Poster Y13 - Erythrocyte-based achiral micromotors for localized therapeutic delivery

Introduction: Micromotors are microscopic devices that can convert local energy into directed propulsion, and they are used in applications such as drug delivery, diagnostics, and biosensing. The biocompatibility of micromotors used in drug delivery is crucial because they will come into direct contact with the endovascular environment. A common strategy to achieve biocompatibility is designing biohybrid micromotors made from inorganic synthetic particles and biological components. Erythrocytes (RBCs) are ideal carriers for drug delivery due to their deformability, long circulation time, and large loading capacity. In 2014, the first RBC micromotor was reported, created by encapsulating magnetic particles into RBCs and propelling them using magnetic and acoustic fields. In 2022, Hou et al. explored synthetic fabrication methods for RBC-coated biomimetic micromotors and actuated them with a rotating magnetic field, causing them to roll along surfaces. Here, we present a straightforward method to fabricate RBC micromotors using biotin-streptavidin specific interactions. These RBC micromotors can be propelled with a single rotating uniform magnetic field and exhibit two modes of motion: swimming and rolling. Additionally, we demonstrated the drug-loading capability of RBC micromotors and their ability to navigate through microfluidic channels, enhancing their therapeutic effectiveness.

Materials and

Methods: RBCs were separated from purchased bovine blood (Carolina biological Supply Company, #828574) and washed twice with PBS. RBCs were then treated with biotin (Thermo Scientific, #21338) and post incubation, biotinylated RBCs were separated into two batches. One batch was incubated with streptavidin. To assemble single-cell RBC micromotor, 1µL of biotinylated RBCs was mixed with 1µL of streptavidin-coated magnetic beads (0.21μm in diameter; Spherotech Inc., #SVM-025-5H) in 100µL of 1X PBS. To assemble two-cell or three-cell achiral micromotors biotinylated RBCs were mixed with magnetic beads, then streptavidin-coated RBCs were added to the RBC suspension, as shown in Figure 1.

Human breast cancer cells (MDA-MB-231) were seeded in the right-side reservoir of the designed microfluidic chamber (as Figure 2a) and incubated for 48 hours. Subsequently, RBCM, RBCM with Doxorubicin hydrochloride (DXR, Sigma #D1515) loaded, or DXR were injected into the left-side reservoir separately. A rotating magnetic field in the y-z plane was applied to orient and propel the rolling RBC achiral micromotors towards the right-side reservoir. The system was then incubated for 48 hours, followed by live dead staining to determine cell viability.

Results, Conclusions, and Discussions: Three types (Single-cell, two-cell and three-cell) of erythrocyte based achiral micromotors were fabricated through biotin and streptavidin specific binding, with attached magnetic beads. Driven by a single homogenous rotating magnetic field, all the micromotor configurations were able to perform both rolling near the substrate and swimming in the bulk suspension. The translational speed and propulsion efficiency of RBC achiral micromotors in PBS and bovine serum were investigated and it was observed that three-cell achiral micromotors have the highest propulsion efficiencies. Further, the hemocompatibility and in vitro biocompatibility of RBC achiral micromotors were proved by incubation with RBCs or HEK-293 cells (human embryo kidney cells). Doxorubicin was loaded in RBC achiral micromotors using hypotonic treatment method for tumor treatment assay. The RBC achiral micromotors were propelled through a microfluidic channel using rotating magnetic fields to demonstrate navigability in complex environments (as Figure 2a). Finally, RBC micromotors loaded with DXR were observed to be effective in tumor cell treatments (as Figure 2b). The fabrication and propulsion method reported in this experiment will assist in the development of future micromotor designs and controlled drug delivery and cancer cell treatment systems. In summary, our research shows that RBC achiral micromotors effectively load and deliver drugs to targeted cancer cell sites through magnetic field manipulation, facilitating efficient treatment.

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