Solubility effects on drug transport through pH-sensitive, swelling-controlled release systems: Transport of theophylline and metoclopramide monohydrochloride

Fabrication and In vitro Evaluation of Carbopol/Polyvinyl Alcohol-based pH-sensitive Hydrogels for Controlled Drug Delivery

BACKGROUND

Diclofenac sodium has a short half-life (about 1.5 hours), requiring repeated administration, and as a result, serious complications, such as GI bleeding, peptic ulcer, and kidney and liver dysfunction, are generated. Hence, a sustained/controlled drug delivery system is needed to overcome the complications caused by the administration of diclofenac sodium.

AIMS

This study aimed to fabricate and evaluate carbopol/polyvinyl alcohol-based pH-sensitive hydrogels for controlled drug delivery.

OBJECTIVE

pH-sensitive carbopol/polyvinyl alcohol graft-poly(acrylic acid) hydrogels (Cp/PVA-g-PAa hydrogels) were developed for the controlled delivery of diclofenac sodium.

METHODS

The combination of carbopol/polyvinyl alcohol, acrylic acid, and ethylene glycol dimethacrylate was used as polymer, monomer, and cross-linker, respectively. The effects of the formulation's composition on porosity, swelling index, and release pattern of diclofenac sodium from the developed hydrogels were investigated.

RESULTS

An increase in porosity and swelling was observed with the increasing amounts of carbopol and acrylic acid, whereas polyvinyl alcohol showed the opposite effect. Due to the formation of a highly viscous system, the drug release decreased with the increasing concentrations of carbopol and polyvinyl alcohol while increased with increasing acrylic acid concentration. The pH-responsive properties of the fabricated hydrogels were demonstrated by dynamic swelling and drug release studies at three different pH values. Higher dynamic swelling and diclofenac sodium (model drug) release were found at high pH values compared to low pH values, i.e., pH 7.4 > 4.6 > 1.2, respectively. Cytotoxicity studies reported no toxic effect of the prepared hydrogels, thus indicating that the prepared hydrogels are safe to be used on clinical basis.

CONCLUSION

The prepared carbopol/polyvinyl alcohol crosslinked hydrogel can be used as a promising carrier for the controlled release of drugs.

Efficacy of Graphene-Based Nanocomposite Gels as a Promising Wound Healing Biomaterial

The development of biocompatible nanocomposite hydrogels with effective wound healing/microbicidal properties is needed to bring out their distinguished characteristics in clinical applications. The positive interaction between graphene oxide/reduced graphene oxide (GO/rGO) and hydrogels and aloe vera gel represents a strong strategy for the advancement of therapeutic approaches for wound healing. In this study, the synthesis, characterization, and angiogenic properties of graphene-based nanocomposite gels have been corroborated and substantiated through several in vitro and in vivo assays. In this respect, graphene oxide was synthesized by incorporating a modified Hummer's method and ascertained by Raman spectroscopy. The obtained GO and rGO were uniformly dispersed into the aloe vera gel and hydrogel, respectively, as wound healing materials. These formulations were characterized via in vitro bio-chemical techniques and were found suitable for the appropriate cell viability, attachment, and proliferation. In addition, in vivo experiments were conducted using male Wistar rats. This revealed that the GO/rGO-based gels stimulated wound contraction and re-epithelialization compared to that of the non-treatment group. From the study, it is suggested that GO/rGO-based aloe vera gel can be recommended as a promising candidate for wound healing applications.

Bioinspired tunable hydrogels: An update on methods of preparation, classification, and biomedical and therapeutic applications

Hydrogels exhibit water-insoluble three-dimensional polymeric networks capable of absorbing large amounts of biological fluids. Both natural and synthetic polymers are used for the preparation of hydrogel networks. Such polymeric networks are fabricated through chemical or physical mechanisms of crosslinking. Chemical crosslinking is accomplished mainly through covalent bonding, while physical crosslinking involves self-healing secondary forces like H-bonding, host-guest interactions, and antigen-antibody interactions. The building blocks of the hydrogels play an important role in determining the mechanical, biological, and physicochemical properties. Hydrogels are used in a variety of biomedical applications like diagnostics (biodetection and bioimaging), delivery of therapeutics (drugs, immunotherapeutics, and vaccines), wound dressing and skin materials, cardiac complications, contact lenses, tissue engineering, and cell culture because of the inherent characteristics like enhanced water uptake and structural similarity with the extracellular matrix (ECM). This review highlights the recent trends and advances in the roles of hydrogels in biomedical and therapeutic applications. We also discuss the classification and methods of hydrogels preparation. A brief outlook on the future directions of hydrogels is also presented.

Formulation and In-Vitro Characterization of pH-Responsive Semi-Interpenetrating Polymer Network Hydrogels for Controlled Release of Ketorolac Tromethamine

Ketorolac tromethamine is a non-steroidal anti-inflammatory drug used in the management of severe pain. The half-life of Ketorolac tromethamine is within the range of 2.5–4 h. Hence, repeated doses of Ketorolac tromethamine are needed in a day to maintain the therapeutic level. However, taking several doses of Ketorolac tromethamine in a day generates certain complications, such as acute renal failure and gastrointestinal ulceration. Therefore, a polymeric-controlled drug delivery system is needed that could prolong the release of Ketorolac tromethamine. Therefore, in the current study, pH-responsive carbopol 934/sodium polystyrene sulfonate-co-poly(acrylic acid) (CP/SpScPAA) hydrogels were developed by the free radical polymerization technique for the controlled release of Ketorolac tromethamine. Monomer acrylic acid was crosslinked with the polymers carbopol 934 and sodium polystyrene sulfonate by the cross-linker N’,N’-methylene bisacrylamide. Various studies were conducted to evaluate and assess the various parameters of the fabricated hydrogels. The compatibility of the constituents used in the preparation of hydrogels was confirmed by FTIR analysis, whereas the thermal stability of the unreacted polymers and developed hydrogels was analyzed by TGA and DSC, respectively. A smooth and porous surface was indicated by SEM. The crystallinity of carbopol 934, sodium polystyrene sulfonate, and the prepared hydrogels was evaluated by PXRD, which revealed a reduction in the crystallinity of reactants for the developed hydrogels. The pH sensitivity of the polymeric hydrogel networks was confirmed by dynamic swelling and in vitro release studies with two different pH media i.e., pH 1.2 and 7.4, respectively. Maximum swelling was exhibited at pH 7.4 compared to pH 1.2 and, likewise, a greater percent drug release was perceived at pH 7.4. Conclusively, we can demonstrate that the developed pH-sensitive hydrogel network could be employed as a suitable carrier for the controlled delivery of Ketorolac tromethamine.

Using Carbomer-Based Hydrogels for Control the Release Rate of Diclofenac Sodium: Preparation and In Vitro Evaluation

The aim of the current research work was to prepare Car934-g-poly(acrylic acid) hydrogels by the free-radical polymerization technique. Various concentrations of carbopol, acrylic acid and ethylene glycol dimethacrylate were employed for the fabrication of Car934-g-poly(acrylic acid) hydrogels. Fourier-transform infrared spectroscopy (FTIR), Thermogravimetric analysis (TGA), Differential scanning calorimetry (DSC), Scanning electron microscope (SEM) and Powder X-ray diffractometry (PXRD) studies were performed to know the structural arrangement, thermal stability, physical appearance and amorphous network of developed hydrogels. FTIR analysis revealed that carbopol reacted with acrylic acid during the process of polymerization and confirmed the grafting of acrylic acid over the backbone of carbopol. TGA and DSC studies showed that developed hydrogels were thermally stable. Surface morphology was analyzed by SEM, which confirmed a porous network of hydrogels. PXRD analysis indicated that crystallinity of the drug was reduced by the amorphous network of hydrogels. Furthermore, swelling studies for all developed hydrogels were performed at both media, i.e., pH 1.2 and 7.4, and higher swelling was exhibited at pH 7.4. Sol–gel analysis was performed to evaluate the soluble unreacted part of the fabricated hydrogels. Similarly, an in-vitro study was conducted for all hydrogel formulations at both acidic (pH 1.2) and basic (pH 7.4) mediums, and a greater drug release was observed at pH 7.4. Different kinetics such as zero-order, first-order, the Higuchi model and the Korsmeyer–Peppas model were applied to know the mechanism of release order of drugs from the hydrogels.

The influence of hydroalcoholic media on the performance of Grewia polysaccharide in sustained release tablets

Co-administration of drugs with alcohol can affect the plasma concentration of drugs in patients. It is also known that the excipients used in the formulation of drugs may not always be resistant to alcohol. This study evaluates effect of varying alcohol concentrations on theophylline release from two grades of Grewia mollis polysaccharides. X-ray microtomography showed that native polysaccharide formulation compacts were not homogenous after the mixing process resulting in its failure in swelling studies. Removal of starch from the native polysaccharide resulted in homogenous formulation compacts resistant to damage in high alcoholic media in pH 6.8 (40%v/v absolute ethanol). Destarched polymer compacts had a significantly higher hardness (375N) than that of the native polysaccharide (82N) and HPMC K4M (146N). Dissolution studies showed similarity at all levels of alcohol tested (f₂=57-91) in simulated gastric media (pH 1.2). The dissolution profiles in the simulated intestinal fluids were also similar (f₂=60-94), with the exception of the native polysaccharide in pH 6.8 (40%v/v absolute ethanol) (f₂=43). This work highlights the properties of Grewia polysaccharide as a matrix former that can resist high alcoholic effects therefore; it may be suitable as an alternative to some of the commercially available matrix formers with wider applications for drug delivery as a cheaper alternative in the developing world.

Diffusion of water-soluble sorptive drugs in HEMA/MAA hydrogels

We measure and, for the first time, theoretically predict four prototypical aqueous-drug diffusion coefficients in five soft-contact-lens material hydrogels where solute-specific adsorption is pronounced. Two-photon fluorescence confocal microscopy and UV/Vis-absorption spectrophotometry assess transient solute concentration profiles and concentration histories, respectively. Diffusion coefficients are obtained for acetazolamide, riboflavin, sodium fluorescein, and theophylline in 2-hydroxyethyl methacrylate/methacrylic acid (HEMA/MAA) copolymer hydrogels as functions of composition, equilibrium water content (30-90%), and aqueous pH (2 and 7.4). At pH2, MAA chains are nonionic, whereas at pH7.4, MAA chains are anionic (pKa≈5.2). All studied prototypical drugs specifically interact with HEMA and nonionic MAA (at pH2) moieties. Conversely, none of the prototypical drugs adsorb specifically to anionic MAA (at pH7.4) chains. As expected, diffusivities of adsorbing solutes are significantly diminished by specific interactions with hydrogel strands. Despite similar solute size, relative diffusion coefficients in the hydrogels span several orders of magnitude because of varying degrees of solute interactions with hydrogel-polymer chains. To provide a theoretical framework for the new diffusion data, we apply an effective-medium model extended for solute-specific interactions with hydrogel copolymer strands. Sorptive-diffusion kinetics is successfully described by local equilibrium and Henry's law. All necessary parameters are determined independently. Predicted diffusivities are in good agreement with experiment.

Controlled Release of Biomolecules from pH-Sensitive Hydrogels Prepared by Radiation Polymerization

Copolymers of 2-hydroxyethyl methacrylate and methacrylic acid based hydrogels were studied as hydrogel drug delivery systems. Radiation copolymerization of 2-hydroxyethyl methacrylate and methacrylic acid (mixed with 3,3'-azobis(6-hydroxy benzoic acid)(ABHB) as an azo derivative of 5-aminosalicylic acid were carried out with various amounts of methacryloyloxyethyl esters of terephthalic acid for crosslinking. The polymer structures were characterized by FTIR, 1H NMR, 13C NMR spectroscopy and glass transition temperature (Tg). The hydrolysis of the drug–polymer conjugates were carried out in dialysis bags containing aqueous buffer solutions (pH 1 and 7.4) at 37°C. The drug-release profiles indicate that the amount of drug release depended on the degree of swelling and crosslinking.

An Oral Delivery System for Insulin

Crosslinked 2-hydroxyethyl methacrylate (HEMA) and methacrylic acid (MAA) copolymer hydrogels were studied as drug delivery systems. Terephthalic acid was covalently linked with 2-hydroxyethyl methacrylate (HEMA), abbreviated as cross-linking agent (CA). Free radical copolymerization of HEMA and MAA with terephthetalic acid (CA) (2, 4, and 6%) as crosslinking agent were carried out at 70°C. The structure of the CA was confirmed by FT-IR, 1H-NMR and 13C-NMR spectroscopy. The composition of the crosslinked three-dimensional polymers were determined by FTIR spectroscopy. Glass transition temperature (Tg) of the network polymers was determined calorimetrically. The effect of copolymer composition on the swelling behavior and hydrolytic degradation was studied in simulated gastric fluid (SGF, pH 1) and simulated intestinal fluid (SIF, pH 7.4). The swelling and hydrolytic behavior of the copolymers depended on the content of MAA which caused a decrease in gel swelling in SGF or an increase in gel swelling in SIF. It was observed that in acidic media hydrogen bonds formed due to the protonation of the carboxylic acid groups of the MAA while in more basic or neutral conditions electrostatic repulsion occurred between the ionized carboxylic acid groups. This complex behavior affected the macroscopic swelling properties of the resultant hydrogels. The amount of drug release depended on the degree of hydrogel swelling and crosslinking.

Stimulus-responsive hydrogels: Theory, modern advances, and applications

Over the past century, hydrogels have emerged as effective materials for an immense variety of applications. The unique network structure of hydrogels enables very high levels of hydrophilicity and biocompatibility, while at the same time exhibiting the soft physical properties associated with living tissue, making them ideal biomaterials. Stimulus-responsive hydrogels have been especially impactful, allowing for unprecedented levels of control over material properties in response to external cues. This enhanced control has enabled groundbreaking advances in healthcare, allowing for more effective treatment of a vast array of diseases and improved approaches for tissue engineering and wound healing. In this extensive review, we identify and discuss the multitude of response modalities that have been developed, including temperature, pH, chemical, light, electro, and shear-sensitive hydrogels. We discuss the theoretical analysis of hydrogel properties and the mechanisms used to create these responses, highlighting both the pioneering and most recent work in all of these fields. Finally, we review the many current and proposed applications of these hydrogels in medicine and industry.

Modified biopolymer-dextrin based crosslinked hydrogels: application in controlled drug delivery

This review describes hydrogels and their classifications along with the synthesis and properties of biopolymer-dextrin based crosslinked hydrogels towards potential application in controlled drug delivery.

Advances in oral controlled drug delivery: the role of drug-polymer and interpolymer non-covalent interactions

INTRODUCTION

After more than four decades of intense research, oral controlled drug delivery systems (DDSs) still represent a topic of major interest for pharmaceutical scientist and formulators. This can be explained in part by considering the economic value of oral DDSs whose market accounts for more than half of the overall drug delivery market. Polymeric systems based on drug-polymer non-covalent interaction represent a limited, but growing part of the field. Despite the large amount of literature and published reviews covering specific aspects, there is still need for a review of the relevant literature providing a general picture of the topic.

AREAS COVERED

The present review aims at presenting the latest findings in drug-polymer and interpolymer non-covalent interactions in oral controlled delivery while providing a specific perspective and a critical point of view, particularly on the tools and methods used for the study of these DDSs. Four main sections are considered: i) ionic interactions between drugs and polymers; ii) interpolymer complexes; iii) hydrogen bond; and iv) hydrophobic interactions.

EXPERT OPINION

The largest part of the scientific literature deals with systems based on drug-polymer ionic interactions while hydrogen bonding and hydrophobic interaction though, very promising, are more difficult to exploit, and therefore less studied. An accurate and exhaustive representation of the specific role of the chemical functions in establishing predictable interactions between drug and polymers is still required.

Effect of different polymers on in vitro and ex vivo permeability of Ofloxacin from its mucoadhesive suspensions

Considering the importance of drug permeation from formulations, in vitro and ex vivo drug permeation characteristics of three oral mucoadhesive suspensions of Ofloxacin were designed and compared. Three suspensions of Ofloxacin were prepared by taking two grades of Carbopol polymer such as Carbopol 934 (C934) and Carbopol 940 (C940); and Hydroxypropyl methylcellulose. The permeability study was performed by using a Franz diffusion cell through both synthetic cellulose acetate membrane and excised goat gastrointestinal membranes in acidic as well as alkaline pH. To know the permeability of the drug from control/formulations through different membranes in acidic/alkaline pH, cumulative percentage drug permeation, apparent permeability (Papp) and flux (J) were calculated. In addition, enhancement ratio (ER) of each formulation was also determined. From our results, it is evident that formulation containing C940 was the best suspension considering Papp and J values of all formulations. Moreover, it was the most beneficial formulation for improving permeation and diffusivity of Ofloxacin even after 16 h. Hence, this suspension was probably the most suitable formulation to obtain prolonged release action of the drug. The ER values of all formulations through the excised goat intestinal mucus membrane in alkaline pH were higher than those formulations through the goat stomach mucosal membrane in acidic pH. ER values of those formulations indicate that the permeability of the drug was more enhanced by the polymers in the intestinal part, leading to more bioavailability and prolonged action in that portion of the gastrointestinal tract. It may also be concluded from our results that in addition to formulation containing C940, other formulations may also show effective controlled release action.

Desorption electrospray ionization high-resolution mass spectrometry for the fast investigation of natural polysaccharide interactions with a model drug in controlled release systems

RATIONALE

The control of drug release involves gaining an understanding of the complex interaction networks among drug-excipients-matrix-biological fluids. Thus, novel analytical methods that will lead to a better understanding of these interaction networks are urgently required.

METHODS

Desorption electrospray ionization high-resolution mass spectrometry (DESI-HRMS) was used to evaluate the behaviour of four biocompatible polysaccharides (chondroitin sulfate, chitosan, sodium alginate and λ-carrageenan) in the release of atenolol (ATN) from drug tablets. An aqueous solution at three different pH values (pH 7.4, 4.5 and 1.2) was electrosprayed onto the tablets, allowing direct, fast, sensitive detection of atenolol as the protonated molecule in positive ion mode. Information about the desorption mechanism was obtained by analyzing the ATN [M+H](+) ion signal as a function of time. ATN-polymer interactions in the drug/polymer mixtures were also studied by Horizontal Attenuated Total Reflectance (HATR) Fourier transform infrared (FTIR) spectroscopy.

RESULTS

The DESI-MS results revealed statistically different ATN desorption trends as a function of the polysaccharide investigated and the pH of the desorbing solution. Different release kinetics were ascribed to the drug-polymer interactions, and to the diffusion process of the drug through the hydrated polymer mesh. In particular, the alginate and λ-carrageenan matrices were able to sustain drug release from the tablet even for a highly soluble drug. The HATR results confirmed the presence of ATN-polymer interactions that, depending on the polymer-drug-solvent combination used, might affect ATN diffusion.

CONCLUSIONS

These results suggest that DESI-MS has a potential role for the micro-environmental analysis of drug diffusion and surface distribution in polymeric matrices.

Drug release kinetics and front movement in matrix tablets containing diltiazem or metoprolol/λ-carrageenan complexes

In this work we investigated the moving boundaries and the associated drug release kinetics in matrix tablets prepared with two complexes between λ-carrageenan and two soluble model drugs, namely, diltiazem HCl and metoprolol tartrate aiming at clarifying the role played by drug/polymer interaction on the water uptake, swelling, drug dissolution, and drug release performance of the matrix. The two studied complexes released the drug with different mechanism indicating two different drug/polymer interaction strengths. The comparison between the drug release behaviour of the complexes and the relevant physical mixtures indicates that diltiazem gave rise to a less soluble and more stable complex with carrageenan than metoprolol. The less stable metoprolol complex afforded an erodible matrix, whereas the stronger interaction between diltiazem and carrageenan resulted in a poorly soluble, slowly dissolving matrix. It was concluded that the different stability of the studied complexes affords two distinct drug delivery systems: in the case of MTP, the dissociation of the complex, as a consequence of the interaction with water, affords a classical soluble matrix type delivery system; in the case of DTZ, the dissolving/diffusing species is the complex itself because of the very strong interaction between the drug and the polymer.

Synthesis of chemically cross-linked polyvinyl alcohol-co-poly (methacrylic acid) hydrogels by copolymerization; a potential graft-polymeric carrier for oral delivery of 5-fluorouracil

Background of the Study

The propose of the present work was to develop chemically cross-linked polyvinyl alcohol-co-poly(methacrylic acid) hydrogel (PVA-MAA hydrogel) for pH responsive delivery of 5-Fluorouracil (5-FU).

Methods

PVA based hydrogels were prepared by free radical copolymerization. PVA has been cross-linked chemically with monomer (methacrylic acid) in aqueous medium, cross-linking agent was ethylene glycol di-methacrylate (EGDMA) and benzoyl peroxide was added as reaction initiator. 5-FU was loaded as model drug. FTIR, XRD, TGA and DSC were performed for characterization of copolymer. Surface morphology was studied by SEM. pH sensitive properties were evaluated by swelling dynamics and equilibrium swelling ratio at low and higher pH.

Results

FTIR, XRD, TGA and DSC studies confirmed the formation of new copolymer. Formulations with higher MAA contents showed maximum swelling at 7.4 pH. High drug loading and higher drug release has been observed at pH 7.4.

Conclusions

The current study concludes that a stable copolymeric network of PVA was developed with MAA. The prepared hydrogels were highly pH responsive. This polymeric network could be a potential delivery system for colon targeting of 5-FU in colorectal cancers.

pH-controlled nanoaggregation in amphiphilic polymer co-networks

Domain formation and control in pH-responsive amphiphilic polymer co-networks are studied theoretically. Two different molecular architectures of the polymer network are considered, depending on whether the pH-sensitive motif is borne by the hydrophobic or the hydrophilic monomer. When the hydrophobic polymer contains acidic groups, such chains form nanometric aggregates at acidic conditions, but they are found in a swollen state at alkaline pH. At intermediate pH, the nanoaggregation behavior of the hydrophobic polymer depends critically on the environment salt concentration. Moreover, our results indicate the presence of microphase separation into domains of swollen and aggregated hydrophobic chains. If the hydrophilic polymer is the ionizable component of the network, the nanoaggregation of hydrophobic monomers is weakly dependent on the pH and salt concentration, and except at very low volume fraction, the aggregate is the most probable conformation of the network in the entire range of pH and salt concentration studied. The two different hydrogels display quantitatively similar swelling transition and apparent pKa, but at the nanoscale, their behavior is qualitatively different. The spatial distribution of electric charge on the network as well as the local density of the different chemical species within the hydrogel can be controlled, as a function of pH and salt concentration, by the molecular architecture of the polymer network. These findings have relevance for applications in biomaterials and nanotechnology, in particular, in the design of oral delivery devices for the administration of hydrophobic drugs.

FTIR and Raman Spectroscopic Investigations of a Norfloxacin/Carbopol934 Polymeric Suspension

Till now very few formulations are available from which the drug is uniformly absorbed, so that the safe and effective blood level of norfloxacin could be maintained for a prolonged period. To fulfill this requirement, a controlled release mucoadhesive suspension was prepared by using a mucoadhesive carbopol934 polymer. The chemical interaction between norfloxacin and the polymer in formulation (prepared by an ultrasonication method) has been studied by FTIR and Raman spectroscopy. From the spectral interpretation, it has been found that in formulation, the carboxylic groups of norfloxacin and hydroxyl groups of carbopol934 undergo chemical interaction, leading to esterification and hydrogen bonding. The formation of micellies due to esterification and hydrogen bonding causes more drug entrapment and a stable formulation. From this it can be concluded that the formulation of norfloxacin may give a better controlled release and mucoadhesive action in the gastrointestinal tract. Hence, carbopol934 could be considered as an effective carrier for norfloxacin.

pH Sensitive graft copolymers for zero order drug release: a mechanistic analysis

Aliphatic polyesters containing pendent unsaturation were synthesized by the polycondensation of a diol, dicarboxylic acid and glycidyl methacrylate. Grafting methacrylic acid (MAA) resulted in graft copolymers containing polyester backbone and MAA grafts. Depending on composition, the polymers swelled extensively and eroded or dissolved at near neutral pH but remained in collapsed state at acidic pH. Three representative drugs differing in solubility, viz., Diltiazem hydrochloride (DH), Indomethacin (IM) and Verapamil hydrochloride (VH) were released at constant rate from tablets made by compressing spray-dried microparticles. The release of DH at constant rate has been attributed to increase in diffusion coefficient of the drug from the swollen layer of matrix. The release of IM and VH at constant rate was governed by erosion and was enhanced in matrices which undergo dissolution. The release rate was enhanced with increasing MAA content and the frequency of grafts along the polyester backbone. Once a day dosage forms for drugs differing in solubility have been developed using a single polymer matrix which is easy to manufacture.

Starch-based polymeric carriers for oral-insulin delivery

The objective of this study is to utilize the pH sensitivity of modified carboxymethyl starch (CMS) for oral delivery of insulin. The chemical modification of natural polymers by grafting has received considerable attention in recent years because of the wide variety of monomers available. Methacrylic-type polymeric prodrugs were synthesized by free radical copolymerization of methacrylic acid, poly(ethyleneglycol monomethyl ether methacrylate) (PEGMA), and carboxymethyl starch (CMS) in the presence of bis-acrylamide as a cross-linking agent (CA) and persulfate as an initiator. The pH sensitive nature and ability to control gel permeability indicate that these materials have significant potential for drug delivery applications. Equilibrium swelling studies were carried out in enzyme-free simulated gastric and intestinal fluids (SGF and SIF, respectively). Insulin was entrapped in these gels, and the in vitro release profiles were established separately in both (SGF, pH 1) and (SIF, pH 7.4). Drug release studies showed that the increasing content of MAA in the copolymer enhances hydrolysis in SIF. In these cases, the biological activity of insulin was retained. These results were used to design and improve protein release behavior from these carriers.

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.

The Relation Between Swelling Properties and Cross-Linking of Hydrogels Designed for Colon-Specific Drug Delivery

Copolymers of 2-hydroxyethyl methacrylate (HEMA) and methacrylic acid (MAA)-based hydrogels containing 5% and 10% of a cross-linking agent were studied as drug delivery systems. Terephthalic acid was covalently linked with HEMA, abbreviated as CA (cross-linking agent). Free radical cross-linking copolymerization of HEMA and methacrylic acid (MAA) in three different molar ratios, mixed with a particulate 3, 3-azobis (6-hydroxy benzoic acid) (ABHB) as an azo derivative of 5-aminosalicylic acid with the various ratios CA as cross-linking agent were carried out with using 2, 2, Azobisisobutyronitrile as initiator at the temperature range 60-70 degrees C. The compositions of the cross-linked three-dimensional polymers were determined by FTIR spectroscopy. Glass transition temperature of the network polymers was determined calorimetrically. The hydrolysis of drug-polymer conjugates was carried out in cellophane membrane dialysis bags containing an aqueous buffer solution (pH 7.4 and pH 1) at 37 degrees C. The drug-release profiles indicate that the amount of drug release depends on its degree of swelling and cross-linking.

An Investigation into the Influence of Hydrogel Composition on Swelling Behavior and Drug Release from Poly(Acrylamide-co-Itaconic Acid) Hydrogels in Various Media

The hydrogels prepared by free radical copolymerization of acrylamide and itaconic acid were investigated with regard to their composition and crosslinking degree to find materials with satisfactory swelling and drug release properties. Samples were characterized by measuring the swelling behavior and in vitro release of paracetamol as a model drug in aqueous media with different pH values. The two-factor, three-level experimental design and response surface methodology were applied to statistically evaluate the influence of investigated factors.

Controlled Release of Biomolecules from pH-sensitive Network Polymers Prepared by Radiation Polymerization

Copolymers of 2-hydroxyethyl methacrylate (HEMA) and methacrylic acid (MAA) based hydrogels containing 5 and 10% of a cross-linking agent were studied as drug delivery systems. Terephthalic acid was covalently linked with HEMA, abbreviated as CA. Radiation copolymerization of HEMA and MAA, mixed with a particulate glibenclamide with the various ratios CA as crosslinking agent were carried out at the room temperature. The structure of the CA was confirmed by FTIR, H NMR and C NMR spectroscopy. The compositions of the cross-linked three-dimensional polymers were determined by FTIR spectroscopy. Glass transition temperature (T) of the network polymers was determined calorimetrically. The hydrolysis of drug-polymer conjugates was carried out in cellophane membrane dialysis bags containing an aqueous buffer solution (pH 7.4 and pH 1) at 37 degree C. The drug-release profiles indicate that amount drug release depends on their degree of swelling and cross-linking.

Preparation of Novel Cationic Copolymer Microspheres and Evaluation of Their Function by In Vitro and In Vivo tests as Ph-Sensitive Drug Carrier Systems

Novel pH-sensitive copolymer microspheres containing methylacrylic acid and styrene cross-linking with divinylbenzene were synthesized by free radical polymerization. The microspheres that were formed were then characterized by Fourier-Transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), size analysis, and X-ray analysis. The copolymer microspheres showed pulsatile swelling behavior when the pH of the media changed. The pH-sensitive microspheres were loaded with diltiazem hydrochloride (DH). The release characteristics of the free drug and the drug-loaded microspheres were studied under both simulated gastric conditions and intestinal pH conditions. The in vivo evaluation of the pulsatile preparation was subsequently carried out using beagle dogs as experimental subjects. The results demonstrated that the drug release exhibited a pulsatile character both in vitro and in vivo.

Final report of the safety assessment of methacrylic acid

Methacrylic Acid is an organic acid used at concentrations between 50 and 88 percent to pretreat the nail and maximize the adhesion between the nail and artificial nail extender. Methacrylic Acid is readily absorbed through mucous membranes of the lungs, the gastrointestinal tract, and the skin; and is distributed to all major tissues. Oral LD50 values for rats ranged from 277 to 2260 mg/kg; acute toxicity symptoms included severe gastric irritation, gasping, labored respiration, prostration and hematuria. In a short-term inhalation study, rats exposed to Methacrylic Acid at 1300 ppm showed nose and eye irritation and weight loss, while necropsy results and blood and urine tests were normal. Methacrylic Acid is an ocular toxicant in animals. Undiluted Methacrylic Acid is corrosive to the skin of rabbits and guinea pigs. Exposure as limited as 3 minutes can cause severe erythema and slight to moderate edema. Exposure from 15 minutes to 24 hours under occlusive patches can cause marked to severe discoloration, slight to severe subcutaneous hemorrhages, necrosis, ulcerations, severe erythema, edema and concave eschar. Methacrylic Acid was irritating and caused strong rubefaction and scab formation in a guinea pig maximization test at challenge concentrations from 10 to 100 percent. It was difficult to determine if the results were type IV hypersensitivity reactions or simple irritation. In three other studies, guinea pigs were not sensitized. Methacrylic Acid was not a reproductive/developmental toxicant in rats or mice. Methacrylic Acid was negative in Salmonella typhimurium mutagenicity tests using strains TA98, TA100, TA1535 and TA1537 both with and without metabolic activation, but was positive in a DNA-cell-binding assay. Case reports involving Methacrylic Acid often involve children. Effects from ingestion include drooling, gagging, and vomiting. Children exposed to Methacrylic Acid as a result of accidental spills caused first and second degree burns to the eyes, face, hands, arms, and chest. The Consumer Product Safety Commission has required child-resistant packaging for liquid household products containing more than 5 percent Methacrylic Acid (weight-to-volume) in a single package. Since Methacrylic Acid is an extremely corrosive chemical, a primary concern about its use as a cosmetic ingredient was the ability to limit exposure to the nail when pretreating the nail prior to application of an artificial nail extender. A videotape presentation demonstrated that a trained professional could use a small applicator brush to dab a limited volume of Methacrylic Acid only to the center of the nail, allowing the monomer liquid to diffuse down the nail without any exposure to the skin. There were no available data to demonstrate that an individual consumer could apply Methacrylic Acid and avoid inadvertent skin contact. In order to minimize any exposure to the acid, the Expert Panel concluded that nail primers containing Methacrylic Acid could be used safely by trained individuals instructed to ensure that there be no contact with the skin. The CIR Expert Panel recognized that there are no chronic inhalation toxicity data on Methacrylic Acid, but was concerned that inhalation of Methacrylic Acid could affect the respiratory tract. Since the inhalation exposure time is significantly increased in a commercial setting, the Panel was more concerned about the safety of the nail technician than the consumer. The Expert Panel concluded that the current NIOSH recommended exposure limit of 20 ppm would provide adequate protection.

On the use of the Weibull function for the discernment of drug release mechanisms

Previous findings from our group based on Monte Carlo simulations indicated that Fickian drug release from Euclidian or fractal matrices can be described with the Weibull function. In this study, the entire drug release kinetics of various published data and experimental data from commercial or prepared controlled release formulations of diltiazem and diclofenac are analyzed using the Weibull function. The exponent of time b of the Weibull function is linearly related to the exponent n of the power law derived from the analysis of the first 60% of the release curves. The value of the exponent b is an indicator of the mechanism of transport of a drug through the polymer matrix. Estimates for b< or =0.75 indicate Fickian diffusion in either fractal or Euclidian spaces while a combined mechanism (Fickian diffusion and Case II transport) is associated with b values in the range 0.75<b<1. For values of b higher than 1, the drug transport follows a complex release mechanism.

Compound transfer efficiency from polystyrene surfaces: application to microarrayed compound screening

In microarrayed compound screening (microARCS), compounds are spotted and dried onto a polystyrene sheet (ChemCard)ata high density and introduced into the assay by contacting with agarose gels that contain reagents for the assay. The authors have conducted studies to characterize the compound transfer process using 59 compounds of diverse properties. The amount of compounds remaining on the ChemCard was determined by liquid chromatography/mass spectrometry after incubation with agarose gels for predetermined time periods. The results showed good correlation with kinetics of compound transfer to phosphate-buffered saline (PBS) buffer, but only moderate correlation with equilibrium solubility of compounds in PBS buffer. These observations indicate that the major factor determining compound transfer efficiency is the kinetics of dissolution of compounds, rather than equilibrium solubility and diffusion of compounds in the gel. Compounds of lower ClogP showed a higher rate of transfer to agarose gels and vice versa. Other compound properties such as molecular weight, size, acid-base, and H-bonding properties did not significantly affect compound transfer. Importantly, the majority of the compounds studied show greater than 20% transfer after a 10-min incubation with agarose gels, providing sufficient amounts of compounds for screening purposes.

Using pH-sensitive hydrogels containing cubane as a crosslinking agent for oral delivery of insulin

The goal of oral insulin delivery devices is to protect the sensitive drug from proteolytic degradation in the stomach and upper portion of the small intestine. Copolymers of 2-hydroxyethyl methacrylate (HEMA) and methacrylic acid (MAA) based hydrogels containing 2, 4, and 6% of a crosslinking agent (CA) were studied as drug delivery systems. Cubane-1, 4-dicarboxylic acid (CDA) was linked to two HEMA groups as CA. Radical copolymerizations of HEMA and MAA with the various ratios of CA were performed at 70 degrees C. The compositions of the crosslinked three-dimensional polymers were determined using Fourier transform infrared spectroscopy. Glass-transition temperature of the network polymers was determined calorimetrically. The effect of copolymer composition on the swelling behavior and hydrolytic degradation was studied in simulated gastric fluid (pH 1) and simulated intestinal fluid (pH 7.4). The swelling and hydrolytic behavior of the copolymers was dependent on the content of MAA groups and caused a decrease in gel swelling in simulated gastric fluid or an increase in gel swelling in simulated intestinal fluid. The drug-release profiles indicate that the amount of drug release depends on their degree of swelling and crosslinking.