Light-responsive Pickering emulsions based on azobenzene-modified particles

Photopharmacology and photoresponsive drug delivery

Light serves as an excellent external stimulus due to its high spatial and temporal resolution. The use of light to regulate biological processes has evolved into a vibrant field over the past decade. Employing light on chemical substances such as bioactive molecules and drug delivery systems offers a promising therapeutic approach to achieve precise control over biological processes. In this review, we provide an overview of the advancements in optochemical technologies for controlling bioactive molecules (photopharmacology) and drug delivery systems (photoresponsive drug delivery), with an emphasis on their relationship and biomedical applications. Gaining a deeper understanding of the underlying mechanisms and emerging research will facilitate the development of optochemically controlled bioactive molecules and photoresponsive drug delivery systems, further enhancing light technologies in biomedical applications.

Computer vision for high-throughput analysis of pickering emulsions

The quanitative analysis of solid-particle stabilized emulsions, known as Pickering emulsions, is crucial for their application in food, cosmetics, and pharmaceuticals. However, size analysis of these emulsion droplets, with diameters ranging from 5 to 500 μm, is challenging due to their non-uniform spatial and polydisperse size-distribution. Here, we investigate the application of the circle-Hough transform (CHT), a well-established computer-vision technique characterised by its ability to detect circular features in noisy images, for the seldom explored quantitative assessment of droplet size from optical microscopy images. This is particularly relevant to images where emulsions are captured in a single 2D focal plane. To implement the CHT with optical images, we have developed an open-source software application ("Hough-Scan"), which incorporates a user-friendly graphical interface for ease of use, and a tiling algorithm allowing localised regions of circles to be processed in parallel and improving computational efficiency. Using Hough-Scan, we demonstrate that the CHT has superior precision, recall and accuracy for the identification of Pickering emulsion droplets and determination of their size, compared to both manual identification and established computer vision methods. Our study demonstrates that CHT implementation using Hough-Scan can significantly increase the ease of image analysis for a diverse range of Pickering emulsion systems of varying spatial and size distribution, as well as visual artefacts common to example microscopy images.

Photo-responsive Pickering emulsions triggered by in-situ pH modulation using a photoacid generator

HYPOTHESIS

Pickering emulsions that respond to changes in pH by the addition of acid or alkali have been extensively studied, but the development of photo-responsive Pickering emulsions has been more challenging. This study attempts to demonstrate a novel approach to achieve photo-responsiveness in Pickering emulsions by incorporating a photoacid generator (PAG) into the oil phase. Upon UV irradiation, the PAG is expected to release protons (H+), which can then regulate the pH of the emulsion system and control its stability.

EXPERIMENTS

Amphiphilic colloidal particles obtained by modifying silica particles with poly (2-(dimethylamino)ethyl methacrylate) (SiO2-PDMAEMA) are used to stabilize the Pickering emulsions. The protonation and deprotonation of the SiO2-PDMAEMA particles at different pH values allow for the tuning of emulsion stability. By introducing the PAG into the stable Pickering emulsion system and applying UV irradiation to trigger the in-situ release of H+, the pH of the emulsion is systematically decreased, and the corresponding changes in emulsion stability are investigated.

FINDINGS

The results show that UV irradiation alone cannot induce emulsion instability. However, when PAG is added to the oil phase, the Pickering emulsions exhibit a significant decrease in pH under UV irradiation, ultimately leading to emulsion destabilization and phase separation. At a UV intensity of 20 mW/cm2 for 2 min, the H+ release from the PAG significantly lower the emulsion's pH, causing the SiO2-PDMAEMA particles to detach from the oil-water interface and resulting in emulsion instability. Higher concentrations of SiO2-PDMAEMA particles in the emulsion require more PAG to induce instability, as confirm by confocal laser scanning microscopy (CLSM) image. This study presents a versatile approach to develop photo-responsive Pickering emulsions which can have potential applications in areas such as drug delivery, cosmetics, and responsive materials.

Controllable Regulation of Diesel Oil-in-Water Pickering Emulsion Stability by Multiresponsive Recyclable Magnetic Polymer Brush Microvessels

To ensure safety and efficiency in the production and transportation of fuel oil, there is an urgent demand to develop intelligent emulsifiers to deal with this challenge. Fe3O4@PDA-P(NIPAM-b-MAA-b-LMA) (MNPDNML) microspheres were prepared by modifying polydopamine and the triblock polymer brush P(NIPAM-b-MAA-b-LMA) on the surface of Fe3O4 nanoparticles via oxidative autopolymerization and SI-RAFT polymerization. Therefore, the MNPDNML microspheres exhibited sensitive stimulus-responsive behavior to pH, temperature, near-infrared (NIR) laser radiation, and magnetic fields. The stability state of the emulsion could be modulated by changing pH, temperature, magnetic field, and NIR radiation, and the reversible switching of emulsification/breaking behavior could be reached at least 10 times. This "intelligent emulsifier" exhibited high emulsification efficiency, long-term stability, and on-demand emulsification/breaking properties. It was notable that MNPDNML microspheres showed excellent emulsification ability for olive oil, kerosene, gasoline, and crude oil, which allowed the material to be widely used in the controlled transportation and separation of fuel oil.

Light-induced destabilisation of oil-in-water emulsions using light-active bolaform surfactants

External stimuli-induced destabilisation of oil-in-water emulsions is of both fundamental and technological importance. In this work we synthesize light-active bolaform-type surfactants (LABSs) and show the preparation of decane-in-water emulsions over a range of surfactant and salt concentrations. Under ultraviolet (UV) illumination, LABSs undergo trans to cis isomerization affecting their interfacial activity. Therefore when stable emulsions stabilized by LABSs are exposed to UV light, they undergo partial destabilization. To induce interfacial flow, a small amount of volatile solvent (methanol, ethanol, tetrahydrofuran, etc.) is added at the emulsification stage and in this case complete phase separation is observed. This study demonstrates a facile route to induce destabilization of surfactant-stabilized emulsions using benign solvents and minimal use of energy (UV light) and this method could be of importance in wastewater treatment, enhanced oil recovery, protein separation, etc. where emulsion destabilization is desired.