Probing lubricated sliding wear properties of HDPE/UHMWPE hybrid bionanocomposite.

The ultra-high molecular weight polyethylene (UHMWPE) used in total joint arthroplasty has been sterilized commonly by gamma radiation. Irradiation and subsequent aging in air reportedly cause extensive oxidation in this material. The original properties of UHMWPE, including wear resistance, can be altered significantly as a result of oxidation. In this study, long-lived free radicals in gamma-sterilized and subsequently shelf-aged UHMWPE tibial components were investigated. UHMWPE bar stock, resin powder, and fibers that had been irradiated with electron beam and then stored in air for three years were also characterized for long-lived free radicals. Significant concentrations of free radicals were found in all irradiated UHMWPE materials. Peroxy radicals are predominant in the UHMWPE materials that are highly accessible to oxygen, while more primary radicals remain in the UHMWPE materials that are isolated from oxygen. Based on this study, it is expected that irradiation of UHMWPE in an inert environment would result in long-lived primary radicals, which could be a potential cause of long-term oxidation.

Stainless steel AISI 316L (SS316L) and ultra-high molecular weight polyethylene (UHMWPE) are widely used materials for artificial hip joint components. The SS316L material is typically used for the acetabular cup, femoral head and the stem, while the UHMWPE material is used for the acetabular liner in an artificial hip joint. The aim of this work is to study the biocompatibility of SS316L and UHMWPE materials by implanting and installing these materials in the tissues of rabbits. The tissues around the implants were examined after eight weeks of the installment. Results showed that the reaction of the rabbit tissues around the implants was positive. It was concluded that the SS316L and the UHMWPE materials are biocompatible and the applications of these materials for implants seems conceivable.

Implants based on solid (nonporous) Ultra High Molecular Weight (UHMW) polyethylene have serious disadvantages such as generation of fine polymer particles, because of the lack of internal natural lubricant inside the implant body. A novel family of porous multilayer composites based on Ultra High Molecular Weight (UHMW) polyethylene commercial fabrics has been developed. These composites are produced using a compaction/sintering process with a compression molding technique. The developed porous materials have much higher tensile strength than solid (nonporous) UHMW polyethylene materials.

Compliance calibration for fatigue crack propagation testing of ultra high molecular weight polyethylene

Reducing the friction between the walls of storage vessels and the bulk solids that they contain is widely known to be beneficial in obtaining more satisfactory flow patterns in such vessels, and to reduce flow problems. In particular, the advantages of low friction in promoting a mass flow discharge pattern are well understood; means of obtaining data to design a hopper for mass flow are also well established. In recent years a number of polyethylene materials have come on to the market, intended for use in lining silos and claimed by their manufacturers to offer low wall friction in comparison with other materials. In this paper, one particular commercial grade of ultra-high molecular weight polyethylene (UHMWPE) material has been tested alongside a commonly used type and finish of ferritic stainless steel. The wall friction has been measured for both materials, with a variety of bulk solid materials and conditions, and the hopper half-angles needed for mass flow computed for each combination. The results show that the UHMWPE material does not always offer a lower friction than the stainless steel; in some cases it offers much lower friction and hence much greater scope for obtaining mass flow discharge. However, in other cases it gives significantly higher friction and is a bad choice for promoting flow. The principal conclusion is that, under certain circumstances, UHMWPE offers substantial advantages over other wall materials. However, this advantage is by no means universal and, if it is to be considered for employment in a hopper design, then a wall friction test should be undertaken. This test should use a sample of the bulk solid to be handled against both the UHMWPE material and other possible materials.

Total joint replacements (TJR) have become the cornerstone of modern orthopedic surgery. A great majority of TJR employs ultrahigh molecular weight polyethylene (UHMWPE) liners. TJR manufacturers use many different types of UHMWPE, which are modified by various combinations of crosslinking, thermal treatment, sterilization and/or addition of biocompatible stabilizers. The UHMWPE modifications are expected to improve the polymer's resistance to oxidative degradation and wear (release of microparticles from the polymer surface). This manuscript provides an objective, non-commercial comparison of current UHMWPE formulations currently employed in total knee replacements. UHMWPE liners from 21 total knee replacements (TKR) were collected which represent the most implanted liners in the Czech Republic in the period 2020-2021. The UHMWPEs were characterized using several methods: infrared microspectroscopy (IR), non-instrumented and instrumented microindentation hardness testing (MH and MHI), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and solubility measurements. The above-listed methods yielded quite complete information about the structure and properties of each UHMWPE type, including its potential long-term oxidation resistance. For each UHMWPE liner, IR yielded information about immediate oxidative degradation (in the form of oxidation index, OI), level of crosslinking (trans-vinylene index, VI) and crystallinity (CI). The MH and MHI testing gave information about the impact of structure changes on mechanical properties. The remaining methods (DSC, TGA, and solubility measurements) provided additional information regarding the structure changes and resistance to long-term oxidative degradation. Statistical evaluation showed significant differences among the samples as well as interesting correlations among the UHMWPE modifications, structural changes, and mechanical performance. Surprisingly enough, UHMWPE materials from different manufacturers showed quite different properties, including the resistance against the long-term oxidative degradation, which is regarded as one of the main reasons of TJR failures. The most promising UHMWPE types were crosslinked materials with biocompatible stabilizers. Current UHMWPE liners from different manufactures used in total knee replacements exhibit significantly different structure and properties. From the point of view of clinical practice, the traditional UHMWPE types, which contained residual radicals from irradiation and/or gamma sterilization, showed inferior resistance to oxidative degradation and should be avoided. The best properties were observed in modern UHMWPE types, which combined crosslinking, biocompatible stabilizers, and sterilization by ethylenoxide or gas plasma. UHMWPE; knee replacements; oxidative degradation; infrared spectroscopy; microhardness.

Anti-ballistic is an indispensable personal protective equipment such as body armour for military and police personnel. This tool has received a lot of attention in recent decades due to increasing threats and insurgencies. Several studies have reviewed the development of anti-ballistic technology. However, there still needs to be discussion related to the development of anti-ballistics using UHMWPE (Ultra High Molecular Weight Polyethylene) and the contours of the surface of the UHMWPE. In addition, anti-ballistic studies are rarely carried out compared to other fields. This is because discussions or research related to weapons are still sensitive discussions. This study aims to determine whether the quality of body armour made using UHMWPE which one of the surfaces is given a specific profile, is better when compared to UHMWPE, which has no contours on all surfaces. UHMWPE material that is given a certain profile is one of the ideas chosen because it has high strength and aesthetic value, so it is expected to withstand bullet impact, comfortable and attractive when used. The antiballistic properties of UHMWPE given the diamond contour were obtained from numerical simulations using the finite element model (explicit dynamics) of ANSYS Workbench software. The two UHMWPE variants used in the multiplelayered configuration consist of UD UHMWPE sheets. Ballistic testing used a 7,62 mm calibre lead bullet with a velocity of 720 m/s. The material model of the bullet and UHMWPE plate used the Johnson-Cook plasticity model.

Purpose This study aims to investigate and compare the tribological behavior of two high-performance polymers, ultra-high-molecular weight polyethylene (UHMWPE) and polyetheretherketone (PEEK), under dry sliding conditions against steel and various polyetherimide (PEI)-based polymer counterfaces. Design/methodology/approach Pin-on-disk wear tests were carried out using the UHMWPE and PEEK pins sliding against four different counterfaces of general purposed (GP)-PEI, wear resistant (WR)-PEI, glass fiber-reinforced PEI (PEI + 20% GFR) and AISI 304 L stainless steel. The experiments were conducted under normal loads of 20, 40 and 60 N at a constant sliding speed and distance. The coefficient of friction (COF), specific wear rate (SWR) and dominant wear mechanisms were evaluated based on the experimental measurements and optical microscopy observations. Findings The UHMWPE consistently exhibited lower COF and specific wear rate values than those of the PEEK, under all test conditions. Its best tribological performance was achieved at a load of 60 N against the GP-PEI counterface, yielding the COF and SWR values of 0.0728 and 7.96 × 10–15 m²/N, respectively. For the PEEK, the optimum values of the COF and SWR were obtained as 0.1856 and 8.79 × 10–15 m²/N, respectively also against the GP-PEI. The superior performance of the UHMWPE was mainly attributed to its self-lubricating behavior and the formation of a stable transfer film. However, the PEEK exhibited higher and more unstable friction behavior, particularly when sliding against the PEI + 20% GFR and steel counterfaces. Originality/value Unlike most previous studies focusing primarily on the metal–polymer tribological pairs, this study provides a comprehensive comparative evaluation of polymer–polymer and polymer–metal interfaces. The findings demonstrate that the UHMWPE outperforms the PEEK in the dry sliding applications and offer valuable insights for the rational selection of tribo-pairs in the engineering applications.

Tresca stress evaluation of Metal-on-UHMWPE total hip arthroplasty during peak loading from normal walking activity

Developing thermoplastic hybrid titanium composite laminates (HTCLS) at room temperature: Low-velocity impact analyses

Wear and/or failure of ultra-high molecular weight polyethylene (UHMWPE) component after total joint replacement are major factors restricting the clinical longevity of artificial joints. In order to minimize the wear and failure of the UHMWPE and to improve the clinical longevity of artificial joints, it is necessary to clarify the factors influencing the wear and failure mechanism of the UHMWPE. The generations of catastrophic wear and/or failure of the UHMWPE acetabular cup liner are frequently observed in retrieved hip prostheses. The primary purpose of this study was to investigate the cause of catastrophic wear and/or failure of the UHMWPE liner in hip prosthesis. The authors focused on change in mechanical state of the UHMWPE liner due to contact with metallic component as a factor influencing the wear and failure mechanism of the UHMWPE liner. Contact analyses between the metallic components and the UHMWPE liner by using the finite element method (FEM) were performed to investigate the mechanical state of the UHMWPE liner. It was found that high contact stresses, which exceed the yield stress of UHMWPE, and considerable plastic deformations occurred in the rim of the UHMWPE liner. It was also found that high stress concentrations occurred near screw holes in the acetabular cup and notches in the UHMWPE liner. This study confirmed that change in mechanical state due to contact with metallic component is the cause of catastrophic wear and/or failure of the UHMWPE liner.

The wear and mechanical properties of GUR 1020 (Perplas IMP 2000-2) Ultra High Molecular Weight Polyethylene (UHMWPE) subjected to gamma-irradiation in an atmosphere of acetylene, were evaluated for a range of processing conditions of irradiation, annealing and ageing. The results were compared with those obtained for the virgin UHMWPE material and material processed using conventional gamma-irradiation in nitrogen. Cross-linking produced by irradiation in acetylene, followed by subsequent annealing was found to be significantly more effective in improving the mechanical and wear properties of UHMWPE compared to when the material was irradiated in nitrogen. Gel fraction analysis on its own, while being able to detect the degree of cross-linking, was found to be insufficient in determining the effectiveness of the cross-links and the resulting mechanical properties of the UHMWPE material. The results suggest that gamma-irradiation in an atmosphere of acetylene may provide significant advantages over conventional UHMWPE processing and irradiation cross-linking techniques.

In this work, the authors have investigated the impact performance of natural rubber (NR) coated high strength, high modulus fabrics. P‐aramid (Kevlar 129) and ultra high molecular weight polyethylene (UHMWPE) fabric were coated with different concentrations of NR solutions (20%, 30%). Samples were produced with different add on percentage. The NR solutions with 20% and 30% solid content provided 4 and 6% add‐on on p‐aramid fabric and 6 and 9% add‐on on UHMWPE fabric. Multilayered fabric structures coated with NR were also studied. Compression molding technique was used to prepare the layered fabric structures. The effect of coating with different add‐on percentages of NR on fabrics was studied. The pull out force increased by ∼480% and 360% on NR‐coated p‐aramid and UHMWPE fabrics, respectively. Although the impact energy absorption of single layer NR‐coated fabrics was lower than that of neat fabrics, there was substantial improvement in the impact energy absorption of the two layered p‐aramid and UHMWPE rubber coated fabrics as compared to untreated two layered ones. The increase was 44% and 81%, respectively, for Kevlar and UHMWPE fabrics. Further, the effect of NR latex treatment on tensile strength of fabrics has also been studied. POLYM. COMPOS., 39:3636–3644, 2018. © 2017 Society of Plastics Engineers

Computational nodal displacement analysis of acetabulum fossa for injection molded cemented polyethylene acetabular liner

BackgroundIn the ultrahigh molecular weight polyethylene (UHMWPE) prosthetic environment, fibroblasts affected by wear particles have the capacity of osteogenesis to reduce osteolysis. We aimed to assess the effects of macrophages on the osteogenic capability of fibroblasts treated with UHMWPE wear particles.MethodsThe effect of different concentrations of UHMWPE (0, 0.01, 0.1, and 1 mg/ml, respectively) on macrophage proliferation were validated by MTT assay to determine the optimum one. The fibroblasts viability was further determined in the co-culture system of UHMWPE particles and macrophage supernatants. The experiment was designed as seven groups: (A) fibroblasts only; (B) fibroblasts + 1 mg/ml UHMWPE particles; and (C1–C5) fibroblasts + 1/16, 1/8, 1/4, 1/2, and 1/1 supernatants of macrophage cultures stimulated by 1 mg/ml UHMWPE particles vs. fibroblast complete media, respectively. Alizarin red staining was used to detect calcium accumulation. The expression levels of osteogenic proteins were detected by Western blot and ELISA, including alkaline phosphatase (ALP) and osteocalcin (OCN).ResultsThe concentration of 0.1 mg/ml was considered as the optimum concentration for macrophage proliferation due to the survival rate and was highest among the four concentrations. Fibroblast viability was better in the group of fibroblasts + 1/16 ratio of macrophage supernatants stimulated by 1 mg/ml of UHMWPE particles than the other groups (1:8, 1:4, 1:2, 1:1). ALP and OCN expressions were significantly decreased in the group of fibroblasts + 1/4, 1/2, and 1/1 supernatants stimulated by 1 mg/ml of UHMWPE particles compared with other groups (1/8, 1/16) and the group of fibroblasts + 1 mg/ml UHMWPE (p < 0.5).ConclusionsMacrophages are potentially involved in the periprosthetic osteolysis by reducing the osteogenic capability of fibroblasts treated with wear particles generated from UHMWPE materials in total hip arthroplasty.