Pressure and microwave sensors and actuators based on a smart hydrogel/conductive polymer nanocomposite

R.E. RIVERO; M.A. MOLINA; C.R. RIVAROLA; C.A. BARBERO

Berlin

Conferencia; 12th International PAT Conference; 2013

Hydrogels sensitive to external parameters (pH, temperature,ionic force, electric field, etc) constitute the socalled smart hydrogels which could react actively tochanges in the environment [1]. Crosslinked acrylamidebased thermosensitive hydrogels are interesting candidatesfor biomedical or pharmaceutical applications,such as drug release [2] because they change volumeand expel a significant amount of its inner solutionwhen a transition is induced by external action as wellthe materials could also be used in chemical [3] ormechanical [4] actuators for technological applications.It would be most interesting to induce the volumechange at a distance using electromagnetic radiation.Smart hydrogel based nanocomposites combines propertiesof both components [5].In this work a nanocomposite is fabricated by formationof a conductive polymer, using in-situ oxidativepolymerization, inside a thermosensitive crosslinked hydrogel.FE-SEM micrographs show the nanometricdomains of the conductive material (polyaniline, PANI)dispersed in the hydrogel matrix (cross linked poly(Nisopropylacrylamide),PNIPAm) (Fig 1).The thermosensitive properties of PNIPAm are notaffected by the presence of conductive polymer nanoparticles.The incorporation of PANI improves themechanical properties of the hydrogel allowing it toswell up to 30000% without breaking. Since the conductivepolymer absorbs strongly microwave (mW) radiationat pH < 4 and is heats up, the nanocompositecontaining PANI suffer phase transition upon mW irradiation.At pH > 4, PANI is not conductive and the nanocompositebecomes insensitive to microwaves.However, using a pH insensitive conductive polymer(polypyrrole, PPy) in the nanocomposite makes it sensitiveto microwaves at all pH values. The nanocompositeis used in a chemomechanical actuator where drugrelease is driven remotely by microwave irradiation.Since the nanocomposite is elastic and electronicallyconductive, is could be used as pressure/force sensor. Itis shown that a compressive force applied on a cylinderof the nanocomposite increases the conductivity ofmaterial. Additionally a switch is built which turns offupon microwave irradiation (Fig 2).Therefore, this nanocomposite is a potential candidatefor different technological applications, such as: aforce/pressure electrical sensor, a drug delivery devicedriven remotely by microwaves and a microwave, pH ortemperature electrical switches.