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We assume that every pair of n players has shared a one-bit key in advance, and that each key has been completely exposed to an eavesdropper, Eve, independently with a fixed probability p (and, thus, is perfectly secure with a probability of \(1-p\)). Using these pre-shared, possibly leaked keys, we want two designated players to share a common one-bit secret key in cooperation with other players so that Eve’s knowledge about the generated secret key will be as small as possible. The existing protocol, called the st-flow protocol, achieves this, but the specific probability that Eve knows the generated secret key is unknown. In this study, we answer this problem by showing the exact leak probability as a polynomial in p for any number n of players.

Various zeolites have been synthesized from coal fly ash (FA) by hydrothermal treatment with NaOH solution. Phillipsite-type zeolite was synthesized selectively from FA (FA-phillipsite), and succeeded in in situ combining the FA-phillipsite with sepiolite to form FA-phillipsite/sepiolite composite. The adsorption behaviour of two harmful heavy metal ions (Pb 2+ and Cd 2+ ) were investigated for the FA-phillipsite and FA-phillipsite/sepiolite composite (30 mass % sepiolite). It was found that the NaOH hydrothermal treatment produced not only phillipsite but also Na + -substituted sepiolite. Both the FA-phillipsite and the FA-phillipsite/sepiolite composite showed high adsorbing-ability for Pb 2+ (2.90 and 2.68 meq g -1 ) and Cd 2+ (1.62 and 1.74 meq g -1 ) ions. The adsorption efficiency of the composite was much higher in the measured value than in the calculated one estimated from the maximum adsorbing-ability of the untreated sepiolite. This indicates that the Na + -substituted sepiolite in the composite has excellent adsorbing-ability for Pb 2+ and Cd 2+ ions. Since sepiolite has superior forming performance, the FA-derived phillipsite/ sepiolite composite powder was able to be molded into various shapes e.g. pellet and tube. The FA-phillipsite/sepiolite composite is expected to be a new adsorbent for practical use.

Some previous studies suggest that aging influences wear and oxidatively degraded nonsterilized ultra-high-molecular-weight polyethylene (UHMWPE) exhibits decreased wear resistance. We therefore asked whether shelf-aging storage conditions influenced degradation and wear resistance of gamma-irradiated UHMWPE. We examined oxidation and wear of 100-Mrad gamma-irradiated UHMWPE (100-Mrad polyethylene) cups shelf-aged for 30 years without (n=2) or with (n=2) packages. The oxidation index of the unpackaged 100-Mrad polyethylene surface (4) was higher than that of the packaged one (2.7). The packaged 100-Mrad polyethylene cup exhibited a high wear resistance with a steady wear rate of 0.5 mg/10(6) cycles. In contrast, the unpackaged 100-Mrad polyethylene exhibited an extremely high initial wear rate of 187.9 mg/10(6) cycles over the first 0.25 x 10(6) cycles with a subsequently reduced wear rate of 5 mg/10(6) cycles after 5 x 10(6) cycles. Packaging over long periods inhibits surface oxidation and maintains the wear resistance of gamma-irradiated UHMWPE cups.

In total hip prosthesis (THP), we have been using alumina ceramic femoral heads to reduce polyethylene debris and the modified cementing technique, which was named “interface bioactive bone cement (IBBC)” method to improve implant fixation. In this study, we investigated the long-term clinical performance of THPs with an alumina ceramic head and IBBC method. From 1986 to 1988, 285 joints (215 patients) were operated on by a senior surgeon, and 265 joints (192 patients) could be followed up. The presence of radiolucent lines, loosening, osteolysis and ultrahigh-molecular-weight polyethylene (UHMWPE) socket wear were observed. In IBBC, a radiolucent line appeared as a ’space’, and loosening appeared as a ’separation’ between the HA layer and the cement. A ‘space’ appeared in 3 joints (1.4%) on the acetabulum and in 4 joints (1.8%) on the femur, while a ‘separation’ appeared in 3 joints (1.4%) on the acetabulum. Osteolysis was noted in 1 joint (0.5%) on the acetabulum and in 2 joints (0.9%) on the femur. No revision surgery was required. In our previous study, we reported that the thickness of the socket affected its clinical wear rate and that the wear rate of sockets with an alumina ceramic head was 20% lower than that of sockets with a metal head. By reducing wear debris through the use of ceramic heads, osteolysis could be reduced. Long-term fixation of THPs to the bone has been achieved by using IBBC. Thus, the long-term clinical results of THPs with an alumina head that were fixed using IBBC were excellent.

The efficacy of a composite of beta-tricalcium phosphate particles and carboxymethyl-chitin (beta-TCP/CM-chitin) for bone repair has already been established in animal experiments. In the present study, subacute systemic toxicity was evaluated to further assess the biological safety of the implanted composite. beta-TCP/CM-chitin (approximately 4 mg/kg and 7 mg/kg in male and female rats, respectively) was implanted for 28 days into penetrating defects (2 mm diameter) made artificially in the shaft of the right femur of rats. Sham operation groups with the defect only were prepared as controls. Haematology, blood chemistry, urinalysis, and the histopathology of 44 organs and tissues were investigated. Body weight measurements and clinical observations were performed daily throughout the study. No subacute systemic toxicity possibly caused by the implantation of beta-TCP/CM-chitin was detected. These findings indicate that beta-TCP/CM-chitin composite is a highly biocompatible bone substitute, at least with an implantation dosage of < 4-7 mg/kg.

Many techniques to restore cartilage defection have been tried. However, the development is still under way because of problems, including loosening of artificial joint, degenerative change of compensated tissue, risk of viral transmission via allograft/autograft, and cost of therapeutic materials for repair. In the previous research, we found that complementing cartilage defective part with carboxymethyl-chitin (CM-chitin)/beta-tricalcium phosphate composite induced regeneration of cartilage in rabbits in vivo, and it is presumable that CM-chitin plays a key role in chondrogenesis causing the regeneration of cartilage. However, the induction mechanism of chondrogenesis with CM-chitin is still unclear. In this study, we investigated the cell responses to CM-chitin by using peritoneal exudate cell (PEC) in mice and found that CM-chitin induced the expression of inflammatory cytokines and growth factors, both of which are both considered to correlate with chondrogenesis. After intraperitoneal injection CM-chitin showed enhanced expressions of mRNA of interleukin-1beta (IL-1beta), interleukin-6 (IL-6), keratinocyte-derived chemokine, tumor necrosis factor-alpha, and transforming growth factor-beta1 (TGF-beta1) in PEC as observed by reverse transcriptase polymerase chain reaction. Productions of TGF-beta1 protein were confirmed by enzyme linked immunosorbant assay. It was also shown that mononuclear cells in PEC were responsible for the TGF-beta1 production. These results suggest that CM-chitin is an inductor of inflammatory cytokines and growth factors and may contribute to regeneration of cartilage.

We started to use a combination of alumina ceramics and ultra-high molecular weight polyethylene (UHMWPE) for total knee arthroplasty (TKA) in the late 1970s based on our good clinical results in total hip arthroplasty as well as the results of knee joint simulator tests. From 1982 to 1985, we performed TKAs in 137 patients, mainly of the alumina/UHMWPE type. Since 1990, cemented alumina or zirconia ceramic/UHMWPE total knee prostheses have been used in more than 530 patients. From these clinical and retrieved studies, we confirmed the efficacy of the ceramic bearing surface in TKA.

A composite mover device constructed with both hydrogen storage and giant magnetostrictive alloy thin films on each side surface of polyimide substrate were prepared by flash vacuum evaporation and DC magnetoron sputtering process, respectively. Although the composite mover device was about 750ppm before hydrogenation, it was about 1150ppm after hydrogenation. The hydrogenation induced strain was approximately corresponded to that of magnetized sample.

Beta-tricalcium phosphate/carboxymethyl chitin composites [TCP/CMCh] of various ratios of TCP granules and CMCh were made and their mechanical properties, handling properties and repair performance for bone defects and for osteochondral defects were investigated. Water pooling ratio of CMCh was approximately 40 times the weight itself. TCP/CMCh of a higher TCP ratio had higher stress at 50%-strain. The stress at 50%-strain of TCP/CMCh with 0, 2.5, 5.0, 7.5, 10 TCP ratios was 0.12, 0.51, 1.08, 1.46, 1.67 (MPa, n=5), respectively. The TCP/CMCh with 5.0 TCP ratios had the best total scores in handling tests. The bone repair rate of TCP/CMCh was TCP ratio 2.5< Blank= TCP ratio 7.5< TCP ratio 5.0. In the implantation test for osteochondral defects, TCP/CMCh was completely absorbed at four weeks after surgery. Regeneration of the articular cartilage was seen with TCP/CMCh and HA/CMCh but not with TCP granules, which remained eight weeks after implantation. The regenerated articular cartilage had remained 32 weeks after implantation. In conclusion, it was demonstrated that this TCP/CMCh composite was a promising material for repairing osteochondral defects.

SmFe2.4 alloy thin films were prepared by DC magnetron sputtering process at different substrate temperatures from 323 K to 623 K and at different Ar gas pressure from 0.5 to 1.0 Pa. The magnetostriction increased with decreasing of an Ar gas pressure as sputtering gas. On the other hand, the large magnetostriction was observed at high Ar gas pressure on heating at 623 K of high substrate temperature. The maximum value of magnetostriction over 1400 ppm at 1.2 MA/m was found in a Sm-Fe film prepared at 423 K of substrate temperature and at 0.5 Pa of argon gas pressure. This value was top data for the compressive (negative) magnetostrictive films up to now. From this result, it was concluded that the amount of a magnetostriction was strongly affected by change in the morphology of the thin film.

In this study, the influence of aluminum content on shape memory effect ofTi-7Cr-Al alloys fabricated using low-grade sponge titanium was investigated by measurement of electrical resistivity and Vickers hardness, along with shape-recovery testing. The results obtained are as follows. In the STQed state, the phase constitution of non-Al added alloy, Ti-7Cr-0Al alloy, was found to consist of retained β phase and athermal ω, whereas those of Al added alloys, Ti-7Cr-1.5Al, 3.0Al and 4.5Al alloys, were found to consist oforthorhombic martensite, α", and retained β phase. Resistivity (p) at liquid nitrogen (LN) and room temperature (RT) increased monotonously with Al content. Resistivity ratio (ρ L N /ρ R T ) increased drastically at 3Al, exceeding unity. Shape recovery was exhibited in the 1.5Al, 3.0Al, and 4.5Al alloys having been fabricated using low-grade sponge titanium as raw material. In the 3.0Al and 4.5Al alloys, shape recovery ratio was about 90% at temperatures above 523 K and recovery surface strain was at least 0.03. The resistivity change indicates that stress-induced orthorhombic martensite was produced during bending of the 4.5A1 alloy.

Influences of composition on magenetostriction of Fe–Sm alloy thin films prepared by D.C. magnetron sputtering process were investigated. Composition of formed film was ranged from 24 to 59 at%Sm. Negative, that is, compressive magnetostriction was observed of Fe– Sm thin films. The magenetostriction of thin films was varied with composition rate of Fe–Sm alloy. The giant magnetostriction (GM) over 1000 ppm at 1200 kA/m was observed from 24 to 34 at%Sm for Fe–Sm amorphous film. The limited value of GM at 1200 kA/m was 1280 ppm of Fe–29.3 at%Sm alloy film.

The alumina-ceramic total knee prosthesis developed by Kyocera Corp. was implanted in 1979, and was in clinical use for 23 years until total knee arthroplasty revision surgery in January 2002. It is believed that this is the longest clinical period of a ceramic total knee prosthesis reported to date in the world. In the present study, we gave consideration to the long-term clinical stability of the alumina-ceramic femoral component as well as the mechanism of in vivo degradation of ultrahigh molecular weight polyethylene (UHMWPE) based on the evaluated wear, oxidation, and fracture toughness of the retrieved UHMWPE. We concluded that the degradation of UHMWPE by progressive oxidation is an issue to be solved in the future. To moderate stress concentration, use of a thin UHMWPE insert should be avoided. The low wear rate and the mild wear pattern observed this time suggest the possibility of reduced wear of the UHMWPE against the alumina-ceramic femoral component, and the usefulness of the alumina-ceramic total knee prosthesis component was recognized even after long clinical use.

A novel bioabsorbable bone substitute composed of a β-tricalcium phosphate (β-TCP) and a carboxymethyl-chitin (CM-chitin) sodium has been developed. Rabbit tibia defects (4 mm in diameter) were repaired after 4 weeks more effectively by the composite compared with a sham-operation group. To further investigate the biological safety of the components, genotoxicity and carcinogenicity of an extract prepared from the composite were determined using four different in vitro assays. The main extract component was identified as CM-chitin sodium [average molecular weight (Mw) ∼230 kDa] as determined by Fourier transform infrared spectroscopy and gel permeation chromatography analysis. The concentrations of P and Ca possibly derived from β-TCP were 17.7 and 37.1 μg/g, respectively, as determined by inductively coupled plasma mass spectroscopy. Both the metabolic activation and nonactivation (−S9) systems of the rat microsome S9 fraction were used to perform a genotoxicity evaluation using the Ames test and chromosome aberration assay on Chinese hamster lung fibroblast cells treated with the extract. In these assays, no genotoxicity was detected with doses ≤5 mg/mL (maximum concentration). The cell transformation assay using BALB/c 3T3 cells and the metabolic cooperation assay with V79 cells both showed negative results for any tumor-promoting activity caused by the extract (∼5 mg/mL). These results indicate that the bioabsorbable β-TCP/CM-chitin composite is a highly biocompatible bone substitute. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 71A: 635–643, 2004

Although ultra-high molecular weight polyethylene (UHMWPE) has stable chemical properties, chemical degradation, such as oxidation reaction, progresses with long-term clinical use. The purpose of this study was to investigate the change in properties of polyethylene (PE) in vivo by examining retrieved UHMWPE sockets and high-dose, cross-linked PE (100 Mrad PE) sockets. Twenty retrieved sockets (including 2 100 Mrad PE sockets), which were implanted from 1970 to 1996, were used for analysis. The oxidation index of 100 Mrad PE sockets was approximately the same as that of the normal UHMWPE sockets in worn areas. These long-term clinical results indicate that 100 Mrad PE is sufficiently stable for clinical use and that free radicals would not affect progression of oxidation significantly.

The purpose of this study was to evaluate the mechanical and chemical characteristics of gamma-irradiated, cross-linked polyethylene after long-term service in vivo. Two gamma-irradiated ultra high molecular weight polyethylene (RCH 1000, molecular weight: 106) total hip replacement sockets were retrieved at 15 and 16 years after implantation. Mechanical and chemical characteristics of the sockets were evaluated in comparison with nonirradiated sockets. Significant surface oxidation occurred in the nonirradiated sockets; up to 75% of that seen in the irradiated ones. The mechanical properties of the irradiated sockets were not subject to increased deterioration in the presence of high free radical content. The cross-link was stable and was retained for a long period both in vivo and in ambient air. These data indicate that gamma-irradiated polyethylene was not subject to increased oxidative degradation during long-term service invivo and confirmed the usefulness of this material as an articulating surface in total hip replacement.© 2001 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 58: 167–171, 2001

山岳トンネルの掘削にあたり破砕帯などに起因する大規模な集中湧水に遭遇した場合, 沢水の枯渇などの環境問題トンネル施工の工程遅延, 工事費の増加などを招く. しかしながら, 岩盤亀裂中の地下水 (裂か水) の挙動は, 一般に非常に複雑で, その湧出箇所および量の予測は容易ではない. そこで, CSA・MT探査から得られた地山比抵抗分布を用いて, 地山岩盤をモデル化し, トンネル掘削に伴う地下水の挙動変化, トンネル湧水量の変化を予測する手法を構築し, トンネル施工時に岩盤性状および湧水量の変化について検証し, 集中湧水を含め良好な一致をみた. なお, 本報告で採用した湧水量予測システムは水理地質構造的に, (1) 表層モデル, (2) 地下水流動モデル, (3) トンネル湧水量算出モデルから構成されている.

Liquid Crystal (LC) microlens which has a graded index property can be attained by using the LC cell with a simple circular hole-patterned electrode which gives an inhomogeneous electric field distribution. The index distribution profile is normally determined by the molecular orientational state in the LC cell which is exactly defined by the combined effects of the substrate boundary and applied electric field. Although the LC microlens can supply a variable focusing property, it usually requires a long response time for the driving voltage. In this work we tried to utilize an extra molecular orientational effect by introducing a small content of UV curable materials and forming a polymer network by UV irradiation in a LC cell for improving electro-optical properties. We have investigated a various optical and electro-optical properties of the LC microlens by adopting up to 20 wt% of polymer concentration. Improvements of the response property and holding effects of gradient index properties can be obtained by optimizing the polymer concentration, alignment layer and other fabricating condition.

UV-curable liquid crystals (LCs) which have a nematic phase at room temperature can be photopolymerized by ultraviolet (UV) irradiation white holding the molecular orientation state in a nematic phase Liquid crystal optical devices with a refractive index distribution property are prepared using the novel LC material. After the graded index properties are produced by a nonuniform electric field, the LC is cured with the voltage and the molecular orientation properties in the LC cell are frozen by the UV irradiation; that is, the functionally-graded-polymer devices are formed. Optical polymer devices such as a microlens array and optical waveguide are easily prepared and demonstrated. Each polymer microlens in the lens array has the parabolic graded-refractive-index profile which shows an excellent focusing property. The polymer optical waveguide can also be prepared using a nonuniform electric field distribution produced by a slit patterned electrode structure and loss parameter is estimated for various waveguide structures.

Recently, y-irradiation of ultrahigh molecular weight polyethylene (UHMWPE) to high doses such as 1 MGy was shown by Oonishi et al. to be very effective in improving the wear resistance of UHMWPE. The present work was undertaken to characterize the UHMWPE irradiated with γ-rays and electron beams to doses ranging from 25 KGy to 5 MGy. The radical concentration was determined by electron spin resonance (ESR) spectroscopy, while infrared spectroscopy was used to study the carbonyl and double bond formation on the irradiated UHMWPE. The change of the melting temperature of UHMWPE upon irradiation was examined by differential scanning calorimetry, while mechanical tests were performed to measure the compressive creep deformation, surface hardness, and tensile strength of the irradiated UHMWPE. The UHMWPE irradiated with γ-rays in air and then stored in air showed that the decrease in polymer radical concentration with time became lower with the increase in radiation dose. The decay of polymer radicals formed upon irradiation with γ-rays in N 2 gas and stored in N 2 gas was slow except for UHMWPE irradiated to 25 KGy. Irradiation with electron beams in air and the subsequent storage in air yielded a high concentration of polymer radicals, but the decay was much faster than that of γ-irradiated UHMWPE. The g-factor evaluated from the ESR spectra revealed that the polymer radicals transformed into oxidized ones during storage in air. The UHMWPE radicals formed by γ-irradiation in N 2 gas to 1-5 MGy remained almost unchanged during storage in N 2 gas. The gel fraction and the carbonyl and double bonds concentration increased with the increase in radiation dose when UHMWPE was γ-irradiated in air, while the melting temperature of UHMWPE increased upon irradiation in air, so far as a UHMWPE block, not powder, was γ-irradiated. The creep deformation decreased and surface hardness increased by γ-irradiation in air, suggesting that crosslinking was introduced into UHMWPE molecules upon irradiation to high doses. In conclusion, irradiation of UHMWPE with γ-rays and electron beams to high doses could introduce crosslinking to UHMWPE, resulting in increase in surface hardness and decrease in creep deformation. The trapped radicals in the irradiated UHMWPE decreased more quickly for electron-beam irradiation than for γ-ray irradiation.

Composite mover device constructed with both negative and positive magnetostrictive thin films on each side surface of silicon substrate were prepared by DC magnetron sputtering process. The magnetic field induced mover strain (an apparent magnetostriction) of composite mover device at 150 kA/m of magnetic field was as same as the sum of magnetostriction values of Sm-Fe negative and Tb-Fe positive magnetostrictive thin films. Although the magnetostrictive susceptibility of Sm-Fe negative and Tb-Fe positive magnetostrictive thin films were over 8.6 and 5.42 ppm/kA•m-1, respectively, an apparent magnetostrictive susceptibility of the composite mover device was 36.4 ppm/kA•m-1. We concluded that composite process tremendously enhanced the apparent magnetostrictive susceptibility. Composite mover device with high responsiveness was developed.

Influences of composition on magenetostriction of Sm-Fe alloy thin films prepared by D.C. magnetron sputtering process were investigated. Composition of formed film was ranged form 25 to 59 at%Sm. Negative magnetostriction were obtained of amorphous Sm-Fe thin films. The magenetostriction of thin films was varied with composition rate of Sm-Fe alloy. The giant magnetostriction over 1000 ppm at 400 kA/m was observed from 29 to 34 at% for Sm-Fe alloy film. The giant magnetostrictive (Sm-Fe) alloy thin film showed its potential use as wireless actuators in microsystem technology.

Wear performance and mechanical properties of cross-linking polyethylene (XLPE) tibial inserts were investigated using a knee simulator, scanning electron microscopy (SEM), and a small punch test (SPT). Ultrahigh molecular weight PE made from GUR1050 resin was irradiated at doses ranging from 0 to 200 kGy and then machined into tibial inserts followed by annealing. The knee simulator was run for up to four million cycles. As the radiation dose increased from 0 to 100 kGy, the wear rate decreased dramatically, yielding 95% wear reduction at 100 kGy. The microwear features observed by SEM supported the dose-dependent wear reduction. The SPT for XLPE after the simulation test showed that, as the radiation dose increased from 0 to 200 kGy, the ultimate displacement decreased dose-dependently, while the ultimate load increased from 0 to 75 kGy and decreased from 75 to 200 kGy. The resulting toughness of the PE increased to its maximum at a dose of 50 kGy and then decreased with higher doses up to 200 kGy. PE cross-linked with radiation doses from 25 to 75 kGy had greater toughness than virgin, nonirradiated PE. However, PE irradiated with 100 kGy or more had lower toughness than virgin PE. These data suggest that a certain amount of irradiation enhances both wear performance and toughness of PE tibial inserts. Although a certain amount of cross-linking would be effective for clinical application of PE tibial inserts, an optimal radiation dose should be much smaller than that used in current XLPE in total hip arthroplasty.

In previous studies, we have reported that the BMP-2-derived peptide KIPKASSVPTELSAISTLYL, corresponding to BMP-2 residues 73-92, binds to a BMP-2-specific receptor, and elevates both alkaline phosphatase activity and osteocalcin mRNA in the murine mesenchymal cell line, C3H10T1/2. This 73-92 peptide conjugated to a covalently crosslinked alginate gel induced ectopic bone formation in rat calf muscle, and activated osteoblasts to promote the repair of rat tibial bone defects. Here, we report repair of 20-mm long rabbit radial bone defects using the 73-92 peptide combined with a porous alpha-tricalcium phosphate (TCP) scaffold. In vitro, the 73-92 peptide was released from the porous alpha-TCP scaffold over more than one week. In vivo, radiomorphometric analysis showed that the 73-92 peptide combined with the porous alpha-TCP scaffold promoted calcification in the implanted area in a dose-dependent manner, and that 5 mg of the 73-92 peptide induced connection of 20-mm long defects, defects of critical size, 12 weeks after implantation. Histological examination revealed newly formed bone and a marrow cavity in the implanted area. The area of bone denser than 690 mg/cm(3) induced by the 73-92 peptide was nearly equal to that of the contralateral radius.

Higher levels of UHMWPE crosslinking currently are being advocated for improved wear resistance of acetabular cups. Pioneering Japanese studies, begun in 1971, have achieved good clinical results with UHMWPE irradiated to 1000 kGy for use with a cemented-cup design. The objective of our study was to use contemporary simulator techniques to determine the in vitro wear performance of such high-dose irradiated cups. Extruded UHMWPE cups were processed with 500, 1000, and 1500 kGy of gamma-radiation doses under vacuum, annealed, and machined to shape. The cups were mated with 26-mm alumina heads and run in a multidirectional simulator with bovine serum. Over a 6-million cycle (Mc) study, the weight loss of the nonirradiated control cups averaged 52.8 mg/Mc + 1.4% (wear = 57.2 mm(3)/Mc). In contrast, the irradiated wear cups had a consistent weight gain. Thus cups with irradiation of 500-1500 kGy had no detectable wear in this study. The original machining marks still were partially evident in the wear zones, along with some macrofissures in the 1000- and 1500-kGy cups. Areas adjacent to the fissures showed delaminating plaques of 100-300 microm in size. It also was noted that the wear cups systematically gained more weight than their corresponding soak controls. Each 200-kGy radiation gain increased the fluid sorption ratio by 10%. The increased fluid sorption and evidence of some surface deterioration may indicate that such high-dose irradiated cups are more susceptible to mechanical damage. This indicates that we should take care to ensure that our desire to reduce the wear debris to a zero amount does not result in a modified UHMWPE that lacks the necessary mechanical properties for contemporary metal-backed cup designs.

The clinical wear rate of cross-linked polyethylene cups (RCH 1000) irradiated in air with 100 Mrad (clinical use, 1971–1978) decreased to 18%. Tensile strength and elongation decreased, but deterioration did not progress, and the toughness greatly increased in retrieved 100-Mrad polyethylene (PE). The degree of oxidation after 18 years slightly increased. In the hip simulator test using 30% bovine serum as lubricant, cross-linked cups irradiated with 50–150 Mrad did not show detectable wear. Wear of ultrahigh molecular weight polyethylene (UHMWPE) irradiated with 6.5 Mrad (Aeonian) decreased to 3% by the hip simulator test without deterioration of physical properties. Oxidation caused by free radicals produced by gamma-ray sterilization was extremely low.

The wear rate of crosslinked sockets irradiated in air with gamma-irradiation of 100 Mrad, which were used in total hip arthroplasty clinically between 1971 and 1978, was 18% of that of non-crosslinked sockets. As the sockets were irradiated in air, the surface was oxidized. The weight-bearing portion of retrieved crosslinked sockets presented a clearly outlined pattern, irregularly lined with smooth ripples of 0.1 um. Delamination, flaking, burnishing, and scratch were not observed. In our wear tests, using cylinder-on-flat, sphero-flat reciprocating, and hip simulator test, crosslinked ultrahigh-molecular-weight polyethylene (UHMWPE) irradiated with 50 to 1000 Mrad showed extremely low wear, even when the UHMWPE was irradiated in the air and the surface was oxidized. In our hip simulator test with 12 channels using 30% bovine serum as lubricant, crosslinked sockets irradiated with 50 to 150 Mrad, in which the oxidized surface was eliminated, showed no wear. After radiation, the mechanical properties of elongation and tensile strength of polyethylene decreased. The hardness and the ultimate tough strength increased. The chemical properties of gel contents, oxidation (C = O), and double bond (C = C) increased.