Physical and Chemical Properties of Poly (l-lactic acid)/Graphene Oxide Nanofibers for Nerve Regeneration

Abstract

The development of biodegradable polymeric nanofiber scaffolds for a potential effort to repair injured nerve cells is of great interest in nerve tissue engineering applications. Poly (L-lactic acid) (PLLA) has been widely used in nerve conduit studies due to its biocompatibility, easily shaped properties and degradation to low toxic lactic acid. However, its hydrophobicity and lack of binding sites for cellular activities restricts its use as implants. In this regard, this study involves the incorporation of graphene oxide (GO) into PLLA nanofibers for enhancing mechanical properties, electrical conductivity and hydrophilicity of PLLA to make it suitable for a potential peripheral nerve regeneration application. For this purpose, PLLA and PLLA/GO nanofibers were prepared via electrospinning. The processing parameters and solution parameters were optimized to adjust physical and mechanical properties of nanofiber in terms of size, porosity and biologically active affinity for cellular interaction. The morphology and composition of the developed electrospun fibers were characterized via, Scanning Electron Microscopy (SEM), Raman Spectroscopy, tensile testing and contact angle measurements. The morphological results showed that using chloroform/DMF ratio of 8/2 for 7wt% PLLA led to the formation of bead free and thinner PLLA fibers than fibers produced from other concentration of PLLA. Moreover, the addition of the GO resulted in decrease of the average diameter of PLLA fibers from 828 nm to 490 nm and the thinnest nanofiber structure was obtained by addition of 10 v/v % GO. The sonication time of GO highly enhanced the porosity of the nanofibers, namely the porosity of the nanofibers increased with increasing sonication time. Raman Spectroscopy exhibits peaks at bands of 1775, 873 and 1455 cm^-1 that are attributed to C=O stretching, C-COO stretching and CH₃ asymmetric deformation respectively for PLLA and 1379 and 1599 cm^-1 which represent structural imperfections and sp2 domain of carbon atoms respectively for GO. Hence, Raman peaks confirmed that GO was mixed in PLLA nanofibers. The incorporation of GO significantly improved the tensile strength from 2.25 MPa of pure PLLA to 8.13 MPa, 10.44 MPa and 12.93 MPa with 5, 7.5 and 10 v/v% of GO addition, respectively. The results revealed that the addition of GO led to enhanced chemical and physical properties of fibers which is promising for nerve regeneration applications.