Deposition, structure, physical and invitro characteristics of Ag-doped β-Ca3(PO4)2/chitosan hybrid composite coatings on Titanium metal

Surface modifications and coatings to improve osseointegration and antimicrobial activity on titanium surfaces: A statistical review over the last decade

Background

Titanium (Ti) is commonly employed therapeutically in many medical sectors associated with bone healing because of its superior mechanical properties and capacity to osseointegrate in the host bone tissue. The titanium surfaces may now be functionalized to offer additional and potentially valuable features. This review article discusses many titanium implant surface modifications, emphasizing their biological significance and the challenges that each one mainly addresses. Before reviewing the genuine reason for titanium surface modification in implanted devices, we briefly explore the process of osseointegration, enhancement of antibacterial properties, biocompatibility, and the historical significance of titanium as an implantable material, and the significant challenges involved. The various physical and chemical alterations that could take place on Ti surfaces are next examined. The rest of our talk will focus on creating inorganic and organic coatings for implanted Ti devices. Finally, we present a synopsis of the surface modification strategies currently being evaluated in clinical settings.

Target

This systematic review aims to evaluate research on titanium implants with significant surface modifications, coatings, and antibacterial capabilities.

Methods

Following the PRISMA paradigm, we searched for three electronic databases (Web of Science, PubMed Central, and Google Scholar) using the keywords "titanium implants," "titanium surface modification," and "titanium osseointegration," and "titanium antibacterial activity."

Results

We identified 1,39,336 articles overall that were published between 2012 and 2021, and we then focused on 8917 articles that concentrated on a particular topic. Clear inclusion and exclusion criteria were used in a rigorous screening procedure. Articles that didn't meet certain requirements (were irrelevant, used incorrect techniques, had unsuitable data values, or were only brief letters or communications) were eliminated. Finally, 120 research publications in total are taken into account for this extensive systematic review.

Conclusion

The report summarises current information on titanium implants with significant surface modifications, antibacterial activity, and coatings. It also gives some strong recommendations for future study topics.

Chitosan coatings on titanium-based implants - From development to characterization and behavior: A systematic review

Chitosan is a promising natural polymer for coatings, it combines intrinsic antibacterial and pro-osteoblastic properties, but the literature still has a gap from the development to behavior of these coatings, so this systematic review aimed to answer, "What is the relationship between the physical and chemical properties of polymeric chitosan coatings on titanium implants on antibacterial activity and osteoblast viability?". PRISMA guidelines was followed, the search was applied into 4 databases and grey literature, without the restriction of time and language. The selection process occurred in 2 blinded steps by the authors. The criteria of eligibility were in vitro studies that evaluated the physical, chemical, microbiological, and biological properties of chitosan coatings on titanium surfaces. The risk of bias was analyzed by the specific tool. Of 734 potential articles 10 were included; all had low risk of bias. The coating was assessed according to the technique of fabrication, FT-IR, thickness, adhesion, roughness, wettability, antibacterial activity, and osteoblast viability. The analyzed coatings showed efficacy on antibacterial activity and cytocompatibility dependent on the class of material incorporated. Thus, this review motivates the development of time-dependent studies to optimize manufacturing and allow for an increase in patents and availability on the market.

Application of advanced surface modification techniques in titanium-based implants: latest strategies for enhanced antibacterial properties and osseointegration

Titanium-based implants, renowned for their excellent mechanical properties, corrosion resistance, and biocompatibility, have found widespread application as premier implant materials in the medical field. However, as bioinert materials, they often face challenges such as implant failure caused by bacterial infections and inadequate osseointegration post-implantation. Thus, to address these issues, researchers have developed various surface modification techniques to enhance the surface properties and bioactivity of titanium-based implants. This review aims to outline several key surface modification methods for titanium-based implants, including acid etching, sol-gel method, chemical vapor deposition, electrochemical techniques, layer-by-layer self-assembly, and chemical grafting. It briefly summarizes the advantages, limitations, and potential applications of these technologies, presenting readers with a comprehensive perspective on the latest advances and trends in the surface modification of titanium-based implants.

Two decades of continuous progresses and breakthroughs in the field of bioactive ceramics and glasses driven by CICECO-hub scientists

Over the past two decades, the CICECO-hub scientists have devoted substantial efforts to advancing bioactive inorganic materials based on calcium phosphates and alkali-free bioactive glasses. A key focus has been the deliberate incorporation of therapeutic ions like Mg, Sr, Zn, Mn, or Ga to enhance osteointegration and vascularization, confer antioxidant properties, and impart antimicrobial effects, marking significant contributions to the field of biomaterials and bone tissue engineering. Such an approach is expected to circumvent the uncertainties posed by methods relying on growth factors, such as bone morphogenetic proteins, parathyroid hormone, and platelet-rich plasma, along with their associated high costs and potential adverse side effects. This comprehensive overview of CICECO-hub's significant contributions to the forefront inorganic biomaterials across all research aspects and dimensionalities (powders, granules, thin films, bulk materials, and porous structures), follows a unified approach rooted in a cohesive conceptual framework, including synthesis, characterization, and testing protocols. Tangible outcomes [injectable cements, durable implant coatings, and bone graft substitutes (scaffolds) featuring customized porous architectures for implant fixation, osteointegration, accelerated bone regeneration in critical-sized bone defects] were achieved. The manuscript showcases specific biofunctional examples of successful biomedical applications and effective translations to the market of bone grafts for advanced therapies.

Osteoblast and bacterial cell response on RGD peptide-functionalized chitosan coatings electrophoretically deposited from different suspensions on Ti13Nb13Zr alloy

Metallic materials for long-term load-bearing implants still do not provide high antimicrobial activity while maintaining strong compatibility with bone cells. This study aimed to modify the surface of Ti13Nb13Zr alloy by electrophoretic deposition of a chitosan coating with a covalently attached Arg-Gly-Asp (RGD) peptide. The suspensions for coating deposition were prepared in two different ways either using hydroxyacetic acid or a carbon dioxide saturation process. The coatings were deposited using a voltage of 10 V for 1 min. The prepared coatings were examined using SEM, EDS, FTIR, and XPS techniques. In addition, the wettability of these surfaces, corrosion resistance, adhesion of the coatings to the metallic substrate, and their antimicrobial activity (E. coli, S. aureus) and cytocompatibility properties using the MTT and LDH assays were studied. The coatings produced tightly covered the metallic substrate. Spectroscopic studies confirmed that the peptide did not detach from the chitosan chain during electrophoretic deposition. All tested samples showed high corrosion resistance (corrosion current density measured in nA/cm2 ). The deposited coatings contributed to a significant increase in the antimicrobial activity of the samples against Gram-positive and Gram-negative bacteria (reduction in bacterial counts from 99% to, for CS-RGD-Acid and the S. aureus strain, total killing capacity). MTT and LDH results showed high compatibility with bone cells of the modified surfaces compared to the bare substrate (survival rates above 75% under indirect contact conditions and above 100% under direct contact conditions). However, the adhesion of the coatings was considered weak.

Polysaccharide-Based Supramolecular Hydrogel Coatings with Corrosion Barrier Zone for Protection of Patina Bronze

Protective coatings for bronze relics should adhere to the basic principles of cultural relic preservation, such as not altering the color and appearance of the artifacts, and being moderately combined with the artifacts to resist erosion due to external environments (such as water and gas). This paper presents the development of a physically crosslinked supramolecular hydrogel produced from guanidinium-based chitosan (GC). The hydrogel exhibits the excellent adsorption protection of bronze, and the addition of clay enhances the water barrier properties of the chitosan film. The supramolecular interaction between sodium polyacrylate/GC/clay confers corrosion buffering capability to the hydrogel coating in corrosive environments, and the gel coating can be self-healing at room temperature for 24 h. The fabricated nanocomposites were comprehensively characterized using various methods (Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, etc.). The electrochemical properties of coated specimens were evaluated, and the impedance spectrum revealed a large impedance arc indicating high charge resistance, which has a corrosion resistance effect.

Molybdate and Phosphate Cross-Linked Chitosan Films for Corrosion Protection of Hot-Dip Galvanized Steel

Environmentally friendly and sustainable methods to protect hot-dip galvanized (HDG) steel from corrosion are extensively studied. Films of the biopolymer polyelectrolyte chitosan were ionically cross-linked in this work with the well-known corrosion inhibitors phosphate and molybdate. Layers on this basis are presented as components in a protective system and could, e.g., be applied in pretreatments similar to a conversion coating. For the preparation of the chitosan-based films, a procedure involving sol-gel chemistry and wet-wet application was utilized. Homogeneous films of few micrometers thickness were obtained on HDG steel substrates after thermal curing. Properties of chitosan-molybdate and chitosan-phosphate films were compared with purely passive epoxysilane-cross-linked chitosan, and pure chitosan. Delamination behavior of a poly(vinyl butyral) (PVB) weak model top coating studied by scanning Kelvin probe (SKP) showed an almost linear time dependence over >10 h on all systems. Delamination rates were 0.28 mm h^-1 (chitosan-molybdate) and 0.19 mm h^-1 (chitosan-phosphate), ca. 5% of a non-cross-linked chitosan reference and slightly higher than of the epoxsyilane cross-linked chitosan. Immersion of the treated zinc samples over 40 h in 5% NaCl solution yielded a 5-fold increase of the resistance in the chitosan-molybdate system, as evidenced by electrochemical impedance spectroscopy (EIS). Ion exchange of electrolyte anions with molybdate and phosphate triggers corrosion inhibition, presumably by reaction with the HDG surface as well described in the literature for these inhibitors. Thus, such surface treatments have potential for application, e.g., in temporary corrosion protection.

Sr and Mg Doped Bi-Phasic Calcium Phosphate Macroporous Bone Graft Substitutes Fabricated by Robocasting: A Structural and Cytocompatibility Assessment

Bi-phasic calcium phosphates (BCPs) are considered prominent candidate materials for the fabrication of bone graft substitutes. Currently, supplemental cation-doping is suggested as a powerful path to boost biofunctionality, however, there is still a lack of knowledge on the structural role of such substituents in BCPs, which in turn, could influence the intensity and extent of the biological effects. In this work, pure and Mg- and Sr-doped BCP scaffolds were fabricated by robocasting from hydrothermally synthesized powders, and then preliminarily tested in vitro and thoroughly investigated physically and chemically. Collectively, the osteoblast cell culture assays indicated that all types of BCP scaffolds (pure, Sr- or Sr–Mg-doped) delivered in vitro performances similar to the biological control, with emphasis on the Sr–Mg-doped ones. An important result was that double Mg–Sr doping obtained the ceramic with the highest β-tricalcium phosphate (β-TCP)/hydroxyapatite mass concentration ratio of ~1.8. Remarkably, Mg and Sr were found to be predominantly incorporated in the β-TCP lattice. These findings could be important for the future development of BCP-based bone graft substitutes since the higher dissolution rate of β-TCP enables an easier release of the therapeutic ions. This may pave the road toward medical devices with more predictable in vivo performance.

Structural and electrochemical corrosion studies of spin coated ZrO2 thin films over stainless steel alloy for bone defect applications

Sol-Gel-based reaction mixture sols have been long used to fabricate dense and uniform bioactive coatings with superior mechanical stability over metallic implants. On account of precise control over synthesis, fabrication, formed and low temperature of processing, this technology is one of the most feasible routes to produce bio-ceramic coatings. The study aims to develop a physical barrier over metal implants in form of bioinert Zirconia coatings, phase-stabilized using Dysprosium. The metallic substrates were cut into 10 mm × 10 mm samples and diamond polished after being polished with a 1000 grade emery sheet. Novel spin-coated zirconia films were fabricated over 316L Stainless steel substrates and were sintered at 600°C to obtain firm and uniform crack-free coatings. The thickness of the coatings was determined by ELCA-D meter thermal analysis was performed using TGA-DTA. Phase determination was performed using X-Ray diffraction followed by morphological investigations using Scanning electron microscopy. The corrosion resistance was evaluated with Polarization studies and electrokinetic data was derived using Tafel extrapolation. Biocompatibility evaluation was performed against MG-63 cell lines and RBCs along with bone-forming ability in vitro in SBF. Stable crack-free 3 Layer coatings fabricated at 2000 rpm for 3 s with a thickness of around 1 μm were found to be optimal for corrosion resistance behavior of steel implants at a low I_Corr value of 0.501 µA/cm² and adhesion strength of 40.93 MPa when untreated falling down to 39.92 MPa when immersed in SBF. The study concludes that medium rpm coatings sustain enough sol to produce crack-free coatings that form a strong physical barrier between body fluid and implant surface thereby reducing the attack of corrosive ions and protecting the implant surface without participating in any form of bioactivity but supporting native bone regeneration capabilities.

Multi-scale hybrid modified coatings on titanium implants for non-cytotoxicity and antibacterial properties

Titanium and its alloys are among the widely used materials in the biomedical field, but they have poor wear resistance and antibacterial properties. In the present study, anodization, photo-reduction, and spin-coating technologies were integrated to prepare a hybrid modified coating for bio-inert titanium implants, having excellent comprehensive performance. The surface roughness of Ti-35Nb-2Ta-3Zr was specifically optimized by surface modification leading to improved wear resistance. Ag ions are still detectable after 28 days of submersion in saline. The antibacterial rate of the composite coating group reaches 100% by plate counting due to the antibacterial mechanism of direct and indirect contact. Both bacteria morphology and fluorescence staining experiments confirm these results. Besides, no cytotoxicity was detected in our fabricated implants during the CCK-8 assay. Accordingly, fabrication of hybrid modified coatings on Ti-35Nb-2Ta-3Zr is an effective strategy for infection and cytotoxicity prevention. These hybrid modified coatings can be regarded as promising multifunctional biomaterials.

Innovative Surface Modification Procedures to Achieve Micro/Nano-Graded Ti-Based Biomedical Alloys and Implants

Due to the growing aging population of the world, and as a result of the increasing need for dental implants and prostheses, the use of titanium and its alloys as implant materials has spread rapidly. Although titanium and its alloys are considered the best metallic materials for biomedical applications, the need for innovative technologies is necessary due to the sensitivity of medical applications and to eliminate any potentially harmful reactions, enhancing the implant-to-bone integration and preventing infection. In this regard, the implant’s surface as the substrate for any reaction is of crucial importance, and it is accurately addressed in this review paper. For constructing this review paper, an internet search was performed on the web of science with these keywords: surface modification techniques, titanium implant, biomedical applications, surface functionalization, etc. Numerous recent papers about titanium and its alloys were selected and reviewed, except for the section on forthcoming modern implants, in which extended research was performed. This review paper aimed to briefly introduce the necessary surface characteristics for biomedical applications and the numerous surface treatment techniques. Specific emphasis was given to micro/nano-structured topographies, biocompatibility, osteogenesis, and bactericidal effects. Additionally, gradient, multi-scale, and hierarchical surfaces with multifunctional properties were discussed. Finally, special attention was paid to modern implants and forthcoming surface modification strategies such as four-dimensional printing, metamaterials, and metasurfaces. This review paper, including traditional and novel surface modification strategies, will pave the way toward designing the next generation of more efficient implants.

Stem Cell-Friendly Scaffold Biomaterials: Applications for Bone Tissue Engineering and Regenerative Medicine

Bone is a dynamic organ with high regenerative potential and provides essential biological functions in the body, such as providing body mobility and protection of internal organs, regulating hematopoietic cell homeostasis, and serving as important mineral reservoir. Bone defects, which can be caused by trauma, cancer and bone disorders, pose formidable public health burdens. Even though autologous bone grafts, allografts, or xenografts have been used clinically, repairing large bone defects remains as a significant clinical challenge. Bone tissue engineering (BTE) emerged as a promising solution to overcome the limitations of autografts and allografts. Ideal bone tissue engineering is to induce bone regeneration through the synergistic integration of biomaterial scaffolds, bone progenitor cells, and bone-forming factors. Successful stem cell-based BTE requires a combination of abundant mesenchymal progenitors with osteogenic potential, suitable biofactors to drive osteogenic differentiation, and cell-friendly scaffold biomaterials. Thus, the crux of BTE lies within the use of cell-friendly biomaterials as scaffolds to overcome extensive bone defects. In this review, we focus on the biocompatibility and cell-friendly features of commonly used scaffold materials, including inorganic compound-based ceramics, natural polymers, synthetic polymers, decellularized extracellular matrix, and in many cases, composite scaffolds using the above existing biomaterials. It is conceivable that combinations of bioactive materials, progenitor cells, growth factors, functionalization techniques, and biomimetic scaffold designs, along with 3D bioprinting technology, will unleash a new era of complex BTE scaffolds tailored to patient-specific applications.

Nanosized-Ag-doped porous β-tricalcium phosphate for biological applications

The treatment of infectious or potentially infective bone defects remains a major problem in clinical practice. Silver has the ability to potentiate antibiotics against resistant bacterial strains. In order to reduce the risk of long-term infections, it is necessary for the biomaterial scaffold to release Ag⁺ in a controlled manner during the entire healing process. In this study, given the antimicrobial characteristics of nanosized Ag (NSAg), we synthesized β-tricalcium phosphate (β-TCP) doped with 5 and 10 wt% NSAg (5 wt% NSAgTCP and 10 wt% NSAgTCP, respectively). The NSAgTCP composites exhibited similar macroporous structures to pure β-TCP. The NSAgTCP samples were examined by scanning electron microscopy at 10,000-times magnification, which revealed that silver was still present at the nanometer scale. X-ray diffraction revealed that silver does not change the crystalline properties of β-TCP. In addition, we observed that the mechanical strength of NSAgTCP increased with increasing amounts of added Ag. The antibacterial, physical, and chemical properties of NSAgTCP were investigated in vitro. We found that NSAgTCP is effective at inhibiting the growth of Staphylococcus aureus and Escherichia coli and is not cytotoxic to human bone marrow mesenchymal stem cells. Moreover, it does not hinder liver or kidney function when tested in vivo. As the bioceramic degrades, Ag ions are slowly released and new bone is formed. No significant cytotoxic effects were observed even when 10 wt% NSAgTCP was used. NSAgTCP has the ability to simultaneously repair bone defects and act as an anti-infective agent; hence, we expect that this material, with its good bone-repairing and anti-infective properties, will find wide spread use as a novel bone substitute.

Electrophoretic Deposition and Characteristics of Chitosan–Nanosilver Composite Coatings on a Nanotubular TiO2 Layer

The surface treatment of titanium implants has been applied mainly to increase surface bioactivity and, more recently, to introduce antibacterial properties. To this end, composite coatings have been investigated, particularly those based on hydroxyapatite. The present research was aimed at the development of another coating type, chitosan–nanosilver, deposited on a Ti13Zr13Nb alloy. The research comprised characterization of the coating’s microstructure and morphology, time-dependent nanosilver dissolution in simulated body fluid, and investigation of the nanomechanical properties of surface coatings composed of chitosan and nanosilver, with or without a surface-active substance, deposited at different voltages for 1 min on a nanotubular TiO2 layer. The microstructure, morphology, topography, and phase composition were examined, and the silver dissolution rate in simulated body fluid, nanoscale mechanical properties, and water contact angle were measured. The voltage value significantly influenced surface roughness. All specimens possessed high biocompatibility. The highest and best adhesion of the coatings was observed in the absence of a surface-active substance. Silver dissolution caused the appearance of silver ions in solution at levels effective against bacteria and below the upper safe limit value.

Electrodeposition of Polysaccharide and Protein Hydrogels for Biomedical Applications

In the last few decades, polysaccharide and protein hydrogels have attracted significant attentions and been applied in various engineering fields. Polysaccharide and protein hydrogels with appealing physical and biological features have been produced to meet different biomedical applications for their excellent properties related to biodegradability, biocompatibility, nontoxicity, and stimuli responsiveness. Numerous methods, such as chemical crosslinking, photo crosslinking, graft polymerization, hydrophobic interaction, polyelectrolyte complexation and electrodeposition have been employed to prepare polysaccharide and protein hydrogels. Electrodeposition is a facile way to produce different polysaccharide and protein hydrogels with the advantages of temporal and spatial controllability. This paper reviews the recent progress in the electrodeposition of different polysaccharide and protein hydrogels. The strategies of pH induced assembly, Ca2+ crosslinking, metal ions induced assembly, oxidation induced assembly derived from electrochemical methods were discussed. Pure, binary blend and ternary blend polysaccharide and protein hydrogels with multiple functionalities prepared by electrodeposition were summarized. In addition, we have reviewed the applications of these hydrogels in drug delivery, tissue engineering and wound dressing.

DDX49 is an RNA helicase that affects translation by regulating mRNA export and the levels of pre-ribosomal RNA

Among the proteins predicted to be a part of the DExD box RNA helicase family, the functions of DDX49 are unknown. Here, we characterize the enzymatic activities and functions of DDX49 by comparing its properties with the well-studied RNA helicase, DDX39B. We find that DDX49 exhibits a robust ATPase and RNA helicase activity, significantly higher than that of DDX39B. DDX49 is required for the efficient export of poly (A)+ RNA from nucleus in a splicing-independent manner. Furthermore, DDX49 is a resident protein of nucleolus and regulates the steady state levels of pre-ribosomal RNA by regulating its transcription and stability. These dual functions of regulating mRNA export and pre-ribosomal RNA levels enable DDX49 to modulate global translation. Phenotypically, DDX49 promotes proliferation and colony forming potential of cells. Strikingly, DDX49 is significantly elevated in diverse cancer types suggesting that the increased abundance of DDX49 has a role in oncogenic transformation of cells. Taken together, this study shows the physiological role of DDX49 in regulating distinct steps of mRNA and pre-ribosomal RNA metabolism and hence translation and potential pathological role of its dysregulation, especially in cancers.

Antimicrobial Nanoparticles Incorporated in Edible Coatings and Films for the Preservation of Fruits and Vegetables

Edible coatings and films (ECF) are employed as matrixes for incorporating antimicrobial nanoparticles (NPs), and then they are applied on the fruits and vegetables to prolong shelf life and enhance storage quality. This paper provides a comprehensive review on the preparation, antimicrobial properties and mechanisms, surface and physical qualities of ECF containing antimicrobial NPs, and its efficient application to vegetables and fruits as well. Following an introduction on the properties of the main edible coating materials, the preparation technologies of ECF with NPs are summarized. The antimicrobial activity of ECF with NPs against the tested microorganism was observed by many researchers. This might be mainly due to the electrostatic interaction between the cationic polymer or free metal ions and the charged cell membrane, the photocatalytic reaction of NPs, the detachment of free metal ion, and partly due to the antimicrobial activity of edible materials. Moreover, their physical, mechanical and releasing properties are discussed in detail, which might be influenced by the concentration of NPs. The preservation potential on the quality of fruits and vegetables indicates that various ECF with NPs might be used as the ideal materials for food application. Following the introduction on these characteristics, an attempt is made to predict future trends in this field.

Structural and bio-mineralization features of alumina zirconia composite influenced by the combined Ca2+ and PO43- additions

The structural and bioactivity features of alumina zirconia composite (AZC) due to Ca²⁺ and PO₄^3- additions are demonstrated. An in situ synthetic approach, starting from the solution precursors is devised for the powder synthesis in which the assorted range of Ca²⁺ and PO₄^3- additions were done to the equimolar concentrations of Al³⁺ and Zr⁴⁺ precursors. The results witnessed the unique crystallization of tetragonal zirconia (t-ZrO₂) at 1100 °C while Ca²⁺, PO₄^3- and Al₂O₃ remained in their amorphous state in the system. On further heat treatment, α-Al₂O₃ crystallized at 1200 °C, which enforced t- → m-ZrO₂ transformation while Ca²⁺ and PO₄^3- still retained their amorphous state. The immersion tests in simulated body fluid (SBF) solution validated the enhanced bio-mineralization activity of AZC due to Ca²⁺ and PO₄^3- additions. The results from the indentation tests demonstrated good uniformity in the elastic modulus and hardness data of the investigated specimens. Further, in vitro cell culture tests ascertained the bioactivity of all the AZC compositions.

Design and structural investigations of Yb3+ substituted β-Ca3(PO4)2 contrast agents for bimodal NIR luminescence and X-ray CT imaging

The quest for the development of bone substitutes with contrast agents for diagnostic imaging subsists to distinguish synthetic bone from native human tissue. To this aim, ytterbium (Yb³⁺) substitutions in β-tricalcium phosphate (β-Ca₃(PO₄)₂, β-TCP) as contrast agents has been developed to differentiate implant materials thereby, facilitating as host for bimodal imaging application by means of NIR luminescence and X-ray computed tomography techniques. A facile aqueous chemical precipitation route with the aid of surfactant is used for the synthesis of Yb³⁺ substitutions in β-Ca₃(PO₄)₂. The characterization results affirms the ability of β-Ca₃(PO₄)₂ to host 4.36 mol% of Yb³⁺ while the excess Yb³⁺ crystallizes as YbPO₄. The structure refinement results favour the occupancy of Yb³⁺ at the Ca²⁺(5) site of β-Ca₃(PO₄)₂. The absorption and photoluminescence spectra in the near infrared region with emission intensity ~1024 nm in the second biological window correspond to ²F_5/2 → ²F_7/2 transitions of Yb³⁺. The designed Yb³⁺ substituted β-Ca₃(PO₄)₂ does not exhibit any toxicity in human osteosarcoma cell lines and delivers an excellent in vitro CT contrast ability allied by the enhanced signal intensity and high X-ray absorption coefficient.

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.

A facile sol-gel synthesis of low-fusing titanium opaque porcelain using borate-silicate system and its bioactivity

The titanium opaque porcelain was synthesized through sol-gel using borate-silicate system. The porcelain was characterized by DSC-TG, X-ray diffraction, N₂ adsorption-desorption isotherms and scanning electron microscope tests. The results of DSC showed that the nitrates could be decomposed completely when the bioglass xerogel precursor was heat-treated at 760 ℃. The XRD results showed that the Na₂Ca₃Si₆O₁₆ was the major phase of the opaque porcelain. The synthesized opaque porcelain powders had an average particle size of about 5-25 µm with nanopores of around 50-70 nm on the surface. The BET average surface area of the porcelain was 12.67 m²/g, while the average pore diameters for adsorption and desorption were 9.73 and 10.16 nm, respectively. The flexure strength significantly increased from 47.4 MPa to 116.2 MPa with the sintering temperature increasing from 575 ℃ to 600 ℃. The XRD, FTIR and EDS results proved that hydroxyapatite had formed on the porcelain surface after incubation in simulated body fluid.

Iron doped β-Tricalcium phosphate: Synthesis, characterization, hyperthermia effect, biocompatibility and mechanical evaluation

The ability of β-Tricalcium phosphate [β-TCP, β-Ca₃(PO₄)₂] to host iron at its structural lattice and its associated magnetic susceptibility, hyperthermia effect, biocompatibility and mechanical characteristics is investigated. The studies revealed the ability of β-Ca₃(PO₄)₂ to host 5.02mol% of Fe³⁺ at its Ca²⁺(5) site. Excess Fe³⁺ additions led to the formation of trigonal Ca₉Fe(PO₄)₇ and moreover a minor amount of CaFe₃(PO₄)₃O crystallization was also observed. A gradual increment in the iron content at β-Ca₃(PO₄)₂ results in the simultaneous effect of pronounced hyperthermia effect and mechanical stability. However, the presence of CaFe₃(PO₄)₃O contributes for the reduced hyperthermia effect and mechanical stability of iron substituted β-Ca₃(PO₄)₂. Haemolytic tests, cytotoxicity tests and ALP gene expression analysis confirmed the biocompatibility of the investigated systems.

Pellino-1 derived cationic antimicrobial prawn peptide: Bactericidal activity, toxicity and mode of action

The antimicrobial peptides (AMPs) are multifunctional molecules which represent significant roles in the innate immune system. These molecules have been well known for decades because of their role as natural antibiotics in both invertebrates and vertebrates. The development of multiple drug resistance against conventional antibiotics brought a greater focus on AMPs in recent years. The cationic peptides, in particular, proven as host defense peptides and are considered as effectors of innate immunity. Among the various innate immune molecules, functions of pellino-1 (Peli-1) have been recently studied for its remarkable role in specific immune functions. In our study, we have identified Peli-1 from the cDNA library of freshwater prawn Macrobrachium rosenbergii (Mr) and analyzed its features using various in-silico methods. Real time PCR analysis showed an induced expression of MrPeli-1 during white spot syndrome virus (WSSV), bacteria (Vibrio harveyi) and lipopolysaccharide (LPS) from Escherichia coli challenge. Also, a cationic AMP named MrDN was derived from MrPeli-1 protein sequence and its activity was confirmed against various pathogenic bacteria. The mode of action of MrDN was determined to be its membrane permeabilization ability against Bacillus cereus ATCC 2106 as well as its DNA binding ability. Further, scanning electron microscopic (SEM) images showed the membrane disruption and leakage of cellular components of B. cereus cells induced by MrDN. The toxicity of MrDN against normal cells (HEK293 cells) was demonstrated by MTT and hemolysis assays. Overall, the results demonstrated the innate immune function of MrPeli-1 with a potential cationic AMP in prawn.

Substitutional limit of gadolinium in β-tricalcium phosphate and its magnetic resonance imaging characteristics

To compensate the limitations of bone tissue magnetic resonance imaging (MRI), a series of gadolinium (Gd³⁺ ) substituted β-Tricalcium phosphate [β-TCP, β-Ca₃ (PO₄ )₂ ] were developed. All the powders were characterized using XRD, Raman spectroscopy, Rietveld refinement of the XRD data and the studies confirmed the Gd³⁺ occupancy at Ca²⁺ (1), Ca²⁺ (2) and Ca²⁺ (3) lattice sites of β-Ca₃ (PO₄ )_2. HR-TEM analysis revealed the spherical nature of particles with diameter about 100 nm. The Gd³⁺ doped β-Ca₃ (PO₄ )₂ exhibited non-toxic behaviour to MG-63 cells in vitro and the room temperature magnetic field versus magnetization measurements confirmed its paramagnetic behaviour. MRI analysis revelas that it shorten both T₁ and T₂ proton relaxation times, thus influencing both r₁ and r₂ relaxivity values that reach 61.97 mM^-1 s^-1 and 73.35 mM^-1 s^-1 . © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2545-2552, 2017.