Cell separation is a powerful technique, which is widely used in many strands of biological and biomedical research and in clinical therapy. The most common technique to separate cells in clinical environment is centrifugation. Larger samples and higher G-forces can require large centrifuges which may not be feasible everywhere. A great alternative to centrifugation could be the utilization of microfluidics for cell sorting. Microfluidics allows us to work at the scale of the cells making the process faster and more efficient. We are trying to develop a low cost and disposable device based on microfluidics. It uses commercially available mesh and the concept of Determinstic Lateral Displacement to separate or capture particles having a size less than the critical diameter.

During an age of technological innovation, automation has become more and more prevalent in various industries, leading to the development of robots to assist in performing tasks in a precise manner, free of human variation. Over the past decade, soft robotics has emerged as a field that aims to “soften” these robots by replacing the circuitry and rigid, metallic bodies with flexible materials in order to make interactions with humans safer, all while maintaining the functionality of the traditional robots. These soft robots are powered through pneumatics rather than electricity, with the manipulation of the empty space of air within the hollow, plastic constructs allowing for actuation of the robot. Stemming from a biomimetic approach, soft robots have proven capable of demonstrating semblances of motor skills and swimming gaits seen in other living organisms; however, the precise timing of movements still requires the reliance on electronics. As such, this study aims to develop approaches to minimizing the footprint of the electromechanical control hardware by employing pneumatic logic.

The concept of pneumatic logic entails the use of air to power logic circuits, which can be designed by arraying together normally-closed valves, formed using polydimethylsiloxane (PDMS) as a flexible membrane, in a microfluidic chip. This results in the development of pneumatic logic gates that act similarly to their electronic counterparts (e.g. AND, OR, NOT), with the key difference being that the pneumatic analog can be used to impede the flow of air rather than electricity, making them suitable for controlling soft robots. Powered by vacuum pressure in particular, this use of monolithic membrane valves in conjunction with pneumatic logic minimizes the electronic control hardware required to operate multiple soft robots independently, with error-checking capabilities present as well. This design also enables a mode of continuous soft robotic actuation without the need for any controllers, requiring only a source of vacuum pressure. Able to operate with low pressures and at the microfluidic scale, pneumatic logic presents itself as an attractive option for controlling soft robots in an efficient manner.

Cell separation is a major sample processing step for many biological and medical assays. Currently in a clinical setting, cell separation is usually achieved through centrifugation. Although centrifugation has a long history of use in clinical settings, it does have its drawbacks. The need for trained personnel to wait by the process from start to finish can make cell sorting using centrifugation a time consuming process. The need for a continuous flow device for cell sorting has resulting in the development of devices such as deterministic lateral displacement devices (DLD) and deterministic cell rolling devices. Although these devices are quite effective at sorting cells, they are not used in clinical settings. This can be attributed to the time consumption and complex nature of their fabrication. Our goal was to develop a device that achieves the principles used by DLD and roll over devices for cell sorting using commercially available meshes. To achieve DLD like results, a segment of mesh was sealed from top and bottom to allow lateral flow through the mesh. The meshes were sealed using either microscope slides to form a rigid device or thermoplastics to form a flexible device. To achieve roll over like results, meshes were placed into an etched channel and sealed using a thermoplastic to allow cells to roll over the mesh. Results from these devices showed consistent displacement as particles maneuvered through and over the mesh. The cost effectiveness of the meshes allow for mass producibilitiy of the device for clinical use.

Sorting cells by their type is an important capability in biological research and medical diagnostics. However, most cell sorting techniques rely on labels, which may have limited availability and specificity. Sorting different cell types by their different physical properties is an attractive alternative to labels because all cells intrinsically have these physical properties. But for some physical properties like cell size, the relatively large cell-to-cell variation within a cell type can make it difficult to identify and sort cells based on their size. In this work we sort different cells types by their density, a physical property with much lower cell-to-cell variation within a cell type (and therefore greater potential to discriminate different cell types) than other physical properties. We accomplish this using a 3D-printed microfluidic chip containing a flowing micron-scale density gradient. Earth's gravity makes each cell in the gradient quickly float or sink to the point where the cell's density matches the surrounding fluid's density, after which the cells are routed to different outlets and therefore sorted by their density. As a proof of concept, we use our density sorter chip to sort polymer microbeads by their material (polyethylene and polystyrene) and blood cells by their type (white blood cells and red blood cells). The simplicity, resolution, and throughput of this technique make it suitable for isolating even rare cell types in complex biological samples, in a wide variety of different research and clinical applications. We also demonstrated a technique for controlling microfluidic chips that requires no off-chip hardware. We accomplish this by using inert compounds to adjust the densities of fluids in the chip. When fluids of different densities flow together under laminar flow, the interface between the fluids quickly reorients to be orthogonal to Earth's gravitational force. If the channel containing the fluids then splits into two channels, the amount of each fluid flowing into each channel is precisely determined by the angle of the channels relative to gravity. This approach allows for sophisticated control of on-chip fluids with no off-chip control hardware, significantly reducing the cost of microfluidic instruments in point-of-care or resource-limited settings.

Tools for identifying substances are important in many different fields and have a wide range of applications. Conventional analytical tools and instruments such as spectroscopy and chromatography systems are exceptional in their ability to measure and analyze samples. However, the cost, size, and complexity of these instruments limit their use in important applications in resource-limited settings. While ''frugal science''— science solutions that prioritize both cost and function— has made strides in expanding access to healthcare and research, there is still an unmet need for more low-cost and accessible research and analytical tools. In this work, I develop simple, low-cost, and effective analytical tools on microfluidic platforms that utilize changes in the physical properties of substances to examine and analyze samples. I introduce microfluidic tools and methods to accurately measure temperature and identify substances, or adulteration of substances, in small volumes. I accomplish this work through three projects. In the first project, a Microfluidic Thermometer, I demonstrate a simple and low-cost technique to accurately measure temperatures in small volumes using a 3D-printed microfluidic chip. With this method, the temperature of a sample can be measured with about a quarter of a degree Celsius uncertainty. For the second project, Chronoprints, I demonstrate a simple and low-cost method for identifying a sample based on visualizing how the sample changes in response to a perturbation over space and time. With this technique, authentic foodstuffs are distinguished from adulterated foodstuffs, adulterated medication is identified, and occasionally-confused pharmaceutical ingredients are easily distinguished. Finally for the third project, Enhanced Chronoprints, I demonstrate a simple and low-cost method for identifying a sample based on visualizing changes in the interaction of a falling metal bead with the sample. The cost, simplicity, versatility, and accuracy of these techniques make them valuable analytical tools in a variety of different fields and settings.

What can microfluidics do? For the past decades, researchers from physics, chemistry, biotechnology, and other fields have used microfluidics to design numerous chips for different applications. As new microfluidic chips keep emerging, we ask ourselves, ``what else? Could we develop any microfluidic chips that human beings cannot design or imagine? Can we design better microfluidic chips with the help of computer algorithms?''

This thesis presents several projects that demonstrate the potential that computer algorithms, simulations, and conventional microfluidics together will help researchers find better microfluidic chips, better design methods, and help us explore new phenomena. In Chapter 1, we start with a small review of how microfluidic chips are designed in the past decades and discuss the advantages and disadvantages of the conventional design method. In Chapter 2, we present a “random design” method to design a function microfluidic solute generator, which is able to generate three arbitrary concentrations at the same time. In Chapter 3, we present a microfluidics-optimized particle simulation algorithm (MOPSA) that simulates the trajectories of cells, droplets, and other particles in microfluidic chips with more lifelike results than particle tracers in existing commercial software. In Chapter 4, we present a microfluidic simulation method that can simulate the behavior of fluids and particles in typical microfluidic chips instantaneously (in around one second), which is able to accelerate the simulation of microfluidic chips. In Chapter 5, we present a microfluidic particle sorter which is designed by the three algorithms in Chapter 2 - 4. In Chapter 6, we automated designed and optimized a microfluidic mixer using Non-dominated Sorting Genetic Algorithm II (NSGA-II). In Chapter 7, we discuss the potential impacts of the projects presented in this thesis and the future directions of computer algorithms that can help microfluidics evolve into the next generation.

The emerging demands for healthcare where access is limited due to political, environmental, or socio-economic factors have been driving research into bio-medical devices that perform in both diagnostic and therapeutic roles at lower costs and greater accessibility. Paper microfluidic devices are used in many applications, particularly medical diagnostics and offer an excellent combination of utility and low cost making them particularly valuable in resource-limited applications and point-of-care usage across a wide variety environmental conditions. Microfluidic biological diagnostics continue to mature as researchers discover new ways to exploit the technological possibilities, and address liabilities. The increasing complexity of paper-based microfluidic devices beyond home pregnancy tests is driving the need to produce new tools and methodologies that enable more robust biological diagnostics and potential therapeutic applications. However, the process of developing new paper microfluidic devices is limited due to having to manually design and fabricate designs to research. Often, researchers must design scores of different devices to find a combination of parameters that functions as expected. In this work, a novel software framework to support automated development of paper-based microfluidic devices is introduced to facilitate both research and fabrication to accelerate the investigative process and reduce material utilization and manpower. Unlike to existing lab-on-a-chip technologies, paper-based microfluidics differs in terms of substrate technologies and use a passive flow method to deliver fluids and reagents for assays. While numerous analogies between microfluidics and semiconductor technologies have been espoused, the physical differences between the fluid dynamics and electrical current are significant which suggests that current trends in physical design for microfluidics must change course in order to be of practical use to designers. Within this framework, a methodology is introduced to address design automation such as dynamically placing and routing microfluidic components in a non-discrete design space while avoiding invalid design layouts, accounting for fluid volume usage, surface area utilization, and the timing required to perform specified biological assays and also optimizing device parameters, enabling researchers to focus on the science and thereby accelerating the development of new, low-resource paper microfluidic devices for a developing world.

Accurate measurements of an object’s fundamental physical properties like mass, volume, and density can provide valuable insights about an object and how it behaves. This is especially true for biological or bioengineered samples that reside in liquid environments. In this thesis, we demonstrate a new method for quantifying the mass, volume, and density of samples in their native liquid environments using resonating mass sensors. By vibrating a liquid-filled glass tube at its resonance frequency and passing a solid sample through the tube, the tube’s resonance frequency changes by an amount that is inversely proportional to the sample’s buoyant mass. This enables microgram-scaled objects to be measured in their native liquid environment with nanogram resolution, without the need for labels or tags. Sensor applications are demonstrated by studying the degradation rates of biomaterials, measuring the physical properties of hydrogels, and evaluating the dissolution rates of drug delivery systems.

In addition to vibrating glass tubes, a low-cost method for measuring liquid density is presented utilizing a 3000-year-old musical instrument called the Mbira. By modifying the metal tine of the Mbira, a density resolution of 0.012 g/mL is achieved, making it an accessible tool for resource-limited settings. This low-cost method has the potential to be a powerful tool for determining the authenticity of liquid medications in developing countries. This idea is expanded by exploring alternative designs for low-cost density meter designs for chemical analysis. We present a simple 3D-printed sensor capable of measuring the density of a substance with high precision. The plastic tuning forks are shown to offer several advantages over their metal counterparts, including reduced costs, increased durability, and improved design flexibility. By providing an inexpensive and easy-to-use method for testing the purity or chemical identity of a sample, these plastic resonators can find uses in many applications, particularly in low-resource settings and developing regions at a low cost.