Abstract
Sol-gel transformations in HPMC (hydroxypropyl methylcellulose) are being increasingly studied because of their role in bio-related applications. The thermo-reversible behavior of HPMC is particularly affected by its properties and concentration in solvent media, nature of additives, and the thermal environment it is exposed to. This article contains investigations on the effects of salt additives in Hofmeister series on the HPMC gelation. Various findings regarding gelation with salt ions as well as with the ionic and non-ionic surfactants are presented. The gel formation in physiological salt fluids such as simulated gastric and intestine fluids is also examined with the interest in oral drug delivery systems. The processes of swelling, dissolution and dispersion of HPMC tablets in simulated bio-fluids are explored and the release of a drug from the tablet affected by such processes is studied. Explanations are provided based on the chemical structure and the molecular binding/association of HPMC in a media. The test results at the body or near-body temperature conditions helped in understanding the progress of the gelation process within the human body environment. The detailed interpretation of various molecule level interactions unfolded the sol-gel mechanisms and the influence of a few other factors. The obtained test data and the established mathematical models are expected to serve as a guide in customizing applications of HPMC hydrogels.
Highlights
Researchers have shown particular interest in the behavior of hydroxypropyl methylcellulose (HPMC), chemically presented as C6H7O2(OH)x(OCH3)y(OC3H7)z with x + y + z = 3, where aqueous solutions of these carbohydrate polymers have revealed gel reversibility with temperature [1]
The results showed that the effects of anions on T of the HPMC solutions followed the sequence of the Hofmeister series
The investigations revealed that most salts added to aqueous solutions of HPMC lead to salting-out effects and promote thermogelation of HPMC
Summary
Many techniques are available for studying the sol-gel transitions in HPMC hydrogels. These processes primarily include dynamic light scattering [8], differential scanning calorimetry (DSC) [9,10], rheological measurements [11,12] and nuclear magnetic resonance (NMR) [13,14]. A control-strain rheometer (ARES 100FRTN1, Rheometric Scientific Inc., NJ, USA) was used to measure the flow properties and dynamic viscoelasticity of gel solutions. The HPMC tablets for studying their behaviour in bio-environment were prepared using the direct-compression method without any binder in Carver Laboratory Press (2158 series, Carver Inc., IN, USA)
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