Alexander Sorger

Investigations of thermotropic phase behavior of newly developed synthetic PEGylated lipids using Raman spectro‐microscopy

In this article, a temperature-controlled Raman spectro-microscopic technique has been utilized to detect and analyze the phase behaviors of two newly developed synthetic PEGylated lipids trademarked as QuSomes, which spontaneously form liposomes upon hydration in contrast to conventional lipids. The amphiphiles considered in this study differ in their hydrophobic hydrocarbon chain length and contain different units of polyethylene glycol (PEG) hydrophilic headgroups. Raman spectra of these new artificial lipids have been recorded in the spectral range of 500-3100 cm(-1) by using a Raman microscope system in conjunction with a temperature-controlled sample holder. The gel to liquid phase transitions of the sample lipids composed of pure 1,2-dimyristoyl-rac-glycerol-3-dodecaethylene glycol (GDM-12) and 1,2-distearoyl-rac-glycerol-3-triicosaethylene glycol (GDS-23) have been revealed by plotting peak intensity ratios in the C-H stretching region as a function of temperature. From this study, we have found that the main phase transitions occur at a temperature of approximately 5.2 and 21.2 degrees C for pure GDM-12 and GDS-23, respectively. Furthermore, the lipid GDS-23 also shows a postphase transition temperature at 33.6 degrees C. To verify our results, differential scanning calorimetry (DSC) experiments have been conducted and the results are found to be in an excellent agreement with Raman scattering data. This important information may find application in various studies including the development of lipid-based novel substances and drug delivery systems.

MEMS acoustic emission sensor with mechanical noise rejection

The presented paper describes the use of a new approach to develop a high frequency acceleration sensor with good low frequency noise rejection and in contrast to conventional resonant sensors a short settling time, as it is needed for acoustic emission testing.

CFD analysis of viscous losses in complex microsystems

This work investigates the possibility to apply general purpose CFD software in order to simulate viscous damping forces in microsystems with arbitrary complex geometries. The paper summarizes various aspects that have to be considered modeling flows and viscous interaction on micrometer scales. Based on the software CFD-ACE+, a general simulation procedure is developed and compared to analytical damping models as well as to measured data. Both comparisons show excellent agreements and finally confirm the presented approach.

A micro-SPM head array with exchangeable cantilevers

In this paper a MEMS based micro-SPM head array is proposed to enhance the performance of the currently available nano-measuring machines and effectively reduce the measurement time for large specimen. It consists of 1 × N ( N = 7 in our case) micro-SPM heads/units, realized in one chip by MEMS technique. And it can be easily extended to a micro- SPM head matrix. The main part of the micro-SPM head is the MEMS-positioning stage, which is realized on the basis of an electrostatic lateral comb-drive actuator. In order to take the advantage of the high lateral resolution of conventional cantilevers, a flexible cantilever gripper was designed to be integrated into the MEMS-positioning stage within the SPM head. Conventional cantilevers can be mechanically mounted onto the MEMS-positioning stage or dismantled from the MEMS-positioning stage after the tip is worn out. In this way, the well-designed and calibrated MEMS-positioning stage can be repeatedly and efficiently utilized. The structure design and simulation of mechanical and electrical performances of the mico-SPM head will be detailed in this paper. First experimental results proved the feasibility of the cantilever gripper design.

Large dynamic range time domain measurement of Q-factor in MEMS

The experimental identification of the quality factor in MEMS is a challenging task regarding signal processing and interpretation. Using logarithmic amplification some benefits regarding the signal processing and the reliability of the results can be achieved. This paper reports on two logarithmic amplification methods which allow an easy to use resource efficient measurement of the quality factor in MEMS. The logarithmic behavior enables the measurement of movement amplitude dependent quality factor in one measurement window. A rectifying amplifier and a full logarithmic amplifier are described and measurement examples are shown.

Temperature-controlled Raman microscopy to study the phase behavior of synthetic PEGylated lipids and nanovesicles

The study of phase transitions in lipids is important to understand various phenomena such as conformational order, trans-membrane diffusion, vesicle formation and fusion as well as drug-and protein-membrane interactions. Several techniques, including Raman spectroscopy, have previously been employed to investigate the phase behaviour of lipids. In this work, temperature-controlled Raman microscopy has been used to detect and analyze the phase transitions in two newly developed synthetic PEGylated lipids trademarked as QuSomesTM and its nanovesicles in phosphate buffered saline (PBS) suspension. The amphiphiles considered in this study differ in their hydrophobic chain length and contain different units of polyethylene glycol (PEG) hydrophilic head groups. Raman spectra of these new artificial lipids and its nanovesicles have been recorded in the spectral range of 500-3100 cm-1 by using a temperature-controlled sample holder attached to a Raman microscope. The gel to liquid-crystalline phase transitions of the sample lipids, composed of pure 1,2-dimyristoyl-rac-glycerol-3-dodecaethylene glycol (GDM-12) and 1,2-distearoyl-rac-glycerol-3-triicosaethylene glycol (GDS-23), have been detected by examining the changes in Raman spectra of the lipids caused by temperature variation. In the liquid phase both of the studied lipids spontaneously form liposomes (nanovesicles) upon hydration. In this study, we have demonstrated the efficacy of the temperature-controlled Raman microscope system to reveal the main phase transition temperature (Tm) profiles of our sample lipids and its nanovesicles in PBS suspension. The phase changes are detected by plotting peak intensity ratios in the C-H stretching region (~I2935/I2883) versus temperature. These ratios correlate with lateral or inter-chain interactions as well as intra-molecular interactions. In particular, we have found that phase transitions occur at a temperature of approximately 5.2°C and 21.2°C for pure GDM-12 and GDS-23, respectively. However, the phase transition temperature becomes significantly higher for lipid nanovesicles formed in aqueous suspensions. Such information about these PEG coated lipids might find applications in various studies including the development of lipid based novel substances and drug delivery systems.

Efficient reduced order modeling of fluid solid interactions for structurally complex perforated MEMS

This paper presents a resource- and time-efficient reduced order modeling (ROM) approach, which allows selective component-wise generation of system-level models for MEMS with high structural complexity. The fluid simulation is realized for perforated regions by means of an automatically generated, physics based lumped-flow-resistance network model. The procedure and performance, in comparison to a conventional FEM approach, is demonstrated and verified on an accelerometer-type MEMS device, for which the simulation results are compared with analytical damping models and experimentally obtained data.