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At least 685 records · Page 38Linked to original sources
PubMed1975

Measurement of renal interstitial fluid pressure with polyethylene matrix capsules.

The renal interstitial fluid pressure was measured in dogs from small chronically implanted solid capsules made of porous polyethylene matrix material (pore size approximately 60 mum). Tissue does not grow into the polyethylene and the matrix creates a permanent fluid-filled space in communication with the interstitium. The fluid pressure in the capsule matrix was measured from a tube leading from the capsule with an active servo-null pressure-measuring device. Renal interstitial fluid pressure measured from 28 hydropenic dogs averaged 6.1 plus or minus 0.51 mmHg (SE). Increasing oncotic pressure inside the capsule to 90 mmHg resulted in a small but significant increase in hydrostatic pressure inside the capsule of 3.3 plus or minus 0.46 mmHg. However, the hydrostatic pressure returned to control levels within 30 min. In vitro studies indicated that the pressure measured from the capsule was highly sensitive to change in surrounding hydrostatic pressure, but insensitive to change in surrounding oncotic pressure. Histological studies showed a small layer of connective tissue surrounding the capsule less than 100 mum thick in many areas. There was no evidence of inflammation or tissue rejection. It is concluded that the small chronically implanted polyethylene capsule is a reliable method for the measurement of renal interstitial fluid pressure.

Animals↗
PubMed1976

Scanning electron microscopy of surface irregularities and thrombogenesis of polyurethane and polyethylene coronary catheters.

Following routine coronary arteriography, surface irregularities and thrombogenesis of the inner and outer wall of six Ducor polyurethane and six RPX polyethylene coronary catheters were studied by scanning electron microscopy. Polyurethane catheters had rough and highly irregular external and internal surfaces. All catheters showed adherent thrombi on their external surface. The internal surface of three catheters showed evidence of thrombosis. Polyethylene differed from polyurethane in several respects. Although the external surface had an irregular and wavelike appearance, the internal surface was smooth and regular. Two polyethylene catheters showed thrombi on their external surface. The internal surface of one catheter showed single platelets in one area. These results confirm recent reports showing that internal and external surface irregularities play a major role in the initiation of thrombosis in and on intravascular catheters. They stress the need for high quality catheter materials with smooth and regular surfaces in the prevention of thromboembolic complications from coronary arteriography.

Adult↗
PubMed1991

Polyethylene glycol-conjugated superoxide dismutase fails to augment brain superoxide dismutase activity in piglets.

We studied the effect of intravenously administered polyethylene glycol-conjugated superoxide dismutase (8,000 units/kg) on brain superoxide dismutase activity in 44 1-2-week-old piglets in the absence and presence of global cerebral ischemia and reperfusion. Four groups (n = 6 each) of piglets not exposed to ischemia were studied. Enzyme administration increased plasma superoxide dismutase activity from less than 5 to 142 +/- 8 units/ml (mean +/- SEM) without increasing brain activity (e.g., activities in the caudate were 7.9 +/- 0.5 and 8.1 +/- 0.4 units/mg protein) for up to 2 hours following administration. Four additional groups (n = 5 each) of piglets were given either enzyme or polyethylene glycol 5 minutes prior to 10 minutes of global cerebral ischemia induced by aortic cross-clamping followed by either 5 or 45 minutes of reperfusion. Enzyme administration increased plasma superoxide dismutase activity from less than 5 to 144 +/- 5 units/ml but failed to increase brain activity even after 45 minutes of reperfusion (e.g., activities in the caudate were 8.5 +/- 0.3 and 8.6 +/- 0.6 units/mg protein). We conclude that intravenous polyethylene glycol-conjugated superoxide dismutase does not increase superoxide dismutase activity in the brain despite global ischemia and reperfusion.

Animals↗
PubMed1993

Does polyethylene oxide possess a low thrombogenicity?

Because of the 'bland' nature of polyethylene oxide towards proteins and cells, considerable effort has been devoted to preparing surfaces rich in polyethylene oxide, using block copolymers, surface immobilization or other methods. It is clear that these modifications result in reduced levels of cell (including platelet) adhesion and protein adsorption, when compared to unmodified and typically hydrophobic substrates. It is far less clear whether the reduced adhesion or adsorption is due specifically to the thermodynamic effects of polyethylene oxide or to the increase in surface hydrophilicity after its immobilization. Even more so, it is unclear whether the reduction in such parameters is evidence of a reduced thrombogenicity.

Animals↗
PubMed1976

Concentration and purification of mycobacteriophages with polyethylene glycol 6000.

Experiments were performed to concentrate and purify mycobacteriophages with polyethylene glycol 6000; 6, 9, and 8 per cent polyethylene glycol 6,000 proved to be optimal concentrations for precipitating phages of Mycobacterium phlei, Mycobacterium smegmatis strain butyricum, and mycobacterium smegmatis strain Rabinowitz, respectively. Preparative polyethylene glycol reverse gradients were constructed for further concentration and purification of the precipitated phages. With the method described, large amounts of crude phage lysates can be concentrated and purified rapidly.

Bacteriological Techniques↗
PubMed2006

Polyethylene organo-clay nanocomposites: the role of the interface chemistry on the extent of clay intercalation/exfoliation.

High density polyethylene (HDPE)/clay nanocomposites have been prepared using three different functionalized polyethylene compatibilizers: an ethylene/vinyl acetate copolymer, a polyethylene grafted with maleic anhydride functions and a (styrene-b-ethylene/butylene-b-styrene) block copolymer. The nanocomposites were prepared via two different routes: (1) the dispersion in HDPE of a masterbatch prepared from the compatibilizer and the clay or (2) the direct melt blending of the three components. For each compatibilizer, essentially intercalated nanocomposites were formed as determined by X-ray diffraction and transmission electron microscopy. With the ethylene/vinyl acetate copolymer, a significant delamination of the intercalated clay in thin stacks was observed. This dispersion of thin intercalated stacks within the polymer matrix allowed increasing significantly the stiffness and the flame resistance of the nanocomposite. A positive effect of shear rate and blending time has also been put into evidence, especially for the process based on the masterbatch preparation, improving both the formation of thin stacks of intercalated clay and the mechanical properties and the flame resistance of the formed nanocomposites.

Aluminum Silicates↗
PubMed2002

Non-constrained titanium-polyethylene total endoprosthesis in the treatment of hallux rigidus. A prospective clinical 2-year follow-up study.

BACKGROUND AND AIMS: To evaluate the outcome in a prospective 2-year follow-up study of a non-constrained titanium-polyethylene total endoprosthesis (ReFlexion) in the treatment of hallux rigidus. MATERIAL AND METHODS: Ten patients with painful hallux rigidus were treated with a non-constrained titanium-polyethylene total endoprosthesis (ReFlexion). The American Orthopaedic Foot and Ankle Society (AOFAS) scoring was used preoperatively and at follow-up. RESULTS: At 2-year follow-up, the AOFAS scoring shbwed 5 instances of excellent, 1 of good, 2 of fair, and 2 of poor outcome. Eight patient were subjectively satisfied and 2 dissatisfied. Five of the patients were painless, 4 had mild, occasional pain, and 1 had moderate, daily pain in the first metatarsophalangeal joint. The mean VAS was 7.6 (SD 2.0) preoperatively and 1.1 (SD 1.4) at 2-year follow-up (p < 0.001). Extension increased by a mean of 25 (13-38) degrees and flexion by a mean of 15 (2-35) degrees (p < 0.001). Eight patients had no activity limitations, while 1 had mild and 1 moderate limitations. Alignment of the metatarsophalangeal joint was good in 7 cases, but some degree of valgus malalignment was seen in 2 and symptomatic malalignment in 1. Complications included one subluxation of a prosthesis, one recurrence of severe valgus alignment and one superficial wound infection. Radiological loosening of one cementless phalangeal component was seen at follow-up. CONCLUSION: The non-constrained titanium-polyethylene total arthroplasty gave satisfactory 2-year outcome in 60% of the patients. It is an alternative treatment for hallux rigidus in low demand patients. We do not recommended it for athletes and young people, because high forces acting on the prosthesis may cause a failure.

Adult↗
PubMed2004

Space radiation transport properties of polyethylene-based composites.

Composite materials that can serve as both effective shielding materials against cosmic-ray and energetic solar particles in deep space, as well as structural materials for habitat and spacecraft, remain a critical and mission enabling component in mission planning and exploration. Polyethylene is known to have excellent shielding properties due to its low density, coupled with high hydrogen content. Polyethylene-fiber reinforced composites promise to combine this shielding effectiveness with the required mechanical properties of structural materials. Samples of polyethylene-fiber reinforced epoxy matrix composite 1-5 cm thick were prepared at the NASA Marshall Space Flight Center and tested against a 500 MeV/nucleon Fe beam at the HIMAC facility of NIRS in Chiba, Japan. This paper presents measured and calculated results for the radiation transport properties of these samples.

Biophysical Phenomena↗
PubMed1990

Comparison of red cell transfusion and polyethylene glycol-modified adenosine deaminase therapy in an adenosine deaminase-deficient child: measurement of erythrocyte deoxyadenosine triphosphate as a useful tool.

The effect of red cell transfusion and polyethylene glycol-modified adenosine deaminase therapy on biochemical abnormalities, clinical status, and immunologic function in an adenosine deaminase-deficient child was investigated. After red cell transfusions, erythrocyte deoxyadenosine triphosphate (dATP) concentrations decreased about 95% and were closely related to adenosine deaminase activities; deoxyadenosine diphosphate concentrations decreased only approximately 30%. The evolution of dATP levels was also closely related to the improvement in clinical status of the patient. However, immune function was not restored. After polyethylene glycol-modified adenosine deaminase therapy, the concentration of erythrocyte dATP decreased to undetectable levels correlated with an increase of T lymphocyte counts and an increase of lymphocyte responses to mitogens. Immune functions were restored only when dATP levels were below 15 mumols/L. It appears that red cell transfusion therapy is not sufficiently effective to reduce and maintain erythrocyte dATP levels at values compatible with normal immune function. On the contrary, polyethylene glycol-modified adenosine deaminase therapy is a suitable treatment to reduce dATP levels to near undetectable values, allowing the immune function to be restored, dATP measurement is a very useful tool for monitoring and evaluating the degree of efficiency of therapy in adenosine deaminase deficiency.

Adenosine Deaminase↗
PubMed2003

Acceleration of aneurysm healing by controlled release of basic fibroblast growth factor with the use of polyethylene terephthalate fiber coils coated with gelatin hydrogel.

OBJECTIVE: The aims of this study were to develop an endovascular delivery system containing gelatin hydrogels for the controlled release of basic fibroblast growth factor (bFGF) with the use of polyethylene terephthalate fiber coils and to analyze whether such a system would promote healing in an experimental aneurysm. METHODS: Carotid aneurysms were constructed in 66 rabbits with venous pouches. The polyethylene terephthalate fiber coils coated with and without gelatin hydrogels with different water volumes containing 0, 10, 50, and 100 microg bFGF were implanted into the aneurysms. Histological specimens were harvested at 1, 2, and 3 weeks and at 6 months after implantation. A histological evaluation was performed while the area occupied by the fibrosis in the aneurysms was calculated. RESULTS: Three weeks after the application of the coils coated with gelatin hydrogels (95 vol%) containing 100 microg bFGF, all aneurysmal orifices were completely closed with neointima. When the coils coated with gelatin hydrogel (98 vol%) containing 100 microg bFGF were used, the orifices in three of the six aneurysms were closed. In contrast, the orifice of the aneurysm was not obliterated when other materials were used. After implanting the coils coated with gelatin hydrogel (95 vol%) containing 100 microg bFGF more than 3 weeks later, the aneurysm was histologically suffused with fibrous tissue, and the area occupied by fibrosis was significantly larger than that observed in the other groups (P < 0.05). CONCLUSION: Local, controlled release of sufficient amounts of bFGF with polyethylene terephthalate fiber coils coated with gelatin hydrogel accelerated the organization of aneurysms.

Aneurysm↗
PubMed2001

The influence of phospholipid concentration in protein-containing lubricants on the wear of ultra-high molecular weight polyethylene in artificial hip joints.

There is considerable interest in the wear of polyethylene and the resulting wear-debris-induced osteolysis in artificial hip joints. Proteins play an important role as boundary lubricants in vivo in the pseudosynovial fluid, and these are reproduced in in vitro tests through the use of bovine serum. Little is known, however, about the effect of phospholipid concentrations within proteinaceous solutions on the wear of ultra-high molecular weight polyethylene (UHMWPE). The effects of protein-containing lubricants with 0.05, 0.5 and 5 per cent (w/v) phosphatidyl choline concentrations on the wear of ultra-high molecular weight polyethylene (UHMWPE) were compared with 25 per cent (v/v) bovine serum which had 0.01 per cent (w/v) lipid; the effects were compared in a hip joint simulator with smooth (n = 4) and scratched (n = 3) femoral heads. The control bovine serum lubricant produced UHWMPE wear of 55 and 115 mm3/10(6) cycles on the smooth and rough heads respectively. The increased phospholipid concentration significantly reduced the wear rate. At the higher concentration (5% w/v phosphatidyl choline) the average wear was reduced to less than 2 mm3/10(6) cycles. Even with the relatively low concentrations of 0.05% w/v phosphatidyl choline the wear was reduced by at least threefold compared with the bovine serum tests for both the smooth and rough femoral heads. There may be considerable differences in the phospholipid concentrations in patients' synovial fluid and this is highly likely to produce considerable variation in wear rates. In vitro, differences in the phospholipid concentration of lubricants may also cause variation in wear rates between different simulator tests.

Hip Prosthesis↗
PubMed1999

The influence of lubricant on the morphology of ultra-high molecular weight polyethylene wear debris generated in laboratory tests.

Since the implication of polyethylene wear debris as a major cause of osteolysis in total joint replacements, there has been much interest in polyethylene wear studies and in cell culture studies using ultra-high molecular weight polyethylene (UHMWPE) wear debris. Studies have shown that particles in the 0.1-10 microns size range are particularly important in causing adverse cellular reactions resulting in osteolysis. The morphology, the mass and size distributions, and the number of wear particles produced at the joint surfaces are influenced by the tribological conditions at the joint. Laboratory wear tests are used to investigate the wear properties of prosthetic joint materials and different research groups have used different lubricants in these tests. This paper shows that the volumetric wear and morphology of UHMWPE particles generated in vitro are influenced by the type of lubricant used. This study compared, quantitatively, UHMWPE wear debris generated in deionized water to debris that was generated in a system lubricated by bovine serum which was diluted to 25 per cent. The wear factors of UHMWPE in water and serum lubricants were significantly different (p < 0.05). UHMWPE wore 14 times more in water than in serum. Quantitative analysis of the wear particles showed that the debris that was generated in serum was morphologically different from debris that was produced in a water-lubricated system. Furthermore, the particles produced in serum showed a closer similarity to those found in retrieved acetabular tissues.

Blood↗
PubMed2006

Effect of ultra-high molecular weight polyethylene thickness on contact mechanics in total knee replacement.

One of the important design parameters in current knee joint replacements is the thickness of the ultra-high molecular weight polyethylene (UHMWPE) tibial insert, yet there is no clear definition of the upper limit of the 'thick' polyethylene insert. Using one design knee implant and subjecting it to the physiological loads encountered throughout the gait cycle, measurements of the lengths of contact imprints generated were compared with the corresponding theoretical predictions for different insert thicknesses under the same applied load. Multiple regression analysis was applied to test whether the dimensions of contact imprints are influenced by UHMWPE thickness. Good agreement was obtained between the theoretical predictions and the experimental measurements of the dimensions of contact imprints when the knee was at 60 degrees flexion. Therefore, it was possible to estimate the contact pressure at the articulating surface using the theoretical model. Contact imprint dimensions increased with increasing applied load. Statistical analysis of the experimental data revealed that, at 0 degree flexion, the overall imprint dimensions increased as the UHMWPE thickness increased from 8 to 20 mm. However, the increment was not significant when the thickness subinterval 10-15 mm was considered. Furthermore, at 60 degrees flexion, thickness was not a significant factor for the overall imprint dimensions. No evidence was found from the data to suggest that an increment in polyethylene thickness over 10 mm would significantly reduce the contact imprint dimensions. These findings suggest that thicker inserts can be avoided, as they require unnecessary bone resection.

Acetabulum↗
PubMed2006

The predictive power of surface profile parameters on the amount of wear measured in vitro on metal-on-polyethylene artificial hip joints.

Various studies report a weak correlation between the average surface roughness R(a) of metallic ballheads and the observed wear rate of the polyethylene cups coupled to them. The aim of this study is to verify, with controlled in vitro experiments, whether other parameters such as the total roughness R(t), and the skewness R(sk) are better predictors of the polyethylene wear when the metallic heads present a surface conditioning that varies substantially from specimen to specimen, as is usually the case with retrieved specimens. Twelve CoCrMo (cobalt-chromium-molybdenum) ballheads were intentionally damaged in order to reproduce a wide spectrum of surface conditioning and were then subjected to the standard wear test against polyethylene cups, using a hip joint wear simulator. After 2 x 10(6) cycles the weight lost by the cups was assessed with a gravimetric procedure, and the surface roughness of the metallic ballheads was qualified in terms of R(a), R(t), and R(sk). The various parameters were correlated to the weight loss using a linear regression analysis. The skewness R(sk) showed a coefficient linear regression R2 = 0.80, while the average roughness R(a), used in most previous studies, presented an R2 = 0.56. It was concluded that when specimens with substantially different surface conditioning are compared, as in retrievals analysis, it is also important to report the skewness R(sk) so that qualify the surface roughness of the specimens can be qualified.

Coated Materials, Biocompatible↗
PubMed1996

The wear of cross-linked polyethylene against itself.

Cross-linked polyethylene (XLPE) may have an application as a material for an all-plastic surface replacement finger joint. It is inexpensive, biocompatible and can be injection-moulded into the complex shapes that are found on the ends of the finger bones. Further, the cross-linking of polyethylene has significantly improved its mechanical properties. Therefore, the opportunity exists for an all-XLPE joint, and so the wear characteristics of XLPE sliding against itself have been investigated. Wear tests were carried out on both reciprocating pin-on-plate machines and a finger function simulator. The reciprocating pin-on-plate machines had pins loaded at 10 N and 40 N. All pin-on-plate tests show wear factors from the plates very much greater than those of the pins. After 349 km of sliding, a mean wear factor of 0.46 x 10(-6) mm3/N m was found for the plates compared with 0.021 x 10(-6) mm3/N m for the pins. A fatigue mechanism may be causing this phenomenon of greater plate wear. Tests using the finger function simulator give an average wear rate of 0.22 x 10(-6) mm3/N m after 368 km. This sliding distance is equivalent to 12.5 years of use in vivo. The wear factors found were comparable with those of ultra-high molecular weight polyethylene (UHMWPE) against a metallic counterface and, therefore, as the loads across the finger joint are much less than those across the knee or the hip, it is probable that an all-XLPE finger joint will be viable from a wear point of view.

Biocompatible Materials↗
PubMed1996

Wear and morphology of ultra-high molecular weight polyethylene wear particles from total hip replacements.

The wear rate of ultra-high molecular weight polyethylene total hip replacement components is known to be influenced by various factors such as material and design. However, it is not known if these factors affect the size or morphology of the wear particles. The aim of this study was to compare the polyethylene wear particles from hip replacements of differing bearing materials and designs. Tissues were obtained at the revision surgeries of patients with surface replacements with titanium alloy or cobalt-chrome alloy femoral components up to 51 mm in diameter, and stem-type hip replacements with cobalt-chrome or alumina ceramic femoral components that were 28 or 32 mm in diameter. The polyethylene particles were isolated following tissue digestion and density gradient separation, and then studied by scanning electron microscopy. A computerized image analysis system was used to measure the diameter and length of the particles. The majority of wear particles were submicron in diameter. No systematic differences in size and morphology were found between the groups in this study. The similarity in size and morphology of the wear particles suggested that the same basic wear mechanisms were occurring in these components.

Adult↗
PubMed1989

[Interaction between polyethylene films and bromhexine HCl in solid dosage forms. I. Effects of moisture contents in the solid dosage forms on the sorption of the drug].

The decrease of bromhexine HCl contents in granules and tablets was determined when the preparations were stored in polyethylene film package. Effects of temperature, contact area with film, excipients and moisture contents in the preparation on the remaining amount of bromhexin HCl were studied in order to investigate the interaction mechanism between bromhexine HCl and polyethylene film. It was observed that the decrease of bromhexine HCl was due to the sorption to the polyethylene film. The results indicated that the moisture contents of the dosage forms determined the rate of sorption predominantly, and that removal of adsorbed water from dosage forms was effective to prevent bromhexine HCl content decrease.

Adsorption↗
PubMed1978

The radiation improvement of polyethylene prostheses. A preliminary study.

The radiation crosslinking of high-density polyethylene prostheses was investigated over a wide range of doses in the presence and absence of gaseous crosslinking agents. It was found that in the bulk polymer the crosslinking pattern is completely different from the homogeneous crosslinking that occurs in polymer films. The presence of crosslinking agents causes highly crosslinked polymer to be formed on the surface while the bulk of the polymer is largely unaffected--which is explained in terms of diffusion phenomena. This surface crosslinking has a profound effect on the mechanical properties of the prostheses and restricts cold flow and deformation of the polymer without sacrificing the excellent abrasion-resistance properties of the polyethylene when subjected to high pressures. Based on this research a number of high-density polyethylene knee prostheses have been radiation-crosslinked and the results in vitro appear to be very promising.

Acetylene↗