A study of long-lived free radicals in gamma-irradiated medical grade polyethylene

Jahan, M. S.; King, M.C; Haggard, W.O.; Sevo, K; Parr, J.E.

doi:10.1016/s0969-806x(01)00431-5

Cited by 95 publications

(55 citation statements)

References 7 publications

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“…In the presence of oxygen, the shift in the ESR spectrum of irradiated polyethylene from the multiple peaks of alkyl and allyl radicals to a sharp singlet (Figs 10 and 11) has previously been ascribed to the formation of oxygen centered radicals such as alkoxy (23,44) and peroxy (23,45,46) radicals and the polyenyl radical (8,18,47). Most of the free radicals trapped in polyethylene in the long term are in the crystalline lamellae, which are not permeable to oxygen.…”

Section: Discussionmentioning

confidence: 92%

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The effect of α-tocopherol on the oxidation and free radical decay in irradiated UHMWPE

2006

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We developed a radiation cross-linked UHMWPE stabilized with a-tocopherol (Vitamin E) as a bearing material in total joint replacements. The stabilizing effect of a-tocopherol on free radical reactions in UHMWPE is not well understood. We investigated the effect of a-tocopherol on the oxidation and transformation of residual free radicals during real-time aging of a-tocopherol-doped, irradiated UHMWPE (aTPE) and irradiated UHMWPE (control). Samples were aged at 22° C (room temperature) in air, at 40°C in air, and at 40°C in water for seven months. During the first month, aTPE showed some oxidation at the surface, which stayed constant thereafter. Control exhibited substantial oxidation in the subsurface region, which increased with time. The alkyl/allyl free radicals transformed to oxygen centered ones in both materials; this transformation occurred faster in a-TPE. In summary, the real-time oxidation behavior of a-TPE was consistent with that observed using accelerated aging methods. This new UHMWPE is oxidation resistant and is expected to maintain its properties in the long-term.

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Section: Discussionmentioning

confidence: 92%

“…Therefore, free radicals travel along the crystal chains and encounter other free radicals to form a double bond or encounter the crystalline/ amorphous interface. The decay of free radicals in the crystalline phase, therefore, is extremely slow, taking as long as years (23).…”

Section: Introductionmentioning

confidence: 99%

The effect of α-tocopherol on the oxidation and free radical decay in irradiated UHMWPE

2006

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“…Due to radiolytic bond scission, free radicals are produced in irradiated UHMWPE [15,18,20,30,38], which react with oxygen and trigger the oxidation cascade [2, 16, 17, 20, 22, 25-27, 54, 69] ( Fig. 2A, Reactions 1-4).…”

Section: Discussionmentioning

confidence: 99%

Vitamin E-stabilized UHMWPE for Total Joint Implants: A Review

Bracco

Oral

2011

Clinical Orthopaedics &Amp; Related Research

256

162

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Background Osteolysis due to wear of UHMWPE limits the longevity of joint arthroplasty. Oxidative degradation of UHMWPE gamma-sterilized in air increases its wear while decreasing mechanical strength. Vitamin E stabilization of UHMWPE was proposed to improve oxidation resistance while maintaining wear resistance and fatigue strength. Questions/purposes We reviewed the preclinical research on the development and testing of vitamin E-stabilized UHMWPE with the following questions in mind: (1) What is the rationale behind protecting irradiated UHMWPE against oxidation by vitamin E? (2) What are the effects of vitamin E on the microstructure, tribologic, and mechanical properties of irradiated UHMWPE? (3) Is vitamin E expected to affect the periprosthetic tissue negatively? Methods We performed searches in PubMed, Scopus, and Science Citation Index to review the development of vitamin E-stabilized UHMWPEs and their feasibility as clinical implants.Results The rationale for using vitamin E in UHMWPE was twofold: improving oxidation resistance of irradiated UHMWPEs and fatigue strength of irradiated UHMWPEs with an alternative to postirradiation melting. Vitamin E-stabilized UHMWPE showed oxidation resistance superior to that of irradiated UHMWPEs with detectable residual free radicals. It showed equivalent wear and improved mechanical strength compared to irradiated and melted UHMWPE. The biocompatibility was confirmed by simulating elution, if any, of the antioxidant from implants.Conclusions Vitamin E-stabilized UHMWPE offers a joint arthroplasty technology with good mechanical, wear, and oxidation properties. Clinical Relevance Vitamin E-stabilized, irradiated UHMWPEs were recently introduced clinically. The rationale behind using vitamin E and in vitro tests comparing its performance to older materials are of great interest for improving longevity of joint arthroplasties.

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“…Irradiation causes crosslinking in the amorphous phase of the UHMWPE [33], but also initiates the formation of free radicals in the crystalline phase [23], unable to recombine due to structural limitations, they become trapped for long periods of time [29]. These residual free radicals are believed to migrate to the crystalline/amorphous interface and cause oxidative degradation in the material [16][17][18]59, 69] through a cascade of reactions with oxygen [32,71].…”

Section: Introductionmentioning

confidence: 99%

Vitamin E diffused, highly crosslinked UHMWPE: a review

Oral

Muratoglu

2010

International Orthopaedics (SICOT)

218

133

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Highly crosslinked UHMWPE has become the bearing surface of choice in total hip arthroplasty. First generation crosslinked UHMWPEs, clinically introduced in the 1990s, show significant improvements compared to gamma sterilised, conventional UHMWPE in decreasing wear and osteolysis. These crosslinked UHMWPEs were thermally treated (annealed or melted) after irradiation to improve their oxidation resistance. While annealing resulted in the retention of some oxidation potential, postirradiation melted UHMWPEs had reduced fatigue strength due to the crystallinity loss during melting. Thus, the stabilisation of radiation crosslinked UHMWPEs by the diffusion of the antioxidant vitamin E was developed to obtain oxidation resistance with improved fatigue strength by avoiding post-irradiation melting. A two-step process was developed to incorporate vitamin E into irradiated UHMWPE by diffusion to obtain a uniform concentration profile. Against accelerated and real-time aging in vitro, this material showed superior oxidation resistance to UHMWPEs with residual free radicals. The fatigue strength was improved compared to irradiated and melted UHMWPEs crosslinked using the same irradiation dose. Several adverse testing schemes simulating impingement showed satisfactory behaviour. Peri-prosthetic tissue reaction to vitamin E was evaluated in rabbits and any effects of vitamin E on device fixation were evaluated in a canine model, both of which showed no detrimental effects of the inclusion of vitamin E in crosslinked UHMWPE. Irradiated, vitamin E-diffused, and gamma sterilised UHMWPEs have been in clinical use in hips since 2007 and in knees since 2008. The clinical outcome of this material will be apparent from the results of prospective, randomised clinical studies. IntroductionOsteolysis triggered mainly by ultrahigh molecular weight polyethylene (UHMWPE) wear particles has been one of the major problems in total hip arthroplasty along with instability/dislocation and infection [7]. Highly crosslinked UHMWPEs were developed using high-dose irradiation (50-100 kGy) to decrease the wear rate of UHMWPE [44,46] and have become the standard-of-care after their first decade of service, especially in North America [61].Irradiation causes crosslinking in the amorphous phase of the UHMWPE [33], but also initiates the formation of free radicals in the crystalline phase [23], unable to recombine due to structural limitations, they become trapped for long periods of time [29]. These residual free radicals are believed to migrate to the crystalline/amorphous interface and cause oxidative degradation in the material [16][17][18]59, 69] through a cascade of reactions with oxygen [32,71].In first generation crosslinked UHMWPEs [34], postirradiation thermal treatment was used to increase the oxidation resistance (Fig. 1). One approach was to annealThe studies discussed here were performed by research funding in part from NIH/NIAMS

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A study of long-lived free radicals in gamma-irradiated medical grade polyethylene

Cited by 95 publications

References 7 publications

The effect of α-tocopherol on the oxidation and free radical decay in irradiated UHMWPE

The effect of α-tocopherol on the oxidation and free radical decay in irradiated UHMWPE

Vitamin E-stabilized UHMWPE for Total Joint Implants: A Review

Vitamin E diffused, highly crosslinked UHMWPE: a review

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