Keegan Owsley

Fabricating Shaped Microfibers with Inertial Microfluidics

DOI: 10.1002/adma.201400268 Using microfl uidics, a few different techniques have emerged for producing fi bers with different cross-sectional shapes; however, for most of these techniques the range of shapes is limited, such as hollow, semi-circular, and ribbon cross-sectional shapes. [ 10 ] One promising microfl uidic technique that is able to realize more complex fi ber cross-sectional shapes is the hydrodynamic focusing method developed by Ligler and coworkers. [ 11 ] This method uses recessed chevron and striped structures in the channel walls to focus the precursor fi ber solution and the sheathing liquids into a desired shape, which can be predicted with computational fl uid dynamics (CFD). Ligler and coworkers demonstrated that they could use custom software, Tiny-Toolbox, [ 12 ] to design their microfl uidic components and simulate the focusing process. In this Communication, we present the synthesis of shaped polymeric fi bers using a software-enabled inertial microfl uidic technique. Using a method described by Amini et al. [ 13 ] where fl uid streams can be sculpted into desired shapes in a microchannel containing a sequence of pillars, we designate one of the sculpted streams as a template for fi ber fabrication to produce fi bers with different noncircular cross-sectional shapes. We use a computer-aided design (CAD) tool, uFlow, that has a stored library of pre-computed fl uid deformations that are produced by individual pillars in the fl ow channel. [ 14 ] In uFlow, these individual pillar-induced deformations are design elements that can be combined to create a unique sequence of pillar positions along and transverse to the fl ow direction that will result in complex sculpted fl uid fl ows of miscible fl uids. As the CFD simulation step is built into the uFlow software, the tool is quick and simple to use, and accessible to users with all computational skill levels as it circumvents the need for any additional time-consuming simulation steps. The software allows the user to immediately observe the effects of adding pillars, changing lateral pillar position, pillar diameter and fl ow rate ratio on the shape of the fl ow deformation. Consequently, uFlow is a useful predictive tool for the rapid screening and design of microchannels for shaped multi-stream fl ows. While other software, optimized for creeping fl ow, can also be used to perform design for shaped fi bers, uFlow models fl ow at a higher Reynolds number, preferred for fi ber shaping because it is associated with large fl uid deformations following fl ow past a sequence of cylinders. We use the program to design channels containing different sequences of pillars specifi cally for fi ber generation using a common poly(ethylene glycol) diacrylate (PEG-DA) photopolymerization. For the experiments presented herein, three monomer solution streams are fl owed into the channel, and the central stream, which is the only stream containing photoinitiator, becomes the template for the solid fi ber. The two outer streams, which are non-reactive because of the absence Among synthetic fi bers, the circular cross-section is most prevalent; however, it is not uncommon to manufacture fi bers with noncircular cross-sections. We will use the term ‘shaped fi bers’ to describe fi bers with any cross-sectional shape that is not circular. Depending on the application, whether the fi bers are used in fabrics and textiles, [ 1 ] as insulating materials for sound and heat, [ 2 ] for light propagation, [ 3 ] as high surface area membranes and fi ltration materials, [ 4 ] or as engineered substrates for biological applications, [ 5,6 ] it has been observed that the cross-sectional shape affects the properties of the fi ber. For example, the crosssectional shape of fi bers manufactured for textile applications is reported to have an effect on bulkiness since packing density is infl uenced by shape, coeffi cient of friction, which imparts fabric roughness and infl uences overall tactility, fl exural rigidity, which affects the softness or stiffness of fabrics, visual properties such as luster and color, and wicking properties. [ 1 ] Shaped fi bers are also being considered for applications in tissue engineering. For example, it has been shown that the higher surface area afforded by shaped fi bers is useful in fi ber scaffolds for improved cell proliferation and more rapid scaffold degradation when compared to fi bers with circular cross-sections. [ 6 ] In addition, multifaceted or ridged fi ber substrates show improved cell orientation and alignment for applications such as guided cell growth when compared to smooth fi bers. [ 5 ]

Rapid Software-Based Design and Optical Transient Liquid Molding of Microparticles.

Microparticles with complex 3D shape and composition are produced using a novel fabrication method, optical transient liquid molding, in which a 2D light pattern exposes a photopolymer precursor stream shaped along the flow axis by software-aided inertial flow engineering.

Flexible and Stretchable Micromagnet Arrays for Tunable Biointerfacing

A process to surface pattern polydimethylsiloxane (PDMS) with ferromagnetic structures of varying sizes (micrometer to millimeter) and thicknesses (>70 μm) is developed. Their flexibility and magnetic reach are utilized to confer dynamic, additive properties to a variety of substrates, such as coverslips and Eppendorf tubes. It is found that these substrates can generate additional modes of magnetic droplet manipulation, and can tunably steer magnetic-cell organization.

Shaped 3D microcarriers for adherent cell culture and analysis

Standard tissue culture of adherent cells is known to poorly replicate physiology and often entails suspending cells in solution for analysis and sorting, which modulates protein expression and eliminates intercellular connections. To allow adherent culture and processing in flow, we present 3D-shaped hydrogel cell microcarriers, which are designed with a recessed nook in a first dimension to provide a tunable shear-stress shelter for cell growth, and a dumbbell shape in an orthogonal direction to allow for self-alignment in a confined flow, important for processing in flow and imaging flow cytometry. We designed a method to rapidly design, using the genetic algorithm, and manufacture the microcarriers at scale using a transient liquid molding optofluidic approach. The ability to precisely engineer the microcarriers solves fundamental challenges with shear-stress-induced cell damage during liquid-handling, and is poised to enable adherent cell culture, in-flow analysis, and sorting in a single format.Adherent cells: microcarriers for flow cytometryA new microcarrier for adherent cells is demonstrated which allows for accurate flow cytometry and high-speed imaging without risk of flow-induced damage. Microcarriers are attractive for accelerated cell culture, passaging and analysis, but they must be designed to promote cell growth and analysis without flow-induced cell damage. A team led by Dino Di Carlo at University of California, Los Angeles now report a 3D-shaped microparticle that features a region of extracellular matrix for cell adhesion and culture physically protected from shear flow. Key to the design is the intersection of two 2D patterns, leading to a shape which can align with flow inside the channel during cytometry, and also provides a cut-away region to protect cells during culture. These microcarriers may facilitate high-speed adherent cell screening for applications such as drug discovery.

Single-Cell Analysis of Morphological and Metabolic Heterogeneity in Euglena gracilis by Fluorescence-Imaging Flow Cytometry

Microalgal biofuels and biomass have ecofriendly advantages as feedstocks. Improved understanding and utilization of microalgae require large-scale analysis of the morphological and metabolic heterogeneity within populations. Here, with Euglena gracilis as a model microalgal species, we evaluate how fluorescence- and brightfield-derived-image-based descriptors vary during environmental stress at the single-cell level. This is achieved with a new multiparameter fluorescence-imaging cytometric technique that allows the assaying of thousands of cells per experiment. We track morphological changes, including the intensity and distribution of intracellular lipid droplets, and pigment autofluorescence. The combined fluorescence-morphological analysis identifies new metrics not accessible with traditional flow cytometry, including the lipid-to-cell-area ratio (LCAR), which shows promise as an indicator of oil productivity per biomass. Single-cell metrics of lipid productivity were highly correlated ( R2 > 0.90, p < 0.005) with bulk oil extraction. Such chemomorphological atlases of algal species can help optimize growth conditions and selection approaches for large-scale biomass production.