Controlled Drug Release from Gels Using Lipophilic Interactions of Charged Substances with Surfactants and Polymers

Development and characterization of eco-friendly biopolymer gellan gum based electrolyte for electrochemical application

Magnesium ion conducting eco-friendly biopolymer electrolyte based on gellan gum has been developed by solution casting technique and characterized by XRD, FTIR, DSC, AC impedance analysis and LSV. Amorphous nature of the polymer electrolyte has been confirmed by XRD analysis. FTIR analysis confirms the complex formation between gellan gum and magnesium nitrate salt. Glass transition temperature of the polymer electrolytes have been found in DSC analysis. Ionic conductivity of polymer electrolyte membrane has been analysized by AC impedance studies, polymer electrolyte 1.0 g gellan gum with 0.7 wt% Mg (NO3)2 has highest ionic conductivity 1.392 × 10−2 S/cm at room temperature. Evan’s polarization method attributes Mg+ cationic transference number as 0.342 for high conducting polymer electrolyte. The high conducting polymer membrane has electrochemical stability 3.58 V. Using this high conducting polymer electrolyte, magnesium ion battery is constructed and the battery performance was studied. The open circuit voltage is found as 1.99 V.

Theoretical Importance of PVP-Alginate Hydrogels Structure on Drug Release Kinetics

BACKGROUND

The new concepts of personalized and precision medicine require the design of more and more refined delivery systems. In this frame, hydrogels can play a very important role as they represent the best surrogate of soft living tissues for what concerns rheological properties. Thus, this paper focusses on a global theoretical approach able to describe how hydrogel polymeric networks can affect the release kinetics of drugs characterized by different sizes. The attention is focused on a case study dealing with an interpenetrated hydrogel made up by alginate and poly(N-vinyl-2-pyrrolidone).

METHODS

Information about polymeric network characteristics (mesh size distribution and polymer volume fraction) is deduced from the theoretical interpretation of the rheological and the low field Nuclear Magnetic Resonance (NMR) characterization of hydrogels. This information is then, embodied in the mass balance equation whose resolution provides the release kinetics.

RESULTS

Our simulations indicate the influence of network characteristics on release kinetics. In addition, the reliability of the proposed approach is supported by the comparison of the model outcome with experimental release data.

CONCLUSIONS

This study underlines the necessity of a global theoretical approach in order to design reliable delivery systems based on hydrogels.

Recent advances in smart biotechnology: Hydrogels and nanocarriers for tailored bioactive molecules depot

Over the past ten years, the global biopharmaceutical market has remarkably grown, with ten over the top twenty worldwide high performance medical treatment sales being biologics. Thus, biotech R&D (research and development) sector is becoming a key leading branch, with expanding revenues. Biotechnology offers considerable advantages compared to traditional therapeutic approaches, such as reducing side effects, specific treatments, higher patient compliance and therefore more effective treatments leading to lower healthcare costs. Within this sector, smart nanotechnology and colloidal self-assembling systems represent pivotal tools able to modulate the delivery of therapeutics. A comprehensive understanding of the processes involved in the self-assembly of the colloidal structures discussed therein is essential for the development of relevant biomedical applications. In this review we report the most promising and best performing platforms for specific classes of bioactive molecules and related target, spanning from siRNAs, gene/plasmids, proteins/growth factors, small synthetic therapeutics and bioimaging probes.

Application of mathematical modeling in sustained release delivery systems

INTRODUCTION

This review, presenting as starting point the concept of the mathematical modeling, is aimed at the physical and mathematical description of the most important mechanisms regulating drug delivery from matrix systems. The precise knowledge of the delivery mechanisms allows us to set up powerful mathematical models which, in turn, are essential for the design and optimization of appropriate drug delivery systems.

AREAS COVERED

The fundamental mechanisms for drug delivery from matrices are represented by drug diffusion, matrix swelling, matrix erosion, drug dissolution with possible recrystallization (e.g., as in the case of amorphous and nanocrystalline drugs), initial drug distribution inside the matrix, matrix geometry, matrix size distribution (in the case of spherical matrices of different diameter) and osmotic pressure. Depending on matrix characteristics, the above-reported variables may play a different role in drug delivery; thus the mathematical model needs to be built solely on the most relevant mechanisms of the particular matrix considered.

EXPERT OPINION

Despite the somewhat diffident behavior of the industrial world, in the light of the most recent findings, we believe that mathematical modeling may have a tremendous potential impact in the pharmaceutical field. We do believe that mathematical modeling will be more and more important in the future especially in the light of the rapid advent of personalized medicine, a novel therapeutic approach intended to treat each single patient instead of the 'average' patient.

Quantifying the release of lactose from polymer matrix tablets with an amperometric biosensor utilizing cellobiose dehydrogenase

The release of lactose (hydrophilic) from polymer tablets made with hydrophobically modified poly(acrylic acid) (HMPAA) have been studied and compared to the release of ibuprofen, a hydrophobic active substance. Lactose is one of the most used excipients for tablets, but lactose release has not been widely studied. One reason could be a lack of good analytical tools. A novel biosensor with cellobiose dehydrogenase (CDH) was used to detect the lactose release, which has a polydiallyldimethylammonium chloride (PDADMAC) layer that increases the response. A sample treatment using polyethylenimine (PEI) was developed to eliminate possible denaturants. The developed methodology provided a good approach to detect and quantify the released lactose. The release was studied with or without the presence of a model amphiphilic substance, sodium dodecyl sulphate (SDS), in the release medium. Ibuprofen showed very different release rates in the different media, which was attributed to hydrophobic interactions between the drug, the HMPAA and the SDS in the release medium. The release of hydrophilic lactose, which did not associate to any of the other components, was rapid and showed only minor differences. The new methodology provides a useful tool to further evaluate tablet formulations by a relatively simple set of experiments.

Using NMR chemical shift imaging to monitor swelling and molecular transport in drug-loaded tablets of hydrophobically modified poly(acrylic acid): methodology and effects of polymer (in)solubility

A new technique has been developed using NMR chemical shift imaging (CSI) to monitor water penetration and molecular transport in initially dry polymer tablets that also contain small low-molecular weight compounds to be released from the tablets. Concentration profiles of components contained in the swelling tablets could be extracted via the intensities and chemical shift changes of peaks corresponding to protons of the components. The studied tablets contained hydrophobically modified poly(acrylic acid) (HMPAA) as the polymer component and griseofulvin and ethanol as hydrophobic and hydrophilic, respectively, low-molecular weight model compounds. The water solubility of HMPAA could be altered by titration with NaOH. In the pure acid form, HMPAA tablets only underwent a finite swelling until the maximum water content of the polymer-rich phase, as confirmed by independent phase studies, had been reached. By contrast, after partial neutralization with NaOH, the polyacid became fully miscible with water. The solubility of the polymer affected the water penetration, the polymer release, and the releases of both ethanol and griseofulvin. The detailed NMR CSI concentration profiles obtained highlighted the clear differences in the disintegration/dissolution/release behavior for the two types of tablet and provided insights into their molecular origin. The study illustrates the potential of the NMR CSI technique to give information of importance for the development of pharmaceutical tablets and, more broadly, for the general understanding of any operation that involves the immersion and ultimate disintegration of a dry polymer matrix in a solvent.

Surfactants modify the release from tablets made of hydrophobically modified poly (acrylic acid)

Many novel pharmaceutically active substances are characterized by a high hydrophobicity and a low water solubility, which present challenges for their delivery as drugs. Tablets made from cross-linked hydrophobically modified poly (acrylic acid) (CLHMPAA), commercially available as Pemulen™, have previously shown promising abilities to control the release of hydrophobic model substances. This study further investigates the possibility to use CLHMPAA in tablet formulations using ibuprofen as a model substance. Furthermore, surfactants were added to the dissolution medium in order to simulate the presence of bile salts in the intestine.

The release of ibuprofen is strongly affected by the presence of surfactant and/or buffer in the dissolution medium, which affect both the behaviour of CLHMPAA and the swelling of the gel layer that surrounds the disintegrating tablets. Two mechanisms of tablet disintegration were observed under shear, namely conventional dissolution of a soluble tablet matrix and erosion of swollen insoluble gel particles from the tablet. The effects of surfactant in the surrounding medium can be circumvented by addition of surfactant to the tablet. With added surfactant, tablets that may be insusceptible to the differences in bile salt level between fasted or fed states have been produced, thus addressing a central problem in controlled delivery of hydrophobic drugs. In other words CLHMPAA is a potential candidate to be used in tablet formulations for controlled release with poorly soluble drugs.

Extended delivery of an anionic drug by contact lens loaded with a cationic surfactant

Drug eluding contact lenses can be very effective vehicles for ophthalmic drug delivery, but are incapable of releasing drug for more than a few hours. We propose to optimize the interactions of the polymer matrix of the contact lens with the hydrophobic tails of ionic surfactants to adsorb the surfactant molecules on the polymer with high packing and thus create a high surface charge. Ionic drugs can then adsorb on the charged surfactant coated surfaces with high affinity to reduce the transport rates, leading to extended release. Specifically, we show control release of an anionic drug dexamethasone 21-disodium phosphate from poly-hydroxyethyl methacrylate (p-HEMA) contact lenses by utilizing cationic surfactant (cetalkonium chloride). The partition coefficient of the drug increase exponentially with surfactant loading in the gel in at least qualitative agreement with the Debye-Hückel theory. The drug adsorbs on the surfactant covered polymer, and can also diffuse along the surface with diffusivity lower than that for the free drug, leading to a reduction in the effective diffusivity, which is the weighted combination of the free and surface diffusivities. The addition of surfactant did not impact transparency of lenses, and had additional benefits of increase in wettability and significant reduction in protein absorption. With a surfactant loading of about 10%, the drug release duration was increased from about 2 h to 50 h in 1-day ACUVUE(®) contact lenses, proving the viability of using surfactant for increasing drug release durations.

Influence of surfactants on the release behaviour and structural properties of sol-gel derived silica xerogels embedded with metronidazole

The aim of this study was to obtain stable and controlled release silica xerogels containing metronidazole (MT) prepared with surfactants with different charges: cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulphate (SDS) and hydroxypropyl cellulose (HPC), which could be the promising carrier materials used as the implantable drug delivery systems. The xerogels were prepared by the sol-gel method. The influence of various formulation precursors on porosity parameters and drug release were investigated. Addition of surfactants showed a promising result in controlling the MT release. Dissolution study revealed increased release of MT from silica modified SDS and CTAB, whereas the release of MT from silica modified HPC considerably decreased, in comparison with unmodified silica. The addition of surfactants showed slight changes in porosity parameters. All xerogels are characterized by a highly developed surface area (701-642 m(2) g(-1)) and mesoporous structure. The correlation between pore size obtained matrices and release rate of drug was also observed. Based on the presented results of this study, it may be stated that applied xerogel matrices: pure silica and surfactants-modified silica could be promising candidates for the formulation in local delivery systems.

Gel formulations containing catanionic vesicles composed of alprenolol and SDS: effects of drug release and skin penetration on aggregate structure

To fully utilize the extended contact time of gel formulations a novel formulation with drug containing catanionic aggregates offering prolonged drug release and skin penetration were investigated. This study aimed to further explore the drug release process from catanionic vesicles in gels. Catanionic vesicles were formed from alprenolol and sodium dodecyl sulphate. Physical gels composed of catanionic vesicles and a SoftCAT polymer were used as well as covalent Carbopol gels. Drug release was measured in vitro using a modified USP paddle method and the skin penetration was studied using dermatomized pig ear skin mounted in horizontal Ussing chambers. The aggregate structure was visualized with cryo-TEM during the drug release and skin penetration process. The study results show that catanionic vesicles are present in the formulations throughout the drug release process and during the clinically relevant skin application time. Hence, the decreased skin penetration rate stems from the prolonged release of drug substance from the gels. The rheological investigation shows that the gel structure of the physically cross-linked gels is maintained even as the drug substance is released and the gel volume is decreased. These findings indicate that the applicability of formulations like these is a future possibility.

Physicochemical interactions between drugs and superdisintegrants

We have evaluated the interactions between superdisintegrants and drugs with different physicochemical characteristics, which may affect the in-vivo absorption e.g. after mucosal administration. The binding of sodium salicylate, naproxen, methyl hydroxybenzoate (methylparaben), ethyl hydroxybenzoate (ethylparaben), propyl hydroxybenzoate (propylparaben), atenolol, alprenolol, diphenhydramine, verapamil, amitriptyline and cetylpyridinium chloride monohydrate (CPC) to different superdisintegrants (sodium starch glycolate (SSG), croscarmellose sodium (CCS) and crospovidone) and one unsubstituted comparator (starch) was studied spectrophotometrically. An indication of the in-vivo effect was obtained by measuring the interactions at physiological salt concentrations. SSG was investigated more thoroughly to obtain release profiles and correlation between binding and ionic strength. The results showed that the main interactions with the anionic hydrogels formed by SSG and CCS were caused by ion exchange, whereas the neutral crospovidone exhibited lipophilic interactions with the non-ionic substances. The effect of increased ionic strength was most pronounced at low salt concentrations and the ion exchange interactions were almost completely eradicated at physiological conditions. The release profile of diphenhydramine was significantly affected by the addition of salt. It was thus concluded that the choice of buffer was of great importance for in-vitro experiments with ionic drugs. At physiological salt concentrations the interactions did not appear to be strong enough to influence the in-vivo bioavailability of any of the drug molecules.

Pharmaceutical applications for catanionic mixtures

Mixtures of oppositely charged surfactants, so called catanionic mixtures, are a growing area of research. These mixtures have been shown to form several different types of surfactant aggregates, such as micelles of various forms and sizes, and lamellar structures, such as vesicles. In this review, a short introduction to the field of catanionic mixtures is presented and the pharmaceutical possibilities offered by such mixtures are reviewed. There are several interesting ideas on how to apply catanionic mixtures to improve the delivery of, for example, drug compounds and DNA, or for HIV treatment.

The Influence of Surfactants and Additives on Drug Release from a Cationic Eudragit Coated Multiparticulate Diltiazem Formulation

A cationic polymethacrylate coated multiparticulate diltiazem formulation exhibited sigmoidal drug release. Lag time prior to drug release was influenced by dissolution media, coat thickness, and by the nature of additives included in the formulation. Incorporation of up to 5% w/w sodium lauryl sulfate (SLS) in the coating membrane resulted in substantial increases in lag times in acidic and neutral media. The extent of drug release in acid was 100%, whereas in phosphate buffer, the extent of release was dependent on the level of SLS. Substituting SLS for various compounds was used to assess the functionality of the SLS molecule responsible for these behaviors. The ability to ion-pair with the polymer and the presence of a hydrophobic moiety were both important functionalities.

Catanionic mixtures involving a drug: A rather general concept that can be utilized for prolonged drug release from gels

The aim of this work was to study at what extent mixtures of drug substances and oppositely charged surfactants form catanionic aggregates and to apply these as a means of obtaining prolonged drug release from a gel. The properties of traditional catanionic mixtures are relatively well known, but only recently we found that not only traditional surfactants form these mixtures, but also structurally more complex surface active drug compounds. In this study, several different compositions of catanionic mixtures were studied visually, by cryogenic transmission electron microscopy (cryo-TEM) and rheologically using a Bohlin VOR Rheometer. Some of the catanionic vesicle and micelle phases were incorporated in and released from gels using the USP paddle method. The drug compounds investigated were lidocaine, ibuprofen, naproxen, alprenolol, propranolol, and orphenadrine. Of the six drug molecules used in this study, five, both positively and negatively charged, were capable of forming catanionic vesicles and/or micelles with oppositely charged surfactants. The drug release studies show that catanionic drug surfactant mixtures are beneficial for obtaining prolonged release from gels, as the drug release using catanionic vesicles and micelles was prolonged between 10 and 100 times compared to the release of pure drug substance from the gel.

Controlled release of lidocaine hydrochloride from the surfactant-doped hybrid xerogels

We investigate the controlled release of lidocaine hydrochloride from the doped silica-based xerogels. In the xerogel preparation, tetraethoxysilane (TEOS), methyltriethoxysilane (MTES), and propyltriethoxysilane (PTES) are used as precursors, and a nonionic surfactant Igepal CO 720 is used as a dopant. The experimental results suggest that the release of lidocaine hydrochloride can be easily controlled by partially substituting TEOS with the organosilanes, and/or by adding the dopant. Adding the organosilane precursors lowers the release of both the drug and the surfactant in the order of TEOS, MTES/TEOS, and PTES/TEOS xerogels. The release from the PTES/TEOS xerogels is much lower than that from the other xerogels. The release of lidocaine hydrochloride is obviously suppressed by the addition of Igepal CO 720, while the release of Igepal CO 720 is slightly promoted by the addition of the drug. The overall release process is found to be diffusion-controlled, and the release behaviors can be well explained by considering the effects of the textual properties of the xerogels and the interactions among the drug, the surfactant, and the xerogel matrices.

Interactions of ibuprofen with cationic polysaccharides in aqueous dispersions and hydrogels

Non-steroidal antiinflammatory drugs, such as ibuprofen, are amphiphilic substances capable of self-association in aqueous solutions and able to be sorbed onto polymers through hydrophobic and electrostatic bonds. The aim of this work was to analyze the association processes of sodium ibuprofen with cationic celluloses (Celquat H-100 (PQ-4) and SC-230 M (PQ-10)) and cationic guar gums (Ecopol 261-S and 14-S) and their repercussions on the properties of the aqueous dispersions and cross-linked hydrogels. The interaction process was studied in aqueous dispersions through transmittance, surface tension, fluorescence, conductivity, viscosity and oscillatory rheometry measurements. Below cmc, the drug molecules weakly interact with the polymers through hydrophobic and ionic interactions. Around the cmc (4%), a notable decrease in the viscosity, and storage and loss moduli of the dispersions (even precipitation in PQ-10 systems) was observed. An additional increase in drug concentration induced the dispersions to recover their initial properties. Since ibuprofen/polymer cationic groups ratio were in all cases above 1, these observations indicate that drug self-association induces the polymer to coil around the micelles and, as the number of micelles increases (more drug concentration) the polymer chains interact with more of them, uncoiling again to some extent. Polymer (1%) dispersions containing 6% ibuprofen showed drug diffusion coefficients much lower than in water. When a surfactant, sodium dodecylsulfate, was added to these systems the diffusion coefficients decreased even more, suggesting the formation of new associative structures. Chemically cross-linked hydrogels made of these cationic polysaccharides absorb considerable amounts of ibuprofen (up to 15 g/g) and showed a pH-dependent release process. At acidic pH, drug-polymer affinity is maintained, preventing drug release. In contrast, at pH 8 the interactions are broken and the release process is sustained for more than 4h. In summary, ibuprofen interactions with cationic polysaccharides strongly determine the performance of their aqueous dispersions and hydrogels.

Catanionic drug-surfactant mixtures: phase behavior and sustained release from gels

PURPOSE

To study mixtures of SDS and the drugs diphenhydramine, tetracaine, and amitriptyline to compile phase diagrams and to investigate the use of interesting phases for sustained release from gels.

METHODS

Phase diagrams were composed by studying large numbers of different compositions of negatively charged SDS and positively charged drug compounds visually, rheologically, and by cryotransmission electron microscopy. Drug release from Carbopol 940 and agar gels containing interesting phases, e.g., vesicle and branched micelle phases, was measured in vitro by the USP paddle method.

RESULTS

Vesicles and elongated and branched micelles were formed on the SDS-rich side in all three systems examined. The tetracaine system differed from the other two in that it showed a vesicle area in the drug-rich side. Release of diphenhydramine from Carbopol 940 gels was slowed by at least a factor of 10 when in the form of vesicles or branched micelles. The same delay was found for both drug-rich and SDS-rich tetracaine vesicles.

CONCLUSIONS

Mixtures of SDS and positively charged drugs form the same interesting phases as traditional catanionic mixtures. This may prove useful in obtaining functional controlled-release systems when using gels as drug carriers.

Dynamic rheological measurements and drug release kinetics in swollen scleroglucan matrices

The structure of scleroglucan gel matrices was characterized by dynamic rheological studies. The results were compared with the release kinetics of theophylline in analogous samples using a Franz diffusion cell, fitting the drug release data with a semi-empirical power law. Dynamic rheology gave information about the viscous and elastic components (loss and storage moduli, respectively) of the gel which could influence the drug-release profiles. Scleroglucan gels showed two structural transitions within the gel regime that coincided with changes in the release pattern. It was found that the introduction of 0.4% (w/w) of theophylline decreased the loss and storage moduli in the 2% (w/w) scleroglucan gels by 50%. The influence of the same wt.% theophylline in other gels was strongly dependent on the gel concentration. These results demonstrated the value of rheological studies to detect matrix structural changes produced by the inclusion of drugs which may modify the drug-release profile.

Evaluation of drug release from gels on pig nasal mucosa in a horizontal Ussing chamber

In this study, controlled release gel formulations containing dihydroalprenolol (DHA), hydrocortisone (HC) or testosterone (TS) in Carbopol 934P (C934) were evaluated using pig nasal mucosa in a horizontal Ussing chamber. The controlled release gel formulations were designed by including DHA in vesicle bilayers formed with sodium dodecyl sulphate (SDS) (1.4 and 36 mM) and by partitioning TS to the core of Brij 58 (B58, 1%) micelles. For comparison, unmodified gels and solutions of the drugs and additives were examined in parallel experiments. The viability and toxicity were evaluated with electrophysiological measurements and light microscopy. The results showed that C934 did not affect the viability of the mucosa and that the rate and profile of the appearance on the receiver side was independent of whether the substances were released from an unmodified gel or an unmodified solution. Continuous electrophysiological measurements made during exposure showed that B58 (1%) and SDS (1.4 mM) inactivated the mucosa, whereas SDS (36 mM) activated it. Investigations made after a 90-min exposure to the formulations showed that all the modified gels had inactivated the mucosa and had negative effects on the morphology. For the TS-B58 (1%) and the DHA-SDS (36 mM) gels, the rate-limiting step in transport was the release from the formulation. The results confirmed that gels from C934 are suitable for nasal administration and also clearly indicated the different degrees of toxicity of the controlled release formulations evaluated in this study. The horizontal Ussing chamber method was a suitable tool for the evaluation of gels for nasal administration.