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Translating fundamental studies of marine mussel adhesion into practical mussel-inspired wet adhesives remains an important technological challenge. To adhere, mussels secrete adhesive proteins rich in the catecholic amino acid 3,4-dihydroxyphenylalanine (Dopa) and positively charged lysine. Consequently, numerous synthetic adhesives incorporating catecholic and cationic functionalities have been designed. However, despite widespread research, uncertainties remain about the optimal design of synthetic mussel-inspired adhesives. Here, we present a study of the adhesion of mussel-inspired pressure-sensitive adhesives. We explore the effects of catechol content, molecular architecture, and solvent quality on pressure-sensitive adhesive (PSA) adhesion and cohesion measured in a surface forces apparatus. Our findings demonstrate that the influence of catechol content depends on the choice of solvent and that adhesive performance is dictated by film composition rather than molecular architecture. Our results also highlight the importance of electrostatic and hydrophobic interactions for adhesion and cohesion in aqueous environments. Together, our findings contribute to an improved understanding of the interplay between materials chemistry, environmental conditions, and adhesive performance to facilitate the design of bioinspired wet adhesives.

The outstanding adhesive performance of mussel byssal threads has inspired materials scientists over the past few decades. Exploiting the amino-catechol synergy, polymeric pressure-sensitive adhesives (PSAs) have now been synthesized by copolymerizing traditional PSA monomers, butyl acrylate and acrylic acid, with mussel-inspired lysine- and aromatic-rich monomers. The consequences of decoupling amino and catechol moieties from each other were compared (that is, incorporated as separate monomers) against a monomer architecture in which the catechol and amine were coupled together in a fixed orientation in the monomer side chain. Adhesion assays were used to probe performance at the molecular, microscopic, and macroscopic levels by a combination of AFM-assisted force spectroscopy, peel and static shear adhesion. Coupling of catechols and amines in the same monomer side chain produced optimal cooperative effects in improving the macroscopic adhesion performance., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Interactions between polymer molecules and inorganic nanoparticles can play a dominant role in nanocomposite material mechanics, yet control of such interfacial interaction dynamics remains a significant challenge particularly in water. This study presents insights on how to engineer hydrogel material mechanics via nanoparticle interface-controlled cross-link dynamics. Inspired by the adhesive chemistry in mussel threads, we have incorporated iron oxide nanoparticles (Fe3O4 NPs) into a catechol-modified polymer network to obtain hydrogels cross-linked via reversible metal-coordination bonds at Fe3O4 NP surfaces. Unique material mechanics result from the supra-molecular cross-link structure dynamics in the gels; in contrast to the previously reported fluid-like dynamics of transient catechol-Fe(3+) cross-links, the catechol-Fe3O4 NP structures provide solid-like yet reversible hydrogel mechanics. The structurally controlled hierarchical mechanics presented here suggest how to develop hydrogels with remote-controlled self-healing dynamics.

Monomeric catechols are displayed on the surface of polymeric nanofibers by robust catechol-thiol interactions to enhance cell adhesion and migration. Dihydroxyphenyl propionic acid is chemically conjugated to primary amine groups of poly(ϵ-caprolactone)-poly(ethylene glycol)-amine (PCL-PEG) nanofibers to display catechol moieties on the surface. At basic pH, catecholized nanofibers incorporate thiol groups at a five-fold higher rate than at acidic pH, while catechol-coated surfaces do not show any pH-dependent binding. Live/dead cell staining indicates that the catecholized nanofibers do not exert any cytotoxic effects. Also, NIH 3T3 cells cultured on the catecholized nanofibers show increased attachment and migration that is proportional to the amount of the immobilized catechol moieties on the surface. These results clearly indicate that 6 nmol of monomeric catechols on the surface of nanofiber can promote cell adhesion and migration by thiol-catehol interactions., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Objective: Iatrogenic preterm prelabour rupture of fetal membranes (iPPROM) remains the main complication after invasive interventions into the intrauterine cavity. The aim of this study was to evaluate the sealing capability and tissue interaction of mussel-mimetic tissue adhesive (mussel glue) in comparison to fibrin glue on punctured fetal membranes in vivo., Study Design: A mid-gestational rabbit model was used for testing the materials. The fetal sacs of pregnant rabbits at day 23 were randomly assigned into experimental groups: unoperated (negative control), unclosed puncture (positive control), commercially available fibrin glue (FG) with decellularized amnion scaffold (DAM), mussel glue (MG) with DAM, or mussel glue alone. Evaluation was done at term (30 days' gestation) assessing fetal survival, fetal membrane integrity and histology of the membranes., Results: Fetal survival was not significantly lower in any of the treatment groups compared to the negative control. All plugging materials could be found at the end of the pregnancy and no adverse effects on the fetus or the pregnant does could be observed. Sac integrity was higher in all treatment groups compared to the positive control group but significant only in the FG+DAM group. Cellular infiltration could be seen in fibrin glue and DAM in contrast to mussel glue which was only tightly adhering to the surrounding tissue. These cells were mostly of mesenchymal phenotype staining positive for vimentin. CD68 positive macrophages were found clustered around all the plugging materials, but their numbers were only significantly increased for the mussel glue alone group compared to negative controls., Conclusions: Mussel glues performance in sealing fetal membranes in the rabbit model was comparable to that of fibrin glue. Taking into account its other favorable properties, it is a noteworthy candidate for a clinically applicable fetal membrane sealant., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.)

A doubly biomimetic PMNC polymer bearing cell antifouling phosphorylcholine and mussel adhesive protein catechol groups is synthesized. The polymer can be deposited onto a variety of substrates by dip-coating in an aqueous solution, adhering to surfaces via the catechol functional group while at the same time forming a cell outer membrane mimetic antifouling surface. Contact angle, ATR-FTIR and XPS measurements confirm polymer coating formation on a variety of inorganic and organic substrates. BSA and bovine plasma fibrinogen protein adsorption on PMNC coated surfaces are reduced significantly compared to unmodified substrates, and platelet adhesion from human serum onto the PMNC coated substrate surfaces is highly suppressed in this study., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A novel cell-targeting, pH-sensitive polymeric carrier was employed in this study for delivery of the anticancer drug bortezomib (BTZ) to cancer cells. Our strategy is based on facile conjugation of BTZ to catechol-containing polymeric carriers that are designed to be taken up selectively by cancer cells through cell surface receptor-mediated mechanisms. The polymer used as a building block in this study was poly(ethylene glycol), which was chosen for its ability to reduce nonspecific interactions with proteins and cells. The catechol moiety was exploited for its ability to bind and release borate-containing therapeutics such as BTZ in a pH-dependent manner. In acidic environments, such as in cancer tissue or the subcellular endosome, BTZ dissociates from the polymer-bound catechol groups to liberate the free drug, which inhibits proteasome function. A cancer-cell-targeting ligand, biotin, was presented on the polymer carriers to facilitate targeted entry of drug-loaded polymer carriers into cancer cells. Our study demonstrated that the cancer-targeting drug-polymer conjugates dramatically enhanced cellular uptake, proteasome inhibition, and cytotoxicity toward breast carcinoma cells in comparison with nontargeting drug-polymer conjugates. The pH-sensitive catechol-boronate binding mechanism provides a chemoselective approach for controlling the release of BTZ in targeted cancer cells, establishing a concept that may be applied in the future toward other boronic acid-containing therapeutics to treat a broad range of diseases., (© 2011 American Chemical Society)

Here we report the synthesis and characterization of pH-responsive, self-healing hydrogels based on boronate-catechol complexation.

Growing evidence supports a critical role of metal-ligand coordination in many attributes of biological materials including adhesion, self-assembly, toughness, and hardness without mineralization [Rubin DJ, Miserez A, Waite JH (2010) Advances in Insect Physiology: Insect Integument and Color, eds Jérôme C, Stephen JS (Academic Press, London), pp 75-133]. Coordination between Fe and catechol ligands has recently been correlated to the hardness and high extensibility of the cuticle of mussel byssal threads and proposed to endow self-healing properties [Harrington MJ, Masic A, Holten-Andersen N, Waite JH, Fratzl P (2010) Science 328:216-220]. Inspired by the pH jump experienced by proteins during maturation of a mussel byssus secretion, we have developed a simple method to control catechol-Fe(3+) interpolymer cross-linking via pH. The resonance Raman signature of catechol-Fe(3+) cross-linked polymer gels at high pH was similar to that from native mussel thread cuticle and the gels displayed elastic moduli (G') that approach covalently cross-linked gels as well as self-healing properties.

In this paper, we demonstrate the first use of a catecholic initiator for surface-initiated polymerization (SIP) from metal surfaces to create antifouling polymer coatings. A new bifunctional initiator inspired by mussel adhesive proteins was synthesized, which strongly adsorbs to Ti and 316L stainless steel (SS) substrates, providing an anchor for surface immobilization of grafted polymers. Surface-initiated atom transfer radical polymerization (SI-ATRP) was performed through the adsorbed biomimetic initiator to polymerize methyl methacrylate macromonomers with oligo(ethylene glycol) (OEG) side chains. X-ray photoelectron spectroscopy, surface FT-IR, and contact angle analysis confirmed the sequential grafting of initiator and polymer, and ellipsometry indicated the formation of polymer coatings of up to 100 nm thickness. Cell adhesion experiments performed with 3T3-Swiss albino fibroblasts showed substantially reduced cell adhesion onto polymer grafted Ti and 316L SS substrates as compared to the unmodified metals. Moreover, micropatterning of grafted polymer coatings on Ti surfaces was demonstrated by combining SI-ATRP and molecular assembly patterning by lift-off (MAPL), creating cell-adhesive and cell-resistant regions for potential use as cell arrays. Due to the ability of catechols to bind to a large variety of inorganic surfaces, this biomimetic anchoring strategy is expected to be a highly versatile tool for polymer thin film surface modification for biomedical and other applications.