Trypanosoma brucei moving in microchannels and through constrictions

Trypanosoma brucei (T. brucei), a single-celled parasite and natural microswimmer, is responsible for fatal sleeping sickness in infected mammals, including humans. Understanding how T. brucei interacts with fluid environments and navigates through confining spaces is crucial not only for medical and clinical applications but also for a fundamental understanding of how life organizes in a confined microscopic world. Using a hybrid multi-particle collision dynamics (MPCD)–molecular dynamics approach, we present our investigations on the locomotion of an in silico T. brucei in three types of fluid environments: bulk fluid, straight cylindrical microchannels, and microchannels with constrictions. We observe that the helical swimming trajectory of the in silico T. brucei becomes rectified in straight cylindrical channels compared to bulk fluid. The swimming speed for different channel widths is governed by the diameter of the helical trajectory. The speed first slightly increases as the channel narrows and then decreases when the helix diameter is compressed. An optimal swimming speed is achieved, when the channel width is approximately twice the bulk helix diameter. It results from an interplay of the trypanosome’s hydrodynamic interactions with the cylindrical channel walls and the high deformability of the parasite. In microchannels with constrictions, the motions of the anterior and posterior ends, the end-to-end distance, and the log-rolling motion of the cell body are characterized and show salient differences compared to the straight-channel case. Depending on the constriction length and width, we observe characteristic slip, stuck, and stuck-slip motions of the model T. brucei within the constriction. Our findings may provide some mechanical insights into how T. brucei moves through blood vessels and tissues, and across the blood-brain barrier.