Biosynthesis of Peptide Hydrogel–Titania Nanoparticle Composites with Antibacterial Properties

The photoantibacterial properties of titania nanoparticles (TiO₂NPs) are attracting much interest, but the separation of their suspension limits their application. In this study, the encapsulation of commercial TiO₂NPs within self-assembling tripeptide hydrogels to form hgel-TiO₂NP composites with significant photoantibacterial properties is reported. The Fmoc-Phe₃ hydrogelator was synthesized via an enzymatic method. The resulting composite was characterized with DLS, ζ-potential, SAXS, FESEM-EDS and rheological measurements. Two different concentrations of TiO₂NPs were used. The results showed that, by increasing the TiO₂NP quantity from 5 to 10 mg, the value of the elastic modulus doubled, while the swelling ratio decreased from 63.6 to 45.5%. The antimicrobial efficacy of hgel-TiO₂NPs was tested against a laboratory <i>Staphylococcus aureus</i> (<i>S. aureus</i>) strain and two methicillin-resistant <i>S. aureus</i> (MRSA) clinical isolates. Results highlighted a concentration-dependent superior antibacterial activity of hgel-TiO₂NPs over TiO₂NPs in the dark and after UV photoactivation. Notably, UV light exposure substantially increased the biocidal action of hgel-TiO₂NPs compared to TiO₂NPs. Surprisingly, in the absence of UV light, both composites significantly increased <i>S. aureus</i> growth relative to control groups. These findings support the role of hgel-TiO₂NPs as promising biocidal agents in clinical and sanitation contexts. However, they also signal concerns about TiO₂NP exposure influencing <i>S. aureus</i> virulence.