Europium Stearate Additives Delay Oxidation of UHMWPE for Orthopaedic Applications: A Pilot Study

Abstract

Background Ultrahigh-molecular-weight polyethylene (UHMWPE) is used as an articulating surface in prosthetic devices. Its failure under various mechanisms after oxidation is of utmost concern. Free radicals formed during the sterilization process using high-energy irradiation result in oxidation. Europium, an element of the lanthanide family, has a unique electron configuration with an unusual lack of preference for directional bonding and notable bonding to oxygen. Because of this, it currently is used in studies for stabilization of polymers such as polyvinyl chloride. Questions/purposes We asked whether europium stearate could enhance the oxidation resistance after irradiation in nitrogen of UHMWPE. Methods Conventional nonirradiated and gammairradiated in nitrogen UHMWPE were compared with polyethylene doped with 375 ppm and 3750 ppm europium(III) stearate under the same treatment conditions. Chemical characterization was performed by Fourier transform infrared (FTIR) microspectroscopy using 200-lm thin films. The oxidation of doped samples with time was compared with that of conventional samples using accelerated oven aging. The types of oxidation products were identified by FTIR and quantified per material and treatment condition as indications of the oxidation level and mechanism. Results The generation rate of hydroperoxides and ketones was decelerated proportionally with concentration of europium stearates. The oxidative mechanism appeared similar to that of conventional polyethylene with the same types of measurable end products as ketones and hydroperoxides. Yet, the rate of generation of the latter appeared to be slowed down by the action of europium stearate. Conclusions Europium stearate mixed in UHMWPE decelerated the oxidation reactions triggered by gamma irradiation in nitrogen, seemingly without major alteration of the oxidation mechanism.

Natural Polyphenols Enhance Stability of Crosslinked UHMWPE for Joint Implants

“…In the first method, thin slices of UHMWPE (one slice for each material) were aged at 120°C to distinguish the antioxidation potency in a relatively short time scale, as reported in the literature [16]. Thin slices of the UHMWPE were microtomed to a thickness of 100 lm and subjected to accelerated aging in a ventilated oven at 120°C until the samples became too brittle to handle.…”

“…The absorbance at 1718 cm À1 (carbonyl groups) was used to evaluate the oxidation level of UHMWPE. The absorbance at 2018 cm À1 (CH 2 twisting), which has been shown to remain relatively unaffected by the changes in the polymer structure induced by thermal, high-energy radiation or mechanical treatments, was used as the internal reference for the normalization of all spectra to an absorbance of 0.05 for a slice thickness of approximately 100 lm [16,40]. The base of this peak was zeroed at 2000 cm À1 .…”

“…Stabilization of irradiated UHMWPE with antioxidants has been studied extensively in vitro and has demonstrated a promising alternative strategy to prevent UHMWPE oxidation [13,16,17,45]. Vitamin E, or more specifically a-tocopherol, has been introduced into clinical use and to date appears to be a successful antioxidant used to stabilize radiation-crosslinked UHMWPE.…”

In vitro analysis of the cytotoxic and anti‐inflammatory effects of antioxidant compounds used as additives in ultra high‐molecular weight polyethylene in total joint replacement components

“…In the area of TJR, it should be pointed out that currently the concentrations or doses of antioxidant compounds being added experimentally to UHMWPE are based on oxidative degradation protection of the polymer25 and measurement of the oxidative index after inclusion of antioxidant compounds at various doses 9, 26–29. Doses chosen (generally 1000 ppm to 3000 ppm) are based on efficiency of resistance to oxidation and are not currently based on any biological consideration 9, 29. Clearly although we want to add antioxidant compounds at doses that will provide oxidative resistance, we also need to be mindful that we do not add these compounds at potentially cytotoxic doses.…”

Surface Modification of the UHMW-PE Film Processing by Hot Compression Molding

“…The non-toxic pollution Ultra-high molecular weight polyethylene (UHMW-PE) which molecular weight is 150 million or even larger shows excellent wear resistance, high strength, and excellent impact strength in liquid nitrogen. It is widely used in the textile, paper, chemical industry, military, medical and health fields [1][2]. UHMW-PE film is high-tech products, applicable to the manufacture of laminated ceramic capacitors, high-capacity and light mobile phones and various electrical accessories [3].…”