Calcium-induced gelation of alginic acid and pH-sensitive reswelling of dried gels.

Yotsuyanagi, Toshihisa; Ohkubo, Tsuneo; Ohhashi, Takafumi; Ikeda, Ken

doi:10.1248/cpb.35.1555

Cited by 129 publications

(62 citation statements)

References 7 publications

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“…These beads have been used in formulations as single or multiple units, with or without the addition of other hydrogels or polymers, intrapenetrating networks (IPNs), nanospheres, polycations, and many more dosage forms for achieving temporal and spatial drug release. [7][8][9][10] Various categories of drugs have been encapsulated such as gastro-irritant nonsteroidal antiinflammatory drugs, enzymes, peptides/proteins, and acid labile. All these drugs show different patterns of drug entrapment and release profiles depending upon their physico-chemical characteristics and method of preparation.…”

Section: +mentioning

confidence: 99%

The effect of drug concentration and curing time on processing and properties of calcium alginate beads containing metronidazole by response surface methodology

2006

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The purpose of present research work was to prepare calcium alginate beads containing water-soluble drug metronidazole using 3 2 factorial design, with drug concentration and curing time as variables. Curing time was kept as low as possible to improve entrapment with increasing drug concentration. Mostly the drugs which had been encapsulated were water insoluble to facilitate drug encapsulation; a characteristic drug release as whole process is aqueous based. Entrapment efficiency was in the range of 81% to 96% wt/wt, which decreased with decrease in polymer concentration and increase in curing time. The beads were spherical with size range between 1.4 and 1.9 mm. Scanning electron microscope (SEM) photomicrographs revealed increase in the leaching of drug crystals with increased curing time and high drug concentrations. In acidic environment, the swelling ratio was 200% in 30 minutes, but in basic medium, it increased to a maximum of 1400% within 120 minutes. In acidic medium, the swelling and drug release properties were influenced by drug solubility, whereas in phosphate buffer these properties were governed by the gelling of polymer and exhibited curvilinear and quadratic functions of both the variables, respectively.

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Section: +mentioning

confidence: 99%

The effect of drug concentration and curing time on processing and properties of calcium alginate beads containing metronidazole by response surface methodology

2006

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“…Recovering microspheres with CaCl 2 increases the degree of alginate cross-linking, which is known to cause gel shrinkage. 45 These water losses may induce adhesion between microspheres resulting in the formation of aggregates probably owing to the formation of new hydrogen bonds created between hydroxyl groups of the polymer. 46 The formation of new hydrogen bonds is apparently avoided in the case of acetate buffer, thus preventing aggregation.…”

Section: E909mentioning

confidence: 99%

“…Theoretically, an inverse effect would be expected, since alginate gelation induced by calcium ions causes microsphere shrinkage and a decrease in size. 45 For this reason, it is thought that microsphere granulometry could be infl uenced during microsphere recovery, and that acetate buffer at pH 5.5 continues the solubilization of CaCO 3 and therefore alginate gelation. In the absence of the oil barrier and in the case in which a lower acid/CaCO 3 molar ratio was used, a higher effect probably took place.…”

Section: E909mentioning

confidence: 99%

Microencapsulation of hemoglobin in chitosan-coated alginate microspheres prepared by emulsification/internal gelation

Silva

Ribeiro²,

Figueiredo

et al. 2005

AAPS J

106

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A BSTRACTChitosan-coated alginate microspheres prepared by emulsification/internal gelation were chosen as carriers for a model protein, hemoglobin (Hb), owing to nontoxicity of the polymers and mild conditions of the method. The infl uence of process variables related to the emulsifi cation step and microsphere recovering and formulation variables, such as alginate gelation and chitosan coating, on the size distribution and encapsulation effi ciency was studied. The effect of microsphere coating as well its drying procedure on the Hb release profi le was also evaluated. Chitosan coating was applied by either a continuous microencapsulation procedure or a 2-stage coating process. Microspheres with a mean diameter of less than 30 μm and an encapsulation effi ciency above 90% were obtained. Calcium alginate cross-linking was optimized by using an acid/CaCO 3 molar ratio of 2.5, and microsphere-recovery with acetate buffer led to higher encapsulation effi ciency. Hb release in gastric fl uid was minimal for air-dried microspheres. Coating effect revealed a total release of 27% for 2-stage coated wet microspheres, while other formulations showed an Hb release above 50%. Lyophilized microspheres behaved similar to wet microspheres, although a higher total protein release was obtained with 2-stage coating. At pH 6.8, uncoated microspheres dissolved in less than 1 hour; however, Hb release from air-dried microspheres was incomplete. Chitosan coating decreased the release rate of Hb, but an incomplete release was obtained. The 2-stage coated microspheres showed no burst effect, whereas the 1-stage coated microspheres permitted a higher protein release.

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“…The negatively charged drops of alginate gel form beads by interaction with positively charged divalent calcium ions (Ca 2+ ) in the CaCl 2 solution due to cross-linking between the carboxylate anions of alginate glucuronate and the calcium ions 36 . This results in the formation of spherical, stable alginateispaghula beads with rough surfaces when a mixture of sodium alginate gel, ispaghula husk gel, and GCD was dropped in solutions containing Ca 2+ ions in various concentrations 23 ( Fig.…”

Section: Resultsmentioning

confidence: 99%

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Nayak¹,

Hasnain²,

Beg³

et al. 2010

ScienceAsia

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Novel mucoadhesive beads were developed and evaluated for oral controlled release of the hypoglycaemic agent gliclazide. Various formulations of mucoadhesive beads were prepared using two different natural polymers, alginate and ispaghula, in various stoichiometric proportions with CaCl2 as a source of counter ions. The mucoadhesive beads were characterized for entrapment efficiency, particle size, surface morphology, and swelling index. The kinetics of drug release and their mucoadhesive nature in vitro using goat intestinal mucosa was also investigated at various physiological pH conditions. The effects of various proportions of the two polymers along with the effect of various percentages of counter ions on mucoadhesion property, size, entrapment efficiency, and drug release behaviour were studied. The effective mucoadhesion property with sustained release profile was observed from optimized mucoadhesive beads consisting of alginate and ispaghula husk (1:1) and polymer (2:1) with 5-10% w/v counter ions (CaCl2). These formulations showed optimum mucoadhesion behaviour having more than 70% w/v of drug entrapment and particle sizes of 896.7 ± 0.8 and 920.6 ± 1.2 µm, respectively.

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Calcium-induced gelation of alginic acid and pH-sensitive reswelling of dried gels.

Cited by 129 publications

References 7 publications

The effect of drug concentration and curing time on processing and properties of calcium alginate beads containing metronidazole by response surface methodology

The effect of drug concentration and curing time on processing and properties of calcium alginate beads containing metronidazole by response surface methodology

Microencapsulation of hemoglobin in chitosan-coated alginate microspheres prepared by emulsification/internal gelation

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