PCL/Magnesium Based Composite Nanofibers for Peripheral Nerve Repair Application Udhab Adhikari, Nava P. Rijal, Devdas Pai, Narayan Bhattarai

Department of Mechanical Engineering, North Carolina A&T State University, Greensboro, NC Department of Chemical, Biological and Bioengineering & Engineering Research Center for Revolutionizing Metallic

Biomaterials, North Carolina A&T State University, Greensboro, NC

Statement of Purpose: The incidence of peripheral nerve (PN) damage is high, affecting at least 300,000 patients in the United States annually and almost 5% of all emergency room visits per year in the US involve peripheral nerve damage [1, 2]. Current surgical techniques for repairing lengthy nerve injuries, usually involve autografts which has disadvantages such as loss of feeling and pain at the donor site, insufficient donor tissue availability, secondary incisions, unavailability of optimal dimensions (diameter and/or length) of the donor nerve to span the injury site. This leads to demand for alternatives to autografts in terms of tissue engineered conduits. We synthesized nanofibers of polycaprolactone (PCL), a well-known biopolymer used in several biomedical applications and magnesium oxide (MgO) powder by using electrospinning technique. PCL and MgO were integrated into nanofibrous constructs and developed into conduits that combine the biological benefits of MgO, and the mechanical properties of PCL. Conduits were produced by electrospinning, a process that allows manipulation of a tissue scaffold’s structural and chemical properties at nanoscale dimensions to closely mimic native extracellular matrices (ECMs). Furthermore, having MgO embedded within the PCL conduit will allow controlled release of Mg. MgO releases magnesium ions (Mg++) which are known to improve recovery of nervous tissues after repair, especially since nervous tissues lose Mg++ after injury. Mg++ makes nerve conduits more conductive and electrically conductive materials have been shown to improve nerve repair by stimulating increased growth factor levels in the nerves.

Methods: Nanofibers were fabricated by electrospinning process. Electrospinning precursor solution is prepared by dissolving PCL or PCL and MgO in 2,2,2-Trifluoroethanol (TFE). The concentration of MgO was varied at 10, 25 and 50% in the solution. These solutions are individually fed into the syringe of 10 mL and then placed into a syringe pump. The syringe pump was set to a flow rate of 2.5 mL/hour. The syringe tip was positioned ~7 cm from a fiber collecting drum. A 20 kV voltage was used to charge the solution. The positive lead from the high voltage power supply was fixed to a 21-gauge needle and a negative charge was grounded. The fibers formed were deposited onto a rotating grounded collector wrapped with aluminum foil. The physicochemical properties of nanofiber membrane, such as morphology, mechanical strength, and integrity in aqueous medium were studied and its cellular compatibility was determined.

Results: Morphology study using Scanning Electron Microscope (SEM) showed uniform fiber distribution

with average diameter of PCL, PCL/MgO (90/10), PCL/MgO (75/25) and PCL/MgO (50/50) nanofiber to be 1.30, 1.10, 1.00 and 0.97 µm respectively. Transmission Electron Microscopy (TEM) images revealed that the array MgO nanoparticles was encapsulated in the PCL nanofibers. Ultimate tensile strength for PCL nanofiber was found to be 2.8 MPa and these values were 1.9, 2.2 and 2.1 MPa for PCL nanofibers which contained 10, 25 and 50% MgO respectively. Similarly, Young’s modulus (YM) for PCL, PCL/MgO (90/10), PCL/MgO (75/25) and PCL/MgO (50/50) was found to be 21.6, 24.8, 25.9 and 25.3 MPa respectively. The average cell viability for PCL, PCL/MgO (90/10), PCL/MgO (75/25) and PCL/MgO (50/50) after day 1 was found to be 100%, 94.5%, 95.6% and 94.9% respectively. Similarly, after day 3 those values were 100%, 106.9%, 91.0% and 90.2 % respectively. In XRD analysis, (200) and (220) peaks of MgO at 2Θ values of 44.5 and 63.25 were also observed in PCL/MgO fibers.

Figure: (A) SEM image showing the morphology of PCL nanofibers (B) TEM image of PCL/MgO (90/50) nanofiber.

Conclusions: PCL and PCL/MgO-based electrospun nanofibers were successfully fabricated. All fiber composition showed uniform surface morphology and structural integrity. XRD confirmed the oxide state of MgO in the nanofiber sample. Alamar Blue Assay showed low-to-no toxicity of these fibers and SEM image confirmed cell adhesion and cell attachment. Cell viability was found to be >75 % for all sample types which is considered safe level. These nanofiber samples showed the attachment of cells to the surfaces by numerous and long filopodia. These novel composite nanofibers could further be designed to have tubular geometry to obtain conduits for nerve repair applications.

References: 1.Taylor CA. Am J Phys Med Rehabil 2008, 87(5):381-385. 2. Robinson LR. Suppl Clin Neurophysiol 2004, 57:173-186