Syringe Printing as a Method of Fabricating Hexagonally Structured Monolayers Composed of Microspheres

Gabriella Sciuchetti1 and Nicholas Boechler2

Center For Study of Capable Youth 1, Department of Mechanical Engineering2, University of Washington, Seattle, WA

AbstractOur research focuses on developing new methods of producing composite structures, namely locally-resonant granular metamaterials and phononic

crystals, particularly at the microscale. Phononic crystals require strict periodicity, involving precise structure and organization between the

individual component spheres. This required precision is difficult to attain through methods of self-assembly, which result in many defects in the

crystal structure, producing scattering effects and restricting testing. The alternative method of syringe printing described here allows for the

placement of individual spheres into specific configurations, with the potential to produce ‘perfectly’ periodic granular crystals. The process uses a pump paired with a syringe of a minute enough volume that spheres can be

dispensed individually, while a two-axis motion stage beneath allows for microsphere positioning. This setup allows for a more refined ability to

create granular crystals on a microscale, introducing the possibility of future studies of the dynamics of locally resonant metamaterials containing

particles of multiple materials. Thus far, we have been able to control the dispensing of several spheres through the syringe; going forward, we hope

to be able to isolate a single microsphere and are currently developing methods for precise spatial control of sphere placement.

Progress

Syringe Tip: • Challenge: Initially used a dispensing nozzle with standard 12° beveled

needle point; couldn’t dispense accurate amounts of spheres.• Progress: have transitioned to using a syringe with a blunt needle pointAngle of syringe:• Challenge: Unable to hold pump steadily enough when mounted

vertically• Progress: Mounting the pump at an angle of incline between 30° and 45°

• Current mounting method uses two parallel bars and a bent metal plate to hold at angle (see diagram below)

Related Works

Boechler, N., Eliason, J., Kumar, A., Maznev, A., Nelson, K., and Fang, N., “Interaction of a Contact Resonance of Microspheres with Surface Acoustic Waves.” Physical Review Letters, 111, 036103 (2013).

Villar, G., A. D. Graham, and H. Bayley, “A Tissue-Like Printed Material.” Science 340.6128: 48-52 (2013).

Xu, C., Chai, W., Huang, Y. and Markwald, R. R., “Scaffold-free inkjet printing of three-dimensional zigzag cellular tubes.” Biotechnol. Bioeng., 109: 3152–3160 (2012).

Method:• Similar to 3-D inkjet printing• Simpler interface and fewer components

than inkjet• Cost effective and less prone to technical

difficultySystem Requirements:• Syringe pump programmable to dispense

precise volumes of fluid at specific rates• Motion stage that can be controlled to

move in consistent increments as small as the diameter of a sphere

• A syringe with an inner diameter slightly larger than that of a sphere

Setup:• Syringe pump inclined

• Causes spheres to align at the tip of needle

• Simplifies calculations by eliminating liquid in tip of needle

• Slide less than 100µm underneath the tip of the syringe• Movement of slide controlled via

stage• Creates water bridge between slide

and needle• Secure Mounting:

• Must be mounted securely to record accurate photos

• We monitor the experiment using a ThorLabs camera with a 4 or 10x lens

• If syringe is not secured, the tip of the needle vibrates slightly, making it impossible to focus camera.

Process:• Set volume is pumped to dispense single

sphere• Pumping stops and slide moved to new

position• Pumping resumes and another sphere is

dispensed.• Repeated as necessary to create a

perfect hexagonally-structured granular crystal.

Theory

Diagram A:The plunger dispenses an initial sphere into a water droplet.

Diagram B:The droplet touches the interface and breaks as the interface moves to the right.

Diagram C:As the water from the initial drop evaporates, leaving the first sphere in place, another sphere is dispensed into a droplet.

Syringe Pump

Bars

Metal PlateSupports

Next Steps

• Increase angle of pump and rework setup to ensure stability• Program motion stage and pump for multi-sphere configurations• Investigate effects of placing multiple spheres in quick succession (without allowing

water to evaporate)