Design, engineering and structural integrity of electro-responsive carbon nanotube-based hydrogels for pulsatile drug release

Triggerable drug delivery from polymeric implants offers the possibility to generate remote-controlled drug release profiles that may overcome the deficiencies of conventional administration routes (intravenous injections and oral administration) including the toxicity due to overdose and systemic administration. An electro-responsive delivery system was engineered to deliver drug molecules in a pulsatile manner, controlled by the on/off application of electric voltage. Pristine multi-walled carbon nanotubes (pMWNTs) were incorporated into a polymethacrylic acid (PMAA)-based hydrogel matrix by in situ radical polymerisation. The effect of pMWNTs and cross-linker concentration on the electrical and mechanical properties of the hydrogel hybrids was thoroughly investigated. The incorporation of pMWNTs into the polymeric network improved the electrical properties of the hydrogel hybrids and drug release from the gels was significantly enhanced at high pMWNT concentrations, reaching 70% of the loaded dose after two short electrical stimulations. The presence of pMWNTs within the hydrogel matrix affected however the mechanical properties of the hydrogel by decreasing the pore size and therefore the swelling/de-swelling of the gels. The damage to the hybrid gel surfaces after electrical stimulation and the loss of the pulsatile release profile at high cross-linker concentrations suggested that the mechanism of drug release involved a compressing effect and intensified the stress on the polymeric network as a result of the electrical properties of pMWNTs.