Mesenchymal stem cell interaction with Ti6Al4V alloy pre-exposed to simulated body fluid

Titanium and its alloys are widely used for substitution of hard tissues, especially in orthopaedic and dental surgery. Despite the benefit of the use of titanium for such applications, there are still questions which must be sorted out. Surface properties are crucial for cell adhesion, proliferation and differentiation. Mainly, micro/nanostructured surfaces positively influence osteogenic differentiation of human mesenchymal stem cells. Ti₆Al₄V is a biocompatible α + β alloy which is widely used in orthopaedics. The aim of this study was to investigate the interaction of the nanostructured and ground Ti₆Al₄V titanium alloys with simulated body fluid complemented by the defined precipitation of hydroxyapatite-like coating and to study the cytotoxicity and differentiation capacity of cells with such a modified titanium alloy. Nanostructures were fabricated using electrochemical oxidation. Human mesenchymal stem cells (hMSC) were used to evaluate cell adhesion, metabolic activity and proliferation on the specimens. The differentiation potential of the samples was investigated using PCR and specific staining of osteogenic markers collagen type I and osteocalcin. Our results demonstrate that both pure Ti₆Al₄V, nanostructured samples, and hydroxyapatite-like coating supported hMSC growth and metabolic activity. Nanostructured samples improved collagen type I synthesis after 14 days, while both nanostructured and hydroxyapatite-like coated samples enhanced collagen synthesis on day 21. Osteocalcin synthesis was the most enhanced by hydroxyapatite-like coating on the nanostructured surfaces. Our results indicate that hydroxyapatite-like coating is a useful tool guiding hMSC osteogenic differentiation.

Titanium and its alloys are widely used for substitution of hard tissues, especially in orthopaedic and dental surgery.     

Novel fabrication of porous titanium by a resin-impregnated titanium substitution technique for bone reconstruction

The purpose of this study was to develop a novel porous titanium material with superior mechanical strength and osteoconduction for bone reconstruction. Porous titanium samples were fabricated by titanium-slurry impregnate to prepare urethane forms with several porosities (high-porosity; 92%, middle-porosity; 85% and low-porosity; 65%). Porous HA (mean porosity; 75.3%) was used as a control. To evaluate the characteristics of these materials, we performed porosity measurements, scanning electron microscopy (SEM), three-point bending testing, and cell proliferation assays. To evaluate the osteoconduction ability, porous titanium was placed into the femurs of rabbits and histological and histomorphometric evaluations were performed after 3 weeks. In SEM images, porous three-dimensional structures were observed in all samples. The bending strength significantly increased as porosity increased (Ti-65 > Ti-85 > porous HA > Ti-92, P < 0.05; respectively). Ti-65, Ti-85, and porous HA showed good cell proliferation. Newly formed bone was observed in the central portion of Ti-65, Ti-85, and porous HA. Ti-92 was mainly detected in the bone marrow tissue. The bone formation areas of Ti-65, Ti-85, and porous HA were significantly higher than that of Ti-92 (P < 0.05). It was suggested that novel developed porous titanium composed of Ti-65 and Ti-85 showed superior mechanical strength and osteoconduction.

The purpose of this study was to evaluate the characteristic structures and osteoconduction ability of porous titanium structures using a resin-impregnated titanium substitution fabrication technique.     

One-step electrosynthesis of visible light responsive double-walled alloy titanium dioxide nanotube arrays for use in photocatalytic degradation of dibutyl phthalate

Using Ti-6Al-4V (TC4) alloy as a substrate, double-walled alloy titanium dioxide nanotube arrays (DW-ATNTAs) with a special porous inner wall and visible light response are synthesized in situ by an improved anodization method. During the anodization, the V element in the TC4 alloy converts into V₂O₅ which dominates the visible light response of DW-ATNTAs. After 3 h of irradiation with visible light, there is a nearly 97% reduction of dibutyl phthalate (DBP) by DW-ATNTAs in which the degradation kinetic constant is 50 and 7 times higher than that of titanium dioxide nanotube arrays (TNTAs) and alloy titanium dioxide layers (A-TiO₂(plate)), respectively. The richly porous inner wall structure of DW-ATNTAs can provide sufficient vacancies for adsorption and active sites for photocatalytic reaction. Furthermore, the differences in the morphology of the inner and outer walls are attributed to the thicker carbon and fluorine-rich oxide layer (C, F-rich oxide layer) resulting from a longer time that the inner wall spends in contact with the electrolyte during the anodization process. This special porous inner wall structure was formed due to the anti-corrosion properties of the alloy caused by appropriate amounts of V and Al as well as the removal of C and F elements during the calcination process.

The double-walled alloy titanium dioxide nanotube arrays (DW-ATNTAs) with special porous inner walls exhibit superior photocatalytic activity under visible light for rich porous inner wall provided sufficient vacancy for adsorption and active sites.     

Bioactive calcium silicate ceramics and coatings

CaO–SiO₂ based ceramics have been regarded as potential candidates for artificial bone due to their excellent bone bioactivity and biocompatibility. However, they cannot be used as implants under a heavy load because of their poor mechanical properties, in particular low fracture toughness. Plasma spraying CaO–SiO₂ based ceramic coatings onto titanium alloys can expand their application to the hard tissue replacement under a heavy load. Plasma sprayed wollastonite, dicalcium silicate and diopside coatings have excellent bone bioactivity and high bonding strength to titanium alloys. It is possible that these plasma sprayed CaO–SiO₂ based ceramic coatings will be applied in clinic after they are widely and systematically researched.     

医用钛合金在3种不同生理电解液中的耐腐蚀行为

背景:钛合金种植体已经广泛应用于临床,但作者所查对于牙种植体植入后的耐腐蚀性,尤其在不同生理电解溶液中耐腐蚀行为的对比报道很少.目的:对比观察医用钛合金在生理盐水,模拟人工唾液,模拟人工体液3种电解溶液中的耐腐蚀情况.设计、时间及地点:随机分组设计,对比观察实验,于2008-11/2009-03在兰州大学口腔医学院和中国科学院兰州化学物理研究所固体润滑实验室完成.材料:医用钛合金(Ti-6Al-4V)制备成10mm×10mm×1 mm板片,随机分为3组,每组10个.方法:利用电化学方法分析医用钛合金在生理盐水,模拟人工唾液,模拟人工体液中的腐蚀情况,扫面电镜观察腐蚀表面形貌,CA-A型接触角测试仪测试钛合金表面被腐蚀后接触角的变化.主要观察指标:医用钛合金在3种生理电解液中腐蚀4 d后的阳极极化曲线、表面形貌、接触角.结果:钛合金在3种生理电解液中的腐蚀情况依次是:模拟人工唾液>模拟人工体液>生理盐水.扫面电锖观察表明,医用钛合余绎生理盐水腐蚀后,表面出现了许多腐蚀孔,经模拟人体体液腐蚀后,表面变得粗糙不平整,腐蚀孔数目变化不大,钛合金经人工唾液腐蚀后,腐蚀孔数目增多,部分腐蚀孔孔径明显增大.经3种生理电解液腐蚀后,钛合金表面接触角都减小.结论:医用钛合金在人工唾液中的腐蚀最严重,在临床应用中应给予相应的防范措施.     

Solvothermal synthesis and structural characterization of three polyoxotitanium-organic acid clusters

Three new titanium oxo-clusters Ti₄O₂(OⁱPr)₁₀(OOCPhMe)₂ (I), Ti₆O₄(OEt)₈(OOCPhMe)₈ (II) and Ti₆O₆(OEt)₆(OOCCHPh₂)₆ (III) were obtained by easy one-step solvothermal reactions of titanium(iv) isopropoxide, alcohols and carboxylic acids. The three compounds were characterized by single-crystal and powder X-ray diffraction, TGA/DSC, optical and electron microscopy, and FTIR and NMR spectroscopy. X-ray powder diffraction and spectroscopy confirmed the purity of the compounds. Structural analysis indicates that in all compounds the titanium(iv) ions are six-coordinated (distorted octahedra). (I) is a tetranuclear complex containing a Ti₄(μ₄-O)(μ₂-O) core, which is linked by two (μ₂-OOCPhMe), four (μ₂-OⁱPr) and six OⁱPr ligands. (II) and (III) are hexanuclear complexes with different cores, respectively Ti₆(μ₃-O)₂(μ₂-O)₂ and Ti₆(μ₃-O)₆. The coordination sphere of the Ti atoms is filled by eight (μ₂-OOCPhMe), two (μ₂-OEt) and six OEt in (II) and six (μ₂-OOCHPh₂) and six OEt in (III). Different steric hindrance of substituents attached to the carboxyl group or different concentrations lead to three main different cluster geometries with two ligands. The tetranuclear and the hexanuclear clusters were obtained with the OOCPhMe ligand, while the hexagonal prism cluster was obtained with the OOCCHPh₂ ligand. Hirshfeld surface calculations indicated that the packing is driven by C–O⋯H–C weak hydrogen bonds. The clusters can be used as molecular models of organic molecules bonded to titania surface, used in organic photovoltaic (dye sensitized solar cells) or other optoelectronic applications.

Crystal structures of three novel titanium oxo-clusters with different cores and ligands obtained by an easy and convenient solvothermal method.     

An open-label, multicenter study of the combination of amorolfine nail lacquer and oral itraconazole compared with oral itraconazole alone in the treatment of severe toenail onychomycosis

Background: Data indicate that combination therapy may provide enhanced clinical and economic benefits over monotherapy in the treatment of onychomycosis.Objective: The aim of this study was to compare the efficacy of 2 topical amorolfine/oral itraconazole combination regimens with oral itraconazole alone in the treatment of severe toenail onychomycosis. Cost implications of all treatments were assessed in a pilot pharmacoeconomic analysis.Methods: In this multicenter, open-label, 24-week study, patients were randomized to 3 parallel treatment groups: 5% solution of amorolfine nail lacquer applied once weekly for 24 weeks plus itraconazole 200 mg once daily for either 6 weeks (group AI-6) or 12 weeks (group AI-12), or itraconazole alone for 12 weeks (group I-12).Results: Mycologic cure at week 12 was achieved in 93% of patients in group AI-6, 83% in group AI-12, and 41% in group I-12. Combination therapies were significantly more effective than itraconazole monotherapy (P < 0.001). Global assessment (combined measure of mycologic and clinical cure rates) at 24 weeks demonstrated cure rates of 84% for patients in group AI-6, 94% in group AI-12, and 69% in group I-12. The difference between the AI-12 group and the I-12 group was statistically significant (P < 0.05). There were no serious adverse events during the study, and the distribution of adverse events was not significantly different between groups. Pharmacoeconomic assessment demonstrated that both durations of combination therapy were more cost-effective than monotherapy.Conclusions: Our results show that topical amorolfine combined with oral itraconazole was more effective in treating severe toenail onychomycosis than was itraconazole monotherapy. Combination with a short course of oral therapy had a marked pharmacoeconomic advantage over the other regimen, suggesting that switching from the current 12-week itraconazole monotherapy to the 6-week combination therapy would cure more patients for a lower cost.     

An angiotensin I-protein complex isolated by SDS-polyacrylamide gel electrophoresis from rat serum incubated with angiotensin I

Angiotensin I (AI) protein complex with M_r 25,000 and an angiotensin I immunoreactive protein with M_r 60,000 were isolated from rat serum. The proteins were separated from AI by sodiumdodecylsulphate polyacrylamide gel electrophoresis under denaturing and reducing conditions using SDS and 2-mercaptoethanol (SDS-PAGE). The M_r 60,000 protein was isolated from non-incubated serum. Special attention was given to the M_r 25,000 AI-protein complex, called AI-25,000, which was generated in rat serum incubated with both synthetic and native AI for 1–5 h at 24°C and neutral pH. The AI-25,000 was determined in two radioimmunoassays using two anti-AI antisera and ¹²⁵I-AI. The experiments showed that AI reacts with a serum protein and forms a stable complex with a high molecular mass.     

Biocorrosion of pure and SLA titanium surfaces in the presence of Porphyromonas gingivalis and its effects on osteoblast behavior

Objective: The study aims to investigate the biocorrosion behavior of Porphyromonas gingivalis on pure and SLA titanium surfaces and its effects on surface characteristics and osteoblast behavior. Methods: Pure and SLA titanium specimens were immersed in culture medium with P. gingivalis and incubated for 7 days. P. gingivalis colonization on the pure and SLA titanium surfaces was observed by scanning electron microscopy (SEM). The pure and SLA titanium surface characteristics were analyzed via X-ray photoelectron spectroscopy (XPS), surface roughness and surface wettability. The corrosion behaviors of pure and SLA titanium specimens were evaluated by electrochemical corrosion test. The osteoblast behavior of MC3T3-E1 cells on the pure and SLA titanium surfaces after P. gingivalis colonization was investigated by cell adhesion and western blot assays. Results: P. gingivalis colonized on the pure and SLA titanium surfaces was observed by SEM. The XPS analysis demonstrated reductions in the relative levels of titanium and oxygen and obvious reductions of dominant titanium dioxide (TiO₂) on both titanium surfaces after immersing the metal in P. gingivalis culture. In addition, their roughness and wettability were changed. Correspondingly, the electrochemical corrosion test results revealed significant decreases in the corrosion resistance and increases in the corrosion rate of the pure and SLA titanium specimens after immersion in P. gingivalis culture. The results of the in vitro study showed that the pre-corroded pure and SLA titanium surfaces by P. gingivalis exhibited lower osteocompatibility and down-regulated the adhesion, spreading and osteogenic differentiation abilities of MC3T3-E1 cells. Conclusions: P. gingivalis was able to colonize on the pure and SLA titanium surfaces and weaken their surface properties, especially a decrease in the protective TiO₂ film, which induced the biocorrosion and further negatively affected the osteoblast behavior.

The study demonstrated that P. gingivalis could colonize on pure and SLA titanium surfaces and weaken their surface properties, especially the protective TiO₂ film, which induced the biocorrosion and further negatively affected osteoblast behavior.     

Revealing unusual rigid diamond net analogues in superhard titanium carbides

Transition metal carbides (TMCs) are considered to be potential superhard materials and have attracted much attention. With respect to titanium and carbon atoms, we confirm the pressure-composition phase diagram of the Ti–C system using structure searches and first-principles calculations. We firstly discovered stable TiC₄ which was expected to be synthesized at high pressure, as well as metastable TiC₂ and TiC₃. These layered titanium carbides are diamond net analogues due to the unusual C-layers in the form of puckered graphene-like, diamond-like and double diamond-like C-layers. The existence of diamond-like C-layers might help to understand the formation of diamond. All the studied titanium carbides could be recoverable at ambient pressure and exhibited great mechanical properties (strong ability to resist volume and shear deformations, small anisotropy, and high hardness). Moreover, we crystallized the structure of TiC₄ in other transition metal carbides and obtained five superhard TMC₄s (TM = V, Zr, Nb, Hf and Ta). Interactions between layers were revealed to be the source of the great mechanical properties and high hardness through combining detailed analyses of electronic structure and chemical bonding, namely, weak ionic interactions of neighboring Ti- and C-layers and the strong covalent interactions of C- and C-layers.

We found three diamond net analogues in titanium carbides firstly, including hard TiC₂, superhard TiC₃ and TiC₄. Their hardness mainly originates from the strong covalent interactions of diamond-like C-layers.     

Study of 223Ra uptake mechanism on hydroxyapatite and titanium dioxide nanoparticles as a function of pH

The mechanism of ²²³Ra uptake on hydroxyapatite and titanium dioxide nanoparticles was studied as a function of pH. Both materials are widely used in food industry and medicine. They offer properties suitable for labelling with medicinal radionuclides, particularly for targeted radionuclide therapy. The selected isotope, ²²³Ra, is an alpha emitter widely used in targeted alpha particle therapy due to high-dose delivery in very small tissue volume, nevertheless the results are applicable for any radium isotope including ²²⁶Ra. The study was performed in the pH range 4.5 to 12 for hydroxyapatite nanoparticles and 2 to 12 for titanium dioxide nanoparticles in Britton–Robinson buffer solution. Both nanomaterials at pH 6 and higher showed that over 95% of the radium has been sorbed. According to the applied chemical equilibrium model, the most important species playing a role in sorption on the edge-sites were RaCO₃, RaPO₄⁻, RaHPO₄ and Ra(Ac⁻)₂, and Ra²⁺ and RaH₂PO₄⁺ on layer-sites. All experiments were conducted under free air conditions and no negative impact of CO₂ was found. The surface complexation model was found suitable for describing radium uptake by the studied hydroxyapatite and titanium dioxide nanomaterials.

The mechanism of ²²³Ra uptake on hydroxyapatite and titanium dioxide nanoparticles was studied as a function of pH.     

Construction and photocatalytic performance of fluorinated ZnO–TiO2 heterostructure composites

Titanium dioxide, as a promising photocatalytic material, has attracted extensive attention in the field of photocatalytic degradation of organic pollutants in sewage. However, the photocatalytic performance needs to be further improved. In this work, fluorinated ZnO–TiO₂ composites (F-ZTO) were prepared by a simple coprecipitation method. The photocatalytic performance of the samples was studied in detail with methyl orange as the target degradation product. The results indicated that under the same conditions, the degradation rates of 6% F-ZTO, F-TiO₂ and TiO₂ for methyl orange reached 93.75%, 76.56% and 62.89% respectively. This showed that the method used in this work could effectively improve the photocatalytic degradation performance of titanium dioxide. 6% F-ZTO showed an excellent photocatalytic activity, which was attributed to the small grain size, the large specific surface area and the effective inhibition of photoelectron–hole recombination due to fluorination and zinc oxide coupling. In three consecutive cycles, the photocatalytic activity was almost maintained, indicating that 6% F-ZTO had a good recycling performance.

Fluorinated ZnO-TiO₂ composites (F-ZTO) were prepared by a simple coprecipitation method, the method used could effectively improve the photocatalytic property of titanium dioxide, and 6% F-ZTO showed an excellent activity and recycling performance.     

钛合金表面介孔二氧化钛涂层的制备及表征

背景：介孔结构的二氧化钛涂层除了具有一般介孔材料的优点外,还具有很好的生物相容性和独特的抗菌性,并且在钛及钛合金表面很易形成。目的：对介孔诱导型二氧化钛涂层和普通的二氧化钛涂层进行形貌结构分析和比较,为钛合金表面介孔结构二氧化钛涂层在生物医学领域的应用提供实验和理论基础。方法：在Ti-6Al-4V合金表面采用模板法和非模板法制备介孔诱导型二氧化钛涂层和普通二氧化钛涂层,使用场发射扫描电子显微镜、快速比表面积/孔隙分析仪和X射线衍射仪对两种二氧化钛涂层的表面形貌结构进行比较分析。结果与结论：在Ti-6Al-4V合金表面制备的稳定介孔二氧化钛涂层,其平均介孔孔径、比表面积和孔容分别为6.6680nm、124.1906m^2/g和0.256470cm^3/g,具有介孔结构大比表面积和孔容的特点,适合对医用钛及钛合金改性。     

Impact of stem taper damage on the fracture strength of ceramic heads with adapter sleeves

BackgroundUsing a new ceramic head with a titanium adapter sleeve offers the possibility of maintaining a well fixed stem when conducting cup revision of a total hip arthroplasty. The aim of this study is to test the impact of stem taper damage on the fracture strength of sleeved ceramic heads.MethodsPristine zirconia-toughened alumina heads with titanium adapter sleeves (BIOLOX®OPTION System) were tested on damaged Ti-4Al-6V stem tapers in accordance with ISO7206-10. Four distinctive damage types classified as intolerable by the manufacture were investigated, representing various reductions in contact area between the stem taper and sleeve taper as well as damage incurred from previous ceramic head fracture.FindingsThe largest reduction in fracture strength occurred for a loss of contact for the entire length of the stem taper. Nonetheless, the fracture strength in all investigated cases was several times higher than that defined by the FDA standards.InterpretationThe use of a titanium sleeve recreates a uniform contact situation between the ceramic head and the outer sleeve taper in situations of damaged stem tapers. For the investigated damage types a high fracture strength of the ceramic head was maintained. This study supports the clinical use for sleeved ceramic heads in instances of greater damages of stem tapers than previously defined in order to spare patients from stem removal.     

Vancomycin-loaded titanium coatings with an interconnected micro-patterned structure for prophylaxis of infections: an in vivo study

Titanium (Ti) and its alloys are widely applied as orthopedic implants for hip and knee prostheses, fixation, and dental implants. However, Ti and its alloys are bioinert and susceptible to bacteria and biofilm formation. Thus, surface biofunctionalisation of Ti is essential for improving the biofunction of Ti. The current in vitro study indicated that calcium phosphate bone cement with vancomycin doped on micro-patterned Ti with a grid-like structure surface could preserve the property of inhibition of bacterial adhesion and biofilm formation while not affecting the osteogenic differentiation. The present study investigated whether the biological performance of the bactericidal effect is preserved in vivo. The rabbit osteomyelitis model with tibial medullary cavity placement of Ti rods was employed to analyze the antibacterial effect of vancomycin-loaded Ti coatings with interconnected micro-patterned structure (TV). Thirty female rabbits (N = 10) were used to establish the implant-associated infection. Prior to implanting the T0 and TV rods into the medullary cavity of the left tibia of the rabbits, 10⁶ CFU mL⁻¹ methicillin-resistant Staphylococcus aureus (MRSA) was injected into the medullary cavity of the left tibia of the rabbits. The sterile Ti rod (NT) was used as the blank control. After 3 weeks, bone pathology was evaluated using X-ray and micro-CT. The in vivo study proposed that TV has the potential for prophylaxis against MRSA infection. Thus, the interconnected micro-patterned structured Ti rods loaded with vancomycin could be applied for preventing Ti implant-associated infections.

Vancomycin-loaded titanium coatings with an interconnected micro-patterned structure for prophylaxis of titanium implant associated infection.     

Structure and mechanical behavior of in situ developed Mg2Si phase in magnesium and aluminum alloys – a review

The demand for lightweight, high specific strength alloys has drastically increased in the last two decades. Magnesium and aluminum alloys are very suitable candidate materials. Research on alloys with an Mg₂Si phase started about three decades ago. The current scenario is that magnesium and aluminum alloys containing an Mg₂Si phase are very popular in the scientific community and extensively used in the automotive and aerospace industries. Mg₂Si is a very stable phase and exhibits excellent mechanical, thermal, electrochemical and tribological properties. This paper presents a brief review of Mg–Si binary alloys, and Mg–Si–Al and Al–Si–Mg alloys. Grain refinement methods and mechanical properties have been reported on lightweight alloys containing Mg and Si. The available results show that silicon reacts with magnesium and forms an intermetallic compound with the stoichiometric formula Mg₂Si. There is in situ formation of an Mg₂Si phase in Mg–Si, Mg–Si–Al and Al–Mg–Si alloys by the diffusion or precipitation process. The morphology and size of an in situ developed Mg₂Si phase depend on the synthesis route and base metal or matrix. In the liquid metallurgy process the precipitation sequence depends on the cooling rate. The morphology of the Mg₂Si phase depends on the precipitation sequence and the mechanical properties depend on the morphology and size of the Mg₂Si phase within the alloy matrix.

The demand for lightweight, high specific strength alloys has drastically increased in the last two decades.     

Synthesis,characterization and olefin polymerization behaviors of phenylene-bridged bis-β-carbonylenamine binuclear titanium complexes

Binuclear and multinuclear complexes have attracted much attention due to their unique catalytic performances for olefin polymerization compared with their mononuclear counterparts. In this work, a series of phenyl-bridged bis-β-carbonylenamine [O⁻NS^R] (R = alkyl or phenyl) tridentate ligands and their binuclear titanium complexes (Ti²L₁–Ti²L₅) were synthesized and characterized by ¹H NMR, ¹³C NMR, FTIR and elemental analysis. The molecular structure of ligand L₂ (R = ⁿPr) and its corresponding Ti complex Ti²L₂ were further investigated by single-crystal X-ray diffraction, which showed that each titanium coordinated with six atoms to form a distorted octahedral configuration along with the conversion of the ligand from β-carbonylenamine to β-imino enol form. Under the activation of MMAO, these complexes catalyzed ethylene polymerization and ethylene/α-olefin copolymerization with extremely high activity (over 10⁶ g mol (Ti)⁻¹ h⁻¹ atm⁻¹) to produce high molecular weight polyethylene. At the same time, wider polydispersity as compared with the mononuclear counterpart TiL₆ was observed, indicating that two active catalytic centers may be present, consistent with the asymmetrical crystal structure of the binuclear titanium complex. Furthermore, these complexes possessed better thermal stability than their mononuclear analogues. Compared with the complexes bearing alkylthio sidearms, the complex Ti²L₅ bearing a phenylthio sidearm exhibited higher catalytic activity towards ethylene polymerization and produced polyethylene with much higher molecular weight, but with an appreciably lower 1-hexene incorporation ratio. Nevertheless, these bis-β-carbonylenamine-derived binuclear titanium complexes showed much higher ethylene/1-hexene copolymerization activity and 1-hexene incorporation ratios as compared with the methylene-bridged bis-salicylaldiminato binuclear titanium complexes, and the molecular weight and 1-hexene incorporation ratio could be flexibly tuned by the initial feed of α-olefin commoners and catalyst structures.

Phenyl-bridged bis-β-carbonylenamine binuclear titanium complexes were synthesized, characterized and used to catalyze ethylene (co)polymerization with extremely high activity.     

AI-2/LuxS Is Involved in Increased Biofilm Formation by Streptococcus intermedius in the Presence of Antibiotics

Bacteria utilize quorum-sensing communication to organize their behavior by monitoring the concentration of bacterial signals, referred to as autoinducers (AIs). The widespread detection of AI-2 signals and its enzymatic synthase (LuxS) in bacteria suggests that AI-2 is an inter- and intraspecies communication signal. We have previously shown that antibiotic susceptibility is affected by AI-2 signaling in Streptococcus anginosus. Since chronic infections involve persistent biofilms resilient to antibiotic treatment, we explored the role of AI-2/LuxS in Streptococcus intermedius biofilm formation and cell viability when the organism was exposed to sub-MICs of ampicillin, ciprofloxacin, or tetracycline. The S. intermedius wild type (WT) and its isogenic luxS mutant, strain SI006, were exposed to sub-MICs of ampicillin, ciprofloxacin, or tetracycline. Biofilms were formed on polystyrene discs in microtiter plates. To assess planktonic cell viability, the ATP microbial viability assay was performed and the numbers of CFU were determined. For complementation assays, the AI-2 precursor dihydroxy pentanedione (DPD) was used as a supplement for SI006. Relative luxS expression was quantified by real-time PCR. The sub-MICs of all three antibiotics increased biofilm formation in S. intermedius WT. However, biofilm formation by SI006 was either unaffected or reduced (P ≤ 0.05). Bacterial viability tests of biofilm and planktonic cell cultures indicated that SI006 was more susceptible to antibiotics than the WT. DPD complemented the luxS mutant phenotype. Real-time PCR revealed modest yet significant changes in luxS expression in the presence of antibiotic concentrations that increased biofilm formation. In conclusion, in S. intermedius, AI-2/LuxS was involved in antibiotic susceptibility and increased biofilm formation at sub-MICs of antibiotic.Bacteria colonize biological and inert surfaces in the form of persistent, sessile, matrix-encapsulated communities referred to as biofilms. Bacterial biofilms account for the majority of chronic diseases, including gingivitis, endocarditis, and nosocomial infections (10). Biofilms represent an obstacle to clinical treatment due to their resistant nature, which shelters bacteria from the immune response and penetration by antibiotics. Bacteria may also resist the antibiotic effect through efflux pumps, antibiotic inactivation, modification of susceptible targets, or persister cell formation (13, 27). The bioavailability of antibiotics depends on the dose, drug regimen, absorption, distribution, elimination, and mode of administration (5, 15). Therefore, following antibiotic treatment, bacteria may be exposed to supra-MICs as well as sub-MICs of antibiotics. Intriguingly, several studies report that low antibiotic doses may promote the formation of bacterial biofilms (4, 11, 18).Bacterial microorganisms exist in large cooperative populations by employing communications systems necessary for their virulence and survival. Quorum sensing is one such system that enables bacteria to coordinate their gene regulation and trigger collective population behaviors. Through this quorum-sensing system, bacteria are able to monitor their population by releasing autoinducer (AI) signals and consequently responding to a specific threshold accumulation of AI signals. AI-2 is a collective term given to describe cyclic derivatives of 4,5-dihydroxy-2,3-pentanedione (DPD), a highly reactive metabolic by-product of the activated methyl cycle. The AI-2 signal and its enzymatic synthase LuxS are broadly encountered in gram-positive and gram-negative bacteria, suggesting that AI-2 is an inter- and intraspecies communication signal (7, 26). This communication system has been shown to play a role in the vital functions, including virulence and biofilm formation, of several bacteria (26).Streptococcus intermedius, a commensal bacterium and a member of the Streptococcus anginosus group, has been isolated from patients with periodontitis and fatal purulent infections, especially brain and liver abscesses (6, 28). In both Streptococcus anginosus and S. intermedius, AI-2 has been shown to be involved in biofilm formation (2, 16). We have also demonstrated that AI-2/LuxS affects susceptibility to ampicillin and erythromycin in S. anginosus (1). Since chronic infections involve persistent biofilms resilient to antibiotic treatment, we investigated the role of AI-2/LuxS in biofilm formation by S. intermedius in the presence of sub-MICs of antibiotics. Three antibiotics with distinct modes of action and different bacterial targets were chosen to study the role of AI-2 in biofilm formation and antibiotic susceptibility: ampicillin, a β-lactam antibiotic that targets protein cell wall synthesis; ciprofloxacin, a fluoroquinolone that targets DNA gyrase; and tetracycline, a protein inhibitor that acts on peptidyl transferase (27). S. intermedius has shown moderate susceptibility to ampicillin, ciprofloxacin, and tetracycline, although resistant strains are developing (20, 22, 25).We show that certain low, sub-MICs of antibiotics with distinct modes of action may increase biofilm formation in the S. intermedius wild type (WT) but not in its luxS mutant. These results may implicate AI-2/LuxS in the antibiotic response mechanisms of S. intermedius biofilms.     

In vitro and in vivo evaluations of mechanical properties,biocompatibility and osteogenic ability of sintered porous titanium alloy implant

A new sintering technique using Ti₆Al₄V powder suspension was performed to prepare porous Ti₆Al₄V alloys. The porous alloys could be fabricated with different porosities and pore sizes by controlling the quantity and size of spacer particles added to the Ti₆Al₄V powder. The characteristics and biological properties of the porous Ti₆Al₄V with two different porosities were evaluated by mechanical tests, cell tests and implantation. Dense Ti₆Al₄V was used as the control. Compared with the control group, the porous Ti₆Al₄V showed good biocompatibility and osteogenic ability, which makes this type of porous alloy a good prospective material for biomedical application. And compared with 50% porosity, the alloy with 75% porosity had the optimal mechanical properties, and suitable pore size and porosity, which allowed more bone ingrowth.

The sintered porous Ti₆Al₄V with 75% porosity has optimal mechanical properties, good biocompatibility and osteogenic ability for more bone ingrowth.     

Solid state interdigitated Sb2S3 based TiO2 nanotube solar cells

TiO₂ nanotubes generated by anodization of metallic titanium sputter-coated on indium tin oxide (ITO) substrates are used as a conductive scaffold for all solid-state Sb₂S₃-sensitized extremely thin absorber (ETA) solar cells. A blocking layer of TiO₂ placed between Ti and ITO in combination with optimized Ti deposition and anodization conditions enables the formation of crack-free layers of straight, cylindrical TiO₂ nanotubes of tunable length and diameter. ALD (atomic layer deposition) is subsequently used to coat this substrate conformally with a highly pure Sb₂S₃ light absorber layer under an inert atmosphere. The high absorption coefficient of Sb₂S₃ as compared to molecular dyes allows for the utilization of very short nanotubes, which facilitates the infiltration of the organic hole transport material and formation of a p–i–n heterojunction in an interdigitated and tunable geometry. We investigate the influence of nanotube length and of the absorber thickness to enhance the photocurrent value to twice that of planar reference structures.

TiO₂ nanotubes generated by anodization of metallic titanium sputter-coated on indium tin oxide (ITO) substrates are used as a conductive scaffold for all-solid-state Sb₂S₃-sensitized extremely thin absorber (ETA) solar cells.