Bioadhesive poly(methyl methacrylate) microdevices for controlled drug delivery.

Oral delivery is the preferred route of drug administration. However, the breakdown of molecules and low levels of absorption in the gastrointestinal system render the oral delivery of proteins and peptides ineffective. Bioadhesive delivery devices can be used to circumvent these problems by protecting the drug from gastrointestinal denaturation, localizing and prolonging a drug at a specific target site, and maintaining direct contact with the intestinal cells, thereby increasing the drug concentration gradient. Microfabrication technology may offer some potential advantages over conventional delivery technologies. The benefits of microfabrication include the ability to tailor the size, shape, reservoir volume, and surface characteristics of the drug delivery vehicle. In this study, bioadhesive properties were introduced to microfabricated poly(methyl methacrylate) (PMMA) microdevices by attachment of lectins, a group of proteins capable of specifically targeting cells in the gastrointestinal tract. In this process, the PMMA microdevices were chemically modified by aminolysis to yield amine-terminated surfaces. Avidin molecules were covalently bound to the surface of the particles using a hydroxysuccinimide catalyzed carbodiimide reagent and then incubated in an aqueous solution of biotinylated lectin. The lectin-modified microdevices were examined in vitro in terms of their bioadhesive characteristics.     

Poly(ethylene glycol)-containing hydrogels in drug delivery.

The use of hydrogels as carriers for protein delivery has been a subject of significant recent research. In our recent work, we have shown that diffusion controlled delivery of proteins from hydrogels containing poly(ethylene glycol) (PEG) can be possible and controlled by the three-dimensional structure. In addition, a number of these hydrogel carriers are mucoadhesive and can be used for protein delivery. PEG star polymer gels have also been prepared by gamma-irradiation and have been used for protein delivery with and without molecular imprinting. The presence of a large number of functional groups in a small volume makes these polymers important for use in biological and pharmaceutical applications. PEG star polymer hydrogels were synthesized using gamma-irradiation and were characterized using swelling techniques. Equilibrium swelling studies were conducted to investigate the effects of molecular weight, number of star arms, concentration, and radiation dose.     

Toxicology of methyl methacrylate: the rate of disappearance of methyl methacrylate in human blood in vitro.

1. The rate of disappearance of methyl methacrylate in blood has been determined using an isotope dilution technique. 2. At a concentration of 10(-4) mol dm(-3), methyl methacrylate disappears with pseudo first order kinetics. 3. The half-life of methyl methacrylate in blood at 37 degrees C lies in the range 20--40 min. 4. The half-life showed no dependence on the age or sex of the blood donor. 5. A major, possibly the only, pathway of metabolism is by hydrolysis to methacrylic acid.     

Poly(D,L-lactic-co-glycolic acid) microspheres for sustained delivery and stabilization of camptothecin.

Camptothecin (CPT) and its water-insoluble derivatives are known as topoisomerase-I inhibitors exhibiting high antitumoral activity against a wide spectrum of human malignancies. Until now clinical application of CPT is restricted by insolubility and instability of the drug in its active lactone form resulting in less antitumor potency and poor bioavailability. For these reasons CPT-loaded-microspheres were prepared by the solvent evaporation method using the H-series of poly(D,L-lactide-co-glycolide) (H-PLGA), which contain more carboxylic acid end chains and hydrate faster than the non-H-series. At 1.2% CPT-payload the drug was molecular dispersed throughout the matrix whereas at higher CPT-payload the amount of crystalline CPT-islets increased with the CPT content. The release pattern of CPT was biphasic comprising a first burst effect delivering 20-35% of the payload and increasing with drug-loading. This phase was followed by sustained delivery of CPT releasing 40-75% of the payload within 160 h. In comparison to PLGA-microspheres, the CPT-release rate from H-PLGA was twofold higher and accelerated. The active CPT-lactone was maintained during preparation, storage and release due to hindered diffusion of acidic oligomers among other mechanisms. Thus stabilization and sustained release of CPT from PLGA-microspheres might reduce local toxicity combined with prolonged efficacy offering new perspectives in CPT chemotherapy.     

Poly(2-hydroxyethyl methacrylate) particles for preoperative endovascular occlusion of extensive angiodysplasias.

The application of superselective endovascular occlusion in vascular radiology has broadened the scope of possible radical surgery of giant angiodysplasias by reducing considerably the risk of severe haemorrhage during the surgery. Occlusion was performed on 229 patients using spherical and cylindrical particles of porous poly(2-hydroxyethyl methacrylate). The treatment of a patient suffering from angiodysplasia of the pelvis is described as an example. The first day following endovascular occlusion a hypercoagulation reaction developed, with a decrease of both the level of fibrinolysis and of anticoagulant factors. This was mainly due to a decrease of the level of antithrombin III and activation of the factor XIII indicating a strong tendency of intravascular thrombosis. During the third day, the hypercoagulation reaction increased. However, on the fifteenth day, parameters of the haemostasis system were close to normal values. Only the activity of the factor XIII remained high suggesting the stabilization and the organization of fibrin clot in the embolized blood vessel territory.     

Poly(amidoamine)-mediated intracytoplasmic delivery of ricin A-chain and gelonin.

Poly(amidoamine)s (PAAs) are water-soluble synthetic polymers designed to be biodegradable and biocompatible. Moreover, they display membrane disruptive properties in response to a decrease in pH. This attribute confers PAAs with endosomolytic properties in vitro and in vivo. A model system was developed to quantify their ability to promote the endosomal escape of macromolecules that may be interesting as therapeutic agents. Here, two PAAs (ISA 1 and 4) were incubated with B16F10 cells in vitro together with two non-permeant toxins: either ricin A-chain (RTA) or gelonin. The relatively non-toxic PAAs ISA 1 and 4 (IC50>1.5 mg/ml) restored activity to the inherently inert toxins. The IC50 values for the ISA 1/RTA and ISA 1/gelonin combinations were 0.65+/-0.05 and 0.55+/-0.12 mg/ml, respectively. Similarly, when ISA 4 was incubated with a non-toxic combination of RTA and gelonin the IC50 value decreased to 0.57+/-0.03 and 0.43+/-0.26 mg/ml, respectively. In contrast, the neutral polymer dextran and the PAA ISA 22 were unable to mediate this effect. These observations suggest that specific PAA-toxin combinations warrant further development as novel therapeutics.     

Poly(L-lysine)-g-poly(D,L-lactic-co-glycolic acid) micelles for low cytotoxic biodegradable gene delivery carriers.

Poly(lactic-co-glycolic acid) (PLGA)-grafted poly(L-lysine) (PLL) (PLL-g-PLGA) was synthesized to demonstrate its micelle-forming property in an aqueous solution. The micelles were used as a gene delivery carrier. The hydrodynamic diameter of PLL-g-PLGA micelles in an aqueous solution was ca. 149 nm with a narrow size distribution. Critical micelle concentration (cmc) was 9.6 mg/l. The PLL-g-PLGA micelles could be used to produce compact nanoparticulate complexes with plasmid DNA, which could efficiently protect the complexed DNA from enzymatic degradation by DNase I. The micelle/DNA complexes had highly compacted structure sized between 200-300 nm with a positive surface charge value. The PLL-g-PLGA micelles exhibited much higher transfection efficiency with lower cytotoxicity than PLL. Here, we demonstrated that biodegradable and cationic PLL-g-PLGA micelles could be used as an effective DNA condensation carrier for gene delivery system.     

Poly(ethylene oxide)-modified poly(beta-amino ester) nanoparticles as a pH-sensitive biodegradable system for paclitaxel delivery.

The main objective of this study was to develop and characterize a pH-sensitive biodegradable polymeric nanoparticulate system for tumor-selective paclitaxel delivery. A representative hydrophobic poly(beta-amino ester) (poly-1) was synthesized by conjugate addition of 4,4'-trimethyldipiperidine with 1,4-butanediol diacrylate. Poly-1 (M(n) 10,000 daltons) nanoparticles were prepared by the controlled solvent displacement method in an ethanol-water system in the presence of Pluronic) F-108, a poly(ethylene oxide) (PEO)-containing non-ionic surfactant. Control and PEO-modified nanoparticles were characterized by Coulter counter, scanning electron microscopy (SEM), zeta potential measurements, and electron spectroscopy for chemical analysis (ESCA). Polymer degradation studies were performed in phosphate-buffered saline (PBS, pH 7.4) at 37 degrees C. Paclitaxel loading capacities and efficiencies were determined and release studies were performed in Tween)-80 (0.1%, w/v)-containing PBS at 37 degrees C. Control and PEO-modified nanoparticles, labeled with rhodamine-123, were incubated with BT-20 cells to examine the uptake and cellular distribution as a function of time. PEO-modified nanoparticles with an average size of 100-150 nm and a positive surface charge of 37.0 mV were prepared. SEM analysis showed distinct smooth, spherical particles. The ether (-C-O-) peak of the C(1s) envelope in ESCA confirmed the surface presence of PEO chains. Polymer biodegradation studies showed that almost 85% of the starting material degraded after 6 days. The maximum paclitaxel loading efficiency attained was 97% at 1.0% (w/w) of the drug. Paclitaxel release studies showed that approximately 10% was released in the first 24 h, 80% after 3 days, and the entire content was released in approximately 5 days. After 1 h of incubation, a large fraction of the administered control and PEO-modified poly-1 nanoparticles was internalized in BT-20 cells. Results of this study demonstrate that PEO-modified poly-1 nanoparticles could provide increased therapeutic benefit by delivering the encapsulated drug to solid tumors.     

Poly(lactic acid)-poly(ethylene glycol) nanoparticles as new carriers for the delivery of plasmid DNA.

The purpose of the present work was to produce and characterize poly(lactic acid)-poly(ethylene glycol) (PLA-PEG) nanoparticles (size lower than 300 nm) containing a high loading of plasmid DNA in a free form or co-encapsulated with either poly(vinyl alcohol) (PVA) or poly(vinylpyrrolidone) (PVP). The plasmid alone or with PVA or PVP was encapsulated by two different techniques: an optimized w/o/w emulsion-solvent evaporation technique as well as by a new w/o emulsion-solvent diffusion technique. Particle size, zeta potential, plasmid DNA loading and in vitro release were determined for the three plasmid-loaded formulations. The influence of the initial plasmid loadings (5, 10, 20 microg plasmid DNA/mg PLA-PEG) on those parameters was also investigated. The plasmid loaded into the nanoparticles and released in vitro was quantified by fluorimetry and the different molecular forms were identified by gel electrophoresis. PLA-PEG nanoparticles containing plasmid DNA in a free form or co-encapsulated with PVA or PVP were obtained in the range size of 150-300 nm and with a negative zeta potential, both parameters being affected by the preparation technique. Encapsulation efficiencies were high irrespective of the presence of PVA or PVP (60-90%) and were slightly affected by the preparation technique and by the initial loading. The final plasmid DNA loading in the nanoparticles was up to 10-12 microg plasmid DNA/mg polymer. Plasmid DNA release kinetics varied depending on the plasmid incorporation technique: nanoparticles prepared by the w/o diffusion technique released their content rapidly whereas those obtained by the w/o/w showed an initial burst followed by a slow release for at least 28 days. No significant influence of the plasmid DNA loading and of the co-encapsulation of PVP or PVA on the in vitro release rate was observed. In all cases the conversion of the supercoiled form to the open circular and linear forms was detected. In conclusion, plasmid DNA can be very efficiently encapsulated, either in a free form or in combination with PVP and PVA, into PLA-PEG nanoparticles. Additionally, depending on the processing conditions, these nanoparticles release plasmid DNA either very rapidly or in a controlled manner.     

Poly(methylidene malonate 2.1.2) nanoparticles: a biocompatible polymer that enhances peri-adventitial adenoviral gene delivery.

Vascular gene therapy is currently limited by low and transient levels of gene transfection. The objectives of this study were to determine whether peri-adventitial delivery of adenovirus coupled to nanoparticles could improve transfection efficiency and duration. Adenovirus was absorbed to the surface of nanoparticles that were made from poly(methylidene malonate)2.1.2 (PMM2.1.2). These complexes were found to have good adhesive properties to both cultured vascular smooth muscle cells and to the luminal and adventitial layers of excised rabbit carotid arteries. Adenovirus encoding to beta-galactosidase coupled to PMM2.1.2 nanoparticles or adenovirus alone were delivered locally to the adventitia of rabbit carotid arteries. Transfection rate was assessed histologically by the percentage of beta-galactosidase positive cells in the vessel wall at 1 and at 2 weeks. There was significantly higher transfection rate when adenovirus was complexed with nanoparticles as compared to free adenovirus (At 1 week: 10+/-3.9% beta-gal positive cells vs. 2.4+/-0.3% and at 2 weeks: 4.3+/-4.1% vs. 0%, P<0.005 for all). This difference was present in both the medial and adventitial layers. In conclusion, adenoviral mediated gene therapy was significantly enhanced by adsorbing the virus to PMM2.1.2 nanoparticles. This delivery method may be a good therapeutic strategy for the treatment of various vascular diseases.     

Poly(ethylene carbonate)s, part II: degradation mechanisms and parenteral delivery of bioactive agents.

The degradation and drug carrier properties of poly(ethylene carbonate) (PEC) were investigated in vitro and in rats and rabbits. PEC was found to be specifically degraded in vivo and in vitro by superoxide radical anions O2-*, which are, in vivo, mostly produced by inflammatory cells. No degradation of PEC was observed in the presence of hydrolases, serum or blood. PEC is biodegraded by surface erosion without significant change in the molecular weight of the residual polymer mass. The non-hydrolytic biodegradation by cells producing O2-* is unique among the polymers used as biodegradable drug carriers. The main degradation product of PEC in aqueous systems is ethylene glycol, formed presumably by hydrolysis of ethylene carbonate. The splitting off of a five-membered ring structure from the polymer chain indicates a chain reaction mechanism for the biodegradation. PEC is a suitable drug carrier, particularly for labile drugs. Using human interleukin-3 and octreotide as model drugs, surface erosion of the PEC formulations was indicated by a 1:1 correlation between drug release and polymer mass loss.     

Correlation of the surface hydrophobicity of C-poly(methyl methacrylate) nanoparticles to their body distribution

Poly (methyl methacrylate) nanoparticles for intravenous injection were surface-modified by the adsorption of poloxamine 908, Antarox DM 970 and Klucel EF. The coated particles were characterized in parameters relevant to their in vivo distribution: adsorption layer thickness, particle charge, surface hydrophobicity, interaction with serum components. The body distribution of the ¹⁴C-labeled particles was determined after i.v. injection into rats over 7 days and correlated to the in vitro characterization data. The physicochemical characterization methods allowed to identify carriers which will be taken up by liver and spleen macrophages in vivo. Coating materials with potential protective effect against uptake could be placed in order of increasing efficiency.     

Mono-acrylated isosorbide as a bio-based monomer for the improvement of thermal and mechanical properties of poly(methyl methacrylate)

Despite its optical clarity and good weatherability, poly(methyl methacrylate) (PMMA) cannot meet the needs of special occasions due to its deficient thermal and mechanical properties. To overcome these shortcomings, a type of novel bio-based monomer, mono-acrylated isosorbide, was used as a comonomer for the poly(methyl methacrylate) via a solution polymerization process. The chemical structure, the thermal and mechanical properties of the copolymerized PMMA were characterized. When the molar content of the mono-acrylated isosorbide was increased from 0% to 15%, the glass transition temperature T_g of the copolymerized PMMA was increased from 151.2 °C to 172.5 °C, and the initial decomposition temperature (T_5%) was increased from 323.1 °C to 396.3 °C. Moreover, the impact strength of copolymerized PMMA increased from 10.59 kJ m⁻² to 17.19 kJ m⁻² and the tensile strength improved from 84.02 MPa to 97.56 MPa when the mono-acrylated isosorbide was incorporated with different contents. The incorporation of rigid and thermally stable isosorbide could contribute to the improved thermal and mechanical properties of PMMA, which would find important applications in the military and aeronautical materials under harsh service environments.

With bio-based monoester of acrylated isosorbide as the comonomer, copolymerized poly(methyl methacrylate) showed improved thermal stability and mechanical properties.     

Preparation and in vitro characterization of valsartan-loaded ethyl cellulose and poly(methyl methacrylate) nanoparticles

Valsartan is an antihypertensive drug used primarily orally, however, due to its hydrophobic nature it has got low bio-availability thus requiring higher dosage/frequency and causing more side effects. The aim of our work was to prepare valsartan-loaded nanoparticles by using ethyl cellulose and poly(methyl methacrylate) polymers which can be administered orally and to investigate the preparation conditions and their significance as potential drug carriers for valsartan delivery by in vitro release studies. Ethyl cellulose and poly(methyl methacrylate) polymers were used for the preparation of nanoparticles by single emulsion-solvent evaporation technique. The formation of drug-loaded nanoparticles was designed by experimental design for size and encapsulation efficiency, in addition the prepared nanosuspensions were nano spray dried in order to gain a powder form that is easy to handle and store. Both of the nano spray dried formulations had an amorphous structure in contrast to the pure drug according to differential scanning calorimetry and X-ray diffraction analysis, which can be advantageous in drug absorption. The originally processed ethyl cellulose-valsartan nanoparticles increased the solubility of the drug in the model intestinal medium, while poly(methyl methacrylate)-valsartan nanoparticles enabled substantially prolonged drug release. The release kinetics of both types of nanoparticles could be described by the Weibull model.

Valsartan-loaded ethyl cellulose and poly(methyl methacrylate) nanoparticles were prepared and nano spray-dried. The active agent was structurally changed in the nanoparticles, which could be advantageous in the intestinal absorption.     

Effects of methyl acetyl phosphate, a covalent antisickling agent, on the density profiles of sickle erythrocytes.

Methyl acetyl phosphate specifically acetylates valine-1, lysine-82, and lysine-144 in the 2,3-diphosphoglycerate binding cleft of hemoglobin S, thereby inhibiting its gelation (greater than 32 gm/dl) at pH 7.4. To extend these findings, the effect of methyl acetyl phosphate on the density of sickle cells has been evaluated by phthalate ester gradient centrifugation and by Larex-Percoll density centrifugation. After treatment with methyl acetyl phosphate (40% modification of the intracellular hemoglobin S), oxygenated sickle erythrocytes had a lowered density profile, as measured in a phthalate ester gradient. Thus 83% of untreated oxygenated sickle cells had densities greater than 1.098 gm/ml, whereas after treatment with methyl acetyl phosphate, 52% of the cells were in this density range. Under anaerobic conditions, methyl acetyl phosphate was even more effective in lowering cell density. For example, 50% of untreated deoxygenated cells had densities greater than 1.098 gm/ml, but none of the cells treated with methyl acetyl phosphate were this dense. For studies with Larex-Percoll density gradients, sickle erythrocytes were first separated into two fractions (densities greater than and less than 1.1 gm/ml) by Percoll-Hypaque centrifugation. The amount of oxygenated sickle cells exhibiting densities greater than 1.074 gm/ml decreased by about 32% on treatment with methyl acetyl phosphate. For deoxygenated sickle cells, treatment with methyl acetyl phosphate resulted in an average decrease of approximately 24% in the number of cells with densities greater than 1.074 gm/ml.(ABSTRACT TRUNCATED AT 250 WORDS)     

Phase separation behavior of poly(methyl methacrylate)/poly(styrene-co-maleic anhydride) in the presence of hollow silica nanotubes

The phase separation behavior of poly(methyl methacrylate) (PMMA)/poly(styrene-co-maleic anhydride) (SMA) blends with and without one-dimensional hollow silica nanotubes (HSNTs) was investigated using time-resolved small-angle laser light scattering. During isothermal annealing over a range of 100 °C above the glass transition temperature, the Arrhenius equation is applicable to describe the temperature dependence of phase separation behavior at the early and late stages of spinodal decomposition (SD) for unfilled and filled PMMA/SMA systems. The mechanical barrier effect of HSNTs on the macromolecular chain diffusion of the blend matrix may retard the concentration fluctuation at the early stage and slow down the domain coarsening at the late stage of SD phase separation for the blend matrix to result in the decrease of apparent diffusion coefficient D_app, the postponement of the relaxation time and the decline of temperature sensitivity for the phase separation rate.

The applicability of Arrhenius equation to the phase separation behaviors for filled systems indicates that HSNTs results in the decline of temperature sensitivity for phase separation rate, but hardly changes the viscous diffusion essence of chains.     

Poly(amidoamine) dendrimers as ophthalmic vehicles for ocular delivery of pilocarpine nitrate and tropicamide.

The purpose of this study was to determine the influence of a controlled incremental increase in size, molecular weight and number of amine, carboxylate and hydroxyl surface groups in several series of poly(amidoamine) (PAMAM) dendrimers for controlled ocular drug delivery. The duration of residence time was evaluated after solubilization of several series of PAMAM dendrimers (generations 1.5 and 2-3.5 and 4) in buffered phosphate solutions containing 2 per thousand (w/v) of fluorescein. The New Zealand albino rabbit was used as an in vivo model for qualitative and quantitative assessment of ocular tolerance and retention time after a single application of 25 microl of dendrimer solution to the eye. The same model was also used to determine the prolonged miotic or mydriatic activities of dendrimer solutions, some containing pilocarpine nitrate and some tropicamide, respectively. Residence time was longer for the solutions containing dendrimers with carboxylic and hydroxyl surface groups. No prolongation of remanence time was observed when dendrimer concentration (0.25-2%) increased. The remanence time of PAMAM dendrimer solutions on the cornea showed size and molecular weight dependency. This study allowed novel macromolecular carriers to be designed with prolonged drug residence time for the ophthalmic route.     

Observations with a tri-phasic oral contraceptive (Tri-Regol) in everyday clinical practice.

The theoretical general principles of triphasic oral contraception are discussed in the introduction. This method, which is the closest to a physiological dosage, seems to be the most advantageous today. International data and the advantages and wide indication field of such "step-up" tablets are also discussed. The observations with the Hungarian Tri-Regol tablet are described in detail. In the course of controlling 355 cycles of 79 women pregnancy was not observed, the tablets were well tolerated by the women-except for some milder side-effects. The use of Tri-Regol needed not be discontinued due to, any unwanted effect or complication. The rate of intermenstrual bleeding was very low, and the triphasic therapy proved to be beneficial in case of manifesting cycle disorders or if the change of the contraceptive tablet became necessary because of intolerance. According to the opinion of the authors the oral contraceptive Tri-Regol is today's drug of choice due to its reliable ovulation inhibitory action, low hormone content, and favourable tolerability.     

Poly(vinyl alcohol) and poly(acrylic acid) sequential interpenetrating network pH-sensitive microspheres for the delivery of diclofenac sodium to the intestine.

Sequential interpenetrating network (IPN) of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA) were prepared and crosslinked with glutaraldehyde (GA) to form pH-sensitive microspheres by the water-in-oil (w/o) emulsification method. Microspheres were used to deliver a model anti-inflammatory drug, diclofenac sodium (DS), to the intestine. The formed IPN was analyzed by Fourier transform infrared spectroscopy (FTIR). Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses were done on the drug-loaded microspheres to confirm the polymorphism of DS. Results indicated a molecular level dispersion of DS in the IPN. Microspheres formed were spherical with the smooth surfaces as evidenced by scanning electron microscopy (SEM). Particle size and size distribution was studied using laser light diffraction particle size analyzer. Particle size analysis was also done by optical microscope for the selected microspheres; the change in diameter of the microspheres when soaked in different media at different time intervals was measured by optical microscope. Microspheres showed a pulsatile swelling behavior when the pH of the swelling media was changed. The swelling data were fitted to an empirical equation to understand the phenomenon of water transport as well as to calculate the diffusion coefficient (D). Values of D in acidic media were lower than those found in basic media. The values of D decrease with increasing crosslinking of the matrix. In-vitro release studies have been performed in 1.2 and 7.4 pH media to simulate gastric and intestinal conditions. The results indicated a dependence on the pH of the release media, extent of crosslinking and the amount of drug loading.