher surface coverage also translates in more hydrophilic properties of obtained lysozyme layer. Comparison of CD and PM-IRRAS spectra in solution and adsorbed state respectively showed changes in the secondary structures of lysozyme. These changes are dependent on pH, but fundamentally they go in the direction of the increase of β-turn/random content with a simultaneous decrease in β-sheet fraction, which suggests that aggregation is not occurring. The combination of MP-SPR and QCM-D measurements allowed the estimation of the number of water molecules associated with the lysozymes films. It has been observed that hydration decreases from 70% in pH = 4 to 30% in pH = 11. This data indicates that hydration is driven mainly by the degree of protonation of lysozyme molecules.

Contamination of titanium dental implants: a narrative review

Contamination of titanium dental implants may lead to implant failure. There are two major types of contaminants: the inorganic and organic contaminants. The inorganic contaminants mostly consist of elements such as calcium, phosphorus, chlorine, sulphur, sodium, silicon, fluorine and some organic carbons. Whereas organic contaminants consist of hydrocarbon, carboxylates, salts of organic acids, nitrogen from ammonium and bacterial cells/byproducts. Contaminants can alter the surface energy, chemical purity, thickness and composition of the oxide layer, however, we lack clinical evidence that contaminations have any effect at all. However, surface cleanliness seems to be essential for implant osseointegration.These contaminants may cause dental implants to fail in its function to restore missing teeth and also cause a financial burden to the patient and the health care services to invest in decontamination methods. Therefore, it is important to discuss the aetiology of dental implant failures. In this narrative review, we discuss two major types of contaminants: the inorganic and organic contaminants including bacterial contaminants. This review also aims to discuss the potential effect of contamination on Ti dental implants.

Influences of sodium tantalite submicro-particles in polyetheretherketone based composites on behaviors of rBMSCs/HGE-1 cells for dental application

Dental implanted materials require excellent mechanical properties, biocompatibility as well as integration with bone tissue and gingival tissue to achieve early loading and long-term stability. In this study, cubic shape sodium tantalite (ST) submicro-particles with the size of around 180 nm were synthesized by a hydrothermal method, and ST/polyetheretherketone (PEEK) composites (TPC) with ST content of 20 w% (TPC20) and 40 w% (TPC40) were prepared by melting blend. The results showed that the compressive strength, thermal properties, surface roughness, hydrophilicity and surface energy as well as adsorption of proteins on TPC40 were also significantly enhanced compared with TPC20 and PEEK. Moreover, the responses (adhesion and proliferation as well as differentiation) of rat bone marrow mesenchymal stem cells (rBMSCs), and responses (adhesion, and proliferation) of human gingival epithelial (HGE-1) cells to TPC40 were significantly promoted compared with TPC20 and PEEK. The results demonstrated that ST content in TPC had remarkable effects on the surface properties, which played key roles in stimulating the responses of both rBMSCs and HGE-1 cells. TPC40 with increased surface properties and excellent cytocompatibility might have great potential as an implanted material for dental application.

In-vivo performance of plasma-sprayed CaO-MgO-SiO2-based bioactive glass-ceramic coating on Ti-6Al-4V alloy for bone regeneration

The CaO-MgO-SiO₂-based bioactive glass-ceramic coating (named M2) on Ti-6Al-4V alloy has been proven to behave well in vitro. But how to make full sense of its performances in terms of osteogenesis and osseointegration in vivo matters very much. For this, the M2-coated Ti-6Al-4V cylinders were prepared by atmospheric plasma spraying (APS) and implanted into New Zealand rabbit for 1, 2 and 3 months, respectively, by setting commercial HA-coated Ti-6Al-4V as the control. It is encouraging that, the two groups bonded with the surrounding tissues stably and newly formed bone grew towards or around the implants after 3-month implantation according to radiographic images. From the histological sections, it is obvious that, compared to the control, the M2-coated implant was more favorable for the osteogenesis and neo-vascularisation in the whole experimental process and demonstrated a better osseointegration with the host bone, indicating the former possessed better osteoconductivity, osteoinductivity and osteogenic ability. The study indicated that the M2-coated Ti-6Al-4V implant exerted a great potential to substitute the commercial HA-coated Ti-6Al-4V implant in repairing load-bearing bone defects.

Proteomic analysis of calcium-enriched sol-gel biomaterials

Calcium is an element widely used in the development of biomaterials for bone tissue engineering as it plays important roles in bone metabolism and blood coagulation. The Ca ions can condition the microenvironment at the tissue-material interface, affecting the protein deposition process and cell responses. The aim of this study was to analyze the changes in the patterns of protein adsorption on the silica hybrid biomaterials supplemented with different amounts of CaCl₂, which can function as release vehicles. This characterization was carried out by incubating the Ca-biomaterials with human serum. LC-MS/MS analysis was used to characterize the adsorbed protein layers and compile a list of proteins whose affinity for the surfaces might depend on the CaCl₂ content. The attachment of pro- and anti-clotting proteins, such as THRB, ANT3, and PROC, increased significantly on the Ca-materials. Similarly, VTNC and APOE, proteins directly involved on osteogenic processes, attached preferentially to these surfaces. To assess correlations with the proteomic data, these formulations were tested in vitro regarding their osteogenic and inflammatory potential, employing MC3T3-E1 and RAW 264.7 cell lines, respectively. The results confirmed a Ca dose-dependent osteogenic and inflammatory behavior of the materials employed, in accordance with the protein attachment patterns.

Intrasurgical Protein Layer on Titanium Arthroplasty Explants: From the Big Twelve to the Implant Proteome

PURPOSE

Aseptic loosening in total joint replacement due to insufficient osteointegration is an unsolved problem in orthopaedics. The purpose of the study is to obtain a picture of the initial protein adsorption layer on femoral endoprosthetic surfaces as the key to the initiation of osseointegration.

EXPERIMENTAL DESIGN

The paper describes the first study of femoral stem explants from patients for proteome analysis of the primary protein layer. After 2 min in situ, the stems are explanted and frozen in liquid nitrogen. Proteins are eluted under reducing conditions and analyzed by LC-MS/MS.

RESULTS

After exclusion of proteins identified by a single peptide, the implant proteome is found to consist of 2802 unique proteins. Of these, 77% are of intracellular origin, 9% are derived from the plasma proteome, 8% from the bone proteome, and four proteins with highest specificity score could be assigned to the bone marrow proteome (transcriptome). The most abundant protein in the adsorbed total protein layer is hemoglobin (8-11%) followed by serum albumin (3.6-6%).

CONCLUSIONS

A detailed knowledge of the initial protein film deposited onto the implants, as demonstrated here for the first time, may help to understand and predict the response of the osseous microenvironment to implant surfaces.

Role of the Complement System in the Response to Orthopedic Biomaterials

Various synthetic biomaterials are used to replace lost or damaged bone tissue that, more or less successfully, osseointegrate into the bone environment. Almost all biomaterials used in orthopedic medicine activate the host-immune system to a certain degree. The complement system, which is a crucial arm of innate immunity, is rapidly activated by an implanted foreign material into the human body, and it is intensely studied regarding blood-contacting medical devices. In contrast, much less is known regarding the role of the complement system in response to implanted bone biomaterials. However, given the increasing knowledge of the complement regulation of bone homeostasis, regeneration, and inflammation, complement involvement in the immune response following biomaterial implantation into bone appears very likely. Moreover, bone cells can produce complement factors and are target cells of activated complement. Therefore, new bone formation or bone resorption around the implant area might be greatly influenced by the complement system. This review aims to summarize the current knowledge on biomaterial-mediated complement activation, with a focus on materials primarily used in orthopedic medicine. In addition, methods to modify the interactions between the complement system and bone biomaterials are discussed, which might favor osseointegration and improve the functionality of the device.

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.