In this review, the second in a series, the viscosity–molecular weight (Mark– Houwink–Sakurada) relationships have been critically evaluated. Polymer Solutions F. Mark-Howink-Sakurada equation: The relationship between intrinsic viscosity and molecular weight [η]: intrinsic viscosity. Mark–Houwink–ncsuk.infod. ncsuk.infoonal. ncsuk.infothm,ncsuk.info ncsuk.info solution.
This article has been cited by other articles in PMC.
Abstract Guar Gum is a natural polysaccharide that, due to its physicochemical properties, is extensively investigated for biomedical applications as a matrix for modified drug delivery, but it is also used in the food industry as well as in cosmetics. A commercial sample of Guar Gum was sonicated for different periods of time, and the reduction in the average molecular weight was monitored by means of viscometric measurements.
At the same time, the rheological behaviour was also followed, in terms of viscoelasticity range, flow curves, and mechanical spectra. Sonicated samples were used for the preparation of gels in the presence of borate ions. The effect of borax on the new samples was investigated by recording mechanical spectra, flow curves, and visible absorption spectra of complexes with Congo Red.
The anisotropic elongation, observed in previous studies with tablets of Guar Gum and borax, was remarkably reduced when the sonicated samples were used for the preparation of the gels. Introduction It is well known that viscometric properties of macromolecules are significantly affected by their molecular weight. The aim of this study was to examine the effect of the reduction of Guar Gum GG molecular weight for an appropriate modulation of its flow and gelling properties, according to specific needs and possible applications in the field of pharmaceutics, cosmetics, and food industry.
Furthermore, a reduced molecular weight should allow conjugation with hydrophobic moieties which should lead to self-assembled structures suitable as systems for drug delivery and targeting as previously proposed with gellan gum, which was sonicated and chemically linked to prednisolone [ 1 ].
Furthermore, following previous investigations carried out using another polysaccharide i. The helix conformation, assumed by the GG chains in the presence of borax [ 3 ], was tested to be stable even at high pH values by means of Congo Red complexation experiments. This seed gum, generally recognised as safe GRASbecause of its gelling, viscosifying, and thickening properties is used in pharmaceutics [ 5 ] for the stabilization of emulsions and suspensions; it is also employed in tablet manufacturing as a binder and disintegrating agent and for drug micr-encapsulation.
Furthermore, GG is suitable as a food supplement [ 6 ]. It has been proposed in the therapy of hypercholesterolemia, hyperglycemia, and obesity [ 7 ], but also in textile, paper, and paint industries, as well as in cosmetics.
As pointed out, most practical applications of GG are related to its rheological and gelling properties; furthermore, GG is pable to form hydrogels when crosslinked with glutaraldehyde [ 8 — 11 ] and in the presence of borax [ 3 ]. For the reduction of GG molecular weight, the probe sonication approach was used because in such case no chemicals are needed, and such aspect represents an important prerequisite for the marketing approval of the obtained polymer.
Materials and Methods 2. All products and reagents were of analytical grade.
Mark–Houwink equation - Wikipedia
The molecular weight cut-off of dialysis tubing was 12,—14, The viscosity of the nascent gel layer formed on the matrix tablet has a major influence on both the water uptake kinetics and the erosion rate, and thereby determines the gel-layer robustness during periods of increased physical stress. The viscosity of the nascent gel layer can be adjusted by using different viscosity grades of the polymers and by varying the amount of the polymer in the tablet bulk The polymer viscosity grade is linked to the intrinsic viscosity of the polymer, which is in turn related to the polymer molecular weight, the degree and type of substitution, and the particular polymer—solvent system used.
Several studies to date have described polymer properties that affect the release from matrix tablets 17 These studies predominantly evaluated the viscosity grades of the polymers tested, whereby viscosity was measured in water solution at a prescribed concentration.
This polymer property is called apparent viscosity and needs to be experimentally determined separately for each polymer grade and concentration using a procedure that is time-consuming and subject to errors due to differences in methodology and experimental setup own data. Moreover, various polymer types and grades employ different experimental procedures to characterize their apparent viscosity as part of their specification.
As such, it is tedious and not straightforward to assess the equivalence of characteristics of different polymer types by simply comparing their apparent viscosities. Intrinsic viscosity, however, is a physical polymer property independent from polymer concentration and can be directly compared across different types and grades of polymers, which makes it advantageous compared to apparent viscosity measurements.
At low polymer concentrations, the intrinsic viscosity is related to the rate of increase of apparent viscosity as a function of polymer volume fraction. Therefore, polymers with higher intrinsic viscosity are more effective at increasing the apparent viscosity of the solution.
In our study, the intrinsic polymer viscosity was correlated specifically with the mechanical susceptibility MS of matrix tablets. The more pronounced or higher the mechanical susceptibility of the gel layer, the faster the release of the incorporated drug substance after mechanical manipulation. Our results show that an increased intrinsic viscosity value resulted in a decrease of mechanical susceptibility of the swollen gel layer.
Considering this, two simple rules for designing robust matrix tablets with respect to the mechanical stresses was obtained. To establish the rules, formulations with different cellulose ether polymers—hydroxypropyl cellulose HPC and hydroxypropylmethyl cellulose HPMC —were prepared and their gel-layer robustness was evaluated using a specially designed dissolution testing procedure.
Materials and methods Materials A model drug indapamide with pH independent solubility of less than 0. Preparation of the Tablet Formulations Studied Five tablet formulations containing 1. The drug exhibits weakly acidic properties pKa 8. A model drug, lactose monohydrate, and polyvinylpyrolydone were blended and granulated with purified water using a Collette Gral—PRO 25 Machines Collette, Belgium high shear granulator.
The granulate loss on drying LOD was 2. These granules were used for all five formulations investigated.