Florián-Algarín, Vivian M.

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    Rheology and gelation of physical polymer gels
    (2011) Florián-Algarín, Vivian M.; Acevedo-Rullán, Aldo; College of Engineering; Velazquez, Carlos; Rinaldi, Carlos; Torres-Lugo, Madeline; Department of Chemical Engineering; Romañach, Rodolfo
    The discovery of new potent and water-insoluble drugs has emphasized the need for novel drug-delivery systems and personalized dosification. Biopolymers solutions are an alternative over conventional methods since they can acts as a suspending medium for strong hydrophobic drugs, and have the potential to form gel networks, which can be used to encapsulate and improve long-term stability. Nevertheless, polymer-particle interactions can affect the rheology and gelation process of the system making it unsuitable for the application or affecting the drugs activity. Much more complex interactions are introduced by incorporation of additional components into the system, such as surfactants to improve particle stability or flavorants for taste-masking. The objective of this research work was to determine the effects of fluid formulation parameters on the physical gelation and rheology of biopolymer solutions with suspended solid particles. In this work, rheological measurements have been used to determine, understand and control the processing conditions which are related to the final product properties. Gelation temperature (Tgel) was determined using stress control temperature ramp and the dynamic oscillatory methods and rheology of polymer solution was studied above Tgel. The effect of operational and formulation parameter on Tgel were also determine. In Chapter 2 and 3, the effect of particle size and concentration on the gelation temperature of two cold-setting gels, gelatin and sodium alginate (NaAlg), were studied. It was observed that Tgel is not affected by stress at applied stress of up to 10 Pa, and decreases with increasing cooling rate. On the other hand, as polymer concentration increases gelation temperature increases. Yet, pH has a very mild effect, as shown in Chapter 2. In Chapter 3, the thermotropic gelation of NaAlg solution was demonstrated using three independent rheological measurements. Both systems were unaffected by the presence of model silica particles ranging from the micron to the nano scale. This was attributed to polymer-particle repulsion due to similar net charges. In Chapter 4, the effect of an active ingredient and the interaction between type of surfactants and the polymer-particle system was determined by the rheology and gelation temperature measurements. In this case, the model polymer system was the hot-setting hydroxypropylmethyl cellulose (HPMC), an uncharged cellulose derivative. The effect of particle size on solution properties was studied using griseofulvin particles as model drugs. Tgel showed complex dependence on particle size, concentration, and surface selectivity. Surfactants with similar net charge as the active ingredient can be either replaced by the polymer on the active’s surface or aggregate with the polymer, thus increasing viscosity of the solution and improving gelation due to bridging effects. On the other hand, positively charged and neutral surfactants have minimum polymer-surfactant interactions and are able to effectively stabilize the particles due to the preferential interactions with the active’s surface. Rheological methods were useful to demonstrate physical gelation for a weak gel, propose particles stabilization mechanisms and establish particle size and concentration effects on gelation. This information can be extended to other systems such as characterization of a weak gel, or systems with similar characteristics, where use of surfactant is needed for charge particle stabilization. These data and mechanisms can be correlated to final product properties as drug dissolution, adhesion, or mechanical properties, important in but not limited to films.