**4. Conclusions**

This study showed that ASC and PSC extracted from Nile tilapia skin have typical type I collagen characteristics. No significant differences were found in the amino acid composition and physicochemical properties of ASC and PSC. Both ASC and PSC have a complete triple-helix structure. The thermal stability of PSC was slightly lower than that of ASC, similar to mammals, and higher than cold-water fish. ASC has the effect of promoting osteogenesis and fibroblastation, while PSC is beneficial to the formation of vascular endothelial cells by comparison, and neither ASC nor PSC cause acute systemic toxicity. In summary, collagen extracted from Nile tilapia skin is a biocompatible type I collagen with potential as a biomedical material.

**Author Contributions:** Conceptualization, W.-K.S.; validation, L.-L.S.; formal analysis, W.-K.S.; resources, D.L. and H.H.; data curation, W.-K.S.; writing—original draft preparation, W.-K.S.; writing—review and editing, H.H.; supervision, B.-F.L.; project administration, H.H.; funding acquisition, B.-F.L.

**Funding:** This work was supported by National Natural Science Foundation of China (Nos. 31772046 and 31471606), Key Research & Development Plan of Shandong Province (Nos. 2017YYSP015, 2016YYSP005 and 2016YYSP017), and National Key R&D Program of China (2018YFC0311200).

**Acknowledgments:** The authors acknowledge Yuan-Yuan Wang (Marine Biomedical Research Institute of Qingdao) for the kind contribution of cell cultures.

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