Tribological properties and structure of ultra-high molecular weight polyethylene after gamma irradiation

Abstract

The aim of the present study was to investigate the effects of irradiation and post treatment on the molecular structure, mechanical, and tribological properties of ultra-high molecular weight polyethylene (UHMWPE). UHMWPE was irradiated by gamma ray at doses of 120, 250, and 500 kGy in air and encapsulation by plastic film, and then posttreated in vacuum. The tribological properties were investigated by sliding UHMWPE against Si3N4 ceramic ball on a ball-on-disc tribometer in the presence of distilled water lubricant. The result showed that, after gamma irradiation, the crystallinity and cross-linking degree of UHMWPE increased with dose increasing, whereas its toughness and the elongation decreased sharply. All irradiated samples exhibited lower wear rates with dose in the range from 120 to 250 kGy, but, higher friction coefficients, compared with those un-irradiated. However, over 250 kGy, the wear factor began to increase, which may be associated with the ductile-brittle transition in its mechanical properties. Posttreatment in vacuum promoted residual radicals to cross-link and improved wear resistance of UHMWPE further. The 250 kGy irradiated and posttreated sample showed the best wear resistance. The wear mechanism of un-irradiated UHMWPE and those posttreated ones was mainly plowing, plastic deformation, and adhesion, whereas the irradiated samples were characterized mainly by abrasive wear.

Friction, wear, and tensile properties of vacuum hot pressing crosslinked UHMWPE/nano‐HAP composites

“…The enhanced wear resistance of filled samples was consider to be the reason of supporting function of filling particles on the contact surface, where filling particles could act as rigid spots against the counterface to reduce the normal load and shear stress of polymers, resulting in a lower wear rate 37. For irradiated samples, crosslinked molecular chains would form a compact three‐dimensional structure to improve the resistance of plastic deformation on the contact surface, which might have led to a decreased wear rate 18. Furthermore, the delamination of nonirradiated UHMWPE would cause a large amount of wear debris, resulting in a higher wear rate as compared with all the other samples, which did not exhibit any evidence of delamination.…”

“…However, ion implantation and grafting only form a shallow penetration depth on UHMWPE surface, 15–17 which is not suitable for the long time service of artificial joints. Radiation crosslinking and filling have attracted more attention to enhance wear resistance of UHMWPE 8, 14, 18. Crosslinked UHMWPE is generally obtained by exposing the polymer to gamma ray or e‐beam irradiation along with a subsequent annealing or remelting heat treatment to remove residual free radicals 19.…”

Friction properties of novel PVP/PVA blend hydrogels as artificial cartilage

“…Friction properties were investigated by sliding against stainless steel balls with a diameter of 20 mm under different lubrication conditions on a self‐made ball‐on‐disc tribometer 5. Surface roughness of the stainless steel ball is 0.1 ± 0.05 μm.…”

“…Durability of artificial joints remains a major problem for clinical use, especially for younger and more active patients. Wear debris of the prosthesis components can induce a series of adverse tissue reactions, causing osteolysis and concomitant loosening, and eventually leading failure of the artificial joints 3–5. Then, it needs joint revision, which requires a new surgical intervention and has a poorer outcome than the original one 1.…”

“…Then, it needs joint revision, which requires a new surgical intervention and has a poorer outcome than the original one 1. Many measures have been taken to improve friction properties of artificial joints, such as modifying the existed prosthesis material, searching for new bearing material, and altering bearing couples (metal‐on‐metal, ceramic‐on‐metal, or polymer‐on‐metal) 5–10. But, artificial joints always work under a mixed lubrication regime, where some load is supported by fluid film and some by solid‐to‐solid contact, which causes the wear debris and the failure of the prosthesis 11.…”