Hydrogels can be prepared using the commercially available Fmoc-phenylalanine or Fmoc-tyrosine as the gelator. Gelation is triggered by careful adjustment of the pH of the solution using glucono-delta-lactone (GdL). Model dyes have been entrapped in the hydrogels, and the release of the dyes from the hydrogels has been monitored. The release ratios indicate that the systems are under Fickian diffusion control. A range of dyes with different radii of gyration diffuse from the Fmoc-phenylalanine hydrogels with similar diffusion coefficients, implying that the network is not specifically retaining even relatively large (5 nm) dyes. On the other hand, the larger dyes are restricted in their diffusion from Fmoc-tyrosine hydrogels. These results correlate with the rheological measurements for the hydrogels, where those formed from Fmoc-tyrosine were shown to have significantly higher storage moduli than those formed from Fmoc-phenylalanine. In addition, the frequency-dependent behavior of the hydrogels demonstrates that Fmoc-tyrosine shows the classic response of a strong gel with a storage modulus that is nearly independent of frequency. However, for Fmoc-phenylalanine, the frequency dependence of moduli is very strong and very similar to that displayed by a transient network, where the interconnections between junction zones in the network are highly flexible and able to withstand large deformations.

The mechanical properties of gels are critical to the final targeted applications. Depending on the application, different properties may be required. Here, we show that the mechanical strength and ability to recover of gels formed using a low molecular weight gelator can be controlled by two independent factors (i) the volume fraction of co-solvent (in this case DMSO) in the system and (ii) the temperature cycle used. These differences correlate with the large scale structure of the network that is formed from the self-assembled fibres. This opens up the potential to prepare gels with very different properties at the same final conditions, allowing the effect of microstructure to be probed.Scheme 1 Structure of FmocLG.

Here we report a new class of hydrogels formed by polymers that are cross-linked through subcomponent selfassembled metal−organic cages. Selective encapsulation of guest molecules within the cages creates two distinct internal phases within the hydrogel, which allows for contrasting release profiles of related molecules depending on their aptitude for encapsulation within the cages. The hydrogels were fabricated into microparticles via a droplet-based microfluidic approach and proved responsive to a variety of stimuli, including acid and competing amine or aldehyde subcomponents, allowing for the triggered release of cargo.

An alkaline form of ‘dry water’—a ‘dry base’—is prepared by the high-speed mixing of aqueous solutions of metal carbonates or organic amines with hydrophobic silica nanoparticles.

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