There is a close relationship between materials and electricity. For example, based on the phenomenon of frictional electrification, a friction nano-generator that converts mechanical energy into electrical energy can be successfully prepared by selecting appropriate materials and circuit designs. When an electric field is applied to a material, It can affect many aspects of the material, such as changing the amount of charge and charge distribution of the material. By contrast, what is less known is that biological cells are also constantly undergoing intensive, delicate, active electrical activity. The production of energy necessary to maintain metabolism is achieved through the transfer of electrons between a series of proteins in the respiratory chain. The respiratory chain-associated proteins of eukaryotic cells are located in mitochondria, and the respiratory chain-related proteins of microorganisms such as bacteria Located on the cell membrane. Therefore, microorganisms are more sensitive to external electrical disturbances.
Many implanted materials can be physically modified or chemically modified on the surface to obtain a certain degree of antibacterial performance and thus more adaptable to the needs of implantation. The mechanism of action of these modifications can all fall on the 'electricity'. Such as in titanium-based materials The surface is implanted with silver, zinc and other nanoparticles by ion implantation. The titanium substrate can acquire antibacterial properties due to microscopic electrochemical reactions with the titanium substrate around silver and zinc nanoparticles. Another example is through chemical modification on the surface of the material. Modifying the positively charged polymer to change the charge on the surface of the material can also provide antibacterial properties for materials that do not have antibacterial activity. Furthermore, electric fields can be directly applied to the surface of nanomaterials, due to the small size of nanomaterials. A high-voltage electric field can be formed on the surface to cause electroporation of bacteria, and it can also cause sterilization.
Recently, the Beijing Institute of Nano-Energy and Systems, Chinese Academy of Sciences, discovered and confirmed in the experiment a new way of working with materials that can achieve antibacterial properties. The results of the study were published on May 24th in Nature-Communications. (Nature Communications) (DOI: 10.1038/s41467-018-04317-2).
This study found that the research originated from the research work of Li Zhou and Wang Zhonglin of the Nano Energy Institute in joint research on Nano Energy in 2017. Assistant research fellow Feng Hongqing was the first author. In that work, they will Collecting the wave energy of the frictional nano-generator output voltage, the current is connected to the carbon cloth electrode modified by the zinc oxide nanowires and nano-silver particles, and let the bacterial solution flow from the carbon cloth to the electric field. They detected the generator work. When the voltage and current are supplied, the bacteria that have passed through the system are killed. After the generator stops working and the system is no longer powered, they continue to detect the bacteria being killed for a period of time. They found a strange phenomenon. The phenomenon: During the period of 20 minutes after the generator stops supplying power, the carbon cloth electrode modified with zinc oxide and nano silver still has a strong killing effect on the bacteria flowing through them! If there is no power supply before the generator The same carbon cloth electrode modified with zinc oxide and nanosilver has no such strong bactericidal effect. Because the bacterial solution of this experimental system only flows through once Electrodes, electrochemical products that may occur during energization have flowed along with the previous solution, so the antibacterial properties after power off are not caused by the residual electrochemical products, but an electric field caused by the 'residual effects' of the material. The researchers found that the larger the capacitance of the electrode material (zinc oxide nanosilver double modification> zinc oxide single modification> original carbon cloth), the stronger the long-term antibacterial performance after this power failure. At the same time, the treatment after power off In the bacterial cell body, a strong ROS signal was detected.
On this basis, Feng Hongqing directed doctoral student Wang Min to carry out experimental work. The Li Zhou Group of Nano Energy Institute and the Zhu Jianhao Group of City University of Hong Kong worked closely together to conduct a systematic study of this phenomenon. In this study, They used a new antibacterial system and new capacitive electrode materials: from the original dynamic flow system to a static treatment system, a capacitive material based on titanium dioxide nanotubes was used to modify the carbon material to increase the capacitance of the material. Conventional DC and AC power sources charge the electrode material and detect the antibacterial properties of the electrode after power off. Consistent with Nano Energy's findings, they also detected in the new system that the electric field did give the original antibacterial Capacitance materials have new antibacterial properties, and the antibacterial capacity is positively related to the material capacitance. In addition to using the previous nanogenerators to power, the use of common DC, AC power supply can produce such effects; In the treated bacterial cells In vivo, the active oxygen signal was also detected. Based on this, they confirmed that charging can give the original non-antibacterial capacitance The antibacterial properties of the materials are a universal phenomenon. They named this phenomenon 'post-charging anti-bacterial property'. They also found that charging this operation against carbon-doped titanium dioxide The biocompatibility of the surface did not produce any adverse effects, and even promoted the adhesion and growth of osteoblasts on the substrate.
The discovery and confirmation of 'antibacterial properties after charging' provides a new method of imparting antibacterial properties to medical implant materials. For example: In addition to traditional physical and chemical surface modification methods, people simply charge The antibacterial properties of titanium dioxide on implanted orthopaedic materials can be reduced, thereby reducing the risk of postoperative infections and complications. This new method of 'antibacterial after charging' can also avoid the negative effects of traditional physical and chemical modification methods. Promote the adhesion and growth of osteoblasts on the surface of implants, which is very beneficial to the repair treatment after fracture. At the same time, the discovery of the phenomenon of 'antibacterial after charging' also makes people think about electricity, materials and biology. With the new understanding of interactions, it is hoped that more electric modification programs for materials will be designed and more uses will be developed. The deeper mechanism of this phenomenon is worth further exploration. This work is a case of Feng Qingqing and Wang Guomin. An author, Li Zhou and Zhu Jianhao, researcher of the Institute of Advanced Technology of the Chinese Academy of Sciences Wang Huaiyu is the author of the paper's side by side.
Fig. 1 When using nano-generators for electroporation water body sterilizing experiments, it was found that after the electric field was applied to the ZnO/Ag electrodes, the de-energized electrodes still had the ability to kill bacteria. The capacitance of the materials and the effect of sterilization after power off Positive correlation.
Fig. 2 Mechanism of 'antibacterial effect after charging'. The violent charge transfer between the positive electrode sheet and the bacteria after charging causes an ROS burst and causes the death of the bacteria. This may be caused by this phenomenon. the reason.
