A Thermoresponsive Hydrophobically Modified Hydroxypropylmethyl Cellulose/Cyclodextrin Injectable Hydrogel for the Sustained Release of Drugs.

The objective of this study was to develop a thermoresponsive injectable hydrogel for the sustained release of drugs by taking advantage of host-guest interactions between a hydrophobically modified hydroxypropylmethyl cellulose (HM-HPMC) and cyclodextrin (CD). A thermoresponsive injectable hydrogel was prepared by simply adding CDs to HM-HPMC hydrogel. The HM-HPMC hydrogel was converted into a sol with a low viscosity through host-guest interactions with CDs. The HM-HPMC/β-CD hydrogel became a gel near body temperature where the host dissociated from the hydrophobic moieties of the polymer in response to the temperature. The yield stress of the HM-HPMC became progressively lower on the addition of β-CD which was desirable in the case of developing an injectable formulation. When the HM-HPMC/β-CD hydrogel containing indocyanine green (ICG) was subcutaneously administered to mice, the fluorescence of the ICG remained relatively constant for 24 h after the administration, which was substantially longer than that for ICG alone or an HPMC formulation. The plasma insulin level was maintained for a longer period of time when the HM-HPMC/β-CD containing insulin was administered and the MRT value was increased by 1.6 times compared to a solution of insulin alone. In addition, the HM-HPMC/β-CD hydrogel formulation showed a prolonged hypoglycemic effect in response to the insulin which was slowly released from the hydrogel. A thermoresponsive injectable hydrogel was successfully constructed from the highly viscous HM-HPMC and β-CD, and the resulting formulation functioned as a sustained release carrier for drugs.