Construction Of Lipid Membrane Systems And Their Mimicking Of Cell Chemical Signal Transduction

Biomembranes include cell membranes and organelle membranes.They hold many vital functions such as energy and chemical transport,signal recognition and transduction,which are important in the survival,growth,self-reproduction,and differentiation of cells.Therefore,it is of great importance to understand the structure and functions of biomembrane to unveil the secret of life.While the biomebrane components are very complicated,researchers are devoted to constructing artificial membranes using bottom-up method to study the physiochemical properties of biomembranes and mimick the structure and functions of natural cells.In the field of artificial cell membranes,the construction of 2D lipid membrane array is meaningful for the high throughput study.In terms of 3D artificial membrane(giant unilamellar vesicle,GUV)arrays,there are a few methods to fabricate them and the typical GUV array is limited to homogeneous.Herein,the 2D lipid membrane array is prepared on indium tin oxide(ITO)surface with both transparency and excellent electrical conductivity.High impedance lipid membrane system is constructed on droplet-sollid support interface.The 3D membrane(GUV)arrays and GUV/cell arrays are generated in the acoustic field for the first time to investigate the chemical transport and chemical signal communication among giant unilamellar vesicles(GUVs)or between GUV and cancer cells.Lipid bilayer arrays with clear boarder and good quality were formed on ITO electrodes coated with a patterned trimethoxy(octadecyl)silane self-assembled monolayer(TODS-SAM).The TODS-SAM was patterned by deep UV irradiation(254 nm)through a mask.The intact TODS-SAM regions(nonirradiated)remained a hydrophobic surface for lipid monolayer formation;while the irradiated domains became hydrophilic for lipid bilayer formation.The lipid bilayer arrays were characterized by fluorescence microscopy,atomic force microscopy,and electrochemical techniques.The diffusion coefficients and mobile fractions of lipid bilayer and lipid monolayer were 0.86±0.05?m~2/s,87%and 0.59±0.07?m~2/s,80%respectively.The fluidity of the lipid bilayer was better than that of the lipid monolayer.The average penetration distance of two steps force curve and one step force curve were 3.9 nm and 1.9 nm,respectively,which matched very well with the thickness of DLPC bilayer and monolayer.The fitting patterned membrane capacitance(0.96±0.05?F/cm~2)is comparable with calculated one(1.135?F/cm~2).The roughness of ITO surface makes lipid mebrane with defects leading to the current leakage in electrochemical measurements.This system with low resistance is not suitable to study ion channels.To circumvent it,a droplet-solid interface lipid bilayer membrane(DSLM)with high impedance was developed by controlling the contact area between an aqueous droplet and electrode.The lipid bilayer size can be adjusted down to 30?m in radius.The droplet-solid interface lipid bilayer membranes were characterized by cyclic voltammetry(CV),electrochemical impedance spectroscopy(EIS),and fluorescence microscopy.The membrane resistance of the DPhyPC bilayer(R_m)is 26.3 G?.The normalized resistivity calculated from the membrane area is 15 M?cm~2,which is higher than those of reported lipid membrane systems.Melittin with different concentrations(0,1,2.5,5?mol/L)were used to study the interaction between melittin and lipid membrane.The membrane resistance values were determined to be 14.6,13.2,10.7,3.7 M?cm~2.The resistivity of the bilayer membrane decreased linearly with the increase of melittin concentrations in the membrane.To better mimic the real cell,giant unilamellar vesicle with similar lipid membrane components and size to real cell is used as synthetic cell model.One dimensional or two dimensional GUV arrays with controllable spacings(150.6,112.9,85.2?m)and various lattice arrangement(square,rectangle,triangle)were prepared by engineering the density difference between the interior of the GUV and the continuous media in an acoustic standing wave pressure field.Local mono-GUV array,local double-GUV array and multi-GUV array were generated by controlling the number of vesicles in the solution.Different types of heterogeneous GUV arrays containing two populations of GUV(red GUV and green GUV)were obtained by controlling the ratio of two different vesicles.By trapping GUVs containing horse radish peroxidase(HRP)and GUVs containing glucose oxidase(GOx)in the same node,resorufin formation by cascade enzyme reaction was realized inside the HRP-containing GUV.Acoustic standing waves were also used to fabricate micro-arrays consisting of clusters of HepG2 cells and GUV to investigate an enzyme-mediated signal transduction process for the localized killing of the cancer cells.