## 1 Introduction
Hydrogels are versatile and have been used to deliver microbicides, labor inducers, and other substances in the vagina [22]. Furthermore, the localized vaginal hydrogels delivery (mainly mucosal route) allows women to self-administer contraceptives, but it also reduces adverse effects and frequency of the dosage [15; 23]. With excellent biocompatibility advantages, natural polymer hydrogels have been used as a vaginal drug delivery system [24]. [PERSON] et al. first obtained a sponge by lyophilization of cellulosic derivative hydrogels, and then the prepared sponge could be adhered to the vaginal cavity and rehydrated by the small amount of vaginal fluids to form hydrogels again as drug delivery system [12]. [PERSON] et al. designed an in situ-forming and pH-responsive hydrogel based on chitosan as mucoadhesive hydrogel for vaginal delivery of therapeutic agents [25]. Gelatin hydrogels using polysaccharides (e.g., maltodextrin, dextran, and sodium carboxymethyl cellulose) have been used in vaginal delivery of antimicrobials, such as metronidazoleazole, for the treatment of bacterial vaginosis [26]. One problem through conventional hydrogels as vaginal drug delivery system is rapid removal from the application site, but also uneasy self-administration for users. Stimulus-responsive synthetic degradable hydrogels, such as in situ-forming hydrogels, is a good solution to overcome rapid removal, and their physical characteristics were altered as a result of exposure to changes of vaginal environments [27; 28]. Thermosensitive vaginal hydrogels are capable of gelling in response to temperature change, such as, from ambient to body temperature [29]. Furthermore, thermosensitive hydrogels have great promise due to their stability, adhesion properties and adjustable drug release kinetics [30]. In general, gelation temperatures in the range of 25-37 \({}^{\circ}\)C have been considered suitable for vaginal site application. Commonly synthetic polymers for thermosensitive hydrogels include \(N\)-isopropyl acrylamide copolymers, poloxamers and their copolymers, poly(ethylene oxide)/poly (\(D\),\(L\)-lactic acid-\(\alpha\)-glycolic acid) copolymers, and so on [31]. The terpolymer of N-isopropyl acrylamide, butyl methacrylate, and acrylic acid was used as a thermosensitive and pH-sensitive polymer hydrogel for loading and releasing microbicides for the prevention of sexual transmission of HIV and other sexually transmitted diseases (STDs) [32]. Poloxamer (such as F127 and F68) could be designed as the thermosensitive contraceptive vaginal hydrogel for in situ loading curcumin for contraception [33; 34; 35]. [PERSON] et al. designed the poloxamer-based in situ vaginal hydrogels with loading nonoxynol-9 as a model drug, different poloxamer 407/poloxamer 188 ratios were used for adjusting hydrophilic content of hydrogel formulations, and further regulating hydrogels erosion, drug release, and intravaginal elimination [36]. The poloxamer with the clotrimazole loaded nanostructured lipid carriers could be diluted with simulated vaginal fluid (SVF) to form thermo-hydrogels for treating fungal vaginal infections [37]. Poly(ethylene glycol) (PEG)/Polyester copolymer hydrogels perhaps represented the most extensive research system in recent years, while the biodegradable rate was regulated by adjusting the ratio of lactic acid to glycolic acid (LA/GA). [PERSON] et al. synthesized a thermo-gelling poly(lactic acid-\(\alpha\)-glycolic acid)-poly(ethylene glycol)-poly(lactic acid-\(\alpha\)-glycolic acid) (PLGA-PEG-PLGA) triblock copolymer, then the triblock copolymer could form to micelles in water and serve as a reservoir for the solubilization of hydrophobic levonogestrel (LNG) molecules. The PLGA-PEG-PLGA thermo-gel markedly extended the release of LNG, which was promising for long-term contraception and fertility control [38].