Effects of microtomy on the material properties of ultra high molecular weight polyethylene

In order to study the properties of retrieved orthopaedic prosthetic implants, microtomy is often used to produce pieces suitable for examination. However, the cut made with the microtome can change the characteristics of the material to be studied and thus give an incorrect picture of some of its actual properties. This paper is based on a thorough investigation of the effects of different cutting depth, cutting velocity and cutting angle on the orientation and crystallinity of ultra high molecular weight polyethylene. It was found that the orientation decreases with greater cutting depth and cutting velocity and increases slightly with a greater cutting angle. The degree of crystallinity as measured by FTIR and calculated from the first DSC heating was found to increase with greater cutting depth. The crystallinity calculated from the second heating, however, always gave an average value of 50.5 +/-0.5%. Cutting angle and cutting velocity did not influence the crystallinity. Two different knives were used ii the investigation. One was old and left scratch marks on the film while the other had recently been sharpened. The main difference between the two knives, apart from the scratch marks, was that the films cut with the old knife had a lower degree of crystallinity than the ones cut with the new knife when measured immediately after cutting. The crystallinity did, however, increase during ageing in ambient atmosphere, and after about 2 months it was the same as for the samples cut with the new knife. (C) 2001 Elsevier Science Ltd. All rights reserved.