Methods

The brace works by strapping a femoral component tightly to a polyethylene insert by applying compression force between the sole of the foot and the thigh. Holes of 1, 2, 5, 10 mm in diameter and 0.1, 0.2, 0.5 and 1 mm in depth were created in the posteromedial part of polyethylene inserts. The inserts were provided from Teijin-nakashima Co. ltd. (Jodo, Okayama, Japan). The Hi-tech knee artificial joint (Teijin-nakashima Co. ltd.) was applied to a cadaveric knee and CT images of the knee were taken with a combination of insets with varying diameters and depths holes, using Aquilion ONE (Toshiba Medical Systems Corporation, Ohtawara, Japan). The finding conditions were as follows, Voltage; 120V, Current; 5A, slice thickness; 0.5 mm helical. The patient, who received total knee arthroplasty over 15 years ago, wore the brace and was examined using computed tomography. Afterward, the patient received revision surgery to replace the worn insert into new one. The removed insert was measured with a three-dimensional measuring machine (Cyclon, Mitsutoyo Co. ltd., Kawasaki, Japan).

Results

At a 1.0 mm depth, all holes could be detected. At a 0.5 mm depth, holes of 2, 5, 10 mm in diameter could be detected. At a 0.1∼0.2 mm depth, there was no hole detected. After revision surgery, a three-dimensional measuring machine revealed a 1.8 mm thickness of the insert on the medial side. The CT reconstruction image showed a1.84 mm thickness similar to the virtually measured figure.

MATERIALS & METHODS

Virgin samples were manufactured via Direct Compression Molding (DCM) technique from UHMWPE GUR1050 resin powder (Ticona, USA). For vitamin E (VE)-blended sample, the resin was mixed with VE at 0.3 wt% and the mixture was then molded using DCM. The crosslinked virgin samples were made by gamma ray irradiation to UHMWPE GUR1020 resin sheet (Meditech, USA) with doses of 95kGy ±10% and annealed. The VE-blended crosslinked samples were made by electron beam irradiation to VE-blended samples with doses of 300kGy and annealed. The material conditions were summarized in Figure 1. To pulverize the samples, the Multi-Beads Shocker (Yasui Kikai, Japan) was used.

After pulverization, samples were dispersed in an ethanol solution and sequentially filtered through polycarbonate filters. Over 100 sections of the filter were selected randomly and images of the particles were analyzed using scanning electron microscope (SEM).

To analyze the macrophage biological response, an inverted cell culturing process was used (2). The mouse macrophage-like cells were seeded at densities of 4×105cells per well in a 96-well culture plate and incubated for 1h. UHMWPE particles suspended in the culture medium were then added to each well in the appropriate amount. After that, fresh medium was added to fill the wells, and a sealing film was used to cover the culture plate. The culture plate was then inverted to cause the UHMWPE particles interact with the adhered macrophages. The inverted culture plate was incubated for 8h. The amount of TNF-α was measured by enzyme-linked immunosorbent assay (ELISA).

Materials and methods

The FerVID family (Fujitsu Co. Ltd., Tokyo, Japan) was prepared as the RFID tag. It was radio-resistant below the dose of 50kGy, which allowed gamma sterilization. The RFID tags were embedded into the anterior side of GUR 1050 UHMWPE inserts and 0.3wt% vitamin E blended UHMWPE. The UHMWPE inserts were manufactured by thecompression molding method at the maximum temperature of 220°C and the maximum compressive force of 245kgf/cm². The manufactured inserts were implanted in fresh cadaveric knees. The tibial base plate was made of Ti6Al4V. The femoral components were made of Co-Cr-Mo or Ti-6Al-4V. Communication Performance was measured with the interrogator (DOTR-920 MHz-band, Tohoku Systems Support Co. Ltd., Miyagi, Japan). The transmission output was up to 1W. Received Signal Strength Indicator (RSSI) was measured 500 times at 15 mm away from the surface of skin in the extension and 90° flexion of the knee (Fig1).

Method

VE blended samples were manufactured via direct compression molding following the blending of UHMWPE resin powder (GUR1050, Ticona Inc.) with VE (dl-α-tocopherol, Eisai Co. Ltd.) at 0.3wt%. The virgin samples were derived similarly, but without the addition of VE. Both materials underwent crosslinking by irradiation via a 10MeV electron beam at 300kGy and were then heat treated at several temperatures (25, 80, 110, 130 and 150 °C) for 24 hours.

Gel content, which can be interpreted as cross-link density, was determined by measuring the weight of the samples before and after soaking in decahydronaphthalene at 150 °C for twelve days.

Tensile tests were carried out following JIS K 7113, with the cross head speed set at 50 mm/min.

Crystallinity was determined by using DSC and integrating over the enthalpy curve from 80 to 150 °C and normalizing with the enthalpy of melting for 100% crystalline polyethylene.

Materials & Methods

UHMWPE resin powder (GUR 1050, Ticona, USA) was mixed with dl-a-Tocopherol (vitamin E) at 0.3 wt% and molded under direct compression at 25 MPa and 220°C. Virgin samples were produced by the same process, but without the addition of vitamin E (VE). Cylindrical pins (length: 40 mm, diameter: 3.5 mm) were then machined from these samples, packaged in a vacuum, and irradiated by electron-beam at 300 kGy. Samples were subsequently doped with either ascorbic acid 6-palmitate (Sigma, Japan) or ethanol (Ethanol 99.5%, Kishida, Japan) and subjected to a hydrostatic pressure of 100 MPa for 7, 14, and 21 days at room temperature. Radical measurements were made using ESR at 9.44 GHz and room temperature. All ESR spectra were recorded at 0.1 mW microwave power and 0.1 mT modulation amplitude.

Materials and Methods

VE blended samples (GUR_VE xx%) were manufactured via direct compression molding following the blending of UHMWPE resin powder with VE at several concentrations (0, 0.1, 0.3, 1.0%). Cross-linking for the VE samples was achieved by 10 MeV electron beam at several irradiance doses (30, 90, 300 kGy) and annealed below the melting point of UHMWPE.

Knee and hip simulator testing were carried out according to ISO 14243 and ISO 14242, respectively, and the volumetric wear was calculated. The gel fraction was determined by measuring the weight of the samples before and after soaking in decahydronaphthalene at 150°C. The oxidative resistance of the material was determined by measuring the Oxidation Index (OI) following ASTM F2102 before and after compulsory aging (ASTM2003). Radical measurements were made using high-sensitivity X-band ESR.

MATERIALS & METHODS

Both pure UHMWPE and Vitamin E added (0.3% w/w) resin was used to produce bulk specimens via vacuum direct compression molding at 220°C under 25 MPa for 30 min. Cylindrical pins (3.5 mm diameter, 40 mm length) for ESR measurement were then machined and placed in vacuum packaging. The pins were irradiated at 300 kGy, with half of each test group annealed at 80°C for 24 hours. Free radical measurements were made using a high-sensitive X-band ESR operating at 9.44 GHz. Detection of Vitamin E radicals was performed by comparing the characteristic symmetrical spectrum of oxidized Vitamin E to the spectra observed for the pins using both g-value and linewidth as references. Crosslink density was measured via gel fraction analysis and was performed in accordance with ASTM D2765. Thin sections (20 × 40 mm², 200 μm) were machined from the bulk specimens, which were then placed in vacuum packaging, irradiated and annealed at the same conditions as those for the ESR measurements. Two of these thin sections were then placed in a stainless-steel cage (200 µm pore diameter) and were immersed in decahydronaphtalene at 200°C for 24 hours. These specimens were then extracted using soxhlet extractor at 100°C for 24 hours and dried in vacuum at 150°C for 12 hours.