Micro and Nanosystems - Volume 5, Issue 2, 2013

Microfluidic systems provide powerful tools for controlling the in vitro cellular microenvironment which best mimick the in vivo biological matrix. Such devices have been applied to both temporal and spatial manipulation of cell growth and stimuli by micro-scaled channels, patterns, and fluidic systems, creating new opportunities for biologists to study cellular behaviors under different physical and chemical conditions. In this paper, we review the concepts and strategies in designing microfluidic devices for culturing, manipulating, and stimulating cells under well-established microenvironments. We further discuss their various biological applications and potential integrations with other observation- based systems.

Biosensing fields have seen great advances in the past twenty years for cell study. Impedance based biosensor is one of the most important biosensors which can rapidly detect cellular behaviors in real time. The recent manufacturing development in micro-technology opens new horizons to develop microfluidic chip based impedance based biosensor as a real-time and label-free technique for a wide range of cellular studies. This review paper mainly focuses on the development of impedance based microfluidic biosensor for cell study in the past twenty years. The most recent developments of microhole or nanoporous membrane based impedance cell based biosensors are also discussed.

Fluorescence Correlation Spectroscopy (FCS) is a fluorescent spectroscopic technique that can be applied to measure the flow dynamics of a microfluidic channel. The principle of FCS is fluorescent molecules traveling through a tightly focused light volume inside a fluidic channel causes the fluorescent signal to fluctuate as the fluorescent molecules enter and exit the laser light focus. The flow parameter of the fluidic channel can be extracted from the autocorrelation function calculated from the measured fluorescent fluctuation. Several geometrical variations of FCS have been implemented to non-invasively map the flow characteristics of microfluidic devices in various ways to aid future designs of fluidic devices. Combining cross-correlation FCS (uses two types of fluorescent molecules) with microfluidic devices allows several important biomedical applications, including antigen detections and DNA-protein binding studies. In this article, the theory of FCS and its biomedical applications are reviewed.

Over the past several decades, many in vitro three-dimensional hepatocyte culture systems have been established, including collagen sandwiches, Matrigel™ cultures and microencapsulation systems. In addition, several studies have shown that materials with galactose ligands conjugated to their surfaces can improve hepatocyte attachment and allow the cells to maintain most of their functions. Pectin is a heterogeneous polymer of α-(1–4)-D-galacturonic acid with varying degrees of esterification and neutral sugar substitution and a variable molecular weight. In our work, we utilized pectin as a matrix to encapsulate hepatocytes. We evaluated the cellular functions of hepatocytes encapsulated in pectin and compared these functions with those of cells encapsulated in alginate. Based on the results of this work, we concluded that encapsulated HepG2 cells in pectin gel had a higher viability and superior urea synthesis function than cells in alginate microcapsules.

To study the effect of membrane morphology variation on biodegradation and the behavior of adhering cells, three types of poly(L–lactic acid) (PLLA) membranes with different morphologies—particulate, porous, and dense—were prepared. Degradation of the PLLA membranes was performed at 37°C in hydrogen peroxide solution to accelerate degradation. In addition, these degradation curves were compared with degradation in PBS solution. The estimations of degradation in the two solutions were analyzed by gel permeation chromatography, scanning electron microscopy, and differential scanning calorimetry for 12 and 24 weeks. In addition, cell behavior on the three types of PLLA membrane was also investigated. The results showed that the molecular weight of PLLA membranes dropped gradually during the in vitro degradation period in both hydrogen peroxide and PBS solutions. The surface morphologies of the three types of membrane were observed to differ in the accelerated degradation system, suggesting that morphology affected the crystallinity and resulted in different degradation rates. Adhering cell behavior was also affected by surface morphology, with cells on the particulate membrane displaying the best viability. As the degradation rate of the particulate membrane was the slowest and its biocompatibility was the best, the particulate PLLA membrane may be most suitable for long-term orthopedic implants.

Due to its unique physicochemical properties, graphene has received increasing attention. This article selectively reviews the application of graphene for direct electrochemistry of enzymes, small biomolecules, DNA sensing, and environmental analysis. Graphene oxide (GO) and reduced graphene oxide (RGO) have been used as sensors for gases and heavy metal ions. In all cases, the sensors performed well, proving to be highly sensitive, selective, and stable.

Graphene (Gr) is considered to be an ideal, two-dimensional catalytic support, due to its excellent electrical and thermal conductivity, mechanical strength and high surface area. In this paper we review recent progress in graphene applications as a catalyst support for graphene-supported metal nanoparticle heterogeneous catalysts, MeNP/Gr. For each catalyst the preparation method is described, and also the most significant properties that affect the catalytic behavior of the MeNP/Gr composite are discussed. The catalytic results, activity and selectivity are presented, emphasizing the role of the graphene support in the catalytic processes. Palladium was the most-used noble metal and a series of Pd/Gr, Pd/magnetite/Gr and Pd-Me/Gr composites were proposed for possible applications in different catalytic processes. Platinum- containing graphene composites were prepared and tested for hydrogenation and CO oxidation reactions. Among the applications, the most studied were processes involving hydrogen: hydrogenations, reductions and hydrogen generating reactions. Other reactions that are discussed are C-C cross coupling and CO oxidation. The role of graphene in the catalytic reactions is ascribed to its very good properties for dispersing and stabilizing the MeNPs, to the more favorable accessibility of reagent molecules to active centers due to the 2D configuration of the support, and to the intimate interaction between the MeNPs and graphene, which leads to efficient electron transfer and/or mass transport between the support and the metal.

Nanotechnology, defined as the science of very small matter called nanomaterial, comprises the study of chemical and physical properties of particles which are structured in sizes ranging from 1 to 100 nanometers. At this size range, nanomaterial exhibits superior chemical and physical characteristics as compared to those displayed while existing in normal size. To date, multiple nanotechnology research centers within the United States are investigating the potential use of different types of nanoparticles as carbon nanotubes (CNT) in the construction industry to attain superior characteristics of building materials, improve their durability and increase the life span of different structures, and minimize the life cycle cost of construction projects. The major impediments to the widespread implementation of nanotechnology include high nanomaterial cost, lack of industrial experience, and absence of standard specifications for building materials incorporating nanoparticles. This research paper presents a review for the advance in nanotechnology applications in the construction industry in the United States, current research and industrial projects regarding nanoparticles incorporation in building materials as cement, attained advantages as concrete high tensile strength, lower permeability, and improved long-term performance. In addition, the challenges impeding further development of nanotechnology in construction research and industry are overviewed. Significant achievements are anticipated for the near future due to the growing attention of the nanotechnology on a state and federal level within the United States.