Active systems consist of self-propelled agents, e.g. motile organisms or synthetic particles, that convert energy into mechanical movement. Examples of active matter include bacterial suspensions, bird flocks, fish schools, or even human crowds [1]. The intrinsic out-of-equilibrium nature of active systems leads to complex behaviors that often cannot be captured by well-established thermodynamic description. These behaviors, however, open wide perspectives for practical uses of self-propelled particles. Recent theoretical efforts have been focused on the principles of dynamic self-organisation and flocking, principles of self-propulsion, and microwimming [2]. A number of exciting applications of self-propelled particles have been proposed including nanomedicine [3,4] and waste water treatment [5]. The focus of this workshop is on microscopic active particles and swarms, their design and applications.
Through billions of years of evolution, microorganisms mastered unique individual and collective swimming behaviors to thrive in complex fluid environments. It has proven difficult so far to mimic the versatility and performance of living microswimmers. However, the progress both in the theoretical understanding of the principles of swimming and in modern microfabrication technologies open new opportunities in designing artificial swimmers with pre-determined properties. For example, pre-programmed responses can be implemented in artificial swimmers such as using precise 3-D printing.

Investigation of active matter systems in the limit of low Reynolds number, i.e. microscopic systems, has shown growing interest [2]. This interest is stimulated by our growing capacity to quantify and control microorganisms, and to implement their abilities into synthetic systems. Microorganisms have been demonstrated to readily adapt to environmental changes. In particular, bacterial systems show a wide variety of complex behaviors, including spontaneous alignment in the presence of chemical gradients and altering rheological properties of the fluid [6]. Translating these complex behaviors to artificial systems is especially attractive for applications in fluid transport, small-scale mixing, and targeted cargo delivery but is hard due to intrinsic nanofabrication limitations.

Recent advances in self-propelled swimming particles have shown micro- and nanomotors are capable of mimicking complex features of bacterial systems. For instance, chemically-powered bimetallic nanorods randomly swim in their environments, in a manner somewhat akin to the swimming of microorganisms like E. coli [7]. In addition, the artificial swimmers are able to autonomously reorient themselves to swim against flows, thus replicating biological rheotaxis behavior [8,9]. However, so far these ”simple” artificial swimmers lack the swimming fidelity and multi-responsive behaviors of their biological counterparts; leaving much to be realized before using the micromotors for applications [10].

This workshop will highlight the most recent progress and discuss challenges in the fabrication, control, and functionalization of biological and synthetic microswimmers as well as in their computational modelling. A synergetic group of physicists, chemists, engineers, and mathematicians will be brought together for the exchange of ideas and the development of new cross-disciplinary collaborations. We plan to hold sessions on experimental challenges as well as on theoretical advances.