Marine Bioinspired Underwater Contact Adhesion - ACS Publications

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Marine bio-inspired underwater contact adhesion Sean K. Clancy, Antonio Sodano, Dylan J Cunningham, Sharon Sherry Huang, Piotr J. Zalicki, Seunghan Shin, and B. Kollbe Ahn Biomacromolecules, Just Accepted Manuscript • DOI: 10.1021/acs.biomac.6b00300 • Publication Date (Web): 05 Apr 2016 Downloaded from http://pubs.acs.org on April 5, 2016

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Marine bio-inspired underwater contact adhesion

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Sean K. Clancy§†, Antonio Sodano §†, Dylan J. Cunningham§†, Sharon S. Huang§†, Piotr J.

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Zalicki§†, Seunghan Shin‡*, and B. Kollbe Ahn†*

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†

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USA

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‡

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Chungnam 31056, South Korea

Marine Science Institute, University of California Santa Barbara, Santa Barbara, CA 93106,

Green Materials and Process Group, Korea Institute of Industrial Technology, Cheonan,

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ABSTRACT: Marine mussels and barnacles are sessile biofouling organisms that adhere to a

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number of surfaces in underwater environments and maintain remarkably strong bonds. Previous

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synthetic approaches to mimic biological wet adhesive properties have focused mainly on the

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catechol moiety, present in mussel foot proteins (mfps), and especially rich in the interfacial

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mfps, e.g., mfp-3 and -5, found at the interface between the mussel plaque and substrate.

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Barnacles, however, do not use Dopa for their wet adhesion, but are instead rich in non-

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catecholic aromatic residues. Due to this anomaly, we were intrigued to study the initial contact

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adhesion properties of copolymerized acrylate films containing the key functionalities of

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barnacle cement proteins and interfacial mfps, e.g., aromatic (catecholic or non-catecholic),

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cationic, anionic, and/or non-polar residues. The initial wet contact adhesion of the copolymers

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was measured using a probe tack testing apparatus with a flat-punch contact geometry. The wet

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contact adhesion of an optimized, bio-inspired copolymer film was ~15.0 N/cm2 in deionized

ACS Paragon Plus Environment

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water and ~9.0 N/cm2 in artificial seawater, up to 150 times greater than commercial pressure-

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sensitive adhesive (PSA) tapes (~0.10 N/cm2). Furthermore, maximum wet contact adhesion was

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obtained at ~pH 7, suggesting viability for biomedical applications.

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INTRODUCTION

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Wet environments pose challenges for initial contact adhesion due to the presence of a

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superficial hydration layer.1 However, wet conditions do not appear to restrict the marine fouling

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of mussels and barnacles. Mussels and barnacles are major marine biofouling organisms that

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maintain adherence to hard surfaces in environments conventionally hostile to current adhesive

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technologies (Figure 1).2,3 Interfacial mussel foot proteins (mfps), e.g., mfp-3 and mfp-5 (Figure

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2a), are located at the plaque-substratum interface and contain ~20-30 mol% of 3,4-

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dihydroxyphenylalanine (Dopa), a key functional group in the adhesive mechanism of mussel

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plaques.4,5 Mussel-inspired Dopa (or catechol) functionalization has, therefore, been translated to

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synthetic systems with the intent to mimic the strong wet adhesive properties of mussels6,7,8 for

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numerous underwater applications.9,10 However, barnacle adhesive cement proteins, e.g.,

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Megabalanus rosa cement proteins (mrcps), contain non-catecholic aromatic functionalities such

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as tyrosine, tryptophan, and phenylalanine rather than Dopa.11 Mrcp-100k and mrcp-52k (Figure

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2b) appear plentifully in barnacle cement and are presupposed as cooperative agents of adhesive

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cement formation in wet environments.12

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Although the adhesive mechanisms of mussels and barnacles are not yet fully understood,

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instantaneous wet contact adhesion of these proteins is required for the sessile organisms to

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adhere to marine surfaces. Other interfacial interactions contributing to adhesion in these

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organisms, e.g., hydrophobic and electrostatic interactions, are less often translated to synthetic

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systems, as previous studies have often neglected to replicate the structural presence of non-


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Figure 1. Barnacles and mussels attach to a variety of surfaces in intertidal marine environments

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(Campus Point, UC Santa Barbara, Santa Barbara, CA).

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catechol moieties or otherwise integrate only a single electrostatic functionality.13 Nevertheless,

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recent studies incorporating hydrophobic and electrostatic interactions with catechol in

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polyampholytes14 and zwitterionic small molecules15 showed record high underwater adhesion

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energy values up to an order of magnitude greater than previously reported in natural,16

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recombinant,17 or fusion adhesive proteins.18

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Therefore, we sought to study the effects of catecholic and non-catecholic (benzyl) components

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and the contribution of the key functional analogs on initial contact adhesions under various

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conditions, e.g., dry, deionized water, and artificial seawater environments. As such, we

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combined structural motifs from these marine adhesive proteins into a series of bio-inspired UV-

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cured poly(acrylate) films. These synthetic copolymers retain the important functionalities of

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both mfps and mrcps, e.g., aromatic (Dopa, tyrosine, and tryptophan), cationic (lysine, arginine,

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and histidine), anionic (aspartic acid), and non-polar (glycine, leucine, alanine, and proline)

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residues. Initial contact adhesion of the copolymers was measured using a probe tack testing

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apparatus and compared in relation to the proportion of each functional group.


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Figure 2. Color-coded sample sequences of interfacial mfps (a) and mrcps (b), along with the

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key functional groups incorporated in their synthetic analogs.

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EXPERIMENTAL SECTION

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Materials and Methods

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Sample preparation. Benzyl acrylate (BA) purchased from Sigma-Aldrich (USA) and a silyl-

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protected catechol acrylate (CA) provided by Osaka Chemical (Japan) were employed as analogs

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of the benzyl and catechol moieties of natural marine adhesive proteins, respectively.

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Additionally, 2-ethylhexyl acrylate (EHA), 2-(dimethylamino)ethyl methacrylate (DMAEMA),

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and acrylic acid (AA) were purchased from Sigma-Aldrich to serve as analogs of non-polar,

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cationic, and anionic residues, respectively, of the natural proteins. The monomers were used as

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received and mixed in accordance with the molar ratios presented in Table 1 along with 2 wt.%

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of a radical photoinitator (Irgacure 819, Bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide)

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(BASF, USA) dissolved in toluene. The role of the organic solvent was to ensure homogeneous

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distribution of the solid photoinitiator in the formulation. The comonomer mixtures were then


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vortexed to further ensure homogenization. Ratios of AA and DMAEMA were varied in the

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samples at 1:2 and 2:1 ratios. The catechol-containing copolymer films were

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Figure 3. An approach to determine the initial contact adhesion of the UV-cured copolymer

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films under ambient dry and wet testing conditions.

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prepared from a silyl-protected catechol acrylate due to the spontaneous autoxidation of the

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catechol functional group. The silyl-protecting groups were later cleaved in an aqueous pH 1-2

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HCl solution at room temperature to produce a catechol-functionalized acrylate film, based on a

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previously described method.14,19 After immersion for 20 minutes, the samples were removed

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from the acidic solution and dried via air stream.


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Fusion UV System. UV radical polymerization was carried out with the Fusion UV system

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(provided by Heraeus Noblelight America, USA) which consisted of a 300 watt/inch (2.54 cm) H

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lamp and LC6B benchtop conveyor belt. The lamp’s distance from the conveyor belt was 10 cm.

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This UV system recorded UVA Band (320-390 nm) and 615–660 mJ/cm2 of UV radiation dose

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Table 1. Molar percentages of acrylate monomers in the prepared samples. Composition Aromatic Non-polar Ionica Sample 1 0% 50% 50% Sample 2 0% 60% 40% Sample 3 0% 70% 30% Sample 4 0% 80% 20% Sample 5 0% 90% 10% Sample 6 0% 100% 0% Sample 7 10% 50% 40% Sample 8 10% 60% 30% Sample 9 10% 70% 20% Sample 10 10% 10% 80% Sample 11 10% 90% 0% Sample 12 20% 50% 30% Sample 13 20% 60% 20% Sample 14 20% 70% 10% Sample 15 20% 80% 0% b 30% 50% 20% Sample 16 Sample 17 30% 60% 10% Sample 18 30% 70% 0% Sample 19c 40% 50% 10% Sample 20 40% 60% 0% Sample 21d 50% 50% 0% a Ionic ratios of either 1:2 AA:DMAEMA or 2:1 AA:DMAEMA. b-d Samples selected for further analysis.

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at a belt speed of 20 feet/min at focus, as measured by an EIT Power Puck 1 Radiometer

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(Sterling, USA). Neat free radical UV-initiated polymerization was carried out at room

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temperature in air. The dose of UV radiation and the exposure time were controlled by adjusting

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the belt speed and the number of scans.14


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Incubation. Incubation (prepolymerization) of the comonomer mixtures was required to form a

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uniformly thick adhesive film. Each mixture was scanned in vitro at 20 feet/min to produce a

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more viscous solution. Samples in dram vials were fixed to a stainless steel plate and put through

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the UV light system to create a polymer precursor with desired viscosity. The number average

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molecular weight (Mn) of the incubated viscous mixture was ~3000-5000 Da (Table 2), as

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measured by Gel Permeation Chromatography (GPC) (Figure S1).

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Neat UV free radical polymerization. After the incubation process, roughly 300 µL of each

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sample was placed on individual sheets of 50 µm thick Mylar® PET backing (CS Hyde

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Company, USA). A #40 EC-100 wire wound “Mayer” rod (Cheminstruments, USA) was then

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slowly passed over the sample to create a 100 µm thick layer. The PET sheets were then passed

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through the previously described UV system at a belt speed of 10 feet/min, which corresponds to

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a UV dose of 1230-1320 mJ/cm2 per pass. Optimum cohesion and adhesion of the copolymerized

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films was obtained after three passes through the system.

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Dry Probe Tack Test. Once each adhesive film was polymerized and allowed to cool for 5

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minutes, 0.5 cm x 1 cm strips of the copolymer films on PET backing were placed directly on the

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PT-1000 Polyken Probe Tack (PT) Machine (Cheminstruments) stage opening (Figure 3) and

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fixed to the stage with lab tape. Each strip was tested once in ambient dry conditions with a flat-

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ended cylindrical steel probe tip (diameter = 5 mm; contact area ~0.20 cm2) with an approach

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and separation speed of 61 cm/min, contact time (tc) of 5 seconds, and an applied load of 768.9

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mN ± 7.9 mN. All parameters were held constant throughout testing. A representation of the

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typical probe tack test curve is included in the Supporting Information (Figure S2). The area

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underneath the probe tack curves was used to determine the work of detachment (Wad), as

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outlined in a previous study.20


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Wet Probe Tack Test. To investigate the role of the differing aromatic functional groups,

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benzyl group-containing copolymer samples with the highest measured tack strengths (Samples

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16, 19, and 21) (Figure 4) were made again with direct substitution of BA for CA. Both the

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benzyl- and catechol-containing copolymers were then tested under wet conditions (Figure 5).

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75 µL of deionized (DI) water or artificial seawater was placed on the probe tip surface prior to

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sample contact with the probe tip, and probe tack strength was then measured. Additional PT

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testing was then completed under a range of various pH conditions (Figure 7), utilizing an

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identical set up to the previous wet PT tests. Solutions of pH 3, 7, 9, and 11 were used to test the

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adhesives. DI water was used for the pH 7 environment, acetic acid was used to decrease pH of

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DI water to 3, and sodium carbonate was used to increase pH of DI water to 9 and 11.

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Probe Tack Test for Commercial Tapes. In order to establish the relative probe tack strength

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of our selected samples, additional PT tests were performed with two commercially available

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PSAs, Fisherbrand™ Colored Label Tape (Fisher Sci, USA) and Scotch® Packaging Tape (3M,

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USA) under both dry and wet conditions. These adhesives were adhered directly onto the PT

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stage, with stage placement, tc, approach speed, applied load, and separation speed kept

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consistent with the aforementioned parameters.

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Statistical analysis. The Mann-Whitney U test was used to compare the median probe tack

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strengths of different treatments. A statistically significant difference was determined when p-

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values were less than 0.05.

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RESULTS AND DISCUSSION

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A total of forty-one copolymer samples were prepared with differing ratios of anionic, cationic,

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non-polar, and aromatic functional groups (Table 1). Samples containing greater proportions of


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aromatic residues exhibited increasing probe tack strength. Samples 16, 19, and 21, containing

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30-50% aromatic, 0-20% charged, and 50% non-polar groups, showed greater dry probe tack

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strength, regardless of charged acrylate composition (Figure 4), and were selected for further

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studies.

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Despite the absence of crosslinking agents in the formulations, the polymers exhibited sharp

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increases in viscosity and were insoluble in organic solvents after polymerization. The reduced

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mobility of free radicals along the polymer backbone resulted in more proximal free radical side

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branching as well as a decrease in the termination rate. As a result, these side branches generated

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interchain crosslinkages, leading to the formation of a polymer network in a process known as

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the Trommsdorff-Norrish effect.21,22

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Due to this effect, GPC results (Table 2) were obtained from linear, non-crosslinked portions of

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the polymers, as insoluble, crosslinked components must be filtrated prior to analysis. For this

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reason, GPC results obtained from samples after incubation did not differ from the results

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obtained after polymerization. The presence of this gel effect also prevented other forms of

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analysis, e.g., H-NMR, after polymerization.

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Neat UV polymerization generates broad molecular weight distributions that enable deformation

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of acrylate polymers on rough surfaces so as to improve tack properties.23 Acrylic PSAs are

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produced without purification or washing as to maintain this broad range. PSAs require not only

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broad molecular weight dispersity21 but also lower Tg values in order to adequately wet the

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substrate and create tackiness at bonding sites. Our samples exhibited high polydispersity and Tg

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ranging from -27.5 °C to -9.1 °C (Table 2 and Figures S10-12).

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Table 2. Molecular weights, polydispersity, and glass transition temperatures of selected

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incubated mixtures.


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Sample 16 Sample 19 Sample 21

Mn (g/mol) 2730 5064 3749

Mw(g/mol) 12787 66424 82279

Đm (Mw/Mn) 4.7 13.1 22.0

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Tg(°°C) -19.4 -27.5 -9.1

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Attenuated Total Reflection Infrared Spectroscopy (ATR-IR) was used to monitor UV radical

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polymerization as a function of increasing UV dose in proportion to the number of UV scans.

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ATR-IR analysis (Figures S3-S5) showed a decrease in the intensity of peaks attributed to C=C

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acrylate double bonds, found at 810 cm-1 (Figure S6) and 1410 cm-1, after prolonged exposure to

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UV radiation, suggesting successful UV-initiated radical polymerization. Gas Chromatography

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(GC) was also used to monitor monomer consumption and polymerization. GC (Figures S6-S8)

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revealed that there

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Figure 4. An initial comparison of dry probe tack strengths from samples with differing ionic

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charge ratios. Error bars indicate standard deviation, n=5.

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were only trace amounts of unreacted monomers, and no residual solvent after UV

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polymerization, suggesting polymer compositions nearly equal to the feeding monomer ratio.

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Copolymer samples with a 2:1 ratio of anionic to cationic groups afforded greater probe tack

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strength than cationic-dominant alternatives in ambient dry conditions (Figure 5). Samples


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prepared with a 2:1 AA:DMAEMA ratio displayed probe tack strengths of 19.4 ± 5.5 N/cm2

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(Sample 16) and 23.8 ± 3.1 N/cm2 (Sample 19), greater than the results obtained from

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formulations prepared with a 1:2 AA:DMAEMA ratio, 15.2 ± 1.7 N/cm2 (Sample 16) and 22.3 ±

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2.0 N/cm2 (Sample 19) (Figure 5). The work of detachment values, Wad, were 18.3 ± 2.2 mJ/cm2

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for Sample 16 and 24.3 ± 2.9 mJ/cm2 for Sample 19 prepared with 2:1 AA:DMAEMA, whereas

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the values obtained from samples prepared with 1:2 AA:DMAEMA were 13.3 ± 1.8 mJ/cm2 for

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Sample 16 and 23.8 ± 3.7 mJ/cm2 for Sample 19 . These results are consistent with the

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composition of most commercial PSAs made for dry adhesion, which contain ~10% anionic

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residues. Conversely, mfp-5, the most wet-adhesive natural protein, contains a 1:2 ratio of

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anionic to cationic residues. Copolymer samples with 1:2 ratio of anionic to cationic residues

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showed greater wet probe tack strengths than anionic-dominant films in artificial seawater

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environments. Interestingly, Sample 21, lacking ionic functionalities, exhibited even greater wet

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probe tack adhesion values in DI water (15.2 ± 1.4 N/cm2) and seawater (8.7 ± 1.0 N/cm2).

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Sample 21 also exhibited comparatively large work of detachment values in DI water (Wad =

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15.3 ± 1.9 mJ/cm2) and seawater (Wad = 7.5 ± 0.3 mJ/cm2). Samples 16 and 19 with cationic-

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dominant compositions and Sample 21 were consequently selected for further analysis due to

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their appreciable probe tack strengths in artificial seawater.

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Figure 5. A comparison of probe tack strengths of selected copolymer films under ambient dry

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and wet conditions. Error bars indicate standard deviation, n=5.

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In order to investigate the effects of catechol moieties on initial contact adhesion, the samples

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were then prepared with catechol acrylate (CA) in place of benzyl acrylate (BA). The probe tack

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test results from the catechol-functionalized copolymers were then compared to benzyl-

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functionalized copolymers (Figure 6). The median probe tack strengths of the BA and CA

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samples in DI water were 13.6 N/cm2 and 10.5 N/cm2, respectively; the distribution of the two

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groups was not found to differ significantly (Mann–Whitney U = 42, n1 =12; n2 = 11, P > 0.05,

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two-tailed). The median probe tack strengths of the BA and CA samples in artificial seawater

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were 5.5 N/cm2 and 4.3 N/cm2, respectively; the distribution of the two groups did not differ

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significantly (Mann–Whitney U = 91, n1 = 14; n2 = 9, P > 0.05, two-tailed). With the exception

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of the dry probe tack strength of Sample 21 (34.3 ± 3.2 N/cm2) and its work of detachment (Wad

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= 29.5 ± 3.7 mJ/cm2), the probe tack strengths of the benzyl-functionalized samples were

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comparable to the catechol-functionalized samples across all other testing conditions. These

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results suggest that the benzyl-functionalization, though comparatively inexpensive, might offer

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similar wet adhesion performance to catechol alternatives.

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Figure 6. A comparison of probe tack strengths of benzyl-functionalized copolymers, catechol-

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functionalized copolymers, and commercial PSAs under ambient dry and wet conditions. Error

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bars indicate standard deviation, n=3-15.

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Fisherbrand™ Colored Label Tape and 3M™ Scotch Packaging Tape were selected as

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commercial PSA controls for wet contact adhesion because they exhibited a comparable range of

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dry probe tack strengths (14.2 – 21.1 N/cm2) to our bio-inspired benzyl films (12.3 – 24.3 N/cm2)

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(Figure 6). However, when subjected to ambient wet conditions, commercial adhesives were

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found to have tack strength values (0.1 – 3.2 N/cm2) and work of detachment values (Wad = 0.2 –

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2.6 mJ/cm2), up to 150 times smaller than our benzyl-functionalized Sample 21 (15.2 N/cm2, Wad

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= 15.0 mJ/cm2). The median probe tack strengths of the BA samples in DI water was 13.6

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N/cm2, while the median values for both Scotch Packing Tape and Fisher Lab Tape was ~0.5

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N/cm2. The difference in probe tack strengths was determined to be statistically significant

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(Mann–Whitney U = 0, n1 = 15; n2 = 11, P < 0.05, one-tailed). Additionally, while the benzene

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functionalized samples were seen to have probe tack strengths approaching 9.0 N/cm2 in ambient

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seawater conditions, the commercial alternatives produced near-zero probe tack values.

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The samples were also tested across a range of different pH conditions (Figure 7). While the

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samples presented substantial wet probe tack strengths at neutral pH (12.9 ± 0.94, 8.3 ± 1.0

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N/cm2 and 15.2 ± 1.4 N/cm2 from Samples 16, 19, and 21, respectively), the initial contact

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adhesion values were negligible at pH 3 and pH 11. Benzene functionalization might therefore

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be suitable for biomedical applications near the physiologically relevant pH ~7.


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Figure 7. A comparison of probe tack values of benzyl acrylate copolymer samples in varying

3

pH conditions. Error bars indicate standard deviation, n=5.

4 5

CONCLUSION

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In this study, we prepared copolymer films functionalized with aromatic, non-polar, and/or ionic

7

moieties as analogs of the residues found in mfps and mrcps, and investigated their contact

8

adhesion strengths in relation to the proportion of each residue. The enhanced probe tack

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strength of the marine bio-inspired adhesive films over current commercial pressure-sensitive

10

adhesives demonstrates the viability of aromatic functionalization for conveniently engineered

11

adhesive films with greater wet contact adhesion. Furthermore, benzyl-functionalized copolymer

12

films exhibited similar performance to catechol-functionalized copolymer films without concerns

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about the inherent oxidative instability of catechol residue.

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AUTHOR INFORMATION

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Corresponding Authors

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*Email: [email protected]


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Author Contributions

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BKA conceived and designed the research. BKA and SKC wrote the manuscript. §These authors

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equally contributed to this work.

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Notes

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The authors declare no competing financial interests

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Supporting information

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Gel Permeation Chromatography; Probe Tack Test curve; Gas Chromatography; Attenuated

9

Total Reflection Infrared spectra; Differential Scanning Calorimetry. This material is available at

10

free of charge via the Internet at http://pubs.acs.org.

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ACKNOWLEDGMENTS

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The authors gratefully acknowledge support from the Office of Naval Research N000141310867

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and the Korea Institute of Industrial Technology. The authors also wish to thank Claus D.

14

Eisenbach (Institute for Polymer Chemistry - University of Stuttgart) for his comments during

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the revision of this manuscript.

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ABBREVIATIONS

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AA, acrylic acid; ATR-IR, Attenuated Total Reflection Infrared Spectroscopy; BA, benzyl

18

acrylate; CA, catechol acrylate, DI, deionized water; Đm, mass dispersity; DMAEMA, 2-

19

(dimethylamino)ethyl methacrylate; Dopa, 3,4-dihydroxyphenylalanine; DSC, Differential

20

Scanning Calorimetry; EHA, 2-ethylhexyl acrylate; GC, Gas Chromatography; GPC, Gel

21

Permeation Chromatography; mfp, mussel foot protein; Mn, number average molecular weight;


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mrcp, Megabalanus rosa cement protein; Mw, mass average molecular weight ; PET, polyester

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film; PSA, pressure-sensitive adhesive; PT, Probe Tack; tc, contact time; Tg, glass transition

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temperature; UV, ultraviolet; Wad, work of detachment.

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REFERENCES

6

1. Akdogan, Y.; Wei, W.; Huang, K.-Y.; Kageyama, Y.; Danner, E. W.; Miller, D. R.; Martinez

7

Rodriguez, N. R.; Waite, J. H.; Han, S., Intrinsic Surface-Drying Properties of Bioadhesive

8

Proteins. Angewandte Chemie International Edition 2014, 53, (42), 11253-11256.

9

2. Stewart, R.J., Protein-based underwater adhesives and the prospects for their biotechnological

10

production. Appl Microbiol Biotechnol 2011, 89, (1), 27-33.

11

3. Stewart, R. J., Weaver, J. C., Morse, D. E. and Waite, J. H., The tube cement of

12

Phragmatopoma californica: a solid foam. J. Exp. Biol 2004, 207, 4727-4734.

13

4. Filpula, D. R.; Lee, S. M.; Link, R. P.; Strausberg, S. L.; Strausberg, R. L., Structural and

14

functional repetition in a marine mussel adhesive protein. Biotechnology Progress 1990, 6, (3),

15

171-177.

16

5. Waite, J. H., Adhesion à la Moule. Integrative and Comparative Biology 2002, 42, (6), 1172-

17

1180.

18

6. Lee, H.; Dellatore, S. M.; Miller, W. M.; Messersmith, P. B., Mussel-inspired surface

19

chemistry for multifunctional coatings. Science 2007, 318, (5849), 426-30.


16

Page 17 of 20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Biomacromolecules

1

7. Chung, H.; Grubbs, R. H., Rapidly Cross-Linkable DOPA Containing Terpolymer Adhesives

2

and PEG-Based Cross-Linkers for Biomedical Applications. Macromolecules 2012, 45, (24),

3

9666-9673.

4

8. Zhou, J.; Defante, A. P.; Lin, F.; Xu, Y.; Yu, J.; Gao, Y.; Childers, E.; Dhinojwala, A.;

5

Becker, M. L., Adhesion Properties of Catechol-Based Biodegradable Amino Acid-Based

6

Poly(ester urea) Copolymers Inspired from Mussel Proteins. Biomacromolecules 2015, 16, (1),

7

266-274.

8

9. Lee, S.-B.; González-Cabezas, C.; Kim, K.-M.; Kim, K.-N.; Kuroda, K., Catechol-

9

Functionalized Synthetic Polymer as a Dental Adhesive to Contaminated Dentin Surface for a

10

Composite Restoration. Biomacromolecules 2015, 16, (8), 2265-2275.

11

10. Li, H.; Chen, S.; Chen, J.; Chang, J.; Xu, M.; Sun, Y.; Wu, C., Mussel-Inspired Artificial

12

Grafts for Functional Ligament Reconstruction. ACS Applied Materials & Interfaces 2015, 7,

13

(27), 14708-14719.

14

11. Urushida, Y.; Nakano, M.; Matsuda, S.; Inoue, N.; Kanai, S.; Kitamura, N.; Nishino, T.;

15

Kamino, K., Identification and functional characterization of a novel barnacle cement protein.

16

FEBS J 2007, 274, (16), 4336-46.

17

12. Kamino, K.; Inoue, K.; Maruyama, T.; Takamatsu, N.; Harayama, S.; Shizuri, Y., Barnacle

18

cement proteins. Importance of disulfide bonds in their insolubility. J Biol Chem 2000, 275, (35),

19

27360-5.

20

13. White, J. D.; Wilker, J. J., Underwater Bonding with Charged Polymer Mimics of Marine

21

Mussel Adhesive Proteins. Macromolecules 2011, 44, (13), 5085-5088.


17

Biomacromolecules

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 20

1

14. Seo, S.; Das, S.; Zalicki, P. J.; Mirshafian, R.; Eisenbach, C. D.; Israelachvili, J. N.; Waite, J.

2

H.; Ahn, B. K., Microphase Behavior and Enhanced Wet-Cohesion of Synthetic

3

Copolyampholytes Inspired by a Mussel Foot Protein. J Am Chem Soc 2015, 137, (29), 9214-7.

4

15. Ahn, B. K.; Das, S.; Linstadt, R.; Kaufman, Y.; Martinez-Rodriguez, N. R.; Mirshafian, R.;

5

Kesselman, E.; Talmon, Y.; Lipshutz, B. H.; Israelachvili, J. N.; Waite, J. H., High-performance

6

mussel-inspired adhesives of reduced complexity. Nat Commun 2015, 6.

7

16. Danner, E. W.; Kan, Y.; Hammer, M. U.; Israelachvili, J. N.; Waite, J. H., Adhesion of

8

Mussel Foot Protein Mefp-5 to Mica: An Underwater Superglue. Biochemistry 2012, 51, (33),

9

6511-6518.

10

17. Zeng, H.; Hwang, D. S.; Israelachvili, J. N.; Waite, J. H., Strong reversible Fe3+-mediated

11

bridging between dopa-containing protein films in water. Proceedings of the National Academy

12

of Sciences 2010, 107, (29), 12850-12853.

13

18. Zhong, C.; Gurry, T.; Cheng, A. A.; Downey, J.; Deng, Z.; Stultz, C. M.; Lu, T. K., Strong

14

underwater

15

Nanotechnol 2014, 9, (10), 858-66.

16

19. Ahn, B. K.; Lee, D. W.; Israelachvili, J. N.; Waite, J. H., Surface-initiated self-healing of

17

polymers in aqueous media. Nat Mater 2014, 13, (9), 867-72.

18

20. Zosel, A., Adhesion and tack of polymers: Influence of mechanical properties and surface

19

tensions, Colloid & Polymer Sci 1985, 263, 541-553.

20

21. Fengjun, H.; Mengping, Q., Synthesis of self-crosslinking sodium polyacrylate hydrogel and

21

water-absorbing mechanism, J Mater Sci 2001, 36, 731 – 738.

adhesives

made

by

self-assembling

multi-protein

nanofibres. Nat


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Biomacromolecules

1

22. Phinyocheep, P.; Duangthong S. Ultraviolet-Curable Liquid Natural Rubber, J Appl Polym

2

Sci 2000, 78, 8, 1478–1485.

3

23. Silva, L. F. M. da; Öchsner Andreas; Adams, R. D. Handbook Of Adhesion Technology;

4

Springer: Heidelberg, 2011.

5 6 7 8 9 10 11 12 13 14 15 16 17


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Biomacromolecules

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Marine Bioinspired Underwater Contact Adhesion - ACS Publications

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