Effect of polymer concentration and thermal history on the inverse thermogelation of hydroxypropylcellulose aqueous solutions

Design of berberine hydrochloride sustained-release cold sol using hydroxypropyl methyl cellulose K100M to achieve superior drug dissolution and transdermal absorption

In this study, berberine hydrochloride (Ber) was used as model drug to prepare a sustained-release cold sol using hydroxypropyl methyl cellulose (HPMC) to achieve superior drug dissolution and transdermal absorption effects. For comparison, a Ber cold sol without HPMC was also prepared using the same method. The preparation process was optimized based on the in vitro release and transdermal permeability of the drug. The results indicated that 1.67 wt% Carbomer 940 and 1.33 wt% HPMC K100M were selected as matrix components with the best sustained-release effect, and drug dissolution of cold sol prepared by combination of these two matrices was significantly slower than the cold sol without HPMC. In addition, transdermal absorption result demonstrated that 0.67 wt% glycerin and 1.33 wt% peppermint oil were the best osmotic enhancers for the optimization of Ber sustained-release cold sol. Herein, HPMC K100M performed important functions in the external application of Ber.

Hysteresis in the thermally induced phase transition of cellulose ethers

Functionalized cellulosics have shown promise as naturally derived thermoresponsive gelling agents. However, the dynamics of thermally induced phase transitions of these polymers at the lower critical solution temperature (LCST) are not fully understood. Here, with experiments and theoretical considerations, we address how molecular architecture dictates the mechanisms and dynamics of phase transitions for cellulose ethers. Above the LCST, we show that hydroxypropyl substituents favor the spontaneous formation of liquid droplets, whereas methyl substituents induce fibril formation through diffusive growth. In celluloses which contain both methyl and hydroxypropyl substituents, fibrillation initiates after liquid droplet formation, suppressing the fibril growth to a sub-diffusive rate. Unlike for liquid droplets, the dissolution of fibrils back into the solvated state occurs with significant thermal hysteresis. We tune this hysteresis by altering the content of substituted hydroxypropyl moieties. This work provides a systematic study to decouple competing mechanisms during the phase transition of multi-functionalized macromolecules.

Determination of Microstructural Impact on the Release of Drug from Hydroxypropyl Cellulose Gel by Validated In Vitro Release Test Method

Microstructure of a semisolid system is greatly influenced by the formulation composition and the processing parameters. Different polymers exhibit different three-dimensional structure and these have a great impact on the drug release properties. The current research focuses on studying the impact of hydroxypropyl cellulose gel microstructure on the release properties of chlorhexidine gluconate (CHX G). The two main investigating methods of microstructure were used namely, rheology and texture analysis to determine the differences in the formulations studied. The CHX G drug release study was performed using a developed and validated in vitro release test method, which is reproducible, discriminative, and robust to detect the formulation differences. The drug release results showed that there was appreciable difference in the release rates of the different formulations. The rheology and texture analysis data correlated well with the difference in the release rates. The formulations differences were further confirmed by a statistical approach using analysis of variance.

Oscillatory rheology of carboxymethyl cellulose gels: Influence of concentration and pH

The flow properties of ionic polysaccharides are determined by the interplay of electrostatic and hydrophobic interactions, which depend on the ionic strength and pH of the solvent. We explore the LVE and LAOS rheology of carboxymethyl cellulose (CMC) in aqueous media, focusing on its gelling behaviour. We find that addition of HCl promotes gel formation and addition of NaOH suppresses it. The former effect is interpreted as being caused by a decrease of the charge density of the polymer, which facilitates interchain associations and the later effect can be assigned to solubilisation of cellulose backbone by NaOH. Our results along with a review of the literature allow us to establish the concentration regimes and associated properties of physical gels of carboxymethyl cellulose. At neutral pH, the storage modulus of NaCMC gels of varying molecular weight and DS at a given concentration does not vary by more than a factor 5.

Temperature-Dependent Rheological and Viscoelastic Investigation of a Poly(2-methyl-2-oxazoline)-b-poly(2-iso-butyl-2-oxazoline)-b-poly(2-methyl-2-oxazoline)-Based Thermogelling Hydrogel

The synthesis and characterization of an ABA triblock copolymer based on hydrophilic poly(2-methyl-2-oxazoline) (pMeOx) blocks A and a modestly hydrophobic poly(2-iso-butyl-2-oxazoline) (piBuOx) block B is described. Aqueous polymer solutions were prepared at different concentrations (1-20 wt %) and their thermogelling capability using visual observation was investigated at different temperatures ranging from 5 to 80 °C. As only a 20 wt % solution was found to undergo thermogelation, this concentration was investigated in more detail regarding its temperature-dependent viscoelastic profile utilizing various modes (strain or temperature sweep). The prepared hydrogels from this particular ABA triblock copolymer have interesting rheological and viscoelastic properties, such as reversible thermogelling and shear thinning, and may be used as bioink, which was supported by its very low cytotoxicity and initial printing experiments using the hydrogels. However, the soft character and low yield stress of the gels do not allow real 3D printing at this point.