**Preface to "Multi-Functional Collagen-Based Biomaterials for Biomedical Applications"**

Polymeric biomaterials represent an essential tool in the biomedical field. Their high biocompatibility and ability to provide adequate regenerative support are fundamental for the development of new therapeutic devices. In particular, biomaterials derived from living organisms exhibit not only structural roles but are also implicated in cellular processes. Among them, type I collagen plays a dominant role in maintaining the biological and structural integrity of various tissues. In recent years, with the goal of developing multi-functional collagen-based devices able to better promote the functional recovery of damaged tissues, numerous studies focused on novel techniques, and methods for the development of innovative and advanced high-performance formulations. The ability to tune collagen-based biomaterials performance is an extremely important knowledge to acquire when specific multi-functionalities are sought.

The present Special Issue collected 12 peer-reviewed interdisciplinary contributions on the broad topic of multi-functional collagen-based biomaterials for biomedical applications, with a focus on their development and customization methods as well as their functions enhancement. An update on the clinical efficacy and safety of collagen-based injectables for aesthetic and regenerative medicine applications was done by Salvatore et al., while the most recent outcomes of collagen matrices for endodontic treatment were provided by Sugiaman et al. To finely control material-cell interaction, collagen-fibronectin binding domains were identified by Liu et al. and the interaction between material-related parameters and the resulting performance was investigated by Ludolph et al.. Since various factors affect the network structure, Maher et al. investigated the effect of different collagen forms on hydrogel-forming properties. The network structure of collagen matrices was also subjected to optimization for corneal regeneration. In this context, Osidak et al. developed and in vivo tested a collagen membrane for replacing damaged corneal stroma and Montalvo-Parra et al. for the treatment of corneal opacities. To further improve collagen bioactivity and make multifunctional collagen-based constructs, Kilb et al. developed an antibiotic-enriched collagen laminate for the treatment of hard-to-heal wounds. Melo et al. developed a new approach to the treatment of severe osteoporotic fractures, by combining biomaterials with biofabrication techniques. Lastly, new collagen sources were investigated to both find more effective formulations for certain applications and overcome issues related to mammal-derived collagens. Gallo et al. extracted collagen from fish skin in pure and native form. Similarly, Anohova et al. demonstrated the possibility of using squid collagen for biomedical applications. Chen et al. developed a fish scale-derived collagen/hydroxyapatite membrane for bone regeneration.
