Search

Thermal sensors are mainly based on the selective heating of specific areas, which in most cases is a critical feature for both the operation and the performance of the thermal device. In this work, we evaluate the thermoelectrical response of two graphitic materials, namely (a) a commercial 2.4%wt graphene–ethyl cellulose dispersion in cycloxehanone and terpineol (G) and (b) a custom functionalized reduced graphene oxide (f-rGO) ink in the range of −40 to 100 °C. Both inks were printed on a flexible polyimide substrate and the Thermal Coefficients of Resistance (TCR) were extracted as TCRG = −1.05 × 10−3 °C−1 (R2 = 0.9938) and TCRf-rGO = −3.86 × 10−3 °C−1 (R2 = 0.9967). Afterward, the inkjet-printed devices were evaluated as microheaters, in order to exploit their advantage for cost-effective production with minimal material waste. f-rGO and G printed heaters reached a maximum temperature of 97.5 °C at 242 mW and 89.9 °C at 314 mW, respectively, applied by a constant current source and monitored by an infrared camera. Repeatability experiments were conducted, highlighting the high robustness in long-term use. The power–temperature behavior was extracted by self-heating experiments to demonstrate the ability of the devices to serve as heaters. Both static and dynamic evaluation were performed in order to study the device behaviors and extract the corresponding parameters. After all the experimental processes, the resistance of the samples was again evaluated and found to differ less than 13% from the initial value. In this work, fabrication via inkjet printing and demonstration of efficient and stable microheaters utilizing a custom ink (f-rGO) and a commercial graphene ink are presented. This approach is suitable for fabricating selectively heated geometries on non-planar substrate with high repeatability and endurance in heat cycles.

Cell-based biosensors appear to be an attractive tool for the rapid, simple, and cheap monitoring of chemotherapy effects at a very early stage. In this study, electrochemical measurements using a four-point probe method were evaluated for suspensions of four cancer cell lines of different tissue origins: SK–N–SH, HeLa, MCF-7 and MDA-MB-231, all for two different population densities: 50 K and 100 K cells/500 μL. The anticancer agent doxorubicin was applied for each cell type in order to investigate whether the proposed technique was able to determine specific differences in cell responses before and after drug treatment. The proposed methodology can offer valuable insight into the frequency-dependent bioelectrical responses of various cellular systems using a low frequency range and without necessitating lengthy cell culture treatment. The further development of this biosensor assembly with the integration of specially designed cell/electronic interfaces can lead to novel diagnostic biosensors and therapeutic bioelectronics.

The airway epithelium is the primary site where inhaled and resident microbiota interacts between themselves and the host, potentially playing an important role on allergic asthma development and pathophysiology. With the advent of culture independent molecular techniques and high throughput technologies, the complex composition and diversity of bacterial communities of the airways has been well-documented and the notion of the lungs' sterility definitively rejected. Recent studies indicate that the microbial composition of the asthmatic airways across the spectrum of disease severity, differ significantly compared with healthy individuals. In parallel, a growing body of evidence suggests that bacterial viruses (bacteriophages or simply phages), regulating bacterial populations, are present in almost every niche of the human body and can also interact directly with the eukaryotic cells. The triptych of airway epithelial cells, bacterial symbionts and resident phages should be considered as a functional and interdependent unit with direct implications on the respiratory and overall homeostasis. While the role of epithelial cells in asthma pathophysiology is well-established, the tripartite interactions between epithelial cells, bacteria and phages should be scrutinized, both to better understand asthma as a system disorder and to explore potential interventions.

The present work reports on the detailed electro-thermal evaluation of a highly water dispersible, functionalized reduced graphene oxide (f-rGO) using inkjet printing technology. Aiming in the development of printed electronic devices, a flexible polyimide substrate was used for the structures’ formation. A direct comparison between the f-rGO ink dispersion and a commercial graphene inkjet ink is also presented. Extensive droplet formation analysis was performed in order to evaluate the repeatable and reliable jetting from an inkjet printer under study. Electrical characterization was conducted and the electrical characteristics were assessed under different temperatures, showing that the water dispersion of the f-rGO is an excellent candidate for application in printed thermal sensors and microheaters. It was observed that the proposed f-rGO ink presents a tenfold increased temperature coefficient of resistance compared to the commercial graphene ink (G). A successful direct interconnection implementation of both materials with commercial Ag-nanoparticle ink lines was also demonstrated, thus allowing the efficient electrical interfacing of the printed structures. The investigated ink can be complementary utilized for developing fully printed devices with various characteristics, all on flexible substrates with cost-effective, few-step processes.

The development and the corresponding evaluation of a multidirectional thermal flow sensor are presented in this work. The sensor was fabricated on a flexible substrate, allowing for new applications, since it provides the possibility of installation in nonplanar surfaces such as pipelines. Furthermore, the sensing elements are not in direct contact with the fluid, which increases the device reliability, extends its application range, and allows the noncontact monitoring of fluids. This was achieved by utilizing the substrate as a protective layer between the sensing elements and the fluid under measurement. The operation principle is based on the determination of the flow-induced temperature profile variations. A dedicated experimental setup was designed and used for the device evaluation. Both flow velocity value and direction were successfully extracted, while the results were consistent with the predicted theoretical values. A single-layer back propagation neural network that correlates the sensors’ readouts to the angle of rotation was implemented, which leads to a mean absolute direction estimation error in the order of 2.7 degrees independent to the training procedure datasets.

Cancer cell lines are important tools for anticancer drug research and assessment. Impedance measurements can provide valuable information about cell viability in real time. This work presents the proof-of-concept development of a bioelectrical, impedance-based analysis technique applied to four adherent mammalian cancer cells lines immobilized in a three-dimensional (3D) calcium alginate hydrogel matrix, thus mimicking in vivo tissue conditions. Cells were treated with cytostatic agent5-fluoruracil (5-FU). The cell lines used in this study were SK-N-SH, HEK293, HeLa, and MCF-7. For each cell culture, three cell population densities were chosen (50,000, 100,000, and 200,000 cells/100 &mu, L). The aim of this study was the extraction of mean impedance values at various frequencies for the assessment of the different behavior of various cancer cells when 5-FU was applied. For comparison purposes, impedance measurements were implemented on untreated immobilized cell lines. The results demonstrated not only the dependence of each cell line impedance value on the frequency, but also the relation of the impedance level to the cell population density for every individual cell line. By establishing a cell line-specific bioelectrical behavior, it is possible to obtain a unique fingerprint for each cancer cell line reaction to a selected anticancer agent.

This work concerns the evaluation of a novel sensor for determining the air intake of a typical low power engine. The sensor is based on PCB technology enabling effective thermal isolation and direct communication to the macroworld. The device was integrated into a DIESEL engine testbed for characterization purposes while a commercially available mass air flow sensor was employed as a reference; the proper functionality of the developed prototype has been validated. Key features of the proposed device are robustness, simplicity and low-cost suggesting numerous potential applications in the automotive area.

A standalone, portable system for characterization and electrical measurements of thermal sensors was developed and evaluated. The system is able to provide an adjustable power to the heating element, under any of the common modes of operation (e.g. CR, CV, CC), and simultaneously measure the resulting output. Four independent constant current excitation sources and measurement channels are also available for the connection of respective sensing elements; therefore various principles of operation (e.g. hotwire, calorimetric) can also be supported. The output data can either be displayed on a built-in LCD graphic display, stored on integrated, non-volatile memory or directly transmitted to a PC via the USB interface. The custom implementation provides a low-cost, high precision alternative to commercial general purpose measurement systems and can also be utilized for electrical characterization of various experimental devices as well as other laboratory applications.

This work presents the evaluation of a multiparametric sensing device on paper fabricated by inkjet printing, for applications such as smart packaging-labeling and disposable biosensors where biocompatibility and low cost are key factors. The device is able to measure simultaneously relative humidity, temperature and compressive and tensile bending. Commercial silver nanoparticle ink and PEDOT:PSS were printed onto inkjet photo glossy paper using a drop-on-demand inkjet printer forming an interdigitated electrode array and a meander shaped micro-ribbon. Humidity measurements revealed that sensor response, which is effectively expressed by the relationship between paper substrate resistance and relative humidity was similar for both materials utilized as electrodes. Temperature coefficients of resistance (TCR) were extracted for Ag-nanoparticle and PEDOT:PSS - based temperature sensors respectively in the range of 25–45 °C. The bending tests indicated that both materials exhibited similar trend in tensile bending, with resistance increasing in a linear manner up to a maximum tensile length of 900 μm. Ag-nanoparticle ink outperformed PEDOT:PSS ink in terms of repeatability, sensitivity and hysteresis. In compressive bending measurements Ag-nanoparticle and PEDOT:PSS gauge factors exhibited similar gauge factor of opposite sign.

In this work we present the development of a low-cost humidity and temperature sensing platform on paper by inkjet printing, using a commercial AgNPs conductive ink. The humidity sensing module was capable of measuring relative humidity in the range of 0⁻90%rH, exhibiting linear response with minimal memory effect when returning to 0%rH baseline signal while the temperature sensor performed linearly as well in the range of 25⁻75°C. Process repeatability has been verified by electrical and optical characterization. Mechanical bending results highlight the platform’s capability to serve as an easy to install, flexible multi-parametric sensing platform.

The evaluation of glucose metabolic activity in immune cells is becoming an increasingly standard task in immunological research. In this study, we described a sensitive, inexpensive, and non-radioactive assay for the direct and rapid measurement of the metabolic activity of CD4+ T cells in culture. A portable, custom-built Cell Culture Metabolite Biosensor device was designed to measure the levels of acidification (a proxy for glycolysis) in cell-free CD4+ T cell culture media. In this assay, ex vivo activated CD4+ T cells were incubated in culture medium and mini electrodes were placed inside the cell free culture filtrates in 96-well plates. Using this technique, the inhibitors of glycolysis were shown to suppress acidification of the cell culture media, a response similar to that observed using a gold standard lactate assay kit. Our findings show that this innovative biosensor technology has potential for applications in metabolic research, where acquisition of sufficient cellular material for ex vivo analyses presents a substantial challenge.

A thermal gas flow sensor was developed and evaluated. The presented implementation requires only low-cost manufacturing techniques and readily available components, while maintaining a high level of detection range and sensitivity. Heater and sensing elements were integrated on a flexible substrate and the device was formed by bending the substrate so that the active elements were placed on the external surface of the formed channel, therefore zero flow interference is achieved and a wide variety of fluids can be measured without compromising the sensor integrity. Evaluation was made using air flow rates in the range of 0-65SLPM utilizing electrical measurements and IR imaging techniques simultaneously.

In this work, the assessment of the interactions of a bioactive substance applied to immobilized cells in either a two-dimensional (2D) or three-dimensional (3D) arrangement mimicking in vivo tissue conditions is presented. In particular, dopamine (DA) was selected as a stimulant for the implementation of an impedance analysis with a specific type of neural cells (murine neuroblastoma). The aim of this study was the extraction of calibration curves at various frequencies with different known dopamine concentrations for the description of the behavior of dopamine applied to 2D and 3D cell cultures. The results present the evaluation of the mean impedance value for each immobilization technique in each frequency. The differential responses showed the importance of the impedance when frequency is applied in both 2D and 3D immobilization cases. More specifically, in 2D immobilization matrix impedance shows higher values in comparison with the 3D cell culture. Additionally, in the 3D case, the impedance decreases with increasing concentration, while in the 2D case, an opposite behavior was observed.

A flexible gas flow sensor was developed and characterized. The sensor was fabricated on a flexible PCB substrate and is able to quantify flow rate based on the thermal transfer principle. Direct electrical communication to the macroworld is achieved, while the effective thermal isolation enhances sensor performance. Characterization in the range of 1-10 SLPM is presented.

A thermal accelerometer was developed and evaluated. The presented device was fabricated directly on an organic substrate, which ensures a high level of thermal isolation, while also facilitating direct electrical communication to the macroworld. The role of the seismic mass was utilized by a fluid (water), which was confined in a tank adjusted on the sensor surface. Acceleration quantification is achieved by the monitoring of the cooling effect on the heating element. A sensor signal of 32 mV for an acceleration of 1 g was obtained.

Recent advances in flow control have the potential for significant impact on the engineering design. Fluidic flow control is a method for altering flows over aerodynamic surfaces which does not rely upon altering the physical shape of the surface (typically through moving control surfaces such as flaps). The steady air flow along a basic geometry of a backward facing step is used to study the alterations of the resulting recirculation area ether spontaneously or by applying pulsating fluid injection below the edge of the step as control actuator. The PIV method is used to monitor the velocity field and determine the reattachment point. Applying flow sensors based on hot wire anemometry on the bottom wall boundary it is possible to estimate parameters such as the recirculation length or even the region of intense turbulent activity as compared and verified by the PIV. Preliminary measurements by thermal sensors reveals fingerprints of the reattachment zone applying time-frequency analysis.

The behaviour of a thermal flow sensor attached to the wall of a square tube is examined, exposed to gas flow for Reynolds numbers in the range 0–4.1 × 10 4 . Consisting of a polysilicon heater and a pair of thermopiles, the sensor’s three output signals (heater power, its electric resistance and the thermopile signal) are analyzed as a function of Re . Employing three different modes of operation (constant power (CP), constant voltage (CV) and constant temperature (CT)), it was found that the sensor sensitivity maximizes in CT mode. Heater power and its resistance vary with Re a where a changes significantly for Re > 2000. The thermopile signal, which corresponds to the streamwise temperature gradient across the heater, in contrast to the other two signals, is more sensitive in detecting flow disturbances. Its fluctuations increase with a high rate close to Re = 1800, a value which is smaller than the corresponding increase of the other two signals. The probability density function (pdf) of its fluctuations is negatively skewed consistently for the range 1500 Re Re > 11,000 it turns to a symmetric one. The pdf of the other two signals do not show any systematic trends with Re . The most striking difference of the thermopile signal behaviour compared to the other two is its multivalued relationship with Re in the range 2000 Re

This work presents a new method for the fabrication of buried microchannels, covered with porous silicon (PS). The specific method is a two-step electrochemical process, which combines PS formation and electropolishing. In a first step a PS layer with a specific depth is created at a predefined area and in the following step a cavity underneath is formed, by electropolishing of silicon. The shape of the microchannel is semi-cylindrical due to isotropic formation. The method allows accurate control of the dimensions of both PS and the cavity. The formation conditions of the PS layer and the cavity were optimized so as to obtain smooth microchannel walls. In order to obtain stable structures the area underneath the PS masking layer was transformed into n-type by implantation, taking advantage of the selectivity of PS formation between n- and p-type silicon. With this technique, a monocrystalline support for the PS layer is formed on top of the cavity. Various microchannel diameters with different thickness of capping PS layer were obtained. The process is CMOS compatible and it uses only one lithographic step and leaves the surface of the wafer unaffected for further processing. A microfluidic thermal flow sensor was fabricated using this technology, the experimental evaluation of which is in progress.

Electrochemical Impedance Spectroscopy (EIS) has become a technique that is frequently used for biological assays. Impedance is defined as a complex – valued generalization of resistance and varies depending on its use per application field. In health sciences, bioimpedance is widely used as non-invasive and low cost alternative in many medical areas that provides valuable information about health status. This work focuses on assessing the effects of a bioactive substance applied to immobilized cells. Dopamine was used as a stimulant in order to implement impedance analysis with a specific type of cells. Dopamine constitutes one of the most important catecholamine neurotransmitters in both the mammalian central and peripheral nervous systems. The main purpose is to extract calibration curves at different frequencies with known dopamine concentrations in order to describe the behavior of cells applied to dopamine using an impedance measurement device. For comparison purposes, non-immobilized cells were tested for the same dopamine concentrations.

The present study demonstrates an inkjet – printed interdigitated electrode array on paper substrate and its evaluation as humidity sensor. Inkjet droplet formation analysis has been performed in order to achieve repeatable results regarding generated droplets, based on the driving pulses applied on the inkjet piezoelectric element. Droplet formation has been monitored using stroboscopic effect. Three different paper substrates, namely high glossy inkjet photo paper, glossy inkjet photo and matte inkjet photo paper have been evaluated to investigate compatibility with the ink. Relative humidity measurements have been carried out in a controlled environment. Material degradation, long term response and memory effect are some of the aspects which were studied within the frame of the present work. The proposed sensor provides the opportunity for novel biomedical applications given the flexible substrate nature and the low – cost, single – step fabrication approach.

Growth without growth hormone (GH) has occasionally been described in patients with organic pituitary pathology, and even more rarely in patients with idiopathic pituitary hormone deficiency. The mechanism of growth without GH remains a mystery. We describe a 17-year old male who grew 38.5 cm in height over a 7-year period, despite the fact that he had established panhypopituitarism. The hypopituitarism was initially attributed to a presumptive hypothalamic hamartoma which was not, however, confirmed on subsequent and prolonged follow-up. Regular endocrine evaluation confirmed persistent anterior and posterior pituitary hormonal deficiencies with severe concomitant hyperinsulinemia as shown by an exaggerated insulin response to a standard oral glucose tolerance test. In our patient, a postulated mechanism could be the severe hyperinsulinemia, acting either through the insulin and/or IGF receptors and thus potentiating the mitogenic effect. This case illustrates that final height attainment within or above target height may occur in patients with idiopathic pituitary hormonal deficiency despite persistent, severe GH insufficiency.

A new technology that allows the formation of thermal sensors on organic substrates by combining the standard PCB technology with the well established microelectronic techniques, is proposed. The obtained structures consist of low thermal conductivity material, therefore the heat dissipation to the substrate is minimized, which result to the enhancement of the device sensitivity and the improvement of the corresponding response time. The proposed technology exhibits a series of advantageous characteristics such as significant cost reduction, elimination of both wire-die bonding and die cutting, direct integration with electronics and potential expansion on flexible substrates. Furthermore, the final structure provides a planar surface, which allows for further lithographic steps to take place, but is also a major advantage for specific type of applications such as non-invasive flow measurements. In the context of the proposed technology, a thermal gas flow sensor was fabricated and tested in a specially designed experimental set-up. The sensor consisted of three thin Pt strips directly connected to the copper tracks of the organic substrate. The middle Pt resistor act as a heater while the other two serve as temperature sensing elements.

A new type of capacitive sensor based on flexible organic material is presented. The device fabrication is based on a lamination process of copper-clad laminated composites. The device was evaluated both as pressure and tactile sensor. The proposed fabrication technology presents several advantages concerning the direct integration with the corresponding electronics, the flexibility of the structure, the direct modification of the final geometry and the simplicity of the process.

The complete characterization of a polymer microfluidic flow sensor is presented in this paper. The device fabrication is based on a combination of PCB and MEMS techniques, enabling effective thermal isolation and direct communication to the macroworld. The sensor performance can be tuned based on the precise definition of structural and operational parameters, these being the microchannel crossection, the sensing element positioning, and the sensor operating principle. By combining the aforementioned parameters, an extended measurement range and high sensitivity in specified flow rate regions can be achieved.

This work concerns the development of a novel actuator based on water electrolysis for use in microfluidic systems. The electrolysis is performed inside a confined micro-reservoir integrated on a PCB substrate which is connected to a microchannel. During the electrolysis process, the generated gases within the enclosed structure lead to a significant pressure increase which can be employed in order to move a liquid inside the microchannel. In order to demonstrate the device's principle of operation, water is driven through a meander micro-structure which is connected at the output of the micro-tank. Furthermore, the effectiveness of employing electrolysis as an actuating principle has been investigated by monitoring the obtained pressure increase for a device with a larger reservoir; preliminary results are clearly promising.