Conductive hydrogel preparation and evaluation
Single-walled carbon nanotubes (CNTs; 76.9 mg, P3, 3-6-wt% R-COOH;
Carbon Solutions Inc., Riverside, CA, USA) with a bundle diameter of
~4–5 nm and a bundle length of ~1 µm
were purified with nitric acid and added to an aqueous solution of a
nonionic, noncytotoxic surfactant Pluronic F127 BioReagent (10 mL,
0.1-wt%; Sigma-Aldrich, Merck KGaA, Darmstadt, Germany). After heating
for 8 hours at 70°C, the mixture was sonicated for 16 hours creating a
0.77-wt% dispersion of CNTs. Nanofibrillated cellulose (NFC; 2 g≈2 ml,
3-wt%, carboxymethylated nanocellulose, charge density
~515 μeq/g; Innventia AB, Stockholm, Sweden) was
Electron Beam sterilized and then combined with 2 ml of the dispersion
using a SpeedMixerTM (FlackTek Inc., Landrum, SC, USA)
at 2000 rpm twice for 2 minutes each. The result was a homogeneous
hydrogel with dry matter of 20-wt% and NFC:CNT dry weight ratio of 4:1.
Our method for assessing conductivity of the hydrogel has been described
previously(12).