Can you imagine that in the near future, doctors will be able to enter your blood vessels for “surgery”? The movie “magical journey” tells the story of five doctors’ miraculous experience of shrinking into the patient’s blood vessels, finding the bleeding point smoothly and finally saving lives. Although we can’t shrink the doctor into the body like a movie, the micro robot may be able to replace the doctor!
The following is a speech by Xu Tiantian, associate researcher of Shenzhen Institute of advanced technology, Chinese Academy of Sciences
As early as 1959, Mr. Feynman, the Nobel Laureate in physics, once said that he had a fantasy that if we could swallow a surgeon, many complicated operations could become very interesting and simple.
At that time, it was just an idea for him, hoping to leave it to us to realize.
Ten years later, in 1966, Americans made it into a movie.
1966, science fiction film: Fantastic Journey
The story is about a Soviet scientist who fled to the United States and died because his brain vessels were damaged by spies. Then you came up with a way to reduce the size of five doctors to one millionth of a million, and then inject them into the blood vessels of Soviet scientists.
The five surgeons went through a series of adventures in his body, and finally found the bleeding point and successfully saved the scientist’s life.
It sounds like movies with the characteristics of the cold war, but the movies of the cold war are all about the highest technology. It was at that time that the concept of micro doctors in the body was first popularized to the general public.
In fact, we can’t really make a surgeon smaller. We can only consider whether we can make some small robots to replace the smaller surgeons in our body.
To make such a tiny robot will face many challenges. The first is how to make it move in the body, how to make it move in the body according to the path I want, and how to adapt to the complex environment in the body.
This concept has been quiet until the beginning of the 21st century, when scientists completed the production of some micro robots. Maybe there is a big difference between micro robot and humanoid robot.
From the above figure, a micro robot is just a few particles, a spiral tube and a tail. How can it be called a robot?
In fact, robots have three most important elements: perception, movement and decision-making. It can sense the surrounding environment, perform some movements and make some decisions. As long as it meets these three elements, it can be called a robot.
For example, our familiar robot usually has two cameras as eyes to perceive the environment, arms and legs to perform some movement, and a central processing unit as its brain to make decisions.
So let’s see if micro robots have these three elements.
Move! To be a robot
First of all, let’s start from the most important point, how to make the micro robot move.
In fact, this is not easy, because in the micro world, many physical laws are different from those in the macro world.
In 1976, Nobel physicist Purcell put forward the so-called “scallop law”, that is, the reciprocating motion like scallop can not cause effective displacement in the micro world.
What do you mean? It’s the scallop that quickly opens its shell and then slowly closes it. But because of its inertia, when it opens quickly, it moves forward, and the scallop just moves forward.
However, in the micro world, its opening and closing motion can not make it move forward, because in the micro world, the inertial force in front of the viscous force is negligible.
It goes forward when it opens, but it comes back when it closes. It is this kind of reciprocating motion that can only make the micro objects move forward and backward in the micro environment, unable to move forward.
So how can we have efficient movement in the micro world?
We get some inspiration from nature.
One is Escherichia coli.
It has a head and a spiral tail that can rotate its body in liquid.
Just now I mentioned that in the micro world, viscous force plays a leading role in front of inertial force, which is equivalent to E. coli turning itself in a very sticky environment, just like we are forcing a screw to turn and walk.
According to this principle, we made the first kind of bionic mechanism human – spiral robot, let it think of a way to turn up and walk efficiently.
Flexible vibration of sperm
The second way is sperm flexible vibration, which has a very long tail, and then forms flexible vibration by patting its own tail.
In this way, we have created a second kind of bionic micro robot, which is to find a way to make it vibrate, drive its tail, and form an efficient movement.
Let’s look at the history of microrobots.
Development timeline of new micro robot system
At the beginning, scientists found that small screws could move in a viscous liquid. Later, with the development of micro manufacturing technology, micro robots became smaller and smaller, once hundreds of nanometers. In recent years, with the development of soft intelligent materials, we have made soft micro robots.
How to drive micro robot?
We can attach magnets to microrobots.
Under the action of gradient magnetic field, all objects with magnetic field will form tension. All magnetic objects in a uniform magnetic field, will be subject to rotational force, let it toward the direction of the magnetic field and its magnetic field in the same direction.
So how to generate a uniform magnetic field?
We usually use Helmholtz coils. That is to say, there are a pair of identical coils with the same number of ties and the same direction of current. Then its distance and radius are equal, so that it can produce a uniform magnetic field in its axial direction.
A pair of coils can produce a magnetic field in one direction. If we design a three-dimensional orthogonal three pairs of coils, we will have three bases, and then we can produce a magnetic field with any direction in space.
By editing the given current in the coil, we can edit some rotating magnetic field, vibrating magnetic field, conical moving magnetic field, and we can edit the magnetic field.
Then we put the micro robot in the middle of three pairs of coils, and let it be driven by the magnetic field to make some vibration or rotation in response to the magnetic field. In this way, the robot can move.
Then, two external cameras are used to sense its orientation and positioning, and the host computer acts as its brain. As a decision-making, through the whole complex system, a micro robot is formed.
This is my soft film micro robot.
Take a silica gel and mix some magnetic particles in it. Before making it, put it in a strong magnetic field and make a specific magnetization direction. In this way, it will form a spiral motion in a rotating magnetic field.
If we let the micro robot listen to the command, we design a path tracking method.
What is path following?
In short, it can be compared to autopilot. I have a planned path, and I want the robot to follow this path.
Of course, micro robots are more difficult than autonomous driving, because autonomous driving on the road is a two-dimensional motion, and micro robots walking in the body is a three-dimensional motion, which is equivalent to three-dimensional autonomous driving.
We use the path differentiation method to divide any given path into segments, and let it find its nearest segment at each point to control its direction.
After that, we are not satisfied with a spiral movement of the soft film. We want it to have a variety of movements.
For example, if you add flexible vibration, you can make it crawl on the ground in the vibration field; then you add a horizontal vibration field to it, you can make it swim like a water snake; then you give it a rotating field, you can make it roll on the ground like a wheel; and then there is spiral motion.
Climb, swim, roll, fly, everything
In fact, the environment inside the human body is very complex, and various movements can be suitable for different “terrain”.
For example, there is a very narrow and flat gap that you need to climb through; if there is a very narrow passage, you need to swim across; if there is a slope that needs to go up the steps, you need to make it roll up like a wheel; if there is a very high obstacle, you can use the screw type to fly like a kite.
One part is that it goes up the steps like a wheel, and then it hits a high platform, and it flies like a kite; the other part is through the narrow horizontal and horizontal gaps.
Then I made a small strip of membrane robot into a cross shape. When it was rolled up, the cross shape was like the bucket of an excavator, which could carry some things.
We simply did the experiment of moving objects, moving three small balls from their initial position to their final position. It can also do some micro assembly and screening of objects.
For example, in biological research, some cells are often selected. We use probes to select cells under a magnifying glass. It takes both hands and eyes, and there are not many. The micro robot can automate the work and greatly improve the efficiency and repeatability.
Back to the medical application, the micro robot can be used as a drug carrier, directly carrying the drug in the human body, and deliver the drug to the place it needs, that is, targeted treatment; it can be used as a carrier of surgery, to explore and sample the place where the human body equipment can not go, and collect the samples that the doctor wants; it can also be directly used as a performer of surgery, for example, in the blood vessels, to collect the blood samples Thrombolysis broken, and then brought out, can directly solve the problem of thrombosis.
As far as I know, there is no laboratory in the world that really does it in vivo. In fact, it is still in such a tentative stage.
But I have discussed with many doctors. They are very excited when they hear about the micro robot. They think that it can really change some medical methods.
For example, an ophthalmologist said that there are some diseases that can’t be cured fundamentally. Such as retinal artery embolism, now some micro plastic projects, injection of hyaluronic acid into the face, if the formation of thrombosis, accidentally to the retina, is very dangerous.
If it blocks a small blood vessel, you can’t see that area, but if it blocks a large blood vessel in the retina, you may be blind in the whole eye.
However, now doctors have no way to treat the retinal artery embolism. They can only inject some vasodilator drugs locally. Maybe you are lucky that the thrombus rushes to other unimportant positions. If you are not lucky, you may be blind forever.
With microrobots, we can inject microrobots near the blockage.
It can automatically find the site of vascular embolism, use the thrombolytic drugs to remove the embolism, and then bring out the embolism, so that the disease can be completely cured.
We are looking forward to this day earlier.