Using nature as inspiration, scientists at the Indian Institute of Technology Madras and the Institute of Mathematical Sciences, in Chennai, India have created a design to rapidly move small particles through gels or fluids. Friction in fluid can impede movement, like trying to swim in molasses. The investigators used data on that kind of friction to inform the creation of a transport engine. They have published their work in The Journal of Chemical Physics.
"Microorganisms have developed specialized organelles, such as cilia and flagella, to overcome the challenges of, in the words of Nobel laureate [Edward] Purcell, 'life at a low Reynolds number,'" said Raj Kumar Manna, a graduate student in the Department of Physics at the Indian Institute of Technology Madras. "Recent experiments demonstrated that flagella-like 'beating' could be achieved in vitro, proving it's possible to obtain a periodic 'beating' motion without complex biological regulation." He said they were able to make a totally artificial microscopic transport system by fusing biologically independent regulation with "successful synthesis of self-propelling, inorganic particles.”
The investigators took advantage of computer simulation to research designs for what they would create in the laboratory. Manna credited mathematician George Stokes' work on the eponymous equations for slow viscous flow, done over a century ago for paving the way for their new developments. Physicist Marian Smoluchowski used Stokes’ data in his work, performed in the early 1900s, that computed the friction, termed hydrodynamic interaction, between spherical particles moving through a viscous fluid. "We applied these techniques to the new situation of swimming within a viscous fluid," said Manna. Get a look at their simulation in the following video.
The researchers have demonstrated that colloidal cargo can be moved using synthetic active filaments. "We've provided a design for a fully biocompatible motility engine that can be put to a wide variety of uses," Manna said. "Speed and efficiency aren't related within these systems," said Manna. "As an analogy, consider the energy spent by a 100-meter sprinter and a marathon runner. For a given budget of energy, it can be expended in a brief burst to achieve high speed, or more slowly to achieve long distances. This requires different design considerations, so our work provides a way of switching the behavior of our synthetic swimmer between these two modes."
These developments could aid in the creation of targeted drug delivery and insemination methods. The work is also applicable to therapeutic interventions in which defective motility in physiology is a hurdle.
"It's difficult to predict the timing for a computer design to be realized experimentally, and then go beyond clinical trials to medical use. But, if past development within this area is any guide, we expect some of these technologies to become feasible within a decade or so," said Manna, who also explained what is next for the research group. "We'd like to include increasing degrees of realism within our analysis to achieve an environment more akin to blood, look at geometries that are more like branched capillaries, explore designs for greater energy efficiency, and also collaborate more closely with experimentalists."