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PubMed1996

Exponential model for the tensile true stress-strain behavior of as-irradiated and oxidatively degraded ultra high molecular weight polyethylene.

Following sterilization by gamma radiation, ultra high molecular weight polyethylene components for total joint replacement undergo oxidative degradation upon exposure to air and the in vivo environment. Oxidative degradation is accompanied by an increase in density. The primary objective of this study was to develop a mathematical model to predict the monotonic tensile mechanical behavior of these sterilized components as a function of changes in density arising from oxidative degradation. Tensile specimens of ultra high molecular weight polyethylene were sterilized with gamma radiation and then oxidatively degraded in an air furnace. The average density of each specimen was measured using a density gradient column. Differential scanning calorimetry and Fourier transform infrared spectroscopy were conducted on selected specimens to characterize the physical and chemical changes due to accelerated aging as opposed to ambient shelf aging. Mechanical testing was conducted in monotonic uniaxial tension. An exponential model was fitted to the true stress-strain data (up to a true strain of 0.12). The observed fitted stress had a correlation coefficient of 0.996. The model permits a quantitative prediction of the association between the true stress-strain curve and density for the ultra high molecular weight polyethylene components. The proposed exponential model effectively describes changes in the large-strain monotonic tensile behavior of as-irradiated and oxidatively degraded ultra high molecular weight polyethylene components.

Air↗
PubMed1997

Effects of polyethylene on macrophages.

A system was developed to expose macrophages to polyethylene in vitro. Exposure of macrophages to these particles in isolation led to the release of tumor necrosis factor alpha and prostaglandin E2. Exposure of macrophages in co-culture with osteoblasts to polyethylene particles increased the release of prostaglandin E2 and also led to the release of interleukin-6. Incubation of radiolabelled calvariae with conditioned medium from macrophages exposed to polyethylene particles alone or to particles in co-culture with osteoblasts led to bone resorption reflected by release of 45Ca. Incubation with pamidronate was effective in inhibiting resorption stimulated by conditioned medium from macrophages exposed to these particles alone or in co-culture with osteoblasts. This demonstrates that pamidronate, or other bisphosphonates, may be effective in inhibiting bone resorption at the implant/bone interface in association with the macrophage response to particulate polyethylene. Further investigation into the possible use of pamidronate or other bis-phosphonates in the treatment of aseptic loosening is warranted.

Animals↗
PubMed1978

Benzocaine diffusion from polyethylene glycol through human stratum corneum.

The diffusion, penetration, and surface effects of benzocaine incorporated in various polyethylene glycol ointment bases through human stratum corneum were studied. Benzocaine diffusion was measured by following the benzocaine concentration in the receiving compartment of a diffusion cell. The ointment was placed in the other cell compartment and was separated from the receiving compartment by sheets of human stratum corneum. Surface effects were monitored by scanning electron micrographs of the stratum corneum. Results showed a decrease in drug diffusion in the presence of relatively high amounts of the lower molecular weight portions of polyethylene glycol. Scanning electron microscope studies showed that both benzocaine and polyethylene glycol affect the surface structure of the stratum corneum. Thermal analysis indicated that benzocaine dissolves in polyethylene glycol.

Adult↗
PubMed1982

Erythrocyte changes in aqueous polyethylene glycol solutions containing sodium chloride.

The behavior of rabbit erythrocytes in aqueous solutions of polyethylene glycol 300 (I) and polyethylene glycol 400 (II) containing sodium chloride was investigated during 2-120 min incubation at 37 degrees. No hemolysis was found in I (0-10.1%) and II (0-12.9%) solutions in the presence of sodium chloride (0.45-1.35%), but prelytic potassium ion loss and changes in the appearance of the erythrocytes proceeded with the passage of time. The potassium ion loss increased with increasing concentration of polyethylene glycol and/or sodium chloride. The mean cellular volume of erythrocytes decreased temporarily (during the first 2 min) in both I (6.7%) and II (8.6%) solutions containing sodium chloride (0.68-1.35%), and then increased progressively to the same value as that determined by solution of sodium chloride at the same concentration but without polyethylene glycol (approximately 30 and 120 min in I and II solutions, respectively). Both I (10.1%) and II (12.9%) induced a stomatocytic transformation of erythrocytes, but at the higher concentrations (0.9-1.35%) of sodium chloride, II accelerated the progress of spontaneous transformation of erythrocytes, but at the higher concentrations (0.9-1.35%) of sodium chloride, II accelerated the progress of spontaneous transformation to echinocytes. The results indicate that these solutions were not isotonic with rabbit erythrocytes.

Animals↗
PubMed1984

Degradation of fenprostalene in polyethylene glycol 400 solution.

The kinetics of degradation of fenprostalene (I) in polyethylene glycol 400 solution was examined using HPLC. The degradation of I at 80 degrees C was shown to depend on the presence of oxygen and a large number of polar products were produced, as evidenced by using 3H-labeled I. Evidence that autoxidation of the polyethylene glycol 400 was concurrent with degradation of I was found from a drop in the apparent pH. Antioxidants were very effective in retarding the rate of degradation in the presence of oxygen. Degradation of I in polyethylene glycol 400 appears to arise from a reaction between the drug and reactive peroxide intermediates formed through air-oxidation of polyethylene glycol 400. This is supported by the finding that I reacts exclusively by a slow transesterification reaction in diethylene glycol, a solvent that is stable to autoxidation.

Chromatography, High Pressure Liquid↗
PubMed1993

Reagents for the preparation of chromophorically labeled polyethylene glycol-protein conjugates.

We have developed a new class of reagents (2) for the covalent attachment of polyethylene glycol to proteins. These reagents (2) are the monomethoxypolyethylene glycol esters of 4-fluoro-3-nitrobenzoic acid. The reaction of 2 with lysine epsilon-amino groups produces a chromophore which can be used to quantitate the polyethylene glycol to protein molar ratio. Bovine (Zn, Cu) superoxide dismutase was used as a model protein for conjugation with 2. When monomethoxypolyethylene glycol of average molecular weight 2105 was used, a conjugate was obtained with a polyethylene glycol to protein molar ratio of 8.88 retaining 100% of native enzymatic activity; monomethoxypolyethylene glycol of average molecular weight 5210 yielded a conjugate with a polyethylene glycol to protein molar ratio of 9.96 retaining 73% of native enzymatic activity.

Animals↗
PubMed1994

Cleavage of type I procollagen by C- and N-proteinases is more rapid if the substrate is aggregated with dextran sulfate or polyethylene glycol.

The enzymes procollagen C- and N-proteinases specifically cleave carboxyl- and amino-terminal propeptides of procollagens. After cleavage of the propeptides, the resulting collagens self-assemble into fibrils. In most previous experiments with the enzymes, the substrate was monomeric type I procollagen. Here we have prepared aggregates of type I procollagen from chick embryo tendons by using 1 to 100 micrograms/ml of 500-kDa dextran sulfate or 3 to 5% (w/v) polyethylene glycol (M(r) 3350). Aggregation of the substrate with dextran sulfate increased its rate of cleavage by purified or crude C-proteinase from chick embryo tendons 10- to 15-fold. Aggregation of the substrate with 25 to 100 microgram/ml of dextran sulfate increased the rate of cleavage by purified N-proteinase about 4-fold. The rate of cleavage by crude N-proteinase was enhanced only about 2-fold, apparently because of partial precipitation of the enzyme by dextran sulfate. Using polyethylene glycol to aggregate the substrate increased the rate of cleavage by procollagen C-proteinases 5- to 20-fold. Aggregation with polyethylene glycol also increased the rate of cleavage by purified procollagen N-proteinases 2- to 5-fold. With crude N-proteinase, the rate of cleavage was increased only 1.5-fold. The results suggest that the rate of cleavage of the substrate by both enzymes is increased by the aggregation of the substrate itself by dextran sulfate or polyethylene glycol. The increased rates of cleavage seen after aggregation of substrate can be used to develop more sensitive assays for the enzymic activities.

Animals↗
PubMed1990

Massive wear of a steel ball head by ceramic fragments in the polyethylene acetabular cup after revision of a total hip prosthesis with fractured ceramic ball.

The purpose of this case study of severe metallosis is to draw the attention of orthopedic surgeons to extremely serious results of this kind in the event of the fracture of the ceramic ball in a total hip prosthesis. Eleven months after implantation of a KJF hip prosthesis with an aluminum oxide ceramic ball in combination with a polyethylene acetabular cup, fracture of the ceramic ball was observed. After examining the polyethylene cup during the revision operation, the operating orthopedic surgeon merely replaced the fractured ceramic ball with a metal ball head made of stainless steel. Twenty-five months after this procedure, radiography revealed massive wear of the steel ball head with resulting severe metallosis of the surrounding tissues. All prosthetic components therefore had to be removed. Careful examination of the removed prosthetic components clearly showed that sharp-edged ceramic particles originating from the fractured ceramic ball had become embedded in the bearing surface of the polyethylene cup. These tiny ceramic fragments, ranging from 0.05 to 2 mm, were too small to be seen by the operating surgeon's unaided eye. It is these extremely hard ceramic fragments that were responsible for the massive wear of the steel ball head, the hardness of which is approximately ten times less than that of aluminum oxide ceramic. The fracture of the ceramic ball further resulted in damage to the metal taper of the stemmed femoral component. In cases of this kind it is consequently absolutely essential to remove both the polyethylene cup and the ball head, and--if necessary--the femoral component as well.

Acetabulum↗
PubMed1984

Histological results with cement-free implanted hip joint sockets of polyethylene.

The histological appearance of the implant-bone boundary in eight preparations from seven deceased patients in whom a polyethylene acetabulum socket had been inserted without cement between 3 weeks and 3 years previously is described. In all cases, a good or excellent clinical result had been present up to death. All sockets were firmly anchored macroscopically in the bone of the acetabulum. Three zones were defined in accordance with the mechanical strain on the surface of the cup: (a) zone of compression; (b) zone of transition in which mainly shear forces act; and (c) zone of decompression, which corresponds to the region below the "equator." It was noticeable that a layer of connective tissue separated the implant from the bone over almost the entire surface. This layer was very thin in the region of the pressure transfer layer, and thicker in the decompression zone. At sites at which pressure and shear forces act a fibrocartilaginous tissue was found, and the "subchondral" bone was only occasionally in direct contact with the polyethylene surface. At some sites, but above all in the region of the compression zone, very tiny particles that were birefringent in polarized light were found. Either these derive from very fine grindings from the prosthesis surface or they are to be interpreted as a result of "biodegradation" of the polyethylene. This observation permits the conclusion that the biocompatibility of the implant can be improved further by coating the polyethylene surface.

Aged↗
PubMed1979

The applicability of porous polyethylene for tympanoplasty; an animal experimental study.

The problem of a replacement material for the reconstruction of the posterior wall of the auditory canal, as well as for the obliteration of the radical cavity has not been solved satisfactor;ly so far. In order to examine the possible applicability of porous plastics, the posterior wall of the auditory canal of guinea pigs was first removed and then reconstructed using porous polyethylene and filling the bulla tympanica with fine polyethylene chips. One third of the animals had an infected middle ear at the time of implantation. Histologic assessments were made until 24 weeks after implantation. In 80% of the animals the implant settled well, even in cases where the middle ears had been originally infected. By proliferation of vessels and connective tissue, the polyethylene had almost been completely integrated into the surrounding tissue after one week. Extent and frequency of metaplastic osseous growth was greater inthe chip-filled bulla than in the reconstructedposterior wall(Fig. 9). After four weeks, the new osteoid substance was firmly connected with the regional bone (Fig. 4). According to these results, it would seem possible to use porous polyethylene even for the nonaseptic implant bed as it is found in the chronically infected middle ear.

Animals↗
PubMed1984

Alterations in phospholipid polymorphism by polyethylene glycol.

The fusogen polyethylene glycol is shown to alter the polymorphism of dimyristoyl phosphatidylcholine, soybean phosphatidylethanolamine, bovine phosphatidylserine, egg phosphatidylcholine/cholesterol mixture, dilinoleoylphosphatidylethanolamine/palmitoyl-oleoylphosphatidy lcholine mixture, and egg lysolecithin. Suspension of these lipids in 50% polyethylene glycol (mol wt = 6000) reduces both the lamellar and the hexagonal II repeat spacings as measured by X-ray diffraction. An increase in the gel to liquid crystalline and bilayer to hexagonal transition temperatures are observed by freeze-fracture, X-ray diffraction, differential scanning calorimetry and 31P NMR. Freeze-fracture electron micrographs revealed different bilayer defects depending on the physical states of the lipid. Lipidic particles in mixtures containing unsaturated phosphatidylethanolamine is eliminated. Some of the influences of polyethylene glycol on lipids may be explained by its dehydrating effect. However, other nonfusogenic dehydrating agents failed to produce similar results. These findings are consistent with the proposal that close bilayer contact and the formation of bilayer defects are associated with the fusogenic properties of polyethylene glycol.

Animals↗
PubMed1981

Lipid-polyethylene glycol interactions: I. Induction of fusion between liposomes.

Fusion between unilamellar vesicles of both egg phosphatidylcholine and bovine phosphatidylserine was induced by polyethylene glycol. Aggregation and fusion events were monitored by electron microscopy and turbidity measurements. The threshold concentration of polyethylene glycol for aggregation and fusion is found to be independent of lipid concentration. Typically, aggregation of phosphatidylcholine vesicles starts at 2.5% (wt/wt) polyethylene glycol, but fusion is not significant until the polyethylene glycol concentration reaches 35%. Multilamellar vesicles were formed as a result of fusion.

Animals↗
PubMed2000

Bowel preparation with oral polyethylene glycol electrolyte solution vs. no preparation in elective open colorectal surgery: prospective, randomized study.

PURPOSE: Efficient mechanical bowel preparation has been regarded as essential in preventing postoperative complications of colorectal surgery, but the necessity of bowel cleansing has been disputed recently. The aim of this study was to evaluate the outcome of elective colorectal surgery in patients with or without bowel preparation. METHODS: Altogether, 267 consecutive adult patients admitted for elective open colorectal surgery were randomly assigned either to the bowel preparation group with oral polyethylene glycol electrolyte solution (138 patients) or no preparation group (129 patients). Patients who were unable to drink polyethylene glycol electrolyte solution, those who had had bowel preparation within the previous week, and patients not needing opening of the bowel were excluded. Routine colorectal surgery was undertaken, and infectious and other complications were registered daily. Late complications were checked up one to two months after surgery. RESULTS: No deaths were recorded, and 76 percent of the patients in the polyethylene glycol electrolyte solution group and 81 percent in the unprepared group recovered without complication. Anastomotic leaks occurred in 4 percent of the polyethylene glycol electrolyte solution patients and in 2 percent of the other cases, and other surgical site infections occurred in 6 and 5 percent, respectively. None of the differences was statistically significant. There was no difference in restoration of bowel function. The median postoperative stay was eight days in both groups. CONCLUSIONS: Preoperative bowel preparation seems to offer no benefit in elective open colorectal surgery.

Adolescent↗
PubMed1998

Effectiveness of polyethylene glycol antegrade gut lavage bowel preparation for colonoscopy--timing is the key!

PURPOSE: Polyethylene glycol gut lavage is an effective bowel preparation for colonoscopy. The quality of the preparation is not uniform however, and most studies report a rate of suboptimal cleansing of 10 percent or more. One of the possible reasons for a poor preparation is the length of time between the lavage and the examination. The aim of this study was to assess the effect of timing of polyethylene glycol gut lavage on the quality of the preparation achieved. METHODS: Patients referred for elective outpatient colonoscopy with afternoon appointments were randomized to take polyethylene glycol gut lavage either the same morning as their examination (Group 1) or the afternoon of the day before (Group 2). The colonoscopist was unaware of the preparation timing until after the examination was over. During the examination the endoscopist scored the quality of bowel preparation in the cecum, ascending colon, and transverse and left colon. Patient demographics and clinical data were recorded. RESULTS: There were 157 patients in Group 1 (colonoscopy complete in 152 patients) and 160 in Group 2 (colonoscopy complete in 159 patients). The groups were similar in age and gender, indication for colonoscopy, and previous colonic surgery. Patients who drank gut lavage on the morning of their colonoscopy had a greatly better preparation in all areas of the colon than the patients who took their preparation the night before. In the cecum, 97 Group 1 patients had an excellent preparation (vs. 14 Group 2 patients), 45 had a good preparation (vs. 103 Group 2 patients), and 10 had a fair preparation (vs. 33 Group 2 patients). In the ascending colon, numbers of patients with excellent, good, fair, and poor results were 103, 45, 5, and 0 for Group 1 and 12, 107, 32, and 7 for Group 2. Results in the transverse and left colons were 102, 50, 5, 0 and 93, 55, 7, 2 for Group 1 and 15, 116, 27, 5 and 18, 114, 24, 3 for Group 2, respectively. CONCLUSION: The timing of administration of polyethylene glycol-based gut lavage is a major determinant of the quality of the bowel preparation achieved.

Colonoscopy↗
PubMed2005

The crescent sign: dissociation of the polyethylene liner from a modular acetabular component in total hip arthroplasty.

OBJECTIVE: To study whether there was a common pattern of clinical symptoms, signs and radiographic features for the dissociation of the polyethylene liner from an acetabular component and to postulate reasons for these features. DESIGN AND PATIENTS: Retrospective study of notes and radiographs of cases of revision hip arthroplasty for polyethylene liner dissociation of the cementless Harris-Galante I porous-coated acetabular component (Zimmer Inc, Warsaw, IN) at the Avon Orthopaedic Centre, Bristol, UK and St. Mary's Hospital, Bristol, UK between 1995 and 2004. Patients were contacted to confirm preoperative symptoms. RESULTS: Nine cases of late polyethylene liner dissociation of this prosthesis have been revised in these institutions. All patients presented with a reduction in mobility, groin pain and limp. Eight patients reported an audible noise on hip movement. In all cases, radiographs showed radiolucency medial to the femoral neck in association with an eccentrically placed femoral head showing contact with the acetabular metal shell, which we have termed the "crescent sign." CONCLUSIONS: There is a typical clinical presentation in this study. The diagnosis can be made from a single anteroposterior pelvic radiograph without the need for previous films for comparison, or the need for arthrography. Clinicians should look specifically for the crescent sign when an eccentrically placed femoral head has been noted, in order to differentiate the more unusual diagnosis of dissociation from that of polyethylene wear. Early revision surgery can prevent damage to the femoral head and metal acetabular shell, thus reducing the complexity of revision surgery.

Adult↗
PubMed2003

Increased volumetric wear of polyethylene liners with more than 3 years of shelf-life time.

We analyzed 20 retrieved gamma-sterilized polyethylene liners (Biomet Hexloc). The long-term durability varied significantly depending on shelf-life time before implantation. Liners with a shelf-life time of 3 years or more evinced significantly ( P 0.002) higher volumetric wear than those with a shelf life time less than 3 years. Infrared spectroscopy and scanning calorimetry showed that all explanted implants underwent substantial in vivo oxidation and crystallization. The oxidative ageing of polyethylene renders the polyethylene liner susceptible to severe wear. Scanning electron microscopy of the bearing surface of the liner revealed abrasive wear as a dominant mechanism. Moreover, poor acetabular design produces excessively thin liners, substandard locking mechanism, and backside wear of the liner. The primary reason for severe wear in the Hexloc liner was poor modular design and oxidative degradation of the polyethylene.

Adult↗
PubMed2006

Long-term results of uncemented acetabular cups with an ACS polyethylene liner. a 14-16-year follow-up study.

We assessed the clinical and radiographic results of 40 porous-coated acetabular cups with an Acetabular Cup System polyethylene liner over a minimum 14-year follow-up. Femoral head penetration was estimated using a software package. Fifteen cups were revised, 11 due to polyethylene liner rupture. All cups but two were radiographically stable, and 11 hips showed acetabular osteolysis. The overall femoral head penetration rate in hips without liner fracture with reference to the early penetration point was 0.1188+/-0.070 mm per year. Polyethylene liner fractures were associated with higher early femoral head penetration (P<0.0001) and a vertical cup position (P=0.0016). The 14-year survival without cup revision for any reason was 63.9%, 71.8% with no ACS polyethylene liner fracture and 65.3% with no acetabular osteolysis. Most cups showed a good clinical outcome in general, but major Acetabular Cup System liner failure and osteolysis were frequent. Patients with the ACS cups still in place should be monitored closely.

Aged↗
PubMed2001

Influence of polyethylene and femoral head surface quality on wear: a retrieval study.

Thirty-two polyethylene sockets and 22 femoral heads were retrieved because of aseptic loosening more than 9 years after total hip arthroplasty. The volumetric wear rates of the retrieved polyethylene sockets were significantly greater in those coupled with an alumina head (P < 0.05). The retrieved alumina heads showed significantly better surface roughness and roundness than heads of Co-Cr and of stainless steel (P < 0.05). However, no significant difference was found in polyethylene quality demonstrated as fusion defects among the three different groups. The present study suggests that maintaining better surface roughness and roundness of the femoral heads does not always result in an in vivo reduction of polyethylene wear.

Adult↗