A number of models exist for assessing encrustation on biomaterials employed as devices in the urinary tract. However, static urine models are suitable only for assessment of biomaterials residing in the bladder and the dynamic models available suffer from a number of disadvantages, notably their complexity and limitation to short-term assessment. The dynamic model described herein is a relatively simple design incorporating the ability to assess a large number of biomaterials in replicate fashion and over long periods of time. The biomaterials tested in the dynamic model conform to the urethral catheter and ureteral stent devices that experience urine flow within the urinary tract. The model was initially validated using Percuflex as a test biomaterial. The mass of calcium and magnesium, representing hydroxyapatite and struvite encrustation, respectively, on Percuflex was detected by atomic absorption spectrometry. No significant differences in encrustation levels were detected either between vessels or between biomaterial positions on any mandrel within the vessels, indicating the suitability of the dynamic model for reproducible determination of biomaterial encrustation. The dynamic model was then used to compare the encrustation of biomaterials commonly employed in urinary-tract devices, namely polyurethane, Percuflex and silicone. Calcium and magnesium levels on polyurethane and Percuflex were shown to be statistically similar, whereas silicone exhibited significantly reduced encrustation. When, subsequently, comparisons were made of biomaterial encrustation between the dynamic model and a static model, calcium and magnesium levels arising from the latter model were significantly higher on each of the biomaterials. However, the same rank order of encrustation resistance was observed for the biomaterials in both models, with silicone performing better than polyurethane or Percuflex. The prediction of in-vivo performance based on in-vitro models of encrustation is often difficult, although the model described provides a more accurate method for assessing the potential of novel and existing biomaterials for use in urinary medical devices requiring flow of urine.

A selection procedure has been developed to identify suitable commercial materials for use in compliant-layer artificial hip joints. Mechanical requirements, notably hardness and strength, as well as biocompatibility, constituted the specification for the compliant layer. Applying these constraints, candidate materials were identified in a broad range of polymeric material classes. Detailed sourcing and literature searching helped to identify materials appropriate to the application, with suitable mechanical and physical properties, as well as a history of successful clinical use. Some likely materials were identified but were prohibited from further consideration by limited commercial availability. Physical and mechanical characterization together with literature data were used to determine the relative ranking of the candidate materials and through a weighted materials property selection procedure the materials of choice were identified. The linear segmented aromatic polyurethanes, Tecothane 1085 and Estane 5714F1, emerged as the preferred materials.

SYNOPSISHigh-impact polystyrene (HIPS) and acrylonitrile butadiene styrene ( ABS ) have been subject to y irradiation in doses up to 20 and 12.5 Mrad, respectively. During tensile testing, both longitudinal extension and lateral contraction were simultaneously measured, allowing determination of volume strain, and from this to identify the relative contributions of crazing and shear yielding to the tensile deformation process. Both materials show a doserelated increase in the strain at which crazing commences, though the relative change with dose in HIPS is much greater than in ABS. However, the contribution of crazing to total deformation remains high in HIPS when compared with ABS. Shear yielding is an important deformation process in ABS and the results indicate that this is relatively unaffected by irradiation, whereas the ability to craze is severely limited. The reduced ability to craze observed in both materials is considered to be the result of crosslinking in the rubbery phase. The notched impact strength of ABS is particularly sensitive to irradiation and again reflects the reduced ability to craze observed in the tensile testing. ABS fracture surfaces examined by scanning electron microscopy display reduced ductility in the irradiated material.

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