System optimization for realizing a miniaturized gas chromatograph sensor for rapid chemical analysis

Rapid and comprehensive on-site analysis of chemicals in applications ranging from industrial process control to homeland security is of significant importance to improve the environment and save human life. The need for sensors that are fast, reliable, and portable has never been greater. For the challenging task of on-site instrumentation, where power sources can be limited, shrinking the size of the device is the most effective way to conserve power. Although gas chromatography is a mature technique well suited for these applications, current instrumentation has deficiencies that limit its usage. Speed of analysis and non portability are severe hindrances to using the bench top and portable instruments for on-site applications. This focus of this research is to provide a transition from a portable gas chromatograph (GC) instrument to a handheld GC sensor. The significant issues for realizing a handheld GC sensor were addressed. One important design criterion was that the sensors have the same analytical capability as a commercial GC instrument. Of the many components of a GC, the separation column primarily defines the resolution and the analysis time. Thorough theoretical analysis led to the conclusion that high aspect ratio, rectangular cross-section columns have a distinct advantage over capillary columns. A column including an on-chip sample loop and a makeup gas manifold were designed. Previously reported attempts to fabricate rectangular columns have focused on low aspect ratio or square cross-section columns. Contrasting all prior efforts, significant strides in process development were made to realize nickel GC columns using the LiGA technology with aspect ratios as high as 20. Through process control, a device yield of over 90% was achieved. Tests on these columns yielded more than 20,000 plates for unretained species. Four hydrocarbons were separated in less than 2 s at 100 °C on a 50 μm wide by 600 μm tall by 0.5 m long coated LiGA column. For the first time reported, 2-D GC was implemented using MEMS columns

Towards a three-dimensional microfluidic liver platform for predicting drug efficacy and toxicity in humans

Although the process of drug development requires efficacy and toxicity testing in animals prior to human testing, animal models have limited ability to accurately predict human responses to xenobiotics and other insults. Societal pressures are also focusing on reduction of and, ultimately, replacement of animal testing. However, a variety of in vitro models, explored over the last decade, have not been powerful enough to replace animal models. New initiatives sponsored by several US federal agencies seek to address this problem by funding the development of physiologically relevant human organ models on microscopic chips. The eventual goal is to simulate a human-on-a-chip, by interconnecting the organ models, thereby replacing animal testing in drug discovery and development. As part of this initiative, we aim to build a three-dimensional human liver chip that mimics the acinus, the smallest functional unit of the liver, including its oxygen gradient. Our liver-on-a-chip platform will deliver a microfluidic three-dimensional co-culture environment with stable synthetic and enzymatic function for at least 4 weeks. Sentinel cells that contain fluorescent biosensors will be integrated into the chip to provide multiplexed, real-time readouts of key liver functions and pathology. We are also developing a database to manage experimental data and harness external information to interpret the multimodal data and create a predictive platform

Is there an autoimmune basis for schizophrenia?

Etiology of schizophrenia still remains a mystery. Schizophrenia with coexistence of myasthenia gravis in the same patient raises the suspicion of autoimmune mechanisms involved in causation of schizophrenia

Microfluidic Device for Examining Directional Sensing in Dendritic Cell Chemotaxis

Dendritic cell chemotaxis is an important process involved in the acquisition of adaptive immunity. Despite several studies, our understanding of this process remains limited. One of the reasons for this is the lack of experimental models that give us real-time information on dendritic cell locomotion. Here, using tools in microfluidics, we have fabricated a microdevice that allows us to monitor dendritic cell migration in a chemokine gradient in real time. We successfully observed the migration of dendritic cells derived from a myeloid leukemia cell line (MUTZ-3) in a soluble chemokine (CCL-19) gradient. Our experiments suggest the utility of microdevices in monitoring dendritic cell chemotaxis in real time and getting important information regarding migration speeds and distances previously not available from conventional chemotaxis assays. This kind of data is useful for building mechanistic mathematical models of dendritic cell chemotaxis that may give us novel insights to the process of dendritic cell chemotaxis

Microfluidic Device for Examining Directional Sensing in Dendritic Cell Chemotaxis

Dendritic cell chemotaxis is an important process involved in the acquisition of adaptive immunity. Despite several studies, our understanding of this process remains limited. One of the reasons for this is the lack of experimental models that give us real-time information on dendritic cell locomotion. Here, using tools in microfluidics, we have fabricated a microdevice that allows us to monitor dendritic cell migration in a chemokine gradient in real time. We successfully observed the migration of dendritic cells derived from a myeloid leukemia cell line (MUTZ-3) in a soluble chemokine (CCL-19) gradient. Our experiments suggest the utility of microdevices in monitoring dendritic cell chemotaxis in real time and getting important information regarding migration speeds and distances previously not available from conventional chemotaxis assays. This kind of data is useful for building mechanistic mathematical models of dendritic cell chemotaxis that may give us novel insights to the process of dendritic cell chemotaxis

Internet addiction and its determinants among medical students

Background: Exponential use of internet has resulted in internet addiction in recent times. Students are particularly at risk because of their unique personal, social, and academic needs. Objectives: The study was designed to evaluate the prevalence of internet addiction and its determinants among medical students. Materials and Methods: A cross-sectional study was conducted in 282 medical students with the help of semi-structured questionnaire consisting of questions related to demographic information, information related to internet use, and Young's internet addiction test. Results: We found prevalence of internet addiction among medical students to be 58.87% (mild – 51.42%, moderate –7.45%) and significantly associated factors with internet addiction being male gender, staying in private accommodation, lesser age of first internet use, using mobile for internet access, higher expenditure on internet, staying online for longer time, and using internet for social networking, online videos, and watching website with sexual content. Conclusion: Medical students are vulnerable for internet addiction and efforts should be taken to increase awareness and prevent the problem of internet addiction in them

Novel Microfluidic Colon with an Extracellular Matrix Membrane

Collagen is a key element of basal lamina in physiological systems that participates in cell and tissue culture. Its function is for cell maintenance and growth, angiogenesis, disease progression, and immunology. The goal of our present study was to integrate a micrometer resolution membrane that is synthesized out of rat-tail type I collagen in a microfluidic device with apical and basolateral chambers. The collagen membrane was generated by lyophilization. In order to evaluate the compatibility of the resulting membrane with organs-on-chips technology, it was sandwiched between layers of polydimethylsiloxane (PDMS) that had been prepared by replica molding, and the device was used to culture human colon caco 2 cells on the top of the membrane. Membrane microstructure, transport, and cell viability in the organs-on-chips were observed to confirm the suitability of our resulting membrane. Through transport studies, we compared diffusion of two different membranes: Transwell and our resulting collagen membrane. We found that mass transport of 40 kDa dextran was an order of magnitude higher through the collagen membrane than that through the Transwell membrane. Human colon caco 2 cells were cultured in devices with no, Transwell, or ECM membrane to evaluate the compatibility of cells on the ECM membrane compared to the other two membranes. We found that caco 2 cells cultured on the collagen membrane had excellent viability and function for extended periods of time compared to the other two devices. Our results indicate a substantial improvement in establishing a physiological microenvironment for in vitro organs-on-chips

Machine Learning: A Crucial Tool for Sensor Design

Sensors have been widely used for disease diagnosis, environmental quality monitoring, food quality control, industrial process analysis and control, and other related fields. As a key tool for sensor data analysis, machine learning is becoming a core part of novel sensor design. Dividing a complete machine learning process into three steps: data pre-treatment, feature extraction and dimension reduction, and system modeling, this paper provides a review of the methods that are widely used for each step. For each method, the principles and the key issues that affect modeling results are discussed. After reviewing the potential problems in machine learning processes, this paper gives a summary of current algorithms in this field and provides some feasible directions for future studies

Organ-Chip Models: Opportunities for Precision Medicine in Pancreatic Cancer

Pancreatic Ductal Adenocarcinoma (PDAC) is an expeditiously fatal malignancy with a five-year survival rate of 6–8%. Conventional chemotherapeutics fail in many cases due to inadequate primary response and rapidly developing resistance. This treatment failure is particularly challenging in pancreatic cancer because of the high molecular heterogeneity across tumors. Additionally, a rich fibro-inflammatory component within the tumor microenvironment (TME) limits the delivery and effectiveness of anticancer drugs, further contributing to the lack of response or developing resistance to conventional approaches in this cancer. As a result, there is an urgent need to model pancreatic cancer ex vivo to discover effective drug regimens, including those targeting the components of the TME on an individualized basis. Patient-derived three-dimensional (3D) organoid technology has provided a unique opportunity to study patient-specific cancerous epithelium. Patient-derived organoids cultured with the TME components can more accurately reflect the in vivo tumor environment. Here we present the advances in organoid technology and multicellular platforms that could allow for the development of “organ-on-a-chip” approaches to recapitulate the complex cellular interactions in PDAC tumors. We highlight the current advances of the organ-on-a-chip-based cancer models and discuss their potential for the preclinical selection of individualized treatment in PDAC