Biomedical subjects

K E Tanner

Publications and source records attributed to K E Tanner.

57 records · Page 4Linked to original sources

PubMedDate not supplied

Tensile mechanical properties of polyacetal after one and six months' immersion in Ringer's solution.

The engineering polymer polyacetal (also known as polyoxymethylene) has a long history of clinical use including in the femoral component of the Freeman all-polymer knee replacement. The polymer is a promising material for novel applications including the femoral component of hip resurfacing prostheses. However, no work following the effect on mechanical properties of extended immersion in the physiological environment has been reported. Samples of five grades of polyacetal were obtained and tested on an MTS Bionix 858 at 37 degrees C in physiological saline. Three groups of specimens were tested: "as received"; immersed in Ringer's solution at 37 degrees C for one month; immersed in Ringer's solution at 37 degrees C for six months'. While there were negligible reductions in the ultimate tensile strengths, the Young's moduli of all polymer grades showed significant reductions (p < 0.01) of up to 19.5% following one months' immersion. There were negligible changes in ultimate tensile strength and stiffness between one and six months' immersion, however some polymers showed a small, but significant (p < 0.05) increase in stiffness. The percentage elongation and true stress for plastic instability showed negligible changes following immersion for one and six months'. These results encourage the use of polyacetal in load-bearing orthopaedic applications.

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PubMedDate not supplied

Tensile properties of a bone cement containing non-ionic contrast media.

The addition of contrast media such as BaSO4 or ZrO2 to bone cement has adverse effects in joint replacements, including third body wear and particle-induced bone resorption. Ground PMMA containing particles of the non-ionic water-soluble iodine-based X-ray contrast media, iohexol (IHX) and iodixanol (IDX), has, in bone tissue culture, shown less bone resorption than commercial cements. These water-soluble non-ceramic contrast media may change the mechanical properties of acrylic bone cement. The static mechanical properties of bone cement containing either IHX or IDX have been investigated. There was no significant difference in ultimate stress between Palacos R (with 15.0 wt % of ZrO2) and plain cement with 8.0 wt % of IHX or IDX with mass median diameter (MMD) of 15.0 or 16.0 microm, while strain to failure was higher for the latter (p < 0.02). The larger particles (15.0 or 16.0 microm) gave significantly higher (p < 0.001) ultimate tensile strengths and strains to failure than smaller sizes (2.4 or 3.6 microm). Decreasing the amount of IHX from 10.0 wt % to 6.0 wt % gave a higher ultimate tensile strength (p < 0.001) and strain to failure (p < 0.02). Scanning electron microscopy (SEM) showed the smaller contrast media particles attached to the surface of the polymer beads, which may prevent areas of the acrylate bead surface from participating in the polymerization. In conclusion, the mechanical properties of bone cement were influenced by the size and amount of contrast medium particles. By choosing the appropriate amount and size of particles of water-soluble non-ionic contrast media the mechanical properties of the new radio-opaque bone cement can be optimized, thus reaching and surpassing given regulatory standards.

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PubMedDate not supplied

Effect of filler type on the mechanical properties of self-reinforced polylactide-calcium phosphate composites.

Bioabsorbable polymers are of interest as internal fracture fixation devices. Self-reinforcement has been developed to improve the mechanical properties of the material and the addition of calcium phosphate fillers improves the bioactivity. Composite plates, produced by compression molding preimpregnated sheets of polylactide fibers coated in a polylactide matrix have been degraded in simulated body fluid for up to 12 weeks. Some samples also contained hydroxyapatite or tricalcium phosphate filler particles. Degradation was measured by monitoring the water uptake and mass decrease of the samples, as well as carrying out four point bend tests to assess the mechanical properties of the material. By 12 weeks, it was found that the unfilled samples absorbed more water and showed greater mass loss than the samples containing calcium phosphate fillers. Also, the flexural modulus and yield stress decreased significantly at week 12 for the unfilled samples. Adding hydroxyapatite (HA) or tricalcium phosphate (TCP) to the composite increased the flexural modulus and yield strength to values within the range of those reported for cortical bone and these values were maintained over the 12-week period.

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