A team of engineers and researchers have developed tiny “bio-hybrid” devices that are capable of swimming, in a way comparable to that of sperm and certain forms of bacteria. These self-propelled machines are the very first synthetic constructions that can independently move through the viscous fluids of biological environments.
The bio-hybrid machine was designed and compiled by engineers at the University of Illinois. The paper was published in the Journal Nature Communications, entitled A Self-Propelled Biohybrid Swimmer at Low Reynolds Number.
Led by Taher Saif, a University of Illinois Gutgsell Professor of mechanical science and engineering, the bio-bots were designed after single-celled organisms that possess long, tail-like appendages, called flagella. These biological structures are primarily used for the purposes of locomotion, but are also invaluable – in certain microorganisms – for sensory perception of their environment; this includes detection of temperature and various chemicals. An example of a eukaryote – a nucleus-containing cell – that boasts a flagellum is the sperm, which harnesses the structure to propel itself through the female reproductive tract.
The researchers manufactured the bio-bots by employing a flexible, silicon-based organic polymer (polydimethylsiloxane) to act as the machine’s filament. The team cultured cardiomyocyte cells (a.k.a heart cells) close to the point where the head fuses with the tail, which spans a length of just 1.5 millimeters. A fibronectin coating, extending along the surface of the bio-bot’s 454 micrometer-long head, was used to encourage attachment of cardiomyocyte cells and fibroblasts.
At first, the cardiomyocytes would begin contracting in a haphazard fashion, and coordinated locomotion was not possible. Eventually, however, the cells self-align to act in synchrony with one another. Once the cardiomyocytes start “beating” in synchrony, they transmit a wave down the tail that spurs its movement. The maximum speed that is achieved by an individual bio-bot is between five and 10 micrometers per second.
Saif, who also works for the Beckman Institute for Advanced Science and Technology, describes the ability of the cardiomyocyte cells to arrange themselves as a “remarkable” phenomenon. He also indicates that the precise means by which the cells communicate with one another, along the highly flexible polymer tail, is yet to be comprehensively explained. Saif goes on to briefly outline the basic principles behind the device’s construction:
“It’s the minimal amount of engineering – just a head and a wire… Then the cells come in, interact with the structure, and make it functional.”
The engineers then went on to build a series of two-tailed bio-bots, capable of swimming even faster – reaching speeds of around 80 micrometers per second. The attachment of multiple “bio-robotic flagella” could also have implications on the machine’s ability to effectively navigate. In looking to the future, the researchers believe they can fabricate bio-bots that offer advanced sensory capabilities, including detection of light and chemicals. This could, for example, be exploited for implementation in medical and environmental applications, using the sensory functions of bio-bot devices to guide them to a specific target.
Saif also questions whether, in the future, it could be possible to seed stem cells onto simple structures and use the resultant, differentiated cells to deliver drugs, target cancerous cells and perform less invasive surgery.
A professor of Biological and Mechanical Engineering at the Massachusetts Institute of Technology, Roger Kamm, expressed his enthusiasm for the bio-bot machines, conjecturing their potential applications to be tremendously diverse. Kamm explains the fascinating possibility of applying biological design to the production of swimming bio-bots:
“The most intriguing aspect of this work is that it demonstrates the capability to use computational modeling in conjunction with biological design to optimize performance, or design entirely different types of swimming bio-bots.”
By James Fenner