Wednesday, July 10, 2013

Diamond-like-carbon to bolster prosthetic hips

ScienceNetwork in Western Australia

SUPER-hard yet tough diamond-like-carbon (DLC) coatings on replacement metal joints have been shown to significantly improve load and durability on prosthetic hip implants in the most recent round of simulations.

The study, conducted jointly by Edith Cowan University School of Engineering’s Dr Xiaoli Zhao and University of Adelaide School of Mechanical Engineering’s Dr Zonghan Xie explored innovative design strategies to combat early replacement joint failure where metal particles from abrasion can cause metalliosis, permanent disability and even death.

Using the common replacement joint alloy of Cobalt-Chromium-Molybdenum, the researchers placed different stratum of DLC coatings to a thickness of ~4um on joints.

The DLC coatings ranged from one, three and five graded sublayers and were placed on the surface of the CoCrMo ball, and tested using COMSOL Multiphysics software in the presence of wear particles.

Three types of cracks were observed under different stress levels: ring, radial and lateral.
Researchers also noted particle size effects and delamination failure under mechanical loading.
“The results for three and five graded multilayer DLC can lower stress levels up to 40 per cent, and in so doing increase the load-carrying ability of the artificial joints,” Dr Zhao says.

The multilayer structures are able to resist wear particle damage, and Dr Zhao says this has two advantages.

“The effects of wear particles are twofold: firstly, they reduce the operation life of the artificial joints by surface scratching, and secondly, when wear particles come into contact with surrounding tissues, they can cause pains and inflammation.”

Particles can range from 0.25 to 10um and given the tolerance of joints amount to micro-meters, particles can be irritants through to debilitating.

There is also no acceptable size for wear particles in replacement joints across the industry; failed joints pose a significant impact on patient mortality and health services.

Dr Zhao says with the increase of life expectancy in Australia and around the western world, joint replacements are expected to last 20 years or more, however current CoCrMo alloy bearings have a life span of around 10 years.

Dr Zhao and Dr Xie are currently working with surface engineers and medical researchers for preparation and tests of the newly designed coating.

A Four Corners report has explored replacement joints for hips lasting only 5 years before catastrophic failure.

Dr Xie says the study was inspired from the extremely strong, biologically compatible structure of Mother-of-Pearl

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