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Molecules (Basel, Switzerland) Jan 2019Catalytic transfer hydrogenation reactions, based on hydrogen sources other than gaseous H₂, are important processes that are preferential in both laboratories and... (Review)
Review
Catalytic transfer hydrogenation reactions, based on hydrogen sources other than gaseous H₂, are important processes that are preferential in both laboratories and factories. However, harsh conditions, such as high temperature, are usually required for most transition-metal catalytic and organocatalytic systems. Moreover, non-volatile hydrogen donors such as dihydropyridinedicarboxylate and formic acid are often required in these processes which increase the difficulty in separating products and lowered the whole atom economy. Recently, TiO₂ photocatalysis provides mild and facile access for transfer hydrogenation of C=C, C=O, N=O and C-X bonds by using volatile alcohols and amines as hydrogen sources. Upon light excitation, TiO₂ photo-induced holes have the ability to oxidatively take two hydrogen atoms off alcohols and amines under room temperature. Simultaneously, photo-induced conduction band electrons would combine with these two hydrogen atoms and smoothly hydrogenate multiple bonds and/or C-X bonds. It is heartening that practices and principles in the transfer hydrogenations of substrates containing C=C, C=O, N=O and C-X bond based on TiO₂ photocatalysis have overcome a lot of the traditional thermocatalysis' limitations and flaws which usually originate from high temperature operations. In this review, we will introduce the recent paragon examples of TiO₂ photocatalytic transfer hydrogenations used in (1) C=C and C≡C (2) C=O and C=N (3) N=O substrates and in-depth discuss basic principle, status, challenges and future directions of transfer hydrogenation mediated by TiO₂ photocatalysis.
Topics: Catalysis; Hydrogenation; Light; Titanium
PubMed: 30658472
DOI: 10.3390/molecules24020330 -
Journal of Applied Biomaterials &... Jan 2018Titanium is well known as one of the most corrosion-resistant metals. However, it can suffer corrosion attacks in some specific aggressive conditions. To further... (Review)
Review
Titanium is well known as one of the most corrosion-resistant metals. However, it can suffer corrosion attacks in some specific aggressive conditions. To further increase its corrosion resistance, it is possible either to modify its surface, tuning either thickness, composition, morphology or structure of the oxide that spontaneously forms on the metal, or to modify its bulk composition. Part 2 of this review is dedicated to the corrosion of titanium and focuses on possible titanium treatments that can increase corrosion resistance. Both surface treatments, such as anodization or thermal or chemical oxidation, and bulk treatments, such as alloying, are considered, highlighting the advantages of each technique.
Topics: Alloys; Corrosion; Surface Properties; Titanium
PubMed: 29192718
DOI: 10.5301/jabfm.5000396 -
International Journal of Nanomedicine 2022Titanium implants have been widely applied in dentistry and orthopedics due to their biocompatibility and resistance to mechanical fatigue. TiO nanotube arrays (TiO... (Review)
Review
Titanium implants have been widely applied in dentistry and orthopedics due to their biocompatibility and resistance to mechanical fatigue. TiO nanotube arrays (TiO NTAs) on titanium implant surfaces have exhibited excellent biocompatibility, bioactivity, and adjustability, which can significantly promote osseointegration and participate in its entire path. In this review, to give a comprehensive understanding of the osseointegration process, four stages have been divided according to pivotal biological processes, including protein adsorption, inflammatory cell adhesion/inflammatory response, additional relevant cell adhesion and angiogenesis/osteogenesis. The impact of TiO NTAs on osseointegration is clarified in detail from the four stages. The nanotubular layer can manipulate the quantity, the species and the conformation of adsorbed protein. For inflammatory cells adhesion and inflammatory response, TiO NTAs improve macrophage adhesion on the surface and induce M2-polarization. TiO NTAs also facilitate the repairment-related cells adhesion and filopodia formation for additional relevant cells adhesion. In the angiogenesis and osteogenesis stage, TiO NTAs show the ability to induce osteogenic differentiation and the potential for blood vessel formation. In the end, we propose the multi-dimensional regulation of TiO NTAs on titanium implants to achieve highly efficient manipulation of osseointegration, which may provide views on the rational design and development of titanium implants.
Topics: Adsorption; Osseointegration; Osteogenesis; Surface Properties; Titanium
PubMed: 35518451
DOI: 10.2147/IJN.S362720 -
Molecules (Basel, Switzerland) Jul 2020The 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...
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.
Topics: Animals; Cell Adhesion; Cell Differentiation; Coated Materials, Biocompatible; Femur; Implants, Experimental; Male; Materials Testing; Osteoblasts; Osteogenesis; Random Allocation; Rats; Rats, Sprague-Dawley; Sheep; Titanium
PubMed: 32727093
DOI: 10.3390/molecules25153399 -
Regulatory Toxicology and Pharmacology... Dec 2022Titanium dioxide is a ubiquitous white material found in a diverse range of products from foods to sunscreens, as a pigment and thickener, amongst other uses. Titanium... (Review)
Review
Titanium dioxide is a ubiquitous white material found in a diverse range of products from foods to sunscreens, as a pigment and thickener, amongst other uses. Titanium dioxide has been considered no longer safe for use in foods (nano and microparticles of E171) by the European Food Safety Authority (EFSA) due to concerns over genotoxicity. There are however, conflicting opinions regarding the safety of Titanium dioxide. In an attempt to clarify the situation, a comprehensive weight of evidence (WoE) assessment of the genotoxicity of titanium dioxide based on the available data was performed. A total of 192 datasets for endpoints and test systems considered the most relevant for identifying mutagenic and carcinogenic potential were reviewed and discussed for both reliability and relevance (by weight of evidence) and in the context of whether the physico-chemical properties of the particles had been characterised. The view of an independent panel of experts was that, of the 192 datasets identified, only 34 met the reliability and quality criteria for being most relevant in the evaluation of genotoxicity. Of these, 10 were positive (i.e. reported evidence that titanium dioxide was genotoxic), all of which were from studies of DNA strand breakage (comet assay) or chromosome damage (micronucleus or chromosome aberration assays). All the positive findings were associated with high cytotoxicity, oxidative stress, inflammation, apoptosis, necrosis, or combinations of these. Considering that DNA and chromosome breakage can be secondary to physiological stress, it is highly likely that the observed genotoxic effects of titanium dioxide, including those with nanoparticles, are secondary to physiological stress. Consistent with this finding, there were no positive results from the in vitro and in vivo gene mutation studies evaluated, although it should be noted that to definitively conclude a lack of mutagenicity, more robust in vitro and in vivo gene mutation studies would be useful. Existing evidence does not therefore support a direct DNA damaging mechanism for titanium dioxide (nano and other forms).
Topics: Reproducibility of Results; Metal Nanoparticles; Titanium; Comet Assay; DNA Damage; Mutagens; DNA
PubMed: 36228836
DOI: 10.1016/j.yrtph.2022.105263 -
Nanotheranostics 2021Titanium is considered to be a metal material with the best biological safety. Studies have proved that the titanium implanted in the bone continuously releases titanium... (Review)
Review
Titanium is considered to be a metal material with the best biological safety. Studies have proved that the titanium implanted in the bone continuously releases titanium particles (Ti particles), significantly increasing the total titanium content in human body. Generally, Ti particles are released slowly without causing a systemic immune response. However, the continuous increased local concentration may result in damage to the intraepithelial homeostasis, aggravation of inflammatory reaction in the surrounding tissues, bone resorption and implant detachment. They also migrate with blood flow and aggregate in the distal organ. The release of Ti particles is affected by the score of the implant surface structure, microenvironment wear and corrosion, medical operation wear, and so on, but the specific mechanism is not clear. Thus, it difficult to prevent the release completely. This paper reviews the causes of the Ti particles formation, the damage to the surrounding tissue, and its mechanism, in particular, methods for reducing the release and toxicity of the Ti particles.
Topics: Corrosion; Dental Implants; Humans; Inflammation; Surface Properties; Titanium
PubMed: 33732603
DOI: 10.7150/ntno.56401 -
Scientific Reports Mar 2022Titanium alloys, in particular, medical-grade Ti-6Al-4 V, are heavily used in orthopaedic applications due to their high moduli, strength, and biocompatibility. Implant...
Titanium alloys, in particular, medical-grade Ti-6Al-4 V, are heavily used in orthopaedic applications due to their high moduli, strength, and biocompatibility. Implant infection can result in biofilm formation and failure of prosthesis. The formation of a biofilm on implants protects bacteria from antibiotics and the immune response, resulting in the propagation of the infection and ultimately resulting in device failure. Recently, slippery liquid-infused surfaces (LIS) have been investigated for their stable liquid interface, which provides excellent repellent properties to suppress biofilm formation. One of the current limitations of LIS coatings lies in the indistinctive repellency of bone cells in orthopaedic applications, resulting in poor tissue integration and bone ingrowth with the implant. Here, we report a chitosan impregnated LIS coating that facilitates cell adhesion while preventing biofilm formation. The fabricated coating displayed high contact angles (108.2 ± 5.2°) and low sliding angles (3.56 ± 4.3°). Elemental analysis obtained using X-ray photoelectron spectroscopy (XPS) confirmed the availability of fluorine and nitrogen, indicating the presence of fluorosilane and chitosan in the final coating. Furthermore, our results suggest that chitosan-conjugated LIS increased cell adhesion of osteoblast-like SaOS-2 cells and significantly promoted proliferation (a fourfold increase at 7-day incubation) compared to conventional titanium liquid-infused surfaces. Furthermore, the chitosan conjugated LIS significantly reduced biofilm formation of methicillin-resistant Staphylococcus aureus (MRSA) by up to 50% and 75% when compared to untreated titanium and chitosan-coated titanium, respectively. The engineered coating can be easily modified with other biopolymers or capture molecules to be applied to other biomaterials where tissue integration and biofilm prevention are needed.
Topics: Bacteria; Biofilms; Chitosan; Methicillin-Resistant Staphylococcus aureus; Osseointegration; Surface Properties; Titanium
PubMed: 35354896
DOI: 10.1038/s41598-022-09378-4 -
International Journal of Nanomedicine 2022The nanostructural modification of the oral implant surface can effectively mimic the morphology of natural bone tissue, allowing osteoblasts to achieve both...
INTRODUCTION
The nanostructural modification of the oral implant surface can effectively mimic the morphology of natural bone tissue, allowing osteoblasts to achieve both proliferation and differentiation capabilities at the bone interface of the dental implant. To improve the osteoinductive activity on the surface of titanium implants for rapid osseointegration, we prepared a novel composite coating (MAO-PDA-NC) by micro-arc oxidation technique and immersion method and evaluated the proliferation, adhesion, and osteogenic differentiation of osteoblasts on this coating.
METHODS
The coatings were prepared by micro-arc oxidation (MAO) technique and immersion method, and characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM) for different coatings; the loading of PDA was examined using Fourier transform infrared spectroscopy (FTIR); the ion release capacity of the coatings was determined by inductively coupled plasma emission spectrometry (ICP-OES); the interfacial bonding of the coatings was examined using nanoscratch experiment strength. The cytotoxicity of the coating was examined by live/dead staining kit; cell proliferation viability was examined by CCK-8 kit; adhesion and osteogenic effect of the coating were examined by immunofluorescence staining and RT-PCR; osteogenic differentiation was examined by alkaline phosphatase staining.
RESULTS
The surface morphology of titanium implants was modified by micro-arc oxidation technology, and a new MAO-PDA-NC composite coating was successfully prepared. The results showed that the MAO-PDA-NC coating not only optimized the physical and chemical properties of the titanium implant surface but also significantly stimulated the biological properties of osteoblast adhesion, proliferation, and osteogenic differentiation on the coating surface.
CONCLUSION
These results show that MAO-PDA-NC composite coating can significantly improve the surface properties of titanium implants and achieve a stable bond between implant and bone tissue, thus accelerating early osseointegration.
Topics: Alkaline Phosphatase; Cell Adhesion; Cell Differentiation; Coated Materials, Biocompatible; Dental Implants; Indoles; Osseointegration; Osteogenesis; Oxides; Polymers; Sincalide; Surface Properties; Titanium
PubMed: 36246934
DOI: 10.2147/IJN.S378387 -
Histochemistry and Cell Biology Jul 2019Dental implant material has an impact on adhesion and spreading of oral mucosal cells on its surface. Platelet-rich fibrin (PRF), a second-generation platelet...
Dental implant material has an impact on adhesion and spreading of oral mucosal cells on its surface. Platelet-rich fibrin (PRF), a second-generation platelet concentrate, can enhance cell proliferation and adhesion. The aim was to examine the regulatory effects of PRF and titanium surfaces on cellular adhesion, spread, and cytokine expressions of gingival keratinocytes. Human gingival keratinocytes were cultured on titanium grade 4, titanium grade 5 (Ti5), and HA discs at 37 °C in a CO2 incubator for 6 h and 24 h, using either elutes of titanium-PRF (T-PRF) or leukocyte and platelet-rich fibrin (L-PRF), or mammalian cell culture medium as growth media. Cell numbers were determined using a Cell Titer 96 assay. Interleukin (IL)-1β, IL-1Ra, IL-8, monocyte chemoattractant protein (MCP)-1, and vascular endothelial growth factor (VEGF) expression levels were measured using the Luminex xMAP™ technique, and cell adhesion and spread by scanning electron microscopy. Epithelial cell adhesion and spread was most prominent to Ti5 surfaces. L-PRF stimulated cell adhesion to HA surface. Both T-PRF and L-PRF activated the expressions of IL-1 β, IL-8, IL-1Ra, MCP-1, and VEGF, T-PRF being the strongest activator. Titanium surface type has a regulatory role in epithelial cell adhesion and spread, while PRF type determines the cytokine response.
Topics: Cell Adhesion; Cells, Cultured; Cytokines; Gingiva; Healthy Volunteers; Humans; Keratinocytes; Platelet-Rich Fibrin; Surface Properties; Titanium
PubMed: 30767049
DOI: 10.1007/s00418-019-01774-8 -
International Journal of Molecular... Jul 2022TiO has aroused considerable attentions as a promising photocatalytic material for decades due to its superior material properties in several fields such as energy and... (Review)
Review
TiO has aroused considerable attentions as a promising photocatalytic material for decades due to its superior material properties in several fields such as energy and environment. However, the main dilemmas are its wide bandgap (3-3.2 eV), that restricts the light absorption in limited light wavelength region, and the comparatively high charge carrier recombination rate of TiO, is a hurdle for efficient photocatalytic CO conversion. To tackle these problems, lots of researches have been implemented relating to structural and material modification to improve their material, optical, and electrical properties for more efficient photocatalytic CO conversion. Recent studies illustrate that crystal facet engineering could broaden the performance of the photocatalysts. As same as for nanostructures which have advantages such as improved light absorption, high surface area, directional charge transport, and efficient charge separation. Moreover, strategies such as doping, junction formation, and hydrogenation have resulted in a promoted photocatalytic performance. Such strategies can markedly change the electronic structure that lies behind the enhancement of the solar spectrum harnessing. In this review, we summarize the works that have been carried out for the enhancement of photocatalytic CO conversion by material and structural modification of TiO and TiO-based photocatalytic system. Moreover, we discuss several strategies for synthesis and design of TiO photocatalysts for efficient CO conversion by nanostructure, structure design of photocatalysts, and material modification.
Topics: Carbon Dioxide; Catalysis; Nanostructures; Titanium
PubMed: 35897719
DOI: 10.3390/ijms23158143