Name: Prescribed 3-D Direct Writing of Suspended Micron/Sub-micron Scale Fiber Structures via a Robotic Dispensing System (Video) | JoVE Journal
Uploaded: 2015-06-12T13:00:00.000+00:00
Duration: 10 min 36 s
Description: Learn to fabricate suspended micron and sub-micron polymer fibers using an automated robotic dispensing system with precise 3D control. This method enables complex web-like structures for biomaterials and microfluidic applications.

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5 minutes

This work is supported by the NSF-EPSCoR (grant #0814194) and the Department of Bioengineering.

1. Equipment Set-up
<ol>
	<li>Assemble dispensing system and connect valve controller and syringe barrel to the pneumatic source, via a pressure regulator, to set the pressure at 15 psi to dispense the polymer solution from the needle tip at a flow rate of 2.45 µl/min.</li>
	<li>Insert the 3-axis robot and dispensing system into a thermal enclosure to ensure a stable working environment (Figure 2).</li>
	<li>Install Joint-Robot Control Points (JR-C Points) software provided by the system manufacturer and connect 3-axis robot to a computer via serial communication port.</li>
	<li>Mount dispensing valve to 3-axis robot and install needle tip onto the valve.</li>
	<li>Level the robotic stage platen according to the manufacturer’s guidelines to ensure flatness with respect to the height of the valve tip15.</li>
	<li>Assemble a feedback-controlled heater in the enclosure to add environmental control.</li>
</ol>
<img alt="3-Axis dispensing robot setup; includes valve, microscope, feedback heater for precision fluid handling." src="/files/ftp_upload/52834/52834fig2.jpg" data-altupdatedat="1787630408000" data-alt="Figure 2"> 
Figure 2. (A) 3-Axis dispensing robot with required accessories housed inside an enclosure; and, (B) close up image of the dispensing valve with attached USB microscope for visualization. <a href="https://www.jove.com/files/ftp_upload/52834/52834fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
2. Experimental Materials and Controlling Factors
<ol>
	<li>Controlling factors and their combination.
	<ol>
		<li>Vary feed rate from 1% speed (5 mm/sec) up to 100% (500 mm/sec), by the JR C-Points software. For this application, use a 2% speed (10 mm/sec) to fabricate the fiber structures presented in this work.</li>
		<li>Vary polymer solution concentrations to attain specific viscosity, surface tension and volatility parameters required for desired application. For this application, use a 24% polymethylmethacrylate (PMMA) in Chlorobenzene solution to fabricate the fiber structures presented in this work.</li>
		<li>Vary control valve dispense time from 0.02 sec to 1 sec in order to eject solutions via pneumatic air. For this application, use 0.02 sec to fabricate the fiber structures presented in this work.</li>
		<li>Select a gauge size of high precision needle tips to dispense polymer solutions. For this application, use a 30 G (inner diameter (ID) = 152.4 µm) tip to fabricate the fiber structures presented in this work.</li>
		<li>Set the operating temperature range between 70 °F to 100 °F in the thermally insulated box to maintain a constant evaporation rate of the polymer sample. For this application, use a temperature of 70 °F to fabricate the fiber structures presented in this work.</li>
	</ol>
	</li>
	<li>Preparation of polymer solutions.
	<ol>
		<li>Mix polymer resins of polymethyl methacrylate (PMMA; 0.72 g) with the solvent Chlorobenzene (2.28 g) under a chemical flow hood.</li>
		<li>Calculate the weight of the polymer (PMMA) and its solvent (chlorobenzene) to achieve the desired concentration of polymer in solution. For this application, use a 24% polymethylmethacrylate (PMMA) in Chlorobenzene solution to fabricate the fiber structures presented in this work.</li>
		<li>Place desired amount of polymer powder/resin into glass vial. For this application, use 0.72 g of PMMA resin to attain a 24% concentration of PMMA.</li>
		<li>Transfer solvent onto polymer within vial by pipette until the total weight of 3 g is reached.</li>
		<li>Mix the vial for 1 min using a vortex shaker and ultrasonically process them for 5 hr to completely dissolve the polymer powder/resin.</li>
		<li>Check the transparency of solutions, if there is any cloudiness or opaqueness to sample continue to sonicate until clear.</li>
	</ol>
	</li>
	<li>Viscosity measurement of polymer solutions.
	<ol>
		<li>Measure solution viscosities via cone-and-plate viscometer (e.g., LVDV-II+ and RVDV-II+)16.</li>
		<li>Load 0.5 ml of known viscosity standard sample (a glycerin-based and water mixture) provided by the viscometer manufacturer to calibrate the viscometer in order to minimize errors in the viscosity measurements. The manufacturer provided a variety of standard samples for calibrating the viscometer. Use the glycerin-based standard sample with a viscosity of 100,000 cP.</li>
		<li>Connect water jacket to viscometer to maintain the test fluid at a constant operating temperature.</li>
		<li>Start test fluid measurement by moving the On/Off switch to the On position to initiate rotation of the spindle. Once the value of the torque on the display panel has stabilized, record the torque and calculate the final viscosities using the relationship between torque, spindle multiplier constant and speed of spindle16 
		<img alt="Static equilibrium equation ηs=TK×SMC×(10000/RPM); formula diagram for mechanical analysis." src="/files/ftp_upload/52834/52834eq1.jpg" data-altupdatedat="1787630408000" data-alt="Equation 1"> 
		where is viscosity, RPM is the speed of the spindle affixed to cone, TK is the torque (0.09373 for LVDV-II+, 1 for RVDV-II+), SMC is the spindle multiplier constant that depends on the specific spindle being used during the viscosity measurement. For this study, the CP-52 spindle was used which has a spindle multiplier constant of 9.83.</li>
	</ol>
	</li>
	<li>Surface tension measurement of polymer solutions.
	<ol>
		<li>Measurement method refers to the Wilhelmy technique.14</li>
		<li>Place 1 ml test solutions in a glass vial onto a high-resolution balance (scale resolution = 0.001 g). Dip a glass rod of known diameter into test solutions.</li>
		<li>Control the position of rod via a servo or stepper controlled linear actuator to touch surface and partially immerse into test solutions with zero contact.</li>
		<li>Monitor and record the change in mass measurement on the balance when removing rod from solution surface.</li>
		<li>Calculate surface tension by force change, perimeter of rod and contact angle of fluid on the rod. 
		<img alt="Stress formula, σ=F/(l·cosθ), equation in physics, diagram for static equilibrium study." src="/files/ftp_upload/52834/52834eq2.jpg" data-altupdatedat="1787630408000" data-alt="Equation 2"> 
		where is the wetted perimeter of rod (l = 10.05 mm with diameter = 3.2 mm), θ is contact angle of fluid on the rod, F is force change due to surface tension of test fluid on the tip of rod.</li>
	</ol>
	</li>
	<li>Mass transfer coefficient measurement of solutions.
	<ol>
		<li>Measure mass transfer coefficients of polymer solutions by thermogravimetric analysis.14</li>
		<li>Load 30 µl of the 24% (by weight) PMMA polymer solution onto a platinum plate before taring the balance.</li>
		<li>Vent the chamber, program the device to run at desired operating temperature (70 °F) for 2 hr to monitor mass of target solutions.</li>
		<li>Calculate the mass transfer coefficients by changes in the solution’s mass, area of solution/air interface and density. 
		<img alt="Polymer absorption coefficient formula, χ = equation 3; optical study, material analysis." src="/files/ftp_upload/52834/52834eq3.jpg" data-altupdatedat="1787630408000" data-alt="Equation 3"> 
		 
		where m(t) is the mass of PMMA solutions, A is the area of the solution/air interface (equals 78.5 mm2 for standard plate), mPOLYMER is the polymer mass in the solution and is the density of the solution.</li>
	</ol>
	</li>
</ol>
3. Direct Write Experiment Procedure
<ol>
	<li>Dispensing system sample loading protocol.
	<ol>
		<li>Load 3 ml of polymer solution into the syringe barrel, place piston into syringe barrel to eliminate inconsistent pneumatic pressure distribution.</li>
		<li>Twist the inlet line adapter on the syringe barrel, connect it to the source line air tube.</li>
		<li>Choose desired gauge size of the precision needle tip to perform experiment.</li>
		<li>On the dispense controller panel, switch to purge state and click “cycle” button to fill the dispense valve with polymer solution until discharged from the needle tip.</li>
		<li>Wipe residual polymer solution from the tip in preparation of a programmed fiber writing procedure.</li>
	</ol>
	</li>
	<li>Direct write polymer fibers with 3-axis robot and dispensing system.
	<ol>
		<li>Determine the robot stage offset to reposition the tip of the dispensing needle from the default home position to the initiation point of the prescribed micro/sub-micron fiber structure to be drawn. Mount a USB microscope (magnification = 200X) to the dispensing system valve bracket, which translates along the Z-axis. Manually focus on the dispenser tip by adjusting the focusing knob on the USB microscope that assists in precisely positioning the valve tip to the desired location, prefabricated substrate or device.</li>
		<li>Create/design the desired fiber structure pattern (Figures 3A, 4A, and 5A) using a CAD software package. Input the spatial coordinates (x, y, z) in the robot JR-C controlling software for all initiation and termination points in sequential order with respect to the desired pattern created within the CAD program (Figure 3B, 4B, and 5B). 15</li>
		<li>Transfer the completed fiber structure design program from the computer to the robot by clicking “Send C&amp;T Data” under the Robot menu within the JR-C software15.</li>
		<li>Load 3 ml of PMMA solution sample of known concentration (24%) into syringe barrel, purge valve and needle, set all the dispensing parameters for the valve controller and robot controlling software.</li>
		<li>Place prefabricated substrate onto the robot stage platen, close the thermal enclosure doors to prevent ambient air flow, which can induce unstable evaporation of the polymer solution.</li>
		<li>Start writing the fibers onto the substrate by clicking the robot menu from JR-C software and selecting “test running”15.</li>
		<li>DC sputter coat a conductive gold metal layer for 2 min until a 2 nm thick layer of gold is deposited onto the drawn fibers to allow visualization of the fibers in the scanning electron microscope.</li>
		<li>Measure the diameter and structure of fibers via scanning electron microscope17. Microscope parameters: High voltage level: 2.00 kV; Objective: InLens, Working Distance (9.0 mm).</li>
	</ol>
	</li>
	<li>Perform the dispensing system cleaning procedure under a chemical flow hood.
	<ol>
		<li>Place the dispensing system in a chemical flow hood to perform the cleaning procedure.</li>
		<li>Disassemble needle valve according to manufacturer’s protocol.</li>
		<li>Place all the metal parts into a beaker, pour acetone into the beaker until all parts are immersed.</li>
		<li>Place beaker in an ultrasonic bath for 30 min to remove all polymer remnants.</li>
		<li>Rinse all parts under flowing DI water, then use air gun to blow them dry.</li>
	</ol>
	</li>
</ol>
<img alt="Static equilibrium, ΣFx=0, diagram, lattice structure, beam analysis, node numbering method." src="/files/ftp_upload/52834/52834fig3.jpg" data-altupdatedat="1787630408000" data-alt="Figure 3"> 
Figure 3. (A) Example of designed “quad” web structure on a 10 mm x 10 mm frame, (B) sequential point-to-point spatial instructions to be inputted into JR-C point software. <a href="https://www.jove.com/files/ftp_upload/52834/52834fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Perspective grid diagram illustrating vanishing points and horizon lines for 3D drawing methods." src="/files/ftp_upload/52834/52834fig4.jpg" data-altupdatedat="1787630408000" data-alt="Figure 4"> 
Figure 4. (A) Example of designed “symmetric” web structure on a 10 mm x 10 mm frame, (B) sequential point-to-point spatial instructions to be inputted into JR-C point software. <a href="https://www.jove.com/files/ftp_upload/52834/52834fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Static equilibrium; truss diagram; numbered nodes for structural analysis; educational use." src="/files/ftp_upload/52834/52834fig5.jpg" data-altupdatedat="1787630408000" data-alt="Figure 5"> 
Figure 5. (A) Example of designed “dual chevron” web structure on a 10 mm x 10 mm frame, (B) sequential point-to-point spatial instructions to be inputted into JR-C point software. <a href="https://www.jove.com/files/ftp_upload/52834/52834fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

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The authors have nothing to disclose.

Before attempting each trial, it is critical that the viscosity, mass transfer coefficients and surface tension test of the polymer solutions be accurately measured in order to determine whether the robot and dispensing system is capable of processing the desired polymer. As described previously by our group, the polymer solutions must retain adequate: 1) surface tension to enable the formation of liquid filaments into micron/sub-micron structures; 2) viscosity to withstand capillary break up; and, 3) evaporation rate to enhance fiber solidification18. The synergy between these parameters is key to successfully produce fibers over a specified range of diameters. At the same time, instability in any of these parameters prevents the formation of micron/sub-micron scale fibers. To maintain the synergy between these parameters during fiber fabrication, it is important to ensure that the needle and needle valve are thoroughly cleaned after a direct-write session to prevent: 1) contamination of the solution; 2) a reduction in the polymer solution flow rate through the needle; and, 3) excessive growth in the polymer bead at the tip of the needle. In addition, the temperature-controller on the heater must be set to the desired temperature to maintain a constant evaporation rate of the polymer solution.
The bifurcated branch fibers were 59%, 41% and 24% larger in diameter than that of the support structures in Figures 6-8, respectively, using the 24% PMMA solution. This is primarily due to the distance at which the fibers are drawn. Specifically, the support structures are drawn across the entire width of the substrate (10.0 mm in X and Y directions; 14.4 mm diagonally). As a result, these are the longest fibers of the overall suspended structures. The bifurcated branch structures are significantly shorter, ranging from 7 mm maximum length down to 2.5 mm. This shorter fiber drawing length does not effectively induce the fiber strain required during the fiber thinning process in order to produce the small diameter fibers. On the other hand, larger diameter wires are required to serve as the support fibers in order to effectively sustain the tugging and deformation induced during the bifurcated branch drawing process. As the bifurcation branches are drawn across the support fibers, a remodeling of the support fiber geometry can occur due to the drawing forces as well as a localized dissolution of the PMMA polymer at the interface between the support and branched fibers from the solvent present in the polymer solution. Thus, in some instances, the support fibers may need to be fabricated from a polymer solution consisting of a higher concentration of polymer to produce larger diameter and mechanically stronger fibers.
There are primarily three effective methods for modifying the existing protocol to generate a wider range of support and branched fiber diameters: 1) initially dispense the polymer from a larger needle tip (e.g., 25 G; ID = 254 &#956;m) to generate the support fibers and then exchange for a smaller needle tip (e.g., 32 G; ID = 101.6 &#956;m) to fabricate the smaller branched fibers; 2) as noted above, use multiple polymer concentrations; and/or, 3) adjust the feed rate, i.e., the speed at which the stage traverses, where increasing the feed rate produces smaller diameter fibers and decreasing the feed rate creates larger diameter fibers. To date, we have been able to successfully fabricate fibers as small as 90 nm; however, the fiber yield at this dimension is low due to capillary breakup.
One limitation of the automated direct write process is that only one concentration of polymer solution can be dispensed at a time. This restricts the level of complexity of the suspended structures to be developed without having to: 1) add a second dispensing valve to the robot; or, 2) remove the existing valve and perform the cleaning protocol (Section 3.4) before dispensing the second polymer solution, which takes additional time. A second limitation is the feed rate (or print speed), where the maximum feed rate that the system is capable of achieving is 500 mm/sec. However, there is a tradeoff between feed rate and fiber formation. Specifically, if the inertial forces (forces due to the feed rate) are greater than the surface tension forces and evaporation rate of the polymer solution, fiber formation does not occur. On the other hand, if the feed rate is too low, fibers will fracture due to excessive evaporation before and during the elongation process. Thirdly, fiber and structure dimensions are limited to the operating range of the stage of the robot, i.e., 200 mm, 200 mm and 25 mm (with a 10 &#956;m positional accuracy) in the x, y and z directions, respectively. Nonetheless, this process does enable the formation of high aspect ratio (fiber length:diameter) fibers. Strategically varying the dispensing tip size and the polymer solution concentration would allow for a broader fiber diameter range, creating the ability to generate freely suspended structures of higher complexity.
By following the protocols stated above, micron and submicron diameter polymer fibers can be generated with a high level of spatial control by exploiting the surface tension-driven fluid mechanics of the polymer solutions, which cannot be controlled with any other wet, dry or electrospinning processes. From prior work8,19, we know that this technique can be utilized to fabricate intricate micro/submicron fluidic devices19 and bioengineered scaffolds8. This cheap and easy technique has its own advantages over traditional planer fabrication methods in many ways.

Over the past several decades, a variety of fabrication techniques, such as wet spinning, dry spinning and electrospinning, have been employed to create novel polymer fiber structures with diverse and robust biological, chemical, electrical and mechanical properties1-12. Although these spinning techniques are capable of generating suspended three-dimensional fibers, they are limited in their ability to precisely control fiber orientation in three dimensions since fiber deposition via these processes are random in nature. In addition, these techniques are restricted in their dimensional range for fiber fabrication; specifically, fibers produced via wet and dry spinning vary in diameter from tens to hundreds of microns, while electrospinning yields fibers with diameters ranging from tens of nanometers to a single micron13.
To provide more precise control of fiber orientation in 3-D space, our group developed a self-assemble or “direct-write” fiber fabrication process that directly ejects a polymeric material out of a hollow capillary and then draws individual filaments which thin and solidify into predictable fiber diameters by exploiting surface tension-driven fluid mechanics14. Our initial direct-write system for increasing the level of control of fiber position and diameter consisted of a custom fabricated spring loaded syringe dispensing system attached to the head of a custom made Ultra-High Precision Micromilling Machine (Figure 1). The UHPMM had a stage with a positional resolution of 1.25 nm in the X and Y directions and 20 nm in the Z direction that was programmatically controlled to create micron and sub-micron scale wires and structures. One limitation of this particular direct write system was the lack of flow control of the polymer solution through the needle tip. Although the spring loaded dispensing system successfully generated constant flow through the tip, a continuously expanding spherical bead of polymer solution was created at the outlet of the syringe tip, which varied in size and volume depending on environmental conditions.
<img alt="Spectroscopy setup with microscope for optical excitation measurement; equipment for spectral analysis." src="/files/ftp_upload/52834/52834fig1.jpg" data-altupdatedat="1787630408000" data-alt="Figure 1"> 
Figure 1. Image of Ultra High Precision Micromilling Machine: the first direct write system employed in fabricating micron/sub-micron scale structures. <a href="https://www.jove.com/files/ftp_upload/52834/52834fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
The inconsistency of this source bead impacted the ability of the system to repeatedly fabricate wires of a prescribed diameter. Albeit, structures were successfully generated using this direct write process, enhancement of the process by increasing control of the flow of polymer solution would allow for more precise, prescribed fiber diameters through regulation of the bead size at the syringe tip. Thus, this work describes the implementation of a 3-axis automated dispensing system with pneumatically actuated dispenser valve to precisely control the polymer solution flow rate and tip bead size to create prescribed, micron/sub-micron suspended structures.

<table><tbody><tr><td>ROBOT DR2203N 3 AXES 200MM X 200MM</td><td>Nordson EFD</td><td>7023145</td><td>3-Axis Robot</td></tr><tr><td>CONTROLLER 7100, DISPENSE VALVE</td><td>Nordson EFD</td><td>7015340</td><td>Valve Controller</td></tr><tr><td>MICRODOT VALVE</td><td>Nordson EFD</td><td>7021233</td><td>Microdot Valve</td></tr><tr><td>ROBOT ACC FIXTURE PLATE 200MM</td><td>Nordson EFD</td><td>7028276</td><td>Fixture Platen</td></tr><tr><td>ROBOT ACC DRN / DSRN POINTS SOFTWAR</td><td>Nordson EFD</td><td>7023144</td><td>JR-C Software</td></tr><tr><td>ROBOT MOUNT VALVE UNIVERSAL</td><td>Nordson EFD</td><td>7028273</td><td>Microdot Valve Mount</td></tr><tr><td>15 PSI BARREL PRESS. REGULATOR</td><td>Nordson EFD</td><td>7020585</td><td>Barrel Regulator</td></tr><tr><td>KIT O BRL/PIST 5CC CL/WH 40</td><td>Nordson EFD</td><td>7012096</td><td>5CC Barrels with Pistons</td></tr><tr><td>ADAPTER ASM O 5CC BL</td><td>Nordson EFD</td><td>7012054</td><td>Pneumatic Barrel Adapter</td></tr><tr><td>TIP 30GA .006X.25 LAVNDR 50PC</td><td>Nordson EFD</td><td>7018424</td><td>30 gauge Needle Tip (0.250&quot; length)</td></tr><tr><td>Electric Baseboard Heater (500&amp;nbsp;W, 30&quot; length)</td><td>Cadet</td><td>2F500</td><td>Heater</td></tr><tr><td>Temperature Controller with Timer</td><td>Control Company</td><td>130726596</td><td>Temperature Controller</td></tr><tr><td>eScope USB Microscope</td><td>OiTez</td><td>DP-M02</td><td>200X USB Microscope</td></tr><tr><td>Poly(methyl methacrylate)</td><td>Aldrich</td><td>182265-500G</td><td>PMMA Powder</td></tr><tr><td>Chlorobenzene</td><td>Sigma Aldrich</td><td>284513</td><td>Solvent to dissolve PMMA</td></tr></tbody></table>

prescribed 3-d direct writing of suspended micron/sub-micron scale fiber structures via a robotic dispensing system

Prescribed 3-D Direct Writing of Suspended Micron/Sub-micron Scale Fiber Structures via a Robotic Dispensing System

A 3-axis dispensing system is utilized to control the initiating and terminating fiber positions and trajectory via the dispensing software. The polymer fiber length and orientation is defined by the spatial positioning of the dispensing system 3-axis stages. The fiber diameter is defined by the prescribed dispense time of the dispensing system valve, the feed rate (the speed at which the stage traverses from an initiating to a terminating position), the gauge diameter of the dispensing tip, the viscosity and surface tension of the polymer solution, and the programmed drawing length. The stage feed rate affects the polymer solution&#8217;s evaporation rate and capillary breakup of the filaments. The dispensing system consists of a pneumatic valve controller, a droplet-dispensing valve and a dispensing tip. Characterization of the direct write process to determine the optimum combination of factors leads to repeatedly acquiring the desired range of fiber diameters. The advantage of this robotic dispensing system is the ease of obtaining a precise range of micron/sub-micron fibers onto a desired, programmed location via automated process control. Here, the discussed self-assembled micron/sub-micron scale 3D structures have been employed to fabricate suspended structures to create micron/sub-micron fluidic devices and bioengineered scaffolds.

Images of the actual structures produced via the 3-axis robot and direct write method for each of the respective designs and JR C-Point algorithms defined in Figures 3-5A &amp; B above are shown in Figures 6A, 7A &amp; 8A. As can be seen in the resulting images, three-dimensional, freely suspended fibers have been successfully “written” onto the substrates by precisely manipulating the dispenser tip to prescribed spatial locations including the initiating/terminating points as well as points of intersection. The insets of these figures magnify the intersection points of suspended fibers, which demonstrate the system’s ability to precisely control fiber orientation (Figures 6B, 7B &amp; 8B) in 3-D space.
<img alt="Crystalline network, microscope image, structural detail magnified, material science study." src="/files/ftp_upload/52834/52834fig6.jpg" data-altupdatedat="1787630408000" data-alt="Figure 6"> 
Figure 6. (A) Optical image of fabricated “quad” suspended web structure having 2 support fibers (diagonals) and 12 bifurcated branched PMMA fibers (15X optical magnification; scale bar = 1 mm), (B) SEM image of a single bifurcated fiber (289X magnification; scale bar = 100 μm). <a href="https://www.jove.com/files/ftp_upload/52834/52834fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Graphene nanostructure analysis, microscopy image; highlights electron pathways, material study." src="/files/ftp_upload/52834/52834fig7.jpg" data-altupdatedat="1787630408000" data-alt="Figure 7"> 
Figure 7. (A) Optical image of fabricated “symmetric” suspended web structure having 1 support fiber (horizontal) and 11 bifurcated branched PMMA fibers (15X optical magnification; scale bar = 1 mm), (B) SEM image of a single bifurcated fiber (107X magnification; scale bar = 100 μm). <a href="https://www.jove.com/files/ftp_upload/52834/52834fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Microscopic structure analysis; magnified image of fiber network; material study, microscopy technique." src="/files/ftp_upload/52834/52834fig8.jpg" data-altupdatedat="1787630408000" data-alt="Figure 8"> 
Figure 8. (A) Optical image of fabricated “dual chevron” suspended web structure having 1 support fiber (horizontal) and 22 bifurcated branched PMMA fibers (15X optical magnification; scale bar = 1 mm), (B) SEM image of a single bifurcated fiber (80X magnification; scale bar = 100 μm). <a href="https://www.jove.com/files/ftp_upload/52834/52834fig8large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Figure 9 displays close up view of the sequential point-to-point order of fiber fabrication at which the 3-axis robot and dispensing system can generate the freely suspended web-like structures. The polymer contact points displayed with numbers correspond to the programmed initiating and terminating points in the JR-C software referenced in Figure 3B above. The arrows represent robot trajectory. Figure 10 displays micron and submicron polymer fibers, which demonstrates the direct write system’s ability to fabricate wires of varying sizes.
<img alt="Microscopy of microfluidics; diagram shows fluid flow paths; experiment setup for fluid dynamics." src="/files/ftp_upload/52834/52834fig9.jpg" data-altupdatedat="1787630408000" data-alt="Figure 9"> 
Figure 9. SEM image illustrating the sequential point-to-point fabrication order for drawing the micron and submicron polymer fibers (29X magnification; scale bar = 200 μm). <a href="https://www.jove.com/files/ftp_upload/52834/52834fig9large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Microscopy image of nanowire fabrication, showing fiber alignment in microengineering process." src="/files/ftp_upload/52834/52834fig10.jpg" data-altupdatedat="1787630408000" data-alt="Figure 10"> 
Figure 10. SEM image of micron (6.5 µm) and sub-micron (555 nm) fibers drawn using a 20% concentration PMMA polymer solution (2,270X magnification; scale bar = 2 μm). <a href="https://www.jove.com/files/ftp_upload/52834/52834fig10large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Polymer fiber length and diameter were measured using scanning electron microscopy. Table 1 shows the average wire diameter for each unique structure presented in Figures 6-8 above corresponding to the bifurcated branch fibers and the support fibers. Table 2 displays the polymer parameters that were measured from the 24% PMMA solutions that were utilized to fabricate the structures noted above.
<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td></td>
			<td>Structure diameter in Figure 6</td>
			<td>Structure diameter in Figure 7</td>
			<td>Structure diameter in Figure 8</td>
		</tr>
		<tr>
			<td>Support fibers </td>
			<td>8.65 ± 1.43 µm</td>
			<td>9.39 ± 1.23  µm</td>
			<td>9.31 ± 1.65  µm</td>
		</tr>
		<tr>
			<td>Branch fibers</td>
			<td>20.96 ± 3.35 µm</td>
			<td>15.92 ± 1.44  µm</td>
			<td>12.24 ± 5.42  µm</td>
		</tr>
	</tbody>
</table>
Table 1. Average diameters of the suspended support and branch fibers shown in Figures 6-8 for a 24% PMMA solution.
<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td></td>
			<td>24% PMMA</td>
		</tr>
		<tr>
			<td>Viscosity (Pa*sec)</td>
			<td>35.19</td>
		</tr>
		<tr>
			<td>Surface Tension (mN/m)</td>
			<td>262.01</td>
		</tr>
		<tr>
			<td>Mass Transfer Coefficient (m/sec)</td>
			<td>8.59 x 10-8</td>
		</tr>
	</tbody>
</table>
Table 2. Polymer parameters of the 24% PMMA solutions that were utilized to fabricate the fiber structures presented in this work.

Here, we present a protocol to fabricate freely-suspended, micron/sub-micron scale polymer fibers and &#8220;web-like&#8221; structures generated via automated direct writing procedure by means of a 3-axis dispensing system.

A 3-axis dispensing system is utilized to control the initiating and terminating fiber positions and trajectory via the dispensing software. The polymer ...

The overall goal of this procedure is to fabricate freely suspended micron to sub micron scale polymer fibers and web-like structures using an automated direct writing procedure by means of a three axis dispensing system. This is accomplished by first setting up the automated equipment with the valve controller and dispensing system. After the mechanical setup, the liquid polymer sources are synthesized and quality control is assessed by assaying for real logical parameters such as surface tension and viscosity.Next, the structures are designed using a CAD software. Then the spatial coordinates of the design structures are transferred to the robotic controller software. Subsequently, the robot will translate the dispensing needle to the predetermined locations to fabricate freely suspended micron, sub micron scale polymer fibers and web-like designs.The primary advantage of this technique over others, such as wet, dry, and electro spinning, is that we can precisely control the fiber diameter and the fiber orientation and dimension in all three spatial dimensions. Generally, individuals new to this technology will struggle because the synergy between surface tension with scarcity evaporation rate and feed rate will be okay to success successfully producing the fibers over a space fire range of diameters. Demonstrating the procedure today will be Han Yon, a graduate student in my laboratory To set up the robotic apparatus begin by assembling the dispenser system on the lab bench.The four pneumatic components to be connected during this process are the pressure source, the regulator that controls the source pressure, the downstream valve controller, and the main syringe barrel. After the pneumatic components have been assembled, adjust the main regulator to 15 PSI. This will allow the polymer solution to be dispensed from the needle tip at a flow rate of 2.45 microliters per minute.Next, place the three axis robotic base into a dedicated thermal enclosure and mount the entire dispensing system along with the valve controller on top of the robotic base. The climate controlled enclosure will provide a stable environment for both the polymer solution and the sensitive electronics to operate in in the next phase of the robotic assembly process. First, make a serial port connection between the robotic base and a computer.Then install the dedicated controller software onto the computer and test the software hardware communication prior proceeding. Further level the robotic stage platinum. According to the manufacturer's guidelines, this ensures that dispensing tip will be globally orthogonal to the robotic stage during lateral actuations.Moreover, this will also ensure precise movement along the Z axis during vertical needle actuations. To prepare a polymer solution at a particular concentration of interest begin by calculating the amount of polymer powder and solvent needed in order to satisfy two simultaneous criteria. Their weight ratio should equal to the desired concentration percentage, and also the total weight of the two components should add up to exactly three grams.For instance, if a 24%acrylic solution is to be used for the fiber processing, the mixture can be prepared by first weighing point 72 grams of polymethyl methacrylate or PMMA and then adding two point 28 grams of chloro benzene. Next place an empty glass vial on the micro balance. After zero weight balancing, add the PMMA powder into the vial.Then using a glass pipette, dispense chloro benzene into the vial until the total weight of both chemicals reaches three grams. To facilitate, fold the solution of the polymer pellets. Vortex the vial for one minute and place the vial into an ultrasonic bath for approximately five hours.Check the transparency of the resulting solution if it is still opaque. Repeat the ultrasonic agitation step until the solution becomes fully transparent. In order to design a fiber pattern using CAD software, a relationship between the physical positional coordinates of the stage origin and the CAD drawing origin is required to ascertain this origin referencing relationship.Begin by fixing a USB microscope onto the mounting bracket next to the dispensing valve. Then place a prefabricated substrate onto the robotic stage and perform a rough stage translation such that the desired region for polymer deposition comes into the microscopes field of view. Manually adjust the microscope until the dispenser needle comes into focus.Using software control, apply additional fine adjustments on the X, Y, and Z access such the physical location of the needle matches the corresponding structural origin within CAD drawing. Now record the current XY stage coordinates into the computer using the stage coordinate as the design origin code, the initiation and termination coordinates of each line segment of the polymer fiber design. Finally, choose the sense c and t data command under the robot menu and upload the CAD file from the computer to the robot.The robot is now ready to be prepped for polymer solution loading and direct writing of the fiber network. While avoiding bubble formation, carefully load three milliliters of the clarified polymer solution into the syringe barrel. Then insert the piston into the syringe barrel.This will eliminate inconsistent pneumatic pressure distribution during subsequent steps. Next, twist the inlet line adapter on the syringe barrel to facilitate a direct connection between the barrel and the air source line. Switching attention to the other end of the syringe barrel.Choose a needle tip of the desired gauge size and mount the precision needle onto the dispensing valve. With the needle installed, locate the dispense controller panel and switch the state to purge and click the cycle button to fill the dispensing valve with the polymer solution. When the polymer solution starts to drip from the precision needle, wipe away any excess polymer discharge from the needle.Finally load the necessary dispensing parameters into both the dispense valve and the robot controller, and commence the direct writing routine by selecting the test running option from the main robot menu. Video light microscopy is used to qualitatively visualize the structures and scanning electron microscopy is used to attain quantitative dimensional data on the fibers and the structures. These images are of a structure formed from 24%PMMA solution.As illustrated, the direct writing process synthesized a three dimensional fiber matrix in which the relative location pattern and diameters of the support fibers and the branch fibers can all be independently tailored to weave a given web pattern. The robotic stage is programmed to move in sequential directions in which liquid polymer is simultaneously being dispensed. By lowering the PMMA concentration to 20%and changing the feed rate, the dynamic range of the polymer fiber diameter can vary on the order of tens of microns down to sub micron levels.Once master, this joint technique can be done in 30 minutes if it is performed properly. However, with inclusion of the preparation of the PMA solutions, designing the structure in the car software loading dispensing system with PMA solution and laying 30 minutes of drawing the fibers, the entire process will take approximately six hours. While attempting this procedure, it's important to note the trade offs between fiber formation and feed rate.For example, if the inertial forces that are generated by the feed rate are higher than the surface tension and the evaporation rate of the particular fluid material that we're working with, we will have capillary breakup and the wires will not form. Conversely, if our feed rate is too slow, we will lose control of the diameter of that Particular wire after its development. This technique enabled us and other researchers in the micro fabrication and nano fabrication community to be able to develop new microfluidic devices and platforms, both three dimensional as as well as traditional and develop new biological platforms and scaffolds in the field of bioengineering.

prescribed-3-d-direct-writing-suspended-micronsub-micron-scale-fiber

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JoVE Journal

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Learn to fabricate suspended micron and sub-micron polymer fibers using an automated robotic dispensing system with precise 3D control. This method enables complex web-like structures for biomaterials and microfluidic applications.

Prescribed 3-D Direct Writing of Suspended Micron/Sub-micron Scale Fiber Structures via a Robotic Dispensing System

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