Direct monitoring of calcium-triggered phase transitions in cubosomes using small-angle X-ray scattering combined with microfluidics

Abstract

This article introduces a simple microfluidic device that can be combined with synchrotron small‐angle X‐ray scattering (SAXS) for monitoring dynamic structural transitions. The microfluidic device is a thiol–ene‐based system equipped with 125 µm‐thick polystyrene windows, which are suitable for X‐ray experiments. The device was prepared by soft lithography using elastomeric molds followed by a simple UV‐initiated curing step to polymerize the chip material and simultaneously seal the device with the polystyrene windows. The microfluidic device was successfully used to explore the dynamics of the structural transitions of phytantriol/dioleoylphosphatidylglycerol‐based cubosomes on exposure to a buffer containing calcium ions. The resulting SAXS data were resolved in the time frame between 0.5 and 5.5 s, and a calcium‐triggered structural transition from an internal inverted‐type cubic phase of symmetry Im3m to an internal inverted‐type cubic phase of symmetry Pn3m was detected. The combination of microfluidics with X‐ray techniques opens the door to the investigation of early dynamic structural transitions, which is not possible with conventional techniques such as glass flow cells. The combination of microfluidics with X‐ray techniques can be used for investigating protein unfolding, for monitoring the formation of nanoparticles in real time, and for other biomedical and pharmaceutical investigations.

Cubosomes: The Next Generation of Smart Lipid Nanoparticles?

“…The DOPE containing cubic phases were not similarly affected although the transition to the hexagonal phase was shifted to higher mole fractions of DOPE. [98] In cubosome systems, salts have been exploited as a method to influence vesicle to cubosome transitions and reversibly form cubosomes, [99] study calcium triggered phase transitions, [100,101] in ionic surfactants incorporated into cubosomes and to vary ionic strength to induce phase transitions. [102] Whilst there are clearly many questions still to be addressed in the rational design of cubosomes, there is significant information and characterisation that already exists to enable the field to begin engineering tailor-made cubosomes for diverse applications.…”

Mask-Free Laser Lithography for Rapid and Low-Cost Microfluidic Device Fabrication

“…37 This presents huge advantages in terms of device fabrication over existing approaches, such as the use of silicon nitride windows on Kapton foils, 38,39 for example, or the use of polystyrene windows on chips cast from UV photocurable adhesives. 40 Our approach, therefore, represents the ideal for investigators wishing to adopt a rapid and low-cost microfluidic platform for SAX/WAX studies. These features highlight the huge potential of LL as a viable method for microfluidic device fabrication, particularly given how well it could lend itself to assembling multi-layered platforms.…”

Recent advances in X-ray compatible microfluidics for applications in soft materials and life sciences

“…It has been used for protein crystallization screening. 24,28,29 UV-curable adhesives used either alone, 30,31 in combination with silicon nitride windows, 26 or with polystyrene windows 32 have also been used for the fabrication of X-ray chips for X-ray studies. Both PDMS and UV-curable adhesives can be patterned via soft lithography, ensuring an easy replication of the chips.…”

“…Both PDMS and UV-curable adhesives can be patterned via soft lithography, ensuring an easy replication of the chips. In the case of offstoichiometry thiol-ene (OSTE), 32 the flexibility of the final cured material can be tuned by varying the composition of the reactants.…”