Scanning electron micrograph of PDA/Ag nanocomposite particles. Courtesy of Ziwei Deng and Bo Peng.
Scanning electron micrograph of PDA/Ag nanocomposite particles. Courtesy of Ziwei Deng and Bo Peng.

Inspired by the adhesive properties of mussels, researchers have synthesized antibacterial nanocomposite particles of polydopamine and Ag through an easy, green process that could be suitable for biomedical applications [C. Wu, et al., Materials Science & Engineering C (2015), doi: 10.1016/j.msec.2015.05.032,].

The team from the University of Oxford, Shaanxi Normal University and Huazhong Agricultural University in China created spherical monodisperse polydopamine (PDA) particles by oxidizing dopamine monomers in an alkaline water-ethanol solution at room temperature and then self-polymerizing. Dopamine is a biomolecular analogue of the naturally occurring proteins in mussels that enable them to adhere tightly to surfaces. The molecules contain amine and catechol groups that readily absorb silver precursor [Ag(NH3)2]+ ions and facilitate reduction to metallic Ag nanoparticles, which have well known antibacterial effects.

The resulting PDA/Ag nanocomposite particles created by Bo Peng, Dingzong Guo, and Ziwei Deng do indeed demonstrate antibacterial effects against Escherichia coli (Gram-negative bacteria) and Staphylococcus aureus (Gram-positive bacteria). Meanwhile, the composite shows no significant cytotoxicity on human embryonic kidney cells.

“We used mussel-inspired chemistry based on polydopamine, which is adhesive and eco-friendly, to develop an inexpensive and efficient process for the fabrication of polydopamine/Ag nanocomposite particles as the novel and effective antibacterial agents,” explain Deng and Peng.

The environmentally friendly synthesis process is simple and cheap, point out the researchers, with no need for additional reductants, toxic reagents, or complicated equipment. And the approach has other advantages as well, claim the researchers. The PDA particles could serve as a universal platform, which could be decorated with other nanoparticles instead of Ag such as metal oxides, ceramics, or other polymers. Where Ag is used, varying the concentration of the precursor ion allows the coverage of Ag nanoparticles – and, therefore, the bacterial effect – to be tuned. Furthermore, the submicron size and stability of the PDA/Ag nanocomposite particles indicates that it may be possible to recycle particles after use, via sedimentation.

“PDA/Ag nanocomposite particles may useful for various biomedical applications, for instance as a biocide in the clinic against infection, as an antimicrobial additive in animal food, or to inhibit bacterial growth at a laboratory level,” Deng and Peng told Materials Today.

The researchers are now planning to examine the antibacterial activity of the PDA/Ag nanocomposite particles using in vivo animal tests and investigate the activity of other materials such as ZnO and Fe3O4 in the quest to develop multi-functional or responsive materials.