Laser direct writing and characterizations of flexible piezoresistive sensors with microstructures

Functional materials with high viscosity and solid materials have received more and more attentions in flexible pressure sensors,which are inadequate in the most used molding method.Herein,laser direct writing(LDW)method is proposed to fabricate flexible piezoresistive sensors with microstructures on PDMS/MWCNTs composites with an 8%MWCNTs mass fraction.By controlling laser energy,microstructures with different geometries can be obtained,which significantly impacts the performances of the sensors.Subsequently,curved microcones with excellent performance are fabricated under parameters of f=40 kHz and v=150 mm·s^(-1).The sensor exhibits continuous multi-linear sensitivity,ultrahigh original sensitivity of 21.80%kPa^(-1),wide detection range of over 20 kPa,response/recovery time of~100 ms and good cycle stability for more than 1000 times.Besides,obvious resistance variation can be observed when tiny pressure(a peanut of 30 Pa)is applied.Finally,the flexible piezoresistive sensor can be applied for LED brightness controlling,pulse detection and voice recognition.

Nanofiber self-consistent additive manufacturing process for 3D microfluidics

3D microfluidic devices have emerged as powerful platforms for analytical chemistry,biomedical sensors,and microscale fluid manipulation.3D printing technology,owing to its structural fabrication flexibility,has drawn extensive attention in the field of 3D microfluidics fabrication.However,the collapse of suspended structures and residues of sacrificial materials greatly restrict the application of this technology,especially for extremely narrow channel fabrication.In this paper,a 3D printing strategy named nanofiber self-consistent additive manufacturing(NSCAM)is proposed for integrated 3D microfluidic chip fabrication with porous nanofibers as supporting structures,which avoids the sacrificial layer release process.In the NSCAM process,electrospinning and electrohydrodynamic jet(E-jet)writing are alternately employed.The porous polyimide nanofiber mats formed by electrospinning are ingeniously applied as both supporting structures for the suspended layer and percolating media for liquid flow,while the polydimethylsiloxane E-jet writing ink printed on the nanofiber mats(named construction fluid in this paper)controllably permeates through the porous mats.After curing,the resultant construction fluid–nanofiber composites are formed as 3D channel walls.As a proof of concept,a microfluidic pressure-gain valve,which contains typical features of narrow channels and movable membranes,was fabricated,and the printed valve was totally closed under a control pressure of 45 kPa with a fast dynamic response of 52.6 ms,indicating the feasibility of NSCAM.Therefore,we believe NSCAM is a promising technique for manufacturing microdevices that include movable membrane cavities,pillar cavities,and porous scaffolds,showing broad applications in 3D microfluidics,soft robot drivers or sensors,and organ-on-a-chip systems.