Dr Daniela Wilson showcases her groundbreaking development of self-assembling, autonomous active targeting nanomotor systems, for use in supramolecular approaches to chemotherapeutics Could you briefy outline your project’s aims and objectives? The aim of our group is to develop a truly active targeting system for chemotherapeutics. Years of hard synthetic work has been undertaken in an attempt to chemically build molecular motors, and yet this labour has yielded very little control in movement and few realistic applications. But why not let the ‘motor’ build itself? Using simple building blocks predisposed to self-associate, we let them ‘assemble’ in nanocontainers named polymersomes. We can place a motor in these vesicles and let them go, giving them the emergent function to overcome slow diffusion. This supramolecular approach to construct nanomotors, using self-assembled block- copolymers for the construction of the engine and catalysis as the driving force for autonomous movement, is unprecedented. Assembled nanomotors are functional, effective, real nanometre-sized transporters, which we believe will become the constituents of next-generation nanoengined delivery systems. Polymersomes are currently used to deliver sensitive drugs, but they lack the ability to target diseased organs with precision and speed. How can this ineffciency be overcome? The efficiency of targeted drug delivery is still limited largely due to the fact that these structures rely almost exclusively on passive accumulations, a result of the leaky vasculature formed by rapid tissue growth found in tumours. However, delivery carriers equipped with a locomotive motor system obtained by placing a catalytic active motor inside polymersomes may overcome the slow diffusion limitation of such delivery systems. We are achieving this by building on the tracking signals used by many biological systems. Bacteria, for example, are able to direct their movement according to the presence of chemicals in their environment. They use positive chemotaxis to move towards higher fuel concentrations or negative chemotaxis to move away from danger. In the same way, self-assembled vesicular nanomotors fuelled by chemicals in the environment may be able to control their directionality using chemotaxis to find sick cells. Stomatocytes have a unique shape that enhances nanomotor capabilities. How do these loaded cells function as miniature monopropellant rocket engines? The design of the nanomotor involves a nanocavity provided by the stomatocyte morphology, an active nanoparticle entrapped inside the structure and a controlled opening resembling – on the macroscopic scale – rocket engines where the ‘nozzle’ is the opening and the ‘rocket’ body is provided by the stomatocyte nanocavity. The fuel diffuses inside the structure and is decomposed by the active catalyts entrapped inside the structure. The fast discharge of jet gases (oxygen) through an outlet generates thrust by jet propulsion like rocket engines. You conducted a detailed analysis of nanomotor trajectories with nanoparticle tracking. What insight did you gain on the mechanism of movement? Nanoparticle tracking analysis was designed to look at the Brownian motion of particles and determine their size through the Stokes-Einstein equation. Knowing the particle size was very important to establish the size distribution of our self-assembled nanomotors, as well as entrapment of catalytic particles inside the bowl-shape structures. However, even more important for us was the ability to track the movement of the motors in the presence of the fuel. This provided definitive proof of directed motion resulting from the fast discharge of oxygen. We showed that indeed the catalyst had to be entrapped inside the structure to observe directed particle motion, while the mixture of active catalyst (nanoparticles) and empty stomatocytes did not show directed movement, only Brownian motion. What are your plans for the future, both in terms of disseminating your results and furthering your research? I will be presenting my group’s results at several conferences, some presented by my students and some as plenary lectures and invited talks. I have already been invited to talks at several events in 2014, including the opening of the Leibnitz Institute in Aachen and the Micro- Nanomachines symposium in July 2014. We are also interested in expanding the scope of self-assembled catalytic nanomotors towards biological fuels, which would allow the realisation of biologically compatible nanorockets circumnavigating the biological world. Further studies are in progress to demonstrate the ability of nanomotors to move in a gradient of fuel (chemotaxis) as well as developing nanomotors for which their structure and function can be manipulated by external fields and stimuli for sensory devices. Right on target WWW.RESEARCHMEDIA.EU 35 DR DANIELA WILSON