Metal-containing polymer networks are widespread in biology, particularly for load-bearing exoskeletal biomaterials. Mytilus byssal cuticle is an especially interesting case containing moderate levels of Fe 3þ and cuticle protein-mussel foot protein-1 (mfp-1), which has a peculiar combination of high hardness and high extensibility. Mfp-1, containing 13 mol % of dopa (3, 4-dihydroxyphenylalanine) side-chains, is highly positively charged polyelectrolyte (pI ∼ 10) and didn't show any cohesive tendencies in previous surface forces apparatus (SFA) studies. Here, we show that Fe 3þ ions can mediate unusually strong interactions between the positively charged proteins. Using an SFA, Fe 3þ was observed to impart robust bridging (W ad ≈ 4.3 mJ∕m 2 ) between two noninteracting mfp-1 films in aqueous buffer approaching the ionic strength of seawater. The Fe 3þ bridging between the mfp-1-coated surfaces is fully reversible in water, increasing with contact time and iron concentration up to 10 μM; at 100 μM, Fe 3þ bridging adhesion is abolished. Bridging is apparently due to the formation of multivalent dopa-iron complexes. Similar Fe-mediated bridging (W ad ≈ 5.7 mJ∕m 2 ) by a smaller recombinant dopa-containing analogue indicates that bridging is largely independent of molecular weight and posttranslational modifications other than dopa. The results suggest that dopa-metal interactions may provide an energetic new paradigm for engineering strong, self-healing interactions between polymers under water.byssus | metal coordination | tris-catecholato-iron (III) complex M etallopolymers are increasingly viewed as a transformative platform for the next generation of materials. This platform is related in part to their capacity for multifunctionality, but also to their wide and adjustable range of electronic, photonic, and magnetic properties (1). The load-bearing properties of metallopolymers are equally important but have received less attention with few exceptions (2). This oversight needs to be rectified given how widespread metal-containing polymer networks are in biology, particularly for load-bearing exoskeletal biomaterials (3, 4). The byssal cuticle of mussels in the genus Mytilus is an especially interesting case study because of its peculiar combination of hardness (100-150 MPa) and extensibility (>70% strain) (5). Mytilus byssal cuticle contains moderate levels of Fe 3þ and a single protein-mussel foot protein-1 (mfp-1) (6). Mfp-1 has a mass of about 108 kDa in Mytilus edulis (7) and consists largely of tan-
The chemistry of mussel adhesion has commanded the focus of much recent research activity on wet adhesion. By comparison, the equally critical adhesive processing by marine organisms has been little examined. Using a mussel-inspired coacervate formed by mixing a recombinant mussel adhesive protein (fp-151-RGD) with hyaluronic acid (HA), we have examined the nanostructure, viscosity, friction, and interfacial energy of fluid-fluid phase-separated coacervates using the surface forces apparatus and microscopic techniques. At mixing ratios of fp-151-RGD:HA resulting in marginal coacervation, the coacervates showed shear-thickening viscosity and no structure by cryo-transmission electron microscopy (cryo-TEM). However, at the mixing ratio producing maximum coacervation, the coacervate showed shear-thinning viscosity and a transition to a bicontinuous phase by cryo-TEM. The shear-thinning viscosity, high friction coefficient (>1.2), and low interfacial energy (<1 mJ m−2) observed at the optimal mixing ratio for coacervation are promising delivery, spreading and adhesion properties for future wet adhesive and coating technologies.
Mussel foot proteins (mfps) have been investigated as a source of inspiration for the design of underwater coatings and adhesives. Recent analysis of various mfps by a surface forces apparatus (SFA) revealed that mfp-1 functions as a coating, whereas mfp-3 and mfp-5 resemble adhesive primers on mica surfaces. To further refine and elaborate the surface properties of mfps, the force-distance profiles of the interactions between thin mfp (i.e. mfp-1, mfp-3 or mfp-5) films and four different surface chemistries, namely mica, silicon dioxide, polymethylmethacrylate and polystyrene, were measured by an SFA. The results indicate that the adhesion was exquisitely dependent on the mfp tested, the substrate surface chemistry and the contact time. Such studies are essential for understanding the adhesive versatility of mfps and related/similar adhesion proteins, and for translating this versatility into a new generation of coatings and (including in vivo) adhesive materials.
The adhesive plaques of Mytilus byssus are investigated increasingly to determine the molecular requirements for wet adhesion. Mfp-2 is the most abundant protein in the plaques, but little is known about its function. Analysis of Mfp-2 films using the surface forces apparatus detected no interaction between films or between a film and bare mica; however, addition of Ca 2؉ and Fe 3؉ induced significant reversible bridging (work of adhesion W ad ≈ 0.3 mJ/m 2 to 2.2 mJ/m 2 ) between two films at 0.35 M salinity. The strongest observed Fe 3؉ -mediated bridging approaches the adhesion of oriented avidin-biotin complexes. Raman microscopy of plaque sections supports the co-localization of Mfp-2 and iron, which interact by forming bis-or tris-DOPA-iron complexes. Mfp-2 adhered strongly to Mfp-5, a DOPA-rich interfacial adhesive protein, but not to another interfacial protein, Mfp-3, which may in fact displace Mfp-2 from mica. In the presence of metal ions or Mfp-5, Mfp-2 adhesion was fully reversible. These results suggest that plaque cohesiveness depends on Mfp-2 complexation of metal ions, particularly Fe 3؉ and also by Mfp-2 interaction with Mfp-5 at the plaque-substratum interface.The mussel holdfast or byssus is emerging as an effective model system for studying the requirements for opportunistic underwater adhesion (1). The 3,4-dihydroxyphenylalanine (DOPA) 4 -rich mussel foot proteins (MFPs) of the adhesive footprint, namely Mfp-3 and Mfp-5, have been subjected to particular scrutiny (2-3) given the recent demonstration that DOPA is capable of mediating reversible adhesion to titania surfaces at forces of nearly 1 nanonewton/DOPA (4). Musselinspired catecholic polymers are engineered increasingly for moisture-resistant adhesive and coating applications (5-8).At least five other proteins known mostly as MFPs are present in the byssal plaque and contribute presumably to its adhesive performance: Mfp-1, Mfp-2, Mfp-4, Mfp-6, the prepepsinized collagens (9), and thread matrix protein ( Fig. 1) (10). Of these, only two have reasonably well established functions: Mfp-1 complexed to Fe 3ϩ provides a protective outer coating for the plaque and thread (11)(12), and the prepepsinized collagens are fiber-forming collagens that mediate the fusion of thread and plaque (13). Other proteins have been partially characterized and sequenced, but their role in byssal structure is largely speculative. Mfp-2 is particularly intriguing because it is the most abundant protein of byssal plaques comprising Ͼ25% of the plaque by weight (14). Mfp-2 has a mass of 45 kDa and consists of 11 tandem repeats of an EGF motif, each of which resembles a knot-like structure stabilized by three disulfide bonds (Fig. 2) (15-16). DOPA content is comparatively low at 3-5 mol % with an average of two residues per EGF repeat and three to four residues at the N-and C-terminal ends of Mfp-2. Surface binding studies of Mfp-2 using attenuated total reflectance Fourier transform infrared spectrometry showed the protein to be adsorbed rapidly to a variety of s...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.