## 3 Results
### In Vitro Drug Release Profiles  
The drug release profile was mainly depended on the degradable properties of the copolymer, and the lactic/glycolide (LA/GA) mol ratio had a markedly influence on degradability of star-shaped PLGA-mPEG copolymer hydrogel, which was reported in our previous papers [44; 46]. The release profiles of IMC, GSD, and EE from star-shaped PLGA-mPEG copolymer hydrogels with different LA/GA mol ratios were first investigated here. Figure 3 showed cumulative release profiles of three mixed drugs packed by star-shaped PLGA-mPEG copolymer hydrogels with the same drug content (middle) and various LA/GA mol ratios in PLGA blocks at the previously defined days. Cumulative  
Figure 2: (a) The UV-Vis spectra of indomethacin (IMC), gestodene (GSD), and ethinyl estradiol (EE) were recorded using HPLC with a UV-Vis detector from 180 to 400 nm, (b) HPLC curves of IMC, GSD and EE in methanol at various mixture ratios of methanol and water, (c) HPLC curves of IMC, GSD, EE, and their mixture (methanol/water ratio is 53:47).  
release amount of IMC, GSD, and EE in copolymer hydrogels increased with the decrease of LA/GA mol ratio from 9 to 1. In other words, better degradability of copolymer hydrogels with lower LA/GA mol ratios gave rise to a faster release of three drugs. The drug release rate might be mainly controlled by drug diffusion and degradability of copolymer hydrogels, the released amounts of drugs from hydrogels with different LA/GA mol ratios were obviously different in one month, as shown in Figure S3a-c.  
Figure 3: The release profiles of indomethacin (IMC), gestodene (GSD), and ethinyl estradiol (EE) from prepared 4 sPLGA-mPEG block copolymer hydrogels. Cumulative release of IMC (**a**), GSD (**b**), and EE (**c**) packed by copolymer hydrogel with the same middle drug content and various lactic/glycolide (LA/GA) mol ratios. Cumulative release of IMC (**d**), GSD (**e**), and EE (**f**) loaded by CP-2 copolymer (LA/GA = 3) hydrogel with various drug contents (high, middle, and low). Copolymer concentration was 30 wt%.  
On the other hand, the release amount and cumulative release profiles of three mixed drugs from CP-2 copolymer hydrogels loaded with various drugs contents (high, middle, and low) were studied, and the results were shown in Figure S3d-f and Figure 3. With the increase of drug content in CP-2 copolymer hydrogel, the release amount of IMC and GSD were also higher at different days, however, the cumulative release of IMC and GSD increased faster with the decrease of drug loading amount. For EE release profile, the loading content had a slight influence on the release amount from CP-2 copolymer hydrogels (Figure S3f), and the cumulative EE release profiles still increased faster with the decrease of initial EE loading amount.  
Synchronic release profiles of three drugs were fitted by three drug release models, namely, zero-order, first-order and Higuchi model. Table S2 listed all fitting parameters using above-mentioned drug kinetic models. The high correlation coefficient (\(R^{2}\)) values and good linear relation of fitting curves by Higuchi model, indicated that release profiles of IMC, GSD, and EE were well fitted with Higuchi model. Take the cumulative release of GSD from CP-3 copolymer hydrogel (LA/GA = 1) as an example, the fitting curve was shown in Figure S4, the correlation coefficient was 0.996.