High throughput micropatterning of interspersed cell arrays using capillary assembly

Pushing the Limits of Capillary Assembly for the Arbitrary Positioning of Sub-50nm Nanocubes in Printable Plasmonic Surfaces

The fabrication of high quality nanophotonic surfaces for integration in optoelectronic devices remains a challenge because of the complexity and cost of top-down nanofabrication strategies. Combining colloidal synthesis with templated self-assembly emerged as an appealing low-cost solution. However, it still faces several obstacles before integration in devices can become a reality. This is mostly due to the difficulty in assembling small nanoparticles (<50 nm) in complex nanopatterns with a high yield. In this study, a reliable methodology is proposed to fabricate printable nanopatterns with an aspect ratio varying from 1 to 10 and a lateral resolution of 30 nm via nanocube assembly and epitaxy. Investigating templated assembly via capillary forces, a new regime was identified that was used to assemble 30-40 nm nanocubes in a patterned polydimethylsiloxane template with a high yield for both Au and Ag with multiple particles per trap. This new method relies on the generation and control of an accumulation zone at the contact line that is thin as opposed to dense, displaying higher versatility. This is in contrast with conventional wisdom, identifying a dense accumulation zone as a requirement for high-yield assembly. In addition, different formulations are proposed that can be used for the colloidal dispersion, showing that the standard water-surfactant solutions can be replaced by surfactant-free ethanol solutions, with good assembly yield. This allows to minimize the presence of surfactants that can affect electronic properties. Finally, it is shown that the obtained nanocube arrays can be transformed into continuous monocrystalline nanopatterns via nanocube epitaxy at near ambient temperature, and transferred to different substrates via contact printing. This approach opens new doors to the templated assembly of small colloids and could find potential applications in various optoelectronic devices ranging from solar cells to light-emitting diodes and displays.

Deciphering HER2-HER3 Dimerization at the Single CTC Level: A Microfluidic Approach

Simple Summary

Among these different biomarkers, circulating tumor cells have proven to be of high interest for different types of cancer and in particular for breast cancer. Here we focus our attention on a breast cancer subtype referred as HER2-positive breast cancer, this cancer being associated with an amplification of HER2 protein at the plasma membrane of cancer cells. Combined with therapies targeting the HER2 protein, HER2-HER3 dimerization blockade further improves a patient’s outcome. In this work, we propose a new approach to CTC characterization by on-chip integrating proximity ligation assay, so that we can quantify the HER2-HER3 dimerization event at the level of single CTC.

Abstract

Microfluidics has provided clinicians with new technologies to detect and analyze circulating tumor biomarkers in order to further improve their understanding of disease mechanism, as well as to improve patient management. Among these different biomarkers, circulating tumor cells have proven to be of high interest for different types of cancer and in particular for breast cancer. Here we focus our attention on a breast cancer subtype referred as HER2-positive breast cancer, this cancer being associated with an amplification of HER2 protein at the plasma membrane of cancer cells. Combined with therapies targeting the HER2 protein, HER2-HER3 dimerization blockade further improves a patient’s outcome. In this work, we propose a new approach to CTC characterization by on-chip integrating proximity ligation assay, so that we can quantify the HER2-HER3 dimerization event at the level of single CTC. To achieve this, we developed a microfluidic approach combining both CTC capture, identification and HER2-HER3 status quantification by Proximity Ligation Assay (PLA). We first optimized and demonstrated the potential of the on-chip quantification of HER2-HER3 dimerization using cancer cell lines with various levels of HER2 overexpression and validated its clinical potential with a patient’s sample treated or not with HER2-targeted therapy.

High-throughput deterministic pairing and coculturing of single cells in a microwell array using combined hydrodynamic and recirculation flow captures

Single-cell level coculture facilitates the study of cellular interactions for uncovering unknown physiological mechanisms, which are crucial for the development of new therapies for diseases. However, efficient approaches for high-throughput deterministic pairing of single cells and traceable coculture remain lacking. In this study, we report a new microfluidic device, which combines hydrodynamic and recirculation flow captures, to achieve high-throughput and deterministic pairing of single cells in a microwell array for traceable coculture. Compared with the existing techniques, the developed device exhibits advantages with regard to pairing efficiency, throughput, determinacy, and traceability. Through repeating a two-step method, which sequentially captures single cells in a meandering channel and a microwell array, cell number and type can be easily controlled. Double and triple single-cell pairings have been demonstrated with an efficiency of 72.2% and 38.0%, respectively. Cellular engulfment using two breast cell lines is investigated on a developed microfluidic chip as a biological case study, in which the morphological characteristics and the incidence rate are analyzed. This research provides an efficient and reliable alternative for the coculture of single cells on the microfluidic platform for various biomedical applications, such as studying cellular engulfment and tumor sphere formation under single-cell pairing condition.

Patterning of Particles and Live Cells at Single Cell Resolution

The ability to manipulate and selectively position cells into patterns or distinct microenvironments is an important component of many single cell experimental methods and biological engineering applications. Although a variety of particles and cell patterning methods have been demonstrated, most of them deal with the patterning of cell populations, and are either not suitable or difficult to implement for the patterning of single cells. Here, we describe a bottom-up strategy for the micropatterning of cells and cell-sized particles. We have configured a micromanipulator system, in which a pneumatic microinjector is coupled to a holding pipette capable of physically isolating single particles and cells from different types, and positioning them with high accuracy in a predefined position, with a resolution smaller than 10 µm. Complementary DNA sequences were used to stabilize and hold the patterns together. The system is accurate, flexible, and easy-to-use, and can be automated for larger-scale tasks. Importantly, it maintains the viability of live cells. We provide quantitative measurements of the process and offer a file format for such assemblies.

Gravitational sedimentation-based approach for ultra-simple and flexible cell patterning coculture on microfluidic device

Combining patterning coculture technique with microfluidics enables the reconstruction of complex in-vivo system to facilitate in-vitro studies on cell-cell and cell-environment interactions. However, simple and versatile approaches for patterning coculture of cells on microfluidic platforms remain lacking. In this study, a novel gravitational sedimentation-based approach is presented to achieve ultra-simple and flexible cell patterning coculture on a microfluidic platform, where multiple cell types can be patterned simultaneously to form a well-organized cell coculture. In contrast to other approaches, the proposed approach allows the rapid patterning of multiple cell types in microfluidic channels without the use of sheath flow and a prepatterned functional surface. This feature greatly simplifies the experimental setup, operation, and chip fabrication. Moreover, cell patterning can be adjusted by simply modifying the cell-loading tubing direction, thereby enabling great flexibility for the construction of different cell patterns without complicating the chip design and flow control. A series of physical and biological experiments are conducted to validate the proposed approach. This research paves a new way for building physiologically realistic in-vitro coculture models on microfluidic platforms for various applications, such as cell-cell interaction and drug screening.

Single-Cell Patterning Based on Immunocapture and a Surface Modified Substrate

Micropatterning technology offers powerful methods for biological analyses at the molecular level, enabling the investigation of cell heterogeneities, as well as high throughput detection. We herein propose an approach for single-cell patterning. The substrate was prepared using micro fabrication and surface modification processes, and the patterning template was prepared using bovine serum albumin and streptavidin, which can be employed for the patterning of any biological molecules containing biotin. Subsequent to photolithography, etching, chemical vapor deposition (CVD), and polyethylene glycol (PEG) treatment, the optimized patterns were obtained with high accuracy, strong contrast, and good repeatability, thus providing good foundations for the subsequent single-cell patterning. The surface passivation method was proven effective, preventing unwanted binding of the antibodies and cells. Based on this streptavidin template, the specific binding between the biotinylated antibodies and the antigens expressed on the surface of the cells was enabled, and we successfully achieved single-cell patterning with a single-cell capture rate of 92%. This single-cell array offers an effective method in the investigation of cell heterogeneity and drug screening. Further, these methods can be used in the final step for the screening and enrichment of certain cells, such as circulating tumor cells.

Capillary assembly as a tool for the heterogeneous integration of micro- and nanoscale objects

During the past decade, capillary assembly in topographical templates has evolved into an efficient method for the heterogeneous integration of micro- and nano-scale objects on a variety of surfaces. This assembly route has been applied to a large spectrum of materials of micrometer to nanometer dimensions, supplied in the form of aqueous colloidal suspensions. Using systems produced via bulk synthesis affords a huge flexibility in the choice of materials, holding promise for the realization of novel superior devices in the fields of optics, electronics and health, if they can be integrated into surface structures in a fast, simple, and reliable way. In this review, the working principles of capillary assembly and its fundamental process parameters are first presented and discussed. We then examine the latest developments in template design and tool optimization to perform capillary assembly in more robust and efficient ways. This is followed by a focus on the broad range of functional materials that have been realized using capillary assembly, from single components to large-scale heterogeneous multi-component assemblies. We then review current applications of capillary assembly, especially in optics, electronics, and in biomaterials. We conclude with a short summary and an outlook for future developments.

Methods of Micropatterning and Manipulation of Cells for Biomedical Applications

Micropatterning and manipulation of mammalian and bacterial cells are important in biomedical studies to perform in vitro assays and to evaluate biochemical processes accurately, establishing the basis for implementing biomedical microelectromechanical systems (bioMEMS), point-of-care (POC) devices, or organs-on-chips (OOC), which impact on neurological, oncological, dermatologic, or tissue engineering issues as part of personalized medicine. Cell patterning represents a crucial step in fundamental and applied biological studies in vitro, hence today there are a myriad of materials and techniques that allow one to immobilize and manipulate cells, imitating the 3D in vivo milieu. This review focuses on current physical cell patterning, plus chemical and a combination of them both that utilizes different materials and cutting-edge micro-nanofabrication methodologies.