Biomedical subjects

Jiro Tamura

Publications and source records attributed to Jiro Tamura.

13 recordsLinked to original sources

PubMed2006

Bioactive and bioresorbable cellular cubic-composite scaffolds for use in bone reconstruction.

We used a novel composite fibre-precipitation method to create bioactive and bioresorbable cellular cubic composites containing calcium phosphate (CaP) particles (unsintered and uncalcined hydroxyapatite (u-HA), alpha-tricalcium phosphate, beta-tricalcium phosphate, tetracalcium phosphate, dicalcium phosphate dihydrate, dicalcium phosphate anhydrate or octacalcium phosphate) in a poly-D/L-lactide matrix. The CaP particles occupied greater than or equal to 70 wt% (greater than or equal to 50 vol%) fractions within the composites. The porosities of the cellular cubic composites were greater than or equal to 70% and interconnective pores accounted for greater than or equal to 70% of these values. In vitro changes in the cellular geometries and physical properties of the composites were evaluated over time. The Alamar Blue assay was used to measure osteoblast proliferation, while the alkaline phosphatase assay was used to measure osteoblast differentiation. Cellular cubic C-u-HA70, which contained 70 wt% u-HA particles in a 30 wt% poly-D/L-lactide matrix, showed the greatest three-dimensional cell affinity among the materials tested. This composite had similar compressive strength and cellular geometry to cancellous bone, could be modified intraoperatively (by trimming or heating) and was able to form cortico-cancellous bone-like hybrids. The osteoinductivity of C-u-HA70, independent of biological growth factors, was confirmed by implantation into the back muscles of beagles. Our results demonstrated that C-u-HA70 has the potential as a cell scaffold or temporary hard-tissue substitute for clinical use in bone reconstruction.

Absorbable Implants↗

PubMed2005

In vivo evaluation of a porous hydroxyapatite/poly-DL-lactide composite for use as a bone substitute.

We investigated the biocompatibility, osteoconductivity, and biodegradability of a porous composite of hydroxyapatite (HA) and poly-DL-lactide (PDLLA) implanted into rabbit femoral condyles and compared it with porous HA. Six weeks after implantation, the HA/PDLLA was covered with bone and contacted the bone directly. The amount of newly formed bone in the pores was similar in both materials during the examined period. The newly formed bone in the HA/PDLLA tended to increase over 26 weeks, but that in the HA did not show a significant increase after 12 weeks. By 26 weeks, remodeling of the newly formed bone in the pores was seen and bone marrow tissue was found in the pores of the HA/PDLLA. The porous HA/PDLLA was resorbed much faster than the porous HA. Porous HA/PDLLA was resorbed continuously through bone formation and remodeling. Conversely, porous HA was scarcely resorbed throughout the period. HA/PDLLA is thought to be degraded almost completely after about 1 year, and in this study, porous HA/PDLLA showed excellent osteoconductivity and faster resorption than HA. Therefore, HA/PDLLA might be a desirable material for bone substitutes.

Animals↗

PubMed2005

A 5-7 year in vivo study of high-strength hydroxyapatite/poly(L-lactide) composite rods for the internal fixation of bone fractures.

The biocompatibility and biodegradation of hydroxyapatite (HA)/poly(L-lactide) (PLLA) composite bone implant rods were studied using two types of HA particles as reinforcing fillers, uncalcined-HA (u-HA) or calcined-HA (c-HA). Composite rods of u-HA/PLLA and c-HA/PLLA were implanted into the distal femurs of 25 rabbits. Four of these rabbits lived for more than 5 years after implantation, with one living for 7 years 4 months. Samples were retrieved after the rabbits died naturally and specimens were examined by light microscopy and scanning electron microscopy (SEM). For u-HA/PLLA, the shrinkage of the rods progressed further after 4 years, and some were almost completely resorbed. We could not find traces of the rod in some sections from more than 6 years. Remodeled bone encircled the residual material, and trabecular bone bonded directly to the rod was found toward the center. For u-HA/PLLA 30%, results were similar to u-HA/PLLA 40%, and the cross-sectional area had decreased by 4.0% at over 7 years. Most of the PLLA had been released from the rods. Neither obvious osteolytic nor osteoarthritic changes were found after 4 years.

Animals↗

PubMed2005

Effect of alumina femoral head on clinical results in cemented total hip arthroplasty: old versus current alumina.

BACKGROUND: The wear rate of polyethylene against alumina was demonstrated to be lower than against metal, and the results of early clinical studies of alumina-on-polyethylene combination were as good as expected, but the long-term results of alumina ceramic heads were not as good, as reported by several authors. The purpose of this study was to assess the clinical results over 10 years of cemented total hip arthroplasty (THA) with two types of alumina head: old and current alumina. METHODS: We compared the clinical results of these two types of alumina used for cemented THA. The first type was old alumina (containing 7% yttria), and 77 hips with a 28-mm head (group I) were included. The second type was current alumina (highly purified alumina), and 50 hips with a 26-mm head (group II) and 88 hips with a 22-mm head (group III) were included. The mean follow-up was 17 years 4 months in group I, 12 years 3 months in group II, and 10 years in group III. RESULTS: The Kaplan-Meier survival analysis, with revision for any reason as the endpoint, predicted 10-year survival rates of 90.8%, 100%, and 97.5% for groups I, II, and III, respectively. The survival curves differed significantly only between groups I and II. The probabilities of 10-year survival of the pros-theses with radiological loosening as the endpoint were 77.2%, 91.6%, and 96.5%, respectively. The survival curves showed significant differences only between groups II and III. CONCLUSIONS: The old alumina showed a higher wear rate and rougher surface on the femoral head than did the current alumina in our previous study. The clinical results also indicated superiority of current alumina over old alumina. The difference in the size of the femoral head (26 vs. 22 mm) did not affect the clinical results.

Adult↗

PubMed2004

Displacement of a cemented socket after reduction of a dislocated total hip arthroplasty.

Acute displacement of the cemented acetabular component of a hip arthroplasty after attempted reduction of a dislocation is described. The causes of displacement of the socket, which was not radiologically loose, are discussed. Potential causes include impingement of the femoral head and the ceramic screw head overhanging the acetabular bone, which was used to fix the bone graft.

Aged↗

PubMed2004

In vivo absorption of porous apatite- and wollastonite-containing glass-ceramic.

The behavior of porous apatite- and wollastonite-containing glass-ceramic (AW) in the bone marrow cavity was investigated. Cylinders of porous AW (4 mm in diameter and 20 mm long, mean porosity of 70% and mean pore diameter of 200 microm) were implanted into the bone marrow cavity of rabbit femurs, and analyzed by chronological radiograms and by scanning electron microscopy one, three, six, and 12 months later. The pores of porous AW are interconnected and homogeneously distributed, and its compressive strength is nearly equal to that of human cancellous bone. Bone formed in the pores at the center of the material by one month and bonded to the material directly. The volume of newly formed bone in the material pores reached a peak at three months, and decreased gradually after six months. The trabecular structures of AW were gradually remodeled by newly formed bone, while AW-bone bonding was maintained during bone remodeling and material absorption. AW was absorbed continuously, and at six and 12 months the residual material corresponded to about 64 and 30% of the starting material, respectively. Porous AW may therefore be useful as an absorbable bone substitute.

Absorbable Implants↗

PubMed2003

Phase stability after aging and its influence on pin-on-disk wear properties of Ce-TZP/Al2O3 nanocomposite and conventional Y-TZP.

Recently zirconia/alumina composites have been examined by many researchers as the new generation of bearing materials in total joint replacements. In this study, the phase stability of a Ce-TZP/Al(2)O(3) nanocomposite and conventional Y-TZP after aging, and its influence on wear resistance, were investigated. Very slight phase transformation was observed in both types of ceramics 18 months after the implantation of Ce-TZP/Al(2)O(3) or Y-TZP samples into rabbit tibiae. However, Y-TZP showed marked phase transformation (approximately 80%) after aging in an autoclave (121 degrees C) for 190 h or in physiological saline at 62 degrees C for 18 months, whereas the new composite remained almost resistant to degradation. According to the results of self-pairing pin-on-disk wear tests using ceramic specimens with or without autoclave aging, the wear factor was almost the same between Ce-TZP/Al(2)O(3) samples with and without aging (6.74 +/- 0.36 x 10(-8) and 6.04 +/- 0.95 x 10(-8) mm(3)/Nm, respectively). In contrast, although non-aged Y-TZP had the lowest wear factor (4.88 +/- 0.51 x 10(-8) mm(3)/Nm) of all specimens tested, aged Y-TZP showed 10-fold greater wear than nonaged Y-TZP. The present study suggests that Ce-TZP/Al(2)O(3) nanocomposite has much greater phase stability than Y-TZP, and that its wear properties are not influenced by aging.

Aluminum Oxide↗

PubMed2003

Long-term study of high-strength hydroxyapatite/poly(L-lactide) composite rods for the internal fixation of bone fractures: a 2-4-year follow-up study in rabbits.

Biodegradation of hydroxyapatite (HA)/poly(L-lactide)(PLLA) composite bone implant rods was studied with the use of two types of HA particles as reinforcing fillers: uncalcined HA (u-HA) or calcined HA (c-HA). Composite rods of u-HA/PLLA and c-HA/PLLA containing 30 or 40% (w/w) HA were implanted in the distal femur of 21 rabbits, and specimens were examined by light microscopy, scanning-electron microscopy (SEM), and transmission-electron microscopy (TEM) 2-4 years later. For u-HA/PLLA, trabecular bone bonding directly onto the rod was maintained for up to 2 years. By 3 years, surface collapse had begun, and the implants were shrinking. By 4 years, they had shrunk further, with complete bone encapsulation. The u-HA particles were small and needle shaped in the peripheries, and TEM confirmed their resorption. The cross-sectional area after 4 years decreased by 23.3+/-8.4%. The mean ratio of bony ingrowth to the initial cross-sectional area around the shrunken rods was 6.7+/-1.3 %. The viscosity molecular weight of PLLA reduced from 2 x 10(5) to less than 1 x 10(3). Thus, most of the PLLA had released from the rods. The c-HA/PLLA implants also showed good osteoconductivity, but shrinkage and infiltration of histiocytes were less. No osteolytic or osteoarthritic changes were found.

Absorbable Implants↗

PubMed2003

Wear mode and wear mechanism of retrieved acetabular cups.

Nineteen ultra-high-molecular-weighted polyethylene (UHMWPE) cups were retrieved at revision surgery. The implant period was on average 9.9 (0.25-20.7) years. The cups were classified into the high-wear group (wear rate above 140 mm(3)/year), intermediate-wear group (wear rate 80-140 mm(3)/year) and low-wear group (wear rate below 80 mm(3)/year). The wear rate was measured by a fluid displacement method. The cups were studied using scanning electron microscopy. Ripples mainly appeared on the cups in the low-wear group, and nodules and fibrils mainly appeared in the high-wear group. Folding was observed in all cups, but folding with numerous fibrils was conspicuous in the high-wear group. The cup retrieved at 3 months already exhibited folding. From these results, the wear response appeared to be a three-step process: (1) foldings are generated, (2) ripples are formed on the surface, and (3) fibrils are produced from the surface and delaminated, leading to the formation of wear debris.

Adult↗

PubMed2003

Histological and mechanical investigation of the bone-bonding ability of anodically oxidized titanium in rabbits.

The purpose of this study was to histologically and mechanically investigate the in vivo bone-bonding ability of anodically oxidized titanium (AO Ti) with an anatase crystal layer on its surface. AO Ti plates, anodically oxidized at 155 V in 1 M H2SO4, were implanted into the proximal metaphyses of mature rabbit tibiae for 4, 8, 16, and 24 weeks and investigated by light microscopy, scanning electron microscopy and detaching test. High bone-bonding ability, comparable to our previous study data of the bioactive titanium produced by sodium-free alkali and heat treatment, was observed at the early stages of implantation. However, no substantial increase was demonstrated. AO Ti plates bonded to bone directly, with no intervening soft tissue layer, and no breakage of the AO Ti layer was observed. The AO Ti layer was porous through to the titanium substrate, while the porosity was low. Apatite-like deposition into the pores of the AO layer was observed only in the superficial zone. The lack of improvement of bone-bonding ability in the later stages of implantation may be attributed to the low porosity and to the superficial ingrowths of apatite-like deposits into the pores of the AO Ti layer.

Animals↗

PubMed2002

Interfacial tensile strength between polymethylmethacrylate-based bioactive bone cements and bone.

We have developed two types of polymethylmethacrylate (PMMA)-based bioactive bone cements containing bioactive glass beads (designated GBC) or apatite-wollastonite containing glass-ceramic powder (designated AWC) as the filler. A new method was used to evaluate the bone-cement interfacial strength of these bioactive bone cements. Two types of bioactive bone cements (GBC and AWC) and PMMA cement (CMW-1) were put in a frame attached to the smooth tibial metaphyseal cortex of the rabbit and polymerized in situ. The load required to detach the cement from the bone was measured at 4, 8, and 16 weeks after implantation. The interfacial tensile strength of GBC and AWC showed significantly higher values than PMMA cement from 4 weeks, and increased with time. For GBC, strength reached a maximum value of 12.39 +/- 1.79 kgf 16 weeks after implantation. Histological examination of rabbit tibiae up to 16 weeks demonstrated no intervening layer between the bioactive bone cements and the bone, whereas fibrous tissue was observed at the interface between the PMMA cement and the bone. From this study, we conclude that PMMA-based bioactive bone cements have a relatively higher adhesiveness at the interface than the conventionally used PMMA cement, showing potential as a promising alternative.

Animals↗

PubMed2002

Micro-wear patterns on UHMWPE tibial inserts in total knee joint simulation.

The objective of this study was to examine both simulator and retrieved total knee replacement polyethylene inserts to confirm, using scanning electron microscopy, whether similar micro-wear patterns to those seen on retrieved inserts were reproduced on simulator specimens. The simulator specimens consisted of samples subjected to sliding and rolling movement (Experiment 1) and to sliding movement only (Experiment 2). Samples from Experiment 1 demonstrated longitudinal patterns in the middle of the wear track and transverse patterns in the anterior and posterior ends, whereas in Experiment 2, only transverse patterns were observed. In the retrieved specimens, both longitudinal and transverse patterns were observed. The results showed that the simulator study reproduced similar patterns of micro-damage on polyethylene, and that the longitudinal micro-wear pattern was related to the rolling movement that is distinctive in knee kinematics.

Biomechanical Phenomena↗

PubMed2002

Ce-TZP/Al2O3 nanocomposite as a bearing material in total joint replacement.

The objectives of this study were to investigate the biocompatibility, phase stability, and wear properties of a newly developed Ce-TZP/Al(2)O(3) nanocomposite, as compared to conventional ceramics, and to determine whether the new composite could be used as a bearing material in total joint prostheses. In tests of mechanical properties, this composite showed significantly higher toughness than conventional Y-TZP. For biocompatibility tests, cylindrical specimens of both the Ce-TZP/Al(2)O(3) nanocomposite and monolithic alumina were implanted into the paraspinal muscles of male Wistar rats. The tissue reactions were almost the same, and at 24 weeks after implantation, thin fibrous capsules with almost no inflammation were observed around both of them. There were no significant differences in membrane thickness between the two ceramics. After hydrothermal treatment in 121 degrees C vapor for 18 h, the new composite showed complete resistance to aging degradation, whereas Y-TZP showed a phase transformation of 25.3 vol% (initial 0.4%) to the monoclinic form. According to the results of pin-on-disk tests, the wear rates of Ce-TZP/Al(2)O(3) nanocomposite and alumina were 0.55 +/- 0.04 x 10(-7) and 2.12 +/- 0.37 x 10(-7)mm(3)/Nm, respectively. The results of this study suggest that the Ce-TZP/Al(2)O(3) nanocomposite is a promising alternative ceramic component for total joint replacement.

Aluminum Oxide↗