Revisiting the adhesion mechanism of mussel-inspired chemistry.

Chao Zhang,Zhi-Kang Xu,Zuankai Wang,Li Xiang,Jiawen Zhang,Hongbo Zeng,Chang Liu

doi:10.1039/d1sc05512g

Abstract

Mussel-inspired chemistry has become an ideal platform to engineer a myriad of functional materials, but fully understanding the underlying adhesion mechanism is still missing. Particularly, one of the most pivotal questions is whether catechol still plays a dominant role in molecular-scale adhesion like that in mussel adhesive proteins. Herein, for the first time, we reveal an unexplored adhesion mechanism of mussel-inspired chemistry that is strongly dictated by 5,6-dihydroxyindole (DHI) moieties, amending the conventional viewpoint of catechol-dominated adhesion. We demonstrate that polydopamine (PDA) delivers an unprecedented adhesion of 71.62 mN m−1, which surpasses that of many mussel-inspired derivatives and is even 121-fold higher than that of polycatechol. Such a robust adhesion mainly stems from a high yield of DHI moieties through a delicate synergy of leading oxidation and subsidiary cyclization within self-polymerization, allowing for governing mussel-inspired adhesion by the substituent chemistry and self-polymerization manner. The adhesion mechanisms revealed in this work offer a useful paradigm for the exploitation of functional mussel-inspired materials.

Highlights

The results show that the adhesion of PDA is several times higher than that of catechol groups and their synergy with amine groups, demonstrating that DHI moieties play a dominant role in adhesion over the conventional catechol group
In situ characterization of adhesion strength To revisit the adhesion mechanism of mussel-inspired chemistry and investigate the impact of molecular architecture and polymerization manner, five kinds of mussel-inspired derivatives were selected as model objects, including catechol, dopamine (R1, R2, R3 = H), L-DOPA (R2 = COOH; R1, R3 = H), adrenaline (R1 = OH; R2 = H; R3 = CH3), and noradrenaline (R1 = OH; R2, R3 = H) (Fig. 1a), in which they possess similar ability to self-polymerize into catechol-based adhesive though their molecular architecture and polymerization rate vary
The surface forces apparatus (SFA) measurement results show that the adhesion of PDA is as high as 71.62 mN m-1, which is 121, 68, 18, and 5-fold higher than that of polycatechol, poly(L-DOPA), polyadrenaline and polynoradrenaline, respectively

Summary

Introduction

Marine mussels have orchestrated extraordinary principles for achieving robust wet adhesion by the elegant manipulation of the secreted adhesive proteins containing 3,4dihydroxy-L-phenylalanine (DOPA) groups.[1,2,3] Since this seminal work, mussel-inspired chemistry has evolved as a powerful platform for surface engineering in many fields as diverse as bioengineering,[4,5,6] energy storage and conversion,[7, 8] environmental remediation,[9] and wearable electronics.[10,11,12] Distinct from the conventional methods, mussel-inspired chemistry possesses a set of intriguing merits such as surfaceadaptive adhesion, ease of implementation, eco-friendly process, and versatile functions integration.[13,14,15,16] Up to date, exciting achievements have been made in the synthesis and application of mussel-inspired derivatives, including dopamine, levodopa (L-DOPA), norepinephrine, polyphenols, and catechol-based polymers.[13, 17,18,19,20] In striking contrast, the fundamental mechanism, especially responsible for wet adhesion in mussel-inspired chemistry, has been not well understood so far.d.Jiangsu Key Laboratory of Construction Materials, School of Materials Science and Engineering, Southeast University, Nanjing 211189, China.Several advanced force measurement techniques have been recently deployed to investigate the adhesion mechanism of mussel-inspired chemistry, which include singlemolecule atomic force microscope (SM-AFM),[21,22,23] colloidal probe AFM,[24] and surface forces apparatus (SFA).[2, 25,26,27] The measured results have manifested the key significance of catechol groups in forming multiple non-covalent and covalent interactions with various surfaces for contributing to the adhesion. By combining the results oDf OfIo: r1c0e.10m39e/aDs1uSCre0m55e12nGt with molecular-scale simulations, we attribute the strong adhesion of PDA to its high yield of DHI moities by virtue of the synergy effect of oxidation and intramolecular cyclization for forming sufficient DHI-enabled interactions (especially cation- interaction).

Results

Conclusion