Mg Of Polymer Research Articles

Sustained release of mitomycin-C from poly(DL-lactide)/poly(DL-lactide-co-glycolide) films

Mitomycin-C (MMC)-loaded poly(DL-lactide) (PLA)/poly(DL-lactideco-glycolide) (PLGA) films which have different drug loading capacities and thicknesses were prepared by a solvent-evaporation technique. Degradation and release studies were conducted at 37°C in pH 7.4 phosphate buffered saline. The results showed that both the rate and the percentage of released MMC increased as the glycolide content in the copolymer increased from 10 to 30% (w/w) and the drug load increased from 0.5 to 2 mg MMC per 300 mg of polymer. In contrast, they decreased depending upon increasing film thickness from 80 to 300 μm and polymer molecular weight. It was found that the drug release mechanism is diffusion-controlled according to a non-Fickian diffusion mechanism.

Collagen Immobilization onto P(EGDMA/HEMA) Microbeads for Cell Affinity Systems

Both nonswellable and swellable poly(EGDMA/HEMA) microbeads were produced by suspension copolymerization. These microbeads were modified by immobilization of a spacer-arm (hexamethylene diamine, HMDA) and collagen. The optimal values for modifications were as follows: sodium periodate concentration: 0.467 × 10-2 mmol/mL; HMDA concentration: 3.5 × 10-2 mmol/mL; and glutaraldehyde concentration: 0.70 × 106 mmol/mL. Adsorption of collagen onto plain and periodate oxidized poly(EGDMA/HEMA) microbeads were similar, 0.25 and 0.50 mg collagen/g polymer, respectively. Collagen immobilization on poly(EGDMA/HEMA) microbeads was studied at various temperatures, times, and pH by using protein solution containing various amounts of proteins. The optimal values for immobilizations were as follows: the initial collagen concentration: 0.25 mg/mL; temperature: 4°C; pH 7; and the immobilization time; 120 min. Both fibroblastic 3T3 and epithelial MDBK cells were attached to these unmodified and modified microbeads. The attachments of 3T3 and MDBK cells, especially to the collagen immobilized swellable microbeads were very high. Almost 96% of the 3T3 cells available in the cell culture medium became attached to these microbeads (2297 ± 122 cells per mg of polymer). There was no significant effect by swelling on cell attachment.

Deactivation of mycotoxins. I. An in vitro study of zearalenone adsorption on new polymeric adsorbents

This study describes the elimination of zearalenone concentrations in vitro using two new polymeric forms of cross‐linked polyvinylpyrrolidone (cryogels of cross‐linked PVP). Adsorption of zearalenone was studied under isothermal conditions and simulating pH of intestinal environment. A Freundlich isotherm was used to describe the adsorption data obtained. The results showed significant decrease of zearalenone concentrations, ranging from 33.5–66.2 % per 25 mg of polymer. Adsorption capacity (k) was estimated to be higher than that of previously tested adsorbents, including crospovidone. The data indicate the need to investigate structure peculiarities in order to improve mycotoxin deactivation procedures using PVP derivatives.

A potential cell affinity sorbent: Fibronectin carrying poly(EGDMA/HEMA) microbeads

Both non-swellable and swellable poly(EGDMA/HEMA) microbeads were produced by suspension copolymerization. These microbeads were modified by immobilization of a spacer-arm (hexamethylene diamine, HMDA) and fibronectin. The optimal values for modifications were as follows: the sodium periodate concentration 1.0 mg ml-1; the HMDA concentration 4 mg ml-1; and the glutaraldehyde concentration 0.070 μg ml-1. Adsorption of fibronectin onto the plain and periodate-oxidized poly(EGDMA/HEMA) microbeads were very similar, and were 0.025-0.035 mg fibronectin per g polymer, respectively. Fibronectin immobilization on poly(EGDMA/HEMA) microbeads were studied at different temperature, time and pH using single protein solution containing different amount of proteins. The optimal values for immobilizations were as follows: the initial fibronectin concentration 0.1 mg ml; temperature + 25°C; pH 7; the immobilization time 120 min. Both fibroblastic 3T3 and epithelial MDBK cells were attached to these unmodified and modified microbeads. The attachments of both 3T3 and MDBK cells, especially to the fibronectin-immobilized swellable microbeads, were very high. Almost 96% of the 3T3 cells available in the cell culture medium did attach to these microbeads (2345 ± 98 cells per mg of polymer).

Reconcentration of diluted polymer solutions by full adsorption/desorption procedure — 1. Eluent switching approach studied by size exclusion chromatography

A Full Adsorption-Desorption (FAD) procedure is proposed for the controlled reconcentration of diluted polymer solutions. In the first step, macromolecules are quantitatively trapped from their diluted solution onto an appropriate adsorbent. In the second step, polymer is released by a small amount of desorption promoting liquid.The efficiency of this reconcentration process was tested with poly(methyl methacrylate) (PMMA), polytetrahydrofuran (PTHF), poly(ethylene oxide) (PEO) and polystyrene (PS). Bare nonporous silica packed into FAD minicolumns was used for reconcentration of dilute solutions of PMMA, PTHF and PEO in toluene and chloroform. Nonporous silica bonded with aliphatic C18 groups was applied to reconcentrate PS solutions from dimethylformamide (DMF). The desorbing liquid was tetrahydrofuran for PMMA and PTHF, DMF for PEO and toluene for PS. The efficiency of reconcentration was tested by size exclusion chromatography that was coupled on-line with the FAD minicolumn. The efficiency of reconcentration was found to be very high in the case of medium polar and polar polymers PTHF, PMMA and PEO: full recovery of macromolecules was demonstrated by the SEC peak sizes and shapes. Consequently, agreement was found between the values of mean molar mass and polydispersity obtained for a series of polymer samples before and after the reconcentration procedure if the size of the FAD column was optimized. On the other hand, it was more difficult to effectively reconcentrate polystyrene which was not fully adsorbed on bare silica from the most common solvents. Agreement was obtained for molecular characteristics of PS before and after reconcentration from dimethylformamide on C18 bonded silica for higher molar masses above ca. 9 × 104 g mol−1. Very diluted solutions containing 5 mg of polymer per litre of solution could be easily treated in this way and no problems are anticipated even with more diluted systems.The FAD procedure also allows ready exchange of the sample solvent and it can be used in various analytical methods, especially in multidimensional liquid chromatography of macromolecules where effluent from a column separating in the ‘first dimension’ is further separated in the ‘second- and higher dimension’ columns. The reconcentration of polymer mixtures including the selective reconcentration of one blend component and thus the preseparation of blends is also feasible. Preparative reconcentration based on the controlled full adsorption-desorption processes is also expected to be possible. In any case, the appropriate adsorbent and both adsorbing and desorbing liquid must be carefully chosen.

Collagen and Fibronectin Carrying PHEMA Microbeads as Cell Affinity Sorbents

PHEMA microbeads, produced by suspension polymerization, were modified by the immobilization of a spacer (hexamethylene diamine, HMDA), and two proteins, collagen or fibronectin. Adsorption of collagen and fibronectin onto the plain and periodate oxidized PHEMA microbeads were similar; 0.05-0.1 mg of collagen and 0.04-0.05 mg of fibronectin per g of polymer, respectively. Collagen and fibronectin immobilization on PHEMA microbeads were studied at different temperatures, time and pH. The optimal values for immobilization were 0.1 mg/mL for fibronectin; and 0.25 mg/mL for collagen at 25°C for fibronectin and 4°C for collagen; pH 7 in 120 min. Both fibroblastic 3T3 and epithelial MDBK cells were attached to unmodified and modified microbeads. The attachments of both 3T3 and MDBK cells, to the fibronectin and collagen immobilized microbeads were more than 2000 cells per mg of polymer.

Dicarboxylic Acids and Ketoacids Formed in Degradable Polyethylenes by Zip Depolymerization through a Cyclic Transition State

The intermediate and final degradation products formed in six different low-density polyethylene (LDPE) films modified with either starch and/or pro-oxidants or photosensitizers (Scott−Gilead formulation [SG]) were investigated. We propose that dicarboxylic acids and ketoacids, formed in the materials to varying degrees, are due to both secondary oxidation products and a zip depolymerization mechanism by backbiting through a cyclic transition state. Hydrocarbons, ketones, carboxylic acids and dicarboxylic acids are formed during early stages of photo-oxidation, and the ketones disappeared while several ketoacids appeared and the relative amount of dicarboxylic acids increased in the most severely degraded materials. During prolonged photo-oxidation, additional oxidation of ketones and monocarboxylic acids to dicarboxylic acids explains the high amount of dicarboxylic acids. In the thermo-oxidized samples the amount of ketones and monocarboxylic acids remained high even in the most degraded samples. Mono- and dicarboxylic acids were formed in several micrograms per 100 mg of polymer, while the ketones and ketoacids were formed in fewer micrograms per 100 mg of polymer. LDPE modified with the iron dimethyldithiocarbamate (SG1) was the most susceptible material to photo-oxidation, while LDPE containing starch and pro-oxidants (LDPE-MB) was the most susceptible material to thermo-oxidation. Degraded LDPE-MB demonstrated less formation of degradation products; e.g., only in UV-initiated samples thermally degraded at 80 °C for 5 weeks could degradation products be detected. Larger amounts of ketones and ketoacids were formed in the SG materials than in the starch-filled materials.

Electrogeneration of poly(2,5-di-(2-thienyl)-pyrrole) in acetonirile. Kinetics, productivity and composition of the oxidized form

Poly(2,5-di-(2-thienyl)-pyrrole) (poly(SNS)) was synthesized on a Pt electrode by flow of an anodic constant current density of 0.5 mA cm −2 through a solution containing the monomer SNS and LiClO 4 in acetonitrile. The obtained polymer weight was followed by ‘ex situ’ ultramicrogravimetry. Kinetics were followed as a function of temperature, monomer concentration and electrolyte concentration. Two different kinetic regions were found at lower or greater polarization times than 100 s. Productivities of the polymerization charge (as mg of polymer produced per mC of consumed charge), composition (by elemental analysis) and the subsequent number of electrons required to incorporate a monomeric unit into the polymer were determined from different samples.

Optimized preparation of poly d,l (lactic-glycolic) microspheres and nanoparticles for oral administration

A rotatable central composite design (RCCD) was applied to optimize the preparation of cyclosporine-loaded poly D,L (lactide-glycolide) (PLAGA) nanoparticles (NP) and microspheres (MS) by solvent displacement and solvent evaporation techniques, respectively. The joint influence of needle gauge, polymer amount and the injection rates on the mean particle size, relative standard deviation (RSD), yield and drug encapsulation percentage in NP were evaluated. With regards to MS, the polymer amount and the stirring rate were evaluated. Scan electron microscopy of MS and NP showed spherical particles with a dense polymeric network in the first case. From the statistical analysis of data polynomial equations were generated. The mean particle size ranged from 50 to 150 nm for NP and from 1.5 to 30/pm for MS. Smallest nanoparticles (46 nm) were obtained by using the lowest polymer amounts, the highest injection rates and the lowest needle gauges ( r 2 = 0.9443). Under these conditions the drug entrapment percentage was maximum (85.2%), suggesting the drug might be entrapped and adsorbed on the nanoparticle surface. The relative standard deviation was only affected by the polymer amount ( r 2 = 0.8034) and the yield rose with the amount of PLAGA ( r 2= 0.9016). A very important increase in particle size ( r 2 = 0.9855), relative standard deviation ( r 2 = 0.9353) and encapsulation percentage ( r 2 = 0.9669 ) were observed for MS by decreasing emulsification stirring rates and increasing polymer amounts, the stirring rate being the most significant independent variable ( α < 0.0001) in all cases. The highest experimental encapsulation value (97.69 ± 0.78%) correspond to samples prepared from 150 mg of polymer and a global stirring rate of 2000 rpm. By using response surface diagrams and the mathematical models proposed, it is possible to easily deduce experimental conditions to prepare NP and MS with the desired properties.

Effect of Adsorbing Polyelectrolytes on a Balanced Nonionic Surfactant−Water−Oil System

We have studied the effects of an adsorbing polyelectrolyte (hydrophobically modified sodium polyacrylate) on the phase behavior of a balanced nonionic surfactant−water−oil system. As seen from the variation of phase volumes in a three-phase (Winsor III) equilibrium, the effect of polymer adsorption can be described as an increase of the spontaneous curvature of the film away from water. With increasing polymer concentration the middle phase microemulsion first increases its water-to-oil ratio, whereas above a certain polymer concentration the trend is reversed. Following Kabalnov1 et al., this reversal is interpreted as a saturation in the polymer adsorbtion. The saturation value corresponds to approximately 0.2 mg of polymer per m2 of the surfactant film and is similar to that in the Kabalnov experiment with a different polymer. The phase behavior at equal volumes of water and oil was also studied as a function of surfactant concentration for various aqueous polymer concentrations. While the polymer is ...

Direct biosensor coating with a photopolymerised microlayer through a controllable step-procedure

Biosensors are based on the intimate association of a transducer and of a sensing layer. The latter can be a preformed membrane further connected to the transducer, or a thin film directly deposited on its surface. As the stability is a key parameter to be considered, a polymer with high potentialities for this purpose was chosen to form a direct surface coating: a poly(vinyl alcohol) bearing styrylpyridinium groups (PVA-SbQ). Choline oxidase was entrapped in this photo-cross-linkable gel for making an enzyme electrode through controllable steps. The influence of the ratio PVA-SbQ/enzyme was studied and the stability of the resulting modified electrodes was determined. After deposition of minute volumes (10–45 μl) including no more than one unit of choline oxidase and 0.3 mg of polymer, an efficient choline sensor was obtained. It exhibited a fast response time lower than 30 s, a low detection limit of 2.5 nM choline, a wide linear range extending up toca. 10–4 M and good stability, both operational and on storage. This method appears promising for making miniaturized biosensors.

Polypyrrole electrogeneration from a nucleophilic solvent (DMF)

In spite of difficulties pointed out in the literature thick polypyrrole film can be obtained on platinum from NaClO 4-DMF solutions. The polymerization rate increases at constant potential when the potential increases from 900 to 2400 mV(SCE) and the rate decreases at higher anodic potentials. The productivity of the consumed charge, as mg of polymer generated per mC of charge, decreases at increasing potentials. When temperature decreases the polymerization rate increases pointing to a high activation energy of parallel passivation reactions during polymerization. From the ‘ex situ’ microgravimetric method the following empirical kinetics was obtained: Rp = k[pyrrole] 0.5[ClO 4 −] 1.3. The formation of polymeric films was controlled by cyclic voltammetry in the background electrolyte. From the stored charge and the polymer weight the stored charge per mg of electrogenerated polymer for each film could be estimated. When the concentration of ClO 4 − ions increases both the polymerization rate and the capacity to store electrical charge in films increases, which indicates that ClO 4 − ions act as retarding agents of passivation processes during polymerization. In general, the ability to store electrical charge in polypyrrole electrogenerated in different solvents decreases when the donor ability of the solvent increases. At higher temperatures a faster nucleophilic attack of the solvent to the positively charged polymer is proposed to occur, promoting an increasing passivity of the film. The productivity of the polymerization charge decreases at increasing temperatures and increases at increasing concentrations of electrolyte and passes through a maximum when the concentrations of monomer increase.

Doxorubicin-loaded nanospheres bypass tumor cell multidrug resistance

We have demonstrated that in vitro resistance of tumor cells to doxorubicin (Dox) can be fully circumvented by using doxorubicin-loaded nanospheres (Dox-NS), consisting of biodegradable polyisohexylcyanoacrylate polymers of 300 nm diameter and containing 2.83mg of Dox per 31.5mg of polymer. Five different multidrug-resistant cell lines, characterized by mdr1 amplification, were used in this study: Dox-R-MCF7, a human breast adenocarcinoma; SKVBL1, a human ovarian adenocarcinoma; K562-R, a human erythroleukemia; and two murine lines: P388-Adr-R, a monocytic leukemia of DBA2 mouse, and LR73MDR, a Chinese hamster ovarian cell line. These lines were 38.7, 210, 232, 143 and 20 times more resistant than their corresponding sensitive counterparts, respectively. Using Dox-NS, we obtained complete reversion of drug resistance in vitro, i.e. cell growth inhibition comparable with that obtained with sensitive cells exposed to free Dox. In vivo, we significantly prolonged the survival of DBA2 mice which had previously received P388-Adr-R cells by i.p. injections of Dox-NS, while free Dox injection was ineffective toward this rapidly growing tumor. (Prolongation of survival time: 115% vs 167% after Dox vs Dox-NS treatment, respectively.) Using the MCF7 cell line and its resistant variant, we studied the intracellular concentration and the cytoplasmic and nuclear distribution of Dox by laser microspectrofluorometry (LMSF). In sensitive cells, we observed a similar accumulation and distribution of Dox whatever the form of Dox delivery, i.e. whether free or carried by nanospheres. Analysis by LMSF showed that 99% of intranuclear Dox was bound to DNA after treatment with both forms of Dox. Of Dox, 81 and 83% were found in the intranuclear compartment of sensitive cells incubated with free Dox and Dox-NS, respectively. Resistant cells incubated with Dox-NS accumulated the same amount of Dox as sensitive cells incubated with free Dox or with Dox-NS. Dox, when loaded in nanospheres, bypasses the efflux mechanism responsible for multidrug resistance. LMSF analysis showed that Dox, transported and released by nanospheres, interacts with DNA identically in sensitive and resistant cells.

Adsorption of plasma proteins onto anticoagulant polystyrene derivatives: a fluorescence study

Quenching of fluorescence was used to monitor adsorption of thrombin (T), antithrombin (AT) and their inactive complex (T-AT) onto three anticoagulant biomaterials made of polystyrene beads bearing the functional groups of heparin. An adsorption capacity of 0.12 μmol of T per mg of polymer allowed the formation of a monolayer of protein at the polymer surface. An affinity constant of 3 × 10 7 l.mol −1 between thrombin and polymer was estimated, whatever the polymer used. The affinity of T-AT was similar although weaker. Desorption of proteins from the polymeric interface by means of polycations (polybrene and polylysine) showed that the inactive complex T-AT is more quantitatively and easily released than thrombin.

Determination of constants of the Mark-Kuhn-Houwink equation using microamounts of polymers on the basis of microcolumn exclusion chromatography

A chromatographic method of determining the Mark-Kuhn-Houwink constant for polymers in a new solvent, based on the use of narrow-dispersion samples of known MM is proposed. The use of microcolumn exclusion chromatography enables the results to be obtained with only 1 mg of polymer.

Hydroxyl group determination in prepolymers by 1H NMR spectroscopy

AbstractA fast and specific method has been developed for the determination of hydroxyl content in prepolymers that contain hydroxymethylene functional groups. This method involves reaction of the sample with either trifluoroacetic anhydride or hexafluoroacetone to separate the terminal oxymethylene signals in the 1H NMR spectrum from those of the repeating unit and integration against an internal trinitrobenzene standard. This procedure generally requires less than 50 mg of polymer and has been employed in the analysis of prepolymers with number average molecular weights ranging up to 10000. The analysis has been tested using several different prepolymers. Precision of analysis was determined to be within 2.7 percent using a Varian XL‐200 spectrometer.

Aspartate glucan, glycine glucan, and serine glucan for the removal of cobalt and copper from solutions and brines

Aspartate glucan, glycine glucan, and serine glucan obtained by reductive amination of oxalacetic acid, glyoxylic acid, and beta-hydroxypyruvic acid, respectively, with polyglucosamine were tested as chromatographic chelating media. Crosslinked glycine glucan exhibited high capacities for cobalt and copper, even in acidic solutions (pH 2.9). Breakthrough points for 10 mg/L solutions through 6.0 x 0.6 cm columns containing 200 mg of polymer were at 1.8 L for both ions; for 1 mg/L solutions, they were at 4.0 and 12.0 L for cobalt and copper, respectively. Crosslinked glycine glucan could remove microgram amounts of cobalt and copper from fluoride and chloride brines. Cobalt and copper could be separated by elution with 0.25M sulfuric acid.

Characterization of Elution Chromatography Fractions from CIS-Polybutadiene by GPC

Abstract A preparative fractionation of about 23 g of a commercial cis-polybutadiene rubber is described. The method employed was a solvent elution chromatographic method with very little temperature gradient. The molecular weight distributions of the fractions obtained were determined by an analytical fractionation of 20 mg of polymer. The method was similar to the preparative fractionation and involved solvent elution chromatography. The fractions obtained were assayed for quantity, molecular weight, and molecular weight distribution by GPC. The low molecular weight fractions of the preparative fractionation had molecular weight distributions which could be closely approximated by two log normal distributions, the low molecular weight component having the narrower width. The ratio of weight to number average molecular weight was found to be about 1.1 for these samples. The higher molecular weight fractions could also be approximated by two log normal distributions; however, in these fractions the low molecular weight component had a very broad distribution but constituted only a small portion of the sample. The widths of the GPC curves of the fractions correlate satisfactorily with the molecular weight distributions found by the analytical refractionations. The GPC width is a sensitive criterion of the width of the molecular weight distribution even when only two columns are used. It is felt that the analytical fractionation procedure presented gives more detailed information on the molecular weight distribution than is easily obtainable from an ordinary GPC curve.

Precipitin-like reactions of polysaccharides with gelatin in aqueous solution

The following polysaccharides and polysaccharide derivatives give precipitin-like reactions with gelatin in distilled, de-ionized water: glycogen, soluble starch, lichenan; phosphates of soluble starch, glycogen, and dextran; phosphono- D-mannan, and phosphono- D-galactan. Uronic acid-containing, and sulfated polysaccharides which elicited precipitin reactions were: dextran sulfate (mol. wt. 2 x 10 6), agar, poly- D-galacturonic acid, gum karaya, L-arabinan, pectin, gum tragacanth, and gum arabic. The following acidic polysaccharides and phosphorus-containing biopolymers elicited precipitin reactions, but only at high concentrations of gelatin (10—30 mg of gelatin per mg of polymer): dextran sulfates (mol. wt. 1.8 x 10 4 and 5 x 10 5), fucan, carrageenans, chondroitin sulfate, hyaluronic acid, sodium pectate, D-xylan, RNA, DNA, poly(adenylic acid), phosvitin, and ovalbumin. With the exception of dextran sulfates and fucan-gelatin interactions, all polymer-gelatin precipitin reactions were inhibited, either partially or totally, in the presence of 0.145 M sodium chloride. In contrast, the dextran sulfates and fucan showed enhanced precipitation with gelatin in the presence of 0.145 M sodium chloride. All polymer-gelatin precipitin reactions were inhibited by 1.0 M urea or 0.3 M byguanidine. The complex, phenol-extracted, bacterial lipopolysaccharides of Salmonella and Escherichia genera also elicited precipitin reactions with gelatin in distilled, de-ionized water, whereas the corresponding lipopolysaccharide preparations extracted with 5% trichloroacetic acid (TCA) failed to elicit precipitin reactions. Both trypsin-digested and 5% TCA-extracted lipopolysaccharides from Serratia marcescens elicited precipitin curves similar to the acidic polysaccharide-gelatin precipitin curves. Soluble starch, glycogen, and lipopolysaccharides of E. coli 0111:B4 gave rise to characteristic u.v.-scattering spectra when complexed with gelatin. The i.r. absorption spectra of gelatin and gelatin- D-glucan complexes indicated spectral shifts on complexation in the regions of 1650–1450 cm −1 and 1100–900 cm −1. Optical rotatory dispersion spectra were used to detect formation of a complex between gelatin and neutral D-glucans. The effects of sodium chloride, urea, and guanidine hydrochloride, in conjunction with u.v. difference spectra, on various biopolymeric, gelatin complexes are discussed in terms of the electrostatic and hydrogen-bonding forces most probably responsible for specific polymer-gelatin, precipitin-reactions.

Use of Polymers to Control Clay Swelling

Abstract The injection of water to displace oil is one of the main methods used to increase oil recovery. High injection rates are generally desired, and in some cases the flood will not be economic unless high rates are maintained. The presence of clays which swell in the presence of water offers a complication to the problem of maintaining adequate infectivity. In the course of this study we observed that certain polymers, when present in dilute concentrations in the water, had the ability to reduce the response of these clays to fresh water. Two polymers, one anionic and the other nonionic, were found to be very effective in controlling the clays present in Berea cores. Successful control of clay swelling was obtained by the use of solutions containing as little as 1.0 ppm of polymer, but at this low concentration appreciable volumes of treating solution were required. These results suggest that some minimum amount of polymer must be adsorbed to prevent clay swelling. In Berea sandstone, this minimum amount appeared to be of the order of 0.03 mg per cc of pore space. A series of tests made using 10.0 ppm polymer showed that the polymer could be made to move through the porous system in which 0.066/mg of polymer was adsorbed per cc of pore space. This amount, equivalent to 0.023 lb of polymer per barrel of pore space, appears to be of economic interest.