Development of Mussel-inspired Antifouling Coatings and Underwater Adhesive Materials and the Associated Surface Interaction Mechanisms
Creators: Pan, Mingfei
Publisher: name: University of Alberta Library
Year: 2022

<p>Nature biology like blue mussels, barnacles, and sandcastles can tightly attach to solid surfaces in the ocean, even under dynamic and turbulent environments. Exploration of these organisms has revealed the significance of catechol-enriched adhesive proteins as the unique paradigm for the development of synthetic systems for a broad range of applications. However, studies on the corresponding intermolecular interactions between the catechol-containing materials are limited which brings the challenge to realize the delicate control of catechol chemistry and the full recapitulation of the biological adhesive functions. In this thesis, three original research works regarding the molecular design and engineering of mussel-inspired antifouling coating and adhesive hydrogel materials are presented, with the assistance of drop and colloidal probe atomic force microscope (AFM) techniques to investigate the correlated surface interaction mechanisms, which hold great promises in industrial and medical applications under practical conditions.<br><br>
In the first work, a mussel-inspired antifouling coating formed by polydopamine (PDA) codeposited with cationic {2-(methacryloy-loxy)ethyl}trimethylammonium chloride (MTAC) and anionic acrylic acid (AA) was demonstrated bearing adjustable surface charge property, employing tunable long-range electrostatic interaction to achieve adaptive antifouling performance in response to the varying electrical characteristic of the contaminants, i.e., emulsions. The results from surface forces measured by drop probe AFM technique indicated that modulating the surface electrical properties of the coatings through varying the solution pH could effectively alter their electrostatic interactions with emulsions from attraction to repulsion, in combination with hydrodynamic interactions, to enable emulsion repellence of the coatings. Meanwhile, by properly modulating the surface charge of a PDA-PAA-PMTAC-deposited polyvinylidene fluoride (PVDF) membrane, an enhanced water permeability with durable antifouling property was achieved for efficient and universal water purification.<br>
Achieving robust adhesion on wet biological tissues for hydrogels containing high water content is still challenging, as water disrupts the surface boding, thus resulting in weak adhesion strength. In the second work, mimicking the structure of the Mytilus byssal thread covered by a thin protective cuticle, a design strategy was proposed to construct a soft armour-like hydrophobic interface as the outermost adhesive layer over the hydrophilic hydrogel matrix to realize instant and robust wet adhesion. The external hydrophobic shell generates a water depletion region at the contact interface to promote rapid adhesion (within 5 s) and protect the weakening of interfacial bonds from water penetration even under high hydraulic pressure. Atomic force microscope (AFM) colloidal probe technique was also used to investigate the assembling mechanisms for the hydrophobic layer of the hydrogel. The developed hydrogel adhesives are further applied in the wet intraoral environment to facilitate the high-contrast imaging for ultrasound diagnosis, which benefits the integration of human-machine interface for biomedical applications.<br>
Development of soft conductive materials has enabled the promising future of wearable sensors for health monitoring. However, conventional soft conductive materials typically lack robust adhesive and on-demand removable properties for a target substrate. In the third work, a novel hydrogel ionic conductor was developed composed of a cationic micelle cross-linked polymer network. The developed ionic conductor possesses a range of desirable properties including mechanical performances such as excellent stretchability (&gt;1100%), toughness, elasticity (recovery from 1000% strain), conductivity (2.72 S·m-1), self-healing capability, and antimicrobial property, owing to multiple non-covalent supramolecular interactions (e.g., hydrogen bonding, hydrophobic, and π-π/cation-π interactions) present in the cross-linked network. Moreover, the ionic conductor was integrated with bridging polymers to form a motion-sensing entirety. The environment-adaptive wet adhesion of the motion sensor for various substrates (adhesion strength up to ~ 30 kPa) was achieved by the introduction of pH or temperature-responsive polymers as the bridging agent that can form a topological connection with the hydrogel network and substrate surfaces. Further, the on-demand removability can be achieved by the external stimuli of environmental pH or temperature. The resulting motion sensors possess excellent sensitivity and reliability for the detection of human motions, showing great promise for advanced health monitoring devices with enhanced performances.<br>
This thesis work expands the application of marine mussels-derived dynamic interactions in the development of multifunctional antifouling coating and wet adhesive hydrogels and elucidates the related intermolecular interactions at nanoscale, which devises a new passage on catechol containing-synthetic systems with diverse anchoring, antifouling, adhesive, and cohesive properties for the environmental and biomedical applications.</p>