Interfacial water and its potential role in the function of sericin against biofouling

Abstract

Silk sericin is a globular protein whose resistance against fouling is important for applications in biomaterials and water-purification membranes. Here it is shown how sericin generates a water-exclusion zone that may facilitate antifouling behavior. Negatively charged microspheres were used to mimic the surface charge and hydrophobic domains in bacteria. Immersed in water, regenerated silk sericin formed a 100-µm-sized exclusion zone (for micron-size foulants), along with a proton gradient with a decrease of >2 pH-units. Thus, when in contact with sericin, water molecules near the surface restructure to form a physical exclusionary barrier that might prevent biofouling. The decreased pH turns the aqueous medium unviable for neutrophilic bacteria. Therefore, resistance to biofouling seems explainable, among other factors, on the basis of water-exclusionary phenomena. Furthermore, sericin may play a role in triggering the fibroin assembly process by lowering the pH to the required value.

Keywords:

• Biofouling
• exclusion zone
• pH gradient
• regenerated silk sericin

Acknowledgements

Dr E. R. Macias-Balleza is acknowledged for interesting discussions and Dr J. M. Gutiérrez-Hernández for obtaining the SEM micrographs.

Disclosure statement

No potential conflict of interest was reported by the authors.

Animal rights

All experiments were done with ahimsa silk cocoons. The main purpose of ahimsa is to support sericulture that respects the life of Bombyx mori larvae.

Additional information

Funding

This research was carried out with support from CONACYT, México (Scholarship 575874, and the infrastructure grant 270662 for XPS), the Universidad de Guadalajara, the University of Washington, and SAGST (Software AG Foundation).