Conductive and Thermo-Responsive Composite Hydrogels with Poly(N-isopropylacrylamide) and Carbon Nanotubes Fabricated by Two-Step Photopolymerization

Abstract

Biocompatible and conductive polymer hydrogels are the subject of intensive research in the bioengineering field because of their use in bioelectronic devices and for the fabrication of electro-responsive tissues and drug delivery systems. In this study, we report the synthesis of conductive composite hydrogels consisting of a poly(N-isopropylacrylamide) (PNIPAM) matrix embedding carboxyl-functionalized multi-walled carbon nanotubes (MWCNT-COOH) using a two-step photopolymerization method. Thermo-responsive hydrogels with controlled hydrophilicity and conductivity were prepared by varying the carbon nanotube concentration in the range 0.5–3 wt%. The thermal response of the PNIPAM-based composite hydrogels was measured by differential scanning calorimetry with both ultrapure water and PBS solution as swelling liquid. Results show that the endothermic peak associated with the temperature-induced volume phase transition (VPT) shifts to higher temperatures upon increasing the concentration of the nanotubes, indicating that more energy is required to dissociate the hydrogen bonds of the polymer/filler network. In PBS solution, the swelling ratios and the VPT temperatures of the composite hydrogels are reduced because of salt-induced screening of the oppositely charged polymer/filler assembly, and the electrical resistivity decreases by a factor of 10 with respect to the water-swollen hydrogels.

Fabrication of Alginate/Ozoile Gel Microspheres by Electrospray Process

“…To evaluate the swelling ratio and water content, the gel microspheres were first completely hydrated in deionized water and then dried in an oven at 50 • C for 18 h. The swelling ratio and water content were calculated using the following equations [41]:…”

Current Progress in Conductive Hydrogels and Their Applications in Wearable Bioelectronics and Therapeutics

“…The hybrid hydrogel was prepared from PNIPAM and multi-walled carbon nano tubes by two step polymerizations as shown in Figure 6 b. The results demonstrated the enhanced sensitivity of hydrogel with excellent properties of electroconductivity and sensitivity [ 54 ]. Moreover, the literature highlighted that electroconductive hydrogels are also potential candidates for wearable bioelectronics.…”

“… ( a ) Schematic of the synthesis of the conductive hydrogel from the polypyrrole, Fe 3+ , and hybrid conductive network reprinted with permission [ 53 ]. ( b ) Schematic of the two-step polymerization of the poly(N-isopropylacrylamide) matrix containing carboxyl-functionalized multi-walled carbon nanotubes (PNIPAM/MWCNT-COOH) hydrogel, reprinted from [ 54 ]. …”

Synthesis and Characterization of Alginate Gel Beads with Embedded Zeolite Structures as Carriers of Hydrophobic Curcumin

“…In recent years, researchers have been exploring innovative approaches to enhance drug delivery systems and improve therapeutic outcomes. In this perspective, biocompatible gels have attracted the attention of researchers for their applications as scaffolds, carriers, and controlled drug delivery systems able to respond to physiological stimuli, such as pH and temperature [ 3 , 4 , 5 , 6 ]. Gels are three-dimensional (3D) networks of cross-linked polymers capable of absorbing and retaining large amounts of water [ 7 , 8 ].…”