Light-Responsive Molecular Release from Cubosomes Using Swell-Squeeze Lattice Control.

Stimuli-responsive materials are crucial to advance controlled delivery systems for drugs and catalysts. Lyotropic liquid crystals (LLCs) have well-defined internal structures suitable to entrap small molecules and can be broken up into low-viscosity dispersions, aiding their application as delivery systems. In this work, we demonstrate the first example of light-responsive cubic LLC dispersions, or cubosomes, using photoswitchable amphiphiles to enable external control over the LLC structure and subsequent on-demand release of entrapped guest molecules. Azobenzene photosurfactants (AzoPS), containing a neutral tetraethylene glycol head group and azobenzene-alkyl tail, are combined (from 10-30 wt %) into monoolein-water systems to create LLC phases. Homogenization of the bulk LLC forms dispersions of particles, ∼200 nm in diameter with internal bicontinuous primitive cubic phases, as seen using 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 within the cubosomes isomerizes within seconds, which in turn leads to squeezing of the cubic lattice and a decrease in the lattice parameter. This squeeze mechanism was successfully harnessed to enable phototriggerable release of trapped Nile Red guest molecules from the cubosome structure in minutes. 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 that these systems may have huge potential for the next-generation of nanodelivery.

Förster Resonance Energy Transfer in Luminescent Solar Concentrators.

Luminescent solar concentrators (LSCs) are an emerging technology to collect and channel light from a large absorption area into a smaller one. They are a complementary technology for traditional solar photovoltaics (PV), particularly suitable for application in urban or indoor environments where their custom colors and form factors, and performance under diffuse light conditions may be advantageous. Förster resonance energy transfer (FRET) has emerged as a valuable approach to overcome some of the intrinsic limitations of conventional single lumophore LSCs, such as reabsorption or reduced quantum efficiency. This review outlines the potential of FRET to boost LSC performance, using highlights from the literature to illustrate the key criteria that must be considered when designing an FRET-LSC, including both the photophysical requirements of the FRET lumophores and their interaction with the host material. Based on these criteria, a list of design guidelines intended to aid researchers when they approach the design of a new FRET-LSC system is presented. By highlighting the unanswered questions in this field, the authors aim to demonstrate the potential of FRET-LSCs for both conventional solar-harvesting and emerging LSC-inspired technologies and hope to encourage participation from a diverse researcher base to address this exciting challenge.

Light-responsive self-assembly of a cationic azobenzene surfactant at high concentration.

The formation of high-concentration mesophases by a cationic azobenzene photosurfactant is described for the first time. Using a combination of polarised optical microscopy and small-angle X-ray scattering, optically anisotropic, self-assembled structures with long-range order are reported. The mesophases are disrupted or lost upon UV irradiation.

A single-component photorheological fluid with light-responsive viscosity.

Viscoelastic fluids whose rheological properties are tunable with light have the potential to deliver significant impact in fields relying on a change in flow behavior, such as in-use tuning of combined efficient heat-transfer and drag-reduction agents, microfluidic flow and controlled encapsulation and release. However, simple, single-component systems must be developed to allow integration with these applications. Here, we report a single-component viscoelastic fluid, capable of a dramatic light-sensitive rheological response, from a neutral azobenzene photosurfactant, 4-hexyl-4'butyloxymonotetraethylene glycol (C6AzoOC4E4) in water. From cryo-transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS) and rheology measurements, we observe that the photosurfactant forms an entangled network of wormlike micelles in water, with a high viscosity (28 Pa s) and viscoelastic behaviour. UV irradiation of the surfactant solution creates a less dense micellar network, with some vesicle formation. As a result, the solution viscosity is reduced by four orders of magnitude (to 1.2 × 10-3 Pa s). This process is reversible and the high and low viscosity states can be cycled several times, through alternating UV and blue light irradiation.

Probing the dynamic self-assembly behaviour of photoswitchable wormlike micelles in real-time.

Understanding the dynamic self-assembly behaviour of azobenzene photosurfactants (AzoPS) is crucial to advance their use in controlled release applications such as drug delivery and micellar catalysis. Currently, their behaviour in the equilibrium cis- and trans-photostationary states is more widely understood than during the photoisomerisation process itself. Here, we investigate the time-dependent self-assembly of the different photoisomers of a model neutral AzoPS, tetraethylene glycol mono(4',4-octyloxy,octyl-azobenzene) (C8AzoOC8E4) using small-angle neutron scattering (SANS). We show that the incorporation of in situ UV-Vis absorption spectroscopy with SANS allows the scattering profile, and hence micelle shape, to be correlated with the extent of photoisomerisation in real-time. It was observed that C8AzoOC8E4 could switch between wormlike micelles (trans native state) and fractal aggregates (under UV light), with changes in the self-assembled structure arising concurrently with changes in the absorption spectrum. Wormlike micelles could be recovered within 60 seconds of blue light illumination. To the best of our knowledge, this is the first time the degree of AzoPS photoisomerisation has been tracked in situ through combined UV-Vis absorption spectroscopy-SANS measurements. This technique could be widely used to gain mechanistic and kinetic insights into light-dependent processes that are reliant on self-assembly.

Arterial switch with full-flow cardiopulmonary bypass and limited circulatory arrest: neurodevelopmental outcome.

OBJECTIVES: Neonatal cardiac surgery has been associated with unfavorable neurodevelopmental events. We investigated a patient cohort operated on predominantly with full-flow cardiopulmonary bypass (150 mL x kg(-1) x min(-1), alpha-stat, alpha-blockade, median arrest = 6 minutes, temperature of 22 degrees C) as the major support strategy for neonatal arterial switch operations (transposition of the great arteries and intact ventricular septum). METHODS: Seventy-four patients and "best-friend" control subjects were assessed 109 months (range, 48-166 months) postoperatively with general medical and neurologic evaluation, IQ testing, formal movement scores, and detailed parent-teacher behavioral-social reports. Fetal, neonatal, and perioperative data were collated. RESULTS: The prevalence of perioperative seizures was 6.8% (4/5 cases occurring preoperatively). The incidence of all perioperative neurologic abnormalities was 20%. Patients who had a neurologic event were (as a group) older at the time of operation and had a lower arterial blood pH before the operation. Selected perioperative factors (not related directly to cardiopulmonary bypass variables) predicted early (before discharge) neurologic outcome in a multivariate model. At late assessment, patients were more likely than control subjects to have a mild neurologic abnormality (P = 0.002). Full-scale IQ scores (Wechsler Preschool and Primary Scale of Intelligence and Wechsler Intelligence Scale for Children-Third Edition) were higher in control subjects (101.9 [SD = 13] vs 108.6 [SD = 12], P =.0007), with both groups having scores greater than the population-based test means. Full-scale IQ scores related most significantly to years of paternal education (beta = 1.51, P =.0078) but were also influenced by perioperative neurologic abnormalities, birth weight, and circulatory arrest time. Patients had higher motor impairment scores (Movement Assessment Battery) than control subjects (P =.0004). Parents (Achenbach Child Development Checklist) assigned higher total social-behavioral competence scores to control subjects (P =.05). Teachers (Achenbach Teacher Report Form) suggested that patients were more likely to be perceived as having various speech and expressive language problems, as well as minor behavioral problems. CONCLUSION: With the perioperative strategies used, not all survivors can be considered (neurodevelopmentally) normal at late follow-up, although the risk of important impairment is low. Perioperative events might have long-term prognostic value. On the basis of this study and published data regarding other strategies, continued application of full-flow cardiopulmonary bypass is justified, with the proviso that further investigation is required.