a) The adhesive proteins of the sandcastle worm are secreted from two types of granules (homogeneous and heterogeneous granules) that both contain catechol oxidase. Besides a main compartment, the heterogeneous granules also contain subgranules. Redrawn from ref. [21]. b) Complex coacervates are formed when oppositely charged polyelectrolytes complex and release their counterions. Two phases coexist; a concentrated coacervate phase (left) and a dilute phase (right). Reproduced with permission. [22] Copyright 2015, American Chemical Society. c) The different sandcastle-worm proteins were imaged by fluorescence microscopy after immunological labeling. The cationic proteins (Pc2, Pc4, and Pc5) were labeled green, and Pc3 was labeled red. Hardly any overlap (yellow) of the cationic and anionic proteins was visible. I) Negative control (without any labeling), II) Pc2 and Pc3, III) Pc4 and Pc3, and IV) Pc5 and Pc3 were labeled. Scale bars are 20 µm. Reproduced with permission. [23] Copyright 2012, The Company of Biologists Ltd.

Contexts in source publication

Context 1

... pores are close together, and it is suggested that each pore secretes a particular granule, i.e., a homogeneous or hetero geneous granule. [14] After granule rupture, the fluid- like contents fuse together into a single heterogeneous material without extensive mixing of the anionic and cationic pro- teins ( Figure 2c). [23] Because it is not clear whether specific proteins are solely located at the adhesive interface, [4] it is also not clear which specific interactions are responsible for adhesion. ...

Context 2

... color change occurs over a time span of several hours to days and is caused by the oxidation of DOPA. The enzyme catechol oxidase is enclosed in both adhesive granules ( Figure 2a) and oxidizes DOPA into DOPA-quinone (Figure 3), subsequently leading to the forma- tion of covalent bonds that contribute to the cohesion of the adhesive. [21,31] Adv. ...

Context 3

... strength of electrostatic interactions can be controlled by varying the ionic strength or pH and can thus be used to tune the mechanical properties. In this section, materials based on electrostatic interactions will be discussed, including (complex) coacervation ( Figure 2b) and ion-based crosslinking, of either recombinant proteins or synthetic materials. We will also high- light work where (complex) coacervation is used as a delivery tool for underwater adhesives. ...

Context 4

... strengths of 1.11 MPa to aluminum were measured after incubation with tyrosinase for 4 h at 37 °C ( Table 2). Since complexation with a polyanion was shown to further improve adhesion of mussel foot proteins, [96] a complex coacervate (Figure 2b) was formed by mixing cationic mfp-5 with hyaluronic acid, an anionic poly- electrolyte commonly present in the human body. [6,96,97] After complexation, the shear strength increased to 1.73 MPa and could compete with values previously reported for recombinant mimics of mussel adhesive proteins that were also complexed into coacervates. ...

Context 5

... it is also possible to "melt" the structure (denaturing), multiple research groups have adopted this fea- ture for designing reversible hydrogen-bonded supramolecular adhesives. As a result of its ability to form three hydrogen bonds (Figure 12a), the CG pair is the strongest of the two (K assoc ≈ 10 5 m −1 for CG in chloroform, while only 10 2 m −1 for AT). [129] However, most nucleobase-containing adhesives were based on the AT pair, for the simple reason that dimerization of G can significantly affect the adhesive performance (K dim = 10 4 m −1 for GG). ...

Context 6

... the late 90s, Meijer and co-workers developed the UPy motif, a functional group capable of forming H-bonds similar to the nucleobases discussed in the previous paragraph. In contrast to nucleobase chemistry, complementary pairing is not required for UPy; it can selectively bind to another UPy moiety via four instead of only two (AT) or three (GC) hydrogen bonds (Figure 12b). UPy was demonstrated to be an effective agent for the preparation of viscosity enhancers, linear supramole- cular polymers and reversible networks, when incorporated in small molecules, telechelic poly(dimethylsiloxane) (PDMS) oli- gomers and trifunctional star-shaped polymers, respectively. ...

Context 7

... et al. demonstrated the urea group to be a very ver- satile group for the development of supramolecular poly- mers as well (Figure 12c). [138] A fully biobased material was prepared by combining fatty acids with diethylene triamine that were subsequently treated with urea, resulting in an oligomeric mixture with multiple complementary hydrogen bonding groups, including diamido tetraethyl triurea and di(amino ethyl) urea groups. ...

Context 8

... et al. fabricated hydrogels from a mixture of linear guest copolymers and CB [8], a host that can accommodate two guests simultaneously. [167] A cooperative, ter- nary complex with large association constant (K ≈ 10 14 m −2 ) was formed by inclusion of naphthyl and methyl viologen polymer side groups (Figure 20a). A color change indicated successful charge-transfer complex formation, while no gel was formed when CB [8] was omitted, or when CB [8] was exchanged for CB [7] (smaller cavity) (Figure 20b). ...

Context 9

... A cooperative, ter- nary complex with large association constant (K ≈ 10 14 m −2 ) was formed by inclusion of naphthyl and methyl viologen polymer side groups (Figure 20a). A color change indicated successful charge-transfer complex formation, while no gel was formed when CB [8] was omitted, or when CB [8] was exchanged for CB [7] (smaller cavity) (Figure 20b). The gels were found to be multiresponsive; reduction of methyl viologen or addition of a competitive guest, such as 2,6-dihydroxynaphthalene or an aromatic solvent, all disrupted the supramolecular network. ...

Context 10

... presence of water is, however, required in host-guest chemistry, since expulsion of water from the cavity is the main driving force. In this work, silicon wafers were chemically modified with CB [7] and aminomethylferro- cene (Figure 20c). The host-guest connection could withstand a 2 kg weight in water using only a 1 cm 2 contact area, while the strength further increased to 4 kg cm −2 after air drying. ...

Context 11

... As a result of the different dissociation rate constants, the mechanical properties of the gels could be adjusted by varying the metal ion (i.e., slow or fast crosslinks). Binary mixtures of Cu 2+ , Ni 2+ , and/or Zn 2+ , on the other hand, enabled design of new hydrogels with any desired property, without having to substitute the polymer (Figure 21a). [176] Inclu- sion of such structural hierarchy was a universal approach, as it was applied successfully in two other hydrogel systems: (1) one ...

Context 12

... Mater. 2018, 1704640 Figure 21. Structural hierarchy was used as a universal tool to modify the mechanical properties of metal-coordinated poly(ethylene glycol) hydrogels, without the need to synthesize a new polymer. ...

Context 13

... with permis- sion. [176] Copyright 2015, Macmillan Publishers Ltd. metal ion and two ligands (DOPA and histidine) (Figure 21b), and (2) through a combination of covalent bonding and pH- responsive coordination bonding (Figure 21c). This route ena- bled tuning of the mechanical properties of a bulk material as well, by combining an imidazole-containing butylacrylate copolymer and a mixture of two different metals. ...

Context 14

... with permis- sion. [176] Copyright 2015, Macmillan Publishers Ltd. metal ion and two ligands (DOPA and histidine) (Figure 21b), and (2) through a combination of covalent bonding and pH- responsive coordination bonding (Figure 21c). This route ena- bled tuning of the mechanical properties of a bulk material as well, by combining an imidazole-containing butylacrylate copolymer and a mixture of two different metals. ...

Context 15

... (2,6-bis(1′-methylbenzimidazolyl)-pyridine) ligands for coordination bonding were studied by Heinzmann and col- leagues. [183] A low-molecular-weight telechelic poly(ethylene- co-butylene) copolymer (3.1 kg mol −1 ) was end-functionalized with these groups and blended with Zn 2+ ions (Figure 22a). The as-formed metallo-supramolecular polymer demonstrated excellent adhesion between quartz slides (Figure 22b). ...

Context 16

... A low-molecular-weight telechelic poly(ethylene- co-butylene) copolymer (3.1 kg mol −1 ) was end-functionalized with these groups and blended with Zn 2+ ions (Figure 22a). The as-formed metallo-supramolecular polymer demonstrated excellent adhesion between quartz slides (Figure 22b). Lap joint experiments displayed shear strengths exceeding 2.5 MPa, and the joints could be debonded on demand by exposure to heat or UV irradiation. ...

Context 17

... contrast to UPy-functionalized poly(ethylene- co-butylene), inclusion of a UV sensitizer was not needed, and adhesion was found to be twice as strong. Furthermore, bonding was reversible and full recovery of the initial strength was obtained after fracture (Figure 22c). ...

Context 18

... having studied the influence of the ionic strength, pH, redox chemistry, metal complexation and tem- perature, cation-π complexation between aromatic and quater- nized amino acids was thought to be the best explanation for the substantial cohesion. [198] Inspired by mussel foot protein mfp-5, Gebbie et al. designed and compared wet adhesion of aromatic-rich pro- teins (composed of 36 amino acids) by systematic variation of the aromatic residue (Phe, Tyr, or DOPA) (Figure 23a). [51] Cohesive failure was observed in all cases (Figure 23b), meaning that the measured strength was proportional to the protein interaction. ...

Context 19

... Inspired by mussel foot protein mfp-5, Gebbie et al. designed and compared wet adhesion of aromatic-rich pro- teins (composed of 36 amino acids) by systematic variation of the aromatic residue (Phe, Tyr, or DOPA) (Figure 23a). [51] Cohesive failure was observed in all cases (Figure 23b), meaning that the measured strength was proportional to the protein interaction. Inclusion of an aromatic peptide film always resulted in significantly enhanced adhesion compared to the neat mica substrates or nonaromatic Leu control experi- ment. ...

Context 20

... instance, a layer of poly(methyl methacrylate) could be peeled off manually, while poly(trityl methacrylate) displayed very strong adhesion (1.02 MPa). Moreover, control experiments in which aliphatic polymers were directly compared to their aromatic analogs Figure 23. a) Sequence and structure of mfp-5-inspired peptides. ...

Context 21

... thermore, an external stimulus can trigger debonding, similar to supramolecular adhesives. [199] Inspired by the disulfide linkages present in proteins, Michal et al. prepared a synthetic adhesive based on semic- rystalline, thiol-capped telechelic thioether oligomers and a tetrathiol crosslinker (Figure 24a). [186] Heating of the material first caused melting of the crystalline domains (70 °C), while an additional, but significant drop of the viscosity was observed above 150 °C due to dissociation of the disulfide bridges. ...

Context 22

... Heating of the material first caused melting of the crystalline domains (70 °C), while an additional, but significant drop of the viscosity was observed above 150 °C due to dissociation of the disulfide bridges. The same result was obtained by irradiation of the sample with UV light, and thus enabled rapid wetting of surfaces (Figure 24b). When applied above the melting point, shear stresses required to break glass lap joints were as high as several MPa, whereas application of the adhesive above the second phase transition led to doubled values of the shear strength, up to 5.3 MPa (Figure 24c). ...

Context 23

... same result was obtained by irradiation of the sample with UV light, and thus enabled rapid wetting of surfaces (Figure 24b). When applied above the melting point, shear stresses required to break glass lap joints were as high as several MPa, whereas application of the adhesive above the second phase transition led to doubled values of the shear strength, up to 5.3 MPa (Figure 24c). In addition, similar adhesion to a steel sub- strate was observed and the glue could be used multiple times without any loss in adhesive performance for at least three cycles. ...

Context 24

... of using phenylborate esters, Deng et al. prepared both dynamically crosslinked PEG-hydrogels and PEG-organo- gels based on acylhydrazone bonds (Figure 25a). [188] Fast adhesion between the dynamic organogel and hydrogel was observed, and with an ultimate strength of 64 kPa, this is one of the strongest examples of adhesion between different gels discussed in this review. ...

Context 25

... the choice of the organic medium turned out be equally important, as adhesion was slowed down sig- nificantly (tens of hours vs minutes) when using nitroethane, DMF or DMSO instead of anisole or chloroform. A turbid emulsion interlayer was observed for the successful combina- tions, which presumably provided an increased contact area between both surfaces and could therefore accelerate bond exchange (Figure 25b). Unfortunately, this does not explain the retardation observed for water-miscible organic solvents. ...

Context 26

... ally, CuAAC-induced adhesion was also achieved under water without significant loss of the strength, but its performance reduced by about 50% over a period of several months if kept under moist conditions. Nevertheless, the commercial adhesive failed completely in both scenarios, i.e., both wet gluing and Figure 25. a) Formation of a dynamic covalent acylhydrazone network by reaction of linear and star-shaped PEG caused gelation of both aqueous and organic solutions. ...