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PubMed1998

Cdc42 is required for membrane dependent actin polymerization in vitro.

In vitro actin based motility assays with bacterial pathogens have provided powerful systems to both understand and dissect actin dynamics as well as cell motility. Taking advantage of endogenous membrane vesicles in Xenopus extracts we have developed an in vitro assay to study membrane dependent actin polymerization. Our results demonstrate that membrane dependent actin polymerization, in contrast to Listeria stimulated actin filament assembly, is dependent on small GTPases of the Rho family. Using a combination of depletion and reconstitution experiments we have shown that Cdc42 but not Rac or Rho is required to stimulate actin polymerization from membranes. The in vitro system we have described here is amenable to identification of the downstream effectors of Cdc42 required for membrane dependent actin polymerization.

Actins↗
PubMed2003

Thermally responsive polymeric micellar nanoparticles self-assembled from cholesteryl end-capped random poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide): synthesis, temperature-sensitivity, and morphologies.

Cholesteryl end-capped thermally responsive amphiphilic polymers with two different hydrophobic/hydrophilic chain-length ratios were synthesized from the hydroxyl-terminated random poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) and cholesteryl chloroformate. The hydroxyl-terminated precursor polymers with narrow molecular weight distributions were synthesized by free-radical polymerization using 2-hydroxyethanethiol as a chain-transfer agent. The aqueous solutions of the cholesteryl end-capped copolymers exhibited reversible phase transitions at temperatures slightly above human body temperature, with the lower critical solution temperature values being 37.7 and 38.2 degrees C, respectively. The critical micelle concentration values of the two cholesteryl end-capped polymers were 9 and 25 mg/L, respectively. Polymeric micellar nanoparticles were prepared from the amphiphilic polymers using a dialysis method as well as a direct dissolution method. Transmission electron microscope studies showed that the micellar nanoparticles existed in different morphologies, including spherical, star-like, and cuboid shapes. Pyrene as a model hydrophobic compound could be readily encapsulated in these polymeric nanoparticles, at loading levels of 1.0 and 0.8 mg/g for the two cholesteryl end-capped polymers, respectively. The temperature sensitivity and unusual morphology of these novel polymeric nanoparticles would make an interesting drug delivery system.

Acrylic Resins↗
PubMed2003

Reducing the negative effects of chemical polishing in acrylic resins by use of an additional cycle of polymerization.

STATEMENT OF PROBLEM: The chemical polishing of dentures and orthodontic appliances is an efficient and time-saving technique. However, the process may adversely affect the physical properties of resin. PURPOSE: This study evaluated the effect of an additional polymerization cycle in a microwave or water bath on the physical properties of an autopolymerized acrylic resin submitted to chemical polishing. MATERIAL AND METHODS: Control groups comprised acrylic resin specimens submitted to mechanical (group 1) and chemical (group 2) polishing. Experimental groups comprised chemically polished specimens submitted to an additional cycle of polymerization in a microwave at 450 W for 3 minutes (group 3) or in a hot water bath at 65 degrees C for 1 hour (group 4). For the residual monomer test, 10 standardized half-disc specimens (30 x 3 mm) were fabricated for each of the test groups, and daily ultraviolet spectrophotometric (206 nm) analyses were assessed for 13 days (microg/cm(2)). For transverse strength and internal Knoop hardness (KH) tests, 10 (65 x 10 x 2.5 mm) and 5 (32 x 10 x 2.5 mm) specimens were fabricated for each test group, respectively. Internal Knoop hardness (kg/mm(2)) was assessed at depths of 100, 700, and 1500 microm. Transverse strength (MPa) was measured with a 3-point bending test in a universal testing machine with a 10-kg load cell at a crosshead speed of 5 mm/min. The data were analyzed with 1-way analysis of variance, and the means were compared with Student's t test and Tukey-Kramer intervals (P<.05). RESULTS: At the end of the first day of the test, all groups showed significantly different residual monomer levels (P<.05). The groups in order of decreasing residual monomer were: group 2 (1315.7 +/- 225.5 microg/cm(2)), group 3 (848.2 +/- 150.4 microg/cm(2)), group 4 (295.1 +/- 81.6 microg/cm(2)), and group 1 (136.6 +/- 45.5 microg/cm(2)). After 13 days of water storage, the lowest residual monomer levels were recorded for group 1 (4.6 +/- 1.6 microg/cm(2)). There were no significant differences among group 2 (11.3 +/- 3.1 microg/cm(2)), group 3 (9.6 +/- 1.5 microg/cm(2)), and group 4 (12.3 +/- 1.7 microg/cm(2)). Group 1 demonstrated the highest transverse strength (78.1 +/- 6.1 MPa); the other groups were not significantly different from each other. All groups exhibited lower KH values at the 100-microm depth than at 700- and 1500-microm depths. At the latter depths, group 4 specimens demonstrated the highest hardness values (18.0 +/- 0.5 and 18.8 +/- 0.7 kg/mm(2), respectively). CONCLUSION: Within the limitations of this study, additional polymerization with hot water reduced residual monomer content of chemically polished acrylic resins on the first day. Although additional polymerization increased the internal hardness of the material, however, it did not recover the transverse strength that was decreased by the chemical polishing.

Acrylic Resins↗
PubMed1997

Molecular characterization, antigenicity and immunogenicity of anatoxic polymeric forms conferring protection against scorpion venoms.

Two polymeric forms of Buthus occitamus tunetanus (Bot) G-50 and Androctonus australis hector (Aah) G-50 were obtained by controlled polymerization with glutaraldehyde. Their mol. wts, determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and exclusion high-performance liquid chromatography using radiolabelled toxin, ranged from 14,000 to 90,000 and 90,000 to 100,000 for Aah G-50 and Bot G-50, respectively. Modification of about 20% of the lysine residues yielded completely detoxified Bot G-50 fractions which retained the antigenic cross-reactivity with the native G-50 fraction, venom and toxins. High levels of specific antibodies against venoms and toxins were generated by immunization with prepared polymeric forms because absorbance values higher than 3 units were regularly observed by enzyme-linked immunosorbent assay with immune sera dilutions of 1/10,000. In vitro protection experiments demonstrated that immune sera from mice, horse and monkeys efficiently neutralized either Aah or Bot venom. Depending on the adjuvant and animal model species used, the neutralizing titre estimated by subcutaneous injection in mice varied between 20 and 40 LD50/ml. The in vivo protection assays showed that immunized mice could resist the challenge by six times the LD50 amounts of the toxic fraction. This protection was found to be long-lived. It was concluded that G-50 polymeric forms are highly detoxified and immunogenic, and should be useful for the production of potent polyvalent antivenom against scorpion toxins. They could also be considered for further studies towards the development of vaccine candidates.

Animals↗
PubMed2001

Primary cyclization in the polymerization of bis-GMA and TEGDMA: a modeling approach to understanding the cure of dental resins.

An optimal dental restorative polymeric material would have a homogeneous cross-linking density giving it consistent mechanical strength throughout the material. When multifunctional monomers are polymerized, a pendant double bond can react intramolecularly with the radical on its propagating chain to form a loop, which results in a primary cyclization reaction. Primary cyclization does not contribute to overall network structure, causes microgel formation, and leads to heterogeneity in the polymer. Knowledge of how cure conditions control the degree of primary cyclization and cross-linking in the polymer is important in developing better dental materials. To gain more understanding about the evolving polymer network, the photopolymerization of a typical dental resin (75/25 wt% bis-GMA/TEGDMA) is modeled using a first principals approach. The overall polymerization rate behavior of 75/25 wt% bis-GMA/TEGDMA is predicted using experimentally obtained propagation and termination kinetic rate constants. The effect of chain stiffness and light intensity on the polymerization kinetics is also explored. Furthermore, the model predicts the extent of cross-linking and primary cyclization in the growing polymer network. At 45% conversion, the fraction of bis-GMA and TEGDMA pendant double bonds created that have cycled is 11 and 33%, respectively. The model shows that using a stiff monomer, like bis-GMA, in dental resins diminishes the extent of cyclization and increases the cross-linking density of the polymer. Therefore, better mechanical properties are obtained than if more flexible monomers were used.

Algorithms↗
PubMed2002

Polymerization shrinkage-strain and microleakage in dentin-bordered cavities of chemically and light-cured restorative materials.

OBJECTIVES: The aim of this study was to evaluate in vitro the relationship between polymerization shrinkage and microleakage in dentin-bordered restorations. METHODS: Four light-cured restorative materials in combination with their respective dental bonding agents (DBA) were investigated: Tetric Ceram/Syntac classic (Vivadent), Solitaire/Gluma Solid bond (Heraeus Kulzer), Definite/Etch & Prime 3.0 (Degussa), Solitaire 2/Gluma Solid bond (Heraeus Kulzer). The chemically cured resin Degufill sc microhybrid (Degussa) in combination with ART Bond (Coltène) was also included. Polymerization shrinkage of the restorative materials was measured using three different methods (dilatometer, linometer, buoyancy method) and analyzed with ANOVA. For the determination of microleakage, caries-free human molars were embedded in acrylic resin and subsequently abraded with a wet abrasion machine to produce four level dentin surfaces. One hundred sixty cavities (3 mm diameter/1.5 mm deep) were randomly assigned to four groups of equal size. The groups were restored without (group 1 and 2) and with DBA (group 3 and 4), and either not subjected (group 1 and 3) or subjected (group 2 and 4) to 2000 cycles from 5-55 degrees C. Each group was further divided into five material subgroups of eight cavities each. Microleakage was determined using a dye penetration test assessed at depths of 200, 400 and 600 microm into the fillings. Data were analyzed with the Kruskal-Wallis and the Mann-Whitney test. RESULTS: All three methods of measuring polymerization shrinkage (PS) generated the same, statistically secured ranking for the four light-cured restorative materials: PS Definite < PS Tetric Ceram < PS Solitaire 2 < PS Solitaire. In the microleakage study, only a few statistically significant differences were observed. Etch & Prime 3.0/Definite in group 3 and Solid Bond/Solitaire 2 in group 4 tended to exhibit the least microleakage. Correlation coefficients between aggregated shrinkage and microleakage data were 0.3 for group 3 and -0.2 for group 4. SIGNIFICANCE: The results do not suggest any correlation between polymerization shrinkage and microleakage in dentin of direct adhesive restorations.

Analysis of Variance↗
PubMed2004

Polymerization shrinkage: effects of constraint and filling technique in composite restorations.

OBJECTIVES: To evaluate the linear polymerization shrinkage (LPS) and its effect upon mean gap width, bond strength and cohesive strength of a composite placed under different constraints (C-factors--CF) and filling techniques. METHODS: Composite was placed in cavities sized 4 x 4 x 2 mm3 (CF = 3) or on flat dentin surfaces (CF = 0.3) of bovine incisors, after adhesive application. They were inserted in one or three increments, and light cured (600 mW/cm2) for 80 s. The LPS was measured by placing a probe on the top surface of the composite in order to measure its dislodgment in the top-bottom direction. Half of the sample was sectioned to obtain composite resin sticks subjecting them to tensile forces at 0.5 mm/min. The other half of the sample was sectioned and the mean gap width was measured in both sides of the sections. Then the sections were sliced again to obtain composite/dentin sticks. The mean gap width in the sticks was performed before subjecting them to tensile forces at 0.5 mm/min. Data was analyzed by a two-way ANOVA and the correlation between the bond strength and gap width was analyzed by simple linear regression. RESULTS: (1) Linear polymerization shrinkage: significant differences were observed for the interaction (p < 0.05). Under the low constraint, the LPS were similar for both filling techniques. Under higher constraint, polymerization shrinkage was lower for the incremental technique. (2) Gap width and bond strength: no difference was detected either for interaction, or for technique (p > 0.05). Under higher constraint, the gap width was higher and the bond strength lower. (3) The cohesive strength of composite resin was similar for all groups (p > 0.05). No correlation between bond strength and gap width was found (p = 0.17). SIGNIFICANCE: The effects of polymerization shrinkage were not reduced by the filling technique under the different cavity constraints tested.

Analysis of Variance↗
PubMed1996

Polymeric calcium phosphate cements derived from poly(methyl vinyl ether-maleic acid).

OBJECTIVES: The purpose of this study was to assess the feasibility of forming polymeric calcium phosphate cements from a mixed powder of dicalcium phosphate/tetracalcium phosphate or only tetracalcium phosphate and poly(methyl vinyl ether-maleic acid) (PMVE-Ma), and to study their setting reaction. METHODS: The setting reaction process of the polymeric cements was evaluated by mechanical strength tests, infrared spectroscopy and x-ray diffraction analysis and compared with that of a water-setting calcium phosphate cement. The mechanical strength data were analyzed using ANOVA and Scheffé's multiple comparisons test. RESULTS: Cements prepared from the mixed powder and 25-30 wt% aqueous solutions of PMVE-Ma had high mechanical strength after 24 h storage in distilled water at 37 degrees C. The hardening mechanism depended on an acid-base reaction between the carboxyl groups of PMVE-Ma and the mixed powder, especially its tetracalcium phosphate component. The formation of hydroxyapatite in the polymeric calcium phosphate cement was not detected and is apparently inhibited as a result of the competing reaction of PMVE-Ma with the mixed powder. SIGNIFICANCE: The cement-forming reaction was significantly faster than that of a water-setting calcium phosphate cement and slower than that observed with the mixed powder and polyacids such as poly(acrylic acid). The characteristics of the polymeric cements suggest that the materials may be useful in cavity lining or endodontic sealing.

Analysis of Variance↗
PubMedDate not supplied

Ring-opening bulk polymerization of epsilon-caprolactone and trimethylene carbonate catalyzed by lipase Novozym 435.

The affects of lipase concentration on ring-opening bulk polymerizations of epsilon-caprolactone and trimethylene carbonate were studied by using Novozym 435 (immobilized form of lipase B from Candida antarctica) as biocatalyst. The polymerization of epsilon-caprolactone was carried out in bulk at 70 degrees C. Three lipase concentrations of 9.77, 1.80 and 0.50 mg/mmol epsilon-CL were used in the experiment. The results showed that increasing the lipase concentration used in the polymerization system resulted in an increased rate of monomer consumption. For an enzyme concentration of 9.8 mg lipase per mmol monomer, an 80% monomer conversion was achieved in a 4-h time period, while for the lower enzyme concentration of 1.8 mg lipase per mmol monomer, 48 h were needed to reach monomer conversion. Linear relationships between Mn and monomer conversions were observed in all three enzyme concentrations, suggesting that the product molecular weight may be controlled by the stoichiometry of the reactants for these systems. At the same monomer conversion level, however, Mn decreased with increasing enzyme concentration. After correcting for the amount of monomer consumed in initiation, the plot of ln[([M]o - [M]i)/([Mt] - [M]i)] versus reaction time was found to be linear, suggesting that the monomer consumption followed a first-order rate law and no chain termination occurred. For the TMC systems, the polymerization was carried out in bulk at 55 degrees C. Similar to the epsilon-CL systems, increasing the Novozym 435 concentration from 8.3 to 23.6 mg/mmol TMC increased the rate of monomer conversion. Unlike the epsilon-CL systems, however, nonlinear relationships were obtained between Mn and monomer conversion, indicating that possible chain transfer and/or slow initiation had taken place in these systems. Consistent with the above result, nonlinear behavior was observed for the plot of ln[[M]o/[M]t] versus reaction time.

Candida↗
PubMed2004

Characterization and protein-adsorption behavior of deposited organic thin film onto titanium by plasma polymerization with hexamethyldisiloxane.

Plasma polymerized hexamethyldisiloxane (HMDSO) thin film was deposited onto titanium using a radio-frequency apparatus for the surface modification of titanium. A titanium disk was first polished using colloidal silica at pH=9.8. Plasma-polymerized HMDSO films were firmly attached to the titanium by heating the titanium to a temperature of approximately 250 degrees C. The thickness of the deposited film was 0.07-0.35mum after 10-60min of plasma polymerization. The contact angle with respect to double distilled water significantly increased after HMDSO coating. X-ray photoelectron spectroscopy revealed that the deposited thin film consisted of Si, C, and O atoms. No Ti peaks were observed on the deposited surface. The deposited HMDSO film was stable during 2-weeks immersion in phosphate buffer saline solution. Fourier transform reflection-absorption spectroscopy showed the formation of Si-H, Si-C, C-H, and Cz.dbnd6;O bonds in addition to Si-O-Si bonds. Quartz crystal microbalance-dissipation measurement demonstrated that the deposition of HMDSO thin films on titanium has a benefit for fibronectin adsorption at the early stage. In conclusion, plasma polymerization is a promising technique for the surface modification of titanium. HMDSO-coated titanium has potential application as a dental implant material.

Adsorption↗
PubMed2004

Catalytic generation of nitric oxide from nitrite at the interface of polymeric films doped with lipophilic CuII-complex: a potential route to the preparation of thromboresistant coatings.

A novel approach potentially useful for the development of more thromboresistant polymeric materials is examined. The method is based on the catalytic generation of nitric oxide (NO) via Cu(I) mediated reduction of nitrite ions. Preliminary solution phase studies demonstrate that ascorbate or thiolate anions can generate Cu(I) from Cu(II) with subsequent catalytic conversion of any nitrite ions present to NO by the unstable Cu(I) species. Incorporation of this same chemistry within a hydrophobic polymeric material requires immobilizing Cu(II) ions into a polymeric phase via use of a lipophilic Cu(II) chelating ligand (dibenzo [e,k]-2,3,8,9-tetraphenyl-1,4,7,10-tetraaza-cyclododeca-1,3,7,9-tetraene (DTTCT)). It is shown that this complex can be reduced to its Cu(I) form by appropriate reducing equivalents present in the bathing solution. The resulting Cu(I) complex can then reduce nitrite to NO with the NO generation occurring at the polymer/solution interface at physiological pH. Data from chemiluminescence experiments indicate that the flux of NO at the polymer surface is comparable to that of endothelial cells (>/=1x10(-10)mol/cm(2)min) when 0.5mM nitrite/1mM ascorbate are present in the bathing solution. Potentially more useful NO generation can be achieved by doping the polymer film with the Cu(II) complex along with a lipophilic quaternary ammonium nitrite salt. In this case reducing equivalents within the aqueous phase enable the nitrite derived from the polymer to be converted into NO by the Cu(II/I) ligand complex. Films of this type are shown to generate NO for at least 6h in PBS buffer with fluxes on the order of 1.5x10(-10)mol/cm(2)min. Physiologically relevant levels of NO release are also shown to exist at the polymer interface when films are soaked in fresh plasma as well as undiluted whole blood, indicating that endogenous reducing equivalents present in blood can efficiently reduce the Cu(II)-ligand within the polymer film. The prospects of using these new NO releasing films to devise more biocompatible polymeric coatings for biomedical applications are discussed.

Ascorbic Acid↗
PubMed1997

Polymerization of acrylic bone cement using differential scanning calorimetry.

The polymerization of acrylic bone cement using differential scanning calorimetry (DSC) was investigated. The polymerization reaction of the acrylic bone cement was found to be an approximately first order reaction. Two kinds of reaction rate constants for the polymerization reaction were observed. Both rate constants were calculated before and after the peak time. The effects of the addition of tricalcium phosphate (TCP) on the polymerization reaction of standard Surgical Simplex-P Radiopaque Bone Cement have been investigated by DSC. The TCP content had a strong retardation effect on the rate constants. The thermal stability of the acrylic bone cement was also studied by thermogravimetric analysis.

Acrylates↗
PubMed1998

Actin-binding proteins of invasive malaria parasites and the regulation of actin polymerization by a complex of 32/34-kDa proteins associated with heat shock protein 70kDa.

Movement of the malaria parasite into a host erythrocyte during invasion is thought to involve polymerization of parasite actin. We have used F-actin affinity chromatography to isolate actin-binding proteins from Plasmodium knowlesi merozoites, in an attempt to identify proteins responsible for regulating parasite actin polymerization during invasion. Five major proteins, of molecular masses 75, 70, 48, 40 and 34 kDa, were reproducibly eluted from the F-actin columns. The 70 kDa actin-binding protein was identified by tryptic peptide microsequencing as heat shock protein-70 kDa (HSC70); this identification was confirmed by Western blotting with anti-HSC70 antibody, and binding of the protein to ATP-agarose. A doublet of 32/34-kDa proteins coeluted with parasite HSC70 from the F-actin and ATP-agarose columns; a complex of these three proteins was also observed by gel filtration chromatography Highly enriched fractions containing the Plasmodium HSC70/32/34 complex inhibited the polymerization of rabbit skeletal muscle actin, in vitro. This capping activity was calcium-independent, and abrogated by phosphatidylinositol 4,5-bisphosphate. The average length of the actin filaments polymerized in presence of the HSC70/32/34-kDa complex was significantly shorter than in the absence of the complex, consistent with a capping activity. The capping or uncapping of actin filament ends by the HSC70/32/34-kDa complex during invasion could provide a mechanism for localized actin filament growth and movement of the parasite into the host cell.

Actins↗
PubMed2001

Preparation of controlled release systems by free-radical UV polymerizations in the presence of a drug.

UV free-radical polymerization techniques are often used to synthesize hydrogels for controlled release applications. Numerous techniques exist for immobilizing drugs or solutes in the gel. This work focuses on the entrapment of solute in a hydrogel by conducting a photopolymerization in the presence of the monomer and the solute. A kinetic gelation model has been developed to examine the effect of the solute material on the polymerization process and the ensuing network structure. Kinetic experiments have also been conducted of the polymerization of poly(ethylene glycol) methacrylate in the presence of theophylline. It was found that the presence of the solute led to a more heterogeneous network with numerous microgel regions present. The effect of the size of the solute on the polymerization was also investigated.

Delayed-Action Preparations↗
PubMed2001

N-isopropylacrylamide copolymers for the preparation of pH-sensitive liposomes and polymeric micelles.

Hydrophobically-modified copolymers of N-isopropylacrylamide bearing a pH-sensitive moiety were investigated for the preparation of pH-responsive liposomes and polymeric micelles. The copolymers having the hydrophobic anchor randomly distributed within the polymeric chain were found to more efficiently destabilize egg phosphatidylcholine (EPC)/cholesterol liposomes than the alkyl terminated polymers. Release of both a highly-water soluble fluorescent contents marker, pyranine, and an amphipathic cytotoxic anti-cancer drug, doxorubicin, from copolymer-modified liposomes was shown to be dependent on pH, the concentration of copolymer, the presence of other polymers such as polyethylene glycol, and the method of preparation. Both polymers were able to partially stabilize EPC liposomes in human serum. These polymers were found to self-assemble to form micelles. The critical association concentration was low (9--34 mg/l) and influenced by the position of the alkyl chains. In phosphate buffered saline, the micelles had a bimodal size distribution with the predominant population having a mean diameter of 35 nm. The polymeric micelles were studied as a delivery system for the photosensitizer aluminum chloride phthalocyanine, (AlClPc), currently evaluated in photodynamic therapy. pH-Responsive polymeric micelles loaded with AlClPc were found to exhibit increased cytotoxicity against EMT-6 mouse mammary cells in vitro than the control Cremophor EL formulation.

Acrylamides↗
PubMed2001

Structure and design of polymeric surfactant-based drug delivery systems.

The review concentrates on the use of polymeric micelles as pharmaceutical carriers. Micellization of biologically active substances is a general phenomenon that increases the bioavailability of lipophilic drugs and nutrients. Currently used low-molecular-weight pharmaceutical surfactants have low toxicity and high solubilization power towards poorly soluble pharmaceuticals. However, micelles made of such surfactants usually have relatively high critical micelle concentration (CMC) and are unstable upon strong dilution (for example, with the blood volume upon intravenous administration). On the other hand, amphiphilic block co-polymers are also known to form spherical micelles in solution. These micelles have very high solubilization capacity and rather low CMC value that makes them very stable in vivo. Amphiphilic block co-polymers suitable for micelle preparation are described and various types of polymeric micelles are considered as well as mechanisms of their formation, factors influencing their stability and disintegration, their loading capacity towards various poorly soluble pharmaceuticals, and their therapeutic potential. The basic mechanisms underlying micelle longevity and steric protection in vivo are considered with a special emphasis on long circulating drug delivery systems. Advantages and disadvantages of micelles when compared with other drug delivery systems are considered. New polymer-lipid amphiphilic compounds such as diacyillipid-polyethylene glycol, are described and discussed. These compounds are very attractive from a practical point of view, since they easily micellize yielding extremely stable micelles with very high loading capacity. Micelle passive accumulation in the areas with leaky vasculature (tumors, infarct zones) is discussed as an important physiology-based mechanism of drug delivery into certain target zones. Targeted polymeric micelles prepared by using thermo- or pH-sensitive components or by attaching specific targeted moieties (such as antibodies) to their outer surface are described as well as their preparation and some in vivo properties. The fast growing field of diagnostic micelles is analyzed. Polymeric micelles are considered loaded with various agents for gamma, magnetic resonance, and computed tomography imaging. Their in vitro and in vivo properties are discussed and the results of the initial animal experiments are presented.

Dequalinium↗
PubMed1999

Incorporation of polymeric nanoparticles into solid dosage forms.

Besides parenteral delivery, polymeric nanoparticles have been used for oral drug delivery. In this study, model polymeric nanoparticles (aqueous colloidal polymer dispersions: Eudragit(R) RL 30D, L 30D, NE 30D, or Aquacoat(R)) with different physicochemical properties were incorporated into various solid dosage forms (granules, tablets, pellets or films). The compatibility of the nanoparticles with commonly used tabletting excipients and the redispersibility of the nanoparticles after contact of the solid dosage forms with aqueous media were investigated. Ideally, the nanoparticles should be released from the solid dosage forms with their original properties. The addition of polymeric binders (e.g. polyvinylpyrrolidone, Na carboxymethylcellulose or hydroxypropyl methylcellulose) to the aqueous nanoparticle dispersions prior to wet granulation resulted in phase separation (depletion or bridging flocculation) for many nanoparticle/binder systems. Two critical parameters for the complete redispersibility/release of the nanoparticles with the original particle size properties from the solid dosage forms were a (1) high minimum film formation temperature (MFT) of the polymer dispersion and (2) a good wettability of the dried polymeric nanoparticles. Nanoparticle dispersions with a low MFT were not redispersible, they coalesced into larger agglomerates/films during the drying step. Contact angle measurements correlated well with the redispersibility of the nanoparticles, with ethylcellulose particles having high contact angles and poor redispersibility and Eudragit(R) RL, a polymer stabilized with quaternary ammonium groups, having low contact angles and good redispersibility.

Acrylic Resins↗
PubMed1999

Thermodynamic prediction of active ingredient loading in polymeric microparticles.

The growing use of microparticles as a controlled-delivery system for pharmaceutical and non-pharmaceutical active ingredients (AIs) has prompted a costly trial-and-error development of new and effective microparticle systems. In order to facilitate a more rational design and optimization of AI loadings in microparticles, we have developed a molecular-thermodynamic theory to predict the loading of liquid AIs in polymeric microparticles that are manufactured by a solvent evaporation process. This process involves the emulsification of a liquid polymer solution (consisting of polymer and AI dissolved in a volatile solvent) in an aqueous surfactant solution. The theory describes the equilibrium distribution of the AI between the aqueous phase and the dispersed polymeric droplets. The universal functional activity coefficient (UNIFAC) and UNIFAC-Free Volume (FV) group-contribution methods are utilized to model the nonidealities in the water and polymeric droplet phases, respectively. The inputs to the theory are: (i) the chemical structures, densities and total masses of the manufacturing ingredients, (ii) the manufacturing temperature and (iii) the glass transition temperature of the polymer. Since surfactant concentrations exceeding the critical micellar concentration (CMC) are often required in order to stabilize the dispersed polymeric droplets during the emulsion manufacturing process, the theory also accounts for AI solubilization in surfactant micelles present in the manufacturing solution. To test the AI loading predictions, we compare theoretical predictions of AI loadings in poly(lactic acid), poly(methyl methacrylate) and polystyrene microparticles to experimentally measured ones for five model AIs with varying degrees of hydrophobicity (benzyl alcohol, n-octanol, geraniol, farnesol and galaxolide). We also demonstrate how the developed theory can be utilized to screen polymers with respect to their abilities to load a given AI, as well as to provide guidelines for manufacturing microparticles having the desired AI loading.

Drug Delivery Systems↗