What is the fine-grained topic of the following text: She has been a regular visitor over the past years; this time, she is evaluating the antibacterial potential of titanium dioxide nanoparticles with ligning -as well as their citotoxicity- that could be used in sunscreens. Only return the topic.
Evaluating the antibacterial potential and cytotoxicity of titanium dioxide nanoparticles with lignin for use in sunscreens