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At least 541 records · Page 30Linked to original sources
PubMed2000

Nasal reconstruction using porous polyethylene implants.

Nasal reconstruction presents a significant challenge to the facial plastic surgeon. The dual goals of reconstruction are restoration of the desired aesthetic nasal contour and an improved nasal airway. Autologous cartilage and bone are considered optimal grafting material, but their supply is often limited and harvesting entails additional morbidity. Many synthetic materials have been introduced in nasal reconstruction, but high infection and extrusion rates limited their use. Porous high density polyethylene implants present an alternative to autologous material as they allow for fibrovascular ingrowth, leading to stability of the implant and decreased rates of infection. Herein we describe the use of porous high density polyethylene implants for reconstruction of the platyrrhine nose and in revision rhinoplasty. The use of preformed nasal-dorsal tip and alar batten implants are described, as well as the use of columellar strut and premaxillary plumper implants. We believe that porous high density polyethylene implants provide a safe, desirable alternative in functional and aesthetic nasal reconstruction.

Biocompatible Materials↗
PubMed1992

Interaction between polyethylene films and bromhexine HCl in solid dosage form. V. Effect of packaging materials on the sorption of bromhexine HCl.

A prevention method of the sorption of bromhexine HCl to plastic materials used in packaging was investigated. Four kinds of plastic packaging materials were used: Polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP) and polyacrylonitrile (PAN). Three polyethylenes having different densities were used. No effect of PE density on the sorption of bromhexine HCl from granules was observed. The effects of different kinds of plastics on the sorption of bromhexine HCl from solution and granules were studied. The sorption of bromhexine HCl to PAN, which had a high relative dielectric constant, was the most depressed among the four plastics. The sorption of meclizine HCl to PAN from the solution was also lowest, the same as bromhexine HCl.

Acrylic Resins↗
PubMed1985

An evaluation of ultrastrong polyethylene fiber as an ophthalmic suture.

An ultrastrong polyethylene fiber was evaluated as an ophthalmic suture. Properties of this fiber and of nylon, polypropylene, and polyester sutures were measured by standard techniques for fiber testing and for testing knot characteristics of sutures. Their behavior in cataract and keratoplasty surgery was assessed qualitatively. The ultrastrong polyethylene fiber has great tensile strength, high flexibility, and is very inelastic. Its strength and knot security provide safe incision closure and it has good biocompatibility. Ultrastrong polyethylene fiber is potentially superior to nylon, polypropylene, and polyester in the most important characteristics of a non-absorbable monofilament polymer ophthalmic microsuture.

Biocompatible Materials↗
PubMed2000

New reconstructive technologies in skull base surgery: role of titanium mesh and porous polyethylene.

OBJECTIVE: To report on 8 years of experience with 156 titanium mesh and porous polyethylene implants used for craniofacial reconstruction after skull base surgery in 100 patients. DESIGN: Cohort study with a mean follow-up of 5 years. SETTING: Population based. PATIENTS: A consecutive sample of 100 patients treated for skull base tumors or craniofacial trauma who underwent reconstruction with 156 3-dimensional titanium mesh and/or porous polyethylene implants. A retrospective review of the Skull Base Program database, along with photographic and imaging documentation, was undertaken. MAIN OUTCOME MEASURES: Rate of complications as well as the degree of functional and esthetic reconstruction. INTERVENTION: The reconstructive technique focused primarily on the substitution of removed craniofacial skeleton for oncologic reasons or soft tissue defects. RESULTS: After completion of follow-up (mean, 5 years), all 100 patients remained healed except for 7 patients (7%) with 8 implants (5%). Overall, excellent craniofacial symmetry and stability were achieved with both types of implants. CONCLUSIONS: Immediate craniofacial skeletal reconstruction and soft tissue augmentation is feasible with 3-dimensional titanium mesh and porous polyethylene implants. The reviewed 8-year evolution in the use of these technologies (156 implants in 100 patients) highlights the excellent tolerance of these implants (5% implant complication rate) in 100 patients (7% complication rate). The few encountered complications were judged to be primarily related to the quality of the overlying soft tissue and not to the implants themselves. The advantages of using these implants for immediate 3-dimensional skeletal and soft tissue substitution, including availability, easy contouring, stability, primary healing, and tolerance of adjuvant therapy, translate to an improved function and esthetic appearance, with a better quality of life for patients.

Adolescent↗
PubMed1988

Polyethylene glycol-electrolyte solution for intestinal clearance in children with refractory encopresis. A safe and effective therapeutic program.

Severely constipated children with encopresis in whom outpatient management has failed frequently require several days of hospitalization, as well as conventional treatments involving cathartics and enemas. A balanced electrolyte solution of the nonabsorbable polymer polyethylene glycol (GoLytely, Braintree [Mass] Laboratories Inc) offers a safe and efficient method for clearing the intestine. Twenty-four patients with a mean age of 8.1 years (range, 0.8 to 17.6 years) and an average weight of 31.5 kg received polyethylene glycol-electrolyte solution: eight patients with encopresis were given it as treatment for severe fecal retention unresponsive to outpatient management; the other 16 were being prepared for colonoscopy. Weight, complete blood cell count, and serum electrolyte, serum urea nitrogen, and serum creatinine levels were measured before solution administration and two hours afterward. Abdominal roentgenograms were obtained from the encopretic patients. The two groups were comparable in age and weight. Polyethylene glycol-electrolyte solution was given at a rate of 14 to 40 mL/kg/h until clear fluid was excreted through the rectum. Intestines were cleaned out successfully in all patients, and side effects were minimal. Children with encopresis required an average of 11.8 L (574 mL/kg) given over 22.5 hours, while the other children needed only 4.0 L (128 mL/kg) given over 7.5 hours. Weight and serum electrolyte and creatinine levels did not change significantly in any patient. The hematocrit decreased only in encopretic patients (0.38 to 0.36 [37.6% to 35.8%]) and the serum urea nitrogen level decreased in the patients undergoing colonoscopy (3.6 to 2.0 mmol/L [10 to 8 mg/dL]).

Adolescent↗
PubMed1996

Migration of metal and polyethylene particles from articular prostheses may generate lymphadenopathy with histiocytosis.

Wear particles released from hip or knee prostheses are known to be involved in the fibrohistiocytic membrane interposed between bone and implant. During surgical treatment for pelvic carcinoma (5 cases) and for isolated pseudomalignant lymphadenopathy (4 cases) lymph nodes in 9 patients who had had lower limb articular replacement were harvested. Light microscopy and image analysis of the nodes showed florid endosinusal histiocytosis, predominant in the cortical area. Using Oil Red O staining and polarized light, metal particles and polyethylene particles were detected in the large histiocytes. Scanning electron microscopy with electron backscattering allowed us to localize metal particles and perform elemental microanalysis. Iron, cobalt, chromium, nickel, zirconium, and barium, known to be used in prosthetic and cementing materials, were identified as component of these particles. Large amounts of polyethylene particles appeared in all cases while metal particles were found to be abundant in only 2 cases. Thus, migration of polyethylene debris from the prosthetic site seems to be the major factor in development of the histiocytes induced in satellite lymph nodes.

Aged↗
PubMed1996

Shape and size of virgin ultrahigh molecular weight GUR 4150 HP polyethylene powder.

Sizes and shapes of micron- and submicron-sized structures in four lots of virgin GUR 4150 HP ultrahigh molecular weight polyethylene powder were determined by using low-voltage scanning electron microscopy and image analysis. One thousand two hundred micron-sized virgin powder particles and 1200 of their constituent submicron-sized structures were analyzed. The mean maximum diameter of the micron-sized particles was 81.3 microns, and that of the submicron-sized particles was 0.82 micron. Particle shapes, as determined by the aspect ratio (maximum diameter divided by minimum diameter), were remarkably consistent from lot to lot and between micron- and submicron-sized particles (1.55 versus 1.53, respectively). Significant lot to lot variability was observed in the sizes of the micron-sized particles, and the size distribution of the submicron-sized particles closely follows the size distribution of the submicron-sized particles observed in tissue retrievals. This variability leads to questions about variability in polyethylene quality and in vivo wear performance. Size similarity between the submicron-sized particles retrieved from tissues and that observed in virgin powder supports the hypothesis that polyethylene debris has two origins: particles released from structures retained from the virgin powder, and particles generated de novo by friction and wear.

Biocompatible Materials↗
PubMed1998

Flow-cytometric analysis of leukocyte activation induced by polyethylene-terephthalate with and without pyrolytic carbon coating.

Leukocyte activation is one test for the evaluation of blood-materials interaction. The expression of adhesion molecules analyzed by flow cytometry provides a simple method to evaluate leukocyte activation by biomaterials: any change in these molecules can be predictive of the inflammatory activity of the materials. In this study the contact between leukocytes and uncoated polyethylene terephthalate or pyrolytic carbon-coated polyethylene terephthalate (PET and PET-PC, respectively) was inspected by analyzing whether the expression of some adhesion molecules involved in leukocyte activation, namely LFA-1 (CD11a/ CD18), Mac-1/CR3 (CD11b/CD18), and LECAM-1 (CD62L) can be modified. By flow cytometry expression of the adhesion molecules can be studied separately on lymphocytes and myeloid cells. The materials tested reduced the total numbers of both leukocytes and neutrophils, although not significantly. Neither PET nor PET-PC changed the expression of the adhesion molecules in lymphocytes: this suggests that no specific immune response is stimulated. On the contrary, statistically significant changes were observed for monocytes and granulocytes: the percentage of cells expressing Mac-1 and the density of such antigens on cell membranes increased while the percentage of LECAM-1 positive cells decreased. Similar changes were observed when the cells underwent the inflammatory stimulus provided by an in vitro challenge with bacterial endotoxin. Our results demonstrated that polyethylene terephthalate activates leukocytes by modifying the expression in neutrophils of the molecules involved in the early phase of the inflammatory response. Even after coating PET with pyrolytic carbon, the ability of this material to activate circulating leukocytes was maintained.

Biocompatible Materials↗
PubMed1998

Subsurface oxidation of polyethylene.

Since the 1960s ultrahigh molecular weight polyethylene has been a primary bearing material in orthopedic prostheses. Most polyethylene components have been sterilized by exposure to gamma radiation, but in the presence of oxygen this promotes degradation and correlates with component failure in the body. To better understand the mechanism of degradation, we measured oxidation profiles for components shelf aged 5.8 and 10.9 years. Microtomed sections from each component were analyzed for ketones, which are the primary oxidation products, by FTIR spectroscopy. Maximum ketone concentrations in both cases were found several millimeters below the surface. We propose a model to explain the profiles. Alkyl radicals, which are uniformly generated in the polyethylene during irradiation, react with peroxyl radicals, which are produced by alkyl radicals with oxygen to form ketones. At the component surface ketone levels are low because high oxygen concentrations deplete alkyl radicals, creating an excess of peroxyl radicals. In the bulk material ketones are low because low oxygen concentrations limit the formation of peroxyl radicals. However, just below the surface the concentrations of alkyl and peroxyl radicals balance, promoting ketone production. A computer simulation that accounts for the coupling of these reactions with the diffusion of oxygen shows a good agreement with the measured profiles.

Biocompatible Materials↗
PubMed1999

A miniature specimen mechanical testing technique scaled to articulating surface of polyethylene components for total joint arthroplasty.

The small punch test was developed to investigate the mechanical behavior of polyethylene using miniature specimens (< 14 mg) measuring 0.5 mm in thickness and 6.4 mm in diameter. The objective of this study was to demonstrate the feasibility and reproducibility of the small punch test when applied to clinically relevant polyethylenes. Mechanical behavior was characterized during 66 tests performed on GUR4150HP and GUR4120 specimens following alternate sterilization methods and 4 weeks of accelerated aging at 80 degrees C. The small punch test was found to be highly reproducible with regard to characterizing the ductility, ultimate strength, and fracture resistance of sterilized and aged polyethylene. In the future, the small punch test can be used to directly measure mechanical properties near the articulating surface of retrieved components.

Air↗
PubMed1999

Prevention of fatigue cracks in ultrahigh molecular weight polyethylene joint components by the addition of vitamin E.

Flaking-type wear, so-called delamination, is often observed in polyethylene joint components. This is thought to occur partly due to crack formation and propagation at grain boundaries. This study examined the effect of vitamin E on the crack formation and/or propagation in UHMWPE by using 2-dimensional sliding fatigue testing and micro indenter testing. An in vitro sliding fatigue test was performed under two simplified articulating movements, and the cracks produced were observed by scanning acoustic tomography (SAT). Gamma-irradiated ultrahigh molecular weight polyethylene (UHMWPE) specimens demonstrated a smaller area of accumulated cracks as compared to virgin specimens, when the loading movement was reciprocated on a single linear locus. However, four out of five gamma-irradiated UHMWPE specimens exhibited severe flaking-like destruction under the complicated sliding condition, suggesting that gamma irradiation accelerated crack propagation under multidirectional loading. All the gamma-irradiated vitamin-E-containing specimens demonstrated no subsurface crack formation and no flaking-like destruction. Results using micro indenter testing showed that the dynamic hardness at grain boundary was higher than that in grain, and was increased by gamma irradiation. This hardening at grain boundary was reduced by adding vitamin E. It is possible that the presence of vitamin E prevents crack propagation partly due to reduced hardness at grain boundaries. The gamma-irradiated vitamin-E-containing UHMWPE is a promising material to prevent flaking-like destruction of polyethylene joint components.

Biocompatible Materials↗
PubMed2000

Elemental and morphological identification of third-body particulate and calcium stearate inclusions in polyethylene components.

Third-body particulate such as human bone chips, hydroxyapatite, and bone cement are considered contributing factors in accelerated wear in total joint replacement. Particulate wear debris is now considered the major contributing factor in aseptic loosening of total joint replacements. The ability to distinguish between different third-body particulate is necessary to better understand wear mechanisms when conducting implant retrieval analysis. The objective of this investigation is to demonstrate that backscattered electron imaging with correlated energy dispersive X-ray analysis can accurately identify third-body particulate in retrieved polyethylene components. It is important that this technique can also distinguish between third-body particulate and normal inclusions in the polyethylene such as calcium stearate, based on the distinct morphology and elemental composition of each material. Therefore, the ability to distinguish third-body particulate from calcium stearate inclusions is essential in gaining a better understanding of the contributing factors associated with coating separation and accelerated wear observed in clinically retrieved polyethylene components.

Biocompatible Materials↗
PubMed2001

Gamma-irradiated cross-linked polyethylene in total hip replacements--analysis of retrieved sockets after long-term implantation.

The purpose of this study was to evaluate the mechanical and chemical characteristics of gamma-irradiated, cross-linked polyethylene after long-term service in vivo. Two gamma-irradiated ultra high molecular weight polyethylene (RCH 1000, molecular weight: 10(6)) total hip replacement sockets were retrieved at 15 and 16 years after implantation. Mechanical and chemical characteristics of the sockets were evaluated in comparison with nonirradiated sockets. Significant surface oxidation occurred in the nonirradiated sockets; up to 75% of that seen in the irradiated ones. The mechanical properties of the irradiated sockets were not subject to increased deterioration in the presence of high free radical content. The cross-link was stable and was retained for a long period both in vivo and in ambient air. These data indicate that gamma-irradiated polyethylene was not subject to increased oxidative degradation during long-term service in vivo and confirmed the usefulness of this material as an articulating surface in total hip replacement.

Arthroplasty, Replacement, Hip↗
PubMed2001

In situ complement activation by polyethylene wear debris.

A frequent long-term complication of total joint arthroplasty is aseptic loosening, the end result of wear debris accumulation, synovitis, and osteolysis about the implant-bone or cement-bone interface. Complement, an effector system in plasma, synovial fluid, and tissue, has powerful chemotactic, inflammatory, and osteoclast-activating potentials. This study explored the complement-activating ability of polyethylene, a material used in joint implants. In vitro hemolytic assays using sheep red blood cells (E(sh)), human serum, and particulate polyethylene suggested alternative pathway complement activation, as well as polyethylene adsorption of activated complement components. These results were confirmed by enzyme-linked immunosorbent assay (ELISA) quantification of activated complement factors Bb and C3b. In situ double antibody immunoperoxidase staining for factors Bb, C3a, iC3b, and SC5-9 in synovial tissue from revision hip specimens showed localized alternative pathway activation and component adsorption. These results introduce a likely role for complement activation in particle-mediated recruitment, proliferation, and activation of macrophages during early events in osteolysis and implant loosening.

Biocompatible Materials↗
PubMed1976

Some new studies of the wear behavior of ultrahigh molecular weight polyethylene.

The wear rate of ultrahigh molecular weight (UHMW) polyethylene over a long campaign of sliding distance is not constant. Both unfilled and graphite filled polyethylene show a high rate early, which reduces to a low value. The graphite-filled product shows a late stage increase in wear rate. Increased molding temperature reduces the molecular weight and increases the wear rate. Titanium articulating with UHMW polyethylene develops frequently an abnormally high wear rate with the generation of a black wear product.

Biocompatible Materials↗
PubMed1996

Adaptive finite element modeling of long-term polyethylene wear in total hip arthroplasty.

Adaptive remeshing capability was added to an existing sliding-distance-coupled finite element model of polyethylene wear in total hip arthroplasty. This augmentation allowed earlier postoperative wear simulation to be extended to the clinically more significant long-term regimen (as long as 20 years). Loads and femoral head excursions were taken from a physically validated gait analysis model of a patient with an instrumented total hip replacement. For otherwise identical 22, 28, and 32 mm components, the least volumetric wear but the most linear wear occurred for the 22 mm head. When the polyethylene thickness in a 22 mm component was reduced to the same as that in a 32 mm component, the volumetric wear rate for the 22 mm component was still much less than that for the larger component, indicating that sliding distance (head size), rather than polyethylene liner thickness, was primarily responsible for the difference in rates. A "28 mm" series, for which head sizes were varied across the range of currently accepted industrial tolerances, showed that although initial wear rates were greatest for the least congruent articulations, the long-term volumetric wear was nearly the same, regardless of initial clearance.

Arthroplasty↗
PubMed1978

Solid dispersions of nitrofurantoin, ethotoin, and coumarin with polyethylene glycol 6000 and their coprecipitates with providone 25,000.

The influence of two linear polymers, polyethylene glycol 6000 and povidone 25,000, on the dissolution rate of three poorly soluble drugs, nitrofurantoin, ethotoin, and coumarin, was studied. Povidone 25,000 produced better drug solubilization than polyethylene glycol 6000 with the drug-polymer ratios studied, and an increase in the weight fraction of either polymer gave more rapid dissolution. TLC and IR studies ruled out any interaction between the drugs and polyethylene glycol 6000. IR spectrophotometry provided evidence that there was complex formation between nitrofurantoin and povidone 25,000, probably via hydrogen bonding.

Chemical Precipitation↗
PubMed1979

Sustained release of drugs from ethylcellulose--polyethylene glycol films and kinetics of drug release.

Cast films composed of different ratios of polyethylene glycol and ethylcellulose containing salicylic acid, caffeine, and tripelennamine as model dispersed drugs were prepared and exhibited sustained release. The drug content of the film declined at an apparent first-order rate initially, whereas the drug quantity released was proportional to the square root of time. Data analysis validated the latter treatment, which is in accordance with the diffusional matrix model, and disproved the validity of the apparent first-order conformity. The release rates were independent of film thickness and proportional to drug concentration in pure ethylcellulose films; in polyethylene glycol--ethylcellulose films, a positive deviation from linearity was observed. The logarithm of the rate constant was proportional to the fraction of polyethylene glycol in the film. Unlike in pure ethylcellulose films, the release rate in mixed films was altered by a change in the external fluid pH.

Caffeine↗