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Graphical abstract Highlights • A bio-based adhesive system is presented to provide an alternative to petroleum-derived glues. • Improvements to the synthesis of this polymer system have been achieved. • Bonding is shown to depend upon polymer molecular weight and dispersity. Abstract Renewable materials are in demand to replace the petroleum-based glues we use on a daily basis. Such substitutions will not take place until bio-based adhesives can meet or exceed the performance of current materials. Work presented here examines several chemical parameters in order to improve the molecular weight and synthetic strategy for a polymer that combines polylactic acid with mussel mimicking catechol, ("catechol-PLA"). Altering the polymerization time as well as the deprotection time and temperature afforded better control over both molecular weights and yields. Dispersity and molecular weight were shown to both be parameters tunable to improve adhesion strength. Cross-linking with iron improved the adhesion of low molecular weight polymers, bringing performance up to that of the longer chain counterparts. Such cross-linking and molecular weight effects were seen to alter the balance of adhesive and cohesive interactions. Such development and understanding of renewable polymer systems may help to hasten future competition with petroleum-based adhesives. [ABSTRACT FROM AUTHOR]

High-performance adhesives require mechanical properties tuned to demands of the surroundings. A mismatch in stiffness between substrate and adhesive leads to stress concentrations and fracture when the bonding is subjected to mechanical load. Balancing material strength versus ductility, as well as considering the relationship between adhesive modulus and substrate modulus, creates stronger joints. However, a detailed understanding of how these properties interplay is lacking. Here, a biomimetic terpolymer is altered systematically to identify regions of optimal bonding. Mechanical properties of these terpolymers are tailored by controlling the amount of a methyl methacrylate stiff monomer versus a similar monomer containing flexible poly(ethylene glycol) chains. Dopamine methacrylamide, the cross-linking monomer, is a catechol moiety analogous to 3,4-dihydroxyphenylalanine, a key component in the adhesive proteins of marine mussels. Bulk adhesion of this family of terpolymers is tested on metal and plastic substrates. Incorporating higher amounts of poly(ethylene glycol) into the terpolymer introduces flexibility and ductility. By taking a systematic approach to polymer design, the region in which material strength and ductility are balanced in relation to the substrate modulus is found, thereby yielding the most robust joints. [ABSTRACT FROM AUTHOR]

Marine mussels clinging to rocks inspire the development of novel materials. Characterization of mussel adhesive plaques describes a matrix of proteins containing 3,4-dihydroxyphenylalanine (DOPA), which provides cross-linking chemistry that allows mussels to attach firmly. Several synthetic polymer systems have been developed based on this DOPA chemistry. High strength bonding has been achieved with poly[(3,4-dihydroxystyrene)- co-styrene], a simplified mimic of mussel proteins in which 3,4-dihydroxystyrene provides the cross-linking and adhesion of DOPA. The poly(styrene) host polymer stands in for a protein backbone. Prior efforts showed that a monomer ratio of 1:2 3,4-dihydroxystyrene:styrene within the statistical copolymer poly[(3,4-dihydroxystyrene)- co-styrene] yields the highest adhesion. To enhance adhesive performance of this biomimetic polymer, a systematic study is carried out in which a range of cross-linking agents, cure times, cure temperatures, polymer concentrations, and fillers are examined. Lap shear adhesion testing revealed substantial increases in bond strength from each study. Consensus conditions are then determined and bonding performance is assessed on several substrates. Adhesion of this system turns out to be one of the strongest of all biomimetic polymers. These studies show that DOPA chemistry may be able to stand alongside of cyanoacrylate (e.g., Super Glue) and epoxy when it comes to high strength bonding. [ABSTRACT FROM AUTHOR]

Marine mussels produce a byssal adhesive assembly for attachment to surfaces in the marine environment. The byssus is characterized by an array of adhesive plaques, each attached to threads that are anchored inside the animal. Here we describe a rapid method for determining detachment force, area, and overall adhesion of mussel plaques. Adhesion forces for mussels attached to glass, aluminum, acrylic, polyvinyl chloride (PVC), and Silastic® T2 are reported. This method may aid in the development of new adhesive materials and antifouling surfaces. [ABSTRACT FROM AUTHOR]

Mussel adhesive proteins (MAPs) have received increased attention as potential biomedical and environmental friendly adhesives. However, practical application of MAPs has been severely limited by uneconomical extraction and unsuccessful genetic production. Developing new adhesives requires access to large quantities of material and demonstrations of bulk mechanical properties. Previously, the authors designed fp-151, a fusion protein comprised of six MAP type 1 (fp-1) decapeptide repeats at each MAP type 5 (fp-5) terminus and successfully expressed it in Escherichia coli. This recombinant hybrid protein exhibited high-level expression, a simple purification and high biocompatibility as well as strong adhesive ability on a micro-scale. In the present work, investigations on the bulk adhesive properties of semi-purified (∼90% purity) fusion fp-151 were performed in air. The unmodified recombinant fp-151, as expressed, contains tyrosine residues and showed significant shear-adhesive forces (∼0.33 MPa). Adhesion strength increased (∼0.45 MPa) after enzymatic oxidation of tyrosine residues to l-3,4-dihydroxyphenylalanine (DOPA) groups. Addition of cross-linkers such as iron(III), manganese(III) and periodate (IO4-) generally enhanced adhesion, although too much addition decreased adhesion. Among the three cross-linking reagents examined, the non-metallic oxidant periodate showed the highest shear-adhesive forces (∼0.86 MPa). In addition, it was found that adhesive strengths could be increased by adding weights to the samples. The highest adhesion strength found was that of DOPA-containing fp-151 cross-linked with periodate and having weights applied to the samples (∼1.06 MPa). Taken together, the first bulk-scale adhesive force measurements are presented for an expressed recombinant hybrid mussel adhesive protein. [ABSTRACT FROM AUTHOR]

The article discusses research led by G.P. Maier on mussels that found the organisms use their own protein-based ions to adhere to underwater surfaces. Similarities to bacteria and their use of catechol chemistries are noted as well as how the findings can be applied to the design of synthetic materials.