How much thrust is specifically required for a sperm to "penetrate" the egg membrane before combining with the egg to form a fertilized egg? How can we simulate the deformation-based soft body drive like sperm? Can we manufacture a pair of tweezers that can open and close precisely to manipulate cells such as sperm at will?
To accurately answer the above questions, a large deformation spring with a sensitivity of piconewtons (pN, 10^-12N) is needed. A recent scientific advancement has made this high-precision measurement possible.
Xu Haifeng, a researcher at the Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, and his team, along with collaborators, have constructed a 4D nano-printing technology that includes elastic modulus programming, creating micron robots with a sensitivity of 500 femtonewtons (0.5pN), equivalent to one-thousandth of a cell's gravity.
Moreover, the elasticity and magnetization distribution can be precisely defined, with a response accuracy of up to 1 micrometer per piconewton. In more than 100 fatigue tests, the piconewton spring system can recover more than 99% of the large deformation, ensuring the stability of the work.
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"Our constructed 4D nano-printing technology for elastomers can process various flexible micro-devices with fine structures, such as a visual piconewton-level spring force gauge, a wireless micro-tweezer with precisely controllable gripping force, and a purely magnetically controlled bionic soft micro-robot," said Xu Haifeng.Recently, a related paper titled "3D nanofabricated soft microrobots with super-compliant picoforce springs as onboard sensors and actuators" was published in Nature Nanotechnology [1].
Xu Haifeng, a research associate, is the first author and co-corresponding author of the paper. Dr. Mariana Medina-Mariana from the Leibniz Institute in Germany and Professor Oliver Schmidt from Chemnitz University of Technology in Germany are co-corresponding authors of the paper.
These "picoforce springs" can serve as an energy transfer mechanism for the customized construction of micrometer-scale soft robots. Specifically, after being freely programmed, they can act as actuators to convert the received kinetic energy into potential energy for storage. Then, the potential energy can be released on demand at the appropriate time.
The scale of the "picoforce springs" is similar to that of a single cell, and they integrate sensing and driving functions to perform tasks such as grasping and movement. This method of integrating soft springs into 3D nanomanufacturing can mass-produce soft micro-robots, achieving gentle interaction effects with sensitive targets such as cells and tissues.
It is worth noting that the "picoforce springs" belong to purely mechanically controlled tweezers. Their advantage lies in the ability to safely operate the controlled objects without changing the surrounding environment of the objects being controlled.Due to the exclusive involvement of magnetism throughout the process, not only can interference-free manipulation be achieved without being affected by factors such as pH value, temperature, and laser during cell manipulation tasks, but also the cell clamping force can be precisely adjusted.
Therefore, the "piconewton spring" has a wide range of applications in the field of micrometer-sized robotic systems such as micromanipulators, magnetic manipulators, and other cell-sized devices, providing a piconewton-level precise, bio-safe, and remotely controllable research platform for cell mechanics, cell screening, and transportation studies.
This research is expected to develop portable cell mechanics characterization instruments and automated cell manipulation equipment, providing effective support for cell biology research and minimally invasive surgical treatment.
Firstly, as a micromanipulator (microtweezers), it can perform interference-free multi-degree-of-freedom manipulation on targeted cells without relying on any stimuli that may interfere with the cells. For example, it can be applied in the biomedical field for precise cell manipulation and single-cell sorting.
Secondly, as a spring micromanipulator, it can accurately measure the mechanical performance related to cells in real-time and in situ. For example, it can measure the propulsive force (swimming power) of micro-nano robots such as sperm, chemical motors, and magnetically controlled helices.Once again, precise measurement of static forces at the piconewton level is conducted, including characterization of the mechanical properties of cells, the elastic modulus of cells, and the migration force of cells, etc.
On the other hand, researchers have also applied verification using two types of micro-robots, micro-penguins and micro-sea turtles. Experiments have shown that micro-penguins and micro-sea turtles can achieve free deformation and soft actuation under the condition of being remotely controlled by a magnetic field alone.
Before this, due to rigidity limitations, micro-nano robots could only control simple movements such as forward, backward, and rotation. If they are to achieve more complex movements, it is necessary to add springs to make elastic bodies at a smaller size (around 10 microns).
However, the lithography of elastic bodies itself is an extremely complex issue, and the 4D lithography technology of elastic bodies is the foundation of the entire research. Xu Haifeng and others have constructed a technology that can achieve nano-precision and customized arbitrary shape 3D printing of micro-elastic robots. That is to say, this technology adds an elastic dimension on the basis of 3D printing to achieve the effect of 4D printing.
Xu Haifeng pointed out that according to literature reports, the human body is safe under a magnetic field of 8 Tesla, and our piconewton spring magnetic field strength is 10 millitesla. On the basis of ensuring strong tissue penetration ability, it is absolutely safe for all living organisms.Xu Haifeng completed both his undergraduate and master's degrees at the School of Pharmacy, Peking University. He then pursued his doctoral research at the Leibniz Institute for Solid State and Materials Research in Germany, focusing on the open design of biohybrid robots and their medical applications under the guidance of Oliver Schmidt, a member of the German Academy of Sciences and Engineering. He graduated with the highest honor, summa cum laude.
He continued his postdoctoral research at the same institute, focusing on 3D nanophotonic devices for cell sensing and transport. In August 2020, he joined the Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, as an associate researcher at the Institute of Biomedical and Health Engineering.
Previously, he designed the world's first elastic mechanism-triggered anti-cancer sperm robot, which is an elastic mechanism similar to a quadruped robot. This type of micro-robot can "grab" sperm and accurately deliver them to cancer cells, serving as a new targeted drug delivery method for gynecological cancer treatment [2] (DeepTech reported: Sperm with guidance devices become a new method of targeted drug delivery, to be used in the treatment of gynecological cancer).
Of course, there are still some issues to be resolved in this new research, such as the robot system not yet fully automated, that is, after perceiving the external environment, it can achieve autonomous control response. Based on this, the research team plans to continue in-depth research on automated control cell manipulation platforms and automated control of extremely low biological force measurement platforms in the future.