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At least 19 recordsLinked to original sources
PubMedDate not supplied

An improved technique for the retention of polycarbonate crowns.

The following conclusions may be drawn from this study: Composite resins do not bond to polycarbonate crowns. A technique for priming the internal surfaces of polycarbonate crowns is indicated, in order to create such a bond. Priming the polycarbonate crown with methyl methacrylate monomer alone produces a bond with composite resins. Priming the polycarbonate crown with a syrup of methyl methacrylate monomer and (poly) methyl methacrylate powder appears to produce a stronger bond with composite resins than the monomer alone.

Carbonates↗
PubMedDate not supplied

The retentive ability of various cementing agents for polycarbonate crowns.

The following conclusions may be made within the limitations of this investigation. - A composite resin processed directly against a roughened stainless steel dye, similar in shape to a primary anterior tooth, which has been shaped to receive a polycarbonate crown, shows the highest retentive force measured in pounds per square inch (psi). - A polmethacrylate resin, when used as a cement, also shows high values, probably due to its ability to unite chemically with polycarbonated acrylic and to its low film thickness. - Composite resins of low viscosity, low film thickness, and high compressive and tensile strengths proved also to provide good retentive values and would contribute insolubility to a greater degree than the unfilled resin. - Polycarboxylate, zinc phosphate, and reinforced zinc oxide-eugenol cements are not to be recommended as agents for cementing polycarbonate crowns. - It can be recommended on the basis of retention only, composite crowns should be fabricated directly onto the tooth preparations of carious primary anterior teeth.

Carbonates↗
PubMed1979

Preparation of liposomes of defined size distribution by extrusion through polycarbonate membranes.

Liposomes of defined size and homogeneity have been prepared by sequential extrusion of the usual multilamellar vesicles through polycarbonate membranes. The process is easy, reproducible, produces no detectable degradation of the phospholipids, and can double the encapsulation efficiency of the liposome preparation. Multilamellar vesicles extruded by this technique are shown by both negative stain and freeze-fracture electron microscopy to have mean diameters approaching the pore diameter of the polycarbonate membrane through which they were extruded. When sequentially extruded down through a 0.2 micron membrane, the resulting vesicles exhibit a very homogeneous size distribution with a mean diameter of 0.27 micron while maintaining an acceptable level of encapsulation of the aqueous phase.

Carbonates↗
PubMed1979

Evaluation of new membranes for hemodialysis: preliminary studies with a polycarbonate membrane.

A synthetic polycarbonate (PC) membrane supplied by C.R. Bard Inc. was assessed as to its clinical usefulness and suitability to regular use with artificial kidney. The permeability of the PC membrane to 11 solutes of increasing molecular volumes (Na+, Ca++, K+, Cl-, HPO4-, urea, creatinine, uric acid, glucose, BSP, cyanocobalamine) was measured in vitro by rotating dialysis cells, as compared to that of Cuprophan PT 150. The evaluation of the PC membrane in vivo was carried out during a regular hemodialytic treatment in 5 patients using a Kiil dialyzer. The dialysance of 6 solutes (HPO4-, urea, creatinine, uric acid, hypaque, cyanocobalamine) across the PC membrane was measured at 200 ml/min blood flow rate. Both in vitro and in vivo the PC membrane showed permeability and dialysance coefficients to small molecules approximately the same than standard PT 150; the ultrafiltration rate of the PC membrane was also superimposable to that of PT 150. On the contrary, larger molecules were removed much more efficiently by the polycarbonate membrane than by PT 150. These data suggest that the membrane evaluated in this study possesses some peculiar features which could possibly result in an improvement of the quality of regular hemodialysis.

Animals↗
PubMed1975

Clinical use of NISR 440 polycarbonate membrane for hemodialysis.

1. In order to accredit the NISR440 Polycarbonate Membrane for clinical studies, the following was accomplished and/or established: a. Casting and synthesis were increased from the laboratory level to production scale. b. Quality control of permeabilities and physical properties was within +/- 5%, from membrane lot to lot and within the same roll. c. The target properties of the Artificial Kidney Program (NIH) were reached(7): 1) Middle M. W. solute permeability of marked molecules was established by 3 different laboratories and averaged: Vitamin B12 - 296 x Cuprophan¿; Inulin 3.6 x Cuprophan¿; Bacitracin 2.94 x Cuprophan¿. 2) Low M. W. species permeabilities were approximately the same as Cuprophan¿, to avoid a depletion syndrome. 3) Hydraulic permeability was essentially the same as Cuprophan¿ (UF rate 1.25 to 2.0 x Cuprophan¿) to avoid dehydration and hypotension. 4) Burst strength was 1.5 to 2.0 x Cuprophan¿. d. Toxicology studies were all negative in spot and in serial lot testing. e. Non-thrombogenicity tests (Lindholm test) were up to 36.6% better than Cuprophan¿. f. No protein adsorption was found. g. The membrane could be produced in the wet and dry state with the same permeability and physical properties. 2. In an earlier clinical study at USC, it was established that: a. There were no toxic effects manifested in patients in 25 episodic studies. b. Clearances forlow M. W. solutes and hydraulic permeabilities were, as targeted, approximately the same as Cuprophan¿. c. In 4 1/2 mos of a double blind study of 6 patients, no significant toxic effects were noted for either the patients on Cuprophan¿ or NISR 440 Polycarbonate Membrane. Two patients had an increase of hematocrit. 3. The ability to heat seal the membrane in the periphery and in channels through many layers, combined with its relative rigidity when wet, make possible clinical hemodialyzer designs approximately the size of a package of cigarettes and inexpensive to produce.

Adult↗
PubMed1977

Evaluation of a polycarbonate filter for the detection of microfilaremia in dogs in central Michigan.

Several diagnostic techniques were used in determining the prevalence of microfilaremia in 479 dogs entering the holding facility for research animals at Michigan State University. The modified Knott test and cellulose filter procedures were initially applied, but persistent difficulties with the cellulose filter system prompted evaluation of the use of clear polycarbonate filters. This procedure was found to be equally as sensitive as the modified Knott test and more sensitive than the microhematocrit tube method. Microfilariae trapped on polycarbonate filters were easy to detect, and there were no problems with clogging of the filter pores. Losses of up to 3.5% of the microfilariae occurred with 8-micron pore size filters, but no more than 1% passed through 5-micron pore size filters. Identification of microfilariae was based on size and shape of the parasites. In questionable cases, the diagnosis was confirmed by means of the histochemical test for acid phosphatase distribution. Satisfactory results were obtained when the latter test was applied to microfilariae of Dirofilaria immitis trapped and fixed on filters. Twenty blood samples in the surgery (4.2%) contained microfilariae, all of which were classified as D imitis.

Animals↗
PubMed1992

Evidence that plasma membrane electrical potential is required for vesicular stomatitis virus infection of MDCK cells: a study using fluorescence measurements through polycarbonate supports.

We used fluorescence microscopy of Madin-Darby Canine Kidney (MDCK) cells grown on polycarbonate filters to study a possible link between plasma membrane electrical potential (delta psi pm) and infectivity of vesicular stomatitis virus (VSV). Complete substitution of K+ for extracellular Na+ blocks VSV infection of MDCK cells as well as baby hamster kidney (BHK) cells. When we independently perfused the apical and basal-lateral surfaces of high resistance monolayers, high K+ inhibited VSV infection of MDCK cells only when applied to the basal-lateral side; high K+ applied apically had no effect on VSV infection. This morphological specificity correlates with a large decrease in delta psi pm of MDCK cells when high K+ buffer is perfused across the basal-lateral surface. Depolarization of the plasma membrane by 130 mM basal K+ causes a sustained increase of cytosol pH in MDCK cells from 7.3 to 7.5 as reported by the fluorescent dye BCECF. Depolarization also causes a transient increase of cytosol Ca2+ from 70 to 300 nM as reported by the dye Fura-2. Neither increase could explain the block of VSV infectivity by plasma membrane depolarization. One alternative hypothesis is that delta psi pm facilitates membrane translocation of viral macromolecules as previously described for colicins, mitochondrial import proteins, and proteins secreted by Escherichia coli.

Animals↗
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↗
PubMed1978

A new polycarbonate fast neutron personnel dosimeter.

Registration of fast-neutron-induced recoil and (n,alpha) tracks directly in sensitive polymers especially polycarbonate foils when etched by the electrochemical etching (ECE) method provides a simple, sensitive, and inexpensive means of fast neutron dosimetry. The wide dose range and a dose equivalent response, negligible fading rate, and insensitivity to X, beta, and gamma radiations make such a method feasible for many neutron dosimetry applications, especially personnel dosimetry. Due to very large size of the tracks, even the unaided eye can be used as a reading device.

Carbonates↗
PubMed1978

A polycarbonate ophthalmic-prescription lens series.

Improvements in polycarbonate material, production techniques, and scratch-resistant coatings, combined with a process-oriented design, have resulted in a precision lens series. Surface quality is comparable to that of untreated glass ophthalmic lenses. The repeatability of the process results in closely controlled axial power and off-axis performance. For most lens prescriptions, the ANSI Z80.1 optical-center specifications for prescription accuracy are maintained through a total field of view of 40 deg for an 8-mm range of center-of-rotation distances. Off-axis astigmatism is controlled for near-point seeing. The lenses are both lighter and thinner than those of crown glass. A scratch-resistant coating reduces the reflections normally associated with high-index (1.586) materials. Impact resistance exceeds that required by ANSI Z80.7 and is many times that required by ANSI Z80.1.

Carbonates↗
PubMed1978

Studies on red cell flexibility in spherocytosis using a polycarbonate membrane filtration method.

A method for studying red cell flexibility as reflected by red cell rigidity and fragility is described. Using an infusion pump, suspended red cells are filtered through a polycarbonate membrane with 3 micron pores. The filtration pressure, which is continuously monitored, is considered to reflect red cell rigidity. The hemoglobin released by the disruption of red cells passing through the membrane is regarded as an indirect measure of red cell fragility. In all of the patients with hereditary spherocytosis studied and in some of their symptomless relatives, the decreased flexibility observed was associable with increased rigidity of the red cell. In vitro effects of chlorpromazine and vinca alkaloid on red cell flexibility were also studied. High concentrations of chlorpromazine and vinblastine induced formation of spherocytes displaying altered cell flexibility.

Adult↗
PubMed1978

An investigation of bonding systems for the polycarbonate crown restoration.

Tensile retentive strengths for six polycarbonate crown cementation systems were examined with use of extracted human teeth prepared with and without retentive grooves. From the results of this study, use of unfilled intermediary resins followed by polycarboxylate or zinc phosphate cements is recommended. Retentive grooves did not contribute to overall retention.

Carbonates↗
PubMed1977

Ultrastructure of cells cultured on polycarbonate membranes.

A method is described for preparing undisturbed cell cultures for both scanning and transmission electron microscopy. Cells were propagated on polycarbonate membranes with pores of 0.2 micrometer or less. Cultured cells together with their supports were prepared for both scanning electron microscopy and transmission electron microscopy using routine methods. For transmission electron microscopy a rapid schedule of infiltration and polymerization was used. The method described in this report yielded good results and it allowed the fine structure of cultured cells to be viewed in situ by both scanning electron microscopy and transmission electron microscopy.

Animals↗
PubMed1976

Karyotypes of vasoformative sarcomas arising from BALB/3T3 cells attached to polycarbonate plates.

Four vasoformative sarcoma in vivo tumor lines arising from the s.c. implantation of 3 X 10(4) BALB/3T3 cells attached to a 1- X 5- X 10-mm polycarbonate platelet were shown to be quite similar in chromosome constitution to the parental 3T3 line. All tumors contained the same marker chromosomes that were present in the parent BALB/3T3 cells. The findings conclusively showed that the tumors had derived from BALB/3T3 cells and not from host cells or from the in vivo fusion of the inoculated 3T3 cells with host cells. Each tumor line had a unique karyotype that was markedly more homogeneous than that of the parental BALB/3T3 cells, strongly suggesting that each tumor represented a separate clone. An M1 marker chromosome was consistently present in each of the four tumor lines but was present in only about 50% of the parent BALB/3T3 cells; it therefore appeared to be a distinct and stable feature of the tumors.

Animals↗
PubMed1977

[Properties of alpha-chymotrypsin enclosed into polycarbonate microcapsules. Estimation of the diffusion effect].

The conditions for the microencapsulation of alpha-chymotrypsin into semi-permeable polycarbonate membranes are selected. The diameter of the microcapsules is 100-150 microns. The microencapsulation can be carried out at any value of pH. The effect of the diffusion in the hydrolysis of some esters by microcapsulated alpha-chymotrypsin was estimated. The thermostability of the microencapsulated enzyme was studied.

Carbonates↗
PubMed1992

EPR and 1H and 13C dynamic nuclear polarization studies of a molecularly doped polymer: bisphenol A polycarbonate doped with trianisylamine and trianisylaminium perchlorate.

We have investigated the EPR and DNP behavior of a molecularly doped polymer modeling those used to transport electronic charge in electrophotography. The EPR spectra show no evidence of the superexchange reported for a closely related system based on tri-p-tolylamine. The difference may be due to larger charge-transfer matrix elements in the latter system. An unambiguous interpretation of the observed 1H DNP was rendered difficult by the unanticipated asymmetry of the EPR spectra. We report extensive data on the "three-spin" effect evident in the DNP-enhanced 13C NMR spectra, and comment on its potential for characterizing polymer interfaces.

Aniline Compounds↗