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PubMed1987

Effects of repetitive loading on the integrity of porous coatings.

In spite of the increasing numbers of porous coated total hip femoral components implanted each year, little is known about the shear strength or fatigue performance of the interface between coating and implant substrate. The appearance of loose beads in clinical follow-up roentgenograms suggests that shear failure of bead welds does occur and that the coating could be a weak link in the implant-bone or implant-cement-bone system. In this study, a test specimen design and test regimen for quasistatic and fatigue testing of implant-porous coating shear properties was developed. Both cobalt-chromium (CoCr) alloy and titanium (Ti) bead-substrate interfaces of various surface designs were studied. Results showed that static bead-substrate interface properties for both titanium and CoCr specimens were superior to published values of bone-bead shear strengths. By comparison, fatigue tests showed that the strength of bead welds on a smooth substrate was inadequate, with a preferential failure site being between beads and substrate rather than between beads and cement or beads and bone. However, implant surface contours or a bead recess were found to protect the bead welds, and specimens with those features successfully withstood ten million dynamic loading cycles.

Chromium Alloys↗
PubMed1991

The effect of preformed confluent endothelial cell monolayers on the patency and thrombogenicity of small calibre vascular grafts.

Endothelial cell seeding has been proposed as a method to improve the patency rates in small calibre prosthetic vascular grafts. The seeding methods used at present leave much of the graft luminal surface devoid of endothelial cells and thus still significantly thrombogenic. We have developed a method to preform confluent endothelial cell monolayers, on the grafts prior to implantation, and this study investigates the effect of these monolayers on the early thrombogenicity and patency of polytetrafluoroethylene (PTFE) grafts. Small diameter PTFE grafts were seeded with canine endothelial cells obtained from the external jugular vein. Each of five dogs then received a graft seeded with its own cells and a contralateral, non-seeded control graft. At 1 and 10 weeks after graft implantation graft thrombogenicity was assessed by the use of Indium labelled platelets. The thrombogenicity index (TI) of each graft was determined from counts of gamma activity recorded over a period of 7 days. Grafts were subsequently removed at 12 weeks. At 1 week the mean TI for the seeded grafts was 0.123 (SD 0.019) and that for the controls 0.183 (SD 0.017) (p = 0.005). At 10 weeks only the seeded grafts could be assessed because all of the control grafts had occluded. At this point in time the seeded grafts had a mean TI of 0.159 (SD 0.011) (p = 0.047 vs. seeded at 1 week). By the time of removal at 12 weeks, all control grafts were occluded but only one of the seeded grafts had occluded (p = 0.025). In conclusion, the use of preformed, confluent endothelial cell monolayers for seeding prosthetic grafts significantly reduces the early graft thrombogenicity and improves graft patency. It does not, however, completely halt the increase in thrombogenicity which occurs during the early post-implantation period.

Animals↗
PubMed1994

Surface composition of orthopaedic implant metals regulates cell attachment, spreading, and cytoskeletal organization of primary human osteoblasts in vitro.

The nature of orthopaedic implant surfaces affects the interaction between bone and the implant. To analyze this interaction at a cellular level, this study examined the early phase of cell adhesion to implant surfaces. Using an in vitro model, the cell adhesion of primary human osteoblasts cultured on Ti6A14V (Ti), CoCrMo (CC), and tissue culture polystyrene (PS) was characterized. The osteoblasts were found to adhere in greater numbers to Ti compared with PS and CC during a 12 hour period. Other cellular characteristics related to cell adhesion, such as cell spreading, cytoskeletal organization, and focal contact formation, were also examined. Osteoblasts cultured on Ti were significantly larger, and spread better, compared with those on PS and CC. Also, the rate of cytoskeletal reorganization was enhanced on Ti. Focal contacts remained peripherally located in cells on Ti and CC as cytoskeletal reorganization proceeded. However, for cells on PS, the focal contacts quickly became dispersed along actin filaments. There was no difference between surfaces in the number of cells forming focal contacts, although the cells used a larger percentage of their membrane to attach to CC. These data suggest that osteoblast attachment to Ti is greater because cell spreading and cytoskeletal organization are enhanced. Furthermore, the mechanisms of osteoblast attachment to the underlying substrate may be significantly different between biometals and tissue culture plastic. Substrate specific information regarding the characteristics and mechanisms of cell adhesion may be helpful in the design of implants to optimize bone growth at the interface.

Alloys↗
PubMed1995

Bone-bonding behavior of titanium alloy evaluated mechanically with detaching failure load.

Although titanium (Ti) and Ti alloy are generally classified as bioinert materials in terms of their bonding to bone tissue, it is still unclear whether they bond chemically to bone. In this study, we examined the bone-bonding ability of Ti alloy (Ti-6Al-4V) using smooth-surfaced plates under non-load-bearing conditions. The bone-bonding behavior was evaluated mechanically by means of the detaching test reflecting tensile force. After implantation of the plates into the tibiae of rabbits for 4, 8, 16, and 25 weeks, detaching tests were performed. The failure load of the Ti alloy plates was close to 0 kg at 4 and 8 weeks, but gradually increased with time, reaching 0.334 kg at 16 weeks and 2.852 kg at 25 weeks on average. Histologic examination by Giemsa surface staining and SEM showed no differences between specimens at 8, 16, and 25 weeks, when Ti alloy plate made direct content with bone without any fibrous tissue. By SEM-EPMA, no clear calcium-phosphorus (Ca-P)-rich layer at the interface between the Ti alloy and bone tissue was evident, although a thin bone tissue was observed on the detached Ti alloy plate. The present results indicate that from both mechanical and histologic viewpoints, Ti alloy bonds directly to bone under static conditions after some time, probably more than 8 weeks. The possibility of chemical bone-bonding of Ti alloy was suggested.

Alloys↗
PubMedDate not supplied

Comparison of albumin-(Gd-DTPA)30 and Gd-DTPA-24-cascade-polymer for measurements of normal and abnormal microvascular permeability.

The purpose of this study was to compare a new MR macromolecular contrast medium (MMCM), gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA)-24-cascade-polymer, to a well-studied prototype MMCM, for the potential of distinguishing tissues of varying endothelial permeability. Three tissue models of varying capillary permeability were studied in a total of 46 rats: normal myocardium (normal capillaries), subcutaneously implanted adenocarcinoma (mild capillary leak), and reperfused infarcted myocardium (high capillary leak). TI-weighted MRI was performed before and dynamically after injection of either albumin-(Gd-DTPA)30 or the cascade polymer (each .02 mmol gadolinium [Gd] per kg). Data analysis based on a two-compartment kinetic model yielded estimates of fractional blood volume (BV) (percentage) and fractional leak rate (FLR) (1 per hour). Permeability to the cascade polymer as reflected in FLR was considerable in normal myocardium (8.24 per hour), of similar value in tumors (8.55 per hour), but significantly greater in infarcted myocardium (39.17 per hour, P < .01) versus normal myocardium. The larger albumin-(Gd-DTPA)30 demonstrated minimal extravasation in normal myocardium (FLR .33 per hour); FLR in tumors was 100% higher (.66 per hour, P < .002) and FLR in reperfused capillaries was significantly greater (7.94 per hour, P < .001). Based on capillary permeability measurements, the cascade polymer may have limited utility for detection of mildly increased microvascular permeabilities. For severe tissue injury, the cascade polymer can resolve abnormal microvascular integrity.

Analysis of Variance↗
PubMed2003

Effect of chromium content on structure and mechanical properties of Ti-7.5Mo-xCr alloys.

The present work is a study of a series of Ti-7.5Mo-xCr alloys with the focus on the effect of chromium content on the structure and mechanical properties of the alloys. Experimental results show that low hardness, strength and modulus binary Ti-7.5Mo alloy is comprised primarily of fine, acicular martensitic alpha' phase. When 1 wt % Cr is added, a small amount of beta phase is retained. With 2 wt % or more chromium added, the entire alloy becomes equi-axed beta phase with bcc crystal structure. The average beta grain size decreases with Cr content. When the alloy contains about 2-4 wt % Cr, a metastable omega phase is present. In Ti-7.5Mo-2Cr alloy appears the highest omega intensity accompanied with high microhardness, bending strength and modulus. The omega-induced embrittling effect is most profound in Ti-7.5Mo-2Cr alloy that exhibits a terrace type fracture surface covered with numerous micron-sized dimples. The alloys with higher Cr contents show normal ductile type fractography with much larger deformation dimples. The present results indicate that Ti-7.5Mo-(4-6)Cr alloys seem to be potential candidates for implant application.

Journal Article↗
PubMed2006

N doping of TiO2(110): photoemission and density-functional studies.

The electronic properties of N-doped rutile TiO2(110) have been investigated using synchrotron-based photoemission and density-functional calculations. The doping via N2+ ion bombardment leads to the implantation of N atoms (approximately 5% saturation concentration) that coexist with O vacancies. Ti 2p core level spectra show the formation of Ti3+ and a second partially reduced Ti species with oxidation states between +4 and +3. The valence region of the TiO(2-x)N(y)(110) systems exhibits a broad peak for Ti3+ near the Fermi level and N-induced features above the O 2p valence band that shift the edge up by approximately 0.5 eV. The magnitude of this shift is consistent with the "redshift" observed in the ultraviolet spectrum of N-doped TiO2. The experimental and theoretical results show the existence of attractive interactions between the dopant and O vacancies. First, the presence of N embedded in the surface layer reduces the formation energy of O vacancies. Second, the existence of O vacancies stabilizes the N impurities with respect to N2(g) formation. When oxygen vacancies and N impurities are together there is an electron transfer from the higher energy 3d band of Ti3+ to the lower energy 2p band of the N(2-) impurities.

Journal Article↗
PubMed1999

Effect of fluoride concentration and pH on corrosion behavior of titanium for dental use.

Titanium is used as a metal for biocompatible materials such as dental implants or restorations because of its excellent chemical stability. However, the corrosion of Ti in the prophylactic fluoride-containing environment can become problematic. To clarify the effects of fluoride concentration and pH on the corrosion behavior of Ti, we conducted anodic polarization and immersion tests in NaF solution of various concentrations and pH values. The concentrations of dissolved Ti in the test solutions were analyzed by inductively coupled plasma mass spectroscopy. There were obvious limits of fluoride concentration and the pH value at which the corrosion behavior of Ti changed. The corrosion of Ti in the solution containing fluoride depended on the concentration of hydrofluoric acid (HF). When the HF concentration in the solution was higher than about 30 ppm, the passivation film of the Ti was destroyed. The results of this study revealed a relation between the fluoride concentrations and pH values at which Ti corrosion occurred and provided data on such corrosion in environments where the fluoride concentration and pH value are known.

Corrosion↗
PubMed2000

[Histological and ultrastructural characteristics of interface membrane around aseptically loosened prostheses].

OBJECTIVE: To investigate the effect of wear particles on prosthetic loosening by analyzing the histological and ultrastructural characteristics of interface membrane around aseptically loosened prostheses. METHODS: Slices of interface membranes around aseptically loosened hip prostheses of 51 cases were stained with HE, Safranin O-Briliant green and CD68 Mab immunohistochemical technique respectively. The histological structure of the membranes and the kinds of wear particles and their distribution characters were observed. The size of particles and the number of CD68 positive cells were measured. Ultrastructure of cells in the membrane and the characters and size of the particles phagocytozed by M phi were also observed and measured. RESULTS: Interface membrane consisted of fibromatrix, fibroblasts, M phi[CD68 positive, occupying (23 +/- 5)% (x +/- s)], and foreign body giant cells. In the membranes at the site of osteolysis, great amount of UHMWPE particles, PMMA particles and Ti alloy or CoCr alloy particles collected at the side attaching to the implant and caused chronic foreign body inflammatory reaction. Most of the particles outside M phi were less than 15 microns while that inside M phi were less than 1 micron. Different kinds of wear particles could exist in the lysosomes of one M phi. No particles but cartilage-like tisses appeared in the membranes at the site without osteolysis. CONCLUSION: Wear particles in the interface membrane have relations with osteolysis and fibrous tissue proliferation at bone-implant interface, which plays an important role in aseptic loosening.

Granuloma, Foreign-Body↗
PubMed1981

A mercuric iodide detector unit implantable and externally powered for use in radionuclide tracer studies in small animals.

A small externally powered implantable gamma-radiation detector unit (35 X 12 mm diameter containing a mercuric iodide detector (HgI2), charge amplifier, radiotransmitter and an inductive power supply has been constructed. Since the total weight of the device is 5 g, it is suitable for implantation in laboratory animals such as rats or hamsters. A comparison between the implanted HgI2 detector unit and a conventional stationary 2 X 2 inch NaI(TI) detector has been performed by simultaneous measurements of the 133Xe clearance from a depot. Using 125I-iothalamate a kidney function study of an unrestrained hamster is shown as an example of measurements in the unrestrained animal.

Animals↗
PubMed2003

Bone formation in CaP-coated and noncoated titanium fiber mesh.

The osteogenic activity of calcium phosphate (CaP)-coated and noncoated porous titanium (Ti) fiber mesh loaded with cultured syngeneic osteogenic cells after prolonged in situ culturing was compared in a syngeneic rat ectopic assay model. Rat bone marrow (RBM) cells were loaded onto the CaP-coated and noncoated Ti scaffolds using either a droplet or a suspension loading method. After loading, the RBM cells were cultured for 8 days in vitro. Thereafter, implants were subcutaneously placed in 39 syngeneic rats. The rats were euthanized and the implants retrieved at 2, 4, and 8 weeks postoperatively. Further, in the 8 week group fluorochrome bone markers were injected at 2, 4, and 6 weeks. Histological analysis demonstrated that only the CaP-coated meshes supported bone formation. The amount of newly formed bone varied between single and multiple spheres to filling a significant part of the mesh porosity. In the newly formed bone, osteocytes embedded in a mineralized matrix could be observed clearly. On the other hand, in the noncoated titanium implants, abundant deposition of calcium-containing material was seen. This deposit lacked a bonelike tissue organization. Further analysis revealed that the cell-loading method did not influence the final amount of bone formation. In CaP-coated implants the accumulation sequence of the fluorochrome markers showed that bone formation started on the mesh fibers. In conclusion, our results prove that the combination of a thin CaP coating, Ti-mesh, and RBM cells can indeed generate ectopic bone formation after prolonged in vitro culturing. No effect of the loading method was observed on the final amount of bone.

Animals↗
PubMed1998

In vitro adherence of Streptococcus constellatus to dense hydroxyapatite and titanium.

Bacterial adherence to dense hydroxyapatite (HA) and titanium (Ti) rods was examined in vitro using Streptococcus constellatus ATCC27832. Streptoccus constellatus is associated with dental abscess and was isolated from the peri-implantitis. The dense HA was etched with 5% hydrofluoric acid for 0, 10, 20, 30, 40, and 50 s Adherence to the untreated dense HA was twice as high as the adherence to the Ti. The adherence to saliva-treated Ti was 13% higher than that to untreated Ti. The adherence was increased by acid-treatment of the dense HA, following a sigmoid curve from 20 to 50 s of treatment time. The dense HA has the capacity to receive more bacterial adherence than Ti and furthermore, the etched dense HA becomes more adherent.

Abscess↗
PubMed2006

Sensitivity to implant materials in patients undergoing total hip replacement.

Sensitivity to implant materials is an unpredictable event, which may contribute to the process leading to the failure of the total hip replacement (THR). The aim of the current study was to investigate the informative power of skin testing in detecting the sensitization to the implant components in patients undergoing THR. A consecutive series of 223 patients was enrolled in the study, including 66 candidates to THR, 53 with stable implant, and 104 with THR loosening. The patch testing was performed by using the most relevant components of cobalt-based alloys (CoCrMo), Ti-based alloys (TiAlV), and bone cements. The frequency of positive patch testing in preimplant patients did not differ from that observed after THR. Patients with CoCrMo-failed implant showed a significant low frequency of nickel-positive skin reaction, while patients with TiAlV-THR had a high incidence of vanadium-positive patch testing. The panel of haptens showed a good performance in the identification of patients known to have a contact dermatitis. With regard to the THR outcome, patch testing was not able to discriminate between stable and failed implant. Sensitivity to at least one hapten, namely bone cement, as well as the positive medical history of hypersensitivity, influenced negatively the THR survival. Our results show the reliability of patch testing for investigating the sensitivity to implant components. The cause-effect relationship between sensitization and negative outcome cannot be established, but the shorter lifespan of THR in patients who have a positive patch testing supports the significant role of this event in contributing to the implant failure.

Adult↗
PubMed2004

Immune responses correlate with serum-metal in metal-on-metal hip arthroplasty.

Cell-mediated hypersensitivity associated with metal components may be related to levels of implant debris. We tested this hypothesis by comparing lymphocyte reactivity to soluble Co, Cr, Ni, and Ti of patients with metal-on-polyethylene and metal-on-metal arthroplasties with healthy controls, and patients with osteoarthritis. The metal-on-metal group (n=9) demonstrated significantly elevated serum Co and Cr concentrations (13- and 58-fold, P<.05, respectively) and significantly elevated lymphocyte reactivity to Co (SI>5, P<.004) and Ni (SI>2.5, P<.01) when compared to controls (n=12) and subjects with metal-on-poly implants (n=7). These elevated in vivo metal levels demonstrated positive linear correlation with lymphocyte reactivity supporting our hypothesis that lymphocyte metal-induced reactivity increases with increased metal exposure. These results represent the first direct link between in vivo metal exposure and lymphocyte reactivity. Whether this lymphocyte reactivity to metal debris is etiologically linked to poor implant performance remains uncertain.

Aged↗
PubMed2005

Hydroxyapatite and titania sol-gel composite coatings on titanium for hard tissue implants; mechanical and in vitro biological performance.

Hydroxyapatite (HA) composites with titania (TiO2) up to 30 mol % were coated on a titanium (Ti) substrate by a sol-gel route, and the mechanical and biological properties of the coating systems were evaluated. Using polymeric precursors, highly stable HA and TiO2 sols were prepared prior to making composite sols and coatings. Coatings were produced under a controlled spinning and heat treatment process. Pure phases of HA and TiO2 were well developed on the composites after heat treatment above 450 degrees C. The HA-TiO2 composite coating layers were homogeneous and highly dense with a thickness of about 800-900 nm. The adhesion strength of the coating layers with respect to Ti substrate increased with increasing the TiO2 addition. The highest strength obtained was as high as 56 MPa, with an improvement of about 50% when compared to pure HA (37 MPa). The osteoblast-like cells grew and spread actively on all the composite coatings. The proliferation and alkaline phosphatase (ALP) activity of the cells grown on the composite coatings were much higher than those on bare Ti, and even comparable to those on pure HA coating. Notably, the HA-20% TiO2 composite coating showed a significantly higher proliferation and ALP expression compared to bare Ti (p < 0.05). These findings suggest that the sol-gel-derived HA-TiO2 composite coatings possess excellent properties for hard tissue applications from the mechanical and biological perspective.

Alkaline Phosphatase↗
PubMedDate not supplied

A new thermal shape memory Ti-Ni alloy stent covered with silicone.

An attempt was made to develop an airway stent for nonsurgical transluminal implantation using a bronchofiberscope. The stent is composed of a single wire with a diameter of 0.5 mm. The wire is made of thermal shape memory titanium nickel alloy, with a transition temperature of 25-30 degrees C. To avoid direct contact between the metal and the tissue, the wire is covered with a 300 microns thick coating of silicone. The stent is horseshoe shaped in cross-section. It is 15 mm in outer transverse diameter and 40 mm long. Ten stents were implanted in 10 dogs whose tracheal cartilages had been previously broken. The stents were first cooled in ice water to reduce their diameter and then inserted into the target site. The wire was warmed to body temperature and recovered its initial shape within 10 sec. The dogs were killed for examination between 1 week and 6 months after implantation. All the stents were located at the implantation sites and were patent. Tissue reactions, such as ulceration and granulation formation, were less severe than in those with previously implanted non-silicone covered stents. Microscopic observation showed that the wires became gradually covered with epithelium within 2 months. This transluminal technique for preserving airway patency shows promise for clinical application.

Alloys↗