Characterisation of the physical, chemical and mechanical properties of a radiopaque polyethylene

Abstract

<jats:p> Ultra-high molecular weight polyethylene has a low X-ray attenuation, hence, the performance of the polyethylene implants used for joint replacements cannot be directly investigated using X-ray-based imaging techniques. In this study, the X-ray attenuation of polyethylene was increased by diffusing an FDA-approved oil-based contrast agent (Lipiodol ultra fluid) into the surface of the samples, and the suitability of this novel radiopaque ultra-high molecular weight polyethylene for clinical applications was examined. Different levels of radiopacity were created by controlling the diffusion parameters, and the level of radiopacity was quantified from computed tomography scans and reported in Hounsfield units. The physical, chemical and tensile properties of the radiopaque ultra-high molecular weight polyethylene were examined and compared to untreated and thermally treated controls. The results of this study confirmed that for the samples treated at 115°C or less the diffusion of the contrast agent did not significantly alter the crystallinity ( p = 0.7) or melting point ( p = 0.4) of the polyethylene. Concomitantly, the tensile properties were not significantly different from the control samples ( p &gt; 0.05 for all properties). In conclusion, the radiopaque ultra-high molecular weight polyethylene treated for less than 18 h at a temperature of 115°C or below is a promising candidate for joint replacement applications as it can be identified in a standard X-ray while retaining the tensile properties of clinically used radiolucent ultra-high molecular weight polyethylene. </jats:p>

Chemical stability of oil-infused polyethylene

“…The redistribution of radiopacity can be also associated with the effect of temperature on the crystallinity of polyethylene. 19 The diffusion of macromolecules in polyethylene is limited to the amorphous regions; the elevated temperature and ageing are both likely to cause a Figure 6. The post-yield mechanical properties of oil treated polyethylene; (a) ultimate tensile strength or UTS (b) and elongation at failure.…”

“…Radiopaque samples were immersed in 25 ml of Lipiodol (Guerbet, France) at 105∘C for 18 hours to create Radiopaque polyethylene. 19,20 The second group of samples were immersed in 25 ml of Vitamin E (L- α –tocopherol, Sigma-Aldrich, Kent, UK) at 105∘C for 18 hours to create the Vitamin E samples. Thermally treated samples were treated at the same elevated temperature and time (105∘C for 18 hours) without the presence of any oil; and finally the Untreated control samples were not treated with temperature or any oily fluid.…”

A practical model of the diffusion of oil‐based fluid into polyethylene

“…After processing, the greyscale values were converted to Hounsfield units. The radiopacity has been shown in previous studies to positively correlate linearly with the concentration of Lipiodol within polyethylene, 7 and so hereafter HU will be used to represent concentration in the calculations.…”

“…After processing, the greyscale values were converted to Hounsfield units. The radiopacity has been shown in previous studies to positively correlate linearly with the concentration of Lipiodol within polyethylene, 7 and so hereafter HU will be used to represent concentration in the calculations. For the 1D model, data were compared to linear HU profiles taken through the center of the cuboid samples along both the length (15 mm profile), and the width (10 mm profile).…”

“…5 Antioxidants such as Vitamin E (α-tocopherol) which is a natural oil-based antioxidant can be used to enhance the oxidative stability of polyethylene, and has been used for packaging and medical applications. 6 Another oil-based fluid suitable for medical applications is Lipiodol which is an iodised oil contrast agent containing naturally occurring fatty acids (e.g., α tocopherol, linoleic acid) 7 that can enhance the radiopacity of polyethylene to facilitate post-operative followup of medical devices. 8 For medical applications oil, once contained within polyethylene, has the advantage of being less soluble in aqueous body fluids, which reduces the rate of leaching, 9 but it is nevertheless essential that the oil does not cause any adverse biological reactions.…”