Imparting conformational memory for material adhesion.

Adhesion between similar and dissimilar materials is essential to many biological systems and synthetic materials, devices, and machines. Since the inception of adhesion science more than five decades ago, adhesion to a surface has long been recognized as beyond two-dimensional. Similarly, molecular conformation - the three-dimensional arrangement of atoms in a molecule - is ubiquitous in biology and fundamental to the binding of biomolecules.

Catechol-functionalized hydrogels: biomimetic design, adhesion mechanism, and biomedical applications.

Hydrogels are a unique class of polymeric materials that possess an interconnected porous network across various length scales from nano- to macroscopic dimensions and exhibit remarkable structure-derived properties, including high surface area, an accommodating matrix, inherent flexibility, controllable mechanical strength, and excellent biocompatibility. Strong and robust adhesion between hydrogels and substrates is highly desirable for their integration into and subsequent performance in biomedical devices and systems. However, the adhesive behavior of hydrogels is severely weakened by the large amount of water that interacts with the adhesive groups reducing the interfacial interactions.

A hybrid material that reversibly switches between two stable solid states.

Most types of solid matter have a single stable solid state for a particular set of conditions. Nonetheless, materials with distinct, interchangeable solid states would be advantageous for several technological applications. Here, we describe a material composed of a polymer impregnated with a supercooled salt solution, termed as sal-gel, that assumes two distinct but stable and reversible solid states under the same conditions for a range of temperatures (-90 to 58 °C) and pressure.

Underwater Contact Behavior of Alginate and Catechol-Conjugated Alginate Hydrogel Beads.

Modifying hydrogels with catechol functionality is a promising approach for improving their mechanical and interfacial properties in water, particularly in biological environments. However, the effects of this modification on hydrogels' contact behavior with soft tissues are not well-studied due to the complexity of hydrogels and lack of suitable techniques to probe this behavior. In addition, modification can alter the mechanical properties of hydrogels, resulting in consequences for adhesive strength as well.

A transparent silica colloidal crystal/PDMS composite and its application for crack suppression of metallic coatings.

A silica colloidal crystal (SCC)-polydimethylsiloxane (PDMS) composite with a heterogeneous surface of silica and PDMS was prepared by spreading a premixed PDMS solution on the 3D structured SCCs and curing the solution in-situ. Although the SCCs had a light blue color, the obtained composite of SCC and PDMS, due to the close effective refractive indexes of the materials, was colorless and transparent; the UV-vis spectra indicated a negligible effect of the added SCC on the transmittance of the PDMS sheet (1% reduction). Interestingly, the transparent composite sheet became translucent under stress and became clear again when relaxed.

Bio-inspired dopamine functionalization of polypyrrole for improved adhesion and conductivity.

We report the functionalization of polypyrrole (PPy) with a "sticky" biomolecule dopamine (DA), which mimics the essential component of mussel adhesive protein. PPy is one of the most promising electrically conductive polymers with good biocompatibility. The research findings reveal that the DA functionalization enhances the dispersibility and stability of PPy in water and its film adhesion to substrate surface significantly.

Surface and tribological behaviors of the bioinspired polydopamine thin films under dry and wet conditions.

Dopamine is a "sticky" biomolecule containing the typical functional groups of mussel adhesive proteins. It can self-polymerize into a nanoscale thin film on various surfaces. We investigated the surface, adhesion, friction, and cracking properties of polydopamine (PDA) thin films for their effective transfer to functional devices and biocompatible coatings.

"Contact" of nanoscale stiff films.

We investigated the contact behaviors of a nanoscopic stiff thin film bonded to a compliant substrate and derived an analytical solution for determining the elastic modulus of thin films. Microscopic contact deformations of the gold and polydopamine thin films (<200 nm) coated on polydimethylsiloxane elastomers were measured by indenting a soft tip and analyzed in the framework of the classical plate theory and Johnson-Kendall-Roberts (JKR) contact mechanics. The analysis of this thin film contact mechanics focused on the bending and stretching resistance of thin films and is fundamentally different from conventional indentation measurements where the focus is on the fracture and compression of the films.