Aerogels, an extremely important aggregation state of various self-assembled nanoscale building blocks, have great potential in fields ranging from energy storage to thermal insulation. However, the porosity of aerogels makes them mechanically weak in most cases, and the chemical activity of the resulting aerogel needs consideration. Herein, chemically crosslinked graphene oxide (GO) 3D aerogels with large specific surface areas (up to 850 m(2) g(-1) ), outstanding mechanical performance (up to 20 MPa Young's modulus, 1 MPa yield strength and 45 J g(-1) specific energy adsorption), and superhigh chemical activity (toward some reducing gases such as H2 S, HI, and SO2 ), are fabricated by assembling 2D GO sheets edge-to-edge into uniform, 3D hydrogel networks with subsequent supercritical fluid drying. These aerogels are superior to other 3D frameworks (e.g. graphene aerogels) assembled via partial overlapping of the basal planes of the 2D building blocks.

Supramolecular hydrogels (SMHs) are three-dimensional networks filled with a large amount of water. The crosslinking force in the 3D network is always constructed by relatively weak and dynamic non-covalent interactions, and thus SMHs usually possess extremely high susceptibility to external environment and can show extraordinary stimuli-responsive, self-healing or other attractive properties. However, the overall crosslinking force in hydrogel networks is difficult to flexibly modulate, and this leads to limited functions of the SMHs. In this regard, hierarchical hydrogen bonds, that is, the mixture of relatively strong and relatively weak hydrogen bonds, are used herein as crosslinking force for the hydrogel preparation. The ratio of strong and weak hydrogen bonds can be finely tuned to tailor the properties of resultant gels. Thus, by delicate manipulation of the overall crosslinking force in the system, a hydrogel with multiple (thermal, pH and NIR light) responsiveness, autonomous self-healing property and interesting temperature dependent, reversible adhesion behavior is obtained. This kind of hierarchical hydrogen bond manipulation is proved to be a general method for multiple-functionality hydrogel preparation, and the resultant material shows potential for a range of applications.

A generic approach to make the uniform graphene oxide (GO) hydrogels by using glucono-d-lactone (GDL) as a hydrogel promoter has been put forward for the first time. Either in situ released multivalent metal ions (e.g. La 3+ , Co 2+ , Ni 2+ ) or in situ protonized polyamine (e.g. polyethylenimine, melamine, polyamidoamine) molecules have assembled GO sheets into 3D hydrogel architectures with the assistance of the hydrolysis product of GDL. The permanent network and mechanical property of the resulting GO hydrogels have been studied by rheology investigation. The chemical composition and porous morphology of the resulting GO hydrogels have been revealed by X-ray photoelectron spectroscopy and scanning electron microscopy, respectively. The microstructure of the resulting GO hydrogels has been investigated by Raman spectroscopy and X-ray diffraction. More interestingly, a reversible gel-sol transition initially triggered with the addition of the EDTA solution, depending on which additive (in situ released multivalent metal ions or in situ protonized polyamine molecules) is used for 3D assembly of the GO sheets, has been observed from the resulting GO hydrogels.

Abstract. In the present study, we developed novel insulin-loaded hyaluronic acid (HA) nanoparticles for insulin delivery. The insulin-loaded HA nanoparticles were prepared by reverse-emulsion-freeze-drying method. This method led to a homogenous population of small HA nanoparticles with average size of 182.2 nm and achieved high insulin entrapment efficiencies (approximately 95%). The pH-sensitive HA nanoparticles as an oral delivery carrier showed advantages in protecting insulin against the strongly acidic environment of the stomach, and not destroying the junction integrity of epithelial cells which promise long-term safety for chronic insulin treatment. The results of transport experiments suggested that insulinloaded HA nanoparticles were transported across Caco-2 cell monolayers mainly via transcellular pathway and their apparent permeability coefficient from apical to basolateral had more than twofold increase compared with insulin solution. The efflux ratio of P app (B to A) to P app (A to B) less than 1 demonstrated that HA nanoparticle-mediated transport of insulin across Caco-2 cell monolayers underwent active transport. The results of permeability through the rat small intestine confirmed that HA nanoparticles significantly enhanced insulin transport through the duodenum and ileum. Diabetic rats treated with oral insulin-loaded HA nanoparticles also showed stronger hypoglycemic effects than insulin solution. Therefore, these HA nanoparticles could be a promising candidate for oral insulin delivery.

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