Research On Active Anti-bacterial Adhesion Based On Laplace Pressure Difference Drive To Realize Directional Transport Of Droplet

Harmful bacteria have caused great harm and loss to human society,and the economic burden caused by bacterial adhesion leading to human infection and material corrosion failure is incalculable.Most of the measures taken by researchers to prevent biofilm formation have focused on the initial phase when the interaction with the surface is weak.One of the common methods used by many scientists is to impart a specific structure to the surface by physical and chemical means and then modify the surface of the material with hydrophilic substances so that the material has a very high affinity for water and forms a hydrated layer to keep out bacteria.Similarly,the method of reducing bacterial adhesion by using surface microstructures such as tubular and columnar structures modified with low surface energy substances,so that the surface exhibits high water repellency and the droplets of bacteria cannot infiltrate the material surface through the air layer present in the microstructure,is also popular among researchers.Although both surfaces can provide some barrier to bacterial adhesion,they are limited by this passive defense,and when a bacterial droplet falls on the surface,the superhydrophilic surface cannot guide the droplet away from the surface,while the superhydrophobic surface requires the surface to be tilted to guide the droplet to fall from the surface by gravity,and both surfaces will adhere in the horizontal state as the contact time between the bacteria and the surface increases.In this study,we propose to achieve active anti-adhesion of bacteria on a superhydrophobic surface with a wedge-shaped structure by a self-actuated method of bacterial droplets,and then to achieve the removal of bacteria from a specified area by introducing sensors and micro-sampling systems in response to the release of silver nanoparticles（Ag NPs）antimicrobial agents and the photocatalytic antimicrobial deposition of copper nanoparticles at a fixed point.The main work is as follows:（1）Construction and characterization of droplet self-actuated surfaces:pure titanium plates were used as substrates to obtain wedge-shaped structures by laser lithography,and then Ti O₂ nanotube arrays（TNTs）were formed on the surface by anodic oxidation.Finally,spraying1H,1H,2H,2H-fluorodecyltrimethoxysiloxane（PFDTMS）reduces the surface energy of the material to make it superhydrophobic.The extremely low adhesion and the Laplace pressure imbalance generated by the structure allow the self-actuation of liquid droplets on the wedge.The droplet self-actuated star-shaped smart response platform（DSSRP）and the droplet self-actuated star-shaped photocatalytic antibacterial platform（DSSPP）were constructed based on the combination of sensor and micro-sampling system with both fixed-point deposition of copper nanoparticles for photocatalytic antibacterial purposes.The generation of anatase phase Ti O₂ tubes on the surface and the successful grafting and uniform distribution of PFDTMS on the surface as well as the successful loading of copper nanoparticles were demonstrated by the analysis of the surface SEM,XRD and XPS results.（2）Drive mechanism and drive performance optimization of droplet self-actuated surface:the mechanism of droplet self-actuated directional transport was explained by the force analysis of droplet on the wedge-shaped surface;the motion of droplet on the droplet self-actuated surface was recorded by a high-speed camera and it was found that the droplet could move the farthest distance at the wedge opening angle of 6°and the average speed of the whole process was larger;the laser etching depth was 0.74 mm.The longest distance and average speed of droplet motion tended to be stable with the increase of spraying volume of PFDTMS,and the droplet could move the farthest distance with the spraying volume of 1.0 mg?cm^-2;the larger the droplet,the farther the droplet could move,and the 50μL droplet moved the farthest in the test range;the finite element simulation showed some details of droplet motion and was consistent with the actual motion process.The finite element simulation shows some details of the droplet motion and matches the actual motion.（3）Response performance study of droplet self-actuated star-shaped smart response platform（DSSRP）:The self-actuated and response effects of droplets of different droplet volumes from 0-300μL were tested on the platform,and the results showed that the platform has a very wide droplet response range of 8-200μL;dynamic wettability tests on eight kinds of droplets such as H₂O and tea showed that the platform can realize self-driven and the response of many different droplets,and can be used as an open microfluidic device for microchemical reactions and synthesis.（4）Anti-bacterial adhesion and antimicrobial performance study of droplet self-actuated star-shaped intelligent response platform:a self-actuated dynamic anti-adhesion test of bacterial droplets falling on the surface showed that after about 1000 times of self-actuation,the bacterial droplets had very few bacteria adhered to the movement track,and the anti-bacterial adhesion rates of E.coli and S.aureus reached 99.68%and 99.57%;the bacteria were verified by SEM The results of static anti-adhesion test in the central area showed that the anti-bacterial adhesion rate reached 86.92%and 92.05%without the antimicrobial agent to kill the bacteria.The antibacterial study of silver nanoparticles revealed that the high concentration of Ag NPs achieved 99.999%and 99.998%against E.coli and S.aureus within 180 min.（5）Visible light catalytic bactericidal performance study of droplet self-actuated star-shaped photocatalytic antibacterial platform:the antibacterial results under different conditions showed that the visible light applied alone and the copper nanoparticles loaded alone had a certain promotion effect on the visible light bactericidal effect of Ti O₂ nanotubes,and the visible light applied after the loading of copper nanoparticles could make Ti O₂ nanotubes reach 100%antibacterial rate against both E.coli and S.aureus within 25 min.