Papers by Keyword: UHMWPE

Abstract: Recently, ceramics and metal-armed structures have been replaced by ceramics combined with ultra-high molecular weight polyethylene (UHMWPE) composite laminated structures for NIJ level III and level IV body armor applications. This shift is due to the superior specific energy absorption capabilities of the ceramics/UHMWPE composites compared to traditional ceramics and metal armor; however, it comes at a higher cost. Manufacturing body armor that offers higher specific energy absorption at a lower cost is challenging. As the thickness of UHMWPE increases, both the specific energy absorption and the overall cost of the body armor increase. Additionally, there is limited experimental data to evaluate the thickness of ceramics and UHMWPE to explore the performance of NIJ level III body armor, indicating that further research is needed. In this study, six different types of ballistic plate configurations were manufactured. Following that, high velocity impact tests were conducted to investigate the effects of front and back layer thicknesses of UHMWPE (Type 1 to Type 3 plates), the effects of foam material (Type 4 plate), and the effects of different thicknesses of boron carbide (B₄C) ceramic strike face (Type 5 and Type 6 plates) on the back face signature (BFS) of the ballistic plate. It was found that the BFS of Type 5 and Type 6 ballistic plate configurations is lower by 12% and 8.5%, respectively, compared with that of the Type 4 UHMWPE/polyvinyl chloride low-density foam ballistic plate. However, the Type 5 option is cost-effective and easy to manufacture, making it the preferred choice over the Type 6 variant.

Abstract: Ultra-high molecular weight polyethylene (UHMWPE) laminate composites are widely used in impact-resistant structures due to their high specific strength and exceptional energy absorption capabilities. However, previous studies encountered challenges in characterizing the tensile properties of UHMWPE composites, including specimen slippage, stress concentrations, and failures outside the gauge length. This work presents the design and development of an interchangeable clamp for the tensile testing of UHMWPE composites. This clamp guarantees secure gripping and uniform load transfer across the UHMWPE specimens. The developed clamp can be used interchangeably in quasi-static and high-strain-rate devices, facilitating the evaluation of a broad range of strain rates. The tensile properties of two UHMWPE composites were subsequently assessed using this clamping system, with strain measured through three-dimensional digital image correlation (3D-DIC). The effectiveness of a 3D-DIC technique for measuring strain in the UHMWPE composite is demonstrated. The tests reveal that the designed clamp enables reliable measurements, with tensile strength values reaching approximately 1300 MPa. The measured tensile properties are useful for the input data of numerical simulations, providing valuable insights for developing highly efficient protective structures.

Abstract: A study was conducted on gamma-ray modified nanoHydroxyapatite (HAp)/Ultra High Molecular Weight Polyethylene (UHMWPE) composite as orthopedic implant material. This study aims to characterize the effect of gamma radiation on the physical, chemical, and mechanical properties of UHMWPE/HAp composites so that they can be used as orthopedic implant materials. The composite film was irradiated with gamma rays at a dose variation of 0 kGy, 15 kGy, and 30 kGy and a dose rate of 8 kGy/hour. Composites before and after radiation were tested for physical, chemical and mechanical properties. Physical properties test includes surface microstructure analysis; chemical properties test includes phase and functional group analysis; mechanical properties test, including hardness, tensile strength, and elongation at break. The results obtained are gamma radiation from IRKA changes the chemical properties of composites in terms of crosslinking and the number of radicals, as well as mechanical properties in terms of hardness, tensile strength, and elongation at break with different changes from the initial state before radiation. The best mechanical properties were obtained at 25% HAp composition in a dose of 30 kGy with a hardness (shore A) of 97.17; tensile strength of 18.15 MPa; and elongation at break of 17.85%, so that the UHWMPE/HAp composite has potential as an orthopedic implant material following the Ultimate Tensile Strength (UTS) of cancellous bone ranging from 10-20 MPa.

Abstract: Ultra-high Molecular Weight Polyethylene (UHMWPE) is a highly versatile polymer known for its exceptional mechanical properties, however, its limited life as an implant material for Total Joint Replacement (TJR) necessitates surface modification to extend its lifespan. This study aims to enhance the surface properties of UHMWPE through application of ceramic coatings. Magnetron sputtering method was used to deposit thin film of white Titania (TiO₂) on the material’s surface. To evaluate the surface characteristics, such as surface roughness, uniformity and structure, coated and uncoated samples were analyzed through Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and X-ray Diffraction Analysis (XRD). The material performance in relation to biological context was investigated through Contact Angle measurement. A comparative analysis of coated and uncoated samples was then performed. The coated samples showed better wettability compared to uncoated sample. This fact highlights the hydrophilic nature of film. The results of the coated UHMWPE suggest that this surface modification technique could significantly extend the lifespan of UHMWPE implants in TJR, potentially addressing the current limitations associated with their longevity.

Abstract: Fused filament fabrication (FFF) has nowadays become a popular 3-dimensional (3D) printing technique for the fabrication of polymeric components with customized and complex-shape design, including biomedical implants. However, the use of this technique is often constrained by the limited number of polymeric materials that can be printed to form the final product. Despite excellent wear resistance and widely used as the acetabular component of a joint prosthesis, ultra-high molecular weight polyethylene (UHMWPE) is among such the rarely-found filament material in the market. In this research, preliminary work to fabricate UHMWPE filament for the FFF processing is carried out by using extrusion. The influences of extrusion temperature, addition of polyethylene glycol (PEG), and rotational speed of the extruder’s screw on the physical, chemical, and mechanical properties of the extruded UHMWPE filament were determined. The result demonstrated no change in the chemical compositions of the filament due to the processing parameters applied, as noted from the FTIR spectra. The result of the tensile test showed that the highest tensile strength of UHMWPE filaments could reach 23.5 MPa.

Abstract: Wear is a problem for metal on polymer (MOP) hip implants to perform lifetime endurance. Polymer excessive volumetric loss leads to implant failures. Attempts to solve this problem are usually initiated with tribological tests. The method is time-consuming because the sliding speed is low. There is a faster way to use a computational method to gather wear data. This research aims to investigate the numerical convergence of predicted wear volume with the finite element method (FEM). The model is a commercially pure titanium (cp Ti) and ultra-high molecular weight polyethylene (UHMWPE) MOP hip implant. A dynamic Paul physiological load was applied to the model. Volumetric loss of the polymer was calculated with a wear equation involved nonlinear contact load and contact area. The inputs of calculation are wear factor and the computational contact mechanic performed by FEM. The wear factor was obtained by performing biotribological experiments with a multidirectional pin on disc tribotest. Predicted wear volume was validated with hip simulator experimental data from the literature. Convergences were found at the mesh density of 1.38 elements/mm³. An acceptable numerical error was obtained in the model with 1 mm element size for femoral head and 0.3 mm for acetabular cup. This model was then used for the investigation of load increment effects. The result is that load increment variations do not affect wear volume and contact mechanic numerical outputs. The calculated stresses are below the UHMWPE yield stress limit. In this elastic region, the effects of strain rate caused by load increment are negligible.

Abstract: In order to study the effect of UHMWPE fiber laminate on effective protection area of ceramic composite target, a dynamic analysis software ANSYS/LS-DYNA was used to calculate the effective protection area of ceramic/aluminum/aluminum composite target and ceramic/UHMWPE/aluminum/ aluminum composite target, both of whose areal density were 139.5kg/m², against 14.5mm armor piercing projectile at the speed of 1000m/s. The result showed that UHMWPE fiber laminates will increase the effective protection area by 64.4% for ceramic composite targets under the same areal density.

Abstract: The UHMWPE acetabular cups are the most popular joints for joint prostheses after Charnley introduced UHMWPE for the acetabular component in 1962. It has been demonstrated that polyethylene wear remains the main source of particles in the THR and therefore requires particular attention. The paper presents a series of theoretical and practical aspects regarding the wear of acetabular cups (made of UHMWPE) from the total hip prosthesis component. At the same time, the other tribological phenomena that occur in these MoP (metal on polyethylene) combinations are treated, such as lubrication and friction. Total Hip Replacement & Hip Resurfacing A hip replacement involves replacing the hip joint with a mechanical bearing system which is comprised of a femoral component and an acetabular component. During a hip replacement the acetabulum is reamed and the acetabular component is fitted into the cavity and the femoral component can either be placed over a reamed femoral head, in a procedure referred to as hip resurfacing, or positioned inside the femoral shaft during a total hip replacement [1]. Fig. 1. Total Hip Replacement (a) and Hip Resurfacing Replacement (b) [2].

Abstract: The paper presents a series of aspects regarding the design, manufacturing (through Rapid Prototyping) and FEA analysis of an intervertebral disk made from UHMWPE. In the first part are presented the most used model existing on the market. The CAD model and Finite Element Analysis (FEA) of the intervertebral disc (IVD) were made using the SolidWorks program. As a material, UHMWPE has been preferred due to good mechanical and biocompatibility characteristics.

Abstract: The following research is aimed at understanding the influence of Zirconia-Toughened Alumina (ZTA) and Silicon Nitride (Si₃N₄) on Ultra-High Molecular Weight Polyethylene (UHMWPE) acetabular liners. Bioceramic femoral heads were systematically tested against UHMWPE in controlled environment according to static/load-free coupling in hydrothermal environment, pin-on-ball wear testing, and hip-simulator wear testing. In addition, a retrieved ZTA femoral head has been analyzed and results have been compared to the simulations. Experimental results from X-ray photoelectron (XPS), cathodoluminescence (CL), Raman and Fourier-Transformed Infrared spectroscopy suggest that, despite conventional notions imply that bioceramics are inert, the surface chemistry of bioceramics was relevant to the oxidation rate of polyethylene liners. Non-biointertness could either be advantageous or disadvantageous toward polyethylene oxidation. The main reason resides in the peculiar chemical interactions between polyethylene and different ceramics, and, more specifically, depends on the direction of oxygen flow at the interface between the ceramic and the polymer. ZTA femoral heads were found to release a non-negligible amount of oxygen moieties from their surfaces, thus accelerating oxidative degradation of polyethylene. Conversely, Si₃N₄ ceramics exerted a protective role towards the polyethylene liner by scavenging oxygen from the tribolayer. The results of this work provide new insights into the interaction between bioceramics and polymers, which should also be considered when designing the next generation artificial hip joints with significantly elongated lifetimes.