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At least 757 records · Page 42Linked to original sources
PubMed1988

Enhancement of ribonucleotide reductase activity at low enzyme concentrations by polyethylene glycol.

The estimation of ribonucleotide reductase in cell extracts has been problematical on account of abnormally low activities at low enzyme concentrations, presumably due to subunit dissociation. This problem can be alleviated by assaying the enzyme in the presence of polyethylene glycol. The presence of 15% polyethylene glycol during the assay greatly stimulated ribonucleotide reductase activity at low enzyme concentrations and allowed measurement of enzyme activity in as little as 10(5) mouse L929 cells, a 30-fold enhancement of assay sensitivity. Enzyme activity measured in the presence of 15% polyethylene glycol was proportional to enzyme concentration, thus making possible the accurate measurement of very low levels of ribonucleotide reductase.

Animals↗
PubMed1988

Analysis of surface damage in retrieved carbon fiber-reinforced and plain polyethylene tibial components from posterior stabilized total knee replacements.

The performance of carbon fiber-reinforced ultra-high molecular weight polyethylene was compared with that of plain (non-reinforced) polyethylene on the basis of the damage that was observed on the articulating surfaces of retrieved tibial components of total knee prostheses. Established microscopy techniques for subjectively grading the presence and extent of surface damage and the histological structure of the surrounding tissues were used to evaluate twenty-six carbon fiber-reinforced and twenty plain polyethylene components that had been retrieved after an average of twenty-one months of implantation. All of the tibial components were from the same design of total knee replacement. The two groups of patients from whom the components were retrieved did not differ with regard to weight, the length of time that the component had been implanted, the radiographic position and angular alignment of the component, the original diagnosis, or the reason for removal of the component. The amounts and types of damage that were observed did not differ for the two materials. For both materials, the amount of damage was directly related to the length of time that the component had been implanted. The histological appearance of tissues from the area around the component did not differ for the two materials, except for the presence of fragments of carbon fiber in many of the samples from the areas around carbon fiber-reinforced components.

Carbon↗
PubMed1988

A rat model of resorption of bone at the cement-bone interface in the presence of polyethylene wear particles.

Resorption of bone and the formation of a membrane at the interface between acrylic cement and bone were induced by particles of high-density polyethylene that were similar in size to those that are present in the tissues surrounding a human joint prosthesis. A non-weight-bearing plug of methylmethacrylate was inserted through the knee joint into the distal part of the femur of the rat. The plug rapidly became surrounded by a shell of bone. After repeated injections of particles of high-density polyethylene into the knee joint, resorption of bone occurred at this stable interface. No resorption of bone occurred after the opposite knee was injected with a control preparation that did not contain particles. The resorption of bone that occurred around the plug after the injection of particles of polyethylene took place in the absence of mechanical causes for loosening and in the absence of infection.

Animals↗
PubMed1988

Fractures of the polyethylene bearing insert in Bateman bipolar hip prostheses.

Six cases of fractures of the polyethylene bearing insert of Bateman bipolar hip prostheses were observed in three patients at four to eight years after implantation. Three fractured prostheses were salvaged by replacement with new bearing inserts. In three patients, excessive acetabular cartilage wear was the indication for revision to total hip arthroplasty. Although dislocation and component disassembly have been reported as complications of the Bateman and other bipolar prostheses, fractures of the polyethylene bearing insert seems not to have been previously reported. The presumed mechanism of failure is cyclic loading of a femoral cup that is tipped into varus alignment. This concentrates stress on the weakest part of the polyethylene insert--the deep circumferential groove that joins the leaflets to the main body of the insert. Obesity and overuse were associated factors in this rare complication.

Adult↗
PubMed1985

Effect of a polyethylene-lined administration set on the availability of diazepam injection.

Delivery of diazepam through a polyethylene-lined i.v. administration set and through a polyvinyl chloride (PVC) set was compared. Diazepam was prepared in concentrations of 50 mg/500 mL and 100 mg/500 mL in 0.9% sodium chloride injection and 5% dextrose injection in glass containers. Diazepam concentrations were measured by high-performance liquid chromatography at 0 through 5 hours in samples collected simultaneously from the glass solution containers and from the distal ends of a PVC administration set and a polyethylene-lined (non-PVC) set. Flow rates of 50 and 100 mL/hr were tested. For the non-PVC sets, diazepam concentration in the infusate was not significantly different from concentration in the glass container at any sampling time. The overall percentage of diazepam recovered was 100.7 +/- 6.8%. For the PVC sets, diazepam concentration in the infusate was less than in the container at all sampling times, and the overall percentage of diazepam recovered was 65.4 +/- 13.3% (significantly different from delivery for the non-PVC sets). Delivery through the non-PVC sets was not affected by flow rate, type of solution, or concentration of diazepam. For infusion periods of up to five hours, delivery of diazepam through polyethylene-lined i.v. administration sets was superior to delivery through polyvinyl chloride sets.

Diazepam↗
PubMed1984

[Antigenic properties of nitro aromatic derivatives of polyethylene glycol].

The immunogenic properties of the dihapten and monohapten derivatives of polyethylene glycol with different nitroaromatic groupings were studied. 2,4-dinitrophenyl, 2, 4, 6-trinitrophenyl and trinitrophenyl-ethyl groupings were used as hapten groups. The injection of monohapten compounds was found to induce the accumulation of antibody-forming cells secreting antibodies to trinitrophenyl in the spleen of normal and athymic nude mice. As early as on day 3 the number of antibody-forming cells considerably exceeded their background level, the process of B-cell activation being, to a certain extent, thymus-independent. Dihapten compounds were not immunologically active. The effect rendered by the nitroaromatic derivatives of polyethylene glycol, revealed in this study, is linked with the known capacity of polyethylene glycol to adsorb on the surface of cell membranes.

Animals↗
PubMed1981

Reduction of plasma urate levels in the cockerel with polyethylene glycol-uricase.

Uricase from C. utilis and uricase to which polyethylene glycol had been attached were injected into leghorn cockerels in an attempt to lower plasma urate levels. Twenty units of either enzyme reduced urate levels to near zero for 24 hr on initial injection, whereas 10 U were effective for less than 6 hr. After injection with four-weekly doses of enzyme, unmodified uricase was ineffective in lowering plasma urate levels. Polyethylene glycol-uricase, however, was as effective as on the first injection. Both enzyme preparations appear in the lymph shortly after injection into the rat, although polyethylene glycol-uricase appears slightly sooner and maintains a more constant level than uricase.

Animals↗
PubMed1981

[Effect of polyethylene oxides on erythrocyte aggregation].

The effect of polyethylene oxide of different molecular weight on the aggregation of erythrocytes has been investigated. It was shown that the addition to blood of polymers with molecular weight of 600 and 1 000 weakens this aggregation, whereas the addition of those with molecular weights of 4 000 and 6 000 completely prevents it, simultaneously decreasing their osmotic resistance. Polyethylene oxide with molecular weight from 20 000 to 1 000 000 increase the aggregation of erythrocytes and do not affect their osmotic resistance. The aggregation of erythrocytes is a reversible process. The decrease in polyethylene oxide concentration leads to decreasing aggregation effect. The mechanism of the effect of polymers on cell aggregation is discussed.

Animals↗
PubMed1981

Improved method for determination of high-density-lipoprotein cholesterol I. Isolation of high-density lipoproteins by use of polyethylene glycol 6000.

We describe a modified method of precipitating low- and very-low-density lipoproteins with polyethylene glycol, for quantitation of high-density lipoprotein cholesterol. A 100 g/L concentration of polyethylene glycol 6000 in a buffered (pH 10) solution is used. Under these conditions precipitation of beta-lipoproteins is complete. Values for HDL cholesterol as measured with this method fully correspond to those obtained on separating the lipoproteins by ultracentrifugation or with heparin-Mn2+, 46 mmol/L; are slightly higher than those obtained with heparin-Mn2+, 92 mmol/L; and are significantly higher than those determined after precipitation with polyethylene glycol, 100 g/L at pH 8.0. Comparison with results by the ultracentrifugation method showed excellent correlation (r = 0.957) with a good correspondence of results (slope 1.065 and y-intercept -22.231); comparison with the heparin-Mn2+, 46 mmol/L, method gave r = 0.998 with slope of 0.985 and y-intercept 2.963. The method is unaffected by precipitation and centrifugation time and temperature (up to 24 h with 4-22 degrees C temperature for precipitation and between 10 and 30 min with 4-22 degrees C temperature for centrifugation). This extremely simple method is particularly suitable for routine analyses of many samples, even in small laboratories.

Chemical Precipitation↗
PubMed1995

[Nonelastic deformations of polyethylene inlays in hemiprostheses].

In most models of hip prosthesis, the inlay is formed by a layer of polyethylene. The attrition of polyethylene results from two components, wear and nonelastic deformation. Former studies analysed total attrition. The aim of this trial was to measure solely the non elastic deformation. Nonelastic deformation was investigated using two different types of bipolar hemiprostheses to exclude influences of different shaped metal caps. The bipolar hemiprostheses were tested with a hydraulic pulser. 1 x 10(6) cycles of a halfsinewave with a stress of 4600 N at a frequency of 8 Hz were used. The whole procedure was carried out in isotonic saline solution. Stress was applied along a single axis to prevent any wear. After the test, the inner surface of the polyethylene inlay was analysed with a touchpeg. As the inlays had different inner diameters, the analysis of the surface was defined along radials of 5 degrees, 25 degrees and 45 degrees. The nonelastic deformation in the direction of the main stress at 45 degrees was higher than at the lateral areas. The nonelastic deformation measured was between 0.2 and 0.6 mm/a, i.e. 5 to 30% of total attrition. There was a significant difference between the two types of inlays. The model with several pegs and edges for a complicated snap mechanism had a significant higher nonelastic deformation (alpha = 0.05) than the smooth shaped inlay.

Biomechanical Phenomena↗
PubMed1995

Flat-on-flat, nonconstrained, compression molded polyethylene total knee replacement.

Flat-on-flat, posterior cruciate ligament-sparing total knee prostheses recently have shown problems of wear, loosening, and multiple design changes. Two thousand one Anatomical Graduated Components total knee arthroplasties with compression molded, nonmodular polyethylene tibial components were done between 1983 and 1991 at 3 institutions. All knees were evaluated clinically and radiographically every 2 to 3 years; 71 knees were seen in followup > 10 years. There were 8 failures secondary to revision (5 tibial failures; 2 secondary to metalosis from patellar polyethylene dissociation; and 3 femoral failures) resulting in a 98% survival rate at 10 years. The tibial design was flat-on-flat with a compression molded polyethylene that the authors believe is the primary reason for its success.

Adult↗
PubMedDate not supplied

[The polyethylene oxide correction of the hemodynamic sequelae in the infusion therapy of massive blood loss].

High molecular weight polyethylene oxides (2 x 10(6), 4 x 10(6), and 6 x 10(6)) were tested for their effects on blood pressure, cerebral circulation in rats with massive hemorrhage and turbulent blood flow velocity in the pre- and posthemorrhagic and polyglucine posttreatment. Polyethylene oxide (4 x 10(6) and 6 x 10(6)) alleviated hypotension and cerebral hypoperfusion, which appeared 0.5-1 hour after polyglucine therapy and increased turbulent blood flow velocity. Polyethylene oxide failed to affect spontaneous and alcian blue-induced red blood cell aggregation.

Acute Disease↗
PubMed1995

The cemented acetabular component of a total hip replacement. All polyethylene versus metal backing.

The increasing use of a cementless acetabular component with a total hip replacement requires the need for metal backing, but metal backing with cement in the author's use has been less than optimal. The intention, therefore, was to evaluate all cemented acetabular components, with and without metal backing, used by the author, to offer a standard by which other acetabular components can be compared. From 1969 to 1983, 238 Charnley, 141 Mueller, 555 T-28, 100 Miami Orthopaedic Surgical Clinic total hip replacements with cemented all-polyethylene acetabula, and 134 Miami Orthopaedic Surgical Clinic total hip replacements with a cemented metal-backed acetabula were performed and followed from 1 to 22 years. The cemented acetabular component failure rates for the Charnley, T-28, and all-polyethylene Miami Orthopaedic Surgical Clinic were 14%, 10%, and 9%, respectively. There was a 20% failure rate in the Mueller and metal-backed Miami Orthopaedic Surgical Clinic acetabular components. The Charnley (p < 0.0001), T-28 (p < 0.0001), all-polyethylene Miami Orthopaedic Surgical Clinic (p < 0.0001), and Mueller (p < 0.012) total hip replacements demonstrated statistically improved survival rates as compared with the metal-backed Miami Orthopaedic Surgical Clinic acetabular components. The Charnley (p < 0.0001) and T-28 (p < 0.0003) sockets survived statistically better than the Mueller sockets.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetabulum↗
PubMed1995

[A patient-controlled analgesia system using a disposable balloon catheter, a PCA polyethylene reservoir and a one-way umbrella check valve].

A disposable continuous infuser with differently sized balloon pressure sources (20 ml-3 hr, 40 ml-12 hr and 40 ml-24 hr) with a pressure of approximately 100 mmHg (DIB international Co., Ltd., Tokyo), is connected to a PCA polyethylene reservoir using a Y-connector. Capacity variations of the reservoir are 1 ml (assuming subcutaneous dose), 3 ml (intravenous dose) and 5 ml (epidural dose or peroral dose). The other opening of the Y-connector is equipped with a one-way umbrella check valve (opening pressure, 320-370 mmHg) to prevent the analgesic solution from flowing medially unless the PCA polyethylene reservoir is pressed. By this system, various target lock-out times can be obtained by varying the type of disposable infusor. The target amount of on-demand doses is obtained by varying the capacity of the PCA polyethylene reservoir.

Analgesia, Patient-Controlled↗
PubMedDate not supplied

Giant cell synovitis associated with failed polyethylene patellar replacements.

Destroyed patellar articular surfaces were replaced with a high molecular weight polyethylene prosthesis in two patients. The patellofemoral articulation of the femur consisted of eburnated bone in one case and degenerative cartilage in the other. Both operations failed within one year because of a giant cell synovitis caused by a high volume (0.2 cc) of fine polyethylene (1-100 mu) wear particles. Ultra high molecular weight polyethylene should not be used as a prosthetic bearing surface to articulate against cortical, cancellous or eburnated bone or against degenerative articular cartilage in a major joint.

Aged↗
PubMed1995

Effect of polyethylene quality on wear in total knee arthroplasty.

During evaluation of 29 Ortholoc II tibial polyethylene components retrieved at revision surgery, the authors noticed that components with a lot number prefix of CP (Custom Product) consistently had minimal wear and those with a standard lot number had severe wear, regardless of patient age, weight, gender, and activity level. Non-CP components had earlier and more severe wear than CP components in service for the same amount of time. Microscopic evaluation of the polyethylene revealed major differences in the material. Large subsurface cracks, fusion defects, and intergranular cracks were present in the non-CP components, but these defects were minimal or nonexistent in the CP components. The components with defects had a significantly greater delamination rate than those without defects. Gamma irradiation did not seem to accelerate wear or delamination, because irradiated components that had minimal microscopic signs of fusion defects performed as well as nonirradiated components with a similar microscopic appearance. The manufacturing details disclosed that different materials and processing methods were used for the 2 groups. The results from this study suggest that improved quality control of polyethylene material would greatly decrease wear and delamination of total knee arthroplasty components.

Aged↗
PubMed1995

Polyethylene glycol method is superior to ammonium sulfate and protein-A sepharose-4B method in fractionating thyroid stimulating immunoglobulin in Graves' disease.

BACKGROUND: The purpose of this study is to compare the performance of three methods, i.e., ammonium sulfate, polyethylene glycol (PEG) and protein A sepharose 4B in fractionation of thyroid stimulating immunoglobulin. METHODS: Twelve patients with Graves' disease and twelve age-, sex-matched normal controls were recruited. 0.9 ml of saturated ammonium sulfate was added slowly to 1.1 ml of sera of all subjects and was stirred until reaching 45% saturation. The precipitation was allowed to form at 4 degrees C overnight. The solution was centrifuged at 10,000 x g for 5 minutes. The precipitate was washed twice with 45% ammonium sulfate, dissolved in 0.55 ml of distilled water equal to half of the initial volume of the serum and dialyzed against 200 volumes of phosphate-buffered saline (PBS) for 48 hours. Another 0.5 ml of serum sample from the same patients was mixed with 1.5 ml of 20% polyethylene, followed by centrifugation at 2,800 g for 20 minutes. The pellet was dissolved in 0.6 ml of Hanks' medium without NaCl containing 1.5% bovine serum albumin, 20mM HEPES: 1 ml of sera was applied to 0.75 g of protein A sepharose-4B in PBS buffer and eluted with glycine, pH 2.3. By adding immunoglobulin (Ig) from the different methods to the FRTL-5 tissue culture, we determined the cAMP generation. RESULTS: Patients with Graves' disease were found to have higher serum thyroxine and triiodothyronine concentrations (p < 0.001) and significantly higher free thyroxine concentration than normal subjects. Ig elicited stronger response in cyclic AMP generation when prepared with PEG method, as compared with the other two methods (p < 0.001). With sepharose-4B Ig preparation, 10 out 12 patients (83.33%) showed positive thyroid stimulating immunoglobulin (TSI) while with ammonium sulfate precipitation, nine out 12 patients (75%) showed positive TSI. On the other hand, all patients showed positive TSI with PEG precipitation. When the degree of thyrotoxicosis was classified in terms of thyroid hormone concentrations, there was no correlation between TSI titers and thyroid hormone concentration. CONCLUSIONS: Polyethylene glycol is superior to both ammonium sulfate and protein A sepharose-4B in fractionating TSI in terms of sensitivity and convenience in operation.

Adult↗
PubMed1994

High-density porous polyethylene (Medpor) as a successful anophthalmic socket implant.

BACKGROUND: High-density porous polyethylene (Medpor) has been used successfully as an implant in orbital fracture repair and in the management of both cosmetic and post-traumatic facial deformities. The material is well tolerated, resists infection, is nonantigenic, and promotes tissue ingrowth. Additionally, sutures can be passed through it. These characteristics led to its use as an implant in anophthalmic socket surgery. METHODS: Twenty-one patients with anophthalmia underwent implantation of spherically shaped high-density porous polyethylene implants. The implant was used in six primary enucleations with direct extraocular muscle attachment, ten secondary implant insertions, one repeat secondary implant insertion, and five eviscerations. RESULTS: Postoperative follow-up averaged 19 months. During this period, there were no extrusions, infections, significant inflammatory responses, or implant exposures. One implant was removed 4 months after insertion due to inadequate initial placement secondary to a severe post-traumatic orbital deformity. Successful re-implantation was performed without complication. Postoperatively, all sockets showed good to excellent motility. Results of histologic examination of the removed implant demonstrated minimal inflammatory response and extensive fibrovascular ingrowth involving 60% of the implant substance. CONCLUSIONS: This initial report indicates that high-density porous polyethylene can be used successfully as an implant in anophthalmic socket surgery. Its advantages over other similar implants include a significantly lower material cost and the ability to suture the extraocular muscles directly to it without the need for a covering material such as fascia or sclera. Experimental studies are in progress to determine if this implant can be integrated with an ocular prosthesis to promote improved motility and cosmesis.

Adolescent↗