Feasability of Preventing Encrustation of Urinary Catheters

Colonization of urinary catheters by bacteria which produce urease leads to an increase in urine pH, followed by deposition of the minerals struvite and hydroxyapatite. Adhesion of these encrusting deposits can be reduced, but not prevented, by using catheters with a smooth surface finish. Chemical methods for preventing encrustation are not completely satisfactory. A better way of preventing encrustation would be to prevent colonization of the catheter by bacteria. This might be achieved by controlled release of antimicrobial agents directly into the urine from the catheter itself. Preliminary experiments have demonstrated the feasibility of controlled release from solid silicone. However, a simpler approach is diffusion of an antimicrobial agent from a solution within the retention balloon of the catheter. Further experiments are required to determine the concentrations required and whether they are achievable in practice

Finite element analysis of the effect of fibre shape on stresses in an elastic fibre surrounded

The finite element (FE) method was used to calculate the axial and radial stress distributions as a function of axial distance, z, from the centre, and radius, r, in an elastic fibre surrounded by a plastic matrix. Plastic deformation of the matrix was considered to exert a uniform interfacial stress, τ , along half the length of the fibre. Axisymmetric models were created for uniform cylindrical, ellipsoidal, paraboloidal and conical fibres characterised by an axial ratio, q, and half length, L. Young's modulus for the material of the fibre and L were arbitrarily assigned values of unity, since they act as scaling factors; q also acts as a scaling factor but was assigned a value of 10 to create models with a fibrous appearance. For the cylindrical fibre, the axial stress increased linearly from the end towards the centre; the radial stress was more evenly distributed. At the other extreme, the conical fibre showed a uniform distribution of axial and radial stress. Results for ellipsoidal and paraboloidal fibres were intermediate between these two extremes. In general, the effect of taper is to lower peak stress at the fibre centre and make the stress distribution throughout the fibre more even. These results are in good agreement with recent analytical theories for the axial distribution of surface radial stress and axial stress along the fibre axis. However, FE models have the advantage of predicting full three-dimensional stress distributions. C 2000 Kluwer Academic Publisher

Viscoelastic properties of bovine articular cartilage attached to subchondral bone at high frequencies

<p>Abstract</p> <p>Background</p> <p>Articular cartilage is a viscoelastic material, but its exact behaviour under the full range of physiological loading frequencies is unknown. The objective of this study was to measure the viscoelastic properties of bovine articular cartilage at loading frequencies of up to 92 Hz.</p> <p>Methods</p> <p>Intact tibial plateau cartilage, attached to subchondral bone, was investigated by dynamic mechanical analysis (DMA). A sinusoidally varying compressive force of between 16 N and 36 N, at frequencies from 1 Hz to 92 Hz, was applied to the cartilage surface by a flat indenter. The storage modulus, loss modulus and phase angle (between the applied force and the deformation induced) were determined.</p> <p>Results</p> <p>The storage modulus, <it>E'</it>, increased with increasing frequency, but at higher frequencies it tended towards a constant value. Its dependence on frequency, <it>f</it>, could be represented by, <it>E' </it>= <it>Alog</it>_{<it>e </it>}(<it>f</it>) + <it>B </it>where <it>A </it>= 2.5 ± 0.6 MPa and <it>B </it>= 50.1 ± 12.5 MPa (mean ± standard error). The values of the loss modulus (4.8 ± 1.0 MPa mean ± standard deviation) were much less than the values of storage modulus and showed no dependence on frequency. The phase angle was found to be non-zero for all frequencies tested (4.9 ± 0.6°).</p> <p>Conclusion</p> <p>Articular cartilage is viscoelastic throughout the full range of frequencies investigated. The behaviour has implications for mechanical damage to articular cartilage and the onset of osteoarthritis. Storage modulus increases with frequency, until the plateau region is reached, and has a higher value than loss modulus. Furthermore, loss modulus does not increase with loading frequency. This means that more energy is stored by the tissue than is dissipated and that this effect is greater at higher frequencies. The main mechanism for this excess energy to be dissipated is by the formation of cracks.</p

A Review of the Design Process for Implantable Orthopedic Medical Devices

The design process for medical devices is highly regulated to ensure the safety of patients. This paper will present a review of the design process for implantable orthopedic medical devices. It will cover the main stages of feasibility, design reviews, design, design verification, manufacture, design validation, design transfer and design changes

Biotransformation of Silver Released from Nanoparticle Coated Titanium Implants Revealed in Regenerating Bone

Antimicrobial silver nanoparticle coatings have attracted interest for reducing prosthetic joint infection. However, few studies report in vivo investigations of the biotransformation of silver nanoparticles within the regenerating tissue and its impact on bone formation. We present a longitudinal investigation of the osseointegration of silver nanoparticle-coated additive manufactured titanium implants in rat tibial defects. Correlative imaging at different time points using nanoscale secondary ion mass spectrometry, transmission electron microscopy (TEM), histomorphometry, and 3D X-ray microcomputed tomography provided quantitative insight from the nano- to macroscales. The quality and quantity of newly formed bone is comparable between the uncoated and silver coated implants. The newly formed bone demonstrates a trabecular morphology with bone being located at the implant surface, and at a distance, at two weeks. Nanoscale elemental mapping of the bone−implant interface showed that silver was present primarily in the osseous tissue and colocalized with sulfur. TEM revealed silver sulfide nanoparticles in the newly regenerated bone, presenting strong evidence that the previously in vitro observed biotransformation of silver to silver sulfide occurs in vivo

Patients' perspectives on antiepileptic medication: relationships between beliefs about medicines and adherence among patients with epilepsy in UK primary care.

BACKGROUND: Nonadherence to antiepileptic drugs (AEDs) can result in suboptimal outcomes for patients. AIM: This study aimed to assess the utility of a theory-based approach to understanding patient perspectives on AEDs and adherence. METHOD: Patients with epilepsy, identified by a GP case note review, were mailed validated questionnaires assessing their perceptions of AEDs and their adherence to them. RESULTS: Most (84.9%) of the 398 AED-treated respondents accepted the necessity of AEDs, but over half expressed doubts, with 55% disagreeing or uncertain about the statement 'I would prefer to take epilepsy medication than risk a seizure'. Over a third (36.4%) expressed strong concerns about the potential negative effects of AEDs. We used self-report and medication possession ratio to classify 36.4% of patients as nonadherent. Nonadherence was related to beliefs about medicines and implicit attitudes toward AEDs (p<0.05). Adherence-related attitudes toward AEDs were correlated with general beliefs about pharmaceuticals (BMQ General: General Harm, General Overuse, and General Benefit scales) and perceptions of personal sensitivity to medicines (PSM scale). CONCLUSION: We identified salient, adherence-related beliefs about AEDs. Patient-centered interventions to support medicine optimization for people with epilepsy should take account of these beliefs

Containing medicines costs in the private sector - the example of a medical benefit scheme

Despite a pre-existing cost-containment programme, expenditure on medicines was identified as a source of further cost savings in a medical benefit scheme faced with increasing divergence between income and benefit expenditure. Analysis of medicines utilisation trends showed that a relatively small number of pharmaceutical products accounted for a high percentage of total medicines expenditure, and that a small number of pharmacies were dispensing a very high proportion of prescriptions.On the basis of these findings, a revised cost-containment programme for medicines was implemented. It consisted of a recommended medicines list, designed to rationalise selection and utilisation of medicines, and a 'preferred provider pharmacy' network that allowed further savings to be achieved.In its first 12 months, the programme allowed for savings of R305 000, or 37% of anticipated expenditure on medicines for that year. This represents a decrease over 1988 expenditure notwithstanding an increase in membership and medicine prices over the same period. There are therefore significant savings to be obtained by medical schemes through implementation of cost-containment programmes for medicines