Molecular and Nanoscale Physics

Lipid Membranes

Membrane proteins are key components of the plasma membrane, and are responsible for the control of chemical ionic gradients, for metabolite and nutrient transfer and for signal transduction between the interiors of cells with their external environment.  30% of the genes in the human genome code for membrane proteins1. Furthermore, many of the FDA-approved drugs target such proteins2. However, the structure-function relationships of these are notably sparse due to difficulties in their purification and handling outside of their membranous environment. Methods that permit the manipulation of membrane components such as lipids or membrane proteins, whilst still in the membrane, would have widespread application for the separation, purification, and eventual structure-function determination3.  Here we show that the use of asymmetrically patterned supported lipid bilayers in combination with AC electric fields, applied in the plane of the membrane, can lead to efficient manipulation of mobile charged components. We demonstrate the concentration and trapping of such components through the use of a “nested trap”, and show that this method is capable of yielding around a 15-fold increase in the average concentration in a well-defined region.  Upon removal of the field, material is “trapped” in this region for several hours due to topographically restricted diffusion.  Our results indicate that this method can be used for manipulating, separating, concentrating and trapping charged membrane components whilst still within their membranous environment.  The exact function of these systems may be tuned by means of carefully designed patterned geometries.  We anticipate that this could have widespread application for the manipulation and study of membrane proteins.


Lipid Before
Lipid After

Microfluidics and Microbubbles

Leeds Microbubble Consortium

Targeted, triggered, therapeutic release represents the future for drug delivery in a world where treatment becomes personalised.

The area of targeted drug delivery in which drugs are delivered utilising a specialised carrier directly to the cancerous tumour via immuno-recognition has gained much interest in recent years. Such an approach reduces the side effects of systemic injection and also provides a localised, high concentration treatment directly to the cancer.

At Leeds University we are developing therapeutic microbubbles that double as both agents for contrast enhanced ultrasound imaging (CEUS) and drug delivery vehicles that are targeted to specific cancer cell receptors. Ultimately a large amplitude sound wave will be used to destroy the bubbles and trigger release of the drug at the targeted tumour. Theranostic microbubbles are a simple and versatile drug delivery technique that could potentially improve cancer treatment, both in terms of patient experience and overall drug efficiency. Importantly, they offer new ways of delivery hydrophobic drugswhich have traditionally been difficult to deliver efficiently. Conventionally, MB contrast agents are prepared by the mechanical agitation or shaking of a vial of aqueous media containing a surfactant and a headspace filled with the gas intended for the core of the microbubble. Whilst this approach is undoubtedly simple, robust and produces the desired MB concentration of 10^10 bubbles per mL, it is an inflexible approach with little control over the MB size or functionality. In order to produce therapeutic microbubbles more control is needed in the formulation of the MBs- to provide attachment of the drug payloads (as liposomes, polymersomes, etc) and targeting agents such as antibodies and aptamers. One approach is the use of microfluidics to form MB populations. Microfluidic devices comprise a network of micron-sized channels in glass or polymeric substrates through which small volumes of fluids and/or gases are manipulated. Such an approach allows for the precise control over the formation of MBs and the power to introduce sequential addition of the payload and targeting layers to the MB surface. Microfluidics provides much greater control over MB size. At Leeds we have developed a new method for microfluidic MB production that forms a micro-spray of bubbles through a nozzle this allowed us to increase the bubble concentrations from 10^7 bubbles per mL up to 10^9 bubbles per mL, with an average bubble size of 2 µm.

At Leeds we have developed optimal MB lifetimes with ranges now exceeding those of commercial ultrasound contrast agents. Whilst the encapsulation of drugs into liposomes and their attachment to the MB surface is a convenient way of delivering hydrophilic drugs. There are a large number of difficult to deliver drugs that cannot be administered because of their hydrophobicity. We are currently developing and optimising our microfluidic devices to address these problems by producing MBs coated with a layer of lipid coated oil nanodroplets (LONDS) or by the intercalation of an oil layer at the lipid-gas boundary.

On-going work at Leeds is investigating the acoustic properties of our MBs, in order to optimise US signal, destruction pulses and sonoporation effects. Alongside this, the MBs performance as targeted drug delivery vehicles is being studied in vitro and in vivo models. The project is pushing towards producing a robust and highly versatile drug delivery vehicle that is capable of targeted and controlled release of drugs for a more patient friendly, effective cancer treatment.