Ultra-high Molecular Weight Polyethylene Sample Research Articles

Reversed thermal stability between stress-induced melting and recrystallized crystallites and original inclined ones in moderately stretched ultra high molecular weight polyethylene and high density polyethylene

The structural evolution of tensile stretched ultra high molecular weight polyethylene (UHMWPE) and high density polyethylene (HDPE) samples to an intermediate strain before the completion of fibrillation upon heating was investigated by means of small-angle X-ray scattering (SAXS) and wide angle X-ray diffraction techniques (WAXD). Six-point SAXS patterns illustrated the existence of two populations of lamellae, one at the inclined direction belonging to the original lamellae experienced deformation of slip processes and another at the tensile direction (meridional lamellae) which were newly formed ones due to fibrillation (stress induced melting-recrystallization). Surprisingly, the inclined lamellae exhibit better thermal stability compared to meridional lamellae in UHMWPE sample, whereas in the HDPE sample the situation is opposite. It turns out that this higher stability of original deformed lamellae at the inclined direction is due to the much higher number of tie chains and more stable entangled amorphous network in UHMWPE which minimizes the surface free energy of those lamellae during heating.

3D Neuronal Cell Culture Modeling Based on Highly Porous Ultra-High Molecular Weight Polyethylene

Cell culturing methods in its classical 2D approach have limitations associated with altered cell morphology, gene expression patterns, migration, cell cycle and proliferation. Moreover, high throughput drug screening is mainly performed on 2D cell cultures which are physiologically far from proper cell functions resulting in inadequate hit-compounds which subsequently fail. A shift to 3D culturing protocols could solve issues with altered cell biochemistry and signaling which would lead to a proper recapitulation of physiological conditions in test systems. Here, we examined porous ultra-high molecular weight polyethylene (UHMWPE) as an inexpensive and robust material with varying pore sizes for cell culturing. We tested and developed culturing protocols for immortalized human neuroblastoma and primary mice hippocampal cells which resulted in high rate of cell penetration within one week of cultivation. UHMWPE was additionally functionalized with gelatin, poly-L-lysine, BSA and chitosan, resulting in increased cell penetrations of the material. We have also successfully traced GFP-tagged cells which were grown on a UHMWPE sample after one week from implantation into mice brain. Our findings highlight the importance of UHMWPE use as a 3D matrix and show new possibilities arising from the use of cheap and chemically homogeneous material for studying various types of cell-surface interactions further improving cell adhesion, viability and biocompatibility.

Burnishing of ultra high molecular weight poly ethylene

Ultra-high molecular weight polyethylene (UHMWPE) has been a choice for knee and hip implants since a very long time due to its outstanding tribological properties. UHMWPE has many applications other than biomedical implants like hydrodynamic bearings and marine applications. The main objective of this research work is to enhance the surface properties of UHMWPE and eventually increase its life expectancy for the implants. For this purpose, the UHMWPE sheet has been milled to give it a required shape and then ball burnished with a carbide ball of 6 mm diameter under two different environments viz. room and cryogenic with three different burnishing strategic patterns. A constant load of 150 N is maintained by the tool on UHMWPE sample with a burnishing feed of 4000 mm/min along with a step over a distance of 0.06 mm after every pass for three different carefully chosen burnishing patterns. To understand the wear behaviour of the material, wear test has been performed on reciprocating wear testing machine with a stainless-steel ball as a pin for 6500 cycles in the medium of Hank’s balanced salt solution (HBSS) as a lubricating agent and to maintain the pH value which is same as in the human body. The lowest average surface roughness (Ra = 0.52 µm) is reported for the second strategy pattern which gets burnished under the cryogenic environment. This sample also exhibited better wear resistance than other samples burnished under different environments and using different strategic patterns.

Development of method for welding of ultra-high molecular weight polyethylene by electromagnetic induction

The analysis of scientific, technical and patent literature on polymer welding is carried out. A method has been developed for welding ultra-high molecular weight polyethylene using electromagnetic induction. Welding for experimental samples of the GUR-4150 brand from Celanese was carried out. The mode of welding by the method of magnetic induction is established, which ensures high strength of the welded seam. Providing material heating exclusively in the weld zone is the main advantage of the chosen method. And also a special mold of polytetrafluoroethylene was developed and manufactured, which does not allow the molten ultra-high molecular weight polyethylene sample to flow out and increases the contact pressure due to linear expansion. polytetrafluoroethylene was chosen as the mold due to its unique properties, namely: high heat resistance, low coefficient of friction and very low adhesion. Also, polytetrafluoroethylene is not subject to heating when exposed to magnetic induction. Thus, the most optimal mode for welding UHMWPE of the selected grade is welding at a temperature of 250 ° C and a heating time of 30 seconds at a pressure of 2.3 MPa. Tensile strength is more than 95% in this welding mode and the relative elongation at break is 66% of the value of the monolithic sample.

A comprehensive study of ultra-high molecular weight polyethylene modified by α-tocopherol after exposure to extremely high temperatures

The processes occurring in friction of samples of ultra-high molecular weight polyethylene (UHMWPE) obtained by pressing at 190 °C from discrete UHMWPE particles modified by α-tocopherol (α-T) were studied using X-ray photoelectron spectroscopy, thermogravimetry, thermomechanical analysis, investigation of the oxygen uptake kinetics, and determination of the inhibitory activity. Pressing results in the isolation of α-T on the sample surface, its oxidative destruction, and inhibition of UHMWPE oxidation. After tribological tests, the atomic content of oxygen in the surface layer of the modified sample remains at the initial level, while that in the non-modified UHMWPE sample increases by 50%.

Preparation and Tribological Behaviors of Porous UHMWPE Using as Artificial Cartilage

Porous ultra high molecular weight polyethylene (UHMWPE) materials have been developed by Hot Press molding technique in this investigation. The tribological behaviors of porous UHMWPE with different initial NaCl content were studied. The worn surfaces of UHMWPE and porous UHMWPE samples were examined using a Scanning Electron Microscope (SEM). It was found that the porous structure improved the wear resistance of porous UHMWPE with the proper initial NaCl content under water lubrication condition. The minimal wear loss was about 10.6mg in the case of the UHMWPE filled by 50% initial NaCl content, 43% less than that of pure UHMWPE sample.

Wear properties of UHMWPE/aromatic thermosetting copolyester blends in unlubricated sliding

To improve the wear resistance of ultrahigh molecular weight polyethylene (UHMWPE), blends of UHMWPE, and an aromatic thermosetting copolyester (ATSP) (50/50, v/v) were developed, taking advantage of the crosslinked structure and good wear resistance of ATSP. As a compatibilizer, poly(ethylene-co-acrylic acid) (PEA) was added into the blends with its contents changing from 0 to 20% (w/w). Dynamometer wear tests (sliding against stainless steel surface with contact pressure ranging from 600 to 2500 kPa) showed that the UHMWPE/ATSP blend with 10% PEA had lower wear rate than the UHMWPE sample. The improved wear resistance resulted from the change of the wear mechanism. Scanning electron microscopy (SEM) images of the worn surfaces revealed that the presence of ATSP and PEA would prevent the lamellar alignment in the UHMWPE phase and adding PEA effectively enhanced the interaction between UHMWPE and ATSP.

Oxidation of ultra high molecular weight polyethylene (UHMWPE) part 2: Critical examination of the total luminescence intensity (TLI) method for determining hydroperoxides

The validity of the total luminescence intensity (TLI) method for determining the amount of hydroperoxides in a UHMWPE sample has been assessed. Measurements of hydroperoxides with FTIR before and after a TLI run showed that only about 50% of the hydroperoxides were decomposed at 150 °C. It was also found that this value was not constant with ageing time, which means that the TLI value could not be representative of the total number of hydroperoxides in a sample as a function of ageing time. Thermoluminescence was also found to complicate the measurements and could, if care was not taken, give TLI values that were much too high. In addition it was found that the TLI value is actually connected with the build-up of carbonyls rather than the build-up of hydroperoxides. This last finding is consistent with part one of this study, where it was reported that CL from oxidising UHMWPE is a type of activated CL, where carbonyls are the activating species. From all of these results it is concluded that TLI is not a suitable method for determining hydroperoxides in UHMWPE.

Wear Properties of UHMWPE Oriented under Uniaxial Compression during the Molten State and at Lower Temperatures than the Melting Point

Ultra high molecular weight polyethylene (UHMWPE) has been used as a bearing material for artificial joints since the 1960's, and experience has shown that its wear is one of the limiting factors for long term use in such prosthetic implants. For improving wear resistance, we studied the influence of uniaxial compression on molecule orientation obtained by processing UHMWPE above (Sample A) and below (Sample B) its melting point, respectively. We then compared the wear properties of both UHMWPE samples. Using a slightly cross-linked UHMWPE, sample A was compressed during the molten state. Sample B UHMWPE was compressed at a temperature below the melting point. X-ray refraction tests revealed the (200) crystalline plane of Sample A and B to be oriented parallel to the compression surface. Further tests showed the heat of fusion and the density of Sample A to be higher than Sample B. The storage modulus of Sample A was always higher than in the original untreated UHMWPE (Sample C), while in Sample B it rapidly collapsed with increasing temperature. The αc-peak of Sample A was shifted to about 5°C higher, while the αc-peak of Sample B was shifted to the lower temperature side and the β-peak disappeared, compared with Sample C. Reciprocating wear tests carried out over 2×106 cycles, showed that the wear resistance of the sample A was enhanced by a factor of 10 when compared to Sample C. UHMWPE compressed during the molten state exhibits superior wear characteristics and has the potential to improve implant technology for artificial joints, potentially providing a longer lifetime.