Effect of radiation sterilization and aging on ultrahigh molecular weight polyethylene (original) (raw)
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Change of Physico-Mechanical Properties of Polyethylene During Radiation-Induced Aging
The changes in the physicomechanical properties of LDPE are considered in the kinetic and diffusion regimes of radiation oxidation. In the kinetic regime fall in the instant modulus and strength at low doses is due to degradation of the macromolecules and at high doses to accumulation of oxygen-containing groups. In the diffusion regime strength is determined both by the size of the absorbed dose and depending on the dose rate by the ratio of the thicknesses of the internal crosslinked and external oxidized layers. In the heterogeneous sample the presence of a crosslinked layer does not lead to rise in the strength of the material as compared with that of the uniformly oxidized film.
On the morphology of some irradiated ultra high molecular weight polyethylenes
Polymer Degradation and Stability, 2009
The morphology of various grades of ultra high molecular weight polyethylene (UHMWPE), prepared for use in orthopaedic implants, has been examined using differential scanning calorimetry (DSC), wide and small angle X-ray diffraction (WAX and SAX) and Raman spectroscopy. Preparation included gamma irradiation at various dose rates and mechanical annealing, and post-irradiation changes were of particular interest. The experimental results are interpreted in terms of previous proposals that UHMWPE is best considered as a three phase material, fully amorphous, all-trans amorphous and fully crystalline. The all-trans amorphous material is thought to be interfacial. The phase analysis shows that the age related increase in crystallinity occurs through conversion of all-trans material to fully crystalline, and there is little change in the total amorphous content of the polymers. SAX patterns show a change in the sharpness of the main diffraction peak and the emergence of a second diffraction peak at a higher q value, and this is considered to arise from crystallisation of all-trans amorphous material. Increasing the irradiation dose rate has a similar effect on the crystallography as does ageing the material. Mechanically annealed polymer also shows a similar trend towards a bimodal crystal population, accompanied by a reduction in interfacial material.
Journal of Arthroplasty, 1995
Several studies have indicated that degradation of ultrahigh-molecularweight polyethylene following gamma irradiation in air adversely affects the mechanical properties of the material; however, it is not known how this subsequently affects its wear rate. Wear studies have therefore been performed on three groups of ultrahigh-molecular-weight polyethylene: unirradiated material, recently irradiated material (aged for 2 months), and aged irradiated material (aged for 5 years). The aging took place in sterile packaging on the shelf. The wear studies were carried out on a tri-pin-on-disk wear tester, with a pin from each type of material being studied in each test. In each test the wear rate of the nonirradiated material was slightly lower than the 2-month-aged, irradiated material. The 5-year-aged, irradiated material had the highest wear rate, and this was significantly greater than that of the unirradiated material (P < .05). low wear rates in vivo have been quoted, 3 in general volumetric wear rates in vivo are much higher, with average values for acetabular cups estimated to be in the range 40 to 90 mm3/y. 4 It is recognized that in the body, femoral counterfaces that are initially very smooth can become damaged by bone-cement particles, bone particles, metallic debris from stems, and hydroxyapatite partides. These roughened counterfaces can then cause large increases in the wear rate of UHMWPE. 2 The effect of deterioration of the counterface on increased wear of UHMWPE has been well documented. In contrast, the effect of degradation of UI-IMWPE on wear has received less attention. Clinical wear takes place over much longer periods compared with "accelerated" laboratory tests, and there is increasing concern about the degradation and aging of UHMWPE following gamma irradiation, 5 with oxidative degradation affecting both density and
Journal of Applied Polymer Science, 1989
Ultrahigh molecular weight polyethylene has been irradiated using a cobalt 60 source to give received dose between zero and 50 m a d. Irradiated specimens were subjected to tensile characterization, dynamic mechanical analysis, and differential scanning calorimetry. Changes in tensile and dynamic mechanical properties following irradiation arise from both molecular rearrangement and from increased crystallinity following scission of long interlamella tie chains. The effects of post-irradiation aging on mechanical properties are associated with increasing crystallinity resulting from decomposition of metastable groups formed in the amorphous region during irradiation. Irradiated materials have been subject to sinusoidal stressing between 0.275 and 0.55 of yield stress for 100,OOO cycles, and changes in mechanical and physical properties measured. Increased resistance to creep during stressing was observed with the irradiated materials, behavior which is consistent with previously observed changes in crystallinity and crosslink density. Overall property changes measured following stressing were small compared with those induced by the initial irradiation.
Journal of the mechanical behavior of biomedical materials, 2015
Ultra high molecular weight polyethylene has been subject to γ irradiation whilst in contact with a stainless steel backing. This leads to reflection of the incident radiation and to backscattered electrons, both of which contribute to an effective increase in dose received. Radiation induced damage through scission of inter-lamellae tie chains results in an increase in crystallinity. At a nominal received dose of 100 kGy the effect of the metal backing is to increase crystallinity by approximately a third relative to the increase observed in materials irradiated in the absence of the backing. The metal backing induced reflections cause a bimodal recrystallization distribution giving rise to a more refined crystal population. As implant materials are subject to intermittent, but high, stress levels it is clearly of importance to examine how these reflection induced structural changes influence mechanical properties. Stress/strain results have indicated that subsequent yielding behav...
Ageing of radiation-sterilized polypropylene: changes in semicrystallinity
Biomaterials, 1989
Studies on radiation sterilization of isotactic polypropylene intended for biomedical applications were carried out for uncovered and covered samples. The effect of ageing on these samples was studied by determining the changes in relative crystallinity. The semicrystalline nature of the polymer is responsible for the changes in crystallinity. The transitions between short-and long-range order and short-and longduration stiffness in both covered and uncovered samples, reflected in changes in relative crystallinity, were highly affected by the formation of branches in the backbone of the polymer. The high degree of branching in covered samples resulted in greater long-duration stiffness in the transition between shortand long-duration stiffness. The high degree of branching in covered samples was attributed to the high diffusion of energized oxygen into the polymer matrix compared with uncovered samples. The changes in relative crystallinity were rapid in uncovered samples (70% max; 34% min) but rather slow in covered samples (87% max; 43% min).
Plastics, Rubber and Composites, 2008
As a result of its relatively high strength, high chemical resistance, low creep and low wear rate, ultra high molecular weight polyethylene (UHMWPE) has been widely used as the 'soft' articulating surface for total hip and knee arthroplasty. However, for long term artificial joint replacements, accelerated wear as a result of aging of UHMWPE is one of the most important problems that can lead to joint failure. Therefore, the present work is focused on investigating the effects of thermal and serum aging and UV irradiation dose on the nanomechanical properties (elastic modulus, hardness and visco-elasticity) of UHMWPE (type GUR410) specimens under different deformation rates. The continuous stiffness measurement (CSM) nanoindentation technique is used in the present work to measure the nanomechanical properties. The results show a considerable increase in the nanomechanical properties with increasing deformation rate. It is also demonstrated that the nanomechanical properties of the thermally and serum aged UHMWPE specimens decrease compared to the virgin specimens, while their visco-elastic behaviour increases. For the UV irradiated specimens, the nanohardness and nano-elastic modulus show an increase with irradiation dose especially for small penetration depths. Moreover, a considerable decrease in visco-elastic behaviour was observed for the UV irradiated specimens as a result of the crosslinking effect of the radiation.
Journal of Materials Science: Materials …, 1998
The effects of four sterilization treatments (gamma radiation in nitrogen, electron-beam radiation, ethylene oxide gas, and no sterilization) on the structure and morphology of ultrahigh molecular weight polyethylene (UHMWPE) were monitored as a function of ageing time in air for a period of 1.5 y. Characterization techniques employed include differential scanning calorimetry, density gradient column, transmission electron microscopy, and small-angle X-ray scattering. Ethylene oxide gas does not affect the structure of the polymer. Both forms of radiation lead to measurable alterations of the material's structure, including an increase in crystallinity, an increase in density, and the enhancement of lamellae crystalline stacking. Most changes in structure occur in the first few months with little differences observed upon subsequent ageing in air. The sharpness of the crystalline-amorphous boundaries decreases with time for irradiated UHMWPE and is believed to be linked to the oxidation of the polymer.
The Effect of Irradiation on Mechanical and Thermal Properties of Selected Types of Polymers
Polymers, 2018
This article deals with the influence of electron-beam radiation on the micro-mechanical, thermo-mechanical, and structural properties of selected polymers. In the search for the desired improvement of polymers, it is possible to use, inter alia, one particular possible modification-Namely, crosslinking-Which is a process during which macromolecular chains start to connect to each other and, thus, create the spatial network in the structure. In the course of the treatment of the ionizing radiation, two actions can occur: crosslinking and scission of macromolecules, or degradation. Both these processes run in parallel. Using the crosslinking technology, standard and technical polymers can acquire the more "expensive" high-tech polymeric material properties and, thus, replace these materials in many applications. The polymers that were tested were selected from across the whole spectra of thermoplastics, ranging from commodity polymers, technical polymers, as well as high-performance polymers. These polymers were irradiated by different doses of beta radiation (33, 66, 99, 132, 165, and 198 kGy). The micro-mechanical and thermo-mechanical properties of these polymers were measured. When considering the results, it is obvious that irradiation acts on each polymer differently but, always when the optimal dose was found, the mechanical properties increased by up to 36%. The changes of micro-mechanical and thermo-mechanical properties were confirmed by structural measurement when the change of the micro-hardness and modulus corresponded to the crystalline phase change as determined by X-ray and gel content.