Wenguang Yang

Rapid Fabrication of Hydrogel Microstructures Using UV-Induced Projection Printing

Fabrication of hydrogel microstructures has attracted considerable attention. A large number of applications, such as fabricating tissue engineering scaffolds, delivering drugs to diseased tissue, and constructing extracellular matrix for studying cell behaviors, have been introduced. In this article, an ultraviolet (UV)-curing method based on a digital micromirror device (DMD) for fabricating poly(ethylene glycol) diacrylate (PEGDA) hydrogel microstructures was presented. By controlling UV projection in real-time using a DMD as digital dynamic mask instead of a physical mask, polymerization of the pre-polymer solution could be controlled to create custom-designed hydrogel microstructures. Arbitrary microstructures could also be fabricated within several seconds (l5 s) using a single-exposure, providing a much higher efficiency than existing methods, while also offering a high degree of flexibility and repeatability. Moreover, different cell chains, which can be used for straightforwardly and effectively studying the cell interaction, were formed by fabricated PEGDA microstructures.

Single-pixel camera with one graphene photodetector.

Consumer cameras in the megapixel range are ubiquitous, but the improvement of them is hindered by the poor performance and high cost of traditional photodetectors. Graphene, a two-dimensional micro-/nano-material, recently has exhibited exceptional properties as a sensing element in a photodetector over traditional materials. However, it is difficult to fabricate a large-scale array of graphene photodetectors to replace the traditional photodetector array. To take full advantage of the unique characteristics of the graphene photodetector, in this study we integrated a graphene photodetector in a single-pixel camera based on compressive sensing. To begin with, we introduced a method called laser scribing for fabrication the graphene. It produces the graphene components in arbitrary patterns more quickly without photoresist contamination as do traditional methods. Next, we proposed a system for calibrating the optoelectrical properties of micro/nano photodetectors based on a digital micromirror device (DMD), which changes the light intensity by controlling the number of individual micromirrors positioned at + 12°. The calibration sensitivity is driven by the sum of all micromirrors of the DMD and can be as high as 10(-5)A/W. Finally, the single-pixel camera integrated with one graphene photodetector was used to recover a static image to demonstrate the feasibility of the single-pixel imaging system with the graphene photodetector. A high-resolution image can be recovered with the camera at a sampling rate much less than Nyquist rate. The study was the first demonstration for ever record of a macroscopic camera with a graphene photodetector. The camera has the potential for high-speed and high-resolution imaging at much less cost than traditional megapixel cameras.

High‐Throughput Fabrication and Modular Assembly of 3D Heterogeneous Microscale Tissues

3D hydrogel microstructures that encapsulate cells have been used in broad applications in microscale tissue engineering, personalized drug screening, and regenerative medicine. Recent technological advances in microstructure assembly, such as bioprinting, magnetic assembly, microfluidics, and acoustics, have enabled the construction of designed 3D tissue structures with spatially organized cells in vitro. However, a bottleneck exists that still hampers the application of microtissue structures, due to a lack of techniques that combined high-throughput fabrication and flexible assembly. Here, a versatile method for fabricating customized microstructures and reorganizing building blocks composed of functional components into a combined single geometric shape is demonstrated. The arbitrary microstructures are dynamically synthesized in a microfluidic device and then transferred to an optically induced electrokinetics chip for manipulation and assembly. Moreover, building blocks containing different cells can be arranged into a desired geometry with specific shape and size, which can be used for microscale tissue engineering.

Nano-Manipulation Based on Real-Time Compressive Tracking

Quick tracking in nano-manipulation has been attracting increasing attention among scientific researchers and engineers because it can significantly enhance the effectiveness and efficiency of nano-manipulation. The main reasons that hinder the improvement of accuracy and efficiency of nano-manipulation are the lack of effective real-time tracking and unavoidable perturbations by uncertainties and nonlinearities in the manipulation system. In this paper, we present a new strategy based on compressive sensing to realize quick real-time tracking nano-manipulation trajectory, and build a new kinematic model for objects to be manipulated to overcome the effect of tip positioning and contacting biases on nano-manipulation with AFM. With this approach, the deviation of the object from the predesigned trajectory during the manipulation can be corrected with up to two-thirds of time less than the traditional method, and the object can be smoothly moved to any destination in the nano-space. The approach requires no priori knowledge about the system, environment, and objects being manipulated. It is validated that this strategy works for both hard regular objects and soft irregular samples by experiments.

2D Normalized Iterative Hard Thresholding Algorithm for Fast Compressive Radar Imaging

Compressive radar imaging has attracted considerable attention because it substantially reduces imaging time through directly compressive sampling. However, a problem that must be addressed for compressive radar imaging systems is the high computational complexity of reconstruction of sparse signals. In this paper, a novel algorithm, called two-dimensional (2D) normalized iterative hard thresholding (NIHT) or 2D-NIHT algorithm, is proposed to directly reconstruct radar images in the matrix domain. The reconstruction performance of 2D-NIHT algorithm was validated by an experiment on recovering a synthetic 2D sparse signal, and the superiority of the 2D-NIHT algorithm to the NIHT algorithm was demonstrated by a comprehensive comparison of its reconstruction performance. Moreover, to be used in compressive radar imaging systems, a 2D sampling model was also proposed to compress the range and azimuth data simultaneously. The practical application of the 2D-NIHT algorithm in radar systems was validated by recovering two radar scenes with noise at different signal-to-noise ratios, and the results showed that the 2D-NIHT algorithm could reconstruct radar scenes with a high probability of exact recovery in the matrix domain. In addition, the reconstruction performance of the 2D-NIHT algorithm was compared with four existing efficient reconstruction algorithms using the two radar scenes, and the results illustrated that, compared to the other algorithms, the 2D-NIHT algorithm could dramatically reduce the computational complexity in signal reconstruction and successfully reconstruct 2D sparse images with a high probability of exact recovery.

Spatial Manipulation and Assembly of Nanoparticles by Atomic Force Microscopy Tip-Induced Dielectrophoresis

In this article, we present a novel method of spatial manipulation and assembly of nanoparticles via atomic force microscopy tip-induced dielectrophoresis (AFM-DEP). This method combines the high-accuracy positioning of AFM with the parallel manipulation of DEP. A spatially nonuniform electric field is induced by applying an alternating current (AC) voltage between the conductive AFM probe and an indium tin oxide glass substrate. The AFM probe acted as a movable DEP tweezer for nanomanipulation and assembly of nanoparticles. The mechanism of AFM-DEP was analyzed by numerical simulation. The effects of solution depth, gap distance, AC voltage, solution concentration, and duration time were experimentally studied and optimized. Arrays of 200 nm polystyrene nanoparticles were assembled into various nanostructures, including lines, ellipsoids, and arrays of dots. The sizes and shapes of the assembled structures were controllable. It was thus demonstrated that AFM-DEP is a flexible and powerful tool for nanomanipulation.

Hydrogel Printing Based on UV-Induced Projection for Cell-Based Microarray Fabrication

A considerable number of studies have focused on fabrication of hydrogel microstructures due to its wide applications in tissue engineering, drug delivery, and extracellular matrix construction. Here, we introduce a hydrogel printing method based on UV-induced projection via a digital micromirror device (DMD). Arbitrary microstructures could be fabricated within few seconds (<3) by modulating UV projection using DMD as digital dynamic masks instead of a physical mask, which also offers a high degree of flexibility and repeatability. Furthermore, the ability of PEGDA film to hinder cell adhesion makes it possible to control area over which cells attach.

Patterned microwell arrays for single-cell analysis and drug screening

Nowadays, cells are commonly used for predicting whether the drug compounds will be effective and safe in human. The response of cell groups was usually analyzed, instead of single cell. However, individual cells within the same population even shows various characteristics. Understanding this heterogeneity is critical to studying how effective therapies will be in the clinic. Therefore, highly efficient analysis of single cell has become important for cellular biologists for both fundamental and drug screening. Recently, several methods including microscopy, laser capture microdissection, flow cytometry and microfluidic techniques have been developed for study the single cell. However, miniaturization, simplification and multifunction are still main challenges for the development of single cell analytical tool. In this paper, we have presented an easy-to-use and versatile method to fabricate various microwells for single cell analysis. Cells could grow into arbitrary shapes with constrained microwells. The microwells were able to be removed to investigate cell shapes effect on growth via our method. Furthermore, 3D multicellular spheroids which can be used for dug screening were formed based on micro-wells arrays.

Regulation of cell adhesion to poly(ethylene glycol) diacrylate film by modification with polystyrene nano-spheres

Poly(ethylene glycol) diacrylate (PEGDA) are being investigated for various tissue engineering applications for its biocompatibility and excellent mechanical properties. However, the native PEGDA films can hinder cell adhesion which limits applications in the field of tissue engineering and biomedicine. Recently, nano composite technology has been a particularly hot topic because of it can be used to modify deliver to the materials properties. In this paper, we have added polystyrene nano-spheres into the PEGDA solution to synthesize nanocomposites film. The experimental results show that the adhesion of cell on PEGDA film can be regulated by the concentration of polystyrene nano-spheres. The cell adhesion and spread can be improved through increasing concentration of polystyrene nano-spheres. Furthermore, we find that the spheres can also change the mechanical properties of PEGDA films and further affect the cell growth status.

Fabrication of microstructures using the DMD-based modulating projection printing method

Patterned microstructures of hydrogels have attracted significant attention due to an increasing need for developing scaffolds for tissue engineering, as carriers for drug delivery, and as extracellular matrices for biological studies. However, current tissue engineering approaches lack the flexibility required for developing complex two or three-dimensional (2D/3D) microstructures, which are used to impart suitable cell mechanical microenvironments. In this paper, we present an ultraviolet (UV) light curing method based on a digital mirror device-based modulating projection printing (DMPP) system for fabricating patterned poly(ethylene glycol) diacrylate (PEGDA) hydrogel microstructures. With programmable UV exposure, polymerisation of the PEGDA solution can be induced to create 2D/3D microstructures with high biocompatibility. The main advantage of DMPP is that it is a mask-free method. In addition, the efficiency of the DMPP method is much higher than other methods for patterning PEGDA microstructures. The duration of UV exposure was less than 10 s. In the experiments described below, several types of microstructure arrays have been fabricated. These initial results show that the DMPP method can be used for fabricating highly complex microstructures with controlled accuracy.