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PubMed2000

Inner core segment design for drug delivery control of thermo-responsive polymeric micelles.

Modification of the thermo-responsive behavior of polymeric micelles for specific drug delivery functions was investigated using combinations of micellar inner cores and outer shell polymer chemistries. Polymeric micelles comprised of AB block copolymers of PIPAAm (poly(N-isopropylacrylamide)) with either PBMA (poly(butyl methacrylate)) or PSt (polystyrene) were employed. PIPAAm-PBMA and PIPAAm-PSt block copolymers formed a core-shell micellar structure after dialysis of the block copolymer solutions in organic solvents against water at 20 degrees C. The hydrophobic drug, adriamycin, (ADR) was loaded into the inner core of the polymeric micelles by dialysis. The polymers showed reversible intermicellar dispersion/aggregation in response to temperature cycles through an outer polymer shell lower critical solution temperature (LCST for PIPAAm=32.5 degrees C), observed by DLS (dynamic light scattering) and transmittance measurements. Upon heating above the LCST, PIPAAm-PBMA micelles exhibited an abrupt increase in micropolarity and an abrupt decrease in microrigidity sensed by pyrene and 1, 3-bis(1-pyrenyl)propane (PC(3)P), respectively. In contrast, PIPAAm-PSt micelles maintained constant values with lower micropolarity and higher microrigidity than those of PIPAAm-PBMA micelles over the temperature range 20 to 40 degrees C. From these results, structural deformations produced by outer shell polymer structural change with temperature cycles through the LCST are proposed for the PBMA core possessing a lower T(g) (ca. 20 degrees C) than the outer shell PIPAAm LCST. The PSt core with a much higher T(g) (ca. 100 degrees C) than the outer shell LCST retained its structure, regardless of outer shell changes. PIPAAm-PBMA micelles released ADR only when heated above the LCST, while PIPAAm-PSt micelles did not. Cell cultures treated with PIPAAm-PBMA micelles loaded with ADR showed high in vitro cytotoxicity when heated above the LCST, while PIPAAm-PSt micelles loaded with ADR expressed very low in vitro cytotoxicity irrespective of temperature change through the LCST. The nature of hydrophobic segments comprising the micelle inner core offers an important control point for thermo-responsive drug release and the drug activity of the thermo-responsive polymeric micelle.

Acrylic Resins↗
PubMed2003

The influence of plasma arc vs. halogen standard or soft-start irradiation on polymerization shrinkage kinetics of polymer matrix composites.

OBJECTIVES: To determine polymerization shrinkage kinetics and hardness of photo-activated polymer matrix composites (PMC) after plasma arc vs. halogen standard or soft-start irradiation. METHODS: Polymerization shrinkage was measured using the 'deflecting disk technique', and Knoop hardness was measured at the bottom of 1.5 mm thick specimens stored for 24 h at 37 degrees C. The materials comprised one micro-filled (Silux Plus) and four fine hybrid PMC (Definite, Herculite XRV, Solitaire 2 and Z250). The irradiation protocols included halogen standard irradiation at three intensities (TriLight, ESPE), ramp curing (dito), step curing (HiLight, ESPE), pulse polymerization (VIP Light, BISCO) and plasma curing (Apollo 95E, DMDS; PAC Light, ADT). RESULTS: Standard halogen irradiation at reduced intensity delayed the start and slowed down the progression of shrinkage strain, but (except for Z250) as well produced lower hardness. Soft-start halogen curing produced similar kinetics but maintained hardness. Plasma arc irradiation resulted in an immediate start and a rapid progression of polymerization contraction, but produced low hardness values in Definite (cured by the ADT unit) and in Solitaire 2 (both units). Z250 featured the highest, Silux Plus the lowest maximum rate of contraction. Despite soft-start irradiation, contraction of Z250 progressed faster than that of Silux Plus with halogen standard irradiation at high intensity. CONCLUSIONS: Soft-start halogen irradiation protocols provide better chances for compensation of shrinkage stress by flow within PMC without compromising hardness and may contribute to a better marginal integrity of the restorations. Irradiation protocols should be individually adjusted to compensate for the different curing characteristics of PMC.

Analysis of Variance↗
PubMed2001

NCD activation of tubulin polymerization.

Tubulin dimer (tT) was purified from turkey erythrocytes. The motor domain of Drosophila non-claret disjunctional protein, NCD(335-700), was expressed in E. coli and purified. At 37 degrees C in the presence of GTP, the rate of polymerization of tT to microtubule (tMt) is accelerated over threefold by the presence of NCD(335-700). At 10 degrees C, the rate of tT polymerization is increased from zero, within experimental error, in the absence of NCD(335-700) to rates near those observed at 37 degrees C when NCD(335-700) is present. The NCD(335-700) concentration dependence of the rate indicated the reactive species was NCD(335-700)(n).tT, with n approximately 2. At 10 degrees C in the absence of GTP, polymerization does not occur, but tT activates NCD(335-700) MgATPase activity 10-fold. For the same conditions, using mians-NCD(335-700), which is modified with 2-(4'-maleimidylanilino) naphthalene-6-sulfonic acid, the apparent K(D) for binding to tT is 2.3 x 10(-5) M in the presence of MgADP. Replacing ADP with AMPPNP or ATP has a negligible effect on K(D). Mians-NCD(335-700) binding to tMt is 10-fold stronger than to tT. The above data indicate NCD(335-700) binds at a functional site on tT. The stoichiometry is consistent with the formation of NCD(335-700)(2).tT which in vitro accelerates self-assembly initiation and/or polymerization by binding a second tT in a position favorable for tubulin-tubulin interaction. The data suggest that in vivo functional NCD binding to microtubule involves one motor domain binding to alpha- and beta-subunits at the interface of two different tubulin dimers in a protofilament.

Animals↗
PubMed2003

The effects of Tubulin denaturation on the characterization of its polymerization behavior.

We report here upon a simulation study examining the effect of a dynamic mode of tubulin denaturation upon the kinetic and thermodynamic characterisation of the polymer formed for two idealized models of a tubulin polymerization reaction: (i) an irreversibly polymerizing system; and (ii) a reversibly polymerizing system. The effects of each denaturation mode upon the two model systems behavior are highlighted by interpretation of the data in terms of the classical Oosawa reversible condensation polymerization model. We reveal here findings which suggest that the measurement strategy in concert with Tubulin's instability over the time course of the experiment may bias the results obtained so as to make an irreversible system's behavior conform to the equilibrium model or alternatively distort the results obtained from a truly reversible system to produce values of the critical concentration quite seriously in error. It was also found that Tubulin denaturation may seriously distort parameter estimates gained from a kinetic characterization of the system (e.g. nucleus size and growth rate constant).

Algorithms↗
PubMed2000

Mechanisms by which cyclodextrins modify drug release from polymeric drug delivery systems.

For many drug candidates a modified in vivo drug release is desired to improve efficacy, sustain effect or minimise toxicity. Polymeric delivery systems, such as microspheres, nanospheres and polymeric films, have been extensively researched in an attempt to achieve modified drug release. Cyclodextrins offer an alternative approach. These cyclic oligosaccharides have the ability to form non-covalent complexes with a number of drugs and in so doing alter their physicochemical properties. In addition, the primary and secondary hydroxyl groups of the native (alpha, beta, gamma-) cyclodextrins are potential sites for chemical modification. It follows that the incorporation of these agents into polymeric drug delivery systems, as physical mixtures, covalently bound conjugates or cross-linking agents, frequently permits a greater degree of control of drug release. This paper reviews the incorporation of various cyclodextrins into polymeric formulations. The mechanisms by which cyclodextrin/polymer formulations act to modify drug release are considered.

Cyclodextrins↗
PubMed2003

Preparation of polymeric nanoparticles containing corticosteroid by a novel aerosol flow reactor method.

Polymeric drug-containing nanoparticles were prepared using a novel aerosol flow reactor method. The polymeric drug-containing nanoparticles prepared consist of a poorly water soluble corticosteroid, beclomethasone dipropionate, and polymeric materials Eudragit E 100 or Eudragit L 100. The novel method used in this study allows synthesis of nanoparticles directly as dry powders. The nanoparticles can contain various ratios of drug and polymer, and the use of any additional stabilisation materials is avoided. In this study, nanoparticles with different drug-to-polymer ratios were prepared. Particle size and morphology, crystallinity, and thermal behaviour were determined as a function of particle composition. It was found that all the nanoparticles produced, regardless of particle composition, had geometric number mean diameters of approximately 90 nm, and were spherical showing smooth surfaces. The drug was molecularly dispersed in the amorphous polymeric matrix of the nanoparticles, and drug crystallisation was not observed when the ambient temperature was below the glass transition temperature of the polymer.

Adrenal Cortex Hormones↗
PubMed1999

Non-traditional plasticization of polymeric films.

The objective of this study was to investigate the influence of methylparaben, ibuprofen, chlorpheniramine maleate and theophylline on the thermal and mechanical properties of polymeric films of Eudragit RS 30 D. The effects of methylparaben and ibuprofen in the film coating on the rate of drug release from Eudragit RS 30 D coated beads were also studied. The physical and mechanical properties of the cast films and coated beads were investigated using thermal analysis, tensile testing, X-ray diffraction analysis and dissolution testing. The results demonstrated that the glass transition temperature of the Eudragit RS 30 D decreased with increasing levels of methylparaben, ibuprofen and chlorpheniramine maleate in the film. Theophylline exerted no influence on the thermal properties of the polymer. The higher levels of the ibuprofen and methylparaben incorporated into the film resulted in a decrease in the tensile strength of the film. The decrease in Young's modulus of Eudragit RS 30 D coated beads was attributed to an increase in the flexibility of the polymeric films when the level of methylparaben or ibuprofen in the polymeric dispersion was increased. The dissolution data demonstrated that the rate of release of the ibuprofen from coated beads was decreased by increasing the amount of ibuprofen and methylparaben in the polymeric film coating.

Chlorpheniramine↗
PubMed2001

In-vitro comparative study of buccal mucoadhesive performance of different polymeric films.

A comparison of the buccal mucoadhesive performance of different polymeric films was carried out using texture analyzer TA-XT2i. A large range of putative polymers differing in their chemical nature, molecular structure as well as hydration status was used. The used polymeric films were classified in rank order of buccal mucoadhesive performance, namely carbopol 971P>polycarbophil>Carrrageenan type lambda > Sodium carboxymethylcellulose. Swelling state as well as tensile strength of the used polymeric films was used as measuring parameters of mucoadhesive interaction. These two approaches gave two opposite orders of performance between CMC and Carrrageenan type lambda after a contact time of 15 min. However the measurement of the viscoelastic moduli of the hydrogels gave the same ranking order of mucoadhesive performance after the same contact time. In reference to the previous works, we noted the importance of the molecular weight, the density of charges, the composition of which the chains of molecules are capable to arrange themselves in a network like form, thus those which are characterized by a tan delta<1 (i.e network formation), are those which develop the best synergism with the mucus because of the reinforcement of an established link. The goal of this study is to assess the buccal mucoadhesive performance aiming to optimize the design of drug delivery via buccal mucoadhesive polymeric films

Adhesiveness↗
PubMed1999

Evaluation of aminoalkylmethacrylate nanoparticles as colloidal drug carrier systems. Part I: Synthesis of monomers, dependence of the physical properties on the polymerization methods.

Conventional nanoparticles based on acrylic compounds are lipophilic and possess a negative surface charge. This is due to their manufacturing process and to the chemical structure of the polymer. Hence, these particles are not suitable for the adsorption of hydrophilic anionic drugs. In the present investigation, positively charged copolymer nanoparticles prepared from aminoalkyl- and methylmethacrylates were evaluated, with regard to their physical properties. This report provides a detailed description of the synthesis of the non-commercially available monomers and their polymerization procedure. Various parameters were investigated, such as comonomer content, total amount of monomer, concentration of the radical initiator, and the composition of the polymerization medium. The resulting particle diameter and the surface charge were found to be strongly dependent on the polymerization conditions and on the pH. Optimization of the polymerization procedure yielded nanoparticles of about 200 nm exhibiting a positive surface charge. The charges of the different copolymer particles were then compared at different pH values. N-trimethylaminoethylmethacrylate (TMAEMC) nanoparticles with quaternary ammonium groups located at their surfaces, possessed a nearly constant positive zeta potential at various pH values and, consequently, pH-independent particle diameters. The physical characteristics of the other aminoalkyl copolymers correlated with the basicity of the monomers employed and were found to be strongly dependent on the pH of the dispersion medium. Aminoethylmethacrylate (AEMC), methylaminoethylmethacrylate (MMAEMC), and aminohexylmethacrylate (AHMC) as well as aminoethylmethacrylamide (AHMAC) copolymer nanoparticles exhibited a strong positively charged surface even at physiological pH and, therefore, are useful candidates for the adsorption of anionic drugs.

Biocompatible Materials↗
PubMed2001

Critical role for the EB1 and APC interaction in the regulation of microtubule polymerization.

Human EB1 was originally cloned as a protein that interacts with the COOH terminus of adenomatous polyposis coli (APC). Interestingly, this interaction is often disrupted in colon cancer, due to mutations in APC. EB1 also interacts with the plus-ends of microtubules and targets APC to microtubule tips. Since APC is detected on the kinetochores of chromosomes, it has been hypothesized that the EB1-APC interaction connects microtubule spindles to the kinetochores and regulates microtubule stability. In yeast, EB1 regulates microtubule dynamics, and its binding domain in APC may be conserved in Kar9, an EB1 binding protein involved in the microtubule-capturing mechanism. These results suggest that the interaction of EB1 and APC is important and may be conserved. However, it is largely unknown whether the EB1-APC interaction affects microtubule dynamics. Here, we show that EB1 potently promotes microtubule polymerization in vitro and in permeabilized cells, but, surprisingly, only in the presence of the COOH-terminal EB1 binding domain of APC (C-APC). Significantly, this C-APC activity is abolished by phosphorylation, which also disrupts its ability to bind to EB1. Furthermore, yeast EB1 protein effectively substitutes for the human protein but also requires C-APC in promoting microtubule polymerization. Finally, C-APC is able to promote microtubule polymerization when stably expressed in APC mutant cells, demonstrating the ability of C-APC to promote microtubule assembly in vivo. Thus, the interaction between EB1 and APC plays an essential role in the regulation of microtubule polymerization, and a similar mechanism may be conserved in yeast.

3T3 Cells↗
PubMed2000

Comparative molecular field analysis of colchicine inhibition and tubulin polymerization for combretastatins binding to the colchicine binding site on beta-tubulin.

A molecular modeling study using Comparative Molecular Field Analysis (CoMFA) was undertaken to develop a predictive model for combretastatin binding to the colchicine binding site of tubulin. Furthermore, we examined the potential contribution of lipophilicity (log P) and molecular dipole moment and were unable to correlate these properties to the observed biological data. In this study we first confirmed that tubulin polymerization inhibition (IC50) correlated (R2 = 0.92) with [3H]colchicine displacement. Although these data correlated quite well, we developed two independent models for each set of data to quantify structural features that may contribute to each biological property independently. To develop our predictive model we first examined a series of molecular alignments for the training set and ultimately found that overlaying the respective trimethoxyphenyl rings (A ring) of the analogues generated the best correlated model. The CoMFA yielded a cross-validated R2 = 0.41 (optimum number of components equal to 5) for the tubulin polymerization model and an R2 = 0.38 (optimum number of components equal to 5) for [3H]colchicine inhibition. Final non-cross-validation generated models for tubulin polymerization (R2 of 0.93) and colchicine inhibition (R2 of 0.91). These models were validated by predicting both biological properties for compounds not used in the training set. These models accurately predicted the IC50 for tubulin polymerization with an R2 of 0.88 (n = 6) and those of [3H]colchicine displacement with an R2 of 0.80 (n = 7). This study represents the first predictive model for the colchicine binding site over a wide range of combretastatin analogues.

Bibenzyls↗
PubMed2002

Heme-artemisinin adducts are crucial mediators of the ability of artemisinin to inhibit heme polymerization.

A lack of molecular understanding of the targets and mechanisms of artemisinin action has impeded the improvisation of more efficient antimalarials based on this class of endoperoxide drugs. We have synthesized a heme-artemisinin adduct designated as "hemart" to discover if it mediates the ability of artemisinin to inhibit heme polymerization. Hemart mimics heme in binding to Plasmodium falciparum histidine-rich protein II (PfHRP II) but cannot self-polymerize. Instead, it inhibits all heme polymerizations, including basal and those triggered by PfHRP II, Monooleoyl glycerol (MOG), or P. yoelii extract. Hemart has an edge over heme in displacing heme from PfHRP II, and either low pH or chloroquine dissociates heme but not hemart from PfHRP II. Our results suggest that hemart, by mimicking heme, stalls all mechanisms of heme polymerization, resulting in the death of the malaria parasite.

Animals↗
PubMed2004

The core FH2 domain of diaphanous-related formins is an elongated actin binding protein that inhibits polymerization.

Diaphanous-related formins (Drf) are activated by Rho GTP binding proteins and induce polymerization of unbranched actin filaments. They contain three formin homology domains. Evidence as to the effect of formins on actin polymerization were obtained using FH2/FH1 constructs of various length from different Drfs. Here we define the core FH2 domain as a proteolytically stable domain of approximately 338 residues. The monomeric FH2 domains from mDia1 and mDia3 inhibit polymerization of actin and can bind in a 1:1 complex with F-actin at micromolar concentrations. The X-ray structure analysis of the domain shows an elongated, crescent-shaped molecule consisting of three helical subdomains. The most highly conserved regions of the domain span a distance of 75 A and are both required for barbed-end inhibition. A construct containing an additional 72 residue linker has dramatically different properties: It oligomerizes and induces actin polymerization at subnanomolar concentration.

Actins↗
PubMed2001

Affinity monoliths generated by in situ polymerization of the ligand.

An affinity monolith with a novel immobilization strategy was developed leading to a tailored pore structure. Hereby the ligand is conjugated to one of the monomers of the polymerization mixture prior to polymerization. After the polymerization, a monolithic structure was obtained either ready to use for affinity chromatography or ready for coupling of additional ligand to further increase the binding capacity. The model ligand, a peptide directed against lysozyme, was conjugated to glycidyl methacrylate prior to the polymerization. With this conjugate, glycidyl methacrylate, and ethylene dimethacrylate, a monolith was formed and tested with lysozyme. A better ligand presentation was achieved indicated by the higher affinity constant compared to a conventional sorbent.

Chromatography, Affinity↗
PubMed2003

Chip-based solid-phase extraction pretreatment for direct electrospray mass spectrometry analysis using an array of monolithic columns in a polymeric substrate.

An array of eight porous monolithic columns, prepared in a Zeonor polymeric chip by UV-initiated polymerization of butyl methacrylate and ethylene dimethacrylate, was tested for solid-phase extraction (SPE) cleanup of biological samples prior to directly coupled electrospray mass spectrometry (ESI-MS). The chip, fabricated by hot embossing and thermal bonding, consists of eight parallel channels (10 mm long, 360 microm i.d.) connected via external fused-silica capillaries. The monomer mixture was aspirated simultaneously into the eight channels using a homemade vacuum manifold device and polymerized in parallel for 20 min under UV irradiation. The porous monolithic columns were then characterized by scanning electron microscopy and evaluated by ESI-MS applications with respect to sample capacity, recovery, reproducibility of peak area or peak height ratios, and linearity between peak height ratio and concentration using imipramine as a pharmaceutical test compound. The average sample capacity was estimated to be 0.30 microg with a relative standard deviation (RSD) of 26.5% for the eight monolithic columns on the same polymeric chip. For two chips prepared using the same monomer mixture, the difference in average sample capacity was 7.0%. The average recovery for the eight monolithic SPE columns on the same chip was 79.1% with an RSD of 7.9%. Using imipramine-d3 as an internal standard, the RSD of peak height ratios for the eight different columns was 2.0% for a standard solution containing 1 microg/mL imipramine. A linear calibration curve (R2 = 0.9995) was obtained for standard aqueous solutions of imipramine in the range from 0.025 to 10 microg/mL. To demonstrate the analytical potential of the chip-based SPE system, two different types of real-world samples including human urine sample and P450 drug metabolism incubation mixture were tested. Similar to standard aqueous solution, a linear correlation (R2 = 0.9995) was also found for human urine sample spiked with imipramine in the range of 0.025-10 microg/ mL. When aliquots of a human urine sample spiked with 1 microg/mL imipramine were loaded onto eight different monolithic columns, the RSD of peak height ratios was 3.8%. For a P450-imipramine incubation mixture, the formation of the N-demethylated metabolite (m/z 267.2) and the monohydroxylated metabolite (m/z 297.2) of imipramine was observed following chip-based monolithic SPE sample cleanup and preconcentration.

Journal Article↗
PubMed2006

Preparation of an ion-exchange chromatographic support by a "grafting from" strategy based on atom transfer radical polymerization.

A new "grafting from" strategy based on surface-initiated atom transfer radical polymerization (ATRP) was first used for the preparation of a polymer-based ion-exchange support for HPLC. The most important property of the proposed method is to be applicable for the synthesis of any type of ion exchanger in both the strong and the weak forms. Monodisperse, porous poly(glycidyl methacrylate-co-ethylene dimethacrylate), poly(GMA-co-EDM) particles 5.8 mum in size were synthesized by "modified seeded polymerization". Poly(dihydroxypropyl methacrylate-co-ethylene dimethacrylate), poly(DHPM-co-EDM) particles were then obtained by the acidic hydrolysis of poly(GMA-co-EDM) particles. The ATRP initiator, 3-(2-bromoisobutyramido)propyl(triethoxy)silane was covalently attached onto poly(DHPM-co-EDM) particles via the reaction between triethoxysilane and diol groups. In the next stage, the selected monomer carrying strong cation exchanger groups, 3-sulfopropyl methacrylate (SPM), was polymerized on the initiator-immobilized particles via surface-initiated ATRP. The degree of polymerization of SPM (i.e., length of polyionic ligand) on the particles was precisely controlled by adjusting ATRP conditions. Poly(SPM)-grafted poly(DHPM-co-EDM) particles obtained with different ATRP formulations were tried as chromatographic packing in the separation of proteins by ion-exchange chromatography. The proteins were successfully separated with higher column yields with respect to the previously proposed materials. The plate heights between 100 and 150 mum were achieved with the column packed with the particles carrying the shortest poly(SPM) chains. The plate height showed no significant increase with increasing flow rate in the range of 0.5-16 cm/min.

Journal Article↗
PubMed1996

Preparation of silica gel-bonded amylose through enzyme-catalyzed polymerization and chiral recognition ability of its phenylcarbamate derivative in HPLC.

Amylose was prepared by enzymatic polymerization of alpha-D-glucose 1-phosphate dipotassium catalyzed by a phosphorylase using two kinds of the primers derived from maltopentaose, and then it was chemically bonded to silica gel to be used as a chiral stationary phase (CSP) in high-performance liquid chromatography. In method I, maltopentaose was first lactonized and allowed to react with (3-aminopropyl)triethoxysilane to form an amide bond. Amylose chains with a desired chain length and a narrow molecular weight distribution were then constructed by the enzymatic polymerization. The resulting amylose bearing a trialkoxysilyl group at the terminal was allowed to react with silica gel for immobilization. In method II, maltopentaose was first oxidized to form a potassium gluconate at the reducing terminal. After the enzymatic polymerization was performed with the potassium gluconate, the amylose end was lactonized to be immobilized to 3-aminopropyl-silanized silica gel through amide bond formation. Two amylose-conjugated silica gels thus obtained were treated with a large excess of 3,5-dimethylphenyl isocyanate to convert hydroxy groups of amylose to corresponding carbamate residues. The CSP derived through method II was superior in chiral recognition to the CSP derived from method I and showed better resolving power and higher durability against solvents such as tetrahydrofuran compared with a coated-type CSP. Influences of degree of polymerization of amylose, the spacer length between amylose and silica gel, and mobile phase compositions on chiral recognition were investigated.

Amylose↗
PubMed2001

The effect of limited monomer solubility in heterogeneous step-growth polymerization.

Limited monomer solubility imposes very intriguing features on poly(p-phenylenebenzobisoxazole) polymerization. Only one type of functional group is detected at oligomer chain ends, and a high-molecular-weight polymer is obtained even when an excess of the monomer with low solubility is used. These remarkable phenomena are interpreted as an unprecedented "spoon-feeding-of-monomer" mechanism. A novel apparatus for staged polymerization is described that was triggered by the uniqueness of the heterogeneous step-growth polymerization. Hyperbranched polyesters and a polyurethane/polyethylene blend, which represent two phases in the polymerization process, are also discussed.

Journal Article↗