Smart polyaniline nanoparticles with thermal and photothermal sensitivity

Abstract

Conductive polyaniline nanoparticles (PANI NPs) are synthesized by oxidation of aniline with persulfate in acid media, in the presence of polymeric stabilizers: polyvinilpyrrolidone (PVP), poly(N-isopropylacrylamide) (PNIPAM), and hydroxylpropylcellulose (HPC). It is observed that the size of the nanoparticles obtained depends on the polymeric stabilizer used, suggesting a mechanism where the aggregation of polyaniline molecules is arrested by adsorption of the polymeric stabilizer. Indeed, polymerization in the presence of a mixture of two polymers having different stabilizing capacity (PVP and PNIPAM) allows tuning of the size of the nanoparticles. Stabilization with biocompatible PVP, HPC and PNIPAM allows use of the nanoparticle dispersions in biological applications. The nanoparticles stabilized by thermosensitive polymers (PNIPAM and HPC) aggregate when the temperature exceeds the phase transition (coil to globule) temperature of each stabilizer (Tpt = 32 °C for PNIPAM or Tpt = 42 °C for HPC). This result suggests that an extended coil form of the polymeric stabilizer is necessary to avoid aggregation. The dispersions are reversibly restored when the temperature is lowered below Tpt. In that way, the effect could be used to separate the nanoparticles from soluble contaminants. On the other hand, the PANI NPs stabilized with PVP are unaffected by the temperature change. UV-visible spectroscopy measurements show that the nanoparticle dispersion changes their spectra with the pH of the external solution, suggesting that small molecules can easily penetrate the stabilizer shell. Near infrared radiation is absorbed by PANI NPs causing an increase of their temperature which induces the collapse of the thermosensitive polymer shell and aggregation of the NPs. The effect reveals that it is possible to locally heat the nanoparticles, a phenomenon that can be used to destroy tumor cells in cancer therapy or to dissolve protein aggregates of neurodegenerative diseases (e.g. Alzheimer). Moreover, the long range control of aggregation can be used to modulate the nanoparticle residence inside biological tissues.

Synthesis of a Smart Conductive Block Copolymer Responsive to Heat and Near Infrared Light

“…Temperature of the drops was monitored by a TES 1326S/1327K infrared thermometer calibrated with a type K thermocouple. Duration of experiment was 15 min, recording the temperature at one-minute intervals, as previously described [15]. A thermographic camera Ti10 IR-Fusion Technology (Fluke, Everett, WA, USA) was used to capture IR images.…”

“…In a previous work [15], PANI nanoparticles were stabilized with a water-soluble thermosensitive copolymer containing N -isopropylacrylamide (NIPAM) monomer units. The smart nanoparticles aggregated upon heating or NIR light irradiation by the local photothermal effect.…”

Smart Thermomechanochemical Composite Materials Driven by Different Forms of Electromagnetic Radiation

“…The nanoparticles size should be much smaller than the size of the pores to allow diffusion inside the hydrogel. Since PANI nanoparticles have a size as large as 200 nm [44], they cannot enter the pores of nanoporous hydrogels (pore diameter smaller than 50 nm). To overcome that, the gels should contain large macropores.…”

Photothermally and magnetically controlled reconfiguration of polymer composites for soft robotics

“…Light also provides spatial control, and the amount of heat generated depends on the light wavelength, intensity, duration of illumination, and loading of absorbing species ( 33 ). Several materials have been used to trigger shape recovery of SMPs using photothermal heating, such as gold nanoparticles ( 14 , 15 , 25 ), carbon nanotubes ( 34 , 35 ), and conducting polymers ( 36 , 37 ), but these materials are not simultaneously magnetic. To the best of our knowledge, all of the SMP composites using photothermal heating solely perform shape recovery from a temporary shape to the permanent shape.…”