Akira Watazu

Chronological Changes in the Ultrastructure of Titanium-Bone Interfaces: Analysis by Light Microscopy, Transmission Electron Microscopy, and Micro-Computed Tomography

PURPOSES The objectives of this study were to chronologically examine the titanium-bone interfaces and to clarify the process of osseointegration using light microscopy, transmission electron microscopy (TEM), and micro-computed tomography (CT). MATERIALS AND METHODS Experimental implants (Ti-coating plastic implants) were placed into tibiae of 8-week-old rats. Animals were sacrificed at 1 to 28 days after implant placement and prepared tissue specimens for a light microscope, a TEM, and micro-CT. RESULTS New bone formation began 5 days after implant placement, and osseointegration was obtained by 14 days after implant placement. Osseointegration was well developed by 28 days after implant placement. DISCUSSION TEM and quantitative computer tomography (QCT) results indicated that bone formation in osseointegration of titanium implants did not occur from the surfaces of the implant or preexisting bone, but it was likely that bone formation progressed at a site a small distance away from the surface. The bone formation took place in a scattered manner. Small bone fragments adhered to each other and transformed into reticular-shaped bone, and finally these bones became lamellar bone. CONCLUSION Comparative analysis of the titanium-bone interfaces using light microscopy, TEM, and QCT by micro-CT revealed the precise process of osseointegration.

Billet temperature rise during equal-channel angular pressing

AbstractTheactualbillettemperatureduringequal-channelangularpressingwasmeasuredanddiscussed.Thetemperaturerisesofaluminumalloysandamagnesiumalloyat573Kwerebetween4and6Kat673K,whenthedeformationratewas1mms 1 .Adiabaticcompressionisresponsibleforabout10–20%ofthetotalgeneratedheat. 2002ActaMaterialiaInc.PublishedbyElsevierScienceLtd.Allrightsreserved. Keywords:Equal-channelangularpressing;Temperaturerise;Mechanicalwork;Adiabaticcompression;Heattransfer 1. IntroductionEqual-channelangularpressing(ECAP)isanattractivedeformationprocessthatcanproduceultrafine-grained bulk materials without chang-ingthecross-sectionaldimensionsofabillet.InECAP,abilletisrepeatedlypassedthroughtwodiechannelsofequalcross-sectionconnectedatanangle[1–10].MostofthestudiesonECAPpub-lishedtodateareconcernedmainlywiththeabilityto produce ultrafine-grained microstructures [1]andtheuniquedeformationgeometry[6]oftheECAPprocess.Numericalsimulationsofthede-formationduringECAPhavealsobeenpresented[8]. The production of an ultrafine-grained mi-crostructure in ECAP results from the intenseplastic strains introduced in the material thatdriverecrystallizationinthestrainedmaterial.ThemechanismsofmicrostructuralevolutioninECAPwere discussed for four different deformationgeometriesbyLangdonetal.[11].OneofthefactorsthataffectthegrainsizeinECAPis thetemperatureofthebillet inwhichdeformationandrecrystallizationtakeplace.Prac-tically,thebillettemperatureiscontrolledthroughthe billet preheating temperature. However, theexactbillettemperatureduringanECAPopera-tion may be significantly above the preheatingtemperatureduetotheheatgeneratedbytheme-chanicalwork.Itisthereforenecessarytomeasurethe actual billet temperature during ECAP forprecisecontrolofrecrystallization,andhenceofthegrainsize.ThetemperatureriseduringECAPisconsideredtodependonboththebilletmate-rial and the deformation rate. This study was

Properties of titanium biomaterial fabricated by sinter-bonding of titanium/hydroxyapatite composite surface-coated layer to pure bulk titanium

Abstract A new titanium biomaterial was fabricated by hot press sinter-bonding of titanium/hydroxyapatite composite surface-coated layer to pure bulk titanium. The distribution of the hydroxyapatite particles in the composite surface-coated layer was mainly influenced by the hydroxyapatite volume fraction (Vha) of the composite surface-coated layer. When the Vha was less than 15%, it was uniform. At the temperature of 1023 K, no interfacial reaction layer was observed at the interface between the hydroxyapatite and titanium matrices in the composite surface-coated layer. The tensile strength of the new titanium biomaterial was influenced both by the ratio of thickness of the composite surface-coated layer to the total thickness of the titanium biomaterial and the Vha. Three tensile damage phenomena associated with microstructure of the titanium biomaterial were observed after tensile test. (1) Cracks with small crevice appeared in the composite surface-coated layer and the tensile strength was almost equal to that of pure titanium. (2) Cracks with large crevice appeared in the composite surface-coated layer and the tensile strength was lower than that of pure titanium. (3) No crack appeared in the composite surface-coated layer and the tensile strength was much lower than that of pure titanium. The results of bone conductivity test showed that hydroxyapatite had an ability to improve the bonding between the titanium biomaterial and bone.

Peri-implant bone density in senile osteoporosis-changes from implant placement to osseointegration.

PURPOSE The aim of this study was to examine healing over time after implant body placement in a senile osteoporosis model and a control group. MATERIALS AND METHODS In this study, 16-week-old male mice were used. The senile osteoporosis model consisted of senescence-accelerated prone 6 mice and the control group consisted of senescence-accelerated resistant 1 mice. Titanium-coated plastic implants were used as experimental implants whose dimensions were 3.0 mm in length, 1.1 mm in apical diameter, and 1.2 mm in coronal diameter. Bone samples were collected at 5, 7, 14, 21, and 28 days after implant placement. A micro-quantitative computed tomography (QCT) system was used to scan these samples and a phantom in order to quantitate bone mineral measurements. Bone mineral density (BMD) of each sample was measured. Each sample was also examined by light microscopy after QCT imaging. At 14 and 28 days after implant placement, the bone-implant contact (BIC) ratios were calculated from light microscopy images and were divided into cortical bone and bone marrow regions. RESULTS When BMD was compared between the osteoporosis and control groups using micro-QCT, the osteoporosis group had a significantly lower BMD in the region 0-20 µm from the implant surface in the bone marrow region at 14 days onward after implant placement. Compared with the control group, the osteoporosis model also had significantly lower BMD in all regions 0-100 µm from the implant surface in the bone marrow region at 14 days after placement. However, in the cortical bone region, no statistically significant difference was observed in the regions at the bone-implant interface. Light microscopy revealed osseointegration for all implants 28 days after implant placement. The osteoporosis model tended to have lower BICs compared with that of the control group, although this did not reach statistical significance. DISCUSSION Our results showed that osseointegration was achieved in the osteoporosis model. However, the BMD was 30-40% lower than that of the control group in the region closest to the implant surface in bone marrow region. Peri-implant BMD was lower in a relatively large area in the osteoporosis model during an important time for osseointegration. Therefore, this result suggests that osteoporosis might be considered as a risk factor in implant therapy. CONCLUSION The osteoporosis model had a lower BMD than the control group in the region closest to the implant during an important time for osseointegration. This result suggests that senile osteoporosis might be a risk factor in implant therapy. However, the osteoporosis model and the control group had no difference in peri-implant BMD in the cortical bone region. This suggests that risk might be avoided by implant placement that effectively uses the cortical bone.

Recycling of 6061 Aluminum Alloy Cutting Chips Using Hot Extrusion and Hot Rolling

Possibilities of the consolidation process using hot extrusion and subsequent hot rolling were investigated in order to recycle the cutting chips of the aluminum alloy efficiently. For the rolling process, differential speed rolling (DSR) was also applied in addition to normal rolling. Several kinds of cutting chips with different size and cleanliness were collected through turning 6061 aluminum alloy round bars. From these cutting chips, recycled material sheets were produced under various processing conditions via hot extrusion and subsequent hot rolling. Non-recycled material sheets were also prepared for comparison. All samples were characterized by optical microscopy, SEM(EBSP), X-ray texture analysis, tensile test and corrosion test. As a result, it was found that the recycled material sheets produced under optimum processing conditions had smaller grain sizes than those of the non-recycled ones, therefore the mechanical properties and the corrosion resistance of the recycled material sheets were almost comparable to those of the non-recycled ones. Moreover, concerning the DSR processed sheets, the traces of the chip interface, which were clearly observed in the normally rolled ones, almost disappeared, and the appearances were remarkably improved. Then the DSR processed sheets significantly surpassed the non-recycled ones in the tensile properties and the corrosion resistance.

Formation of Calcium Phosphate/Titanium Oxide/Titanium/ Plastic Composite Implant

Calcium phosphate/ titanium oxide/ titanium/ plastic composite implants with 1.6-mm diameter and 7-mm length were successfully formed using a DC/ RF magnetron sputtering machine. The sample had no cracks and the surface of the sample was uniformly smooth. The chemical composition of the >10-nm-thick calcium phosphate layer was Ca: P: O=1.0: 0.79: 2.8. The sample was implanted into the tibia of an male 8-week-old SD rat for 28 days. When 0.70-μm sections of the tibia were prepared, the titanium layer with titanium oxide layer of the implant was not broken and the surfaces of the layer of the implant had not decomposed. The interaction between living bone and the implant could be clearly observed by light microscope and TEM.

Ti-Ca-P Films Formed by RF Magnetron Sputtering Method Using Dual Targets

Ti-Ca-P films on commercial pure (cp) titanium plates were uniformly deposited using dual target RF magnetron sputtering apparatus with DC magnetron sputtering system under the conditions of 50 W DC power to a cp titanium target and 200 W RF power to a β-tricalcium phosphate (β-TCP) target for 60 min in 2.2×10-1 Pa Ar. Resulting samples had smooth surface like mirror. Crystal structure of the film was amorphous. The film had the chemical composition of about 3: 1.7: 1: 11 in Ti: Ca: P: O ratio under controlling the β-TCP target RF sputtering power and the titanium target DC sputtering power. The film and the method are expected to be useful for remodeling surfaces of various titanium implants.

Effects of homogenization treatment on mechanical properties of hot-rolled AZ31 magnesium alloy

The mechanical properties of the AZ31B alloy sheets processed by differential speed rolling (DSR) from the cast ingots homogenized at two different conditions were investigated. There still existed the uneven distribution of Al and Zn in the ingot homogenized at 673 K for 6 h, while it was homogeneous for the ingot homogenized at 723 K for 24 h. Compare with the sheet rolled from the ingot homogenized at 673 K for 6 h, the sheet rolled from the ingot homogenized at 723 K for 24 h exhibited a lower proof stress, a larger elongation, and a lager strain hardening exponent. The improvement in the ductility can be attributed to the elimination of the microsegregation of Al and Zn in the matrix.

Effects of Manganese on Microstructure and Mechanical Properties of AZ31 Magnesium Alloy Processed by Differential Speed Rolling

A DSR processing with a roll speed ratio of 1.08 was carried out on an AZ31 alloys with Mn additions of 0, 0.2, 0.4 and 0.6 wt.% for investigating the effects of Mn on the microstructural evolution and mechanical properties. The amount of the Al-Mn compounds increased with increasing the Mn content. Compare with the DSR processed sheet without Mn addition with a homogeneous grain size, those with Mn additions exhibited an inhomogeneous microstructure due to the appearance of the shear bands comprising the small grains around 5 μm. The Mn addition exhibited a significant effect in grain refinement even for a low content of 0.2 wt.%, which reduced the average grain size from about 25 μm to 10 μm. The Mn addition resulted in the significant increases in the tensile strength and the 0.2% proof stress by about 25 MPa and 40 MPa, respectively.

Influences of Rolling Conditions on Texture and Formability of Magnesium Alloy Sheets

The AZ61 magnesium alloy was subjected to the differential speed rolling at different rolling conditions including reduction per pass, rotation speed ratio and rolling temperature, and the influences of the rolling conditions on microstructure, texture, mechanical properties and formability of the as-rolled sheets were investigated. Increasing the reduction per pass results in a more homogeneous microstructure and a relatively weaker basal texture. With increasing the rotation speed ratio, the inclination angle of basal pole toward the rolling direction increases and the stretch formability enhances correspondingly. Increasing the rolling temperature has an effect on weakening the basal texture intensity and leads to the enhancement of stretch formability.