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PubMed1996

A comparison of elastic moduli derived from theory, microindentation, and ultrasonic testing.

PURPOSE: The objective of our work was to evaluate the elastic modulus through ultrasonic testing of poly(methyl methacrylate-co-methacrylic acid) (PMMA/coMAA), a viscoelastic polymer similar to the commercial Eudragit, to calculate this modulus, assuming a regular arrangement of interacting groups, and ultimately, assess the accuracy of microindentation as a means of evaluating elasticity in very small samples. METHODS: Knoop indentation testing was performed on cast samples using a Tukon testing apparatus. Solid density and pulse echo testing employing a damped 15 MHz transducer served to quantify the elastic moduli. Using the Hoy method of calculation for molar attraction constants, and assuming pairwise addition, the modulus was calculated and compared with typical experimental values for amorphous and crystalline polymers. RESULTS: Acoustic testing resulted in an average elastic modulus value of 5.67 +/- 0.2 GPa for this copolymer, which concurs with literature values for PMMA. Acoustically derived experimental moduli when normalized and plotted against calculated values, resulted in a relationship, E/(1 - 2v) = 17.0 (Ecoh + xc delta Hm)/V + 6.9, similar to that predicted in theory. CONCLUSIONS: Indentation contact modeling does not adequately describe the real recovery under indentation. In contrast, acoustic testing of pharmaceutical materials affords a simple, reproducible means of characterizing moduli without impairing structural integrity. Acoustically derived moduli further afford insight into the intermolecular interactions, as expressed by the interaction energy terms.

Chemistry, Pharmaceutical↗
PubMed2004

Physicochemical parameters associated with nanoparticle formation in the salting-out, emulsification-diffusion, and nanoprecipitation methods.

PURPOSE: The aim of this work was to relate the physicochemical properties of the aqueous and organic phases used for nanoparticle (NP) preparation to the formation of NP produced by salting-out, emulsification-diffusion, and nanoprecipitation. METHODS: Methacrylic acid copolymer and poly(vinyl alcohol) (PVAL) were selected as NP polymer and emulsifying agent, respectively. Salting-out and emulsification-diffusion NP batches were prepared modifying the PVAL content in the aqueous phase. For nanoprecipitation, NP were produced with variation of the polymer content and type of solvent in the organic phase. RESULTS: For salting-out and emulsification-diffusion, NP formation was discussed in terms of the emulsification theory. The nanoemulsion obtained during NP preparation was visualized by scanning electron microscopy. Aqueous and organic phases used for NP preparation were characterized by their viscosity and surface tension. NP characteristics such as particle mean size, residual surfactant, suspendability in water after freeze-drying, and morphology were explained in terms of these properties. For nanoprecipitation, NP formation was analyzed considering the diffusion-stranding phenomenon. CONCLUSIONS: NP formation by salting-out and emulsification-diffusion was related to PVAL chain interactions at the droplet interface (e.g., reduction in the interfacial tension, mechanical stabilization, and steric stabilization) and in the bulk solution (hydrodynamic stabilization). For nanoprecipitation, chi(solvent-water) and delta(delta solvent-water) of the organic phase solvents were well related to the NP characteristics.

Diffusion↗
PubMed2006

Photoinitiation chemistry affects light transmission and degree of conversion of curing experimental dental resin composites.

INTRODUCTION: The effect of photoinitiator and co-initiator chemistry on the setting reaction and degree of conversion of dental resin-based composites (RBCs) has rarely been determined explicitly. This work examines the effect of type and concentration of photoinitiator and co-initiator on the rate of change of light transmission throughout polymerisation and degree of conversion of model RBC formulations. METHODS: Bisphenol-A diglycidyl ether dimethacrylate (bis-GMA) and triethylene glycol dimethacrylate (TEGDMA) (6:4 molar ratio) resins filled with silanized glass filler (74wt.%) and containing various photoinitiators (camphorquinone; CQ, 1-phenyl-1,2-propanedione; PPD, benzil; BZ), co-initiator types (N,N-dimethyl-p-amino benzoic acid ethyl ester; DABE, N,N-cyanoethyl methylaniline; CEMA, N,N-diethanol-p-toluidine; DEPT) and concentration (0.0-0.3% DABE) were polymerised using a halogen or LED light curing-unit (LCU) for 10, 20 and 40s. The setting reaction was monitored in real-time by measuring the light transmittance through the curing specimen and bulk degree of conversion (DC) evaluated using Fourier transform infra-red spectroscopy. RESULTS: Specimens containing CQ and PPD cured with the halogen LCU did not have a significant effect on DC or changes in light transmission, although a significant increase in DC was observed for CQ compared with PPD specimens cured with the LED LCU. DABE and CEMA were more effective co-initiators than DEPT. Although DC was not limited by co-initiator concentration, the absence of a co-initiator resulted in marked differences in light transmission and decreased DC throughout 40s irradiation with each LCU type. CONCLUSIONS: The spectral range emitted from different types of LCU and absorption characteristics of the photoinitiator chemistry of light-activated resin-based composites play a critical role in the efficiency of polymerisation.

Analysis of Variance↗
PubMed2006

Sodium pantoprazole-loaded enteric microparticles prepared by spray drying: effect of the scale of production and process validation.

Pantoprazole is a prodrug used in the treatment of acid related disorders and Helicobacter pylori infections. It is activated inside gastric parietal cells binding irreversibly to the H(+)/K(+)-ATPase. In this way, pantoprazole must be absorbed intact in the intestinal tract, which indicates that enteric drug delivery systems are required for its oral administration. The purpose of this study was to investigate the physical characteristics of enteric pantoprazole-loaded microparticles prepared by spray drying using a blend of Eudragit S100 and HPMC. The microparticles were produced in different spray dryers and operational conditions at laboratory and pilot scales. Microparticles produced with two fluid nozzle atomizer and air pressure of 196 kPa presented satisfactory encapsulation efficiency and gastro-resistance. Microparticles produced with the same atomizer but using 49 kPa of air pressure presented strings in the powder. The microparticles produced in mixed flow presented very high polydispersity and the ones produced with rotating disc atomizer presented drug crystals adsorbed on the particle surfaces. The microparticles produced with two fluid nozzle atomizer and 196 kPa were prepared in three consecutive days for the process validation. The powders showed reproducible diameter, polydispersity, densities, encapsulation efficiency and gastro-resistance profile.

2-Pyridinylmethylsulfinylbenzimidazoles↗
PubMedDate not supplied

Effect of preliminary treatment of the dentin surface on the shear bond strength of resin composite to dentin.

This study evaluated the effect of two dentin disinfectants (Consepsis, Tubulicid), one aqueous HEMA solution (Aqua Prep), a combination of Aqua Prep and Tubulicid and an air abrasion treatment (50 microns aluminum oxide) on the shear bond strength (SBS) of two acetone-based single bottle adhesives (One Step and Prime & Bond 2.1). The occlusal surfaces of 167 freshly extracted human third molars were ground flat to expose the dentin, then polished with a 600 grit-polishing disc. The teeth were randomly assigned to 12 test groups (two bonding agents, six pretreatment protocols). The exposed dentin was etched with 35% phosphoric acid for 20 seconds, rinsed and briefly (1-2 seconds) air dried. Six pretreatment protocols were then applied. The air abrasion groups were exceptional, as etching was carried out only after pretreatment. One Step, or Prime & Bond 2.1 was applied according to the manufacturer's instructions. Cylinders of Z-100 composite were bonded to the flat dentin surfaces by transparent gelatin capsules. Specimens were thermocycled in water baths between 5 degrees and 55 degrees C, then sheared in an Instron Testing Machine. One-way and two-way ANOVA and Tukey HSD post-hoc tests were used for statistical analysis. In the One Step group, Consepsis yielded a significantly higher SBS (17.8 MPa) than air abrasion (9.5 MPa), Control (11.8 MPa) and Aqua Prep + Tubilicid (11.9 MPa), and a comparable SBS with Tubilicid (12.5 MPa) and Aqua Prep (14.8 MPa). In the Prime & Bond 2.1 group, Aqua Prep (24.9 MPa) showed a significantly higher SBS than all other groups: air abrasion (9.3 MPa), Control (9.97 MPa), Tubilicid (12.2 MPa), Consepsis (13.0 MPa) and Tubilicid + Aqua Prep (13.3 MPa).

Acetone↗
PubMed1996

Water, solute and protein diffusion in physiologically responsive hydrogels of poly (methacrylic acid-g-ethylene glycol).

Grafted poly (methacrylic acid-g-ethylene glycol) [P(MAA-g-EG)] copolymers were synthesized and their pH sensitivity was investigated. P(MAA-g-EG) membranes showed pH sensitivity due to complex formation and dissociation. Uncomplexed equilibrium swelling ratios were 40 to 90 times higher than those of the complexed states and varied according to copolymer composition and poly(ethylene glycol) (PEG) graft length. Mesh sizes in the two states were determined. Swelling under oscillatory pH conditions revealed the dynamic sensitivity of P(MAA-g-EG) membranes as well as the diffusional mechanisms causing network expansion and collapse. Network collapse (complexation) occurred more rapidly than network expansion (decomplexation). A Boltzmann superposition model was used to analyse this behaviour. Mechanical testing was used to evaluate the strength of P(MAA-g-EG) membranes and to elucidate the mesh size under various conditions. Solute diffusion coefficients were higher in uncomplexed than in complexed P(MAA-g-EG) membranes and decreased as solute size increased. Lower diffusion coefficients were observed with membranes or hydrogels containing longer PEG grafts, since in the uncomplexed state the PEG grafts dangled into the polymer mesh space. Membrane permeability was responsive to changing pH conditions, and separation of solutes was achieved.

Chemical Phenomena↗
PubMed2003

Effect of polyacid aqueous solutions on photocuring of polymerizable components of resin-modified glass ionomer cements.

OBJECTIVES: Resin-modified glass ionomer cements (RMGI) are hybrid materials prepared by incorporation of polymerizable components (typically 2-hydroxyethyl methacrylate (HEMA) with possible addition of multifunctional methacrylates) into a conventional acid-base mixture (a polymeric acid with powdered calcium fluoro-aluminosilicate glasses). During setting, the photopolymerization process and the acid-base reaction affect each other. The aim of this work was to examine the effect of a 45% aqueous solution of poly(acrylic acid) (PAA) and the liquid component of a commercial glass ionomer cement on HEMA and triethyleneglycol dimethacrylate (TEGDMA) photopolymerization. METHODS: The polymerization was initiated by 2,2-dimethoxy-2-phenylacetophenone (DMPA) and camphorquinone (CQ)/coinitiator system. The reaction course was monitored under Ar and air by isothermal differential scanning calorimetry. RESULTS: The main effect of addition of polyacid solution (PAA and commercial) up to 10wt% to HEMA on the polymerization initiated with DMPA was earlier onset of autoacceleration. For the process initiated by the CQ-based system, the addition of 5wt% of PAA solution strongly accelerated the polymerization and increased the conversion, both in Ar atmosphere as well as in air. TEGDMA photopolymerization was not influenced or slightly retarded by the presence of 3wt% of PAA solution (the upper limit of solubility), depending on the initiating system used. SIGNIFICANCE: Under initiation conditions used in curing of commercial dental products (CQ-based two component initiating system), the presence of polyacid-aqueous solution in HEMA-based photocurable component increases markedly the polymerization rate and the conversion both in Ar atmosphere as well as in air. This result contributes to a characterization of the setting process of RMGIs.

Acrylic Resins↗
PubMed2000

A novel route to poly(epsilon-caprolactone)-based copolymers via anionic derivatization.

Poly(epsilon-caprolactone) (PCL) is known to biodegrade under composting or water sewage plant conditions. However, as compared with poly(alpha-hydroxy acids) derived from lactic and glycolic acids, PCL is much more resistant to chemical hydrolysis and is achiral, a feature that limits very much the possibility of property modulation through the configurational structure of polymer chains. For the sake of enlarging the family of PCL-type polymers, a novel method is proposed which is based on the anionic activation of PCL chain by the removal of a proton from the methylene group in alpha-position of the ester carbonyl present in the main chain, using a nonnucleophilic base such as lithium diisopropyl amide (LDA). This activation leads to a polycarbanion onto which various electrophile groups can be attached. The feasibility of the process was first shown on poly(methyl acrylate), (PMA), whose polyacrylic main chain is resistant to strong bases. The PMA polycarbanion was modified by various electrophiles, namely benzaldehyde, naphthoyl chloride, benzyl chloroformate, and iodomethane. In a second stage, the same reactions were performed successfully on PCL. The degree of substitution depended on the experimental conditions. PCL underwent main chain degradation during the formation of the polycarbanion whereas the reaction with the electrophiles did not cause any further main chain cleavages. The degradation of PCL chains can be limited enough to give access to novel functional PCL polymers.

Algorithms↗
PubMed2006

Molecular properties of flurbiprofen and its solid dispersions with Eudragit RL100 studied by high- and low-resolution solid-state nuclear magnetic resonance.

PURPOSE: Investigation of the conformational and molecular dynamic properties of the acidic and sodium salt forms of Flurbiprofen and their solid dispersions with Eudragit RL100, obtained by two different preparation methods (physical mixtures and coevaporates), and of the mixing degree between the two components in the dispersions. MATERIALS AND METHODS: 1H and 13C high-resolution solid state NMR techniques, including Single Pulse Excitation-MAS, CP-MAS, FSLG-HETCOR; low-resolution 1H FID analysis; 1H spin-lattice relaxation time measurements. RESULTS: Conformational, molecular packing and dynamic differences were observed between the two pure forms of flurbiprofen, as well as between the pure drugs and the corresponding coevaporates. In the coevaporates of the two flurbiprofen forms, drug and polymer appear intimately mixed; their chemical interactions were detected and characterized. CONCLUSIONS: A combined analysis of several 13C and 1H high- and low-resolution solid state NMR experiments allowed the investigation of the conformational and dynamic properties of the pure drugs and of the solid dispersions with the polymer, as well as of the degree of mixing between drug and polymer and of the chemical nature of their interaction. Such information could be compared to the in vitro drug release profiles given by these solid dispersions.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2003

Release of antimicrobial peptide Dhvar-5 from polymethylmethacrylate beads.

Osteomyelitis is still a major cause of morbidity and remains a difficult complication to treat in orthopaedic surgery. The treatment of choice is a combination of systemic and local antibiotics. The insertion of gentamicin-loaded polymethylmethacrylate (PMMA) beads into the bone results in high local concentrations of gentamicin and low systemic concentrations. However, the effectiveness of this treatment is being hampered by the emergence of antimicrobial resistance. New antimicrobial agents are therefore needed. One new class of promising antibiotics is antimicrobial peptides (AMP). Derived from natural human peptides, these have a low tendency to induce antimicrobial resistance. Dhvar-5 is an antimicrobial peptide based on histatin-5, which is found in human saliva and consists of 14 amino acids. It has demonstrated bactericidal activity in vitro. In order to develop a new local treatment using Dhvar-5 for osteomyelitis, we investigated its release from PMMA beads and its antimicrobial activity against a clinical isolate of methicillin-resistant Staphylococcus aureus (MRSA) before and after release from PMMA beads. Specific amounts of Dhvar-5 were incorporated into PMMA mini beads, containing 120, 600 and 1200 microg of Dhvar-5, respectively. Dhvar-5 was released from the beads in all three groups. Total release from the 120 microg beads was 9 microg per bead after 7 days. However, the release per bead in the 600 and 1200 microg beads was far more, respectively, 416 and 1091 microg over a 28 day period. After release, the Dhvar-5 also retained its antimicrobial activity against MRSA. On the basis of these data we conclude that the amount of Dhvar-5 release from PMMA beads is not proportionate to the amount incorporated; instead, it demonstrated an exponential relationship to the amount of total peptide released. Furthermore, the released peptide remained biologically active against a clinical isolate of MRSA.

Anti-Bacterial Agents↗
PubMedDate not supplied

Preparation and characterization of insulin nanoparticles employing chitosan and poly(methylmethacrylate/methylmethacrylic acid) copolymer.

As most of polypeptides are marginally stable, a mild formulation procedure would be beneficial for the activities of these drugs. The objective of the present study was to develop a novel pH-sensitive nanoparticle system that was suitable for entrapment of hydrophilic insulin but without affecting its conformation. Chitosan was incorporated as a positively charged material, and one of the three poly(methylmethacrylate/methylmethacrylic acid) copolymers, consisting of Eudragit L100-55, L100, and S100, was used as a negatively charged polymer for preparation of three insulin nanoparticles, respectively. Three nanoparticles obtained were spherical. The mean diameters were in the range from 200 nm to 250 nm, and the entrapment efficiencies, from 50% to 70%. The surface analysis indicated that insulin was evenly distributed in the nanoparticles. Polymer ratio of chitosan to Eudragit was the factor which influenced the nanoparticles significantly. Characterization results showed that the electrostatic interactions existed, thus providing a mild formulation procedure which did not affect the chemical integrity and the conformation of insulin. In vitro release studies revealed that all three types of the nanoparticles exhibited a pH-dependant characteristic. The modeling data indicated that the release kinetics of insulin was nonlinear, and during the release process, the nanoparticles showed a polynomial swelling. On overall estimation, the insulin chitosan-Eudragit L100-55 nanoparticles may be better for the oral delivery. This new pH-sensitive nanoparticle formulation using chitosan and Eudragit L100-55 polymer may provide a useful approach for entrapment of hydrophilic polypeptides without affecting their conformation.

Chitosan↗
PubMed2003

Microtensile bond strength testing of luting cements to prefabricated CAD/CAM ceramic and composite blocks.

OBJECTIVES: To investigate the Microtensile bond strength (microTBS) and failure mode of resin cements bonded to composite and ceramic CAD/CAM blocks following various surface treatments. METHODS: Paradigm composite blocks and Cerec Vitablocs received three surface treatments following the control treatment of surface grinding with 600 SiC grit. (1) Application of adhesive resin (Adh), (2) etching with hydrofluoric acid and silanization (HF+S) or (3) combination of the previous two treatments (HF+S+Adh). Three resin cements (Tetric Flow, Nexus 2, RelyX ARC) were applied to these surfaces and built-up in layers. After 24 h water storage at 37 degrees C, the non-trimming version of microTBS test was used to produce 1 mm(2) microbars. The Microbars were subjected to a tensile load using a modified testing device. The broken specimens were examined with a stereomicroscope and SEM to determine the failure mode. RESULTS: All control and adhesive treated groups of the ceramic substrate showed premature debonding during cutting. The overall mean microTBS for the three resin cements bonded to ceramic following HF+S and HF+S+Adh surface treatment, was 27 and 29.2 MPa and for the resin cements bonded to composite substrate was 42.3 and 54.2 MPa, respectively. The mode of failure was 98% adhesive with composite as a substrate and 68% mixed failures with ceramic as a substrate. CLINICAL SIGNIFICANCE: CAD/CAM restorations fabricated from processed composite blocks may have advantage over the ceramic blocks with regard to the higher bond strength with resin cements.

Adhesives↗
PubMed1996

Bond strength of Gluma CPS using the moist dentin bonding technique.

PURPOSE: To investigate the effects of acetone or water based Gluma primers on bonding efficacy when applied to acid-etched wet, dry or rewetted dentin. MATERIALS AND METHODS: Shear bond strength (SBS, 24 hours) was measured on human dentin etched with 20% phosphoric acid gel and rinsed with water in the wet (blot dried), the conventional (2 seconds air blast), the dry (10 seconds air drying), and the rewetted stage (10 seconds air drying, remoistening and blot drying). The priming solution was either the original water based or an acetone based experimental Gluma primer. Cavity sealing performance and depth of resin impregnation were determined by solvent and by technique along the margins of 4.5 mm wide cylindrical dentin cavities with 90 degree cavosurface angle. RESULTS: The SBSs of the wet technique groups were approximately 18 MPa, irrespective of the primer solvent. Conventional drying gave an SBS almost as high (16.5 MPa). Rewetting was highly effective with acetone as the primer solvent. The dry techniques resulted in moderate (water) and poor (acetone) bond strengths. The cavity margins of acetone based primer treated specimens were consistently gap free with the wet technique. The other seven groups showed between two and six gaps in each group of six specimens. The resin impregnated layer (RIL) thicknesses were 12.5 microns approximately in the wet groups, and thus identical with the total depth of demineralization resulting from the 30-second etching. The alternative techniques showed significantly thinner RILs particularly in the dry groups (7.5 microns).

Acetone↗
PubMed2000

Characterization of glucose-sensitive insulin release systems in simulated in vivo conditions.

We studied the glucose-responsive insulin controlled release system based on the hydrogel poly(2-hydroxyethyl methacrylate-co-N,N-dimethylaminoethyl methacrylate), also called poly(HEMA-co-DMAEMA), with entrapped glucose oxidase, catalase and insulin. When exposed to physiological fluids, glucose diffuses into the hydrogel, glucose oxidase catalyzes the glucose conversion to gluconic acid, causing swelling of the pH-sensitive hydrogel and subsequently increased insulin release. The higher the glucose concentration in the medium, the higher and faster the swelling and release rates. The effects of polymer morphology and oxygen availability on hydrogel swelling and on insulin release kinetics were tested. Polymer morphology was modified by changing the crosslinking agent (tetraethylene glycol dimethacrylate) concentration (0-0.95 vol%). Oxygen availability was modified by changing the immobilized catalase concentration (0-15 units catalase per unit glucose oxidase) and by bubbling oxygen through the medium. The results indicated that: (i) Hydrogels without crosslinking agent were found to be stable in water, and their sensitivity to pH and glucose was higher than the chemically crosslinked hydrogels. (ii) Immobilization of catalase in addition to glucose oxidase in hydrogels prepared without crosslinking agent, resulted in enhanced swelling kinetic. In addition, we carried out primary in vivo experiments on rats, which demonstrated that at least some of the entrapped insulin retains its active form and is effective in reducing blood glucose levels. Moreover, no tissue encapsulation was observed around matrices implanted in the peritoneum. In conclusion, the pH-sensitive hydrogel poly(HEMA-co-DMAEMA) can be manipulated to produce glucose-responsive insulin release system that is effective in reducing blood glucose levels.

Animals↗
PubMed2004

(1)H NMR and small-angle neutron scattering investigation of the structure and solubilization behavior of three-layer nanoparticles.

Three-layer nanoparticles were prepared by radiation-induced polymerization of 1-10 g/L of methyl methacrylate dissolved in a 0.1 wt % D(2)O solution of polystyrene-poly(methacrylic acid) (PS-PMA) micelles. According to NMR and small-angle neutron scattering (SANS), most of the poly(methyl methacrylate) (PMMA) is adsorbed at the core-shell interface of the particles. A small fraction of shorter PMMA probably sticks to outer parts of the PMA chains. The absorption kinetics and equilibria of benzene and chloroform were studied by NMR and SANS time-resolved experiments. The diffusion front in the PS core is very narrow but quite broad in the PMMA sheet suggesting, thus, a less compact state of PMMA. According to SANS, the diffusion kinetics is almost independent of the PMMA sheet thickness. In contrast to it, the absorption capacity, reflected by both SANS and NMR, increases markedly with the PMMA content in the particle. The maximum amount of solubilized compound depends on its positive interaction with PMMA (expressed by the chi parameter) but is restricted by the growing interface tension between swollen PMMA and D(2)O. In accordance with this conclusion, a particle saturated with benzene can absorb chloroform only at the expense of a part of benzene expelled into the surrounding medium and vice versa. Starting with 10 g PMMA/L (10 times the weight of the original micelles), the particles become unstable when being swollen with a good solvent.

Magnetic Resonance Spectroscopy↗
PubMed2005

Physicochemical characterization and mechanisms of release of theophylline from melt-extruded dosage forms based on a methacrylic acid copolymer.

The purpose of the current study was to investigate the physicochemical properties of melt-extruded dosage forms based on Acryl-EZE and to determine the influence of gelling agents on the mechanisms and kinetics of drug release from thermally processed matrices. Acryl-EZE is a pre-mixed excipient blend based on a methacrylic acid copolymer that is optimized for film-coating applications. Powder blends containing theophylline, Acryl-EZE, triethyl citrate and an optional gelling agent, Methocel K4M Premium (hydroxypropyl methylcellulose, HPMC, hypromellose 2208) or Carbopol 974P (carbomer), were thermally processed using a Randcastle single-screw extruder. The physical and chemical stability of materials during processing was determined using thermal gravimetric analysis and HPLC. The mechanism of drug release was determined using the Korsmeyer-Peppas model and the hydration and erosion of tablets during the dissolution studies were investigated. The excipient blends were physically and chemically stable during processing, and the resulting dosage forms exhibited pH-dependent dissolution properties. Extrusion of blends containing HPMC or carbomer changed the mechanism and kinetics of drug release from the thermally processed dosage forms. At concentrations of 5% or below, carbomer was more effective than HPMC at extending the duration of theophylline release from matrix tablets. Furthermore, carbomer containing tablets were stable upon storage for 3 months at 40 degrees C/75% RH. Thus, hot-melt extrusion was an effective process for the preparation of controlled release matrix systems based on Acryl-EZE.

Acrylates↗
PubMed2005

Interaction of polyanions with basic proteins, 2(a) : influence of complexing polyanions on the thermo-aggregation of oligomeric enzymes.

The ability of synthetic polyanions to suppress thermo-aggregation of the oligomeric enzymes (glyceraldehyde-3-phosphate dehydrogenase, lactate dehydrogenase, and aspartate aminotransferase) has been established. The ability of the polyanions to reduce the thermo-aggregation increased in the order poly(methacrylic acid) < poly(acrylic acid) < sodium poly(styrene sulphonate), which agreed well with the increase, in the same order, of the charge density of the chains. The lengthening of the chains, as well as the rise in their relative content, resulted in an increase of the ability to reduce thermo-aggregation, mentioned above. Complete prevention of the enzyme aggregation was achieved when highly charged polyanions of a relatively high degree of polymerization were used in a concentration sufficient to solubilize the protein. Complexing with the polyanions prevented thermo-aggregation of the enzymes, but not their thermo-denaturation. The adverse effect of the complexing polyanions on the catalytic activity was reduced by the addition of a synthetic polycation, which resulted in a significant reactivation (up to 40%) of the enzyme. The possibility of preventing the thermo-aggregation of enzyme molecules and then partly restoring the enzyme activity, appears to be of particular interest when studying the aggregation mechanism of proteins that are prone to form the amyloid structures responsible for the development of neurodegenerative diseases like Alzheimer's disease, bovine spongiform encephalopathy and Huntington disease. This finding can also be considered as an important step in the creation of artificial chaperones.

Acrylic Resins↗
PubMed2006

Phosphorylcholine-based pH-responsive diblock copolymer micelles as drug delivery vehicles: light scattering, electron microscopy, and fluorescence experiments.

The micellization behavior of a diblock copolymer comprising a highly hydrophilic and biocompatible poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) corona-forming block and a pH-sensitive poly(2-(diisopropylamino)ethyl methacrylate) (PDPA) core-forming block (PMPC-b-PDPA) has been studied by static and dynamic light scattering (SDLS), transmission electron microscopy (TEM), and potentiometry. Self-assembly of PMPC-b-PDPA copolymers with two different DPA volume fractions (phi(DPA)) leads to narrowly distributed and structurally distinct spherical micelles, as evidenced by their molecular weight (M(w,mic)), aggregation number (N(agg)), hydrodynamic radius (R(H)), corona width (W), and core radius (R(c)). The excellent potential of these pH-responsive micelles as nanosized drug delivery vehicles was illustrated by the encapsulation of dipyridamole (DIP), a model hydrophobic drug that dissolves in acid solutions and becomes insoluble above pH 5.8, which is comparable to the pK(a) of the PDPA block. The influence of micelle structure (namely M(w,mic), N(agg), R(H), W, and R(c)) on drug loading content, drug loading efficiency, partition coefficient, and release kinetics was investigated and confirmed by fluorescence spectroscopy studies. The maximum dipyridamole loadings within PMPC(30)-b-PDPA(30) (R(H) = 14.0 nm; W = 4.8 nm; R(c) = 9.2 nm) and PMPC(30)-b-PDPA(60) (R(H) = 27.1 nm; W = 11.0 nm; R(c) = 16.1 nm) micelles were 7 and 12% w/w(p), respectively. This preferential solubilization of DIP into micelles formed by copolymer chains having longer core-forming blocks (i.e., possessing larger core volumes) reflects the larger partition coefficient (K(V)) of DIP between the aqueous phase and PMPC(30)-b-PDPA(60) micelles (K(V) = 5.7 x 10(4)) compared to PMPC(30)-b-PDPA(30) micelles (K(V) = 1.1 x 10(4)). This enhanced ability of PMPC(30)-b-PDPA(60) aggregates to entrap/stabilize small hydrophobic molecules also produces slower release kinetics. Rapid release can be triggered by lowering the pH to induce micellar dissociation.

Dipyridamole↗