*3.2. Improved Antimicrobial Properties*

Besides the previously mentioned CuO2, nAgs, metronidazole (MNA), doxycycline (Dox), chlorhexidine (CHX), and antimicrobial peptides (AMPs) have been used to improve the antimicrobial properties of the membranes [32].

## 3.2.1. Silver Nanoparticles

Silver is well known to have broad-spectrum antibacterial properties and has been used in various forms due to its low cytotoxicity [99,100]. Many studies have demonstrated the important activity of Ag nanoparticles (nAgs) against bacterial biofilms [101–104]. There exist studies on the promotion of antimicrobial activity using nAg as a coating material for membranes in the oral cavity [30,36,42]. In 2018, Chen et al. reported nAgs-coated collagen membranes through sonication coating or the sputtering coating technique [42]. The nAgscoated membranes showed excellent antibacterial effects against *Staphylococcus aureus* and *Pseudomonas aeruginosa*, and exhibited advanced anti-inflammatory effects by reducing the expression and release of inflammatory cytokines [42]. In 2020, Wang et al. reported that nAgs immobilized a PDA-coated PLLA membrane that showed advanced antibacterial effects against *S. aureus* and a good biocompatibility due to low cytotoxicity [30].
