Pinzón-De la Rosa, Carlos A.

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    Rheological characterization of hydroxypropyl methylcellulose solutions: Gelation and molecular interactions with additives
    (2015) Pinzón-De la Rosa, Carlos A.; Acevedo-Rullán, Aldo; College of Engineering; Córdova, Ubaldo; Ortiz, Patricia; Méndez, Rafael; Department of Chemical Engineering; Vega, Carmen
    The discovery and development of highly hydrophobic drugs represents an additional challenge for the pharmaceutical industry, as traditional methods of encapsulation, administration, and dosage are not always appropriate. Physically formed edible films have been proposed as a solution to this problem due to their ability to encapsulate and stabilize these particles. Many methods have been proposed for the characterization, and improvement of the physical and morphological properties of these films. However, many of these methods are subjective and time-consuming. In this study, it is proposed to evaluate the effect of the addition of various additives, such as flavorants, plasticizers, and two highly hydrophobic BCS (biopharmaceutical classification system) class II drugs, through rheological characterization of the gelation temperature of the precursor solutions. The evaluation of the addition of flavorants with different functional groups in their structure, and the effect of their concentrations in the gelation temperature of polymer solutions was studied. Gelation was affected by the polymer relative solubility, and the interactions between polymer and organic part of the solvent mixture which depends on the functional groups present in the flavorant molecules. These results could be applied in the estimation of the effect of the addition of small soluble molecules with similar chemistry. The ability of the polymer to stabilize these hydrophobic particles through van deer Walls and hydrophobic interactions with the surface of the particles was studied. Results showed a relation between the polymer-particle affinity and the gel formation mechanism. A synergistic effect caused by the polymer molecular weight contribute to the amount of hydrophobic interactions that the polymer can make with other drug or polymer molecules, affecting the flexibility of the system. The effect of the addition of plasticizers to the mixture was evaluated. HPMC solutions with glycerol were further studied because it has been reported that at high concentrations of the plasticizer, phase separation may occur. A combination of steady-state rheology measurements of the polymer solutions and NIR-CI were used to study the relation between solution properties and films morphology. During the film casting process, the evidence of phase separation is measured by NIR-CI and optical images.