The authors are motivated to develop a series of hydrochromic copolymers with fast response, reversibility, repeatability, and visual transparency transition. The hydrochromic block copolymers are based on the rational ratio of hydrophilic segments of poloxamer block and hydrophobic segments of ethyl cellulose according to the preparation method of polyurethane. By tuning the ratio of hydrophilic segments or adding hygroscopic salts, the hydrochromic polymer is endowed with the ability to visualize the transparency in response to the relative humidity. Especially, the response time of the polymer is extremely shortened, up to 1 s for the optimized sample. Within the moisture stimulation, the hygroscopic swelling increases the film thickness, leading to a reversible transparency switching from a highly transparent state (82%) to an opaque white state (20.5%).
Objective Sildenafil citrate (SC) could promote uterine lining development, leading to successful embryo implantation. Due to the low oral bioavailability of the first-pass elimination of SC, it is necessary to develop a gel for vaginal administration to improve the efficacy.Methods A vaginal gel was prepared using the cold method to increase the retention of SC in the uterus, which allows for prolonged contact between SC and the vaginal mucosa. A poloxamer-based thermosensitive in situ gel containing SC (SC-Tsgel) and an HPMC-based standard gel containing SC (SC-Cogel) were prepared. The rheological properties, in vitro drug release, and in vivo retention in the uterus of SC-Tsgel and SC-Cogel were compared.Results The gel formulations significantly prolonged the time it took for drugs to be released following a release study. SC-Tsgel and SC-Cogel administered vaginally increased the duration of drug administration compared to SC solutions injected through the tail vein. Nevertheless, compared with tail vein injection of SC solutions or vaginal administration of the SC-Cogel, the retention of SC in the uterus was increased significantly after vaginal administration of the SC-Tsgel.Conclusions Novel formulations of SC prepared with poloxamer 407 show promise as vaginal medication preparations for the management of a thin endometrium.
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