Abstract
With the advent of small-scale robotics, several exciting new applications like Targeted Drug Delivery, single cell manipulation and so forth, are being discussed. However, some challenges remain to be overcome before any such technology becomes medically usable; among which propulsion and biocompatibility are the main challenges. Propulsion at micro-scale where the Reynolds number is very low is difficult. To overcome this, nature has developed flagella which have evolved over millions of years to work as a micromotor. Among the microscopic cells that exhibit this mode of propulsion, sperm cells are considered to be fast paced. Here, we give a brief review of the state-of-the-art of Spermbots—a new class of microrobots created by coupling sperm cells to mechanical loads. Spermbots utilize the flagellar movement of the sperm cells for propulsion and as such do not require any toxic fuel in their environment. They are also naturally biocompatible and show considerable speed of motion thereby giving us an option to overcome the two challenges of propulsion and biocompatibility. The coupling mechanisms of physical load to the sperm cells are discussed along with the advantages and challenges associated with the spermbot. A few most promising applications of spermbots are also discussed in detail. A brief discussion of the future outlook of this extremely promising category of microrobots is given at the end.
Highlights
Nature becomes an excellent teacher when we seek solutions to complex problems that cannot be solved using contemporary engineering principles [1]
The main weakness is the low sperm cell/load coupling efficiency, the loss of actuation speed of spermbots compared to free sperm cells and the imaging and tracking techniques
An example of advances to overcome some of these challenges is the Simple Periodic ARray for Trapping and isolation (SPARTAN) [104] (Figure 7), a microfluidic sperm-sorting device
Summary
Nature becomes an excellent teacher when we seek solutions to complex problems that cannot be solved using contemporary engineering principles [1]. Any drug-delivery microrobots need to be powered and operated in a physiologically compatible manner Biological cells such as bacteria have inbuilt stimuli responsive systems against low oxygen (hypoxia), temperature (thermotaxis), magnetic field (magnetotaxis), pH (chemotaxis), glucose (glucotaxis), whereas microalgae show phototaxis and so forth [39]. Our lab introduced a bacteria-driven microswimmer lately that combines the sensing capabilities of bacteria for active locomotion with the desirable encapsulation This biohybrid microsystem shows mammalian cell like viscoelastic properties of a soft double-micelle microemulsion for active transport and delivery of cargo (e.g., imaging agents, genes and drugs) to live macrophages and cancer cells [9,41]. Effects of long-term biotransformation of magnetic nanoparticles in the living tissue is being studied [49,50]
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