Deterioration in the superelasticity of Ti sputter coated on NiTi orthodontic wire.

To evaluate the deterioration in the superelasticity of Ti-coated NiTi orthodontic wires, titanium was coated onto wires to form a 1-microm thick film using radio frequency magnetron sputtering. In superelasticity cycle tests, the sigma5.0 value (the stress at 5.0% strain) of a Ti-coated wire was lower than that of a non-coated wire by 6.2% after one cycle, and by 10.4% after 20 cycles. In a three point bend tests, the L2.0 value (the load at 2.0 mm deflection) of a Ti-coated wire was 2.55 N, and this was reduced by 39.0% of the L2.0 value of a non-coated wire (4.18 N). After the non-coated and the Ti-coated wires had been immersed in physiological saline for periods of four and eight weeks, the concentration of Ni ions released into each solution was detected using MIP-Mass, and Ni peak intensity of the wires was measured using XPS. After eight weeks, the concentration of Ni ions released from the non-coated and the Ti-coated wires was 657 and 135 ppb, respectively. In a clinical test, no inflammation was observed during the entire attached period of four weeks in both the non-coated and the Ti-coated wire. In the Ti-coated wire, little exfoliation of the Ti-coating was observed using SEM and EDS. It was concluded that Ti-coated NiTi orthodontic wire has much potential for its application, with a low probability of causing any Ni allergy.

Bone bonding strength of sputtered hydroxyapatite films subjected to a low temperature hydrothermal treatment.

Hydroxyapatite (HA) was coated onto titanium substrates using radio frequency sputtering, and the coated HA films were crystallized in an autoclave at 110 degrees C using a low temperature hydrothermal method. The crystallite size, the Ca/P ratio, and the surface of the films were observed using XRD, EDS, and SEM, respectively. An immersion test was carried out in physiological saline solution, and the film-to-substrate adhesion strength was measured using a pull-out test. From the XRD patterns, a sputtered film subjected to the hydrothermal treatment had crystallized after 24 h, and the crystallite size increased from 38.0+/-8.7 to 81.4+/-19.1 nm. In immersion tests, an as-sputtered film completely dissolved after 1 d, whereas a sputtered film subjected to the hydrothermal treatment survived to 18.7+/-5.8% of the initial film thickness after four weeks. In pull-out tests, the adhesion strength of the sputtered film to the substrate increased from 1.9+/-0.2 to 5.3+/-1.6 MPa after the hydrothermal treatment. A sputtered film subjected to the hydrothermal treatment and a plasma-sprayed coating on titanium columns were implanted in the diaphysis of the femora of six adult dogs, and a pull-out test was carried out after two, four, and 12 weeks. The sputtered film showed higher bone bonding strength than the plasma-sprayed coating at any period.

Inhibition of Ni release from NiTi alloy by hydroxyapatite, alumina, and titanium sputtered coatings.

To alleviate the effects of Ni allergy from NiTi alloy implants, hydroxyapatite (Ca10(PO4)6(OH)2; HA), alumina (Al2O3), or titanium (Ti) was coated onto NiTi alloy plates to form 1-microm thick films using radio frequency magnetron sputtering. The coatings on the plates were characterized using XRD. After the plates had been immersed in physiological saline for periods of one, four, or eight weeks, the concentration of Ni ions released in each solution was detected using a microwave induced plasma mass spectrometer. After eight weeks, the concentration of Ni ions released from the non-coated, the Ti-coated, the HA-coated, and the alumina-coated plates were 238, 19.7, 183, and 106 ppb, respectively. The bonding strength of the Ti film, the HA film, and the alumina film to the NiTi substrate were 3.8 +/- 1.2, 2.6 +/- 0.7, and 3.1 +/- 1.2 MPa, respectively. The non-coated, the HA-coated, the alumina-coated, and the Ti-coated plates were implanted into the femurs of a dog for four weeks for histological observation. In case of the non-coated plates, connective tissue more than 300 microm thick was observed, whereas for the coated plates the thickness of the connective tissue was around 100 microm.

Preparation and osteocompatibility of hydroxyapatite coated on titanium from the reaction of sputtered CaO and vaporized P2O5.

Hydroxyapatite (HA) and other calcium phosphates were synthesized on titanium plates by a solid-gas state reaction of sputtered CaO and vaporized P(2)O(5). The calcium phosphates formed were HA, beta-tricalcium phosphate (beta-TCP; Ca(3)(PO(4))(2)), beta-calcium pyrophosphate (beta-PYR; Ca(2)P(2)O(7)), and beta-calcium metaphosphate (beta-MET; Ca(2)(PO(3))(2)). Their formation depended on the ratio of the sputtered CaO and the reacting P(2)O(5). For a mole ratio of CaO/P(2)O(5)=4 (Ca/P=2), an HA film was synthesized. The surface roughness increased by over seven times after the solid-gas state reaction from Ra = 0.16+/-0.02 microm (for the CaO film) to Ra = 1.15+/-0.25 microm (for the reacted film). The synthesized HA film-coated titanium plates and control non-coated titanium plates were implanted in the femora of two dogs for a period of two, four and 12 weeks, and observed using a soft X-ray radiograph and histological sections. New bone formation was observed without any connective tissue at four weeks around the HA film, whereas over the 12 week experimental period, there was no new bone formation around the control and connective tissue was observed over all periods, reaching a thickness of more than 200 microm at 12 weeks.

The sphericity of the bearing surface in total hip arthroplasty.

This study evaluated the sphericity of bearing surfaces in total hip arthroplasty. The out-of-roundness of metal femoral heads, the inner surface of polyethylene liners, and commercially available ball bearings was measured. The hip prostheses were obtained directly from the manufacturers. The sphericity of the bearing surfaces was significantly inferior to that of the ball bearings. The sphericity of the femoral head on the sagittal plane was inferior to that on the transverse plane. Several significant differences were found among different manufacturers. The sphericity of the femoral head on the sagittal plane and that of polyethylene significantly improved in 1999 and 2000 compared with those in 1995. Further improvement is desirable, however, because good sphericity is expected to prolong the functional performance of the prosthesis after total hip arthroplasty.

Push-out strength of hydroxyapatite coated by sputtering technique in bone.

Hydroxyapatite was coated with 1 microm thickness on titanium columns of a length of 10 mm, an outer diameter of 4.0 mm by radio frequency magnetron sputtering. The hydroxyapatite coating titanium columns were implanted in the diaphysis of femora of 3 adult dogs, and push-out test was carried out after 2, 4 and 12 weeks of implantation using a testing machine. The interface of bone/column was observed histologically after the test. At 12 weeks the push-out strengths of coating and non-coating columns were 3.5 and 1 MPa, respectively. Histological observation indicated a formation of thin connective tissue with 5-30 microm thickness at the interface of the bone/column. No inflammation was observed during the implantation periods.

Surface pitting of heart valve disks tested in an accelerated fatigue tester.

There are various reports on the fracture of mechanical heart valves implanted in humans or animals and it has been pointed out that fractures are induced by erosion of the disk surface due to cavitation bubbles. Cavitation erosion on mechanical heart valves was studied using our originally designed accelerated fatigue tester. Several valve housings with different compliance values were used. The number and position of pits on the valve disk were measured using an optical microscope. Disk-closing velocity was measured and cavitation bubbles were monitored by a high-speed video camera. It was found that disk-closing velocity increased and cavitation erosion was enhanced with an increase in compliance of the valve holder. Therefore, careful attention should be paid to the compliance of an accelerated fatigue tester.

Effect of the sinus of valsalva on the closing motion of bileaflet prosthetic heart valves.

Conventional bileaflet prosthetic mechanical heart valves close passively with backflow. Naturally, the valve has problems associated with closure, such as backflow, water hammer effect, and fracture of the leaflet. On the other hand, in the case of the natural aortic valve, the vortex flow in the sinus of Valsalva pushes the leaflet to close, and the valve starts the closing motion earlier than the prosthetic valve as the forward flow decelerates. This closing mechanism is thought to decrease backflow at valve closure. In this study, we propose a new bileaflet mechanical valve resembling a drawbridge in shape, and the prototype valve was designed so that the leaflet closes with the help of the vortex flow in the sinus. The test valve was made of aluminum alloy, and its closing motion was compared to that of the CarboMedics (CM) valve. Both valves were driven by a computer controlled hydraulic mock circulator and were photographed at 648 frames/s by a high speed charge-coupled device (CCD) camera. Each frame of the valve motion image was analyzed with a personal computer, and the opening angles were measured. The flow rate was set as 5.0 L/min. The system was pulsed with 70 bpm, and the systolic/diastolic ratio was 0.3. Glycerin water was used as the circulation fluid at room temperature, and polystyrene particles were used to visualize the streamline. The model of the sinus of Valsalva was made of transparent silicone rubber. As a result, high speed video analysis showed that the test valve started the closing motion 41 ms earlier than the CM valve, and streamline analysis showed that the test valve had a closing mechanism similar to the natural one with the effect of vortex flow. The structure of the test valve was thought to be effective for soft closure and could solve problems associated with closure.

Reduction of polyethylene wear by concave dimples on the frictional surface in artificial hip joints.

For the purpose of reduction of polyethylene wear generated in artificial hip joints, concave dimples were formed on the surface of the metal femoral head by electrical discharge etching with the constant diameter of 0.5 mm, pitch of 1.2 mm, and depth of 0.1 mm. Using a hip joint simulator, the total amount of polyethylene wear was 7.2 mg in the concave-patterned condition and 23.1 mg in the nonpatterned condition. The reasons for the reduction of polyethylene wear by the concave pattern may be i) a reduction of abrasive wear by providing escape dimples for wear particles and ii) an improvement in the lubricity on the frictional surface by the supply of lubricant that is stored in dimples.

Crystal chemistry of hydroxyapatite deposited on titanium by sputtering technique.

Crystalline hydroxyapatite (HA) powder was coated on titanium substrate by radio frequency (RF) magnetron sputtering. The coating was homogeneous thin film and the thickness was 1microm. Crystallinity of the HA coating was low and Ca/P ratio was high as 3.0. Particle sizes were 40 to approximately 100 nm, and the crystallite size was calculated by 30 to approximately 50 nm using an X-ray diffractometry (XRD) and a transmission electron microscopy (TEM). When the coating was heated at 800 degrees C for 1 h, the low crystalline HA grew up crystalline HA, and a diffraction pattern of CaO appeared. When the coating was immersed in pH 7.4 of bovine serum for 1 week, c-axis of HA increased.

Lymphocyte activation effect of (1-->6)-2,5-anhydro-D-glucitol and it derivatives with 3,4-di-O-methyl and sulfate groups.

(1-->6)-2,5-Anhydro-3,4-di-O-methyl-D-glucitol (2a) and (1-->6)-2,5-anhydro-D-glucitol (2c) and its sulfated derivative (2d) were synthesized and their biological activities were evaluated in regards to the effects on murine lymphocytes. The polymers showed different effects on the lymphocytes depending on the substituent groups. The sulfated polymer (2d) induced mitogenic activities, and specifically activated the CD4(-)CD8(-) subset of lymphocytes.

Preliminary study on the effect of substrate size on cellular immunomodulations.

It is well known that the adsorption behavior of lymphocytes on fiber materials is related to the fiber size. In our previous study, murine lymphocytes cultured on various sizes of fibers showed different interleukin 2 (IL-2) activity, and ultrafine fibers of 1.5 microns showed the highest value. Based upon those results and to further evaluate the effects of fibers of different sizes on the modulation of lymphocyte functions, Concanavalin A (Con A) was immobilized on the surface of fibers having different diameters, and murine lymphocytes were cultured on these fibers. Fiber size effects on the lymphocytes were evaluated in terms of IL-2 production and adhesion morphology. The Con A immobilized fibers could stimulate lymphocytes to levels as high as 70-80% of the maximal value induced by the Con A solution. Statistical differences in IL-2 production were not observed among the fiber sizes although as fibers decreased in size, the contact area of the lymphocytes with fibers became smaller. The results suggest that smaller diameter fibers with less contact to adherent lymphocytes can affect lymphocyte function to similar extents on larger diameter fibers and that ultrafine fibers might be useful substrates for immobilizing immunomodulators.

Blood compatibility of sputter-deposited alumina films.

The surface modification of metals by the application of blood compatible ceramics is one approach to developing durable and blood-compatible materials. The blood compatibility of sputter-deposited alumina films was investigated in vitro. The alumina films were prepared by reactive sputtering and conventional sputtering. Diffractometer studies of the alumina films indicate that the sputter-deposited alumina films have amorphous structures. Electron spectroscopy chemical analysis studies of the alumina films indicate that the sputter-deposited alumina films are nonstoichiometric (O/A1 ratio of 1.15-1.66). We examined the platelet reaction to the alumina films and the intrinsic coagulation factor XII activation by the alumina films. Medical grade segmented polyurethane was also tested. The alumina films experienced an adhesion of about 50% fewer platelets than the segmented polyurethane. Also, fewer platelet morphologic changes were observed on the alumina films than on the segmented polyurethane. Factor XII activation was less on the alumina films than on the segmented polyurethane. Surface modification by the sputter-deposited alumina films is promising for developing blood-compatible and durable materials.

Modification of the frictional surfaces of artificial joints.

To overcome the wear problems associated with artificial joint materials, new surface structures with regular patterning were designed and fabricated. The lubrication properties were studied to evaluate the wear of the frictional surfaces. The surface structure was a pattern of "dents" with a diameter of 0.2-1.0 mm and a pitch of 0.6-2.0 mm. The pattern was fabricated on the stainless steel (SUS) surface by a photochemical etching technique with 3 microns depth, and on an ultrahigh molecular weight polyethylene (UHMWPE) surface by mechanical processes. The time dependent changes of frictional force between SUS and UHMWPE were measured, and the surface morphologic changes were observed. The patterned surface showed lower frictional force than the smooth non-patterned surface, and less wear occurred on the patterned sample than on the sample without a pattern. There were optimum sizes for the diameter and the pitch of the pattern. These results demonstrated that lubrication properties could be improved by patterning of the frictional surfaces. The surface patterning was effective in preventing wear of the frictional surface, and the life of an artificial joint could be extended by such patterning.

Investigation of parameter estimator and adaptive controller for assist pump by computer simulation.

The multi-output adaptive controller of a left ventricular assist device (LVAD) was studied by computer simulation. The controller regulated two outputs--mean aortic pressure (mAoP) and mean atrial pressure (mLAP)--by regulating vacuum pressure (input). The autoregressive models were used to describe the circulatory system. The parameters of the models were estimated by the recursive least squares method. Based on the autoregressive models, the vacuum pressure minimizing a performance index was searched. The index used was the weighted summation of the square errors. Responses of the adaptive controller were simulated when the contractility of the left ventricle was decreased at various rates and the peripheral resistance was changed. Both the mAoP and mLAP were controlled to their predicted values in the steady state. The steady-state errors of the mAoP were less than a few mm Hg, and those of the mLAP were lower than 1 mm Hg. Consequently, the estimated parameters can be regarded as true parameters, and the adaptive controller has the potential to control more than two outputs. The multioutput adaptive controller studied is useful in controlling the LVAD according to the change in circulatory condition.