pH-Sensitive Polymer Blends used as Coating Materials to Control Drug Release from Spherical Beads: Importance of the Type of Core

Ephedra intermedia Schrenk & C. A. Mey Methanol Extract: Nanoencapsulation by Mini-Emulsion Polymerization and its Release Trend under Simulated Conditions of the Human Body

In this research, the extract of Ephedra intermedia Schrenk & C.A.Mey. was encapsulated using the mini-emulsion polymerization method based on methyl methacrylate polymers with a nanometer size. The encapsulated extract was characterized using different analytical techniques. Furthermore, the loading efficiency and release of the plant extract were examined. FT-IR spectroscopy confirmed the formation of an expectational product. The TEM and SEM imaging showed a spherical morphology for the prepared encapsulated extract. The average size of poly-methyl-methacrylate nanoparticles containing Ephedra extract was found to be approximately 47 nm. The extract loading efficiency and encapsulation efficiency test demonstrated a dose-depending behavior on E. intermedia extract for both analyses, which is highly advantageous for traversing biological barriers. The release assay shows a controlled release for the extract at phosphate buffer solution (PBS). A 38 % release was calculated after 36 hours. The results obtained from the present study reveal that encapsulating the plant extract is a suitable alternative to control and increase their medicinal properties.

Towards a Better Understanding of Verapamil Release from Kollicoat SR:IR Coated Pellets Using Non-Invasive Analytical Tools

The aim of this study was to gain deeper insight into the mass transport mechanisms controlling drug release from polymer-coated pellets using non-invasive analytical tools. Pellet starter cores loaded with verapamil HCl (10% loading, 45% lactose, 45% microcrystalline cellulose) were prepared by extrusion/spheronization and coated with 5% Kollicoat SR:IR 95:5 or 10% Kollicoat SR:IR 90:10. Drug release was measured from ensembles of pellets as well as from single pellets upon exposure to acetate buffer pH = 3.5 and phosphate buffer pH = 7.4. The swelling of single pellets was observed by optical microscopy, while dynamic changes in the pH in the pellet cores were monitored by fluorescence spectroscopy. Also, mathematical modeling using a mechanistically realistic theory as well as SEM and Raman imaging were applied to elucidate whether drug release mainly occurs by diffusion through the intact film coatings or whether crack formation in the film coatings plays a role. Interestingly, fluorescence spectroscopy revealed that the pH within the pellet cores substantially differed upon exposure to acetate buffer pH = 3.5 and phosphate buffer pH = 7.4, resulting in significant differences in drug solubility (verapamil being a weak base) and faster drug release at lower pH: from ensembles of pellets and single pellets. The monitoring of drug release from and the swelling of single pellets indicated that crack formation in the film coatings likely plays a major role, irrespective of the Kollicoat SR:IR ratio/coating level. This was confirmed by mathematical modeling, SEM and Raman imaging. Importantly, the latter technique allowed also for non-invasive measurements, reducing the risk of artifact creation associated with sample cutting with a scalpel.

Affinity of Serum Albumin and Fibrinogen to Cellulose, Its Hydrophobic Derivatives and Blends

This work describes the preparation of spin-coated thin polymer films composed of cellulose (CE), ethyl cellulose (EC), and cellulose acetate (CA) in the form of bi- or mono-component coatings on sensors of a quartz crystal microbalance with dissipation monitoring (QCM-D). Depending on the composition and derivative, hydrophilicity can be varied resulting in materials with different surface properties. The surfaces of mono- and bi-component films were also analyzed by atomic force microscopy (AFM) and large differences in the morphologies were found comprising nano- to micrometer sized pores. Extended protein adsorption studies were performed by a QCM-D with 0.1 and 10 mg mL⁻¹ bovine serum albumin (BSA) and 0.1 and 1 mg mL⁻¹ fibrinogen from bovine plasma in phosphate buffered saline. Analysis of the mass of bound proteins was conducted by applying the Voigt model and a comparison was made with the Sauerbrey wet mass of the proteins for all films. The amount of deposited proteins could be influenced by the composition of the films. It is proposed that the observed effects can be exploited in biomaterial science and that they can be used to extent the applicability of bio-based polymer thin films composed of commercial cellulose derivatives.

Curing mechanism of flexible aqueous polymeric coatings

The objective of this study was to explain curing phenomena for pellets coated with a flexible polymeric coating based on poly(vinyl acetate) (Kollicoat® SR 30D) with regard to the effect of starter cores, thickness of drug layer, adhesion of coating to drug-layered-cores as well as coating properties. In addition, appropriate approaches to eliminate the curing effect were identified. Sugar or MCC cores were layered with the model drugs carbamazepine, theophylline, propranolol HCl, tramadol HCl and metoprolol HCl using HPMC (5 or 25% w/w, based on drug) as a binder. Drug-layered pellets were coated with Kollicoat® SR 30D in a fluidized bed coater using TEC (10% w/w) as plasticizer and talc (35-100% w/w) as anti-tacking agent. Drug release, pellet properties (morphology, water uptake-weight loss and osmolality) and adhesion of the coating to the drug layer were investigated as a function of curing at 60°C or 60°C/75% RH for 24h. The film formation of the aqueous dispersion of Kollicoat® SR 30D was complete, and therefore, a strong curing effect (decrease in drug release) at elevated temperature and humidity (60°C/75% RH) could not be explained by the well-known hydroplasticization and the further gradual coalescence of the colloidal polymer particles. According to the provided mechanistic explanation, the observed curing effect was associated with (1) high flexibility of coating, (2) adhesion between coating and drug layer, (3) water retaining properties of the drug layer, and (4) osmotically active cores. Unwanted curing effects could be minimized/eliminated by the addition of talc or/and pore-forming water soluble polymers in the coating, increasing binder amount or applying an intermediate coating, by increasing the thickness of drug layer or using non-osmotic cores. A new insight into curing phenomena mainly associated with the adhesion between drug layer and coating was provided. Appropriate approaches to avoid unwanted curing effect were identified.

Dissipative particle dynamics studies of doxorubicin-loaded micelles assembled from four-arm star triblock polymers 4AS-PCL-b-PDEAEMA-b-PPEGMA and their pH-release mechanism

Dissipative particle dynamics (DPD) simulation was applied to investigate the microstructures of the micelles self-assembled from pH-sensitive four-arm star triblock poly(ε-caprolactone)-b-poly(2-(diethylamino)ethyl methacrylate)-b-poly(poly(ethylene glycol) methyl ether methacrylate) (4AS-PCL-b-PDEAEMA-b-PPEGMA). In the optimized system, the micelles have a core-mesosphere-shell three-layer structure. The drug-loading process and its distribution at different formulations in the micelles were studied. The results show that DOX molecules distributed in the core and the interface between the core and the mesosphere, suggesting the potential encapsulation capacity of DOX molecules. More drugs were loaded in the micelles with the increase in DOX, and the size of micelles became larger. However, some openings start to generate on the PEG shell when the DOX reaches a certain concentration. By changing the pH values of the system, different morphologies of the micelles were acquired after the pH-sensitive blocks PDEAEMA were protonated, the mechanism of which was also analyzed through correlating functions. The results indicated that the sudden increase in solubility parameter of the pH-sensitive blocks and the swelling of the micelles were the key factors on the change of morphologies. Furthermore, with the decrease in pH value, the number and size of the cracks on the surface of the micelles were larger, which may have a direct effect on the drug release. In conclusion, 4AS-PCL-b-PDEAEMA-b-PPEGMA has great promising applications in delivering hydrophobic anticancer drugs for improved cancer therapy.

Ethanol-resistant ethylcellulose/guar gum coatings--importance of formulation parameters

Recently, ethylcellulose/guar gum blends have been reported to provide ethanol-resistant drug release kinetics from coated dosage forms. This is because the ethanol insoluble guar gum effectively avoids undesired ethylcellulose dissolution in ethanol-rich bulk fluids. However, so far the importance of crucial formulation parameters, including the minimum amount of guar gum to be incorporated and the minimum required guar gum viscosity, remains unclear. The aim of this study was to identify the most important film coating properties, determining whether or not the resulting drug release kinetics is ethanol-resistant. Theophylline matrix cores were coated in a fluid bed with blends of the aqueous ethylcellulose dispersion "Aquacoat®ECD30" and guar gum. The polymer blend ratio, guar gum viscosity, and degree of dilution of the final coating dispersion were varied. Importantly, it was found that more than 5% guar gum (referred to the total polymer content) must be incorporated in the film coating and that the apparent viscosity of a 1% aqueous guar gum solution must be greater than 150 cP to provide ethanol-resistance. In contrast, the investigated degree of coating dispersion dilution was not found to be decisive for the ethanol sensitivity. Furthermore, all investigated formulations were long term stable, even upon open storage under stress conditions for 6 months.

Electric field induced morphological transitions in polyelectrolyte multilayers

In this work, the morphological transitions in weak polyelectrolyte (PE) multilayers (PEMs) assembled from linear poly(ethylene imine) (LPEI) and poly(acrylic acid) (PAA) upon application of an electric field were studied. Exposure to an electric field results in the creation of a porous structure, which can be ascribed to local changes in pH from the hydrolysis of water and subsequent structural rearrangements of the weak PE constituents. Depending on the duration of application of the field, the porous transition gradually develops into a range of structures and pore sizes. It was discovered that the morphological transition of the LbL films starts at the multilayer-electrode interface and propagates through the film. First an asymmetrical structure forms, consisting of microscaled pores near the electrode and nanoscaled pores near the surface in contact with the electrolyte solution. At longer application of the field the porous structures become microscaled throughout. The results revealed in this study not only demonstrate experimental feasibility for controlling variation in pore size and porosity of multilayer films but also deepens the understanding of the mechanism of the porous transition. In addition, electrical potential is used to release small molecules from the PEMs.

Ethanol-resistant polymeric film coatings for controlled drug delivery

The sensitivity of controlled release dosage forms to the presence of ethanol in the gastro intestinal tract is critical, if the incorporated drug is potent and exhibits severe side effects. This is for instance the case for most opioid drugs. The co-ingestion of alcoholic beverages can lead to dose dumping and potentially fatal consequences. For these reasons the marketing of hydromorphone HCl extended release capsules (Palladone) was suspended. The aim of this study was to develop a novel type of controlled release film coatings, which are ethanol-resistant: even the presence of high ethanol concentrations in the surrounding bulk fluid (e.g., up to 40%) should not affect the resulting drug release kinetics. Interestingly, blends of ethylcellulose and medium or high viscosity guar gums provide such ethanol resistance. Theophylline release from pellets coated with the aqueous ethylcellulose dispersion Aquacoat® ECD 30 containing 10 or 15% medium and high viscosity guar gum was virtually unaffected by the addition of 40% ethanol to the release medium. Furthermore, drug release was shown to be long term stable from this type of dosage forms under ambient and stress conditions (without packaging material), upon appropriate curing.

"Smart" Materials Based on Cellulose: A Review of the Preparations, Properties, and Applications

Cellulose is the most abundant biomass material in nature, and possesses some promising properties, such as mechanical robustness, hydrophilicity, biocompatibility, and biodegradability. Thus, cellulose has been widely applied in many fields. "Smart" materials based on cellulose have great advantages-especially their intelligent behaviors in reaction to environmental stimuli-and they can be applied to many circumstances, especially as biomaterials. This review aims to present the developments of "smart" materials based on cellulose in the last decade, including the preparations, properties, and applications of these materials. The preparations of "smart" materials based on cellulose by chemical modifications and physical incorporating/blending were reviewed. The responsiveness to pH, temperature, light, electricity, magnetic fields, and mechanical forces, etc. of these "smart" materials in their different forms such as copolymers, nanoparticles, gels, and membranes were also reviewed, and the applications as drug delivery systems, hydrogels, electronic active papers, sensors, shape memory materials and smart membranes, etc. were also described in this review.

Novel platforms for oral drug delivery

The aim of this review is to provide the reader general and inspiring prospects on recent and promising fields of innovation in oral drug delivery. Nowadays, inventive drug delivery systems vary from geometrically modified and modular matrices, more close to "classic" pharmaceutical manufacturing processes, to futuristic bio micro-electro-mechanical systems (bioMEMS), based on manufacturing techniques borrowed from electronics and other fields. In these technologies new materials and creative solutions are essential designing intelligent drug delivery systems able to release the required drug at the proper body location with the correct release rate. In particular, oral drug delivery systems of the future are expected to have a significant impact on the treatment of diseases, such as AIDS, cancer, malaria, diabetes requiring complex and multi-drug therapies, as well as on the life of patients, whose age and/or health status make necessary a multiple pharmacological approach.

Drug release mechanisms from ethylcellulose: PVA-PEG graft copolymer-coated pellets

The aim of this study was to better understand the underlying drug release mechanisms from aqueous ethylcellulose-coated pellets containing different types of drugs and starter cores. Theophylline, paracetamol, metoprolol succinate, diltiazem HCl and metoprolol tartrate were used as model drugs exhibiting significantly different solubilities (e.g. 14, 19, 284, 662 and 800 mg/mL at 37 degrees C in 0.1N HCl). The pellet core consisted of a drug matrix, drug-layered sugar bead or drug-layered microcrystalline cellulose (MCC) bead, generating different osmotic driving forces upon contact with aqueous media. Importantly, the addition of small amounts of poly(vinyl alcohol)-poly(ethylene glycol) graft copolymer (PVA-PEG graft copolymer) to the ethylcellulose coatings allowed for controlled drug release within 8-12h, irrespective of the type of drug and composition of the pellet core. Drug release was found to be controlled by diffusion through the intact polymeric membranes, irrespective of the drug solubility and type of core formulation. The ethylcellulose coating was dominant for the control of drug release, minimizing potential effects of the type of pellet core and nature of the surrounding bulk fluid, e.g. osmolality. Thus, this type of controlled drug delivery system can be used for very different drugs and is robust.

Prediction of drug release from ethylcellulose coated pellets

The aim of this study was to elucidate the underlying drug release mechanisms in pellets coated with aqueous ethylcellulose dispersion, providing long term stable drug release profiles and containing different types of starter cores. The systems were thoroughly characterized using mechanical analysis; the sensitivity of drug release to the osmolality of the release medium was measured; scanning electron microscopy and optical macroscopy were used to monitor the pellets' morphology and dimensions upon exposure to different media, and drug release was measured from single and ensembles of pellets as well as from thin, free films. All experimental results indicate that diltiazem HCl release from pellets coated with ethylcellulose containing small amounts of poly(vinyl alcohol)-poly(ethylene glycol) graft copolymer is primarily controlled by drug diffusion through the intact polymeric membranes, irrespective of the type of starter core (consisting of microcrystalline cellulose or sugar, optionally coated with ethylcellulose). Importantly, the apparent diffusion coefficient of the drug in the macromolecular networks could easily be determined with thin free films and successfully be used to quantitatively predict the release rate from coated pellets. Thus, based on this knowledge and using the presented mathematical theories the development of new/ optimization of existing controlled drug delivery systems of this type can be significantly facilitated.

Loading dependent swelling and release properties of novel biodegradable, elastic and environmental stimuli-sensitive polyurethanes

A novel degradable, elastic, anionic, and linear polyurethane was synthesized from hexamethylene diisocyanate, polycaprolactone diol, and a bicine chain extender. The chemical structure, mechanical properties, degradation rate, and swelling ratio were characterized by comparing the polymer with a polyurethane containing a 2,2-(methylimino) diethanol chain extender. Due to the incorporation of negatively charged carboxyl side groups, the bicine extended polymers exhibited higher micro-phase separation, better mechanical properties in dry condition, and better sensitivity to environmental stimuli than controls, as demonstrated by its high swelling ratio at elevated pH, lower ionic strength, or higher temperature. The swelling ratio of membranes showed reversible change as the function of pH at 37 degrees C, the membranes becoming fully water soluble at pH above 8.3. Nile blue chloride and lysozyme were selected to study their release from this polymer. The release rates of both compounds were significantly influenced by the pH and ionic strength. The swelling ratios were also influenced by lysozyme loading at low pH. The pH dependent properties were used to fabricate scaffolds by drop-on-demand printing. Bicine extended polyurethanes may be of interest for possible drug delivery applications, customizable scaffold fabrication and other potential biomedical applications.

New insight into modified release pellets - Internal structure and drug release mechanism

The aim of the study was to explore the drug release mechanism from pellets, coated with blends of poly(vinyl acetate) (PVAc) and polyvinyl alcohol-polyethylene glycol graft copolymer (PVA-PEG). Water influx and drug solubilization inside the pellets were investigated in correlation to drug release. The highly soluble drug Chlorpheniramine maleate (CPM) was used as a model compound. Modified release pellets were manufactured by fluid bed drug layering and film coating of starter beads. The pellets were characterized using cross section EDX mapping, confirming location and homogeneity of the different layers. A film coat of 23%, containing PVAc/PVA-PEG in 9:1 ratio, resulted in a sigmoid shaped release curve with 2 h lag-time, followed by 3 h of continuous drug release. Using NMR analysis, water influx and drug solubilization inside the pellets were detected within 20 min. Additionally, dissolution of PVA-PEG after several minutes and drug release after the lag-time were measurable. A fast water influx into PVAc/PVA-PEG film coated pellets did not result in a fast drug release. Despite a fast drug solubilization within the pellets, drug release was initiated after 2 h, suggesting a one way stream of water during the observed lag-time.

Novel stimuli-responsive micelle self-assembled from Y-shaped P(UA-Y-NIPAAm) copolymer for drug delivery

A new amphiphilic Y-shaped copolymer, comprised of hydrophobic poly(undecylenic acid) (PUA) and hydrophilic poly(N-isopropylacrylamide) (PNIPAAm), was designed and synthesized. A cytotoxicity study revealed that P(UA-Y-NIPAAm) copolymers did not exhibit apparent inhibition impact on the proliferation of cells when the concentration of the copolymer was below 1000 mg/L. Characterization demonstrated that the P(UA-Y-NIPAAm) copolymer is thermosensitive with a lower critical solution temperature (LCST) of 31 degrees C. In water, the P(UA-Y-NIPAAm) copolymer would self-assemble into micelles with a critical micelle concentration (CMC) of 20 mg/L. Self-assembled P(UA-Y-NIPAAm) micelles exhibited a nanospherical morphology of 40 to approximately 80 nm in size. The controlled drug release behavior of the P(UA-Y-NIPAAm) micelles was further investigated, and self-assembled micelles exhibited improved properties in controlled drug release.

Layer-by-Layer adsorption of biocompatible polyelectrolytes onto dexamethasone aggregates

Using layer-by-layer technology in drug delivery systems is advantageous because of its high precision, mild assembly conditions, and ease of use. In this study, we investigate the use of such a system using a micronized dexamethasone core as the building template. Dexamethasone was chosen because of its hydrophobic structure and role as a cellular differentiation factor. Structural characterization of the assembled structures shows particle size distribution between 3-10 mum with 20% more dissolution than free drug crystals. Additionally, as a measure of drug activity post-encapsulation, in vitro cell culture studies were performed. We suggest that the polyelectrolyte coatings enhance release and augment production of extracellular matrix proteins aggrecan and collagen II.