Preparation of Multiwall Carbon Nanotubes Embedded Electroconductive Multi-Microchannel Scaffolds for Neuron Growth under Electrical Stimulation

Multi-walled Carbon Nanotubes Remediate the Phytotoxicity of Quinclorac to Tomato

In order to remediate the phytotoxicity of quinclorac to tomato by multi-walled carbon nanotubes (MWCNTs), the adsorption of quinclorac to MWCNTs was monitored and the effect of MWCNTs on the phytotoxicity of quinclorac to tomato in soil were studied. The results showed that the Linear equation and Freundlich equation can well fit the adsorption isotherm of quinclorac in the soil containing MWCNTs. The adsorption of quinclorac in soil was significantly enhanced by the addition of MWCNTs; the K_d of soil (1% MWCNTs) was 28.7 times of pure soil. The quinclorac had an obvious inhibitory effect on the growth of tomatoes; serious phytotoxicity was also induced even at the lowest concentration of 0.025 mg/kg. With the MWCNTs content in soil increased to 0.5% and 1%, the phytotoxicity of quinclorac to tomatoes decreased significantly, and the height and fresh weight of tomatoes were even higher than those of the control group, indicating that MWCNTs can promote the growth of tomato. These results provide a reference for resolving the problem of phytotoxicity induced by residual herbicides in farmland.

Enhanced Nerve Regeneration by Bionic Conductive Nerve Scaffold Under Electrical Stimulation

Repair of peripheral nerve defect (PND) with a poor prognosis is hard to deal with. Neural conduit applied to nerve defect at present could not achieve the effect of autologous nerve transplantation. We prepared bionic conductive neural scaffolds to provide a new strategy for the treatment of PNDs. The highly aligned poly (L-lactic acid) (PLLA) fiber mats and the multi-microchannel conductive scaffolds were combined into bionic conductive nerve scaffolds, which were implanted into rats with sciatic nerve defects. The experimental animals were divided into the scaffold group (S), scaffold with electrical stimulation (ES) group (S&E), and autologous nerve transplantation group (AT). The regenerative effect of bionic conductive nerve scaffolds was analyzed. Compared with aligned PLLA fiber mats (APFMs), highly aligned fiber mats had a higher fiber orientation and did not change the tensile strength, Young’s modulus, degradation rate, elongation at break of the fiber membrane, and biocompatibility. The bionic conductive nerve scaffolds were well matched with the rat sciatic nerve. The evaluations of the sciatic nerve in Group S&E were close to those in Group AT and better than those in Group S. Immunohistochemical results showed that the expression levels of neurofilament heavy polypeptide (NF-H) and protein S100-B (S100-β) in Group S&E were higher than those in Group S, and the expression levels of low-density lipoprotein receptor-related protein 4 (LRP4), mitogen-activated protein kinase (MAPK) p38, extracellular signal-regulated kinase (ERK), and mitogen-activated protein kinase kinase (MEK) in Group AT were higher than those in Group S. Bionic conductive nerve scaffolds combined with ES could enhance peripheral nerve regeneration and achieve satisfactory nerve regeneration close to autologous nerve grafts. ERK, p38 MAPK, MEK, and LRP4 may be involved in peripheral nerve regeneration under ES.

Electrospun conductive nanofiber yarns for accelerating mesenchymal stem cells differentiation and maturation into Schwann cell-like cells under a combination of electrical stimulation and chemical induction

Development of multifunctional tube-filling materials is required to improve the performances of the existing nerve guidance conduits (NGCs) in the repair of long-gap peripheral nerve (PN) injuries. In this study, composite nanofiber yarns (NYs) based on poly(p-dioxanone) (PPDO) biopolymer and different concentrations of carbon nanotubes (CNTs) were manufactured by utilizing a modified electrospinning apparatus. We confirmed the successful incorporation of CNTs into the PPDO nanofibers of as-fabricated composite NYs. The PPDO/CNT NYs exhibited similar morphology and structure in comparison with pure PPDO NYs. However, the PPDO/CNT NYs showed obviously enhanced mechanical properties and electrical conductivity compared to PPDO NYs. The biological tests revealed that the addition of CNTs had no negative effects on the cell growth, and proliferation of rabbit Schwann cells (rSCs), but it better maintained the phenotype of rSCs. We also demonstrated that the electrical stimulation (ES) significantly enhanced the differentiation capability of human adipose-derived mesenchymal stem cells (hADMSCs) into SC-like cells (SCLCs) on the PPDO/CNT NYs. More importantly, a unique combination of ES and chemical induction was found to further enhance the maturation of hADMSC-SCLCs on the PPDO/CNT NYs by notably upregulating the expression levels of SC myelination-associated gene markers and increasing the growth factor secretion. Overall, this study showed that our electrically conductive PPDO/CNT composite NYs could provide a beneficial microenvironment for various cell activities, making them an attractive candidate as NGC-infilling substrates for PN regeneration applications. STATEMENT OF SIGNIFICANCE: The morphology, microstructure, and bioelectrical properties of conductive PPDO/CNT NYs have been explored for guiding or controlling cell behaviors. The PPDO/CNT NYs exhibited improved mechanical properties and increased electrical conductivity compared to the CNT-free PPDO NYs. They also presented an obviously enhanced biocompatibility by effectively maintaining the phenotype of rSCs. In addition, when hADMSCs were seeded and cultured on the conductive PPDO/CNT NYs, CI was demonstrated to promote the SC-related growth factor secretion of hADMSCs, and ES was demonstrated to improve the phenotypic maturation of hADMSCs into myelinating SCLCs. Moreover, the combination of CI and ES was found to further synergistically enhance the maturation of hADMSC-SCLCs. The achievement of conductive PPDO/CNT NYs shows potential for application as NGC-infilling substrates for PN regeneration.

Tracing Carbon Nanotubes (CNTs) in Rat Peripheral Nerve Regenerated with Conductive Conduits Composed of Poly(lactide-co-glycolide) and Fluorescent CNTs

Nerve regeneration can be promoted using nerve guide conduits (NGCs). Carbon nanotubes (CNTs) are often used to prepare conductive NGCs, however, the major concern for their applications is the final location of the implanted CNTs in vivo. Herein, photoluminescent multiwalled CNTs (MWCNTs) were prepared and electrospun with poly(lactide-co-glycolide) (PLGA), followed by shaping into multichannel NGCs for repairing of injured rat sciatic nerve, thereby the distribution of CNTs in vivo could be detected via bioimaging. Photoluminescent MWCNTs (MWCNT-FITC) were prepared by functionalization with poly(glycidyl methacrylate) (PGMA) and fluorescein-isothiocyanate-isomer I (FITC) subsequently. The conductivity of the PLGA/MWCNT-FITC fibers was approx. 10^-4 S/cm at 3 wt % MWCNTs. Compared with PLGA fibers, Schwann cells on PLGA/MWCNT-FITC fibers matured at a faster rate, accordingly, nerve regeneration was promoted by the PLGA/MWCNT-FITC NGC. With a confocal laser scanning microscope and small-animal imaging system, the location of MWCNTs was detected. Alongside the degradation of PLGA, MWCNTs intended to aggregate and were entrapped in the regenerated nerve tissue without migrating into surrounding tissues and other organs (liver, kidneys, and spleen). This study provides a useful characterization method for MWCNTs and the guidance for in vivo applications of MWCNTs in tissue engineering.