Electrospinning of Nanofabrics

1. Electrospinning of Nanofabrics Presented by U6: Pavitra Timbalia Michael Trevathan Jared Walker

2. Outline • Introduction • Background • Apparatus • General Applications • Current Research • Future Research • Questions

3. Introduction • Nanofabrics are composed of nonwoven nanofibers • Nanofibers are created by a process called electrospinning. • Electrospinning is a major way to engineer (without self-assembly) nanostructures that vary in: • Fiber Diameter • Mesh Size • Porosity • Texture • Pattern Formation Burger, Christian, et. al. Nanofibrous Materials and Their Applications. 2006. http://en.wikipedia.org/wiki/File:Taylor_cone_photo.jpg

4. Introduction • Grafts: Woven vs. Nonwoven • The nonwoven structure has unique features: • Interconnected pores • Very large surface-to-volume ratio • Enables nanofibrous scaffolds to have many biomedical and industrial applications. (a) Woven fabrics (b) Non-woven fabrics (c) “Soldered” junctions Burger, Christian, et. al. Nanofibrous Materials and Their Applications. 2006.

5. An Example • Take the distance between the Earth and the Moon, L, to be 380,000 km. • It takes only x grams of a polymer fiber filament to make up this distance • ρ = 1 g cm-3and the fiber diameter d = 2r = 100 nm • X = Vρ = πr2Lρ = π (50 nm)2 (380,000 km) (1 g cm-3) • ≈ 3 grams Burger, Christian, et. al. Nanofibrous Materials and Their Applications. 2006.

6. Electrospinning

7. Electrospinning - Procedure • An electrostatic potential is applied between a spinneret and a collector • A fluid is slowly pumped through the spinneret. • The fluid is usually a solution where the solvent can evaporate during the spinning. • The droplet is held by its own surface tension at the spinneret tip, until it gets electrostatically charged. • The polymer fluid assumes a conical shape (Taylor cone). • When the surface tension of the fluid is overcome, the droplet becomes unstable, and a liquid jet is ejected Burger, Christian, et. al. Nanofibrous Materials and Their Applications. 2006.

8. Burger, Christian, et. al. Nanofibrous Materials and Their Applications. 2006.

9. Burger, Christian, et. al. Nanofibrous Materials and Their Applications. 2006.

10. Burger, Christian, et. al. Nanofibrous Materials and Their Applications. 2006.

11. Types of Solvent Stream Ejections Burger, Christian, et. al. Nanofibrous Materials and Their Applications. 2006.

12. Poly(D,L-lactic acid) (PDLA) Nanofibers at voltage of 20 kV, feeding rate of 20 μl min−1 20 wt% Burger, Christian, et. al. Nanofibrous Materials and Their Applications. 2006.

13. Poly(D,L-lactic acid) (PDLA) Nanofibers at voltage of 20 kV, feeding rate of 20 μl min−1 35 wt% Burger, Christian, et. al. Nanofibrous Materials and Their Applications. 2006.

14. Electrospinning Polymers • The small size between the fibers allows the capture of particles in the 100- to 300- nanometer range • That is the same size of viruses and bacteria • Used as air-filter: Airplanes, office, etc. Burger, Christian, et. al. Nanofibrous Materials and Their Applications. 2006.

15. Electrospinning Variables Burger, Christian, et. al. Nanofibrous Materials and Their Applications. 2006.

16. Applications Burger, Christian, et. al. Nanofibrous Materials and Their Applications. 2006.

17. Applications Ultrafiltration in water treatment • High flux, low-fouling membrane • The top layer provides the actual filtration, and the middle and bottom layer provide sting support and are very porous • Increased efficiency • Able to filter without top layer. Burger, Christian, et. al. Nanofibrous Materials and Their Applications. 2006. Burger, Christian, et. al. Nanofibrous Materials and Their Applications. 2006.

18. Applications Anti-adhesion in surgery • Due to their high surface to volume ratio and being able to conform to different sizes, shapes and textures. • Closely match those of native tissue • Nanofabrics have been used as scaffolds for tissue and cell regeneration of organs. Burger, Christian, et. al. Nanofibrous Materials and Their Applications. 2006. Burger, Christian, et. al. Nanofibrous Materials and Their Applications. 2006.

19. Modification, crosslinking, and reactive electrospinning of a thermoplastic medical polyurethane for vascular graft applications Recent Research on Electrospinning

20. Thermoplastic polyurethanes • Used in medical devices and experimental tissue engineering scaffolds • Chemical/mechanical properties hard to balance http://www.allproducts.com/manufacture100/tpu/product1.jpg http://www.perfectex.com/tpu01.jpg http://www.pslc.ws/macrog/images/ureth06.gif

21. Methodology • Synthesis of a model compound • Modification of thermoplastic polyurethane • Pellethane® • Modification Reactions • Sample prep and crosslinking • Swelling behavior • Tensile testing • Scanning electron microscopy • Electrospun grafts J.P. Theron et al./Acta Biomaterialia

22. Modification of Thermoplastic Polyurethane http://upload.wikimedia.org/wikipedia/commons/2/25/Sodium-hydride-3D-vdW.png • Modified with reactive phenol groups – NaH was added - different amounts to observe changes with the polyurethane • Modified polymer was isolated and purified through precipitations in water and vacuum drying • Crosslinking achieved by UV light or heat source • Swelling index was determined by gravimetric behavior • Tensile testing was performed at room temperature and in a cyclical method J.P. Theron et al./Acta Biomaterialia

23. Scanning electron microscopy • Surfaces of the samples – degradation study • Pellethane and Pell 15.0 • Control samples (not subject to the degradation media) – used as references • Determined the amount of degradation on a scale of 1-5 J.P. Theron et al./Acta Biomaterialia

24. Electrospun grafts • Small diameter vascular graft prototypes • Used an electrospinning apparatus – high voltage power supply, infusion pump, syringe, rotating/translating mandrel • Tubes removed from mandrels by swelling in EtOH and dried • Produced crosslinked tubular vascular graft prototype J.P. Theron et al./Acta Biomaterialia

25. Fibers are irradiated with UV light during spinning in order to form crosslinked graft scaffolds Schematic Representation of the Reactive Electrospinning Apparatus J.P. Theron et al./Acta Biomaterialia

26. Experimental Results • Direct linear correlation between NaH addition and degree of modification • By adding the NaH, the research group was able to get between 4.5% and 20% modification of the polyurethane. • After 20% modification, samples were discolored/started degrading J.P. Theron et al./Acta Biomaterialia

27. Experimental Results • The range of modifications was tested for mechanical strength • The sample which ranked the best was the Pell15.0, or a 15% modified sample. J.P. Theron et al./Acta Biomaterialia

28. Experimental Results • The modified Pell15.0 showed a reduced creep when compared to the Pellethane control – reduction of 44% • This is due to the UV crosslinking of Pell15.0. J.P. Theron et al./Acta Biomaterialia

29. Results • Decrease in swelling index with increased degree of modification –an increased modification led to more densely crosslinked material. • Crosslinking also showed a decrease in hysteresis as well as breaking stress and strain. • The scanning electron microscope showed that the crosslinked samples had only a few cracks, while the control samples had severe surface degradation with deep cracks. • The Pell15.0 was spun with UV light into tubular graft structures 40mm in length • Grafts diameter (thickness) can be adjusted depending on specific applications J.P. Theron et al./Acta Biomaterialia

30. Pellethane Pell15.0 Before AgNO3 Degrading After AgNO3 Degrading After Hydrogen Peroxide • Crosslinking improved the resistance to degradation. J.P. Theron et al./Acta Biomaterialia

31. Conclusions of this Research • Exhibit compliance values within physiological range • Can optimize fibers for mechanical, morphological properties, and in vivo response • Tissue regrowth, angiogenesis, inflammatory response • Manipulate processing conditions • Vascular grafts - repetitive, relatively low stress • Bio-degradable scaffolds for tissue regeneration • Can closely match native tissues - good incorporation in already existing tissue J.P. Theron et al./Acta Biomaterialia http://hairyinterfaces.memphys.sdu.dk/DMueller_fig1.jpg

32. Surface-functionalized Elecrospun Nanofibers for Tissue Engineering and Drug Delivery Recent Research on Electrospinning

33. Electrospun Nanofibers • High surface area to volume ratio • Versatile method for preparing nanofibrous meshes • Potential applications: • Biomedical devices • Tissue engineering scaffolds • Drug delivery carriers • Done through Surface Modification • Plasma treatment • Wet chemical method • Surface graft polymerization • Co-electrospinning of surface active agents and polymers • Creates bio-modulating microenvironments to contacting cells and tissues "Surface-functionalized Electrospun Nanofibers for Tissue Engineering and Drug Delivery."

34. Surface Modification Techniques • Synthetic polymers vs. natural polymers • Synthetic: easier processing for electrospinning and more controllable nanofibrous morphology • Natural: difficult to directly process into nanofibers because of unstable nature and weak mechanical properties • Natural polymers can be immobilized onto the surface of synthetic polymers without compromising bulk properties • Can incorporate therapeutical agents directly into the nanofibers http://www.animate4.com/nanotech/nanotechnology/nanomedicine/nano/nanoscale/nanotech-nanotechnology-nano-nanomedicine-moleculare-nanotech-nanoscale.jpg "Surface-functionalized Electrospun Nanofibers for Tissue Engineering and Drug Delivery."

35. Modification – Plasma Treatment • Changes the surface chemical composition • Selection of plasma source – introduce diverse functional groups on surface • Plasma treatments with oxygen, ammonia, or air – generates carboxyl groups or amine groups • Air or argon treatments • When nanofibers were soaked in a simulated body solution – calcium mineralization occurred on surface • Improved wettability • Potential with bone grafts http://www.devicedaily.com/wp-content/uploads/2008/11/fortross-02.jpg "Surface-functionalized Electrospun Nanofibers for Tissue Engineering and Drug Delivery."

36. Modification – Wet Chemical Method • Films and scaffolds under acidic or basic conditions – modify surface wettability • Plasma treatment can not modify surface of nanofibers deep in the mesh • Wet chemical etching methods can modify thick meshes "Surface-functionalized Electrospun Nanofibers for Tissue Engineering and Drug Delivery."

37. Modification – Surface Graft Polymerization • Synthetic biodegradable polymers retain hydrophobic surface – need hydrophilic surface modification for desired response • Introduce multi-functional groups on the surface • Enhanced cell adhesion, proliferation, and differentiation • Initiated with plasma and UV radiation treatment to generate free radicals for polymerization "Surface-functionalized Electrospun Nanofibers for Tissue Engineering and Drug Delivery."

38. Modification – Co-electrospinning • Nanoparticles and functional polymer segments can be directly exposed on surface of nanofibers • Co-electrospinning with bulk polymers • Any combination of electrospinnable polymer and polymer conjugate can be used "Surface-functionalized Electrospun Nanofibers for Tissue Engineering and Drug Delivery."

39. Target Molecule Loading on Surface • Simple physical adsorbtion • Nanopoarticle assembly on surface • Layer by layer multilayer assembly • Chemical immobilization "Surface-functionalized Electrospun Nanofibers for Tissue Engineering and Drug Delivery."

40. http://www.keystonenano.com/library/images/moleculeAsmall.jpghttp://www.keystonenano.com/library/images/moleculeAsmall.jpg Applications – Drug Delivery • Superior adhesiveness to biological surfaces • Variety of structures containing drug molecules • Drug release mechanism – polymer degradation and diffusion pathway • Can tailor drug release profiles by varying polymer properties, surface coating, combination of polymers • Has been successful in laboratory trials – controlled topical release "Surface-functionalized Electrospun Nanofibers for Tissue Engineering and Drug Delivery."

41. Applications – Tissue Engineering • Various cells cultivated on nanofibrous meshes • Embryonic stem cells, mesenchymal stem cells • Better than other tissue engineering methods • Coronary artery cells • Collagen • Limited to in vitro studies because cells could not be loaded within the nanofibrous meshes in large quantities • 3D nanofibrous scaffolds "Surface-functionalized Electrospun Nanofibers for Tissue Engineering and Drug Delivery." http://pcsl.mit.edu/images/nano.jpg

42. Further Research

43. Improvements and Further Research • Develop more precise electrospinning techniques • Mechanisms of electrospinning • Growth rates • Bending Instability • Producing nanofabrics with specific mechanical properties. • Creating 3-dimensional shapes • Capable of being used in controlled release of drugs. Burger, Christian, et. al. Nanofibrous Materials and Their Applications. 2006.

44. Improvements and Further Research • Optimization of parameters • Intrinsic properties of solution • Polarity, surface tension of solvent, MW of polymer, etc. • Controlling nanofiber alignment • Electric field • Modifying type of collector • Better control of fiber alignment http://www.rsc.org/ejga/NR/2010/b9nr00243j-ga.gif "Electrospin Nanofibers for Neural Tissue Engineering."

45. Improvements and Further Research • Reduce Cost of Production • Make economically viable • Increase production rate • Incorporate the use of an array of spinnerets • Safety • Solvents • Dangerous to health and environment • Polymers Burger, Christian, et. al. Nanofibrous Materials and Their Applications. 2006.

46. References • Burger, Christian, Benjamin S. Hsiao, and Benjamin Chu. "Nanofibrous Material and Their Applications." Review. 25 Apr. 2006. Web. 14 Feb. 2010. • Hunley, Matthew T., and Timothy E. Long. "Electrospinning Functional Nanoscale Fibers: a Perspective for the Future." Polymer International 57 (2008): 385-89. Web. 7 Mar. 2010. • NASA Tech Briefs Create the Future Design Contest. Web. 08 Mar. 2010. <http://www.createthefuturecontest.com/pages/view/entriesdetail.html?entryID=1857>. • Theron, J. P., J. H. Knoetze, R. D. Sanderson, R. Hunter, K. Mequanint, T. Franz, P. Zilla, and D. Bezuidenhout. "Modification, Crosslinking and Reactive Electrospinning of a Thermoplastic Medical Polyurethane for Vascular Graft Applications." Acta Biomaterialia (2010). 27 Jan. 2010. Web. 05 Feb. 2010. • Xie, Jingwei, Matthew R. MacEwan, Andrea G. Schwartz, and Younan Xia. "Electrospin Nanofibers for Neural Tissue Engineering." Nanoscale 2 (2010): 35-44. Print. • Yoo, Hyuk S., Taek G. Kim, and Tae G. Park. "Surface-functionalized Electrospun Nanofibers for Tissue Engineering and Drug Delivery." Advanced Drug Delivery Reviews 61 (2009): 1033-042. Print.

47. Questions

48. Rebuttal from U6 We agree that we may have used a few too many filler words and will actively try to reduce them in the second presentation One group thought that we should have been more concise, but we felt like we had the right amount of slides to present the topic thoroughly One group would have liked to see a more integrated presentation; we chose to add title slides throughout to let the audience know what we would be discussing next in the presentation Potential further research was discussed in areas which showed promise in the use of nanofibers and the topics which could be researched are endless – one group suggested some additional topics to research Polyurethane is the material which was used to produce the nanofibers, hence is how it is related to the nanotechnology applications We will keep up the quality of the slides since there were a lot of positive comments about them We appreciate all the comments and will take them into consideration for our next presentation

49. Review of Electrospinning of Nanofabrics Submitted by U1

50. This presentation particularly caught our attention for its wide range of applications like clothing reinforcement and support for tissue regeneration. • Also electrospinning offers the possibility of changing some of the design and material variables to obtain different products makes it very versatile and adaptable for different purposes. • Their comparison of different papers that show electrospining base process for the aid of health issues and drug delivery shows that the technology has great future. • This presentations was really good overall and meet our expectations. The slides were well constructed and pictures were very helpful in recreating many of the concepts. http://www3.interscience.wiley.com/journal/118859172/issue http://realitypod.com/?tag=artificial