Carbon nanotube loaded electrospun scaffolds based on thermoplastic urethane (TPU) with enhanced proliferation and neural differentiation of rat mesenchymal stem cells: The role of state of electrical conductivity

Abstract

Electromagnetic stimulation has been shown as an effective strategy to enhance neural cells regeneration. The use of electrically conductive materials including polymer nanocomposites for the construction of scaffolds with potential to repair the injured nervous system has attracted great attentions. In the present study, attempts have been made to fabricate nanostructured fibrous scaffolds based on flexible thermoplastic polyurethane (TPU) and surface functionalized multiwalled carbon nanotubes (MWNT) via electrospinning process in order to examine and highlight the influence of state of electrical conductivity of scaffolds upon neural cells proliferation and differentiation. For this purpose, various scaffolds comprising different wt.% of MWNTs were prepared and their electrical conductivity, microstructural and mechanical characteristics were studied using two probe electrometer, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and tensile measurements. Cellular behavior, proliferation and neural differentiation of rat mesenchymal stem cells (RMSC) seeded on the fabricated scaffolds with different state of conductivity were investigated both in the presence and absence of an external electromagnetic stimulation. Results revealed a linear correlation between electrical conductivity and cell signaling as well as neural gene expression. It is demonstrated that MWNT particles are encapsulated by the TPU and mostly oriented along the nanofibers axis by the electric field imposed on the jetted fibers during electrospinning process. Reinforcement of both bulk and surface modulus was exhibited by MWNT loaded scaffolds, indicating intensification of the interface between TPU and surface modified MWNT partices. Electrical conductivity of scaffolds versus MWNT wt% showed to follow percolation model with a threshold around 2.5 wt% of MWNTs, implying the involvement of both tunneling and conduction mechanisms for the passage of the electron current throughout the scaffolds upon stimulation. RMSCs cultured on MWNT loaded nanofibrous scaffolds with conductivity above threshold exhibited enhanced neural differentiation, suggesting the crucial role of state of electrical conductivity of the scaffolds for directing the proliferation and differentiation of stem cells towards the neural tissues.