Hypromellose, or hydroxypropyl methylcellulose (HPMC) - has been widely used for biomedical and pharmaceutical applications due to its advantages, including that it is modifiable in terms of viscosity, and it has the ability to form thermally reversible hydrogels. The thermal gelation temperature (TGel) of a given HPMC solution strongly depends on its characteristic grade and the solution concentration. Applying certain additives can modify the TGel even further; depending on their nature and concentration. With the addition of said additives, a lower or higher TGel can be obtained. For example, the addition of sodium chloride (NaCl) reduces the TGel, whilst sodium iodide (NaI) increases the TGel, for a given HPMC solution. Therefore, for a certain application, the gelation temperature of a solution could be modified by adding a selected additive at an appropriate concentration. The effects of various additives have been described in the literature. However, there has been no in-depth experimental reporting on the effect of sodium fluoride (NaF) on the TGel. Here, we investigate the impact of NaF in comparison to NaCl on the thermal gelation temperature of HPMC 2910 using rheological analyses. The sol-gel transition temperature was evaluated by examining the viscosity, the storage modulus, and the loss modulus of HPMC
solutions as a function of concentration. The results indicated that both NaCl and NaF were able to reduce the TGel of HPMC 2910. However, the effect of NaF was found to be significantly greater in reducing the TGel compared to NaCl; the change in TGel as a function of additive composition was approximately 3.6 times higher for NaF compared to that of NaCl. In conclusion, these findings suggest that NaF is a suitable additive to combine with HPMC solutions for in-situ gelation at body temperature. Furthermore, the data indicated that only 1.6% NaF was needed to reduce the gelation temperature of HPMC from 60 ˚C to body temperature (approx. 37 ˚C). HPMC solutions containing NaF can form a viscoelastic solid gel at body temperature; this could potentially be used to prolong the release of fluoride for dental remineralization purposes.
Hypromellose, Sol-Gel Transition, Gelling Aids
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Sadeghi, Elnaz. "Effect of Strong Electrolyte Containing Gelling Aids on the Sol-Gel Transition Temperature of Hypromellose 2910." (2018). https://digitalrepository.unm.edu/bme_etds/25