Switchable adhesion by chemical functionality and topography

Progress in adhesion technology over the last few decades has led to widespread replacement of mechanical fasteners with adhesive bonds. Despite the advances, it remains challenging to produce materials that are sticky on demand. In this feature article we highlight recent efforts to develop reversibly switchable adhesives, that exhibit the ability to trigger adhesion in response to an environmental change – for example, pH, solvent, temperature, mechanics, and electro/magnetic field. We review two initially separate design principles to induce switchable adhesion: (1) chemical functionality and (2) topography. Combining both approaches may lead to novel hierarchical adhesives with interesting property profiles

Adhesive composition

The invention is directed to an adhesive complex coacervate composition, to a method of physically crosslinking an adhesive complex coacervate composition, to a method for adhering a tissue defect in a subject, and to the use of an adhesive complex coacervate composition. The adhesive complex coacervate composition of the invention comprises a polycation and a polyanion, wherein said polycation and polyanion together comprise on average at least two thermoresponsive moieties per polymer chain, said thermoresponsive moieties exhibiting a lower critical solution temperature, wherein said polycation comprises 5-70 mol% of thermoresponsive moieties and/or wherein said polyanion comprises 5-70 mol% of thermoresponsive moieties, and wherein said polycation and/or said polyanion is a graft or block copolymer comprising said thermoresponsive moieties

Effect of Viscoelasticity on Adhesion of Bioinspired Micropatterned Epoxy Surfaces

The effect of viscoelasticity on adhesion was investigated for micropatterned epoxy surfaces and compared to nonpatterned surfaces. A two-component epoxy system was used to produce epoxy compositions with different viscoelastic properties. Pillar arrays with flat punch tip geometries were fabricated with a two-step soft lithography process. Adhesion properties were measured with a home-built adhesion tester using a spherical sapphire probe as a counter-surface. Compared to flat controls, micropatterned epoxy samples with low visco elasticity (i.e., low damping factors) showed at least a 20-fold reduction in pull-off force per actual contact area for both low (E' = 2.3 MPa) and high (E' = 2.3 GPa) storage moduli. This antiadhesive behavior may result from poor contact formation and indicates that the adhesion performance of commonly used elastomers for dry adhesives (e.g., polydimethylsiloxane) is governed by the interfacial viscoelasticity. Adhesion significantly increased with increasing viscoelasticity. Micropatterned samples with high viscoelasticity showed a 4-fold reduction in adhesion for aspect ratio (AR) 1.1 patterns but a 2-fold enhancement in adhesion for AR 2.2 patterns. These results indicate that viscoelasticity can enhance the effect of surface patterning on adhesion and should be considered as a significant parameter in the design of artificial patterned adhesives

Adhesive composition

The invention is directed to an adhesive complex coacervate composition, to a method of physically crosslinking an adhesive complex coacervate composition, to a method for adhering a tissue defect in a subject, and to the use of an adhesive complex coacervate composition. The adhesive complex coacervate composition of the invention comprises a polycation and a polyanion, wherein said polycation and polyanion together comprise on average at least two thermoresponsive moieties per polymer chain, said thermoresponsive moieties exhibiting a lower critical solution temperature, wherein said polycation comprises 5-70 mol% of thermoresponsive moieties and/or wherein said polyanion comprises 5-70 mol% of thermoresponsive moieties, and wherein said polycation and/or said polyanion is a graft or block copolymer comprising said thermoresponsive moieties

Adhesive composition

The invention is directed to an adhesive complex coacervate composition, to a method of physically crosslinking an adhesive complex coacervate composition, to a method for adhering a tissue defect in a subject, and to the use of an adhesive complex coacervate composition. The adhesive complex coacervate composition of the invention comprises a polycation and a polyanion, wherein said polycation and polyanion together comprise on average at least two thermoresponsive moieties per polymer chain, said thermoresponsive moieties exhibiting a lower critical solution temperature, wherein said polycation comprises 5-70 mol% of thermoresponsive moieties and/or wherein said polyanion comprises 5-70 mol% of thermoresponsive moieties, and wherein said polycation and/or said polyanion is a graft or block copolymer comprising said thermoresponsive moieties

Jack of all trades: Versatile catechol crosslinking mechanisms

Catechols play an important role in many natural systems. They are known to readily interact with both organic (e.g., amino acids) and inorganic (e.g., metal ions, metal oxides) compounds, thereby providing a powerful system for protein curing. Catechol crosslinked protein networks, such as sclerotized cuticle and byssal threads of the mussel, have been shown to exhibit excellent mechanical properties. A lot of effort has been devoted to mimicking the natural proteins using synthetic catechol-functionalized polymers. Despite the success in developing catechol-functionalized materials, the crosslinking chemistry of catechols is still a subject of debate. To develop materials with controlled and superior properties, a clear understanding of the crosslinking mechanism of catechols is of vital importance. This review describes the crosslinking pathways of catechol and derivatives in both natural and synthetic systems. We discuss existing pathways of catechol crosslinking and parameters that affect the catechol chemistry in detail. This overview will point towards a rational direction for further investigation of the complicated catechol chemistry