A Leaf-biomimetic Liquid Driven Micropump For Microfludic Chips

Based on the control of microscale liquid,many functions can be accomplished in a microfluidic chip with an area of several square centimeters,such as environment detection,drug screening and disease diagnosis.The advantages of microfluidic chip include small sample consumption,fast analysis,high throughput,small size,easy to carry around and so on.Liquid driven in a microfluidic chip is mainly relied on a micropump.The micropump driven by capillary-evaporation effect has numerous benefits such as needless of external energy input,easy integration,easy control,strong driving force and it has great potential in the development of fluid driven in a microchip.Caused by lack of research on specific work mechanism,the micropump mentioned above fails to realize nice structure optimization.Thus,relevant work mechanism research and structure design of micropump driven by capillary-evaporation effect are investigated in this thesis.The water transport mechanism in plants which was closely related to the capillary-evaporation effect was analyzed.A leaf-biomimetic structure based on leaf stomata transpiration and a liquid transport system driven by a leaf-biomimetic micropump were both proposed.Stomatal transpiration rate is approximately dozens of times faster than evaporation rate in the equal area of the free liquid surface.The negative pressure produced by stomatal transpiration induces long-distance water transport in the plant xylem.The leaf-biomimetic structure could simulate stomatal evaporation.It had an equivalent layer of leaf epidermal cells and an equivalent layer of leaf mesophyll cells.The main body of a leaf-biomimetic micropump was leaf-biomimetic structure.The flow rate of the leaf-biomimetic micropump was equivalent to the evaporation rate of leaf-biomimetic structure and both of them could be impacted by the micropore and environment.The core of liquid transport system proposed in this thesis was the leaf-biomimetic structure and the work load was a microchip.The evaporation characteristics of micropores in the leaf-biomimetic structure were studied.The relationship between evaporation rate of leaf-biomimetic structure and structure of micropores in the leaf epidermal cells equivalent layer was revealed,which provided theoretical support for the optimization design of micropores on micropumps.The flow rate of a leaf-biomimetic micropump was influenced by the shape,size and distribution of micropores.The simulation model of elliptical micropore evaporation rate was established.Vapor diffusion characteristics on micropore opening surface were obtained.The effects of micropore size and distribution on the micropore evaporation rate were quantitatively evaluated.A parameterized evaporation rate calculation model was established to study the influence of the sharp corner angle on the micropore evaporation rate.Leaf-biomimetic devices with micropore array were designed for the model validation and the experimental results were in agreement with the theoretical values:when the evaporation area of a single micropore and the distribution area of micropore arrays were both constant,the decrease of adjacent micropore space magnification or the decrease of sharp corner angle was able to accelerate the leaf-biomimetic structure evaporation rate and then the flow rate of the leaf-biomimetic device was increased.A leaf-biomimetic micropump with adjustable flow rate was developed based on the leaf-biomimetic structure and the effects of opening ratio of micropore array,environmental temperature and humidity on the flow rate of the micropump were studied.A SU-8 negative photoresist membrane with slit-shape micropore array was used as the equivalent layer of leaf epidermal cells and agarose gel was used as the equivalent layer of mesophyll cells.The adjacent micropore space magnification was 3 and the sharp corner angle of slit-shape micropore was 40°.The relationship between the opening ratio of micropore array and the flow rate of the micropump was studied and the experimental results showed that the former was approximately linear with the latter.A temperature and humidity control device was designed to study the influences of temperature and humidity on the flow rate of micropump with slit-shape micropores.The experimental results showed that the flow rate of the micropump decreased with the decrease of temperature or the increase of humidity and the flow rate responses of the micropump to the humidity were not obvious at the room temperature.The leaf-biomimetic micropump was proved to be practicable in the liquid driven of the microfluidic chip.A multilayer modular drug screening microfluidic chip was developed for the application of the micropump.The drug screening microfluidic chip was able to generate five concentrations of drug to its streamline-dependent cell culture chambers.Vertical perfusion mode was adopted in this microfluidic chip to reduce the flow shear stress to cells.With the liquid driven by a leaf-biomimetic micropump,experiment of HeLa cell apoptosis induced by Cisplatin was conducted.The results showed that there was a negative correlation between the survival rate of HeLa cells and the concentration of Cisplatin.It indicated that liquid driven in the drug screening microfluidic chip by the leaf-biomimetic micropump was effective.