Effect of gelation conditions and dissolution media on the release of paracetamol from alginate gel beads

Assessment of temperature-sensitive properties of ionically crosslinked sodium alginate/hydroxypropyl cellulose blend microspheres: preparation, characterization, and in vitro release of paracetamol

Today, polymer systems can be formed to respond to single stimuli or multiple stimuli by changing their properties. The use of these systems, which are designed to be sensitive to stimuli, is expanding in a wide range of applications. Herein, microspheres of sodium alginate (NaAlg) and hydroxypropyl cellulose (HPC) sensitive to dual stimuli for the controlled release of model drug paracetamol were produced by the ionotropic gelation method in the presence of Zn²⁺ ions. FTIR, DSC, TGA, SEM, and particle size measurements were used to describe the blend microspheres. Low critical solution temperatures (LCST) of polymer blends at different ratios were determined and the biggest change according to the LCST value of HPC was found to be approximately 1-2 °C lower than 41 °C in microspheres with a NaAlg/HPC ratio of 50/50. In vitro release experiments of paracetamol from microspheres were carried out in a gastrointestinal tract simulation environment at two different temperatures (37 °C and 47 °C). From the release profiles, paracetamol release varied depending on the NaAlg/HPC ratio, the paracetamol content in the microspheres, the exposure time to Zn²⁺ ions, and the pH of the medium. Among the microsphere formulations, the highest entrapment efficiency was 57.86%, obtained for B₇ formulation microspheres with a NaAlg/HPC ratio of 70/30, a paracetamol loading percentage of 20%, and a crosslinking time of 5 min.RESEARCH HIGHLIGHTSMicrospheres of sodium alginate (NaAlg) and hydroxypropyl cellulose (HPC) sensitive to dual stimuli for the controlled release of model drug paracetamol were produced by the ionotropic gelation method in the presence of Zn²⁺ ions.LCST values of the microspheres with a NaAlg/HPC ratio of 50/50 were significantly lower by 1-2 °C than the LCST value of HPC, and the release results supported the temperature sensitivity of the microspheres.Among the microsphere formulations, the highest entrapment efficiency was 57.86% obtained for B₇ formulation microspheres.These microspheres can be used as a temperature-sensitive drug delivery system in the biomedical field and also as an encapsulation system of cancer drugs for cancer treatment modalities such as hyperthermia.

Microfluidic generation of monodispersed Janus alginate hydrogel microparticles using water-in-oil emulsion reactant

Microparticles with uniform anisotropic structures are widely used in physical, chemical, and biological fields owing to their ability to combine multiple functions on a micro-scale. Here, a microfluidic emulsion-based external gelation method was demonstrated for the first time to produce monodisperse Janus calcium alginate (Ca-alginate) hydrogel microparticles consisting of two compartments. This approach provided a fast reaction condition under which we could prepare magnetic Janus Ca-alginate microparticles with diameters ranging from 148 to 179 μm and a coefficient of variation (CV) less than 4%. Moreover, the boundaries between the two compartments were clear. In addition, the volume fraction of each compartment could be adjusted by varying the flow rate ratio between two dispersed phases. Next, we produced fluorescent Janus beads and magnetic-fluorescent Janus beads with an average diameter of ∼150 μm (CV < 4.0%). The magnetic Janus hydrogel microparticles we produced could be manipulated by applying a magnetic field to achieve self-assembly, rotation, and accumulation. Magnetic Janus hydrogel microparticles are also capable of mammalian cell encapsulation with good cell viability. This article presents a simple and stable approach for producing monodisperse bi-compartmental Janus hydrogel microparticles that could have great potential for application in physical, biochemical, and biomedical fields.

Assessment of Antimicrobic, Antivirotic and Cytotoxic Potential of Alginate Beads Cross-Linked by Bivalent Ions for Vaginal Administration

Antimicrobial agent abuse poses a serious threat for future pharmacotherapy, including vaginal administration. The solution can be found in simple polymeric systems with inherent antimicrobial properties without the need to incorporate drugs, for instance alginate beads cross-linked by bivalent ions. The main goal of the presented study was to provide improvement on the well-documented cytotoxicity of Cu²⁺ cross-linked alginate. Alginate beads were prepared by external ionotropic gelation by cross-linking with Cu²⁺, Ca²⁺ and Zn²⁺ ions, separately and in mixtures. Morphological properties, swelling capacity, ion release and efficacy against the most common vaginal pathogens (C. albicans, E. coli, E. faecalis and virus strain—human herpesvirus type 1) were evaluated. The prepared particles (particle size 1455.68 ± 18.71–1756.31 ± 16.58 µm) had very good sphericity (0.86 ± 0.04–0.97 ± 0.06). In mixture samples, Cu²⁺ hampered second ion loading, and was also released incompletely (18.75–44.8%) compared to the single ion Cu²⁺ sample (71.4%). Efficacy against the selected pathogens was confirmed in almost all samples. Although anticipating otherwise, ion mixture samples did not show betterment over a Cu²⁺ cross-linked sample in cytotoxicity–pathogen efficacy relation. However, the desired improvement was found in a single ion Zn²⁺ sample whose minimal inhibition concentrations against the pathogens (0.6–6.12 mM) were close to, or in the same mathematical order as, its toxic concentration of 50 (1.891 mM). In summary, these findings combined with alginate’s biocompatibility and biodegradability give the combination solid potential in antimicrobial use.

Experimental investigation into size and sphericity of alginate micro-beads produced by electrospraying technique: Operational condition optimization

Alginate spherical hydrogel beads have several applications in biomedical and biological processes in which the bead size and sphericity are critical factors affecting mass transfer phenomena. Electrospraying technology facilitates generation of small and almost uniform beads with higher diffusion rate resulting in process performance improvement. There are several key factors affecting particle size and shape behavior of electrosprayed alginate beads meanwhile interactions between these factors introduce complexity in determining appropriate conditions to produce spherical beads with the size of interest. Thus, the need to achieve reliable products has put growing emphasis on the use of modeling methodology to establish correlations between particle size and affecting variables as well as sphericity coefficient and meaningful factors. Obviously, a more applicable model based on intentionally manipulatable factors would spark a great deal of interest for practical engineering applications. In this regard we employed a central composite design (CCD) and response surface methodology (RSM) to model the diameter and sphericity coefficient of electrosprayed alginate beads for the first time. Two quadratic models were obtained in which the effectiveness order of the variables were found. We could benefit from this RSM-based empirical model not only for better understanding the complex physics of the electrospraying process, but also for selection of factors and their levels to produce alginate micro-beads with appropriate size and sphericity. The results indicate that the alginate concentration, voltage and needle size have the strongest influence on both response variables. The quite spherical beads with a minimum size of 130 μm can be obtained at alginate concentration of 1.5%, voltage of 11 kV, and needle size of 26 G.

Optimization and Evaluation of Gastroretentive Ranitidine HCl Microspheres by Using Factorial Design with Improved Bioavailability and Mucosal Integrity in Ulcer Model

The purpose of our investigation was to develop and optimize the drug entrapment efficiency and bioadhesion properties of mucoadhesive chitosan microspheres containing ranitidine HCl prepared by an ionotropic gelation method as a gastroretentive delivery system; thus, we improved their protective and therapeutic gastric effects in an ulcer model. A 3 × 2² full factorial design was adopted to study the effect of three different factors, i.e., the type of polymer at three levels (chitosan, chitosan/hydroxypropylmethylcellulose, and chitosan/methylcellulose), the type of solvent at two levels (acetic acid and lactic acid), and the type of chitosan at two levels (low molecular weight (LMW) and high molecular weight (HMW)). The studied responses were particle size, swelling index, drug entrapment efficiency, bioadhesion (as determined by wash-off and rinsing tests), and T _80% of drug release. Studies of the in vivo mucoadhesion and in vivo protective and healing effects of the optimized formula against gastric ulcers were carried out using albino rats (with induced gastric ulceration) and were compared to the effects of free ranitidine powder. A pharmacokinetic study in rabbits showed a significant, 2.1-fold increase in theAUC_0-24of the ranitidine microspheres compared to free ranitidine after oral administration. The optimized formula showed higher drug entrapment efficiency and mucoadhesion properties and had more protective and healing effects on induced gastric ulcers in rats than ranitidine powder. In conclusion, the prolonged gastrointestinal residence time and the stability of the mucoadhesive microspheres of ranitidine as well as the synergistic healing effect of chitosan could contribute to increasing the potential of its anti-gastric ulcer activity.

Synergistic effect of divalent cations in improving technological properties of cross-linked alginate beads

Gelling solution parameters are some of the most important variables in ionotropic gelation and consequently influence the technological characteristics of the product. To date, only a few studies have focused on the simultaneous use of multiple cations as gelling agents. With the aim to deeply explore this possibility, in this research we investigated the effect of two divalent cations (Ca²⁺ and Zn²⁺) on alginate beads formation and properties. Alginate beads containing prednisolone (P) as model drug were prepared by prilling technique. The main critical variables of the ionotropic gelation process i.e. composition of the aqueous feed solutions (sodium alginate and prednisolone concentration) and cross-linking conditions (Ca²⁺, Zn²⁺ or Ca²⁺+Zn²⁺), were studied. The obtained beads were characterized and their in vitro release performances were assessed in conditions simulating the gastrointestinal environment. Results evidenced a synergistic effect of the two cations, affecting positively both the encapsulation efficiency and the ability of the alginate polymeric matrix to control the drug release. A Ca²⁺/Zn²⁺ ratio of 4:1, in fact, exploited the Ca²⁺ ability of establish quicker electrostatic interactions with guluronic groups of alginate and the Zn²⁺ ability to establish covalent-like bonds with carboxylate groups of both guluronic and mannuronic moieties of alginate.

Crosslinker effects on functional properties of alginate/N-succinylchitosan based hydrogels

In this paper, physico-chemical, mechanical and antimicrobial properties of hydrogels based on alginate/N-succinylchitosan blends crosslinked by calcium or zinc ions containing cellulose microfibers were investigated and discussed. With respect to plain alginate hydrogels, the addition of N-succinylchitosan significantly improved properties such as swelling degree and stability in saline solution. The water vapour transmission rate confirmed that all the hydrogels were able to assure a moist wound environment. Morphological analysis showed a good embedding of fibres within the zinc crosslinked hydrogels. In addition, zinc-crosslinked hydrogels evidenced antimicrobial activity against two common skin pathogenic bacteria, Staphylococcus aureus and Escherichia coli. Cytotoxicity assays proved that the amount of zinc released is slightly over the toxic level. Overall, the characteristics of the zinc-crosslinked hydrogels showed their potential interest as materials for wound dressing.

Alginate-based strategies for therapeutic vascularization

Therapeutic stimulation of vessel growth to improve tissue perfusion has shown promise in many regenerative medicine and tissue engineering applications. Alginate-based biomaterial systems have been investigated for growth factor and/or cell delivery as tools for modulating vessel assembly. Growth factor encapsulation allows for a sustained release of protein and protection from degradation. Implantation of growth factor-loaded alginate constructs typically shows an increase in capillary density but without vascular stabilization. Delivery of multiple factors may improve these outcomes. Cell delivery approaches focus on stimulating vascularization either via cell release of soluble factors, cell proliferation and incorporation into new vessels or alginate prevascularization prior to implantation. These methods have shown some promise but routine clinical application has not been achieved. In this review, current research on the application of alginate for therapeutic neovascularization is presented, shortcomings are addressed and the future direction of these systems discussed.

Pectin and charge modified pectin hydrogel beads as a colon-targeted drug delivery carrier

The physical and chemical properties of commercial low methoxyl citrus pectins, CP 28 and CP 55, and a pectinmethylesterase (PME) charge modified citrus pectin (MP 38) were compared, and the differences in ability to encapsulate indomethacin in hydrogel beads was determined at 0.5 or 1.0% (w/v) indomethacin ratio, and 100, 200 or 300 mM CaCl(2) solution. In order to investigate the drug release characteristics, indomethacin loaded dried hydrogel beads were immersed in simulated gastric fluids (pH 1.2) for 2h, followed by immersing in simulated intestinal fluids (pH 7.4) for 3h. Pectin type was highly significant (p<0.0001) for encapsulation efficiency and in vitro release assay. Encapsulation efficiency was also highly affected (p<0.0001) by indomethacin ratio and CaCl(2) concentration. The accumulative release rate of indomethacin from pectin hydrogel bead was less than 15% in simulated gastro-intestinal fluids. MP 38 beads showed significantly higher entrapment efficiency and lower release rate than beads formed from CP 28 or CP 55. MP 38 hydrogel formulated with 300 mM CaCl(2) and 0.5% indomethacin ratio showed the highest entrapment efficiency. These studies suggest that charge modification of pectin improves encapsulation efficiency of drugs for colon targeted drug delivery system through oral administration.

Development of formulations to improve the controlled-release of linalool to be applied as an insecticide

In recent studies, insecticide activity of a monoterpene, linalool, has been demonstrated, finding, however, limitations in application because of its rapid volatilization. Potential effectiveness of microcapsules and effects of various types of matrices on its stability as controlled-release systems for the slow volatilization of linalool to be applied as insecticide were evaluated. To study controlled-release, linalool was entrapped into microcapsules, inclusion complexes, and beads, obtained by different methods, inverse gelation (IG1, IG2, IG3, IG4, and IG5), oil-emulsion-entrapment (OEE), interfacial coacervation (INCO), and chemical precipitation (Cyc5 and Cyc10). The encapsulation yield turned out to be different for each formulation, reaching the maximum retention for IG1 and OEE. In controlled-release, OEE followed by INCO presented a long time necessary for releasing as a result of the presence of glycerol or chitosan. These results pointed out remarkable differences in the release behavior of linalool depending on matrix composition and the method of encapsulation.

Novel preparation techniques for alginate-poloxamer microparticles controlling protein release on mucosal surfaces

The objective of this study was to develop novel preparation techniques for protein-loaded, controlled release alginate-poloxamer microparticles with a size range suitable for pulmonary administration. Bovine serum albumin (BSA)-loaded microparticles were prepared by spray-drying aqueous polymer-drug solutions, followed by cross-linking the particles in aqueous or ethanolic CaCl(2) or aqueous ZnSO(4) solutions. The microparticles were characterized with respect to their morphology (optical and scanning electron microscopy), particle size (laser light diffraction), calcium content (atom absorption spectroscopy), alginate content (complexation with 1,9-dimethyl methylene blue) and in vitro drug release (modified Franz diffusion cell). The spray-dried microparticles were spherical in shape with a size range of 4-6μm. Aqueous cross-linking led to a significant size increase (10-15μm), whereas ethanolic cross-linking did not. The substantial drug loss (∼50%) during aqueous CaCl(2) cross-linking could be avoided by using aqueous ZnSO(4) or ethanolic CaCl(2) solutions. Protein release from microparticles cross-linked with ethanolic CaCl(2) solutions was much faster than in the case of aqueous CaCl(2) solutions, probably due to the lower calcium content. The salt concentration and temperature of the cross-linking solutions also affected the composition of and drug release from the microparticles. Cross-linked alginate-poloxamer microparticles can be produced in a size range appropriate for deep lung delivery and with controlled protein release kinetics (time frame: hours to days) with these novel preparation techniques. The systems offer an interesting potential for the controlled mucosal delivery of protein drugs.

Effect of drug loading method on drug content and drug release from calcium pectinate gel beads

Drug-loaded calcium pectinate gel (CaPG) beads were prepared by either mixing, absorption, or swelling method. The effects of drug loading method as well as the drug loading factors (i.e., drug concentration, soaking time in drug solution, type of solvent) on drug content and drug release were investigated. The amount of drug uptake (i.e., drug content) into CaPG beads increased as the initial drug concentration increased and varied depending on the loading method. The in vitro release studies in 0.1 N hydrochloric acid (HCl) and pH 6.8 buffer indicated that the drug loading method affected drug release and release parameter, time for 50% of drug release (T(50)). The mixing method provided a faster drug release and lower T(50) than the absorption method and swelling method, respectively. This is probably due to higher drug content in CaPG beads. The increased concentration of drug in soaking solution and soaking time resulted in higher drug content and thus faster drug release (lower in T(50) values). When using 0.1 N HCl as solvent for soaking instead of water, the drug release was slower owing to the increase in molecular tortuosity of CaPG beads. The drug release was also affected by pH of the release medium in which drug release in 0.1 N HCl was faster than in pH 6.8 buffer.

Pectin-cysteine conjugate: synthesis and in-vitro evaluation of its potential for drug delivery

This study was aimed at improving certain properties of pectin by introduction of thiol moieties on the polymer. Thiolated pectin was synthesized by covalent attachment of cysteine. Pectin-cysteine conjugate was evaluated for its ability to be degraded by pectinolytic enzyme. The toxicity profile of the thiolated polymer in Caco-2-cells, its permeation enhancing effect and its mucoadhesive and swelling properties were studied. Moreover insulin-loaded hydrogel beads of the new polymer were examined for their stability in simulated gastrointestinal conditions and their drug release profile. The new polymer displayed 892.27 ± 68.68 μmol thiol groups immobilized per g polymer, and proved to have retained its biodegradability, upon addition of Pectinex Ultra SPL in-vitro, determined by viscosity measurements and titration method. Pectin-cysteine showed no severe toxicity in Caco-2 cells, as tested by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) and lactate dehydrogenase (LDH) assays. Moreover, the synthesized polymer exhibited a relative permeation enhancement ratio of 1.61 for sodium fluorescein, compared to unmodified pectin. Pectin-cysteine conjugate exhibited approximately 5-fold increased in in-vitro adhesion duration and significantly improved cohesive properties. Zinc pectin-cysteine beads showed improved stability in simulated gastrointestinal media; however, insulin release from these beads followed the same profile as unmodified zinc pectinate beads. Due to favourable safety and biodegradability profile, and improved cohesive and permeation-enhancing properties, pectin-cysteine might be a promising excipient in various transmucosal drug delivery systems.

Mechanical Characterization of Biocompatible Microspheres and Microcapsules by Direct Compression

The mechanical properties of biocompatible microparticles including alginate microspheres and alginate-chitosan microcapsules with different wall thickness were determined using a micromanipulation technique. Single microparticles with diameters of 20-60 microm were compressed to a given deformation and held, and compressed to rupture at different speeds. The corresponding force imposed on them was measured simultaneously by a force transducer. Results showed that the force imposed on these particles increased when they were compressed, but relaxed significantly when they were held. For alginate microspheres, the faster the compression speed was, the greater the force being imposed on them at a given deformation. Alginate-chitosan microcapsules showed less force relaxation when they were held, compared with alginate microspheres. The thicker their wall was, the less significant force relaxation the microcapsules exhibited. The mean rupture force of alginate microspheres increased with the compression speed, but this effect in general became less for alginate-chitosan microcapsules, which depended on their wall thickness. However, the deformation at rupture for all three samples was independent of the compression speed. On average, the alginate-chitosan microcapsules were bigger than alginate microspheres and had a greater rupture force.

Colonic Drug Delivery: Influence of Cross-linking Agent on Pectin Beads Properties and Role of the Shell Capsule type

For colonic delivery, pectin beads obtained by ionotropic gelation method have been already reported as an interesting approach. This study investigated the influence of the cross-linking agent (calcium or zinc) and the type of shell capsule used (classical or enteric capsules) on pectin beads properties and on their performance to target the colon (in vitro dissolution studies with subsequent pH change to mimic overall gastro-intestinal tract). Zinc pectinate beads seemed to be relatively similar to calcium's ones in morphological point, except on the surface aspect. When beads were introduced in classical hard capsules, ketoprofen release was not significantly different between CPG and ZPG beads, and it was too premature and too quick due to a chemical erosion of the pectinate matrix (acid + basic attacks). However, zinc pectinate beads showed slower ketoprofen release compared with calcium pectinate beads when enteric hard capsules were used. This interesting finding could be due to the strength of the network formed during the process between the zinc cations and the LM-pectin following the "egg-box" model. This network was stronger and induced a reduction of swelling and hydration when contact with dissolution medium, then subsequently a decrease of drug release. Thus, the zinc pectinate beads could protect sufficiently drug entrapped from the upper gastro-intestinal conditions and drug release will be controlled by pectin degradation with colonic microflora. Finally, these zinc pectinate beads in enteric hard capsules are promising as a carrier for specific colonic delivery of drugs after oral administration.

Preparation, in vitro and in vivo evaluation of stomach-specific metronidazole-loaded alginate beads as local anti-Helicobacter pylori therapy

Metronidazole (MZ), a common antibacterial drug used in treatment of H. pylori, was prepared in chitosan-treated alginate beads by the ionotropic gelation method. A (3x2x2) factorially designed experiment was used in which 3 viscosity-imparting polymers namely, methyl cellulose, carbopol 934P and kappa-carrageenan, 2 concentrations (0.2 and 0.4% w/v) of chitosan as encapsulating polymer and 2 concentrations (2.5 and 5% w/w) of the low density magnesium stearate as a floating aid were tested. The drug entrapment efficiency (%), the percent of floating beads and the time for 80% of the drug to be released (T(80%)) were the responses evaluated. The bead formula containing 0.5% kappa-carrageenan, 0.4% chitosan and 5% magnesium stearate showed immediate buoyancy, optimum drug entrapment efficiency and extended drug release. The histopathological examination of mice stomachs and in vivo H. pylori clearance tests were carried out by orally administering MZ floating alginate beads or MZ suspension, to H. pylori infected mice under fed conditions as a single daily dose for 3 successive days in different doses 5, 10, 15 and 20 mg/kg. The histopathological examination showed that groups receiving MZ in the form of floating alginate beads at doses 10, 15 and 20 mg/kg were better than the corresponding suspension form, regarding eradication of H. pylori infection. The in vivo H. pylori clearance tests showed that MZ floating beads with a dose of 15 mg/kg provided 100% clearance rate whereas the MZ suspension with a dose of 20 mg/kg gave only 33.33%.

Cross-linking of dried paracetamol alginate granules

This paper reports on the cross-linking of dried (<5% moisture) paracetamol alginate granules with calcium chloride solutions. The effect of calcium concentration, temperature of the treatment solution, stirring speed and time used during cross-linking of granules on water uptake by the granules during cross-linking and physical properties of the cross-linked and dried granules were studied. A full factorial study of these factors each at two levels was used (CaCl2.2H2O: 20, 100 mg/ml; temperature: 25, 45 degrees C; stirrer speed: 25, 240 rpm; time: 1.5 and 5.5 min) to treat dried stock granules (size: 0.8-1.0 mm) containing the model drug paracetamol and sodium alginate powder (1:1) which were prepared using conventional aqueous granulation under low shear. In addition to SEM and photomicrography, the physical properties studied were water uptake during cross-linking, yield, aggregation behaviour, moisture content, drug content, early stage drug release [over 10 s (R10) and the next 50 s (R50)] and calcium and sodium content of the unwashed cross-linked granules. Dry granules were successfully cross-linked. The treatment factors significantly affected most of the response variables. The variables most affected were water uptake (78-254%), drug entrapment (58-86%), early release (R10: 1.2-6.4% and R50: 3.0-12.2%), granule aggregation (0-70%), calcium (6.02-12.4%) and sodium content (1.2-6.44%). SEM photographs suggest that low calcium treated granules were less porous in nature compared to high calcium treated granules. Low shear drug alginate granules can be cross-linked in dried state. The properties of the cross-linked granules can be modified by altering the treatment process.

Novel modulation of drug delivery using binary zinc-alginate-pectinate polyspheres for zero-order kinetics over several days: experimental design strategy to elucidate the crosslinking mechanism

A Box-Behnken design was applied to mathematically establish whether different degrees of crosslinking were induced by Zn2+ and Ca2+ ions in polyspheres composed of alginate and/or pectin, and the model drug ibuprofen. Based on their different crystal structures and coordination numbers, a theoretical model was proposed demonstrating that Zn2+ ions preferentially crosslink alginate and pectin. In addition, the lower coordination number of Zn2+ (4-6) would significantly retard hydration of both polymers, as opposed to Ca2+ (7-9). The responses studied for 28 statistically derived polyspheres included drug encapsulation efficiency, physicomechanical behavior, and in vitro drug release potential. Single-tailed Student's t-tests on data generated for the encapsulation efficiencies, primary facture values, and rupture energies indicated that Zn2+ was statistically superior (p<0.05) in crosslinking alginate and pectin. Further textural analysis revealed a good correlation between the Brinell hardness number and fracture load, while an inverse relationship was found for matrix tensile strength. Viscosity studies demonstrated different in situ crosslinking thresholds for Zn2+. The Durbin-Watson statistic and correlation coefficient revealed that the quadratic regression function was highly accurate in predicting the responses. Using a generalized reduced gradient algorithm on dissolution values obtained after 2 hours (t2h) provided optimized solutions for achieving zero-order release extending from 2 hours to 7 days. Mathematical simulations projected drug release from 25 to 50 days.

Indomethacin release from ion-exchange microspheres: impregnation with alginate reduces release rate

Ion-exchange microspheres (MS) designed as a drug delivery system for embolization coupling ability to occlude vessels and chemotherapy were used to evaluate a manufacturing process allowing to control the drug release rate through reduction of diffusion rate of the drug within the particle by impregnation of calcium alginate inside the porous MS. Impregnation was performed by diffusion of sodium alginate inside DEAE-Trisacryl(R) MS, dispersion of the MS in deionised water and gelling alginate by adding CaCl(2) to the dispersed MS. Studied parameters were alginate concentration, alginate diffusion time and calcium concentration. Indomethacin was loaded into the MS by eluting an aqueous indomethacin solution through a chromatographic column packed with impregnated MS. Indomethacin loading was reduced by alginate. Swelling studies showed indomethacin loading enhanced the hydrophobicity of MS while impregnation had no effect. This had an incidence on indomethacin release rate, which was assessed using the rapid elution of PBS through loaded impregnated MS packed in a column. Indomethacin loading reduced its own rate of release. MS impregnated with 2% w/v alginate gelled with a 40 mM calcium solution presented the lower release rate. This work indicated the manufacturing conditions to display a calcium alginate matrix effect on indomethacin release from DEAE-Trisacryl MS.

Design of controlled-release solid dosage forms of alginate and chitosan using microwave

The influence of microwave irradiation on the drug release properties of alginate, alginate-chitosan and chitosan beads was investigated. The beads were prepared with the highest possible concentration of polymer by an extrusion method. Sulphathiazole was selected as a model drug. The beads were subjected to microwave irradiation at various combinations of irradiation power and time. The profiles of drug dissolution, drug content, drug stability, drug polymorphism, drug-polymer interaction, polymer crosslinkage and complexation were determined by dissolution testing, drug content assay, differential scanning calorimetry (DSC) and fourier transform infra-red spectroscopy (FTIR). The chemical stability of the drug entrapped in the beads was unaffected by the microwave irradiation. However, the drug in the chitosan beads underwent polymorphic changes. Polymorphic changes were prevented by means of drug-alginate interaction in alginate and alginate-chitosan beads. Changes in the polymorphic state of drug were found to have insignificant effect on the drug release profiles of chitosan beads. The release-retarding property of alginate and alginate-chitosan beads was significantly enhanced by subjecting the beads to microwave irradiation. Positively charged calcium ions and chitosan are known to interact with negatively charged alginate. DSC and FTIR analyses indicated that the reduction in rate and extent of drug released from the treated beads was primarily due to additional formation of non-ionic bonds, involving alginate crosslinkage and alginate-chitosan complexation. The results showed that microwave technology can be employed in the design of solid dosage forms for controlled-release application without the use of noxious chemical agents.

Production of alginate microspheres by internal gelation using an emulsification method

Alginate is a natural polysaccharide found in brown algae. Alginates are widely used in the food and pharmaceutical industries and have been employed as a matrix for the entrapment of drugs, macromolecules and biological cells. Alginate microspheres can be produced by the external or internal gelation method using calcium salts. The addition of calcium chloride solution in the final phase of production of microspheres by external gelation method using an emulsification technique causes the disruption of the equilibrium of the system being stirred, resulting in a significant degree of clumping of microspheres. Therefore, in this study, production of alginate microspheres by the internal gelation method using a modified emulsification technique was explored. The influence of calcium salt, added in varying amounts and at different stages, on the morphology of the microspheres was investigated. The effects of other hardening agents and different drying methods were also studied.

Cross-linking mechanisms of calcium and zinc in production of alginate microspheres

Calcium chloride and zinc sulphate were used to cross-link alginate microspheres prepared by an emulsification method. The microspheres cross-linked by a combination of these two salts showed different morphology and slower drug release compared with those cross-linked by the calcium salt alone. From viscosity study, it was found that zinc cations interacted with the alginate molecules to a greater extent than calcium cations. The varying effects of the salts on the properties of the microspheres were largely attributed to their ability to interact with the alginate molecules.

5-Fluorouracil encapsulated alginate beads for the treatment of breast cancer

Alginate beads containing 5-fluorouracil (5-FU) were prepared by the gelation of alginate with calcium cations. Alginate beads loaded with 5-FU were prepared at 1.0 and 2.0% (w/v) polymers. The effect of polymer concentration and the drug loading (1.0, 5.0 and 10%) on the release profile of 5-FU was investigated. As the drug load increased, larger beads were obtained in which the resultant beads contained higher 5-FU content. The encapsulation efficiencies obtained for 5-FU loads of 1.0, 5.0 and 10% (w/v) were 3.5, 7.4 and 10%, respectively. Scanning electron microscopy (SEM) and particle size analysis revealed differences between the formulations as to their appearance and size distribution. The amount of 5-FU released from the alginate beads increased with decreasing alginate concentrations.

Oral delayed-release system based on Zn-pectinate gel (ZPG) microparticles as an alternative carrier to calcium pectinate beads for colonic drug delivery

A new oral timed-release system was developed for colon-targeted delivery of drugs. The system which consists of ketoprofen-loaded Zn-pectinate gel (ZPG) microparticles together with pectin/dextran mixtures in a tablet form, has been investigated, in vitro, using conditions chosen to simulate the pH and times likely to be encountered during transit to the colon. In order to find the suitable ZPG microparticles, the formulations were prepared by utilizing 2(3) factorial design and the effect of various formulation factors on the release and surface characteristics of the microparticles was studied. The results obtained implied that the release of ketoprofen from ZPG microparticles was greatly extended with the pectinate microparticles, which were prepared with 2.5 or 3% w/v pectin, 2.75% w/v Zn(CH3COO)2 and 2.5% w/v drug. Additionally, the analysis of variance results showed that the release of ketoprofen in simulated intestinal fluid (S.I.F., pH 7.4) was strongly affected by crosslinking agent concentration and initial drug amount, but not particularly affected by the amount of pectin added. The investigated drug concentration factor has significantly increased the drug entrapment efficiency (EE). The optimum colonic drug delivery ZPG/tablet system provided the expected delayed-release sigmoidal patterns with a lag-time of 4.125-4.85 h and t(50%) (the time for 50% of the drug to be released) at 7.45-8.70 h, depending on pectin/dextran ratio employed. The results also demonstrated that the untableted ZPG microparticles exhibited drug release profiles which were able to retard the release of ketoprofen in S.I.F. (pH 7.4) to be 5.28-37.82 times (depending on formulation parameters), lower than the conventional calcium pectinate beads. Therefore, this approach suggests that ZPG microparticles and their modified-release formulations are promising as useful controlled-release carriers for colon-targeted delivery of drugs.

Effect of tabletting compaction pressure on alginate microspheres

Alginate and alginate-hydroxypropylmethylcellulose (HPMC) microspheres were prepared by the emulsification method. The compaction of microspheres for producing tablet dosage forms raises concerns about possible damage to microsphere walls with subsequent unpredictable dissolution rates. The effect of different compaction pressures on the integrity of the microspheres was investigated. The addition of a diluent, microcrystalline cellulose (MCC), was required to make compacts containing alginate and alginate-HPMC microspheres. Compacts containing alginate-HPMC (7:3) microspheres had the highest crushing strength followed by compacts containing alginate-HPMC (9:1) microspheres and alginate microspheres. However, compact crushing strength did not vary significantly with increased compaction pressures over the range of compaction pressures investigated. Differences in the drug release profiles of the original non-compacted and compacted alginate and alginate-HPMC microspheres were slight and not marked. Although dentation and distortion of the microspheres were observed with increasing compaction pressures, the microspheres generally remained intact, with minimal rupture/fracture.

Glucose oxidase release from calcium alginate gel capsules

Diffusion of glucose oxidase within calcium alginate gel capsules has been assayed and the experimental data fitted to a simple semi-empirical power equation, which is used to analyse the solute release from polymeric devices. It was found that an increase in the concentration of sodium alginate and calcium chloride gives rise to a reduction in the enzyme leakage. This was verified when glucose oxidase (GOD) diffusion percentages were compared in capsules with thicknesses of the same order of magnitude but obtained under different experimental conditions. So, the use of sodium alginate and calcium chloride solutions of concentrations 0.5% w/v and 2.6% w/v, respectively, lead to a diffusion percentage of 25 +/- 2. This percentage was reduced to 8 +/- 3 when sodium alginate and calcium chloride concentrations were fixed at 1% w/v and 4% w/v, respectively, even though the thicknesses of the capsules were of the same order of magnitude.

A comparison of two controlled-release delivery systems for the delivery of amiloride to control angiogenesis

The diuretic amiloride has been reported to inhibit both Na+-H+ antiport and the urokinase-type plasminogen activator. As a consequence of these inhibitions, neovascularization may also be inhibited. We hypothesized that if amiloride could be effectively delivered in a site-specific manner, a system might be developed that could inhibit localized angiogenesis. In order to evaluate this possibility we conducted a study that compared two different controlled-release systems into which amiloride had been incorporated. The effectiveness of amiloride release from each delivery system was determined by quantitating angiogenic patterns in a chick chorioallantoic membrane (CAM) system using a fractal analysis software program. The two delivery systems compared were sucrose acetate isobutyrate (SAIB) and calcium alginate. Initial HPLC laboratory tests confirmed that amiloride could be released from both SAIB and calcium alginate in vitro in a sustained manner for 72 h. The CAM studies confirmed that neither SAIB nor calcium alginate alone promoted or inhibited angiogenesis when compared to nontreated controls. The release of amiloride from each delivery vehicle resulted in a significant (P < 0.05) inhibition of angiogenesis following both 24 and 48 h of release compared to controls. There was no difference in inhibition of angiogenesis, however, when comparing SAIB + amiloride treated CAMs with calcium alginate + amiloride treated CAMs. These data suggest that both SAIB and calcium alginate may be useful delivery vehicles for the localized application of amiloride to control angiogenesis. Such a system could potentially control tumor angiogenesis without systemic effects.

Formulation and characterization of calcium alginate beads containing ampicillin

The purpose of this work was the preparation and characterization of calcium alginate beads containing ampicillin. Aqueous solutions of drug and sodium alginate (three viscosity grades) were added drop by drop to aqueous solutions of calcium chloride; the droplets instantaneously formed gel beads, which were then dried. Morphological studies and drug contents, in vitro release, and erosion tests were carried out for the characterization of the prepared beads. The dried particles were characterized by irregular shape and a smooth or rough surface, depending on the viscosity grade of the alginate used. The control of the drug for different time intervals depended on the molecular weight of the polymer used; however, the pH-change test showed that this capacity was much lower in the case of acid-treated particles. The results obtained show that the ampicillin beads prepared are suitable for intramammary therapy.

Studies on diffusion in alginate gels. II. Effect of acid and subsequent re-exposure to calcium on the diffusion of caffeine and theophylline in alginate gel films

The aim of this research was to investigate the effect of acid exposure and calcium re-exposure on the diffusion of caffeine and theophylline through calcium alginate gel films. Diffusion was measured using side-by-side glass cells, before and after the films were exposed to simulated gastric fluid (SGF) USP minus pepsin. The permeability increased by about 15-fold for theophylline and 48-fold for caffeine after 5 min SGF exposure. There was no significant further increase by prolonging the exposure time to 4 hr. The diffusion of both drugs was less than through alginate gel films that were not cross-linked with calcium but were gelled in SGF. Treatment of the calcium alginate gel films with SGF depleted the films of all of their calcium content. Calcium alginate gel films that were exposed to SGF for a constant period of 15 min, were re-exposed to 0.34 M calcium chloride solution for periods up to 24 hr. The calcium content returned to 80% of the level in the original calcium alginate films and diffusion was reduced, but not to the level that was observed in the original calcium alginate films. It was concluded that the effect of SGF on calcium alginate was very rapid and that the increase in drug diffusion observed was probably due to removal of calcium from the gel. It was also concluded that the original diffusion properties and calcium content could only be partially regenerated by re-exposing the acid-exposed films to calcium chloride.