Designable 3D Microshapes Fabricated at the Intersection of Structured Flow and Optical Fields

Abstract

of applications, including drug delivery, tissue engineering, self-assembly, and photonics. For example, the shape of hydrogel particles has been shown to affect particle-cell interactions [1][2][3] and the cross-sectional shape of microfibers changes the wicking properties of woven fabrics. [4] In addition, microobjects in nature often take on a nonequilibrium structure to exploit beneficial shapeinduced functionality, such as the biconcave geometry of the red blood cell and the triangular cross-section of Saharan silver ant fibers. [5] Existing techniques to fabricate microobjects with 3D architectures have tradeoffs between throughput and shape selection. Conventional layer-by-layer 3D printing techniques based on fused deposition modelling and stereolithography are resolution-limited, with minimum linear feature sizes of over 45 µm. [6] High-resolution 3D printing methods, such as two-photon polymerization, can produce feature sizes as low as 40 nm, but their low print speed makes them unfeasible for production at scale [7] and their small build volumes are unsuitable for fabricating high aspect ratio microobjects such as fibers. Top-down approaches to particle fabrication, such as PRINT [8] and SEAL, [9] are high throughput, but cannot produce 3D shapes beyond stacked 2D extrusions because they utilize polymeric molds of microfabricated templates. Microfluidic approaches to nonequilibrium particle and fiber synthesis also have a limited library of possible 3D geometries. Droplet-based approaches to nonspherical particle fabrication are restricted to creating particles with equilibrium surface features because the factors that determine the shape of the interface between immiscible fluids are surface tension dominated. [10][11][12][13][14] While flow-lithography based particle fabrication, in which photocurable polymers are flowed through a microfluidic chip and polymerized by UV light passing through a photomask, has shown to have excellent control of particle shape along a single 2D extrusion axis, [15][16][17] a similar level of shape control in the direction of flow is yet to be achieved. [18][19][20] In recent years, there have been efforts to improve the complexity of particles beyond 2D extruded shapes through techniques such as hydrodynamic flow shaping [21][22][23] and nonuniform flow lithography. [24,25] However, the mechanisms enabling these methods, or inertial focusing and nonuniform UV light intensity, are not precise and are difficult to control, limiting particle shape design freedom.3D structures with complex geometric features at the microscale, such as microparticles and microfibers, have promising applications in biomedical engineering, self-assembly, and photonics. Fabrication of complex 3D microshapes at scale poses a unique challenge; high-resolution methods such as two-photon-polymerization have print speeds too low for high-throughput production, while top-down approaches for bulk processing using microfabricated template molds have limited control of microstructure geometries over mu...

Formation of uniform reaction volumes using concentric amphiphilic microparticles

“…[16,17] In addition, spherical particles have more limited barcoding options, and it has been reported that the presence of surfactants leads to higher rates of transport of products of reactions through the continuous oil phase, reducing sensitivity of enzymatic assays. [18,19] A range of fabrication methodologies have been explored over the past decade to create particles with different shapes and functionalities using continuous [20][21][22][23][24] or stop flow lithography techniques [25][26][27][28] combined with hydrodynamic focusing, [29][30][31][32] magnetically tunable color printing, [12,33] vertical flows, [34] structured hollow fibers [35] or inertial forces. [36][37][38][39] Particles comprised of layers of hydrophobic and hydrophilic materials were shown to selectively interact and assemble around aqueous drops.…”

Towards Digital Manufacturing of Smart Multimaterial Fibers

“…1b. Alternative techniques for patterning the cores axially include UV-exposure through photomasks in photopolymeric cores, resulting in non-trivially-shaped microparticles [28]. Other hybrid-functionalization techniques include coating the fiber surfaces with functional materials [10, 29] and confinement of a fiber cladding by a draw [12] to an array of optoelectronic devices fabricated by standard complementary metal-oxide-semiconductor (CMOS) manufacturing.…”

FlowSculpt: software for efficient design of inertial flow sculpting devices

“…Many current applications of flow sculpting were devised and implemented by inertial microfluidics experts, and even then, they sculpted relatively simple flow shapes that were achieved through trial-and-error design. A clear example of this difficulty is particle fabrication via flow sculpting, which remains competitive with state-of-the-art methods such as PRINT, 12 SEAL, 13 two-photon lithography, 14 and hollow fiber templating 15 due to the ability to create multi-material shaped 3D particles at high-throughput using basic microfluidic tools such as soft lithography 16 and 3D printing. 6 However, the flow sculpting approaches currently require the target 3D particle shape to comprise of the intersection of two orthogonally extruded 2D shapes: one from the shape of the sculpted flow stream (which contains a polymer precursor with a photoinitiator), and the other from an optical mask (which shapes polymerizing ultraviolet light).…”