Medical Grade Ultra-high Molecular Weight Polyethylene Research Articles

A comprehensive review summarising the reinforcement of UHMWPE composite scaffolds as an artificial implant biomaterials

As a bearing surface, Ultra High Molecular Weight Polyethylene (UHMWPE) has been a long-standing material of choice due to its distinguished physical and mechanical properties, including lubricity, low coefficient of friction, excellent wear and impact resistance, and high resistance to corrosive chemicals. UHMWPE's oxidative breakdown in an interstitial fluid environment and processing restrictions, however, continue to be problems in biomedical applications. Research has concentrated on enhancing performance by integrating different processes, such as synthesis, manufacturing, the inclusion of organic or inorganic material, and pre- and post-processing approaches, in order to overcome obstacles. The sub-constituent composition and processing methods have an impact on the physical and mechanical properties, which in turn have an impact on how well the implant functions in the clinical setting. According to estimates, the market for medical-grade ultra-high molecular weight polyethylene is worth US$2.39 billion, and from 2015 to 2024, a compound annual growth rate (CAGR) of 5.1% is anticipated. The review manuscript highlights the recent progress on the reinforcement of UHMWPE for improvement in functional characteristics like mechanical and tribological properties and bioactivity. This study also carefully examines UHMWPE's 3D printability for a variety of biomedical applications. This article will serve as a guide for the research community to enhance their conceptual comprehension and perception of the potential of 3D printing biomedical devices and equipment built of UHMWPE.

Laser Melt Infiltration of UHMWPE into the Binary Coatings of Strontium Apatite and Colloidal Silica

Medical-grade ultrahigh molecular weight polyethylene (UHMWPE) is the material of choice for sliding surfaces in various articular joint implants owing to its excellent biocompatibility and superior physical properties, such as an exceptionally low coefficient of friction and excellent durability. However, the bioinert nature of UHMWPE limits its extended use in rapidly advancing medical fronts. In this study, bioactive surface modifications of UHMWPE were addressed using a newly developed laser-melt infiltration technique. UHMWPE was coated with binary mixtures of strontium apatite and colloidal silica particles and irradiated using a 30 W CO2 laser to reach the maximum temperature of 150 ± 5 °C. UHMWPE melts infiltrated the porous matrices of the coatings by capillary force and formed surface-selective composite materials between them. Capillary rise heights were evaluated by observing the uplift of the substrate after the selective dissolution of the coating substances and were found to be much higher than the estimated values based on the Lucas–Washburn equation. This finding suggests that the melt viscosity of UHMWPE confined within the nanopores might be significantly lower than that measured at macroscopic scales. Both strontium and silicate ions are known osteo-inductive factors, and their concentrations eluted from the binary coatings were substantially higher than those found in the single coatings.

Prospects in innovative manufacturing technology of UHMWPE for prostheses and comparison with medical grade UHMWPE

Due to its properties like high load-bearing capacity, biocompatibility, excellent abrasion resistance and strength, ultra-high molecular weight polyethylene (UHMWPE) is widely used as a bearing material in the field of joint prostheses. Currently, UHMWPE is produced by compression molding, ram extrusion or sintering, followed by post-processing techniques, such as milling or machining to finalize the prosthesis geometry and to achieve the final tolerances. With post-processing techniques we are wasting a high cost material, energy and time. In this paper, we collected manufacturing technologies that has have the potential to be used for creating prosthesis with one step production, minimalize material loss and with a view to providing customized manufacturing capabilities. We compared three technologies: (i) ram extrusion (currently used technology for joint prosthesis), (ii) FDM printing and (iii) injection molding. In addition to the feasibility, we focus on the investigation of mechanical properties. Three tests were performed on the manufactured specimens: hardness measurement, tensile test and scanning electron microscope (SEM) to compare the finished parts produced by the different processing technologies.

Short-term creep and recovery behavior of medical grade ultra-high molecular weight polyethylene (UHMWPE)

Purpose: In this study, short-term tensile creep and recovery behaviors of medical gradeultra-high molecular weight polyethylene (UHMWPE) were investigated to contributedeformation behaviour of UHMWPE components in knee and hip prosthesis during daily lifeactivities of patients.Design/methodology/approach: Tensile test specimens were machined fromcompression molded UHMWPE sheets having commercial brand name: Chirulen 1020 andthey were prepared according to ASTM 527-2. The tensile creep tests were performed atconstant stress levels of 5, 9, 13, 18 and 21 MPa as long as 1 hour for each test. Then, thespecimens were allowed to recover unloaded for 1 hour. Automatic extensometer was usedto measure the deformations precisely for each test.Findings: Results show that creep rate linearly increased with increasing the stress levels.Permanent deformations were observed after recovery. Recovery of the material becamedifficult with increasing the applied load at intended time interval.Research limitations/implications: UHMWPE components used in prosthesis havebeen subjected to complex loading conditions during service life. Polymeric materials showthe viscoelastic material properties like strain rate sensitivity, relaxation, creep and recoveryat room temperature. Because of the viscoelastic material properties of the UHMWPE,it makes difficult to predict the failure of the UHMWPE components in hip and knee prosthesis.Therefore, deformation behavior of medical grade UHMWPE should be investigated in manydifferent loading conditions.Practical implications: Medical grade ultra-high molecular weight polyethylene(UHMWPE) have been used commonly in total hip replacements as acetabular cup and intotal knee replacements as tibial insert since early 1960s.

Investigation of the water lubricated tribological behavior of medical grade UHMWPE

In this study, ultrahigh molecular weight polyethylene (UHMWPE) polymer was studied for boundary lubricated friction and wear behaviour under distilled water lubricated conditions. Sliding wear tests were carried out using pin-on-disc apparatus. UHMWPE polymer in the form of the pin was tested against AISI 304L stainless steel disc. Wear tests were performed at room temperature under 50, 100 and 150 N applied loads and at 0.5 and 2.0 m/s sliding speeds. The obtained results show that the coefficient of friction for UHMWPE polymer is significantly influenced by the increase in applied load and sliding speed values. Finally, the average specific wear rate values for UHMWPE polymer under water lubricated condition is in the order of 1.4 × 10−14 m2/N.

The effect of an additional phosphite stabilizer on the properties of radiation cross‐linked vitamin E blends of UHMWPE

Antioxidant stabilization of radiation cross-linked ultrahigh molecular weight polyethylene (UHMWPE) has been introduced to improve the oxidative stability of total joint implant bearing surfaces. Blending of an antioxidant with UHMWPE resin powder followed by consolidation and radiation cross-linking has been cleared by the FDA for use in both total hips and total knees for designs incorporating two antioxidants, namely vitamin E and Covernox™ (a medical grade version of Irganox™ 1010). The antioxidants in the polymer are expected to protect the polymer during consolidation, during radiation cross-linking, on the shelf before implantation, and in vivo after implantation. To maximize the protection of the polymer afforded by the antioxidant in vivo, a novel approach may be the use of multiple antioxidants, especially to protect the primary antioxidant for a longer period of time. We hypothesized that the addition of a phosphite stabilizer (Irgafos 168™) commonly used in conjunction with hindered phenolic antioxidants in polymer processing could improve the oxidative stability of radiation cross-linked blends of vitamin E. To test our hypothesis, we prepared UHMWPE blends with 0.05 wt% Irgafos and 0.05 wt% vitamin E and compared its cross-link density, wear resistance, tensile properties, and impact strength to control blends containing only vitamin E. Our hypothesis was not supported; the cross-link density of UHMWPE was significantly decreased by the additive without additional benefit to oxidative stability. To our knowledge, this was the first attempt at using multiple stabilizers in medical grade UHMWPE.

Tax policy developments, donor inflows and economic growth in Malawi

In this investigation the friction and wear performance of GUR 1020 medical grade ultra-high molecular weight polyethylene (UHMWPE) polymer under dry sliding, distilled water and egg albumen lubrication conditions were evaluated. The sliding experiments were carried out on a pin-on-disc tribometer. The contact configuration used was a polymer pin on a rotating AISI 304L stainless steel disc. Wear tests were carried out for 30 min duration at room temperature with 50, 100 and 150 N applied load values and at 0.50, 1.0 and 2.0 m/s sliding speeds condition. The results show that the coefficient of friction for GUR 1020 medical grade UHMWPE polymer is more significantly influenced by applied load and sliding speed values under dry sliding condition rather than lubricant media condition. Furthermore, the coefficient of friction and specific wear rate increases with the increase in applied load and speed values. This increase is much pronounced under dry sliding condition. Moreover, for the range of load and speed values of this study the specific wear rate using egg albumen lubricant registered lower values than that of the distilled water lubricant and the dry conditions. Finally, the specific wear rate values for GUR 1020 medical grade UHMWPE polymer under dry, water lubricant and egg albumen lubricant conditions are at the levels of 8x10-14, 1.4x10-14 and 0.5x10-14m2/N respectively.   Key words: Medical Grade UHMWPE, tribology, distilled water, wear.

Studies on electron-beam irradiation and plastic deformation of medical-grade ultra-high molecular weight polyethylene

Separated and combined electron-beam irradiation and plastic deformation effects on the structures of ultra-high molecular weight polyethylene (UHMWPE) were studied. It was found that the concentration of carbonyl (ketones, esters and peresters), hydroxyl and vinyl groups increases with the growing dose of adsorbed electrons. It also tends to exhibit a slight increase in the melting point and crystallinity of the samples. A mechanical stress in the polymer was found to accelerate radiation-induced degradation. It was concluded that each of the factors studied (i.e. electron beam sterilization and plastic deformation) had a different impact on the polymer structure. The change in the sequence of action of these factors can dramatically influence the process of UHMWPE destruction. Some effects may be limited or enhanced by the action of other factors. Therefore, the resulting effects of destructive factors depend qualitatively and quantitatively on their intensity and order.

Post electron-beam irradiation oxidation of orthopaedic Ultra-High Molecular Weight Polyethylene (UHMWPE) stabilized with vitamin E

Ultra-High Molecular Weight Polyethylene (UHMWPE) has been the material of choice for load-bearing articular components used in total joint arthroplasty in the past 30 years. However, the durability of the whole implant has often been compromised by oxidation of UHMWPE components. Since the use of a suitable, biocompatible stabilizer would minimize this inconvenience, the possibility to use vitamin E has been introduced. In the present work, medical grade UHMWPE was blended with 1.1, 2.3 and 11 mmol/l of vitamin E and consolidated by compression moulding. Small blocks of reference and of vitamin E-blended UHMWPE were then electron-beam irradiated at 30, 60 and 90 kGy, both in vacuum and in air. FTIR spectroscopy was used to monitor changes in both the polymer and the additive. Thin sections of irradiated virgin and vitamin E-blended UHMWPE were aged in air, at room temperature and in the dark and the kinetics of oxidation followed by FTIR. The reaction between vitamin E and macro-alkyl radicals or unlikely with peroxy radicals has been demonstrated and a correlation between the decrease of macroradicals and the stabilization effect of vitamin E has been shown.

Friction and wear behavior of ultra-high molecular weight polyethylene as a function of polymer crystallinity

In this study the friction, wear and surface mechanical behavior of medical-grade ultra-high molecular weight polyethylene (UHMWPE) (GUR 1050 resin) were evaluated as a function of polymer crystallinity. Crystallinity was controlled by heating UHMWPE to a temperature above its melting point and varying the hold time and cooling rates. The degree of crystallinity of the samples was evaluated using differential scanning calorimetry (DSC). A higher degree of crystallinity in the UHMWPE resulted in lower friction force and an increase in scratch resistance at the micro- and nanoscales. On the nanoscale, the lamellar structure appeared to affect the observed wear resistance. Reciprocating-wear tests performed using a microtribometer showed that an increase in crystallinity also resulted in lower wear depth and width. Nanoindentation experiments also showed an increase in hardness values with an increase in sample crystallinity.

A study of the nanostructure and tensile properties of ultra-high molecular weight polyethylene

Ultra-high molecular weight polyethylene (UHMWPE) has gained worldwide acceptance as a bearing material used in orthopaedic implants. Despite its widespread use, inherent properties of the polymer continue to limit the wear resistance and the clinical lifespan of implanted knee and hip prosthetics containing UHMWPE components. The degree of crystallinity of UHMWPE is known to strongly influence several of its tensile mechanical properties such as Young's modulus, yield stress, strain-hardening rates, work of fracture and ultimate tensile properties. In this study, medical grade UHMWPE was subjected to four different crystallization conditions resulting in UHMWPE with a range of crystalline morphologies. Thereafter, the crystalline nanostructure was quantitatively characterized using a combination of ultra-small angle X-ray scattering and differential scanning calorimetry. Low-voltage scanning electron microscopy was employed as a supplementary technique to compare the crystalline morphology resulting from each crystallization condition. In addition, uniaxial tensile tests were performed to assess the effects of crystallization conditions on the mechanical properties of UHMWPE. This study showed that while crystallization conditions strongly influenced the morphology of UHMWPE, in most cases the mechanical properties of the material were not significantly affected.

Effects of Counterface Roughness and Conformity on the Tribological Performance of Crosslinked and Non-crosslinked Medical-Grade Ultra-High Molecular Weight Polyethylene

AbstractThe tribological behavior of crosslinked ultra-high molecular weight polyethylene (UHMWPE) was compared to that of non-crosslinked UHMWPE, used as control sample. A reciprocating pin-on-disk tribometer was used to determine the effects of countersurface roughness and conformity on wear mechanisms occurring during the initial stage of sliding. Pin samples of two different radii of curvature were slid against medical-grade Co-Cr alloy disks with surface roughness ranging from 0.005 to 0.04 μm in a lubricant of bovine serum. Normal loads were chosen to provide physiological contact stresses. The focus of this study was on the dependence of early wear mechanisms on surface roughness and conformity. Although a correlation between coefficient of friction data and dominant wear mechanisms was not observed, different wear mechanisms were found between control and crosslinked UHMWPE. The results of this study provide insight into the differences of the initial wear behavior of noncrosslinked and crosslinked UHMWPE used in total joint replacements.

Enhanced wear performance of highly crosslinked UHMWPE for artificial joints.

It is well known that osteolysis induced by polyethylene wear debris is the main cause of long-term failure of hip and knee prostheses. We developed a treatment of medical-grade ultra-high molecular-weight polyethylene (UHMWPE) in order to improve its tribologic properties and reduce its wear. Medical-grade UHMWPE was irradiated with a 200 kGy dose of radiation, thermally stabilized at a temperature close to the melting point, and then sterilized with ethylene oxide. The irradiation treatment was performed to crosslink the UHMWPE. The thermal stabilization treatment, contributing to the reaction between the free radicals generated by the irradiation process, was chosen to enhance crosslinking and to prevent oxidation and the shortening of chains. The non-invasive sterilization process with ethylene oxide was chosen to prevent the re-formation of free radicals. The wear performance of this material was compared to UHMWPE, untreated or treated with different sterilization techniques, using gamma and beta irradiation. Insoluble crosslinked constituents were measured with an extraction method. Wear was evaluated using a flat-on-ring wear test machine. While small differences were found among the different sterilization processes, 200 kGy-irradiated UHMWPE followed by thermal treatment and sterilization with ethylene oxide had the least wear and the greatest amount of crosslinking.

Plasma immersion ion implantation of UHMWPE

Ultrahigh molecular weight polyethylene (UHMWPE) has been the material of choice in orthopaedic joint prostheses for over three decades owing to its proven low friction and excellent wear resistance when coupled with smooth Co-Cr-Mo alloy or austenitic stainless steel surfaces in vivo [1]. However, it is gradually recognized that the principal constraint on the longevity of total joint replacements is the body’s reaction to debris, which is mostly UHMWPE [2]. Therefore, how to improve the wear resistance of UHMWPE and thus reduce the volume of wear debris, which promotes implant loosening, is a timely task from both a scientific and technological point of view. Nitrogen ion implantation of UHMWPE has been proved to improve its tribological properties in terms of low friction and extremely low wear rate [3], however, it is difficult in practice to uniformly treat such three-dimensional objects as hip joint sockets without using sophisticated manipulating devices. Recently, an innovative hybrid technology, plasma immersion ion implantation (PI3), has been developed, which can, to a large extent, address the problems with ion implantation of components with complex shapes [4]. However, there appears to have been little, if any, work reported on the surface modification of UHMWPE using the innovative, hybrid PI3 technology with a view to improve its mechanical and tribological properties [5]. In the present investigation, an attempt has been made to explore the feasibility of surface modification of UHMWPE using the novel PI3 technology. The material used in the study was medical grade UHMWPE (GUR-412) in the form of 12.5 diameter, extruded and annealed rod which was obtained from Poly Hi Solidur Ltd (GB). The density of the homogeneous material and the average molecular weight are 0.932 g cm−3 and 3.6× 106 g mol−1, respectively. Specimens were treated in a Mark 1 PI3 unit at the Technical University of Clauthal with the pulse source being (PI3 treatment) or not being (plasma treatment) applied. Specimens were immersed in a low pressure (0.17 Pa) radio frequency plasma discharge, which was generated by a 300 W r.f. power at 13.56 MHz. Table I lists the treatment conditions for plasma treatment (PT) and PI3 treatments. By selecting appropriate pulse length and pulse frequency, the treatment temperature was controlled at below 90 ◦C. Although it has been claimed that ion implantation can decrease the surface roughness of polymeric materials [6], such an improvement was not observed in the present study. Indeed, surface relief appeared on PI3-H specimens largely because of the ion etching effect resulting from nitrogen ion bombardment. Slight surface discoloration was observed for all surface treated specimens, increasing in the order of PT, PI3-L and PI3-H. In view of the fact that the surface modified layers of UHMWPE material usually are very thin and the substrate very soft, the mechanical properties of the untreated and treated UHMWPE specimens were measured using a NanoTest 500. A standard procedure developed by Oliver and Pharr was adopted to process the load-depth data [7]. Fig. 1 depicts characteristic load versus depth hysteresis curves, showing the loadingunloading response of the PI3 treated as well as untreated material. It can be clearly seen that, to reach the same penetration depth (250 nm), a higher load was need for the treated surface relative to the untreated surface. It also demonstrated that PI3 treated material exhibited a higher elastic recovery and less creep during the dwelling time (10 s) than the untreated material.

Dr. Streicher's response to Drs. Walker and Blunn

Although not so stated in their arguments, Drs. Walker and Blunn probably agree that osteolysis initiated by adverse tissue reactions, primary to wear particles and by-products, is a major concern for the long-term outcome of total hip arthroplasty (THA). We are therefore arguing about solving the same problem, but with a different approach. There really is no argument. Drs. Walker and Blunn are advocating the general use of ultrahigh-molecular-weight polyethylene (UHMWPE) in all patients. I make a point for THA with hard-hard, especially metal-metal, articulation only where it makes economic and logical sense, for the high-demand patient. My investigations of the last 15 years were focused on the possibilities of wear reduction. As a result, several improvements for the THA with UHMWPE articulation were introduced during the midand late 1980s. These included specially synthesized and calcium stearate-free medical-grade UHMWPE; gamma sterilization, annealing, and storage in inert gas; alternative ceramics and the development of diffusion-hardened t i tanium alloy, especially for knee joint implants. Drs. Walker and Blunn point out the benefits of using articulations with UHMWPE, but they address the evident drawbacks with the use of this material only in part. Although clinical results have demonstrated that UHMWPE can achieve its intended purpose generally for a limited time, its long-term performance must still be questioned because of its inherent flaws and its vulnerability:

Plasma Surface Modification of Medical-Grade Ultra-High Molecular Weight Polyethylene for Improved Tribological Properties

AbstractUltra-high molecular weight polyethylene (UHMWPE) is the principal material used to replace damaged cartilage in total joint replacement surgeries. This publication presents preliminary results from a new class of surface treatments to modify the surface chemistry and microstructure of UHMWPE under controlled processing conditions. Radio frequency plasmas were used to lightly crosslink the subsurface of UHMWPE and to modify the surface chemical state through the attachment of low-surface-energy fluorocarbon groups. A pin-on-disk apparatus was used to slide CoCrWNi pins with spherical tips on polished disks of plasma- treated and untreated UHMWPE immersed in a bath of preserved bovine serum. The wear resistance and surface chemical composition of tested specimens were characterized by surface profilometry and X-ray photoelectron spectroscopy (XPS), respectively. Changes in the surface hydrophobicity due to plasma treatment were evaluated using contact angle measurements. The prospect of surface plasma treatment in orthopedic applications is elucidated in the context of the obtained friction, wear, distilled water contact angle, and XPS results.

The influence of sterilization technique and ageing on the structure and morphology of medical-grade ultrahigh molecular weight polyethylene.

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.