Chemical stability of oil-infused polyethylene

Abstract

Ultra-high molecular weight polyethylene (UHMWPE) can be made radiopaque for medical imaging applications through the diffusion of an iodised oil-based contrast agent (Lipiodol Ultra Fluid). A similar process is used for Vitamin E incorporated polyethylene which provides antioxidant properties. This study aimed to investigate the critical long-term properties of oil-infused medical polyethylene after 4 weeks of accelerated thermal ageing. Samples treated with an oil (Vitamin E or Lipiodol) had a higher oxidation stability than currently used medical grade polyethylene, indicated by a smaller increase in oxidation index after ageing (Vitamin E + 36%, Lipiodol +40%, Untreated +136%, Thermally treated +164%). The tensile properties of oil treated polyethylene after ageing were significantly higher than the Untreated and Thermally treated controls (p<0.05) indicating less mechanical degradation. There was also no alteration in the percentage crystallinity of oil treated samples after ageing, though the radiopacity of the Lipiodol treated samples reduced by 54% after ageing. The leaching of oil with time was also investigated; the leaching of Lipiodol and Vitamin E followed the same trend and reached a steady state by two weeks. Overall, it can be concluded that the diffusion of an oil-based fluid into polyethylene not only increases the oxidative and chemical stability of polyethylene but also adds additional functionality (e.g. radiopacity) providing a more suitable material for long–term medical applications.

Radiopacity Enhancements in Polymeric Implant Biomaterials: A Comprehensive Literature Review

“…Heavy elements in the form of inorganic metal compounds, organic compounds, and pure metal powders are the most common contrast agents added to medical polymers. One major concern with these contrasts has been their detrimental effect on important mechanical and physical properties of the polymers. , Another concern has been leaching out of the contrast agent, which could result in adverse reactions such as contrast-induced nephropathy or osteolysis, and should be kept below certain threshold levels. ,− …”

“…Zaribaf et al took a different approach, devising a method to enable radiographic visualization of the entire UHMWPE insert of a TKR using Lipiodol Ultra Fluid, an iodized oil used as a clinically injectable contrast agent. ,, This was achieved by diffusing the oil into the polyethylene at an elevated temperature of 105 °C but below the melting point of the polymer (135 °C) . This method had previously been used by Oral et al to diffuse vitamin E oil into UHMWPE. ,,, Due to the load-bearing application of UHMWPE joint components, it was important that the mechanical properties of the insert remained unaltered by the diffusion of the oil. No significant changes in the mechanical and physical properties (i.e., tensile modulus, elongation at failure, ultimate tensile strength, crystallinity, and oxidative stability) were observed.…”

“… 14 , 16 Another concern has been leaching out of the contrast agent, which could result in adverse reactions such as contrast-induced nephropathy or osteolysis, and should be kept below certain threshold levels. 16 , 20 − 23 …”

“…Zaribaf et al took a different approach, devising a method to enable radiographic visualization of the entire UHMWPE insert of a TKR using Lipiodol Ultra Fluid, an iodized oil used as a clinically injectable contrast agent. 14 , 65 , 66 This was achieved by diffusing the oil into the polyethylene at an elevated temperature of 105 °C but below the melting point of the polymer (135 °C). 67 This method had previously been used by Oral et al to diffuse vitamin E oil into UHMWPE.…”

“…Numerous studies have investigated the incorporation of contrast agents to enhance the visibility of polymers in radiographs. ,, Imparting radiopacity to polymers has proven to aid in monitoring the implant to allow precise surgical placement, evaluate biodegradation, or to detect malpositioning, migration, and wear. − We aimed to conduct a thorough search of the literature to identify and summarize these contrast agents.…”