基于液滴技术的微流控芯片实验室

液滴微流控系统是微流控芯片领域的一个新的分支,由于其诸多独特的优势而得到了广泛的研究和报道。本文对液滴的制备和相关的操控技术,包括液滴的分裂、融合、混合、分选、存储和编码等进行了介绍,对液滴技术近年来在化学与生物化学分析等领域中的应用进行了综述,并展望了液滴微流控技术的发展前景。     

Droplet microfluidics

Droplet-based microfluidic systems have been shown to be compatible with many chemical and biological reagents and capable of performing a variety of "digital fluidic" operations that can be rendered programmable and reconfigurable. This platform has dimensional scaling benefits that have enabled controlled and rapid mixing of fluids in the droplet reactors, resulting in decreased reaction times. This, coupled with the precise generation and repeatability of droplet operations, has made the droplet-based microfluidic system a potent high throughput platform for biomedical research and applications. In addition to being used as microreactors ranging from the nano- to femtoliter range; droplet-based systems have also been used to directly synthesize particles and encapsulate many biological entities for biomedicine and biotechnology applications. This review will focus on the various droplet operations, as well as the numerous applications of the system. Due to advantages unique to droplet-based systems, this technology has the potential to provide novel solutions to today's biomedical engineering challenges for advanced diagnostics and therapeutics.     

Droplet Microfluidics—A Tool for Single‐Cell Analysis

Droplet microfluidics allows the isolation of single cells and reagents in monodisperse picoliter liquid capsules and manipulations at a throughput of thousands of droplets per second. These qualities allow many of the challenges in single‐cell analysis to be overcome. Monodispersity enables quantitative control of solute concentrations, while encapsulation in droplets provides an isolated compartment for the single cell and its immediate environment. The high throughput allows the processing and analysis of the tens of thousands to millions of cells that must be analyzed to accurately describe a heterogeneous cell population so as to find rare cell types or access sufficient biological space to find hits in a directed evolution experiment. The low volumes of the droplets make very large screens economically viable. This Review gives an overview of the current state of single‐cell analysis involving droplet microfluidics and offers examples where droplet microfluidics can further biological understanding.     

基于微流控芯片技术的秀丽隐杆线虫研究进展

秀丽隐杆线虫具有体积小、生命周期短、结构简单和高基因保守性等特点,是生命科学研究领域中的一种重要模式生物。微流控芯片的通道尺寸与线虫大小相匹配,并可实现灵活集成的线虫操控,为线虫研究提供了一种全新的平台。在微流控平台上,线虫长期培养、固定、分选、精确刺激传递和单线虫包裹等单元操作已经实现,并被应用于线虫神经生物学、行为学、衰老及发育、药物筛选等研究中。该文着重介绍近几年基于微流控芯片技术的线虫研究最新进展,并对其应用前景予以展望。     

Oil droplet size determination in complex flavor delivery systems by diffusion NMR spectroscopy

Droplet size distribution of flavor oils in two different solid flavor delivery systems were determined with pulsed field gradient NMR spectroscopy: yeast encapsulation system, a spray dried flavor encapsulation system based on empty yeast cells, and glassy encapsulation system, an extruded solid water soluble carbohydrate delivery system. The oil droplet sizes are limited by the yeast cell walls in the yeast encapsulation system and the size distribution is unimodal according to images from transmission electron microscopy. The droplet size determination with diffusion NMR is based on the Murday and Cotts theory of restricted diffusion of liquids in geometrical confinements. Good fits of the diffusion data could be obtained by applying a unimodal, log-normal size distribution model and average droplet sizes of about 2 μm were found that correspond approximately to the inner diameter of the yeast cells. Scanning electron microscopy images showed a multimodal droplet size distribution in the glassy extruded delivery systems. To fit the NMR data a bimodal log-normal distribution function with five independent fitting parameters was implemented that yielded consistent and robust results. The two size populations were found in the micron and sub-micron range, respectively. The method was sufficiently accurate to depict variation of droplet size distributions in glassy encapsulation systems of different formulation.     

Redox‐Sensitive Stomatocyte Nanomotors: Destruction and Drug Release in the Presence of Glutathione

The development of artificial nanomotor systems that are stimuli‐responsive is still posing many challenges. Herein, we demonstrate the self‐assembly of a redox‐responsive stomatocyte nanomotor system, which can be used for triggered drug release under biological reducing conditions. The redox sensitivity was introduced by incorporating a disulfide bridge between the hydrophilic poly(ethylene glycol) block and the hydrophobic polystyrene block. When incubated with the endogenous reducing agent glutathione at a concentration comparable to that within cells, the external PEG shells of these stimuli‐responsive nanomotors are cleaved. The specific bowl‐shaped stomatocytes aggregate after the treatment with glutathione, leading to the loss of motion and triggered drug release. These novel redox‐responsive nanomotors can not only be used for remote transport but also for drug delivery, which is promising for future biomedical applications.     

Biomedical and Pharmacological Uses of Fluorescein Isothiocyanate Chitosan‐Based Nanocarriers

Chitosan‐based nanocarriers (ChNCs) are considered suitable drug carriers due to their ability to encapsulate a variety of drugs and cross biological barriers to deliver the cargo to their target site. Fluorescein isothiocyanate‐labeled chitosan‐based NCs (FITC@ChNCs) are used extensively in biomedical and pharmacological applications. The main advantage of using FITC@ChNCs consists of the ability to track their fate both intra and extracellularly. This journey is strictly dependent on the physico‐chemical properties of the carrier and the cell types under investigation. Other applications make use of fluorescent ChNCs in cell labeling for the detection of disorders in vivo and controlling of living cells in situ. This review describes the use of FITC@ChNCs in the various applications with a focus on understanding their usefulness in labeled drug‐delivery systems.     

Injectable hydrogels for targeted delivering of therapeutic molecules for tissue engineering and disease treatment

Hydrogels are cross‐linked three‐dimensional polymeric networks that play a vital role in solving the pharmacological and clinical limitations of the existing systems due to their unique physical properties such as affinity for biological fluids, tunable porous nature, high water content, ease of preparation, flexibility, and biocompatibility. Hydrogel also mimics the living natural tissue, which opens several opportunities for its use in biomedical areas. Injectable hydrogel allows temporal control and exceptional spatial arrangements and can offset hitches with established hydrogel‐based drug delivery systems. Here, we review the recent development of injectable hydrogels and their significance in the delivery of therapeutics such as cells, genes, and drug molecules and how these innovatory systems can complement the current delivery systems.     

Use of Three‐Dimensional Arterial Models To Predict the In Vivo Behavior of Nanoparticles for Drug Delivery

Nanomaterials have been widely used for applications in biomedical fields and could become indispensable in the near future. However, since it is difficult to optimize in vivo biological behavior in a 3D environment by using a single cell in vitro, there have been many failures in animal models. In vitro prediction systems using 3D human‐tissue models reflecting the 3D location of cell types may be useful to better understand the biological characteristics of nanomaterials for optimization of their function. Herein we demonstrate the potential ability of 3D engineered human‐arterial models for in vitro prediction of the in vivo behavior of nanoparticles for drug delivery. These models enabled optimization of the composition and size of the nanoparticles for targeting and treatment efficacy for atherosclerosis. In vivo experiments with atherosclerotic mice suggested excellent biological characteristics and potential treatment effects of the nanoparticles optimized in vitro.     

Mechanistic studies of droplet electrophoresis: A review

Electrophoresis (EP) of droplets is an intriguing phenomenon that has applications in biological systems, separation strategies, and reactor engineering. Droplet EP is significantly different from the classic particle EP because of droplet characteristics such as a mobile surface charge and the nonrigidity of the interface. Also, the liquid–liquid system, where there is an interplay between the hydrodynamic and electrokinetic forces in both phases, adds to the complexity of electrophoretic motion. Due to the vast amount of potential applications of droplet EP, a mechanistic understanding of the droplet motion in the presence of an external electric field is crucial. This review provides a background on the mechanism of droplet EP and summarizes the intrinsic interplay between the different relevant forces in these systems. The review also describes the key differences between droplet EP and particle EP, and the impact of these differences on droplet mobility. Additionally, we schematically summarize the effects of key parameters on droplet EP mobility, such as electric double layer polarization, the development of internal flow inside a droplet and boundary effects.     

pH‐Responsive Drug‐Delivery Systems

In many biomedical applications, drugs need to be delivered in response to the pH value in the body. In fact, it is desirable if the drugs can be administered in a controlled manner that precisely matches physiological needs at targeted sites and at predetermined release rates for predefined periods of time. Different organs, tissues, and cellular compartments have different pH values, which makes the pH value a suitable stimulus for controlled drug release. pH‐Responsive drug‐delivery systems have attracted more and more interest as “smart” drug‐delivery systems for overcoming the shortcomings of conventional drug formulations because they are able to deliver drugs in a controlled manner at a specific site and time, which results in high therapeutic efficacy. This focus review is not intended to offer a comprehensive review on the research devoted to pH‐responsive drug‐delivery systems; instead, it presents some recent progress obtained for pH‐responsive drug‐delivery systems and future perspectives. There are a large number of publications available on this topic, but only a selection of examples will be discussed.     

Nanostructure Engineering by Simple Tuning of Lipid Combinations

Structural morphology is the key parameter for efficacy of nanomedicine. To date, lipid‐based nanomaterial has been the most widely used material in nanomedicine and many other biomedical applications. However, to the best of our knowledge, there has not been an in‐depth or systematic investigation of the structure–function relationship of lipid‐based nanostructures. In this report, we investigated the formulation of novel lipid‐based nanostructures via simple tuning of lipid combinations. To prove this concept, we used a combination of various ratios of simple and common phospholipids with different chain lengths (14‐carbon chain DMPC: 6‐carbon chain DHPC) to find out whether a myriad of novel lipid nanostructures could be obtained. Interestingly, many combinations resulted in distinct lipid nanostructures. Drug encapsulation tests confirmed that they are able to load large amounts of drugs for biological application. In vivo anti‐tumor efficacy revealed that certain lipid nanostructures possessed superior tumor retardation effects.     

Gold Nanomaterials: Preparation,Chemical Modification,Biomedical Applications and Potential Risk Assessment

Gold nanomaterials (Au NMs) have attracted increasing attention in biomedicine due to their facile preparation, multifunctional modifications, unique optical and electrical properties, and good biocompatibility. The physicochemical properties of Au NMs at nanoscale, like size, shape, surface chemistry, and near field effects, are rendering Au NMs potent candidates in biomedicine. Thus, risk assessment of negative effects of Au NMs on biological systems is becoming urgent and necessary for future applications. In this review, we summarize up-to-date progresses on the preparation and modification of Au NMs and their biomedical applications, including biosensor, bioimaging and phototherapy, gene/drug delivery. Finally, we discuss the potential risk of Au NMs to biological systems, which is instructive for rationally designing and preparing nanomaterials for safe applications in nanomedicine.     

Visible light-curable polymers for biomedical applications

Photocurable systems, which offer advantages such as microfabrication and in situ fabrication, have been widely used as dental restorative materials. Because the visible light-curable (VLC) system causes no biological damage, it is popular as a dental material and is being investigated by many researchers for other medical applications. Here, the principle of the VLC system is explained and recent progress in key components including photoinitiators, monomers, macromers, and prepolymers is discussed. Finally, biomedical applications for drug delivery and soft tissue engineering are reviewed. Considering the recent development of VLC systems, its importance in the field of medical applications is expected to continue to increase in the future.     

Challenges and Perspectives of DNA Nanostructures in Biomedicine

DNA nanotechnology holds substantial promise for future biomedical engineering and the development of novel therapies and diagnostic assays. The subnanometer‐level addressability of DNA nanostructures allows for their precise and tailored modification with numerous chemical and biological entities, which makes them fit to serve as accurate diagnostic tools and multifunctional carriers for targeted drug delivery. The absolute control over shape, size, and function enables the fabrication of tailored and dynamic devices, such as DNA nanorobots that can execute programmed tasks and react to various external stimuli. Even though several studies have demonstrated the successful operation of various biomedical DNA nanostructures both in vitro and in vivo, major obstacles remain on the path to real‐world applications of DNA‐based nanomedicine. Here, we summarize the current status of the field and the main implementations of biomedical DNA nanostructures. In particular, we focus on open challenges and untackled issues and discuss possible solutions.     

A Comprehensive Outlook of Synthetic Strategies and Applications of Redox‐Responsive Nanogels in Drug Delivery

Increasing recognition of the role of oxidative stress in the pathogenesis of many clinical conditions and the existence of defined redox potential in healthy tissues has led to extensive research in the development of redox‐responsive materials for biomedical applications. Especially, considerable growth has been seen in the fabrication of polymeric nanogel–based drug delivery carriers utilizing redox‐responsive cross‐linkers bearing a variety of functional groups via various synthetic strategies. Redox‐responsive polymeric nanogels provide an advantage of facile chemical modification post synthesis and exhibit a remarkable response to biological redox stimuli. Due to the interdisciplinary nature of the subject, a more profound combined conceptual knowledge from a chemical and biological point of view is imperative for the rational design of redox‐responsive nanogels. The present review provides an insight into the design and fabrication of redox‐responsive nanogels with particular emphasis on synthetic strategies utilized for the development of redox‐responsive cross‐linkers, polymerization techniques being followed for nanogel development and biomedical applications. Cooperative effect of redox trigger with other stimuli such as pH and temperature in the evolution of dual and triple stimuli‐responsive nanogels is also discussed.     

Nanofibers for Biomedical and Healthcare Applications

Unique features of nanofibers provide enormous potential in the field of biomedical and healthcare applications. Many studies have proven the extreme potential of nanofibers in front of current challenges in the medical and healthcare field. This review highlights the nanofiber technologies, unique properties, fabrication techniques (i.e., physical, chemical, and biological methods), and emerging applications in biomedical and healthcare fields. It summarizes the recent researches on nanofibers for drug delivery systems and controlled drug release, tissue‐engineered scaffolds, dressings for wound healing, biosensors, biomedical devices, medical implants, skin care, as well as air, water, and blood purification systems. Attention is given to different types of fibers (e.g., mesoporous, hollow, core‐shell nanofibers) fabricated from various materials and their potential biomedical applications.     

Amphiphilic well-defined degradable star block copolymers by combination of ring-opening polymerization and atom transfer radical polymerization: Synthesis and application as drug delivery carriers

Atom transfer radical polymerization (ATRP) is one of the most popular advanced polymerization techniques in macromolecular science, allowing the synthesis of tailor-made polymers with controlled molecular weight, architecture, composition, and functionality. The combination of ATRP and ring-opening polymerization (ROP) provides a straightforward route for the preparation of polymers exhibiting both targeted and well-defined features and biodegradability, which is very interesting for the development of new materials for biomedical applications. Among the different types of polymer architectures, amphiphilic star block copolymers (BCPs) represent a very attractive one, due to their high degree of functionality at the molecular surface, low hydrodynamic volume and higher encapsulation ability, compared to molecular systems based on linear polymers. This review article highlights the research focused on the synthesis of amphiphilic well-defined degradable star BCPs by combination of ROP and ATRP, with particular focus on the development of polymers for biomedical applications, such as anticancer drug delivery, diagnosis therapy, or photodynamic therapy, which is the most investigated field regarding these polymers.     

Reversibly self-assembled pH-responsive PEG-p(CL-g-TMC) polymersomes

Polymersomes have gained much interest within the biomedical field as drug delivery systems due to their ability to transport and protect cargo from the harsh environment inside the body. For an improved drug efficacy, control over cargo release is however also an important factor to take into account. An often employed method is to incorporate pH sensitive groups in the vesicle membrane, which induce disassembly and content release when the particles have reached a target site in the body with the appropriate pH, such as the acidic microenvironment of tumor tissue or the endosome. In this paper, biodegradable poly(ethylene glycol)-poly(caprolactone-gradient-trimethylene carbonate)-based polymeric vesicles have been developed with disassembly features at mild acidic conditions. Modifying the polymer backbone with imidazole moieties results in vesicle disassembly upon protonation due to the lowered pH. Furthermore, upon increasing the pH efficient re-assembly into vesicles is observed due to the switchable amphiphilic nature of the polymer. When this re-assembly process is conducted in presence of cargo, enhanced encapsulation is achieved. Furthermore, the potency of the polymeric system for future biomedical applications such as adjuvant delivery is demonstrated.     

基于各向异性表面的液滴驱动

驱动液滴实现各种动态行为在生物医学、微流控、痕量检测等领域具有重要应用。液滴的驱动主要依赖于对液滴不同位置受力的调节。具有浸润性差异或结构差异的各向异性表面,在对液滴进行驱动时具有操作简便、节约能源等优势,逐渐成为液滴操控领域的研究热点之一。本文结合本课题组的研究工作,对近年来利用各向异性表面驱动液滴的相关研究进行了综述。首先,分析了各向异性表面驱动液滴的基本原理。依据制备方法的不同,将各向异性表面分为浸润性各向异性表面、结构各向异性表面和协同各向异性表面三类,分别归纳了其常见制备方法和在液滴驱动领域的主要应用。最后,本文对各向异性表面驱动液滴的局限性和发展方向进行了总结和展望。