**4. Conclusions**

Thermosensitive ALG–POL copolymer containing a necessitated percentage of POL was successfully synthesized. Such synthesized ALG–POL was found to be suitable for constructing hydrogels with dual network structure through combining with SF. The optimally obtained ALG–POL/SF gels were injectable at room temperature and mechanically strong with their sol-gel transition near physiological pH and temperature. Embedment of mesoporous BG nanoparticles into ALG–POL/SF gel did not significantly modify the gelation temperature, gelation time and pH of the resulting gels. The interior of the dry gels was seen to be highly porous with well-interconnected pore architecture. Direct incorporation of IGF-1 into ALG–POL/SF gels was inadvisable for administrating IGF-1 release. By embedding IGF-1-loaded BG nanoparticles into ALG–POL/SF gels, the resulting IGF-1-loaded BG/ALG–POL/SF gels showed a confirmative ability to administrate IGF-1 release in an approximately linear manner for a few weeks and their IGF-1 release rate could be effectively regulated by the IGF-1 load in BG nanoparticles. Cell tests confirmed that the released IGF-1 was bioactive as compared with the free IGF-1.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/1999-4923/12/6/574/s1, Figure S1. 1H NMR spectra for monoamine-terminated poloxamer (MATP). Figure S2. FTIR spectra for poloxamer (A), alginate (B) and alginate-poloxamer (C). Figure S3. ALG-POL fluids and formed ALG-POL gel after incubation. (Concentration of ALG-POL: 9 wt% (A); and 12 wt% (B)).

**Author Contributions:** Q.M., Y.W., and J.W. conceived and designed the experiments; X.Y., J.L., and Y.Z. performed the experiments; Q.M., Y.W., and J.W. wrote the paper. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was funded by the National Key R&D Program of China (Grant No. 2017YFC1103800) and the National Natural Science Foundation of China (Grant No. 81972065).

**Conflicts of Interest:** The authors declare no conflict of interest.
