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At least 127 records · Page 7Linked to original sources

PubMed1985

Changes in protein adsorption on polycarbonate due to L-ascorbic acid.

When a synthetic material is introduced into blood, plasma proteins are rapidly adsorbed on to its surface, followed by the attachment of formed elements of blood, leading to thrombus formation. Previous research reported that vitamin C (L-ascorbic acid) prolongs the clotting time due to the formation of vitamin C-calcium complexes, which reduce the availability of Ca2+ ions for the clotting mechanism in in vitro conditions. Contact angle and platelet adhesion studies have indicated that vitamin C modifies the surface-protein interaction and surface-platelet binding at the interface. In this paper an increased thickness of protein layer deposited on the polycarbonate substrate has been observed in the presence of vitamin C (approximately 50 A) using ellipsometric measurements. Further polyacrylamide gel electrophoresis (PAG) and infrared attenuated total reflection spectroscopy (IR-ATR) techniques have provided a better understanding of the interfacial phenomena. It seems, that the adsorption of albumin is increased, relatively, in the presence of vitamin C, when compared with that of fibrinogen and gamma-globulin from an equal amount of protein mixture.

Adsorption↗

PubMed1994

Chemotaxis of polymorphonuclear leukocytes towards human pre-ovulatory follicular fluid and serum using a 'sparse-pore' polycarbonate filtration membrane.

The chemotactic responses of polymorphonuclear leukocytes (PMN) towards pre-ovulatory follicular fluid and serum from patients participating in an in vitro fertilization program were tested in a modified Boyden chamber using a 'sparse-pore' polycarbonate filtration membrane method. The chemotactic activities of follicular fluids were generally low, but were significantly higher in conceptual cycles than in non-conceptual cycles. The chemotactic activities of sera were generally high, but were significantly lower in conceptual cycles. The chemotactic activity of few follicular fluids ever exceeded that of serum, regardless of the occurrence of conception. These findings demonstrate for the first time using an appropriate technique, that pre-ovulatory follicular fluids can be chemotactic for PMN, but the relationship between this activity, serum chemotactic activity and successful pregnancy is not clear.

Chemotaxis, Leukocyte↗

PubMed2004

Bonding polycarbonate brackets to ceramic: effects of substrate treatment on bond strength.

This study evaluated the effects of 5 different surface conditioning methods on the bond strength of polycarbonate brackets bonded to ceramic surfaces with resin based cement. Six disc-shaped ceramic specimens (feldspathic porcelain) with glazed surfaces were used for each group. The specimens were randomly assigned to 1 of the following treatment conditions of the ceramic surface: (1) orthophosphoric acid + primer + bonding agent, (2) hydrofluoric acid gel + primer + bonding agent, (3) tribochemical silica coating (silicon dioxide, 30microm) + silane, (4) airborne particle abrasion (aluminum trioxide, 30microm) + silane, and (5) airborne particle abrasion (aluminum trioxide, 30microm) + silane + bonding agent. Brackets were bonded to the conditioned ceramic specimens with a light-polymerized resin composite. All specimens were stored in water for 1 week at 37 degrees C and then thermocycled (1000 cycles, 5 degrees C to 55 degrees C, 30 seconds). The shear bond strength values were measured on a universal testing machine at a crosshead speed of 1 mm/min. Brackets treated with silica coating with silanization had significantly greater bond strength values (13.6 MPa, P =.01) than brackets treated with orthophosphoric acid (8.5 MPa). There was no significant difference (P =.97) between the bond strengths obtained after airborne abrasion with aluminium trioxide particles followed by silanization (12 MPa) and hydrofluoric acid application (11.2 MPa) (ANOVA and Tukey test). Although brackets conditioned with orthophosphoric acid exhibited only adhesive failures of the luting cement from the ceramic surface, other conditioning methods showed mixed types of failures. Airborne particle abrasion with aluminium trioxide or silica coating followed by silanization gave the most favorable bond strengths. The types of failures observed after debonding indicated that the critical parameter was the strength of the adhesive joint of the luting cement to both the bracket and the ceramic.

Analysis of Variance↗

PubMed2004

Response of MG63 osteoblast-like cells onto polycarbonate membrane surfaces with different micropore sizes.

Response of different types of cells on materials is important for the applications of tissue engineering and regenerative medicine. It is recognized that the behavior of the cell adhesion, proliferation, and differentiation on materials depends largely on surface characteristics such as wettability, chemistry, charge, rigidity, and roughness. In this study, we examined the behavior of MG63 osteoblast-like cells cultured on a polycarbonate (PC) membrane surfaces with different micropore sizes (0.2-8.0 microm in diameter). Cell adhesion and proliferation to the PC membrane surfaces were determined by cell counting and MTT assay. The effect of surface micropore on the MG63 cells was evaluated by cell morphology, protein content, and alkaline phosphatase (ALP) specific activity. It seems that the cell adhesion and proliferation were progressively inhibited as the PC membranes had micropores with increasing size, probably due to surface discontinuities produced by track-etched pores. Increasing micropore size of the PC membrane results in improved protein synthesis and ALP specific activity in isolated cells. There was a statistically significant difference (P<0.05) between different micropore sizes. The MG63 cells also maintained their phenotype under conditions that support a round cell shape. RT-PCR analysis further confirmed the osteogenic phenotype of the MG63 cells onto the PC membranes with different micropore sizes. In results, as micropore size is getting larger, cell number is reduced and cell differentiation and matrix production is increased. This study demonstrated that the surface topography plays an important role for phenotypic expression of the MG63 osteoblast-like cells.

Bone Substitutes↗

PubMed2005

Analysis and evaluation of a biomedical polycarbonate urethane tested in an in vitro study and an ovine arthroplasty model. Part II: in vivo investigation.

The polyurethane (PU) elastomer Corethane 80A (Corvita) is being considered as the acetabular bearing material in a novel total replacement hip joint. Its biostability was investigated in vitro (Analysis and evaluation of a biomedical polycarbonate urethane tested in an in vitro study and an ovine arthroplasty model. Part I: material selection and evaluation, Biomaterials, in press) together with three other commercially available biomedical PUs: Pellethane 2363-80A (DOW Chemical), a polyhexamethylene oxide based PU, PHMO-PU (CSIRO, not supplied as a commercial product) and ChronoFlex AL-80A (CardioTech). From the in vitro studies, Corethane 80A displayed the best overall resistance to hydrolysis, ESC, MIO and calcification, followed by ChronoFlex 80A and PHMO-PU, with Pellethane 80A being the least stable. Building on the in vitro investigation, the follow-up in vivo study (reported here) assessed Corethane 80A as the bearing layer in a prototype compliant layer acetabular cup, in a fully functioning ovine total hip arthoplasty (THA) model. PU degradation in the retrieved cups was analysed using a range of analytical and physical-testing methods including mechanical testing, differential scanning calorimetry, Fourier transform infrared spectroscopy and environmental scanning electron microscopy. The Corethane 80A functioned well in the THA model, with the bearing surfaces of the retrieved hip cups showing no significant evidence of biodegradation or wear damage after 3 years in vivo. The findings in this study provide compelling evidence for the biostability and effectiveness of acetabular cups incorporating a Corethane 80A compliant bearing layer.

Absorptiometry, Photon↗

PubMed2005

Phospholipase A2 pathway association with macrophage-mediated polycarbonate-urethane biodegradation.

Activation of the phospholipase A2 (PLA2) pathway is a key cell signaling event in the inflammatory response. The PLA2 family consists of a group of enzymes that hydrolyze membrane phospholipids, resulting in the liberation of arachidonic acid (AA), a precursor to pro-inflammatory molecules. Given the well-documented activating role of biomaterials in the inflammatory response to medical implants, the present study investigated the link between PLA2 and polycarbonate-based polyurethane (PCNU) biodegradation, and the effect that material surface had on PLA2 activation in the U937 cell line. PCNUs were synthesized with poly(1,6-hexyl 1,2-ethyl carbonate)diol, 1,4-butanediol and one of two diisocyanates (hexane 1,6-diisocyanate or 4,4'-methylene bisphenyl diisocyanate) in varying stoichiometries and incubated with adherent U937 cells. PLA2 inhibiting agents resulted in significantly decreased PCNU biodegradation (p < 0.05). Moreover, when activation of PLA2 was assessed (3H-AA release), significantly more 3H-AA was released from PCNU-adherent U937 cells than polystyrene-adherent U937 cells (p < 0.05) which was significantly decreased in the presence of PLA2 inhibitors. The pattern of inhibition of U937 cell-mediated biodegradation and 3H-AA release that was modulated by PCNU surface differences, suggests a role for secretory PLA2 along with cytosolic PLA2. Understanding PCNU activation of intracellular pathways, such as PLA2, will allow the design of materials optimized for their intended use.

Absorbable Implants↗

PubMed2005

The human macrophage response during differentiation and biodegradation on polycarbonate-based polyurethanes: dependence on hard segment chemistry.

Human monocytes, isolated from whole blood, were seeded onto tissue culture grade polystyrene (PS) and three polycarbonate-based polyurethanes (PCNUs) (synthesized with either 1,6-hexane diisocyanate (HDI) or 4,4'-methylene bis-phenyl diisocyanate (MDI), poly(1,6-hexyl 1,2-ethyl carbonate) diol (PCN) and 1,4-butanediol (BD) in different stoichiometric ratios (HDI:PCN:BD 4:3:1 or 3:2:1 and MDI:PCN:BD 3:2:1) (referred to as HDI431, HDI321 and MDI321, respectively). Following their differentiation to monocyte-derived macrophages (MDMs) the cells were trypsinized and reseeded onto each of the PCNUs synthesized with either 14C-HDI or 14C-BD and degradation was measured by radiolabel release (RR). When the differentiation surface was MDI321, there was more RR from 14C-HDI431 than from any other surface (p < 0.0001) whereas the amount of esterase (identified by immunoblotting) as well as the esterase activity was the greatest in MDM differentiated on PS, reseeded on 14C-HDI431 (p < 0.0001). The effect of potential degradation products (methylene dianiline (MDA) and BD) from the PCNUs was carried out to determine possible links between products and substrate-induced activation of MDM. MDA was found to inhibit RR 60% from MDM seeded on 14C-MDI321B (p < 0.0001), approximately 20% from 14C-HDI431 (p = 0.002) and no effect from 14C-HDI321B. MDA inhibited esterase activity 30% from MDM only on 14C-MDI321B (p = 0.003), but no effect on esterase activity was observed for the other two polymers. BD had no inhibitory effect on RR from any PCNU, but did inhibit esterase activity in MDM on 14C-HDI431 (p = 0.025). This study indicates that the degradation of a specific material is a multi-factorial process, dictated by its susceptibility to hydrolysis, the effect of specific products generated during this course of action, and perhaps not as well appreciated, the material's inherent ability to influence enzyme synthesis and release.

Absorbable Implants↗

PubMed2004

Leaching of bisphenol A (BPA) from polycarbonate plastic to water containing amino acids and its degradation by radical oxygen species.

In this study, (1) the change in the concentration of bisphenol A (BPA) leached from polycarbonate plastic (PCP) tube to water samples containing phosphate, sodium barbital, glycine, methionine or albumin at 37 degrees C as a function of time, and (2) the degradation rate of BPA leached from PCP tube to amino acid solutions in the presence of radical oxygen species (ROS) were investigated. The BPA leaching velocity (BPA-LV) from PCP tube to 50 mM glycine at pH 6 or 7 was twice that to control water, and the leaching was enhanced above pH 8. At pH 11, BPA-LV was significantly higher in 50 mM glycine and methionine solutions than in 50 mM NaOH. These results indicate that basic pH and amino acids contained in water could accelerate BPA leaching. The BPA-LV in phosphate buffer was different from the BPA-LVs in other buffers (barbital and glycine) at the same pH. BPA leached to the glycine or methionine solutions at pH 11 was degraded time dependently in a similar manner as the control water in the presence of ROS. The degradation of leached BPA was inhibited in the glycine solution, but was accelerated in the methionine solution. However, degradation of BPA added to freshly prepared methionine was inhibited in a similar manner to BPA in glycine. BPA degradation could be influenced by some kinds of amino acids, but glycine and methionine might be involved in BPA degradation in different ways.

Amino Acids↗

PubMed2005

Use of a light-polymerized composite removable partial denture base for a patient hypersensitive to poly(methyl methacrylate), polysulfone, and polycarbonate: a clinical report.

This article describes a light-polymerized composite denture base used for a patient with hypersensitivity to poly(methyl methacrylate) (PMMA), polysulfone (PSF), and polycarbonate (PC). A urethane-dimethacrylate (UDMA) composite was used as an alternative to fabricate both the denture base and the custom artificial teeth. Immediately after placing the new prosthesis, allergic symptoms disappeared from the patient's mucous membrane. The denture has functioned satisfactorily for more than 2.5 years without recurrence of the hypersensitivity.

Acrylic Resins↗

PubMed2002

Characterisation of the surface Lewis acid-base properties of the components of pigmented, impact-modified, bisphenol A polycarbonate-poly(butylene terephthalate) blends by inverse gas chromatography-phase separation and phase preferences.

Inverse gas chromatography was used to study the surface Lewis acid-base properties of the major components of pigmented, impact-modified, polycarbonate-poly(butylene terephthalate) blends. An investigation of the Lewis acid-base interactions in these polymeric systems has been carried out, based on the values determined for the surface Lewis acidity constant (Ka), surface Lewis basicity constant (Kb) and on the chemical and physical structure of the materials involved. This analysis provided the rationale for an interpretation of the phase separation and the phase preference that exist in these polymer blends, and of the consequences to their physical and mechanical properties.

Acids↗

PubMed2003

Leaching of bisphenol A (BPA) to seawater from polycarbonate plastic and its degradation by reactive oxygen species.

In this study, (1) change in the concentration of bisphenol A (BPA) leached from polycarbonate (PC) tube to control water (BPA free), seawater and river water at 20 and 37 degrees C as a function of time, (2) the fate of BPA caused by addition of H(2)O(2) and Fe(3+) to seawater containing BPA leached from PC tube were assessed. BPA leached from PC tube to all water samples increased with the ascendant of temperature and with the passage of time. The BPA leaching velocity in seawater was the fastest in three samples (11 ng/day for seawater, 4.8 ng/day for river water 0.8 ng/day for control water at 37 degrees C).BPA leaching velocity from PC tube was significantly high at pH 8 (50 mM Na(2)HPO(4)) and increased dose-dependently. There was no difference in the velocity of BPA among the 50 mM phosphate-buffers at pH 6.5, 7.0 and 7.5. BPA was leached three times higher by addition of Na(+) than K(+). However, the higher the K(+) concentration, the larger the BPA leached from PC tube. Na(+) mixed with PO(4)(-) was effective on BPA leaching from PC tube, but not with SO(4)(-) or Cl(-). The results suggested that BPA leaching from PC tube would be attributed to the concentration of bibasic phosphate such as Na(2)HPO(4) and K(2)HPO(4) in water samples. BPA was degraded in both control water and seawater in the presence of radical oxygen species, but the degradation rate was lower in seawater than in control water, suggesting that anti-oxidative system exists in seawater. Neo-synthesized substance in both control water and seawater in the presence of reactive oxygen species was identified as BPA-quinone by LC-MS.

Benzhydryl Compounds↗

PubMed2003

Isolation of methylene dianiline and aqueous-soluble biodegradation products from polycarbonate-polyurethanes.

Polycarbonate-polyurethanes (PCNUs) have provided the medical device industry with practical alternatives to oxidation-sensitive polyether-urethanes (PEUs). To date, many studies have focused on PCNUs synthesized with 4,4'-methylene diphenyl-diisocyanate (MDI). The relative hydrolytic stability of this class of polyurethanes is actually quite surprising given the inherent hydrolytic potential of the aliphatic carbonate group. Yet, there has been little information reporting on the rationale for the material's demonstrated hydrolytic stability. Recent work has shown that PCNU materials have a strong sensitivity towards hydrolysis when changes are made to their hard segment content and/or chemistry. However, knowledge is specifically lacking in regards of the identification of cleavage sites and the specific nature of the biodegradation products. Using high-performance liquid chromatography, radiolabel tracers and mass spectrometry, the current study provides insight into the distribution of biodegradation products from the enzyme-catalyzed hydrolysis of five different PCNUs. The hydrolytic sensitivity of the materials is shown to be related to the distribution of products, which itself is a direct consequence of unique micro-structures formed within the different materials. While an MDI-based polymer was shown to be the most hydrolytically stable material, it was the only PCNU that produced its diamine analog, in this case 4,4'-methylene dianiline (MDA), as a degradation product. Given the concern over aromatic diamine toxicity, this finding is important and highlights the fact that relative biostability is a distinct issue from that of degradation product toxicity, and that both must be considered separately when assessing the impact of biodegradation on biomaterial in vivo compatibility.

Aniline Compounds↗

PubMed1999

Small changes in polymer chemistry have a large effect on the bone-implant interface: evaluation of a series of degradable tyrosine-derived polycarbonates in bone defects.

In a series of homologous, tyrosine-based polycarbonates, small changes in the chemical structure of the polymer pendent chain were found to affect the bone response in a long-term (1280 d) implantation study. Identically sized pins, prepared from poly(DTE carbonate), poly(DTB carbonate), poly(DTH carbonate), and poly(DTO carbonate) were implanted transcortically in the proximal tibia and the distal femur of skeletally mature New Zealand White Rabbits. The tissue response at the bone-implant interface was characterized in terms of the absence of a fibrous capsule (direct bone apposition, indicative of a bone bonding response) or the presence of a fibrous capsule (referred to as the encapsulation response). The relative frequency of direct bone apposition versus encapsulation was recorded for each polymer throughout the entire period of the study. While all four polymers were tissue compatible, there was a correlation between the chemical structure of the pendent chain and the type of bone response observed, with poly(DTE carbonate) having the highest tendency to elicit direct bone apposition. Based on in vivo degradation data and the ability of model polymers with carboxylate groups at their surface to chelate calcium ions, it is proposed that the ability of poly(DTE carbonate) to bond to bone is caused by the facile hydrolysis of the pendent ethyl ester groups which creates calcium ion chelation sites on the polymer surface. The incorporation of calcium chelation sites into the chemical structure of an implant material appears to be a key requirement if direct bone apposition/bone bonding is desired. This study demonstrates that very subtle changes in the chemical composition of an implant material can have significant effects on the long-term tissue response in a clinically relevant model.

Animals↗

PubMed2002

A floating-type oral dosage form for piroxicam based on hollow polycarbonate microspheres: in vitro and in vivo evaluation in rabbits.

A floating type dosage form (FDF) of piroxicam in hollow polycarbonate (PC) microspheres capable of floating on simulated gastric and intestinal fluids was prepared by a solvent evaporation technique. Incorporation efficiencies of over 95% were achieved for the encapsulation. In vitro release of piroxicam from PC microspheres into simulated gastric fluid at 37 degree C showed no significant burst effect. The amount released increased with time for about 8 h after which very little was found to be released up to 24 h. In intestinal fluid, the release was faster and continuous and at high drug payloads, the cumulative release reached above 90% in about 8 h. In vivo evaluation of different dosage forms of piroxicam such as free drug, drug-encapsulated microspheres and microspheres along with a loading dose of free drug in rabbits showed multiple peaking in the plasma concentration-time curve suggesting enterohepatic recirculation of the drug. Pharmacokinetic analysis showed that the bioavailability from PC microspheres alone was about 1.4 times that of the free drug and it was about 4.8 times for the dosage form consisting of the microspheres plus the loading dose. The elimination half life was increased by about three times for the microsphere preparation alone and nearly about six times for the dosage form comprising of microspheres and a loading dose in comparison to the free drug. Data obtained in this study demonstrated that FDF of piroxicam in PC microspheres was capable of sustained delivery of the drug for longer periods with increased bioavailability.

Administration, Oral↗

PubMed1975

In vitro isolation of Plasmodium knowlesi merozoites using polycarbonate sieves.

A culture chamber fitted with a polycarbonate sieve has been used to isolate Plasmodium knowlesi merozoites as they are released from schizonts. A 3 mum pore-size sieve allows passage of normal erythrocytes and red cells containing rings and trophozoites and can be used to concentrate schizonts from a mixed cell population. A 2 mum pore-size sieve retains normal and parasitized cells and provides uncontaminated merozoites in high yield (5 x 10(10) merozoites per ml schizonts). Merozoite viability diminishes rapidly during 30 min after isolation. These preparations should prove valuable for studies of the biochemical, physiological and antigenic properties of this transient phase of the malaria parasite.

Animals↗

PubMed2005

Electrokinetically synchronized polymerase chain reaction microchip fabricated in polycarbonate.

This paper presents a novel method for DNA thermal amplification using the polymerase chain reaction (PCR) in an electrokinetically driven synchronized continuous flow PCR (EDS-CF-PCR) configuration carried out in a microfabricated polycarbonate (PC) chip. The synchronized format allowed patterning a shorter length microchannel for the PCR compared to nonsynchronized continuous flow formats, permitting the use of smaller applied voltages when the flow is driven electrically and also allowed flexibility in selecting the cycle number without having to change the microchip architecture. A home-built temperature control system was developed to precisely configure three isothermal zones on the chip for denaturing (95 degrees C), annealing (55 degrees C), and extension (72 degrees C) within a single-loop channel. DNA templates were introduced into the PCR reactor, which was filled with the PCR cocktail, by electrokinetic injection. The PCR cocktail consisted of low salt concentrations (KCl) to reduce the current in the EDS-CF-PCR device during cycling. To control the EOF in the PC microchannel to minimize dilution effects as the DNA "plug" was shuttled through the temperature zones, Polybrene was used as a dynamic coating, which resulted in reversal of the EOF. The products generated from 15, 27, 35, and 40 EDS-CF-PCR amplification cycles were collected and analyzed using microchip electrophoresis with LIF detection for fragment sizing. The results showed that the EDS-CF-PCR format produced results similar to that of a conventional block thermal cycler with leveling effects observed for amplicon generation after approximately 25 cycles. To the best of our knowledge, this is the first report of electrokinetically driven synchronized PCR performed on chip.

DNA↗

PubMed2007

DNA detection on plastic: surface activation protocol to convert polycarbonate substrates to biochip platforms.

A mild and efficient surface activation protocol to convert polycarbonate (PC) substrates, e.g., plastic bases of compact disks, to biochip platforms for DNA probe immobilization and target detection is described. The preparation procedure (activation, patterning, and coupling) is simple and effective; the on-chip hybridization is sensitive and selective. Particularly, UV/ozone treatment of PC sheets produces a hydrophilic surface with a high density of reactive carboxylic acid groups [(4.8 +/- 0.2) x 10-10 mol/cm2] in less than 10 min at ambient conditions, and no significant aging or physical damage to the substrate is observed. Covalent immobilization of DNA probes via both passive (reagent-less photopatterning and coupling in bulk solution phase) and flow-through (creation of microarrays with microfluidic channel plates) procedures has been demonstrated. Subsequent hybridization shows uniform and strong fluorescent signals for complementary target DNA and allows clear discrimination between fully complementary targets and strands with a single base-pair mismatch. The surface chemistry described herein will facilitate the development of disposable plastic biochips (not limited to DNA microarrays) and the fabrication of biomedical devices that are readable with conventional optical drives.

DNA↗

PubMed2005

Aluminum salen complexes and tetrabutylammonium salts: a binary catalytic system for production of polycarbonates from CO2 and cyclohexene oxide.

A series of complexes of the form (salen)AlZ, where H2salen = N,N'-bis(salicylidene)-1,2-phenylenediimine and various other salen derivatives and Z = Et or Cl, have been synthesized. Several of these complexes have been characterized by X-ray crystallography. An investigation of the utilization of these aluminum derivatives along with both ionic and neutral bases as cocatalysts for the copolymerization of carbon dioxide and cyclohexene oxide has been conducted. By studying the reactivity of these complexes for this process as substituents on the diimine backbone and phenolate rings are altered, we have observed that aluminum prefers electron-withdrawing groups on the salen ligands, thereby producing an electrophilic metal center to be most active toward production of polycarbonates from CO2 and cyclohexene oxide. For example, the complex derived from H2salen = N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-ethylenediimine is essentially inactive when compared to the analogous derivative containing nitro substituents in the 3-positions of the phenolate groups. This is to be contrasted with the catalytic activity observed for the (salen)CrX systems, where electron-donating salen ligands greatly enhanced the reactivity of these complexes for the coupling of CO2 and epoxides. While (salen)AlZ complexes are capable of producing poly(cyclohexene oxide) carbonate with low amounts of polyether linkage along with small quantities of cyclic carbonate byproducts, their reactivities, covering a turnover frequency range of 5.2-35.4 mol of epoxide consumed/(mol of Al x h), are greatly reduced when compared to their (salen)CrX analogues under identical reaction conditions.

Journal Article↗