Patent Application: US-201614995334-A

Abstract:
a process for the large scale manufacturing of vertically standing hybrid nanometer - scale structures of different geometries , including fractal architecture made of flexible materials , on a flexible substrate including textiles is disclosed . the nanometer - scale structures increase the surface area of the substrate . the nanometer - scale structures may be coated with materials that are sensitive to various physical parameters or chemicals such as but not limited to temperature , humidity , pressure , atmospheric pressure , electromagnetic signals originating from biological or non - biological sources , volatile gases , and ph . the increased surface area achieved through the disclosed process is intended to improve the sensitivity of the sensors formed by coating of the nanometer - scale structure and substrate with a material which can be used to sense physical parameters and chemicals as listed previously . an embodiment with nanometer - scale structures on a textile substrate coated with a conductive , malleable and bio - compatible sensing material for use as a biopotential measurement electrode is provided .

Description:
free standing aligned nanostructures can be obtained on a textile electrode surface by using electrostatic and / or pneumatic assisted deposition . such deposition uses an electric field or pneumatic force to drive down millions of individual fibers that have a static charge on them in an environment of air , water , or plasma , the electric field , in particular , aligns the charge fibers vertically , and static charge ensures that they are apart from each other . the vertically aligned fibers or fibers aligned at a glancing angle are driven down on to a flexible surface , such as a textile or polymer substrate , pretreated with adhesive for the fibers to get planted . a schematic of this process is shown in fig1 . synthetic long chain polymers such as polyester , nylon , polypropylene , polybutylene , polylactic acid , poly - acrylonitrile , polycarbonate , polyurethane , polyolefin , polyimide , and polyaramid are melt blown or solution blown , or extruded and spun into fibers on a spinneret . the techniques for drawing out the fibers can be modified to obtain fibers with a diameter in the order of nanometers ( 40 - 2000 nm ). these processes can obtain fibers that are only as wide as the single layer crystal made of polymer chains . the conventional synthetic polymer fiber spinning technology can be improved to produce a composite fiber . a mixture of two polymers , that are mutually immiscible , can be drawn in to fibers by extrusion . such that , one polymer forms long fibers in a matrix of the other . a cross - section of such a fiber shows that 60 - 1500 islands of one polymer fibers are distributed in a sea of the other polymer , thus giving the impression of islands in sea . composite fibers are best suited because they can be flocked as microfibers , and then bundled island polymer nanofibers can be released by dissolving the sea polymer ( fig2 ). a 3 - dimensional helical structure ( fig3 ) can be achieved by extrusion of a composite fiber , where the constituent fibers shrink at different rates upon polymerization . the shrink rate is governed by variation in crystalline / amorphous structures of the polymers and chirality of the polymers . in one exemplary embodiment , the fibers were cut into a small length of 500 μm to 1 . 5 mm using a cryo - blade cooled down to − 20 ° c . to − 40 ° c . in order to get a clean cut with no sticky ends . the free standing nanostructured fibers can be coated with a film of conductive material such as silver , gold , platinum , polyaniline , polypyrrole , poly ( 3 , 4 - ethylenedioxythiophene ) to make them electroactive for applications such as but not limited to health monitoring ekg , eeg , eog , emg electrode application , touch sensors , and the like . they can be coated with metal oxide such as films for capacitive sensing application such as but not limited to respiration rate , air quality , gas sensing , and water quality . they can be coated with piezoelectric material film like polypyrrol for application such as but not limited to motion sensing , acoustic transduction , noise dampening , and impact sensing . for an exemplary ekg monitoring electrode , metallization of the structures is done with silver by electroless plating method . the surfaces of such sensor electrodes have nanoscale and mesoscale free standing conductive structures . this contributes to increasing the effective surface area of the electrodes , and a high aspect ratio of nano / mesoscale structures can overcome the obstruction due to rough skin surface and body hair . a good skin - electrode interface with these nanostructured sensor electrodes is instrumental in detection of electrophysiological signals emanating from the brain and heart to the skin surface . electroless plating electrically functionalizes the nanostructures by enmeshing / decorating them with a conformal conductive thin film of silver . the electroless plating process uses self - nucleation of the silver nanoparticles directly on the surface of the nanofibers . in one exemplary embodiment , the fibers were chemically treated to impart electrostatic charge , a . k . a . activation . the fibers were prepared for the activation process by washing with hot water followed by washing with cold water . the fibers were dried before further treatment . 2 - 3 wt % dried fibers were added to a bath of distilled water with constant stirring at 150 - 200 rpm . the bath was heated with the stirring . when temperature of the bath reached 40 ° c ., aluminum sulfate was added ( 1 . 5 - 1 . 6m ) and ph of the solution was lowered to 4 . 5 with acetic acid . when the bath temperature reached 50 ° c ., tannic acid was added ( 8 . 8 mm - 9 . 4 mm ). at 60 ° c ., aluminum sulfate was further added ( 31 mm - 34 mm ). this solution was maintained at 60 ° c . for 30 minutes with stirring . the solution was drained out and the fibers were retained by filtration and washed with di water 2 - 3 times . 2 - 3 wt % fibers were re - suspended in di water . the temperature was raised under constant stirring . at 40 ° c ., ammonium sulfate was again added ( 0 . 5m - 0 . 55m ) and the ph was brought to 5 . 5 with acetic acid . when the bath temperature reached 50 ° c ., 0 . 3 - 0 . 6 wt % cationic softener was added . the bath temperature was brought up to 60 ° c . and maintained for 30 minutes with constant stirring . the solution was drained out and the fibers were retained by filtration . the fibers were dried at room temperature until only 6 - 8 % of moisture was left . this was done for electrostatic activation of the fibers . the fibers were sifted to remove long fibers . thus prepared fibers can be applied to a fabric such that they are free standing because of mutual repulsion . in one embodiment , the electrostatic and / or pneumatic assisted deposition process used high strength electrostatic field of 2 kv / cm - 10 kv / cm for deposition of electrostatically charged fibers . the fibers move at a high velocity under the influence of electric field applied perpendicular to the substrate ( adhesive coated fabric ) and were attached vertically on it . this resulted in vertically aligned microstructured or nanostructure arrays . in one embodiment , the fabric was electrically functionalized with the help of electroless plating by enmeshing / decorating the nanostructures with a conformal conductive thin film of silver . the electroless plating process used self - nucleation of the silver nanoparticles directly on the surface of the fibers . the process had four steps : 1 ) pretreatment by soaking in mild detergent solution followed by deionized water rinse , 2 ) a 20 minutes long sensitization of fiber surface by adsorption of stannous ( sn 2 + ) colloids ( 15 mm to 18 mm sncl 2 . 2h 2 o and 0 . 32 %- 0 . 4 % v / v hcl ) in di water , 3 ) plating by using a mix of silver salt ( silver acetate 0 . 4 g / ml in aqueous ammonium hydroxide and titration of formic acid at 0 . 08 ml per ml of aqueous ammonium hydroxide ) and reducing agent by soaking the flocked fabric in the mix for 1 hour followed by drying the fabric in nitrogen environment and annealing at temperature in excess of 100 ° c ., and 4 ) post treatment by rinsing with deionized water to remove any unreacted precursors . the sensor fabrication process implementation on an assembly line with air locks ( to hold screens in place and activate screen applicator ) automatic ( conveyor type ) is shown in fig4 . the assembly line has one station each designated to ( i ) mounting a shirt on platen 1 , ( ii ) base layer application for printed electronics 2 , ( iii ) dryer for base layer 3 , ( iv ) conductive layer application for printed electronics 4 , ( v ) dryer for conductive layer 5 , ( vi ) encapsulation layer for printed electronics 6 , ( vii ) dryer for encapsulation layer 7 , ( viii ) adhesive for electrostatic and / or pneumatic assisted deposition 8 , ( ix ) electrostatic and / or pneumatic assisted deposition 9 , ( x ) vacuum suction head for un - attached fibers 10 , and ( xi ) textile finishing 11 . the applicators are programmable ( squeegee pressure , squeegee speed , resident time , screen spacing ) automated screen printing processes , dryers are programmable ( temperature control , resident time ) flash curing process , the electrostatic and / or pneumatic assisted deposition process is programmable ( applied voltage , resident time ) automatic potentiostat assembly with occlusion screen and fiber reservoir . functionalization of the nanostructured fabric is conducted by conducting the process described above using the flow cell shown in fig5 . the cell has injection and aspiration setup in the top plate 12 for coating solution and air . the top plate and bottom plate 19 have heating elements for temperature control for the process . the seal assemblies 13 , 17 ensure a leak - proof clamp around the fabric 16 . the aspiration stencil 14 includes flow channels for injection and aspiration into the chamber formed with sensor stencil 15 and back mesh 18 . the sensor stencil is the shape ( for example , oval , circular , clover leaf , etc .) of a nanostructured region of the fabric that needs to be functionalized for electrical conductivity . the flow cell is mounted as a top part 20 on a press head 21 with the top plate , seal , injection aspiration , and stencil , and a bottom part 22 on platform 23 with back plate , seal , and back mesh . fig6 shows flow cells arranged at the locations of functionalization 24 for multi - sensor assembly for an exemplary textile ekg monitoring system . the nanostructures were realized on textile by deposition of finely cut hybrid nanostructured fibers by electrostatic assisted deposition technique ( fig1 ). these fibers comprised of 200 nanometers diameter polypropylene islands in a 30 μm polylactic acid sea of nanocomposite yarn . the process used for activation and deposition were as described above . the polylactic acid sea was dissolved using heated ( 40 ° c . to 50 ° c .) alkaline etching bath . the structures were electroless plated with silver as described above to become textile - based nanosensors for biopotential measurement . large sensor surface area results in low skin - electrode contact resistance , thus , it helps in increasing the sensitivity of sensor electrodes . this has been shown through impedance analysis of nanostructured textile electrode in comparison with plain textile electrode and silver - silver chloride electrode ( fig7 ). a nanosensor pair can measure differential biopotential across a source organ . in the case of ecg , the signal source is the heart . so a differential potential measurement between the augmented right arm ( ara ) and augment left leg ( all ) results in a lead ii ecg signal as shown in fig8 . the signals from a nanosensor , a plain textile electrode , and an ag — agcl electrode have been plotted in the figure . similarly , an eeg signal can be obtained by placing the nanosensors on one of the defined eeg measurement positions , e . g . occipital lobe position o1 / o2 , and the reference location at the mastoid bone ( fig9 ). 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