Spectral characterization of nanostructured birefringent porous silicon.

We present measurements and analysis of the reflection spectrum of white light from a highly birefringent porous silicon layer at different polarization states. We report an anomalous pattern in the spectrum of linearly polarized light at 45° with respect to the principal axes of the layer. This spectrum comprises a combination of two interference effects, namely the Fabry-Perot-type multiple-beam interference present in a simple thin film, and a two-wave interference caused by the beat of two combined orthogonally polarized waves propagating in the birefringent medium. We perform a Fourier analysis of the measured reflected spectra. This analysis furnishes a powerful tool in order to separate the two interference mechanisms and determine the degree of coherence of their superposition.

The effect of hyaluronan injections into human knees on the number of bone and cartilage wear particles captured by bio-ferrography.

Osteoarthritis is characterized by degradation of cartilage and subchondral bone, releasing wear particles into the synovial fluid. Intra-articular injections of exogenous hyaluronan are often given to patients suffering from osteoarthritis in order to compensate for the reduction in the level of endogenous hyaluronan and to restore the rheological properties of the synovial fluid. The exact effect of these injections is still ambiguous. In this work bio-ferrography was used to capture magnetically labeled cartilage and bone debris from the synovial fluid in human knees before each of four injections (Euflexxa). The wear particles were counted and characterized microscopically and chemically. WOMAC, VAS, SF-36 and KS questionnaires indicated significant pain relief during the treatment, but suffered from inconsistency. Bio-ferrography showed a reduction in the concentration of both cartilage and bone particles, with a minimum after the third hyaluronan injection. The advantages of bio-ferrography as a primary assessment tool are discussed. The results indicate that while hyaluronan treatment may temporarily slow the wear rate to an extent beyond a placebo effect, it does not prevent joint degradation altogether.

Long-term evaluation of a compliant cushion form acetabular bearing for hip joint replacement: a 20 million cycles wear simulation.

Soft bearing materials that aim to reproduce the tribological function of the natural joint are gaining popularity as an alternative concept to conventional hard bearing materials in the hip and knee. However, it has not been proven so far that an elastic cushion bearing can be sufficiently durable as a long term (∼20 years) articulating joint prosthesis. The use of new bearing materials should be supported by accurate descriptions of the implant following usage and of the number, volume, and type of wear particles generated. We report on a long-term 20 million cycle (Mc) wear study of a commercial hip replacement system composed of a compliant polycarbonate-urethane (PCU) acetabular liner coupled to a cobalt-chromium alloy femoral head. The PCU liner showed excellent wear characteristics in terms of its low and steady volumetric wear rate (5.8-7.7 mm(3)/Mc) and low particle generation rate (2-3 × 10(6) particles/Mc). The latter is 5-6 orders of magnitude lower than that of highly cross-linked polyethylene and 6-8 orders of magnitude lower than that of metal-on-metal bearings. Microscopic analysis of the implants after the simulation demonstrated a low damage level to the implants' articulating surfaces. Thus, the compliant PCU bearing may provide a substantial advantage over traditional bearing materials.

Wear rate evaluation of a novel polycarbonate-urethane cushion form bearing for artificial hip joints.

There is growing interest in the use of compliant materials as an alternative to hard bearing materials such as polyethylene, metal and ceramics in artificial joints. Cushion form bearings based on polycarbonate-urethane (PCU) mimic the natural synovial joint more closely by promoting fluid-film lubrication. In the current study, we used a physiological simulator to evaluate the wear characteristics of a compliant PCU acetabular buffer, coupled against a cobalt-chrome femoral head. The wear rate was evaluated over 8 million cycles gravimetrically, as well as by wear particle isolation using filtration and bio-ferrography (BF). The gravimetric and BF methods showed a wear rate of 9.9-12.5mg per million cycles, whereas filtration resulted in a lower wear rate of 5.8mg per million cycles. Bio-ferrography was proven to be an effective method for the determination of wear characteristics of the PCU acetabular buffer. Specifically, it was found to be more sensitive towards the detection of wear particles compared to the conventional filtration method, and less prone to environmental fluctuations than the gravimetric method. PCU demonstrated a low particle generation rate (1-5×106 particles per million cycles), with the majority (96.6%) of wear particle mass lying above the biologically active range, 0.2-10µm. Thus, PCU offers a substantial advantage over traditional bearing materials, not only in its low wear rate, but also in its osteolytic potential.