Deposition of Multilayer Fibers and Beads by Near-Field Electrospinning for Texturing and 3D Printing Applications

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1 Deposition of Multilayer Fibers and Beads by Near-Field Electrospinning for Texturing and 3D Printing Applications Nicolas Martinez-Prieto, Jian Cao, and Kornel Ehmann Northwestern University SmartManufacturingSeries.com

2 Micro manufacturing Applications pol ynano.org/ mitpune.com/ Length scales: <500 μm length, <125 μm diameter, <50 μm width Tolerances: < 1 μm Materials: Stainless steel, Aluminum, Brass, Titanium, Polymers, Semiconductors, etc.

3 Micro manufacturing Current Techniques Trend Inkjet Printing Lithography Laser Machining E-jet printing Nanolithography Mechanical Machining FIB Machining 3D Printing Stereolithography Limited Capability Clean Room Fabrication Methods (+) High resolution (+) Parallel production (-) Expensive (-) Limited in materials (-) Limited prototyping and low-volume production (-)Limited in complexity Martinez Prieto et al. J. Micro Nano Manuf. (2015)

4 Micro manufacturing Current Techniques Trend Inkjet Printing Lithography Laser Machining E-jet printing Nanolithography Mechanical Machining FIB Machining 3D Printing Stereolithography Limited Capability 3D Printing (+) Freeform Printing (+) Prototyping and low-batch production (+) Computer controlled (+) Wide range of material options (+) Low cost and table top versions available (-) Low resolution (-) Limited parallelization Martinez Prieto et al. J. Micro Nano Manuf. (2015)

5 Flow Based Methods Fused Deposition Modeling (FDM) Wikipedia.org Vozzi et al. Tissue Engineering. (2002) Adams et al. Adv. Mater. (2011) Conformal Printing of Electrically Small Antennas on 3D Surfaces Pressure Assisted-Micro Syringe and PCL/PLLA grid Resolution: μm Not enough!

6 Electrohydrodynamic Methods Using pressure to drive smaller flows is difficult High pressure for small nozzles Risk of clogging Use electrohydrodynamic (EHD) forces instead Park et al. Nature (2007) Mishra et al. J. Micromech. Microeng. (2010)

7 Electrospinning Overview Production of nanofibers Hundreds of materials High voltages Limited printing control Mats with Random Orientation ntechopen.com/

8 Near Field Electrospinning (NFES) Overview Idea: Collect fibers before onset of bending instability. Advantages: Improved Control Simple Reduced voltages Freeform 3D structures Multiple materials Schematic diagrams for (a) ES and (b) NFES Martinez Prieto et al. J Micro Nano Manuf (2015) Deposition of Fibers and Beads

9 Near Field Electrospinning (NFES) Deposition Deposition of Fibers Deposition of Beads

10 Near Field Electrospinning (NFES) Multilayer Structures Multilayer Structures have been limited to fibers > 5 micron in diameter Stacking smaller fibers results in improved printing resolution Self-assembled structure Pre-patterned substrate Low Concentration, low molecular weight ink Kim et al. Nanolett (2010) Lee et al. Langmuir (2012) Luo et al. ACS Appl Mater Interf aces (2010) He et al. J Phy s D: Appl Phy s (2016)

11 Near Field Electrospinning (NFES) Challenges Control Limited Resolution Limited Repeatability Modelling Residual Charges Low throughput Process Initiation

12 Control Methods in Electrospinning Electrode rings Steering electrodes Use of AC field and DC field Modified collector geometry Deitzel et al. Polymer (2001) Li et al. Adv Mater (2004) Rotating collector Nurfaizeyl et al. J Mat Sci (2012) Theron et al. Nanotechnology (2001) Magnetic field control of fibers Kessick et al. Poly mer (2004) Wu et al. Chaos, Solitons & Fractals (2007)

13 Proposed Control Methods Control of electric fields actively and passively Take advantage of charged nature of the jet Martinez Prieto et al. J. Micro Nano Manuf. (2015) Horizontal electric fields Modification of electrode geometry

14 Electric Field Modelling (I) Increasing Spacing 5 V V 0 =1200 V V e d e 1 mm 5 V 50 V 1000 V Needle-plate model for nearfield electrospinning 500 V 1000 V Electric potential along main axis for different voltages. Electric potential contours with 0.4 mm electrode spacing

15 Electric Field Modelling (II) 5 V 50V Increasing Spacing 1000 V 1 mm Increasing Vol tage Electric potential contour with 9.6 mm spacing 1

16 Experimental Results Electric Field Control Spinneret ON Electrode Direction OFF Fiber Path 500 μm PEO Solution Guiding Electrode h ON Δh=50 μm OFF Deposition Direction h OFF 500 μm Small features (~50 μm ) can be created OFF Guiding electrode is 30 gauge copper wire (250 μm diameter) Guiding electrode connected to 5 V power supply and connected to a switch ON OFF Electrode Direction ON Repeatability at corners was increased by three fold Martinez-Prieto et al. J. Micro Nano-Manuf. (2015) Deposition Pattern 500 μm

17 Focusing Electric Fields Pin-to-pin setups Microscope Spinneret Sample Holder Grounded Tungsten Electrode 3 axis stage Pin-to-plate Pin-to-pin Experimental Setup Sharp electrode use as ground to focus the electric field onto a single point.

18 Focusing Electric Fields Results Pin to plate Sharp pin electrode modeled as rectangle Electric field magnitude increases by a factor of 3.6 Fiber spacing was reduced from ~50 μm to ~10 μm. Corners are still problematic Pin to Pin Electric Field (kv/m) Pin-Pin Pin-Plate x-coordinate (mm) Pin to plate 50 μm Xu et al. Presented at IWMF2014 Pin to Pin 50 μm

19 Deposition of Bead Arrays Applications 50 μm LEDs - Optics Kim et al. Nano Lett., 2015, 15(2) Biomolecule Patterning Poellmannet al. Macromol. Biosci, 2015, 11(9) Microelectronics Sutanto et al. J. Micromech. Microeng., 2012, 22(4) Microtexturing Chen et al. Adv. Funct. Mater., 2011, 21(24)

20 Deposition of Bead Arrays Mechano-electrospinning Deposition Process: 1. Jet attaches to substrate. 2. Additional material is added to bead. 3. Jet jumps to new location.

21 Deposition of Bead Arrays Challenge Is it possible to extend the technology to deposit 3D patterns? 1) Vibrations 2) Residual Charges

22 Jet Self Attraction for Multi Pass Features

23 High Magnification Videos of Deposition 500 um 100 um 100 um Initiation First Pass Second Pass

24 Deposition of lines and circles 1 Pass 200 μm 5 Pass 5 Pass 200 μm 10 Pass 200 μm 20 Pass

25 Effect of Number of Passes Normalized Metric [-] Run 1 - Area Run 2 - Area Volume 1 Pass 5 Pass 10 Pass Bead Height (μm) Pass 5 Pass 10 Pass Area increases with number of passes. Area increases at the same rate as volume indicating no height change.

26 Bead Growth Mechanism During Deposition After Solvent Evaporation 100 μm Additional passes increase volume Bead final shape is determined by evaporation SEM Image

27 Self Focusing Mechanism 1. Charged droplet builds on the grounded collector 2. Charge dissipates on the droplet between passes 3. On subsequent pass the droplet behaves like a neutral dielectric in an electric field: Negative charges migrate to the top boundary generating a very high electric field 4. Jet is attracted to top of the droplet 5. Process repeats V

28 Ink and Substrate Compatibility PAN-DMF on Copper PEO-Water on Aluminum PEO-Water on Silicon Wafer Does not work for non-conductive substrate (Parafilm, PDMS)

29 Conclusions Near-field electrospinning can be used for low-cost and continuous production of multilayer structures using fibers and bead arrays. Electric field control is an effective technique to increase resolution and repeatability of the process. The bead deposition process displays self-focusing behavior making them promising for controlling bead diameter or producing 3D structures.

30 Acknowledgements National Science Foundation Grant CMMI NUANCE Center at Northwestern University Advanced Manufacturing Processes Laboratory ampl.mech.northwestern.edu