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"Advanced Science and Technology at SUSTech" Series Report - Part 9

Nov 22, 2017 Research

Micro- and nanotechnology refers to the technology related to structures and devices with a characteristic scale on the micrometer or nanometer level, which is invisible to naked eyes. It is everywhere in modern frontier science and technology as shown in Figure 1. A mobile phone that we use in our daily life is a great example of micro- and nanotechnologies. Micro- and nanotechnology enables the production and manufacturing of key components of cell phones, such as LCD or OLED displays, flash memories, micro electro-mechanical sensors (MEMS), and high-density printed circuit boards (PCB).

Figure 1. Micro- and nanometer structures, devices and their applications

The research group of Prof. Xing Cheng from the Department of Materials Science and Engineering of the Southern University of Science and Technology specializes in micro- and nanofabrication technology, including (1) ultra-high resolution lithography (sub-5 nanometer), (2) large-area and low-cost nanofabrication for industrial-scale manufacturing, and (3) three-dimensional printing technology on the micro- and nanometer scale. Cheng’s group is also specialized in the application of micro- and nanofabrication technology in areas such as semiconductor devices, nanooptics, and biomedical engineering. In recent years, Cheng’s group has carried out several innovative researches in the field of microfluidics. China and PCT patents are being applied for based on these developments. In recent years, several US and China patents have also been granted.

 “Processing” in a microscopic world

The fabrication of micro- and nanostructures originated from the microelectronic industry. Using the top-down approach, microscale or nanoscale patterns are produced from blank substrates or materials in a deterministic fashion. For example, the pixels in a flat panel display usually range from tens to hundreds of microns; the characteristic dimensions in MEMS gyroscope chips that sense phone orientations range from tens to hundreds of microns; the sizes of individual bits in information storage devices, such as DVD and blue-ray, are usually around hundreds of nanometers; while in the latest CPU and DRAM chips, the minimum dimensions range down to 10 to 20 nanometers.

In addition to the traditional electronic information industry, micro- and nanotechnology is increasingly applied in life science research and biomedical engineering because the dimensions of human cells, DNA or protein molecules are within the range of the micro- and nanometer scales. For example, the speed and throughput of genetic sequencing has increased by tens of thousands of times by using micro- and nanofabrication technology, thus making it possible to conduct genetic sequencing quickly and cheaply. With the increasing importance of single cell or single molecule study in life science, micro- and nanotechnology will play an irreplaceable role at the forefront of life science research.

To achieve conventional chemical or biological laboratory functions on small chips

In May 2017, the Ministry of Science and Technology issued the “Strategic Development of Biotechnology Innovation in the 13th ‘Five-year Plan’”, aiming to boost the development of biotechnology and related-industries. The Plan mentioned that the development should focus on protein sequencing technology, new mass spectroscopic and microfluidic chip technology, and a series of technologies in the area of single-cell separation, genomic amplification, amplification of transcriptional groups and single-cell genome analysis. Microfluidics will certainly play a significant role in these areas in the future.

Microfluidics or lab on a chip is based on MEMS technology. With a micro channel network as the key structure, the chip controls and manipulates fluidics at the micro and nanoscale through micro pumps and micro valves. It can integrate many basic operation steps such as sampling, dilution, sample injection, reaction, separation and detection into a small chip. Microfluidics are widely used in chemistry and biology to realize the functions of conventional chemical or biological laboratories.

Because microfluidic chips can achieve a flexible and scalable integration of a variety of unit functionalities on a small platform, it can simultaneously analyse hundreds of samples in a few minutes. It can process sample pretreatment and analysis automatically to achieve high levels of integration and automation. With the advantages of compact sizes, minimal reagents usage, fast reaction speed, high-throughput parallel processing and low cost, microfluidic chips have developed into a new research field across disciplines such as biology, chemistry, medicine, fluidics, electronics, materials and mechanics.

Single cell “trapping and pairing” for studying cell-cell interaction

As the basic structural and functional unit of living bodies, the cell is at the center of research on life science and engineering, including reproductive development, heredity, neural activity and diseases. Conventional cell analyses usually end with the average results of a large number of cells, and individual differences among individual cells are ignored. The study on the single cell level can obtain more crucial information. A large amount of research has shown that single cell studies are significant for molecular biology and metabolomics. Single cell analysis is also important for the diagnosis and treatment of diseases.

Cheng’s group recently developed a dielectrophoresis (DEP) microfluidic chip platform to realize high-throughput single-cell trapping and pairing (Figure 2). The DEP chip system can be customized according to different functional requirements and make use of micro and nanofabrication technology. DEP chip in single cell trapping and pairing can control the cells to move to high electric field regions under positive DEP force or to low electric field regions under negative DEP force by changing the frequency of the applied voltage. By trapping different kinds of single cells into a microwell array, Cheng’s group successfully trapped and paired single cells with high throughput. At present, the single cell trapping efficiency is more than 80% and the single cell-cell pairing efficiency is more than 70%. The single cell trapping and pairing technology can be used in the study of various kinds of bioengineering and biomedical engineering, such as single cell sequencing, precise cell fusion, cell-cell interaction and so on.

Figure 2. (a) The microfluidic chip for single cell trapping and pairing; (b, c) the device structure, and (d) the single cell “trapping and pairing” result.

High-efficiency and low-cost tumor diagnosis system

Cancer is a disease that can seriously threaten the health of human beings. Up to 90% of cancer deaths are caused by the metastasis of cancer. As the traditional method for the diagnosis of cancer, tissue biopsy presents disadvantages such as difficulty in sampling, major injuries and complex operations. Liquid biopsy technology extracts human blood or body fluids to analyze tumor cells, and DNA or RNA therein. The advantages of liquid biopsy are high sensitivity, high speed and minimal trauma. It has become an increasingly important new tumor diagnosis technology. Separation, concentration, enumerating and analysis of circulating tumor cells (CTCs) in the blood are important technical means for liquid biopsy of cancer diagnosis. A circulating tumor cell is the collective reference to the tumor cells that fall off from the primary lesion place of the tumor and enter into peripheral circulating blood of a human body. The appearing of CTCs in the bloodstream is a sign of the beginning of tumor metastasis. Therefore, capture and detection of CTCs are of great significance to cancer study and treatment, such as early diagnosis, prognosis analysis, personalized drug evaluation, and single cell sequencing. Currently, CTC liquid biopsy technology has been clinically applied in the diagnoses of colon, breast and prostate cancers, indicating huge application value and significant market potential.

CTCs are extremely rare in the bloodstream. The ratio of blood cell concentration in blood to that of CTCs is more than 106, and the number of CTCs in a milliliter of blood for early cancer patients is below 10. How to effectively separate and enrich CTCs is the key challenge. In collaboration with a medical technology company in Shenzhen, Cheng’s group recently developed a multi-layer microfluidic chip and developed a CTC separation system based on the chip (Figure 3). The system has the key characteristics of high efficiency, high throughput and low cost. It can realize separation, extraction and dyeing of tumor cells in the chip. The microfluidic chip can realize automatic operations by connecting with air pressure pumps, multi-way switches, flowmeters and controllers. Experimental results show that the system can separate CTCs from the blood sample and extract more than 80% of CTCs, with the capacity of processing 10 ml blood samples within 90 minutes.

Figure 3. (a) The microfluidic chip for sorting and enumerating CTCs, (b) the device structure of the microfluidic chip, (c) the SEM image of the cross section of the fabricated chip, and (d) the automatic CTC separation system

Active-matrix Driven Scalable Central Fluid Processing Platform

With the advancement of modern biomedical engineering technology, lab on chip technology is receiving increasing attention. Because of the wide range of requirements of different biological analyses, custom design and fabrication of microfluidic chips is becoming increasingly important. However, due to their complexity, such customized designs and fabrication have become a bottleneck for the application of microfluidic chips.

To address the need of customization, Cheng’s group developed a “central fluid processing unit (CFPU)” based on digital microfluidics (Figure 4) and this generic platform can be used in a wide range of bioanalysis and biosynthesis. Using the electro-wetting-on-dielectric phenomenon, active-matrix circuitry can be used to manipulate droplets in a large array by underlying electrodes without interfering with other droplets. This design brings forth several breakthroughs in the functionality and usability of microfluidic biochips. Firstly, the CFPU for droplet fluids can be used as a generic biological analysis and biosynthesis platform. By changing the ingredients (chemical agents and biological species) in the droplet, completely different applications can be accomplished on the same platform. By selectively activating electrodes in the array, the CFPU can be dynamically reconfigured to accomplish specific tasks. Secondly, the chip has the capability to process a large amount of chemical and biological reactions simultaneously. Driven by the active-matrix circuitry, multiple droplets can be controlled simultaneously. The active-matrix circuitry can easily be extended to thousands of rows and columns, and thus can directly manipulate tens of thousands of droplets. This can greatly reduce the manpower cost and save time for large-scale and complex biological analysis and synthesis tasks.

Combining reliable and proven active-matrix circuitry with digital microfluidics, Cheng’s group collaborated with Dalian Institute of Chemical Physics and the Chinese Academy of Sciences to build a prototype of CFPU for digital microfluidics. This prototype also has peripheral electronic control hardware and software, and has the capability of parallel and continuous manipulation of multiple droplets. Flexibility, easy-to-use, and reusability of the chip make it the ideal platform for massive parallel sample preparations in biomedical researches and applications such as genomics, proteomics and precision medicine.

Figure 4. The digital microfluidic chip platform developed by collaboration with Dalian Institute of Chemical Physics, CAS

Programmable micro-pump for precise and smart drug delivery

Drug injection is one of the most commonly used approach in medical treatment. Injection and infusion devices are widely used in medical equipment in hospitals. With the increasing demands for the precision of drug delivery, higher standards are demanded for drug delivery devices. At the same time, the miniaturization of drug injection and infusion devices provides more convenience for patients and thus greatly promotes the use of drug delivery devices. In order to achieve more accurate and effective treatment, programmable injection and infusion devices have drawn increasing attention. Being small and easy-to-operate, smart micro-wearable injection pump chips are especially suitable for the treatment of the wounded or patients in harsh environments such as remote areas or battlefields.

Recently, Cheng’s group successfully developed a microfluidic pump chip about the size of a coin. Based on the pump chip, the group developed a programmable mini drug injection device (Figure 5) jointly with a medical device company in Shanghai. By combining the advanced microfluidic pump chip design and circuit control system, the smart mini injection system is about the size of a matchbox. The whole injection device weighs no more than 20 grams and it can be attached to the arm or body of the patient or injured person. The device is especially suitable for continuous drug delivery without interfering with the daily activities of the user. Through blue tooth connection with handheld devices, it can achieve customized injection patterns to achieve accurate and effective treatment. Because the microfluidic pump chip injection system is suitable for controlled injection of drugs with rapid in vivo metabolism such as insulin and painkillers, its successful development will play an important role in the treatment of chronic diseases such as diabetes and chronic pains. This ultra-portable injection device is also suitable for use in hospitals or at homes, and can be used for both military and civil purposes, indicating great potential for marketing. Through collaboration, Cheng’s group and the medical company have developed a prototype of the insulin pump. Its size is only half of that of current insulin pumps on the market, and the volume production cost is expected to be much lower than current commercial insulin pumps. With these features, the smart drug delivery device is expected to find many applications in medical treatment.

Figure 5. (a) A microfluidic pump chip, (b) A prototype of the driving circuit board for the pump chip, (c) an ultra-portable insulin injection pump, and (d) A combinatorial pump

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