Light-responsive cubosomes: triggering molecular release with stretch-squeeze lattice control Beatrice Jones 1,2 , Elaine A. Kelly 1 , Nathan Cowieson 2 , Giorgio Divitini 1 and Rachel C. Evans 1 1 University of Cambridge, UK, 2 Diamond Light Source, Oxfordshire Stimuli-responsive materials are crucial to advance controlled delivery systems for drugs and catalysts. Lyotropic liquid crystals (LLCs), formed from the self-assembly of amphiphiles on the addition of a solvent, have well- defined internal structures suitable to entrap guest molecules by restricting diffusion out of these networks. 1 These LLCs can be broken up in excess aqueous solution, using a high-shear input, to form dispersions of nanoparticles. This aids their application as delivery systems, whilst retaining an ordered LLC interior required for entrapment. 2 Previous studies have incorporated photoswitchable functional groups into amphiphiles to create LLCs whose structure can be modified using light as an external stimulus. 3,4 In this work, we demonstrate the first example of light-responsive cubic LLC dispersions, or cubsosomes, by using photoswitchable amphiphiles to enable external control over the LLC structure and subsequent on-demand release of entrapped guest molecules. 5 Two different light-responsive azobenzene photosurfactants (AzoPS) containing a neutral tetraethylene glycol head group, alkyl spacer (of chain length 4 or 8), azobenzene moiety and alkyl tail (of length 6 or 8) were investigated. When combined into monoolein–water systems (10–30wt%), these form hexagonal or lamellar LLC phases, depending on the AzoPS chain length. Homogenisation forms stable dispersions of particles ~200nm in diameter with internal bicontinuous primitive cubic phases, as seen by small-angle X-ray scattering and cryo-transmission electron microscopy. Notably, increasing the AzoPS concentration leads to swelling of the cubic lattice, offering a method to tune the internal nanoscale structure. Upon UV irradiation, AzoPS in the cubosomes isomerises from the trans to cis- predominant states within seconds. The bicontinuous primitive cubic structure remains after isomerisation, but the lattice parameter decreases by up to 39%. This is due to “bending” of the AzoPS tail in the cis state, which changes the tail volume and squeezes the cubic lattice. This squeeze mechanism was successfully harnessed to enable phototriggerable release of trapped Nile Red guest molecules from the cubosome structure, confirmed by a 72% decrease in the fluorescence intensity. This rapid release occurs within minutes, contrasting the minimal diffusion from the matrix measured over 3 hours. The ability to control the internal structure of LLC dispersions using light, and the dramatic effect this has on the retention of entrapped molecules, suggests these systems may have huge potential for the next-generation of nano-delivery. References 1. Mulet, X.; Boyd, B.; Drummond, C., J. Colloid Interface Sci. , 2013, 393 , 1. 2. Amar-Yuli, I.; Wachtel, E.; Shoshan, E.B.; Danino, D.; Aserin, A.; Garti, N., Langmuir, 2007, 23 , 3637. 3. Peng, S.; Guo, Q.; Hartley, P.G.; Hughes, T.C., J. Mater. Chem. C, 2014, 2 , 8303. 4. Houston, J.; Kelly, E. A.; Kruteva, M.; Chrissopoulou, K.; Cowieson, N.; Evans, R.C., J. Mater. Chem. C , 2019, 7 , 10945. 5. Jones, B. E; Kelly, E. A.; Cowieson, N.; Divitini, G.; Evans, R.C., J. Am. Chem. Soc. , 2022, 144 , 19532.
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