Thermodiffusion of latex beads studied with a microfluidic cell

Investigation of the thermodiffusion requires relatively high temperature gradients. The temperature difference at the same time should be small enough because of the temperature dependence of the effect. This can be achieved by reducing the dimensions of the system. Therefore we developed a microfluidic cell which allows us to observe thermophoresis of colloids in the solution. Unlike many existing optical methods our cell is suitable to study big colloids (up to several micrometers) and complex mixtures. The cell can be also applied for investigation of thermophoretic phenomena in biological systems such as living cell and lipid membranes.Our cell consist of three channels (fig 1A): two relatively big ones for providing high flow rate of hot and cold liquid and a small channel in between them which contains the sample to study. The cell is produced either of PDMS by molding on lithographically made Si/SU-8 master or by micromilling the Plexiglas block with a CNC machine. The central channel is made very flat to prevent convection.To characterize the temperature distribution in our cell we used FLIM [1] with Rhodamine B as a temperature sensitive dye. The temperature distribution in the central channel is shown in fig 1B. The temperature difference across the central channel appeared to be around 2°C (the temperature gradient equals 2•104 K/m) although the temperature difference in the cooling and heating channels was much higher (22°C and 47°C respectively) which indicates large temperature drop in the walls.The cell was applied to investigate thermodiffusion of latex microbeads (sulfate modified, 0.5um) in water. The resulting exponential distribution in equilibrium (fig 1C) could be analyzed according to Zhao et al [2]. In order to validate our new method we perform additional measurements with the Thermal Diffusion Forced Rayleigh Scattering setup. Results will be discussed

Accumulation of formamide in hydrothermal pores to form prebiotic nucleobases

Formamide is one of the important compounds from which prebiotic molecules can be synthesized, provided that its concentration is sufficiently high. For nucleotides and short DNA strands, it has been shown that a high degree of accumulation in hydrothermal pores occurs, so that temperature gradients might play a role in the origin of life [Baaske P, et al. (2007) Proc Natl Acad Sci USA 104(22):9346−9351]. We show that the same combination of thermophoresis and convection in hydrothermal pores leads to accumulation of formamide up to concentrations where nucleobases are formed. The thermophoretic properties of aqueous formamide solutions are studied by means of Infrared Thermal Diffusion Forced Rayleigh Scattering. These data are used in numerical finite element calculations in hydrothermal pores for various initial concentrations, ambient temperatures, and pore sizes. The high degree of formamide accumulation is due to an unusual temperature and concentration dependence of the thermophoretic behavior of formamide. The accumulation fold in part of the pores increases strongly with increasing aspect ratio of the pores, and saturates to highly concentrated aqueous formamide solutions of ∼85 wt% at large aspect ratios. Time-dependent studies show that these high concentrations are reached after 45–90 d, starting with an initial formamide weight fraction of 10−3 wt % that is typical for concentrations in shallow lakes on early Earth

Thermophoretic Properties of Aqueous Formamide Solutions and Accumulation in Hydrothermal Pores

Formamide is one of the important compounds from which prebiotic molecules can be synthesized, provided that its concentration is sufficiently high. For nucleotides and short DNA strands it has been shown that a high degree of accumulation in hydrothermal pores occurs, so that temperature gradients might play a role in the 'origin-of-life' [1]. We show that the same combination of thermophoresis and convection in hydrothermal pores leads to accumulation of formamide up to concentrations where nucleobases are formed. The thermophoretic properties of aqueous formamide solutions are studied by means of Infra-Red Thermal Diffusion Forced Rayleigh Scattering. These data are used in numerical finite-element calculations in hydrothermal pores for various initial concentrations, ambient temperatures, and pore sizes. The high degree of formamide accumulation is due to an unusual temperature and concentration dependence of the thermophoretic behaviour of formamide. The accumulation-fold in part of the pores increases strongly with increasing aspect ratio of the pores, and saturates to highly concentrated aqueous formamide solutions of approximately 85 wt% at large aspect ratios. Time dependent studies show that these high concentrations are reached after 45-90 days, starting with an initial formamide weight fraction of $10-3 wt% that is typical for concentrations in shallow lakes on early earth [2].References1. P. Baaske, F. M. Weinert, S. Duhr, K. H. Lemke, M. J. Russell and D. Braun, et al., P. Natl. Acad. Sci. USA, Vol. 104, No. 22 (2007) pp. 9346-9351.2. D. Niether, D. Afanasenkau, J. K. G. Dhont and S. Wiegand, PNAS, accepted, (2016)

A multimodal neuroprosthetic interface to record, modulate and classify electrophysiological biomarkers relevant to neuropsychiatric disorders

Most mental disorders, such as addictive diseases or schizophrenia, are characterized by impaired cognitive function and behavior control originating from disturbances within prefrontal neural networks. Their often chronic reoccurring nature and the lack of efficient therapies necessitate the development of new treatment strategies. Brain-computer interfaces, equipped with multiple sensing and stimulation abilities, offer a new toolbox whose suitability for diagnosis and therapy of mental disorders has not yet been explored. This study, therefore, aimed to develop a biocompatible and multimodal neuroprosthesis to measure and modulate prefrontal neurophysiological features of neuropsychiatric symptoms. We used a 3D-printing technology to rapidly prototype customized bioelectronic implants through robot-controlled deposition of soft silicones and a conductive platinum ink. We implanted the device epidurally above the medial prefrontal cortex of rats and obtained auditory event-related brain potentials in treatment-naïve animals, after alcohol administration and following neuromodulation through implant-driven electrical brain stimulation and cortical delivery of the anti-relapse medication naltrexone. Towards smart neuroprosthetic interfaces, we furthermore developed machine learning algorithms to autonomously classify treatment effects within the neural recordings. The neuroprosthesis successfully captured neural activity patterns reflecting intact stimulus processing and alcohol-induced neural depression. Moreover, implant-driven electrical and pharmacological stimulation enabled successful enhancement of neural activity. A machine learning approach based on stepwise linear discriminant analysis was able to deal with sparsity in the data and distinguished treatments with high accuracy. Our work demonstrates the feasibility of multimodal bioelectronic systems to monitor, modulate and identify healthy and affected brain states with potential use in a personalized and optimized therapy of neuropsychiatric disorders

Supported lipid bilayer as a biomimetic platform for neuronal cell culture

The lipid bilayer is the basis of the cell membrane. It serves as a barrier that separates the cell from the environment and provides platform for membrane proteins helping them to fulfill their functions. To advance studies of the cell membrane, membrane proteins and cell-cell interactions, it would be favourable to create an artificial platform which can mimic the cell membrane. It can help to exclude various factors influencing the experiments carried out on real cells and provide a possibility to focus on the phenomena interesting for researchers. It would allow many advanced methods of investigation which can not be applied for living cells. Such a platform can also help to use some advanced properties of the cell membrane in biosensors and medical applications. Several systems that can mimic the cell membrane have been developed such as liposomes (lipid vesicles) or pore suspended lipid membranes (such as black lipid membranes – a classical membrane system). Although these systems have been used extensively for many years, they possess disadvantages which limit their applications. Such a system as supported lipid bilayer (SLB) can mimic the cell membrane and provides high stability and accessibility for measurement techniques. The SLB consist of a lipid bilayer placed on a solid surface (such as glass, Si, mica) covered with aqueous solution and separated from the substrate by very thin (around 1 nm) hydration layer. It gives a possibility for incorporation of membrane proteins providing natural environment for them. It can be immobilized on the surface of a sensor – optical, electrical or mechanical. There are also ways of patterning of the SLB which enhance possibilities of integration with recording devices and is especially useful in experiments with guiding cells in culture or studying cell adhesion. The SLB can provide a wide spectra of possibilities for studying cells in vitro. They include studying of cell adhesion, cell signaling, redistribution of molecules in the cell membrane. However, by now the SLB has been used for experiments with cells not very intensively. One reason for it is that lipid bilayers made of only natural lipids such as phosphatidylcholine are cell repellent: cells can not adhere to it. Thus, to maintain cells the SLB should be functionalized in a special way. There are many possibilities for it but they are mostly complicated and not well studied. The aim of the present work is to study possibilities of using SLB as a platform for neuronal cell culture. To reach this aim several tasks were considered:1. Development of methods to increase cell adhesion to the SLB2. Utilizing proteins incorporated into the SLB for investigation of cell signaling processes.3. Patterning of the SLBFor increasing adhesion of cells a simple approach was developed: bilayers contained positively charged lipids (DOTAP) were used. Such bilayers, which are very easy to prepare, were shown in this work to promote adhesion of neuronal cells most likely due to electrostatic interaction. A possibility for using these bilayers for long term experiments with neuronal cell was demonstrated. Fluidic properties of the prepared SLB were monitored using fluorescence recovery after photobleaching (FRAP). A MatLab based software was developed to analyse FRAP images and calculate diffusion coefficient. The diffusion coefficient appeared to decrease with the increase of the concentration of positively charged lipid, but even the SLB consisted of only positively charged molecules was found to be fluid with the diffusion coefficient three time lower than for the bilayer made of phosphatidylcholine. Possibilities of using the SLB for studying cell signalling processes were shown in this work. Ephrin A5, a synaptic adhesion protein, which performs also many signalling functions, was incorporated into the SLB. Patch clamp experiments showed that the probability for a neuronal cells growing on such bilayers to develop functional synapses is higher than for control cultures maintained on the usual cell-culture substrates such as poly-L-lysine. For creating patterned SLB the idea of using giant unilamellar vesicles (GUV) was utilized. This method allowed to form patches of the SLBs of different type on a surface without risk of exposing the surface to air (which would destroy SLB) that exist in usually used methods such as droplet deposition. In conclusion, this work demonstrates a possibility of using SLB as a platform for neuronal cell culture which can allow long term experiments directed into studying cell adhesion, cell signaling, and cell development processes

Supported lipid bilayers as a biomimetic platform for neuronal cell culture

$\textit{The lipid bipayer}$ is the basis of the cell membrane. It serves as a barrier that separates the cell from the environment and provides platform for membrane proteins helping them to fulfill their functions. To advance studies of the cell membrane, membrane proteins and cell-cell interactions, it would be favourable to create an artificial platform which can mimic the cell membrane. It can help to exclude various factrors influencing the experiments carried out on real cells and provide a possibility to focus on the phenomeana interesting for researchers. It would allow many advanced methods of investigation which can not be applied for living cells. Such a platform can also help to use some advanced properties of the cell membrane in biosensors and medical applications. Several systems that can mimic the cell membrane have been developed such as liposomes (lipid vesicles) or pore suspended lipid membranes (such as black lipid membranes - a classical membrane system). Although these systems have been used extensively for many years, they possess disadvantages which limit their applications. [...

Supported lipid bilayer as a biomimetic platform for neuronal cell culture

The lipid bilayer is the basis of the cell membrane. It serves as a barrier that separates the cell from the environment and provides platform for membrane proteins helping them to fulfill their functions. To advance studies of the cell membrane, membrane proteins and cell-cell interactions, it would be favourable to create an artificial platform which can mimic the cell membrane. It can help to exclude various factors influencing the experiments carried out on real cells and provide a possibility to focus on the phenomena interesting for researchers. It would allow many advanced methods of investigation which can not be applied for living cells. Such a platform can also help to use some advanced properties of the cell membrane in biosensors and medical applications. Several systems that can mimic the cell membrane have been developed such as liposomes (lipid vesicles) or pore suspended lipid membranes (such as black lipid membranes – a classical membrane system). Although these systems have been used extensively for many years, they possess disadvantages which limit their applications. Such a system as supported lipid bilayer (SLB) can mimic the cell membrane and provides high stability and accessibility for measurement techniques. The SLB consist of a lipid bilayer placed on a solid surface (such as glass, Si, mica) covered with aqueous solution and separated from the substrate by very thin (around 1 nm) hydration layer. It gives a possibility for incorporation of membrane proteins providing natural environment for them. It can be immobilized on the surface of a sensor – optical, electrical or mechanical. There are also ways of patterning of the SLB which enhance possibilities of integration with recording devices and is especially useful in experiments with guiding cells in culture or studying cell adhesion. The SLB can provide a wide spectra of possibilities for studying cells in vitro. They include studying of cell adhesion, cell signaling, redistribution of molecules in the cell membrane. However, by now the SLB has been used for experiments with cells not very intensively. One reason for it is that lipid bilayers made of only natural lipids such as phosphatidylcholine are cell repellent: cells can not adhere to it. Thus, to maintain cells the SLB should be functionalized in a special way. There are many possibilities for it but they are mostly complicated and not well studied. The aim of the present work is to study possibilities of using SLB as a platform for neuronal cell culture. To reach this aim several tasks were considered:1. Development of methods to increase cell adhesion to the SLB2. Utilizing proteins incorporated into the SLB for investigation of cell signaling processes.3. Patterning of the SLBFor increasing adhesion of cells a simple approach was developed: bilayers contained positively charged lipids (DOTAP) were used. Such bilayers, which are very easy to prepare, were shown in this work to promote adhesion of neuronal cells most likely due to electrostatic interaction. A possibility for using these bilayers for long term experiments with neuronal cell was demonstrated. Fluidic properties of the prepared SLB were monitored using fluorescence recovery after photobleaching (FRAP). A MatLab based software was developed to analyse FRAP images and calculate diffusion coefficient. The diffusion coefficient appeared to decrease with the increase of the concentration of positively charged lipid, but even the SLB consisted of only positively charged molecules was found to be fluid with the diffusion coefficient three time lower than for the bilayer made of phosphatidylcholine. Possibilities of using the SLB for studying cell signalling processes were shown in this work. Ephrin A5, a synaptic adhesion protein, which performs also many signalling functions, was incorporated into the SLB. Patch clamp experiments showed that the probability for a neuronal cells growing on such bilayers to develop functional synapses is higher than for control cultures maintained on the usual cell-culture substrates such as poly-L-lysine. For creating patterned SLB the idea of using giant unilamellar vesicles (GUV) was utilized. This method allowed to form patches of the SLBs of different type on a surface without risk of exposing the surface to air (which would destroy SLB) that exist in usually used methods such as droplet deposition. In conclusion, this work demonstrates a possibility of using SLB as a platform for neuronal cell culture which can allow long term experiments directed into studying cell adhesion, cell signaling, and cell development processes

Molar mass and temperature dependence of the thermodifusion of polyethylene oxide in water/ethanol mixtures

In this work we study the molar mass dependence of the thermodiffusion of polyethylene oxide atdifferent temperatures in water, ethanol and in a water/ethanol mixture (C_water = 0.7) in a molar massrange up to Mw=180000 g/mol. Due to the low solubility of polyethylene oxide oligomers in ethanol themeasurements are limited up to Mw=2200 g/mol. The specific water/ethanol concentration 0.7 is chosen,because at this weight fraction the thermal diffusion coefficient, D_T, of water/ethanol vanishes so thatthe system can be treated as a pseudo binary mixtures. The addition of ethanol will degrade the solventquality, so that we expect a change in the interaction energies, which can be calculated using a modelderived by Würger [1]. We also found that with adding ethanol to water, the thermodiffusion behavior ofPEO changes from thermophobic to thermophilic