## 4 Discussion  
It was reported that the world's population would reach 9\(\sim\)10 billion by 2050, the population explosion has become the principal reason for environmental dilapidation with following human poverty and starvation [51]. Controllable unintended pregnancy effectively prevented the increase of population to a certain extent. Nowadays, the characteristics of easy-to-use and multifunctionality are more important factors considered by users for contraception [52], and long-acting contraceptive implants become available to improve family planning services [53]. The thermosensitive hydrogels of a suitable gelation temperature have potentials on the local vaginal site delivery system [54; 55]. The thermo-gelling star-shaped PLGA-mPEG copolymers comprising hydrophobic biodegradable and hydrophilic biocompatible segments are of particular interest to drug delivery systems and tissue engineering applications. In this paper, the four-arm star-shaped 4 sPLGA-mPEG copolymer hydrogels were used as a multi-contraceptive carrier. The in vitro controlled release profiles, in vivo acute toxicity, and antifertility effectivity were systematically reported. In our previous works, the four-arm star-shaped 4 sPLGA-mPEG copolymer was synthesized via the arm-first method [44; 46]. Here, the copolymer was prepared by a core-first method. Compared to the arm-first method, the same number of steps were used during the synthesis, and the same chemical structure was obtained characterized via \({}^{1}\)H NMR analysis (Figure 1b). The prepared 4 sPLGA-mPEG copolymer was dissolved in SVF solution instead of Millipore water, and the sol-gel transition behavior as a function of temperature from 15 \({}^{\circ}\)C to 60 \({}^{\circ}\)C was tested by the viscometer. It was known that the sol-gel behavior of thermosensitive copolymer was susceptive to environmental changes, such as pH or chemicals [56; 57]. The pH of the SVF solution is about 4.2, the sodium chloride, potassium hydroxide, lactic acid, and acetic acid in SVF solution might influence the gelation temperature of the prepared copolymer. Interestingly, the gel transition temperature of 4 sPLGA-mPEG copolymer dissolved in SVF was mainly decided by LA/GA ratio, and chemicals in SVF solution and pH of SVF solution both had a slight influence on gelation temperature. The star-shaped 4 sPLGA-mPEG block copolymers with the hydrophobic PLGA blocks and the hydrophilic mPEG blocks were amphiphilic. For CP-1, CP-2, and CP-3 block copolymers in solution (SVF or water) at a suitable concentration (30 wt%), with temperature increased, the copolymers could form multimolecular micelles, then micellar aggregated to accomplish the sol-gel transition (Figure S8) [58]. With the increase of LA units in block copolymers, the gelation temperature increased, as confirmed in Figure 1c. The packing interaction between micelles was achieved to an optimal dense (hydrogel state) at a suitable temperature, which makes such hydrogel easy for drug encapsulation and biomedical applications, as shown in Scheme 1. The prepared star-shaped 4 sPLGA-mPEG copolymer hydrogel was used as a carrier for delivering three hormonal contraceptives, indomethacin (IMC), gestodene (GSD), and ethinyl estradiol (EE). The multi-drug release profiles could be measured via HPLC by using an optimal mobile phase of methanol/water volume ratio at 53:47. Regarding the retention time of IMC, GSD, and EE are 11.18, 13.11, and 15.57 min respectively, and the UV-vis recording of the maximum absorption peaks (IMC and EE at \(\sim\)210 nm, GSD at \(\sim\)240 nm), and the release profiles of IMC, GSD, and EE were calculated. For three drugs release profiles, it was observed that a higher release rate was presented in the initial 7 days, and the release rate became relatively slower from 7 to 35 days, as shown in Figure 3 and Figure S4.