Document Detail


Water uptake and relaxation processes in mixed unlimited swelling hydrogels.
MedLine Citation:
PMID:  11084245     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
The rheological oscillatory test parameters have been observed for highly concentrated hydroxypropylmethyl cellulose (HPMC), carboxymethylcellulose-sodium (NaCMC) and mixed HPMC/NaCMC hydrogels obtained by swelling of matrix tablets in 0.1 mol cm(-3) HCl and pH 6.8 phosphate buffer. The mechanical spectra of the gels have been analysed using theoretical models, i.e. a generalised Maxwell model and an adapted Maxwell model, both based on Ferry and Williams approximations. The relaxation time spectra as well as the parameters characteristic of linear viscoelastic behaviour have been calculated: zero shear viscosity (eta(0)), plateau moduli (G(N)(0), G(0)' and G(0)"), zero-relaxation time (tau(0)) and mean relaxation time (θ). The mechanical spectra of mixed HPMC/NaCMC hydrogels differ considerably from those of the pure ones, the type of the spectrum depending on the two polymers' ratios. In both media, the rheological models applied define the HPMC gels as homogeneous entangled networks, and those of NaCMC and mixed HPMC/NaCMC as heterogeneous physical gels. The relationship between the kinetic constants of water penetration and the mean relaxation times suggests that the molecular relaxation controls the water uptake velocity. With all the systems tested irrespective of pH of the aqueous phase, an inversely proportional dependence between the viscosity and the water penetration velocity has been noted. Since the degree of hydration is one of the factors determining the degree and velocity of drug release from the hydrogel matrices, the relation between the kinetic parameters of water penetration and the viscosity is a characteristic indicator for the gel structure, the degree of swelling and the drug release rate.
Authors:
V Michailova; S Titeva; R Kotsilkova; E Krusteva; E Minkov
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  International journal of pharmaceutics     Volume:  209     ISSN:  0378-5173     ISO Abbreviation:  Int J Pharm     Publication Date:  2000 Nov 
Date Detail:
Created Date:  2001-01-09     Completed Date:  2001-01-09     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  7804127     Medline TA:  Int J Pharm     Country:  NETHERLANDS    
Other Details:
Languages:  eng     Pagination:  45-56     Citation Subset:  IM    
Affiliation:
Department of Pharmaceutical Technology, Faculty of Pharmacy, Medical University, 2 Dunav St., 1000, Sofia, Bulgaria.
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MeSH Terms
Descriptor/Qualifier:
Absorption
Algorithms
Carboxymethylcellulose
Elasticity
Hydrogels / chemistry*
Hydrogen-Ion Concentration
Kinetics
Lactose / analogs & derivatives
Methylcellulose / analogs & derivatives
Models, Theoretical
Oxazines
Pharmaceutic Aids
Tablets
Viscosity
Water / chemistry*
Chemical
Reg. No./Substance:
0/Hydrogels; 0/Oxazines; 0/Pharmaceutic Aids; 0/Tablets; 63-42-3/Lactose; 7732-18-5/Water; 9004-32-4/Carboxymethylcellulose; 9004-67-5/Methylcellulose; 99705-65-4/MK 458

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine


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