Public defence in Materials Science, M.Sc. Mohammad Awashra

Title of the thesis: Superhydrophobic bio-repellent surfaces

Thesis defender: Mohammad Awashra
Opponent: Prof. Emilia Peltola, University of Turku, Finland
Custos: Prof. Ville Jokinen, Aalto University School of Chemical Engineering

Superhydrophobic surfaces trap a thin air layer, known as the plastron, between the liquid and solid interface, reducing liquid contact and allowing the surface to repel biofluids, resist protein adsorption, and prevent cell adhesion. The challenge, however, lies in maintaining this air layer in complex biological environments, where proteins and biomolecules destabilise it.

This doctoral thesis investigates how the design of superhydrophobic micro- and nanostructures affects plastron stability and bio-repellent behaviour in biological fluids. Using optical imaging and wettability analysis, the work demonstrates how surface geometry and chemistry can extend plastron lifetimes beyond 120 hours in protein-rich media. Proteins and sugars were identified as major destabilising factors, while higher solid fractions, smaller feature sizes, and greater surface roughness improved plastron retention.

The study also examines how plastron-mediated surfaces repel cells. Experiments with A549 epithelial cells revealed that the most effective designs maintain air gaps wider than cell dimensions while preventing liquid penetration. Optimised micropillar arrays with 7.4% solid fraction reduced cell adhesion by up to 95% compared to flat hydrophilic controls.

Finally, two biomedical applications demonstrate the potential of such surfaces: (1) superhydrophilic–superhydrophobic droplet microarrays enabling single-molecule RNA detection using SIBA chemistry, and (2) transparent superhydrophobic alumina nanograss-coated glass capillaries that resist protein fouling and reduce fluid drag by up to 50%. These results establish superhydrophobic bio-repellent surfaces as promising candidates for long-term biomedical and diagnostic applications.

Keywords: superhydrophobic, microfabrication, plastron, biofluid, bio-repellent, biointerfaces, protein adsorption, cell adhesion, droplet microarray, digital SIBA, glass capillaries, drag reduction

Thesis available for public display 7 days prior to the defence at Aaltodoc. 

Contact information: 
moe.awashra@aalto.fi