Facile Fabrication Method of Conical Microwells Using Non‐Uniform Photolithography

Abstract

relatively small size, simplicity of construction, and compatibility with various existing fabrication techniques. In particular, microwells enable the formation of uniformly-size cell spheroids. [9,10] These spheroids are of particular importance as they represent a well-defined 3D model for studying biological events in many developmental processes such as angiogenesis, [11] toxicological screening, and during anti-cancer drug therapies. [12] The design of a microwell defines its applicability for the microwell-mediated cell spheroid formation and modulation of cellular behavior. For instance, in 3D cell culture experiments flat-bottom microwells are typically used for drug testing, [13,14] whereas pyramid-shaped microwells are favored for stem cell aggregation and embryonic body formation. [15] Moreover, the aspect ratio (diameter/height) of the microwell dictates its cell culture performance. A high aspect ratio facilitates longterm cell culture, [16] while the low aspect ratio of shallow microwells favor the formation of spheroids. [15] Cell aggregate formation is determined by the geometry of the microwell. [17] Concave bottoms are most commonly applied to the design of microwell devices for 3D culture as it favors the growth of a single aggregate per microwell. [18,19] Additionally, cubically or cylindrically shaped microwells are more frequently carried out in 3D cell culture, while conically shaped microwells are prone to forming uniformly-sized cell aggregates in each microwell. Even with a low number of cells seeded into conically shaped microwells, well defined spheroids can easily be formed. Conical microwells recuperate oxygen and medium delivery to cell aggregates. [20] Thus, the shape of microwell is crucial for a specific biological application. However, creating tapered bottoms, such as those of conical microwells require additional technical demands compared to the fabrication of flat-bottomed microwells. Several fabrication methods for tapered-bottom microwells have been utilized successfully such as laser micromachining, [21-23] chemical etching, [24] micromilling, [25] inkjet printing, [26] photolithography, [27] and ice lithography. [28] Laser micromachining based on the selective melting of polymeric materials with focused laser heating, requires expensive and specialized equipment. Furthermore, the removal of generated debris is time-consuming and technically demanding. Chemical etching utilizes a liquid chemistry to detach materials from substrates in order to form small structures. This

Zero-Inflated Poisson Distribution of Sedimented Cells in Multi-Layered Microwell Arrays

“…Manzoor et al report a novel fabrication method using non-uniform photolithography to create MWs with conical rather than flat sidewalls. 75 Replacing the flat sidewalls and bottoms of our current dual-layered MWs with the conical sidewalls afforded by Manzoor et al's fabrication method may be worth considering, to see how such a change affects the performance of the revised MWA in trapping cells and confining those cells to the MWs. Ali et al also recently presented a lab-on-a-chip platform featuring a polymeric MWA integrated with an array of nanopillar structures utilizing local surface plasmon resonance-based biosensing for in situ protein detection.…”

Magnetic Bead Manipulation in Microfluidic Chips for Biological Application

“…Besides, the evaporation-assisted seeding process may cause protein denaturation and the loss of enzyme activity, which limits its biological application. Currently, microwells are commonly prepared by microfabrication such as photolithography [ 107 , 108 ], electrochemical micromachining [ 109 , 110 ], and microcontact printing [ 111 , 112 ]. To improve the loading efficiency of the magnetic beads, microwells with a hydrophilic bottom and hydrophobic interwell surface have been manufactured [ 113 , 114 ].…”

Modeling and Numerical Studies of Three‐Dimensional Conically Shaped Microwells Using Non‐Uniform Photolithography

“…To address some of these challenges in the current methods, we developed a simple microfabrication technique based on nonuniform photolithography (NUPL) [27] in combination with microfluidic washing and successfully fabricated conical microwells with both tunable well shape and surface morphology. [28] In this synthesis, we created polymeric conical microwells in a confined pre-polymer solution within a PDMS microfluidic channel via patterned UV exposure across the channel's height with oxygen diffusion asymmetrically across this height. Schematics of 3D conically shaped microwell formation using NUPL and its computation domain: a) Cross-sectional schematic views of our microwell fabrication technique.…”