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

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.