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At least 19 recordsLinked to original sources
PubMed2005

Tantalum complexes with all nitrogen coordination sphere: mixed amido-, imido-, guanidinato complexes of tantalum and their thermal behaviour.

Novel mixed amido-/imido-/guanidinato-complexes of tantalum are reported. The complexes were synthesised by insertion reactions of carbodiimides of the type C(NR)2(R =iso-propyl (i-Pr)) into the M-N bonds of tantalum mixed amido/imido complexes. Three representative complexes were synthesised and fully characterised by 1H-NMR, 13C-NMR, CHN-analysis and mass spectroscopy. The crystal structure of the complex [Ta(NMe2){(i-Pr-N)2C(NMe2)}2(N-t-Bu)](1)(Me = methyl, t-Bu =tert-butyl) is presented and discussed. The complexes are solids that can be quantitatively sublimed at moderate temperatures (120-130 degrees C) without any sign of decomposition. The thermal properties of the new compounds were studied (TGA) and preliminary MOCVD-experiments were performed. TaN films were deposited and characterised by XRD and XPS.

Amides↗
PubMed2007

Well-defined surface imido amido tantalum(v) species from ammonia and silica-supported tantalum hydrides.

The MCM-41 supported hydrides [([triple bond]SiO)(2)TaH(3)], 1a, and [([triple bond]SiO)(2)TaH(3)], 1b, cleave N-H bonds of ammonia at room temperature to yield the well-defined imido amido surface complexes [([triple bond]SiO)(2)Ta(NH)(NH(2))], 2, and 2xNH(3). Additionally, the surface silanes [[triple bond]Si-H] that exist in close proximity to 1a and 1b also react with ammonia at room temperature to give the surface silylamido [Si-NH(2)]. Such reaction is tantalum assisted: surface silanes were synthesized independently and in absence of tantalum by reaction of highly strained silica, SiO(2-1000), with SiH(4) and no reaction with ammonia was observed. Surface-supported complexes 2, 2xNH(3), and [[triple bond]Si-NH(2)] have been characterized by, inter alia, solid-state NMR, IR, and EXAFS and independent synthesis of [[triple bond]Si-NH(2)]. The NMR studies on the fully 15N-labeled samples have led to unambiguous discrimination between imido, amido, and amino resonances of 2*, 2*x(15)NH(3), and [[triple bond]Si-15NH(2)] through the combination of solid-state magic angle spinning (MAS), heteronuclear correlation (HETCOR), 2D proton double-quantum (DQ) single-quantum (SQ) correlation, and 2D proton triple-quantum (TQ) single-quantum (SQ) correlation spectra. The in situ IR monitoring of the reaction of 1a and 1b with regular NH(3) and 15NH(3), and after H/D exchange has yielded the determination of all the NH(x) vibration and deformation modes, with their respective H/D and 14N/15N isotopic shifts. EXAFS study yielded the bond distances in 2 of 1.79(2) Angstrom for Ta=N, 1.89(1) Angstrom for Ta-O, and 1.98(2) Angstrom for Ta-N.

Journal Article↗
PubMed1999

Tantalum-Gold and Tantalum-Copper Trihydride Complexes [Cp'(2)TaH(3)MPPh(3)][PF(6)] (Cp' = C(5)H(4)C(CH(3))(3)). Structure Determination from (1)H T(1) Relaxation Studies.

The reaction of Cp'(2)TaH(3) (Cp' = C(5)H(4)C(CH(3))(3)) with [MPPh(3)][PF(6)] yields the bimetallic complexes [Cp'(2)TaH(3)MPPh(3)][PF(6)] (M = Au (1),M = Cu (2)). The detailed NMR study of 1 and 2 showed the structure with two bridging hydride ligands. The mutual orientation of the Cp' rings has been determined by NOE experiments. The variable-temperature NMR data showed an intramolecular exchange between two outer hydride ligands. The exchange is faster in 1 (DeltaG()(210 K) = 9.3 kcal/mol) than in 2 (DeltaH() = 8.6 +/- 0.2 kcal/mol, DeltaS() = - 5.0 +/- 0.4 eu, DeltaG() (210 K) = 9.6 +/- 0.2 kcal/mol). In contrast, complex 2 undergoes the faster intermolecular PPh(3)/PPh(3) exchange. It has been demonstrated that T(1min), T(1), T(1sel) and T(1bis) measurements are a powerful instrument for quantitative localization of the hydride ligands in solutions of bimetallic complexes. The determined hydride-hydride and metal-hydride distances reproduce well the structural tendencies in the related niobium trihydride [{Nb(C(5)H(3)RR')(2)H(3)}(2)Au][PF(6)] (R = R' = Si(CH(3))(3)) established by the X-ray method. Tantalum-gold complex 1 showed weak exchange couplings.

Journal Article↗
PubMed2002

Determination of boron in high-purity tantalum materials by on-line matrix separation/inductively coupled plasma mass spectrometry.

A method for the determination of ultratrace amounts of boron in high-purity tantalum materials [tantalum metal, tantalum(v) oxide, tantalum pentachloride and tantalum pentaethoxide] is described. On-line anion-exchange matrix separation combined with inductively coupled plasma mass spectrometry (ICP-MS) was employed for the determination of boron at the ng g(-1) level. Tantalum materials were dissolved using HF and/or HNO3 prior to analysis. The loss of boron in the sample preparation procedure was examined as the recovery of boron by adding a definite amount of boron to each tantalum material sample before decomposition, and it was almost negligible. In an anion-exchange method using 0.1 M HF carrier solution, tantalum and boron in the sample solution were first adsorbed on a strongly basic anion-exchange resin. Next, boron was eluted from the resin with 5 M HCl, whereas tantalum was retained strongly adsorbed. The eluted boron was introduced directly into the ICP-MS system for quantitative analysis at m/z 10 and 11. Because of the long elution time of boron, the transient signal was integrated in the time range 70-300 s on the chromatogram. Although the elution of boron in the time range was ca. 40% of total boron in the sample solution injected, the determination limits (10sigma) obtained by the present method were 30, 25, 15 and 13 ng g(-1) for tantalum metal, tantalum(v) oxide, tantalum pentachloride and tantalum pentaethoxide, respectively. The method was applied to the determination of boron in commercially available high-purity tantalum materials and it was found that the concentrations of boron were in the ng g(-1)-microg g(-1) range.

Journal Article↗
PubMed2002

Mechanism of bonelike apatite formation on bioactive tantalum metal in a simulated body fluid.

Development of tantalum metal with bone-bonding ability is paid much attention because of its attractive features such as high fracture toughness, high workability and its achievement on clinical usage. Formation of bonelike apatite is an essential prerequisite for artificial materials to make direct bond to living bone. The apatite formation can be assessed in vitro using a simulated body fluid (SBF) that has almost equal compositions of inorganic ions to human blood plasma. The present authors previously showed that the apatite formation on tantalum metal in SBF was remarkably accelerated by treatment with NaOH aqueous solution and subsequent firing at 300 degrees C, while untreated tantalum metal spontaneously forms the apatite after a long soaking period. The purpose of the present study is to clarify the reason why the NaOH and heat treatments accelerate the apatite formation on tantalum metal. X-ray photoelectron spectroscopy was used to analyze changes in surface structure of the tantalum metal at an initial stage after immersion in SBF. Untreated tantalum metal had tantalum oxide passive layer on its surface, while amorphous sodium tantalate was formed on the surface of the tantalum metal by the NaOH and heat treatments. After soaking in SBF, the untreated tantalum metal sluggishly formed small amount of Ta-OH groups by a hydration of the tantalum oxide passive layer on its surface. In contrast, the treated tantalum metal rapidly formed Ta-OH groups by exchange of Na+ ion in the amorphous sodium tantalate on its surface with H3O+ ion in SBF. Both the formed Ta-OH groups combined with Ca2+ ion to form a kind of calcium tantalate, and then with phosphate ion, followed by combination with large amount of Ca2+ ions and phosphate ions to build up apatite layer. The formation rate of Ta-OH groups on the treated tantalum metal predominates the following process including adsorption of Ca2+ ion and phosphate ion on the surface. It is concluded that the acceleration of the apatite nucleation on the tantalum metal in SBF by the NaOH and heat treatments was attributed to the fast formation of Ta-OH group, followed by combination of the Ta-OH groups with Ca2+ and phosphate ions.

Apatites↗
PubMedDate not supplied

Bone ingrowth characteristics of porous tantalum and carbon fiber interbody devices: an experimental study in pigs.

BACKGROUND CONTEXT: In preclinical and clinical joint replacement applications, porous tantalum has been shown to be osteoconductive and effective for biological fixation. Relatively little research has been undertaken to investigate the porous tantalum implants for potential application in intervertebral spinal fusion. PURPOSE: The current study was designed to assess the radiographic and histological performance of porous tantalum and carbon fiber devices in the porcine anterior lumbar interbody fusion (ALIF) model. STUDY DESIGN: A total of 10 Danish Landrace pigs underwent a three-level anterior intervertebral lumbar arthrodeses at L2-L3, L4-L5 and L6-L7. Each level was randomly allocated to one of three implants: a solid piece of porous tantalum, a porous tantalum ring packed with autograft or a carbon fiber cage, likewise packed with autograft. Two staples for fixation were supplemented in front of implant. METHODS: Pigs were sacrificed 3 months after operation. Specimens were evaluated by plain radiography, conventional tomography and histology. RESULTS: Bone graft filled into the central hole of the porous tantalum ring was less than that of the carbon fiber cage (p<.001). Radiolucencies around the porous tantalum solid were significantly higher than the carbon fiber cage (p=.02) and were not different between the porous tantalum ring and the carbon fiber cage. The bone volume in the hole of implants, within the pores of the porous tantalum and in the implant interface did not differ between implants. Bone volume in the hole of the porous tantalum ring did not differ from that of the adjacent vertebral bone; however, it was significantly different in the carbon fiber cage and the adjacent vertebral bone (p=.005). CONCLUSIONS: In this porcine ALIF model, the radiographic and histological appearances of the porous tantalum ring were equivalent to those of the carbon fiber cage. The high presence of radiolucencies and fibrous tissue layer at the vertebrae-implant interface suggests that an initial stabilizing biomechanical environment is important in order to achieve bone ingrowth in the interbody fusion devices in this ALIF model.

Animals↗
PubMed1998

A comparison of magnetic resonance and computed tomographic image quality after the implantation of tantalum and titanium spinal instrumentation.

STUDY DESIGN: Tantalum- and titanium-based lumbar interbody fusion devices were implanted into two fresh human cadavers, and magnetic resonance and computed tomographic imaging were performed to evaluate adjacent spinal structures and the amount of metallic artifact. OBJECTIVE: The objective of this study was to prospectively compare the preliminary results of magnetic resonance imaging and computed tomography scanning image quality after the implantation of both titanium and tantalum spinal implants. SUMMARY OF BACKGROUND DATA: The availability of tantalum and titanium spinal implants brings theoretical magnetic resonance imaging compatibility along with several other desirable characteristics. The magnetic resonance imaging and computed tomographic imaging of tantalum spinal instrumentation has never been studied previously or compared with titanium instrumentation. METHODS: Titanium and tantalum spinal implants produced for anterior spinal fusion were each placed at two levels in the lumbar spine of two fresh cadaver specimens. Sequential spin echo T1-weighted and T2-weighted magnetic resonance imaging studies and computed tomographic scans were obtained. The resulting images were then graded to describe and compare the behavior of tantalum metal in magnetic resonance imaging and computed tomographic studies. RESULTS: Good T1 and T2 images were obtained that allowed visualization of the neural structures with minimal artifact. The optimal T1 images for tantalum metal were similar in quality to the optimal T1 parameters for titanium metal. T2 images for both tantalum and titanium metal were obtained with similar results for both metals. Gradient echo magnetic resonance imaging scans of both were poorly imaged with a large amount of artifact. Computed tomographic studies of tantalum implants produced a large amount of metal artifact when compared with computed tomographic studies of titanium implants. CONCLUSIONS: High-quality magnetic resonance imaging studies can be obtained after the implantation of both titanium and tantalum spinal instrumentation. Both of the metals produce similar images on magnetic resonance imaging studies with comparable amounts of metallic artifact. High-quality computed tomographic scans of titanium implants can be obtained with minimal distortion secondary to artifact. However, computed tomographic scanning is not the imaging modality of choice for the tantalum spinal implants because of the large amounts of artifact.

Artifacts↗
PubMed2000

Bonding of alkali- and heat-treated tantalum implants to bone.

Alkali- and heat-treated tantalum (Ta) has been shown to bond to bone. The purpose of this study was to investigate the effects of chemical treatments on the bone-bonding ability of tantalum implants in rabbit tibiae. Miyazaki et al. reported in vitro that alkali- and heat-treated tantalum had an apatite forming ability in an acellular simulated body fluid (SBF). In this study, smooth-surfaced rectangular plates (15 x 10 x 2 mm) of pure tantalum and treated tantalum were prepared. The plates were implanted transcortically into the proximal metaphyses of bilateral rabbit tibiae, alkali- and heat-treated plates for one limb and untreated plates for the contralateral limb, which served as a paired control. Bone bonding at the bone/implant interface was evaluated by tensile testing and undecalcified histological examination, at 8 and 16 weeks after implantation. The treated implants showed weak bonding to bone at 8 weeks, and exhibited significantly higher tensile failure loads compared with untreated tantalum implants at 16 weeks. The untreated implants showed almost no bonding, even at 16 weeks. Histological examination by Giemsa surface staining, contact microradiography (CMR), and scanning electron microscopy (SEM) revealed that treated tantalum implants bonded directly to bone tissue. In contrast, the untreated tantalum implants had a intervening fibrous tissue layer between the bone and the plate and did not bond to bone at 8 and 16 weeks. It is clear from these results that alkali and heat treatment induce the bone-bonding ability of tantalum. This new bioactive tantalum should be an effective material for weight-bearing and bone-bonding orthopedic devices.

Alkalies↗
PubMed2006

Porous tantalum trabecular metal scaffolds in combination with a novel marrow processing technique to replace autograft.

INTRODUCTION: Interbody fusion requires a structural member to carry load while the autograft or osteoinductive agent stimulates bone formation. In the present study, we evaluated the potential use of extracted nucleated cells from bone marrow mixed in hyaluronic acid gel as an osteoinductive agent, in comparison to Collagraft loaded with nucleated cells or rhBMP-2 in the porous tantalum ring, in an anterior lumbar interbody fusion (ALIF) in pigs. METHODS: Four 3-month-old female Danish landrace pigs were employed in the current study. Bone marrow was collected by means of aspiration, from the medullary cavity of the proximal tibia. The nucleated cells were isolated with a Ficoll step gradient centrifugation. The cell adhered rate after 24 hours of cultivation and ALP activity in the osteogenic medium following 4 days of cultivation were measured. Cell numbers in the porous tantalum discs were assessed by CyQuant measurement, and fluorescent live/dead cell staining in the porous tantalum discs was performed after periods of 24 hours and 7 days of cultivation. The nucleated cells mixed in hyaluronic acid gel were cultivated on slides for 24 hours, 7 days and 21 days. The live/dead cell staining, ALP staining or osteocalcin staining, were performed. A porous tantalum ring was loaded with nucleated cells in hyaluronic acid gel or packed with Collagraft strips also with nucleated cells or rhBMP-2. Immediately after preparation, one of three implants was inserted into L2-3, L4-5 or L6-7 respectively. The pigs were killed 3 months postoperatively. The lumbar spine specimens were prepared for histological evaluation. RESULTS: The adhered rate, of the nucleated cells, was 2.26+/-0.56%. ALP activity was no different in the osteogenic culture compared to DMEM/10%FBS alone. Cell numbers and live/dead cells showed no difference in the porous tantalum discs. Histological appearance showed that nucleated cells mixed with hyaluronic acid gel, had more mature bone in the central hole of the porous tantalum ring, compared to Collagraft strips with nucleated cells or rhBMP-2. Bone volume fraction did not differ within the three porous tantalum rings; however, more marrow space in the central hole of the porous tantalum ring was present when nucleated cells mixed with hyaluronic acid gel (57.4%) compared to Collagraft strips with rhBMP-2 (29.7%). CONCLUSION: In the current study, we demonstrate that nucleated cells, which were isolated from bone marrow intraoperatively, could be used to replace autograft if nucleated cells mixed with hyaluronic acid gel or with Collagraft strips packed into the porous tantalum ring in the pig ALIF model.

Animals↗
PubMedDate not supplied

Anterior cervical interbody fusion with rhBMP-2 and tantalum in a goat model.

BACKGROUND CONTEXT: Tricortical autogenous iliac crest has long served as the gold standard for arthrodesis after cervical discectomy. The added morbidity resulting from bone graft harvest may be eliminated by the use of a biocompatible synthetic bone graft substitute with osteoconductive abilities, and when used with an osteoinductive agent, such as recombinant bone morphogenic protein (rhBMP)-2, it may facilitate arthrodesis similar to autograft. PURPOSE: To determine by radiographic and histologic analysis whether tantalum with and without rhBMP-2 can facilitate bony ingrowth and arthrodesis in an animal model. STUDY DESIGN/SETTING: Single-level anterior cervical discectomy and fusion was performed using a tantalum bone graft substitute with and without rhBMP-2 in a previously established goat model for anterior cervical fusion. METHODS: Eight goats underwent single-level anterior cervical discectomy and stabilization with a porous tantalum implant. There were four goats in each experimental group. Group A underwent anterior cervical stabilization with tantalum alone, whereas in Group B rhBMP-2 was added to the tantalum implant. The goats were sacrificed at 12 weeks, and their cervical spines were removed for histologic and radiological analysis. RESULTS: Only one of four goats in Group A had any bony ingrowth into the tantalum. Three of four goats in Group B demonstrated bony ingrowth. The average extent of bony ingrowth at the perimeter of the tantalum in Group A was 2.5% compared with 12.5% in Group B. Similarly, the volume of bony ingrowth within the tantalum was 2.5% in Group A and 10% in Group B. The difference was not statistically significant. CONCLUSIONS: The data in this pilot study suggest that tantalum may function as a synthetic osteoconductive bone graft substitute. The addition of rhBMP-2 may facilitate osteoinduction within a synthetic osteoconductive implant. The sample size in this study was too small for statistical significance. The present animal model as used in this study was inadequate for cervical arthrodesis where rigid implant fixation is desired.

Animals↗
PubMed2006

Bacterial adherence to tantalum versus commonly used orthopedic metallic implant materials.

OBJECTIVES: Evaluation of bacterial adhesion to pure tantalum and tantalum-coated stainless steel versus commercially pure titanium, titanium alloy (Ti-6Al-4V), and grit-blasted and polished stainless steel. DESIGN: Experimental in vitro cell culture study using Staphylococcus aureus and Staphylococcus epidermidis to evaluate qualitatively and quantitatively bacterial adherence to metallic implants. METHODS: A bacterial adhesion assay was performed by culturing S. aureus (ATCC 6538) and S. epidermidis (clinical isolate) for one hour with tantalum, tantalum-coated stainless steel, titanium, titanium alloy, grit-blasted and polished stainless steel metallic implant discs. Adhered living and dead bacteria were stained using a 2-color fluorescence assay. Adherence was then quantitatively evaluated by fluorescence microscopy and digital image processing. Qualitative adherence of the bacteria was analyzed with a scanning electron microscope. The quantitative data were related to the implant surface roughness (Pa-value) as measured by confocal laser scanning microscopy. RESULTS: Bacterial adherence of S. aureus varied significantly (p = 0.0035) with the type of metallic implant. Pure tantalum presented with significantly (p < 0.05) lower S. aureus adhesion compared to titanium alloy, polished stainless steel, and tantalum-coated stainless steel. Furthermore, pure tantalum had a lower, though not significantly, adhesion than commercially pure titanium and grit-blasted stainless steel. Additionally, there was a significantly higher S. aureus adherence to titanium alloy than to commercially pure titanium (p = 0.014). S. epidermidis adherence was not significantly different among the tested materials. There was no statistically significant correlation between bacterial adherence and surface roughness of the tested implants. CONCLUSIONS: Pure tantalum presents with a lower or similar S. aureus and S. epidermidis adhesion when compared with commonly used materials in orthopedic implants. CLINICAL IMPLICATION: Because bacterial adhesion is an important predisposing factor in the development of clinical implant infection, tantalum may offer benefits as an adjunct or alternative material compared with current materials commonly used for orthopedic implants.

Alloys↗