Catalytic Janus particles have shown considerable potential for use in biomedical applications. Due to fuel requirements and specialized surrounding fluid properties necessary for the propulsion of these particles, they are not always viable for in vivo applications.

Authors MinJun Kim, Louis Rogowski and Xiao Zhang focused on the development of multimodal-actuated microscale robots that can be used in minimally invasive surgical procedures and targeted drug delivery.

The unique surface chemistry of Janus particles, which consists of two materially different hemispheres, allows diverse interactions and responses to stimuli from the surrounding fluid. Catalytic Janus particles rely on chemical decomposition as their method of propulsion.

Bacterial flagella harvested from Salmonella typhimurium were attached to one hemisphere of a Janus particle. The result was a hybrid microrobot that can propel using either catalytic propulsion generated from chemical decomposition or swimming propulsion induced by remotely controlled rotating magnetic fields.

In addition, these multimodal microrobots, called flagellated Janus particles, can move through different fluid environments. The hybridized particles exhibited reliable velocity responses and directional control in Newtonian and non-Newtonian fluids.

“Both propulsion mechanisms can be used interchangeably allowing different options depending on the fluid environment,” said Kim.

Future studies will focus on optimizing the performance of these microrobots through simulated medical tasks in more complicated fluids.

“We will also investigate nonvisual feedback control and explore different combinations of hemispheres, including gold coatings that can create thermal gradients through laser excitation,” said Kim.

Source: “Flagellated janus particles for multimodal actuation and transport,” by MinJun Kim, Louis William Rogowski, Xiao Zhang, Jiannan Tang, and Micah L. Oxner, Biomicrofluidics (2021). The article can be accessed at