Multimodal Control of Adhesion in Polydopamine Nanomembranes through Texture, Microstructure, and Chemistry Control

2018-10-22T21:00:14Z (GMT) by Ik Soo Kwon
Finding that mussels rely on catechol and amine functional group enriched proteins to achieve robust underwater adhesion prompted scientists to create synthetic polymeric systems mimicking mussel chemistry. Polydopamine (PDA), mussel chemistry inspired polymeric coating, came to a spotlight in 2007. The primary advantage of PDA is that it can be easily deposited into a robust thin film onto various kinds of surfaces, a trait stemming from its rich content in catechol and amine motifs. The versatile functional nature of PDA enables envisioning of potential applications beyond the conformal coating; these characteristics include mixed electronic-ionic conductivity, chelation of cations, catechol-based redox activity, mechanical robustness as a nanomembrane, underwater adhesiveness, biocompatibility, and the presence of many functional groups for post-deposit modification.<br>The coexistence of a variety of characteristics in a single material indicates the possibility of tuning of material properties in programmable and multimodal manners. This thesis explores the fundamentals of macroscopic adhesion in PDA, with a particular focus on achieving the multimodal control of PDA adhesion. Using a custom-built Johnson-Kendall-Roberts apparatus, the adhesive property of PDA nanomembranes was examined in relation to their texture. It was revealed that PDA adhesion is a strong function of its morphology both in air and water, and could be tuned through morphological control. Persson’s roughness theory was extended to model the underwater adhesion of PDA and showed a good agreement with the experiments.<br>PDA nanomembranes were interfaced with Polydimethylsiloxane (PDMS) substrates to create substrates with surface wrinkles. Dynamic control of surface wrinkles with mechanical actuation translated into adhesion variance. A semi-analytical theoretical framework was developed to correlate adhesion of the composite structure to its surface wrinkle geometry.<br>Redox control of PDA adhesion was investigated. Presence of the catechol population with reversible chemistry was investigated through the aid of impedance spectroscopy circuit modeling. Chemical modulation of PDA adhesion through pH control was conducted, and the successful reversible variation of PDA adhesion with pH control was confirmed. Effect of pH and saline condition to PDA adhesion was analyzed in relation to catechol chemistry.<br><div>This thesis is an attempt to develop a framework to understand bulk adhesion of PDA nanomembranes to help the future translation of PDA into adhesive devices.</div><div><br> </div>