Study of molecular mechanisms in underwater adhesion systems of sessile animals

• Main Author: Wang, Jining
• Other Authors: Yu Jing
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2023
• Subjects: Science::Biological sciences::Biochemistry; Science::Biological sciences::Biophysics
• Online Access: https://hdl.handle.net/10356/168705
• Institution: Nanyang Technological University

Through hundreds of millions of years evolution, many marine organisms have developed unique adhesion systems to establish robust adhesion on various types of wetted surfaces which serves as an essential skill for their survival. These underwater creatures are not only frustrating fouling species on man-made architectures but also fascinating biomimetic targets to the design and fabrication of water-resistant adhesives. With the aim to expand the knowledge in underwater adhesion and provide guideline to novel biomimetic designs, we explored the molecular mechanisms in the adhesion systems of two sessile animals, barnacles and mussels. The first study focuses on the adhesive barnacle cement protein 19k (cp19k) with the purpose of finding the interfacial adhesion mechanism of barnacle cement priming layer. Based on the block-copolymer like characteristic of cp19k and the presence of two types of segments, “simple” and “charged”, we prepared two adhesive peptides to investigate the rationale of cp19k sequence design in terms of adhesive function. Both adhesive peptides could bridge one mineral surface and one hydrophobic surface strongly at the same time but fail to bind two mineral surfaces together. Other surface characterization methods such as QCM-D and AFM demonstrated the strong binding capability of the adhesive peptides with individual mineral or hydrophobic substrate. Our results revealed the heterogeneous adhesion strategy adapted by adult barnacles where cp19k as a priming layer established strong interfacial binding with mineral substrates via hydrogen bonds and electrostatic interactions and further formed strong hydrophobic cohesive binding with the hydrophobic bulk cement. In mussel adhesion system, the catecholic post-translationally modified 3,4-dihydroxyphenyl-L-alanine (Dopa) residues play dominant roles in interfacial adhesive interactions, however, only if protected from oxidation damage. In the second study, we thoroughly investigated the molecular mechanism of the complex coacervation, a long-term antioxidation strategy utilized by mussel to keep the catechol moiety in reduced form. We adapted solution electrochemistry and NMR measurements to obtain remarkable insights about coacervates as solvent media for low molecular weight catechols. When catechols are added to dispersions of coacervated polyelectrolytes, there are two significant consequences. Firstly, catechols would preferentially partition up to 14-fold into the coacervate phase. Secondly, coacervates would stabilize catechol redox potentials by up to +45 mV relative to the equilibrium solution. The results suggest that the relationship between phase-separated coacervates and their client molecules is distinct from that existing in aqueous solution. This thesis demonstrates the molecular mechanisms of the interfacial adhesion establishment in barnacles and the catechol preservation strategy in mussels. These fundamental understanding in natural underwater adhesion systems could offer guidelines to the advancement of wet adhesives by addressing the limitation of Dopa-mediated adhesives. Our results could inspire the design of novel underwater adhesive not relying on post-translational modification or promote the efficiency of catechol-based adhesives by providing long-term stability.