A method based on standing surface acoustic waves (SSAWs) is proposed to pattern and manipulate microparticles into a three-dimensional (3D) matrix inside a microchamber. An optical prism is used to observe the 3D alignment and patterning of the microparticles in the vertical and horizontal planes simultaneously. The acoustic radiation force effectively patterns the microparticles into lines of 3D space or crystal-lattice-like matrix patterns. A microparticle can be positioned precisely at a specified vertical location by balancing the forces of acoustic radiation, drag, buoyancy, and gravity acting on the microparticle. Experiments and finite-element numerical simulations both show that the acoustic radiation force increases gradually from the bottom of the chamber to the top, and microparticles can be moved up or down simply by adjusting the applied SSAW power. Our method has great potential for acoustofluidic applications, building the large-scale structures associated with biological objects and artificial neuron networks.
Richard (2019) 3D patterning/manipulating microparticles and yeast cells using ZnO/Si thin film surface acoustic waves. Sensors and Actuators B: Chemical, 299. p. 126991.
Precise, automatic and reliable position control of micro-objects such as single particles, biological cells or bio-organisms is critical for applications in biotechnology and tissue engineering. However, conventional acoustofluidic techniques generally lack reliability and automation capability thus are often incapable of building an efficient and automated system where the biological cells need to be precisely manipulated in three dimensions (3D). To overcome these limitations, we developed an acoustofluidic closed-loop control system which is combined with computer vision techniques and standing surface acoustic waves (SSAWs) to implement selective, automatic and precise position control of an object, such as a single cell or microparticle in a microfluidic chamber. Position of the object is in situ extracted from living images that are captured from a video camera. By utilizing the closed-loop control strategy, the object is precisely moved to the desired location in 3D patterns or along designed trajectories by manipulating the phase angle and power signal of the SSAWs. Controlling of breast cancer cells has been conducted to verify the principle and biocompatibility of the control system. This system could be employed to build an automatic system for cell analysis, cell isolation, self-assembling of materials into complex microstructures, or lab-on-chip and organ-on-chip applications.
Spatial distribution of biological cells plays a key role in tissue engineering for reconstituting the cellular microenvironment, and recently, acoustofluidics are explored as a viable tool for controlling structures in tissue fabrication because of its good biocompatibility, low‐power consumption, automation capability, nature of non‐invasive, and non‐contact. Herein, a reusable acoustofluidic device is developed using surface acoustic waves for manipulating microparticles/cells to form a 3D matrix pattern inside a scaffold‐based hydrogel contained in a millimetric chamber. The 3D patterned and polymerized hydrogel construct can be easily and safely removed from the chamber using a proposed lifting technique, which prevent any physical damages or contaminations and promote the reusability of the chamber. The generated 3D patterns of microparticles and cells are numerically studied using a finite‐element method, which is well validated by the experimental results. The proposed acoustofluidic device is a useful tool for in vitro engineering 3D scaffold‐based artificial tissues for drug and toxicity testing and building organs‐on‐chip applications.
Spinal cord progenitor cells (SCPCs) have the capability to differentiate into multiple cell lineages of a central nervous system. The transplantation of SCPCs derived from human induced pluripotent stem cells (iPSCs) has beneficial effects on treating spinal cord injury (SCI). However, the presence of residual undifferentiated iPSCs amongst their differentiated progeny poses a high risk as it can result in the development of teratomas or other types of tumors post-transplantation. Despite the need to remove these residual undifferentiated iPSCs, there is a severe lack of surface markers that can identify them for subsequent removal. In this study, iPSCs were differentiated into SCPCs through a 10-day differentiation process. By profiling the size of SCPCs, we found that the large-sized group contains significantly more cells expressing pluripotent markers. A sized-based, label-free separation using an inertial microfluidic-based device was exploited to remove tumor-risk cells. The device takes advantage of label-free, non-contact, and high throughput (i.e., > 3 million cells per minute) without affecting cell viability and functions. The sorted cells were verified with immunofluorescence staining, flow cytometry analysis, and colony culture assay. Essentially, our technology has demonstrated its capabilities to reduce the percentage of tumor-risk cells up to 98.07 %. Our technology has great potential for the downstream processing of cell manufacturing workflow, contributing to better quality and safety of the transplanted cells.
List of figures vii PDMS rod. (b) fluorescent images of side and top views of 1 mm rod in hydrogel collagen (scale bar: 1 mm). (c) left to right, top to bottom, experimental and numerical results of two sizes of PDMS rod with diameter of 1 mm and 2 mm, respectively (scale bar: 500 μm). (d) top to bottom, two rods pattern with the gap
Reconstructing of cell architecture plays a vital role in tissue engineering. Recent developments of self‐assembling of cells into three‐dimensional (3D) matrix pattern using surface acoustic waves have paved a way for a better tissue engineering platform thanks to its unique properties such as nature of noninvasive and noncontact, high biocompatibility, low‐power consumption, automation capability, and fast actuation. This article discloses a method to manipulate the orientation and curvature of 3D matrix pattern by redesigning the top wall of microfluidic chamber and the technique to create a 3D longitudinal pattern along preinserted polydimethylsiloxane (PDMS) rods. Experimental results showed a good agreement with model predictions. This research can actively contribute to the development of better organs‐on‐chips platforms with capability of controlling cell architecture and density. Meanwhile, the 3D longitudinal pattern is suitable for self‐assembling of microvasculatures.
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