Supramolecular motifs in dynamic covalent PEG-hemiaminal organogels.

Dynamic covalent materials are stable materials that possess reversible behaviour triggered by stimuli such as light, redox conditions or temperature; whereas supramolecular crosslinks depend on the equilibrium constant and relative concentrations of crosslinks as a function of temperature. The combination of these two reversible chemistries can allow access to materials with unique properties. Here, we show that this combination of dynamic covalent and supramolecular chemistry can be used to prepare organogels comprising distinct networks. Two materials containing hemiaminal crosslink junctions were synthesized; one material is comprised of dynamic covalent junctions and the other contains hydrogen-bonding bis-hemiaminal moieties. Under specific network synthesis conditions, these materials exhibited self-healing behaviour. This work reports on both the molecular-level detail of hemiaminal crosslink junction formation as well as the macroscopic behaviour of hemiaminal dynamic covalent network (HDCN) elastomeric organogels. These materials have potential applications as elastomeric components in printable materials, cargo carriers and adhesives.

Interpenetrating polymer network hydrogel scaffolds for artificial cornea periphery.

Three-dimensional scaffolds based on inverted colloidal crystals (ICCs) were fabricated from sequentially polymerized interpenetrating polymer network (IPN) hydrogels of poly(ethyleneglycol) and poly(acrylic acid). This high-strength, high-water-content IPN hydrogel may be suitable for use in an artificial cornea application. Development of a highly porous, biointegrable region at the periphery of the artificial cornea device is critical to long-term retention of the implant. The ICC fabrication technique produced scaffolds with well-controlled, tunable pore and channel dimensions. When surface functionalized with extracellular matrix proteins, corneal fibroblasts were successfully cultured on IPN hydrogel scaffolds, demonstrating the feasibility of these gels as materials for the artificial cornea porous periphery. Porous hydrogels with and without cells were visualized non-invasively in the hydrated state using variable-pressure scanning electron microscopy.

Modular composite hydrogels from cholesterol-functionalized polycarbonates for antimicrobial applications.

Micellar composite hydrogel systems represent a promising class of materials for biomolecule and drug delivery applications. In this work a system combining micellar drug delivery with supramolecular hydrogel assemblies is developed, representing an elegant marriage of aqueous hydrophobic drug delivery and next-generation injectable viscoelastic materials. Novel shear thinning and injectable micellar composite hydrogels were prepared using an amphiphilic ABA-type triblock copolymer consisting of a hydrophilic middle block and cholesterol-functionalized polycarbonates as terminal hydrophobic blocks. Varying the concentration and relative hydrophobic-hydrophilic content of the amphiphilic species conferred the ability to tune the storage moduli of these gels from 200 Pa to 3500 Pa. This tunable system was used to encapsulate drug-loaded polymeric micelles, demonstrating a straightforward and modular approach to developing micellar viscoelastic materials for a variety of applications such as delivery of hydrophobic drugs. These hydrogels were also mixed with cholesterol-containing cationic polycarbonates to render antimicrobial activity and capability for anionic drug delivery. Additionally, small-angle X-ray scattering (SAXS) and electron microscopy (EM) results probed the mesoscale structure of these micellar composite materials, lending molecular level insight into the self-assembly properties of these gels. The antimicrobial composite hydrogels demonstrated strong microbicidal activity against Gram-negative and Gram-positive bacteria, and C. albicans fungus. Amphotericin B (AmB, an antifungal drug)-loaded micelles embedded within the hydrogel demonstrated sustained drug release over 4 days and effective eradication of fungi. Our findings demonstrate that materials of different nature (i.e. small molecule drugs or charged macromolecules) can be physically combined with ABA-type triblock copolymer gelators to form hydrogels for potential pharmaceutical applications.

Skin-like pressure and strain sensors based on transparent elastic films of carbon nanotubes.

Transparent, elastic conductors are essential components of electronic and optoelectronic devices that facilitate human interaction and biofeedback, such as interactive electronics, implantable medical devices and robotic systems with human-like sensing capabilities. The availability of conducting thin films with these properties could lead to the development of skin-like sensors that stretch reversibly, sense pressure (not just touch), bend into hairpin turns, integrate with collapsible, stretchable and mechanically robust displays and solar cells, and also wrap around non-planar and biological surfaces such as skin and organs, without wrinkling. We report transparent, conducting spray-deposited films of single-walled carbon nanotubes that can be rendered stretchable by applying strain along each axis, and then releasing this strain. This process produces spring-like structures in the nanotubes that accommodate strains of up to 150% and demonstrate conductivities as high as 2,200 S cm(-1) in the stretched state. We also use the nanotube films as electrodes in arrays of transparent, stretchable capacitors, which behave as pressure and strain sensors.