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Internal Research Project - Gener8
Abstract
Abstract
This project presents a cost-effective proof-of-concept device that utilizes acoustic waves to generate microscale droplets, pivotal in microfluidics for precise substance manipulation. Leveraging a piezoelectric element (PZT) and a linear solenoid actuator, the device breaks the surface tension of a small body of fluid at the outlet of a small nozzle. The design is driven by the equation |Δh| ≤ 2σ/ρga, where Δh is the distance between the inlet and outlet of the fluid, σ and ρ are the surface tension and density of the fluid, g is the gravitational constant, and a is the radius of the nozzle outlet. Results demonstrate an average droplet volume of 2 μl, with the prototype being at least 5 times more affordable than competing methods. This achievement signifies a substantial advancement in affordable and accessible droplet generation technology for various applications, including portable diagnostics and biotech research.
Project Statement
Project Statement
Design a proof-of-concept device that utilizes acoustic waves and cost-effective manufacturing methods to generate droplets less than 40 microliters (μl) in volume.
What is Microfluidics?
What is Microfluidics?
Microfluidics is a field in that deals with the precise manipulation of fluids at the microscale level. Acoustic microfluidics is a subsection of microfluidics that leverages acoustic fields to manipulate micro-scale fluids. Microfluidics is very important in the development of portable diagnostic devices and has a wide range of applications in the biotech, healthcare, and environmental monitoring industries. Common examples of microfluidic cartridges include COVID-19 tests, pregnancy tests, and inkjet printing.
Why do we need small droplets?
Why do we need small droplets?
Microscale droplets are useful in this field for the precise control and manipulation of substances; the creation of small droplets allows for more precise dosing and minimizes waste of expensive and rare substances.
Competing Designs
Competing Designs
produces many droplets
expensive to custom manufacture
not customizable after production
Objective
Objective
Design a proof-of-concept device that utilizes acoustic waves and cost-effective manufacturing methods to generate droplets < 40 microliters (μl) in volume.
Design a proof-of-concept device that utilizes acoustic waves and cost-effective manufacturing methods to generate droplets < 40 microliters (μl) in volume.
Concept
Concept
A waveform generator is used to send a pulse to a piezoelectric element (PZT), which causes acoustic vibrations, causing fluid in a reservoir to expel out of a nozzle in the form of single droplets.
Design
Design
The droplet generator design aims for cost-effectiveness and ease of fabrication. It comprises five key elements: a linear solenoid actuator, piezoelectric buzzer, fluid chamber, nozzle, and adjustable fluid reservoir.
The piezoelectric buzzer, along with its relevant electrical components, attach to the fluid chamber using RTV silicone sealant. The linear solenoid actuator is fixtured concentrically above the piezoelectric buzzer. The fluid chamber is a 3D-printed piece that “funnel” fluid down to a hole where the nozzle attaches via an o-ring seal. The fluid reservoir is also constructed via rapid prototyping methods. Various off-the-shelf nozzles of varying diameters are compatible with this design (0.2 mm - 1.0 mm).
Theory
Theory
For static equilibrium, this equation must be true:
|Δh| ≤ 2σ/ρga
σ: surface tension
ρ: density of fluid
g: gravitational constant
a: radius of nozzle outlet
smaller nozzle outlet ⇒ ↑|Δh|
Components
Components
DC Power Supply
DC Power Supply
The DC power supply, specifically the "Kungber 30V 10A lab DC benchtop power supply," provides the necessary power with high precision for the system. It ensures the accurate operation of the operational amplifier & the solenoid.
Waveform Generator
Waveform Generator
SIGLENT’s SDG1000X waveform generator, provides a diverse range of high-fidelity signals. Its ability to generate various waveforms with specific characteristics contributes to the controlled and precise generation of droplets.
Piezoelectric Buzzer
Piezoelectric Buzzer
The piezoelectric buzzer serves as the actuator responsible for transforming electrical signals into mechanical vibrations necessary for droplet formation. A commercially available piezoelectric buzzer is used for this.
Push Pull Solenoid
Push Pull Solenoid
The linear solenoid actuator adds to vibrations necessary for droplet formation, supporting the piezoelectric buzzer. A commercially available solenoid is used for this.
Fluid Chamber
Fluid Chamber
The fluid chamber serves as a containment unit for the liquid utilized in the droplet generation process. It is connected via tube to the fluid reservoir and its y-axis position relative to the reservoir influences the droplet diameter and volume.
Nozzle
Nozzle
Comercially available 3D printer nozzles are used for this project. The diameter of the nozzle (0.2 - 1.0 mm) has a considerable influence on the size of the droplets.
Translation stage
Translation stage
In an effort to conserve budget, the translation stage was constructed using materials that can be found in Gener8’s engineering lab, namely slotted t-rails and their respective screws. The fluid reservoir was designed to interface with this translation stage for the convenient ability to alter Δh.
Fluid Reservoir
Fluid Reservoir
An adjustable fluid reservoir offers flexibility in controlling the fluid pressure at the nozzle, which as described before, is critical in droplet formation. The reservoir consists of a primary chamber and a larger, concentric chamber that collects overflowing fluid in order to maintain a constant fluid level in the primary chamber. This part was 3D printed.
OpAmp + Breadboard
OpAmp + Breadboard
Signals from the waveform generator were fed into a breadboard where they were amplified by an operational amplifier before finally being sent to the PZT. This step was implemented to maximize the buzzing of the PZT.
Fluid Reservoir CAD
Fluid Reservoir CAD
Fluid Chamber CAD
Fluid Chamber CAD
Impact
Impact
This project has the potential to benefit a wide range of stakeholders, including researchers, industries, and academic institutions. The developed droplet generator offers a reliable and accessible solution for diverse scientific and industrial purposes.
This prototype is currently capable of producing 2 microliter droplets with varying consistency. The next steps would focus on optimizing the device to produce even smaller and more precise droplets. These next steps include, but are not limited to implementing an aluminum fluid chamber, sourcing a more powerful PZT, improving fixturing, implementing smaller nozzles, and adding a peristaltic pump to the fluid reservoir.
Results
Results
This prototype costs ~$20 to recreate in Gener8’s engineering lab, where most parts were readily available. The cost to recreate this prototype from scratch is ≈ $210. Competing designs can easily cost > $1000.
Future Directions
Future Directions
Fine-tuning droplet size: Implement advanced control algorithms or design modifications to precisely adjust the droplet size within a desired range. This could involve optimizing parameters such as fluid pressure, nozzle diameter, and actuation timing.
MATLAB imaging/photographing droplets: Integrate MATLAB or similar imaging software to accurately capture and analyze droplet size, shape, and consistency. This would provide valuable data for evaluating the performance of the droplet generator and identifying areas for improvement.
Aluminum fluid chamber: Investigate the use of aluminum or other materials for the fluid chamber to enhance durability and acoustic conductivity, which can be crucial for droplet formation.
Source a more powerful PZT: Research and procure a more powerful piezoelectric transducer (PZT) to increase the effectiveness of droplet ejection and achieve higher throughput rates. This may require collaborating with specialized suppliers or securing additional funding for the acquisition of advanced components.
Smaller nozzles: Experiment with smaller diameter nozzles to produce finer droplets with increased precision and control. This could involve exploring alternative manufacturing methods or sourcing specialized nozzles from suppliers.
Pump: Explore the use of a peristaltic pump to optimize fluid delivery to the fluid chamber. This implementation will minimize changes in Δh over time.
Video Presentation
Video Presentation
Here is a brief video covering the background, goals, and prototype design.
Meet the Team
Meet the Team
Katelyn Kennedy
Katelyn Kennedy
Katelyn is a graduate of UCSD with a major in Bioengineering: Biosystems. She led every phase of this project under the mentorship of engineers at Gener8. She is pursuing a career in medical device design and is working towards a Master of Engineering Degree in UCSD's Bioengineering Department.
Gener8 Team
Gener8 Team
Mentors: Erik Anderson & Bob Weiller
Managing Director: Espir Kahatt
Supporting Engineers: Matt Brungardt, Laurence Lange, Andrew Lin, Jiyang Mei
Project Website
Project Website
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