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PubMed1977

The preferential adsorption of hemoglobin to polyethylene.

Hemoglobin adsorption to foreign surfaces has not previously been considered in studies of blood-material interactions, despite the fact that hemoglobin is the most abundant protein present in blood. A hemoglobin-like protein was detected on a number of surfaces exposed to blood plasma, serum, and red cell suspensions. Hemoglobin adsorption to polyethylene from plasma was found to approximately equal the amount of adsorption of albumin and fibrinogen. The high relative affinity of hemoglobin for polyethylene was further confirmed by adsorption isotherm and direct competition experiments. The data from all four experimental methods support the following ranking of plasma protein affinity for polyethylene: Hemoglobin greater than fibrinogen greater than albumin congruent to gamma-globulin.

Adsorption↗
PubMed1994

Pseudomonas exotoxin A mutants. Replacement of surface exposed residues in domain II with cysteine residues that can be modified with polyethylene glycol in a site-specific manner.

Pseudomonas exotoxin A (PE) is a three-domain protein in which domain Ia is involved in recognition of receptors on eukaryotic target cells, domain II promotes translocation of PE into the cytosol, and domain III enzymatically ADP-ribosylates elongation factor 2. Modification of proteins with polyethylene glycol (PEG) has been shown to prolong circulating plasma lifetime and may reduce or eliminate immunogenicity. However, in the case of toxins, PEG may interfere with or block toxin activity. To investigate the effect of polyethylene glycolation on specific residues located on the surface of PE domain II, we substituted cysteine, for each of the five most exposed surface amino acids (H276, E282, N306, R313, and E327) in domain II. These cysteines can serve as unique sites for PEG modification. The PE-Cys proteins retained most of their cytotoxicity even when the free sulfhydryl group was blocked by 5,5'-dithiobis(nitrobenzoic acid) or glutathione. When the PE-Cys proteins were conjugated with ovalbumin using a cleavable disulfide linkage, cytotoxicity was retained, but it was lost with a non-cleavable thioether linkage. In contrast, cytotoxicity was maintained when PE-Cys mutants were coupled to 5- or 20-kDa mPEG, using either a disulfide or a thioether linkage. Unexpectedly in some cases, the thioether conjugate was more active than the disulfide linkage. Pharmacokinetic studies on one of the polyethylene-glycolated molecules (R313C) showed that the mean residence time (t 1/2) was prolonged to 72 min, compared to 20 min for unpolyethylene glycolated PE-Cys(R313C). These studies show it is possible to derivatize PE at specific residues in domain II, maintain significant cytotoxic activity, and alter pharmacokinetics. These studies also suggest that large mPEG molecules can be translocated to the cytosol while still attached to domain II of PE.

ADP Ribose Transferases↗
PubMed1994

[Long-term results of implantation of polyethylene screw sockets using Edler's method].

High-molecular polyethylene is used in many technical spheres and in orthopaedics it is used in particular as a sliding component. In orthopaedic endoprosthetics it serves as a material for the manufacture of sockets, whereby polyethylene sockets can be anchored with our without cement. Morphological research corroborates the suspicion of inadequate static firmness of the polyethylene used and this may lead to abrasion and thus mechanical loosening of Endler's screw socket and subsequently also of the metal shank. At the orthopaedic department of the General hospital in Zwettel (Austria) between 1984 and 1987 113 Endler sockets were implanted in 101 patients. So far 41 reoperations were made in 39 patients. In 71% of the patients replacement by a non-cemented socket according to Zweymüller followed, in 17% by a cemented socket according to Müller. In 4 joints at the same time also the femoral component had to be replaced, in 13 shanks bone rarefaction in the area of the calcar femoris was detected. In shanks with removable heads the head was always replaced. Clinical evaluation of the operated patients was done according to the procedure of Merle d'Aubigné.

Austria↗
PubMed1996

Proteins involved in the Vroman effect during exposure of human blood plasma to glass and polyethylene.

The amounts of fibrinogen adsorbed to glass from various human blood plasmas have been measured as a function of time. The plasmas were 11 single donor plasmas, pooled plasma, a single donor high molecular weight kininogen (HMWK)-deficient plasma and HMWK-deficient plasma, which had been reconstituted with HMWK. For adsorption times between 1 min and 1 h more fibrinogen adsorbed from HMWK-deficient plasma compared with the amounts of fibrinogen which adsorbed from the other plasmas. This result supports the conclusion of several authors that HMWK is involved in the displacement of fibrinogen, initially adsorbed from normal human plasma to glass. Glass surfaces, pre-exposed to solutions of plasma and subsequently exposed to 1:1 diluted plasma, gives rise to a relatively high adsorption of HMWK which is independent of the plasma concentration of the precoating solution. The results indicate that HMWK from 1:1 diluted plasma is involved in the displacement of proteins from glass surfaces which had been pre-exposed to solutions with a low plasma concentration. Experiments with polyethylene as a substrate reveal that high density lipoprotein (HDL) from 1:1 diluted plasma is involved in the displacement of proteins from polyethylene surfaces which had been pre-exposed to solutions with a low plasma concentration. Moreover, evidence is presented that substantial amounts of albumin and fibrinogen, adsorbed from 1:1000 diluted plasma to glass and polyethylene, are displaced from the surfaces of these materials by proteins from 1:1 diluted plasma different from HMWK and HDL.

Adsorption↗
PubMed1996

[Wear characteristics of different metal-polyethylene beating surfaces. An experimental study of a new model of knee prosthesis].

PURPOSE OF THE STUDY: Wear of artificial components joint is the most important factor in long term durability. Only few studies have analysed in laboratory experimentation the quality of different alloys on the same type of prosthesis. MATERIAL: During the development of a new knee prosthesis, we studied the friction mechanisms of the metal/polyethylene (UHMWPE) couple and particularly the value of titanium alloy (Ti-6AI-4V) treatment using an ionic nitrogen implantation process (IMPLATEC). Two friction surfaces were studied in vitro: one in flexion-extension between femoral component and tibial plateau, the other in rotation between tibial plateau and "metal-back". METHODS: The implanted Ti-6AI-4V was compared with 316L stainless steel, cobalt chromium molybdenium alloy and with Ti-6AI-4V using a prosthesis of each configuration. The samples were tested on a TRIBOCUP friction machine during 3 x 10(6) cycles in Ringer 's solution. The friction couples were controlled every 200,000 cycles and the loss of polyethylene mass every 500,000 cycles. We have also evaluated the roughness and the rubbing surface macroscopically. RESULTS: The results analysis shows that friction couples such as Cobalt Chromium and implanted Ti-6AI-4V are weakest but implanted Ti-6AI-4V over time, tends to match the strength of Ti-6AI-4V without treatment. With implanted Ti-6AI-4V and with Cobalt Chromium alloy, the loss of polyethylene is slight comparatively to the stainless steel and non implanted Ti-6AI-4V. Surface analysis showed good protection of titanium alloy by ionic implantation especially in the femoral component where roughness is close (0.04 micron) to that of Cobalt Chromium alloy (0.07 micron). DISCUSSION: Our study confirms the results with pin-on-disk and cup-on-ball with results for the Ti-6AI-4V implanted and Cobalt Chromium alloys with protection of the metal surface and decrease of polyethylene wear comparatively to stainless steel and non implanted Ti-6AI-4V. CONCLUSION: Our conclusion is for this type of experimental device that the surface condition is satisfactory for such friction couples as implanted Ti-6AI-4V/polyethylene and Cobalt-chromium/polyethylene, with very similar results. However, the long-term durability of the nitrogen implanted on Titanium Alloy remains unknown.

Biodegradation, Environmental↗
PubMed1997

[Polyethylene faults as causes for failure in total hip replacement].

The paper deals with polyethylene faults leading to failure in total hip replacement. The material has well known advantages and is widely used but has also significant disadvantages: excessive wear of some cups, delamination and peeling of the bearing surface of the cup, fracture and fragmentation of the cup and inducing adverse biological reactions that might lead to the loosening of the implant. Final modeling of the polyethylene cup, radiation sterilization and biological factors can alter internal structure of the polyethylene and change mechanical properties of the cup with failure of the hip arthroplasty resulting.

Biocompatible Materials↗
PubMed1997

Dissolution rate of furosemide from polyethylene glycol solid dispersions.

In this study, by preparing the solid dispersions of furosemide, a substance that is poor-soluble in water, with polyethylene glycol 6000, 10,000 and 20,000, the enhancement of the dissolution rate of furosemide has been aimed. Solid dispersions were prepared by the fusion method in proportions of 1:4, 1:6 and 1:10 (active material/polymer). The formation of solid dispersion was tested by the techniques of X-ray diffraction, differential calorimetry (DSC) and infrared spectroscopy (IR). The release rate of active material from the solid dispersions prepared was examined by using the flow through cell method. Also, the effect of particle size of the complexes obtained, on the dissolution rate and the stabilities of these complexes were studied. It was determined that the dissolution rate of furosemide was markedly increased along with the formation of the complex and that a better dissolution profile was obtained even in the physical mixtures prepared for the purposes of comparison. It was found that the molecular weights of different kinds of polyethylene glycols and the various proportions of active material/polymer complexes as well as the particle sizes of the solid dispersions were not efficient in the release rate of active material. It was concluded that the increase of the dissolution rate was being a result of both wettability and solubility enhancing effects of polyethylene glycols.

Calorimetry, Differential Scanning↗
PubMed1978

The production and biology of polyethylene wear debris.

Polyethylene in the form of a concave bearing surface at the hip wears very slowly, and clinical and histological evidence suggests that the volume of debris so released is well tolerated. However, significantly greater volumetric wear rates are produced when (1) polyethylene is used as the convex component of a joint and (2) abrasives such as PMMA or bone enter the joint. Further, large quantities of polyethylene debris lead to the replacement of bone at the bone-cement interface by soft tissue. Evidence is presented which strongly suggests that this mechanism can produce joint component loosening.

Acrylic Resins↗
PubMed1993

Evaluation of wear in an all-polymer total knee replacement. Part 2: clinical evaluation of wear in a polyethylene on polyacetal total knee.

In an effort to improve the long-term result of total joint replacement arthroplasty, we have investigated the use of a polymer-on-polymer articular replacement arthroplasty. Because of their known biocompatibility and previous use in orthopedic surgery, polyethylene and polyacetal (copolymer, Hoechst) were selected. Polyethylene served in its usual role as the concave member of the articulation; polyacetal formed the convex number. Formal wear testing using a multi-channel hip simulator demonstrated superior wear characteristics of the polymer-on-polymer configuration compared to a conventional chrome-cobalt versus polymer (polyethylene) configuration. A clinical series of relatively high-activity patients having a minimum five-year follow-up (N = 26) showed no specific unfavorable reaction to this material combination in a total knee replacement. Given certain potential advantages of polymeric materials, as well as some theoretical disadvantages of metallic materials, a polymer-on-polymer design for a large joint replacement may have some merit.

Acetals↗
PubMed2005

Encapsulation method for the dispersion of NiO onto ordered mesoporous silica, SBA-15, using polyethylene oxide (PEO).

An effective method for dispersing NiO onto ordered mesoporous silica, SBA-15, is described. The procedure involves the use of polyethylene oxide (PEO) as an encapsulating agent. It can be expected that encapsulation between PEO and Ni2+ ions mainly involves complexes between PEO and Ni2+ ions. Both N2 adsorption/desorption isotherm and TEM analyses indicate that a 2-dimensionally hexagonal pore structure with a distinct pore symmetry (space group P6mm) is maintained throughout the procedure, even though both Ni2+ ions and PEO are present in the middle of the self-assembly of mesostructured silica. The particle size of the NiO increases slightly as a function of PEO concentration. When the ratio of PEO to the templating agent (triblock copolymer, polyethylene oxide-polypropylene oxide-polyethylene oxide) reaches a value of 4.5, ordered mesoporous silica with NiO is hardly formed.

Journal Article↗
PubMed1999

Ultra-high-molecular weight polyethylene wear: an in vitro comparison of acetabular metal types and polished surfaces.

The generation of debris from the wear of ultra-high-molecular weight polyethylene (UHMWPE) is a well-recognized factor in the development of osteolysis and the long-term failure of total joint arthroplasties. Wear between the articulation of the femoral head and the polyethylene has been recognized for many years, but more recently, both retrieval and in vitro studies have demonstrated that convex surface wear or backside wear also occurs and may be of significance. Currently, modular acetabular components are being designed with polished surfaces, fewer screw holes, various polyethylene locking mechanisms, and stiffer metal alloys in an attempt to reduce backside wear. The purpose of this study was to determine if differences existed in UHMWPE wear based on the metal alloy used and the surface finish in modular acetabular components. Sixteen components in 4 groups were subjected to 10 million gait cycles using an in vitro joint simulator. All components used 28-mm cobalt chrome femoral heads on cobalt chrome tapered stems. The 4 groups differed only in the type of metal backing and type of interior finished surface: polished cobalt chrome, unpolished cobalt chrome, polished titanium, and unpolished titanium. UHMWPE changes were examined in terms of articular (concave) surface wear, backside (convex) surface wear, and frictional torque. The overall linear and volumetric wear rates were 1.05 mm/10 million cycles and 325 mm3/10 million cycles. No significant differences in linear and volumetric wear rates were detected between the cobalt chrome and titanium acetabular components. Surface finish did not influence wear rates. In terms of backside wear, all specimens in the 4 groups demonstrated total loss of all sputtered gold with the exception of those areas extruded through the screw holes. Extrusion through the screw holes was on the order of 0.0004 inch for all groups, and no significant difference was seen among the groups for this parameter. The measurements of articular frictional torque demonstrated a significant difference among the polished and unpolished cobalt chrome components (17.3 N x m vs 11.5 N x m; P = .0039, 2-way analysis of variance, Student's Newman Keuls method). Some designs in modular acetabular components have favored stiffer alloys, such as cobalt chrome, with polished concave surfaces to decrease wear on both the concave and the convex surfaces. In this study, there was no significant difference in wear rates noted between cobalt chrome and titanium acetabular components, and polishing of the components had no appreciable affect in reducing backside wear.

Acetabulum↗
PubMed2002

Triple tandem catalyst mixtures for the synthesis of polyethylenes with varying structures.

Tandem catalysis in a single medium presents challenges and opportunities for creating novel synthetic protocols. Thus far, only two homogeneous catalysts have been used in tandem. Herein, we report that it is possible to coordinate the action of three well-defined homogeneous catalysts to produce a wide range of branched polyethylenes from a single monomer. Thus, ([(eta(5)-C(5)Me(4))SiMe(2)(eta(1)-NCMe(3))]TiMe)(MeB(C(6)F(5))(3)) (1), [(C(6)H(5))(2)PC(6)H(4)C(OB(C(6)F(5))(3))O-kappa(2)P,O]Ni(eta(3)-CH(2)C(6)H(5)) (2), and ((H(3)C)C[N(C(6)H(5))]C[O-B(C(6)F(5))(3)][N(C(6)H(5))]-kappa(2)N,N)Ni(eta(3)-CH(2)C(6)H(5)) (3) react with ethylene to produce branched polyethylene with structures that cannot be obtained using a single- or a two-component catalyst combination. The properties of the polyethylene depend on the ratio of the three catalysts. High-throughput screening techniques proved essential for optimizing reaction conditions and for probing how the catalyst composition influences the polymer properties.

Journal Article↗
PubMed2005

Structural changes and chain radius of gyration in cold-drawn polyethylene after annealing: small- and wide-angle X-ray scattering and small-angle neutron scattering studies.

Samples made from linear polyethylene were drawn at room temperature and subsequently annealed at high temperatures below the melting point. The structural changes of the crystalline lamellae and lamellar superstructures as well as the single chain radius of gyration were studied by means of combined small- and wide-angle X-ray scattering and small-angle neutron scattering (SANS). After drawing, the polymeric chain segments in the crystalline phase are preferentially oriented along the drawing direction with a high degree of orientation whereas the lamellae in the samples are found to be slightly sheared exhibiting oblique surfaces as evidenced by X-ray scattering. SANS indicates that the chains are highly elongated along the drawing direction. Annealing the deformed samples at temperatures where the mechanical alpha-process of polyethylene is active leads to a thickening of both crystalline lamellae and amorphous layers. The chains in the crystalline phase retain their high degree of orientation after annealing while the lamellae are sheared to a larger extent. In addition, there is also lateral growth of the crystalline lamellae during high-temperature annealing. Despite the structural changes of the crystalline and amorphous regions, there is no evidence for global chain relaxation. The global anisotropic shape of the chains is preserved even after prolonged annealing at high temperatures. The results indicate that the mobility of polyethylene chains-as seen, e.g., by 13C NMR-is a local phenomenon. The results also yield new insight into mechanical properties of drawn PE, especially regarding stress relaxation and creep mechanisms.

Journal Article↗
PubMed2006

An automatic coarse-graining and fine-graining simulation method: application on polyethylene.

Multiscale modeling of a polymeric system is a challenging task in polymer physics. Here we introduce a bottom-up and then top-down scheme for the simulation of polyethylene (PE). The coarse-grained numerical potential for PE is derived through an automatic updating program by mapping its radial distribution function (RDF) from the Lowe-Andersen temperature controlling (LA) simulation onto the one from detailed molecular dynamics (MD) simulation. This coarse-grained numerical potential can be applied in larger systems under the same thermodynamic conditions. We have tested the reliability of the derived potential in two ways. First, the blends of different linear low-density polyethylene (LLDPE) with high-density polyethylene (HDPE) have been simulated in LA with the coarse-grained numerical potentials and reasonable results are obtained. Moreover, Rouse scaling behavior is reproduced for monodispersed polymeric systems with different chain lengths. The atomistic details of the beads can be reintroduced into the coarse-grained HDPE and LLDPE/HDPE models, followed by a few MD runs to alleviate the local tension induced by this fine-graining procedure. The equilibrated large atomistic system can then be used for further studies.

Journal Article↗
PubMed1998

The effects of polyethylene cup thickness on wear of total hip prostheses.

The wear rate of the ultrahigh molecular weight polyethylene cups in combination with a 28 mm alumina femoral head was measured on the radiographs of patients without any complications, and on cups retrieved due to slight loosening of the prosthesis or due to late infection between bone and components. The wear rate on the radiographs did not include the initial wear, but the wear rate on the retrieved cups did include the initial wear. The wear rate on the retrieved cups was higher, by 50%, than that measured on the radiographs. In both cases, the thicker the polyethylene cups, the lower was the wear rate measured. The average wear rate of the 7 and 8 mm thick cups was about twice that of cups 10 and 11 mm thick. From these results, we conclude that polyethylene cups more than 11 mm thick should be used.

Journal Article↗
PubMed1998

Young's and shear moduli of ceramic particle filled polyethylene.

Tensile and shear properties were determined for hydroxyapatite reinforced poly-ethylene composites (HAPEX) for medical applications. Properties of talc or alumina filled polyethylene were also obtained. Hydroxyapatite particles of different median sizes and morphologies were used to reinforce the polyethylene. Furthermore, chemical coupling of hydroxyapatite to polyethylene was investigated. The obtained results are discussed in terms of possible use as orthodontic materials.

Journal Article↗
PubMed2001

Evaluation of endothelial cell integrins after in \ vitro contact with polyethylene terephthalate.

The aim of this research was to evaluate the effect of polyethylene terephthalate (Woven Dacron) on the expression of endothelial integrins. Human umbilical vein endothelial cells were cultured on the material for 24 h. The integrins VLA-2 (alpha2beta1-CD49b/CD29), receptor for laminin and collagen, VLA-5 (alpha5beta1-CD49e/CD29), receptor for fibronectin, VLA-6 (alpha6beta1-CD49f/CD29), receptor for laminin, and alphaVbeta3-CD51/CD61 (receptor for vitronectin) were evaluated by flow cytometry. After contact with polyethylene terephthalate, a slight but significant decrease in the percentage of both CD29 and CD49e positive cells was observed, which suggests a lower number of cells expressing the fibronectin receptor alpha5beta1. Moreover, a significant increase in the mean channel for CD49b and for the vitronectin receptor CD51/CD61 was observed. The reduction in the fibronectin receptor could account for the poor endothelialization observed in vivo on polyethylene terephthalate. The increased expression of the vitronectin receptor, favoring the migration of smooth muscle cells, could give some information about the pathogenesis of intimal hyperplasia, which is a complication of vascular grafts.

Journal Article↗