Narrowing the Diameter of Electrospun Nanofibres Wai Hei Tse The University of Western Ontario Department of Medical Biophysics April 7, 2010

Table of Contents Introduction Materials Applications Results Electrospinning Nanofibers Materials Collagen Polycaprolactone (PCL) Applications Results Conclusions

Introduction Electrospinning: process in which solid fibres are produced from a polymeric solution Based on electrostatic charge repulsion and fluid properties Objective: Narrow electrospun nanofibres to a consistent diameter of 100-250 nm. -Electrospinning : process in which solid fibres are produced from a polymeric solution -the process of spinning is based on fluid properties (surface tension) and electrostatic charge repulsion -resultant fibre production due to overcoming surface tension -Objective: Narrow electrospun nanofibres to a consistent diameter to 100-250 nm. -achieved by increasing the distance between the collector and polymer source, and decreasing the strength of the electric field -many times during the spinning process, due to the splaying of fibres, the resultant fibres usually vary in diameter

Why nanoscale? Why not larger? -Smaller diameter provides higher surface area to volume ratio -As a result provides more available area for cellular interactions -more available support for cells to grow -ability to control pore size as non-woven scaffold -create membranes

Why Collagen and Polycaprolactone? Biocompatibility Cost-effective for large scale electrospinning Collagen PCL Most abundant protein Extracellular matrix (ECM) component FDA approved synthetic polymer Biodegradable Impact resistant Collagen -endogenous -most abundant protein -ECM component -structure support in tension PCL -FDA approved synthetic polymer that is biodegradable

Applications Collagen PCL Spinal cord regeneration Tissue regeneration Tissue engineering ECM mimic Controlled release and drug delivery Collagen *images are SEM (scanning electron microscopy images) Spinal cord regeneration Heart valves, tendon, ligament tissue engineering -since tendon, ligaments, skin, heart, and arteries all contain or are composed of collagen, resulting spun fibres can be applied to engineer replacement tissue Provides natural environment -contributing to aqueous and culture media stability and mechanical properties -provide environment mimicking natural extracellular matrix ECM provides tissue with strength -environment where cells can adhere to, proliferate and grow PCL Tissue engineering: tissue is taken out and replaced at a later time Tissue regeneration: use of a scaffold to promote regeneration of damaged tissue -relies on a nano-fibrous scaffold as an environment to bind with -engineered scaffolds encapsulate bioactive proteins to provide biochemical cues in localized areas Controlled release and drug delivery -engineered scaffolds encapsulating drugs -given biodegradable property it is suitable for therapeutic agent delivery Collagen Scaffold (Mekhail, M. 2009) PCL Fibres (Patcharaporn, W., et al. 2005)

Electrospinning Apparatus Factors Affecting Polymer Diameter Flow Rate Electric Field Gradient Polymer Solution Flow rate: rate at which the solution is forced out the syringe -directly controls diameter of cone -high flow= increase in Taylor cone size -must be set to keep solution at the tip but not high enough to cause dripping Electric gradient: electric field/ distance -the relationship is not gradient dependent alone but rather more dependent on the distance -greater distance allows more time to elongate Polymer solution: concentration, viscosity, conductivity very important -solution concentration: high concentration = more material in jet = increase in fibre diameter -conductivity: greater conductivity = greater repulsion thus more elongation -viscosity: too viscous = too heavy = stronger field to attract the polymer Ambient properties: air flow, temperature, humidity can affect the electrospinning process Method Used for Electrospinning -syringe with polymer solution is charged at the tip (point of ejection) -electrostatic repulsion counteracts surface tension and droplet of polymer solution is stretched and collected at a distant grounded collector -as the liquid polymer jet travels through the air towards the collector, the solvent evaporates -when evaporation occurs the jet of solution becomes a charged polymer fibre strand -elongation occurs due to the whipping process caused by the electrostatic repulsion Nanotechweb.org

Video of Electrospinning Point out where the Taylor cone is Point out where the splaying occurs

Theory Taylor Cone (Doshi, J., and Reneker, D. H.) Electrosplaying (Thompson, C.J., et al.) Taylor Cone is governed by surface tension and electrostatic repulsion -the cone is formed as the intensity of the electric field is increased -a polymer jet is formed when the electrostatic repulsion counteracts the surface tension -repulsion is due to the mutual charge repulsion causing a force directly opposing the surface tension Surface tension is directly proportional to the solvent composition Repulsion/ Splaying -as the jet diameter decreases, the surface charge density increases -the high repulsive forces from the increased charge density splits the jet into smaller jets causing splaying -small jets dry rapidly to form fibres with very small diameter ThePedia.com

Results Inconsistent Diameter of Nanofibres (Erica Lee) Picture 1 (taking from an optical microscope) 0.3 ml/ hour 20 kV 12% PCL -joining of segments: segments separated by relatively large distances along the jet path may contact during the associated bending -if the sections remain liquid, they will merge (CLICK FOR CIRCLE INDICATING) Picture 2 20kV 0.3 ml/hour -strand breakages occur if there is insufficient resistance to electrostatic field -or dripping due to high flow rate such that the Taylor cone is disrupted -electrosplaying causes many smaller jets to form -given random movement of the strands, some will elongate more due to the whipping process and some less Inconsistent Diameter of Nanofibres (Erica Lee)

Objective! Results cont’d Beading of PCL Nanofibre (Erica Lee) Picture 3 (12% PCL 0.2ml/ hour 20kV 10cm) -beading: due to instability of the point of ejection -pertains to the instability of the Taylor cone Picture 2 Example of consistent strands, no beading Approximately 300 nm in diameter PCL fibre Looping is due to electrically driven bending instability -the garland formation seen here is associated with potentially useful nanofibre structures Consistent PCL Fibres (Erica Lee)

Conclusion Future Investigation Flow rate and electric field gradient are the most important factors in determining the fibre diameter The resultant fibre diameter is relative to the contributing factors Future Investigation Conclusion Flow rate and electric field gradient are the most important factors in determining the fibre diameter -increasing distance between the collector requires a stronger field -greater the distances allows for more time for evaporation and splaying to occur Polarity of the electric potential did not have any effect on the process -switching the ground and the charge did not effect the outcome of the fibres -ie: the process did not fail The resultant fibre diameter is relative -dependent on volumetric charge density, polymer solution concentration, applied electric field, distance between the tip and collector Future Investigation Reduce surface tension: surfactants Volumetric charge density: addition of salts to create higher charge density in the elongating strands to promote more splaying -resulting in thinner strands? Co-axial spinning -core-sheath -2 different material -use the outer material to drag (“viscous dragging”) due to friction, the inner material Reduce surface tension with additives Increase volumetric charge density with salts Co-axial Spinning

Acknowledgements Dr. Wankei Wan Dr. Martin Zinke-Allmang Erica Lee Department of Chemical and Biochemical Engineering Dr. Martin Zinke-Allmang Department of Medical Biophyiscs Erica Lee M. E. Sc. Candidate; Biomedical Engineering Images are courtesy of Erica Lee

Questions?

Method 12% PCL solution by weight Dissolved in tetrafluoroethylene (TFE) 12% PCL solution by weight Dissolved in tetrafluoroethylene (TFE) -used b/c boiling point at -76.3 C; evaporate quickly The Electrospinning set up is composed of a) a syringe pump mechanically controlled by a motor to be precise b) metal collector c) voltage supply to provide electric field Either the tip or collector is charged while the other acts as a ground (controls where the fibre will land) Nanotechweb.org