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Berta Esteban-Fernández de Ávila et al. / Science Robotics, 2018
American researchers have created a medical microrobot from a gold particle covered with a hybrid membrane, which, in turn, is made of membranes of red blood cells and platelets. The robot is able to capture dangerous bacteria and the toxins they produce, and its movement in the body can be controlled by ultrasound, the authors in the journal Science Robotics.
Scientists are developing not only large robots, but also microscopic ones, intended also for work inside the human body. They can solve different tasks – for example, to perform point delivery of drugs or the capture of individual cells. Since it is very difficult to create artificial motors and sensors for such small robots, developers often equip them with elements from living organisms. For example, last year, German researchers turned a sperm into a hybrid drug delivery vehicle to a cancerous tumor.
A group of scientists from the University of California at San Diego, led by Joseph Wang, used a similar approach and created a micro robot using natural cell membranes to capture bacteria and toxins. The authors decided to target the robot to Gram-positive bacteria, in particular, to Staphylococcus aureus (Staphylococcus aureus). These bacteria release pore-forming toxins that create holes in the cell membranes that can lead to lysis.
Robot operation scheme
Researchers were able to create a robot that captures both the bacteria themselves and the toxins they produce. Since in the body gram-positive bacteria are often associated with platelets, and pore-forming toxins with erythrocytes, scientists decided to combine their properties, creating a hybrid membrane. They took a solution with erythrocytes and platelets, and mixed it with ultrasound, creating from them a single vesicle of two types of membranes. After this solution was mixed with elongated gold particles about two micrometers in length, the membranes spontaneously attached around the particles.
Staphylococcus aureus, captured by robot
The movement of the robot can be controlled by ultrasound – it moves in the opposite direction from the radiator. The authors showed the effectiveness of moving robots, comparing them with static ones. Scientists placed the robots in media containing a strain of Staphylococcus aureus and one of the groups was sonicated. Then they compared the number of caught bacteria with a fluorescent marker and saw that in the group of moving particles the intensity of the glow was 3.5 times higher. In addition, the researchers tested the effect of robots on the toxins of bacteria and found that the presence of such robots in the solution with red blood cells leads to a significantly lower level of hemolysis – by 5.5 percent.
Recently, German scientists have created another robot based on living cells. They attached a bacterium of Escherichia coli with flagella to the erythrocyte containing the drug, as well as superparamagnetic particles. As a result, the authors created a design in which the bacterium is responsible for moving forward, and the erythrocyte corrects the direction under the action of an external magnetic field.