Z. Fekete

Effects of chemical modification on stereoselectivity of Pseudomonas cepacia lipase

Abstract Two chemically modified forms of lipase from Pseudomonas cepacia were prepared by acylation of the free amino groups of the protein with acetic and succinic anhydrides. The catalytic activity, the enantioselectivity and the thermal stability of the modified enzymes were compared with that of the native form. Succinylation determined an increase of stability without affecting the catalytical properties of the enzyme in the hydrolysis of chiral esters. Acetylation resulted in an enhanced catalytic activity coupled to a decreased stereoselectivity and thermal stability.

Neurobiochemical changes in the vicinity of a nanostructured neural implant

Neural interface technologies including recording and stimulation electrodes are currently in the early phase of clinical trials aiming to help patients with spinal cord injuries, degenerative disorders, strokes interrupting descending motor pathways, or limb amputations. Their lifetime is of key importance; however, it is limited by the foreign body response of the tissue causing the loss of neurons and a reactive astrogliosis around the implant surface. Improving the biocompatibility of implant surfaces, especially promoting neuronal attachment and regeneration is therefore essential. In our work, bioactive properties of implanted black polySi nanostructured surfaces (520–800 nm long nanopillars with a diameter of 150–200 nm) were investigated and compared to microstructured Si surfaces in eight-week-long in vivo experiments. Glial encapsulation and local neuronal cell loss were characterised using GFAP and NeuN immunostaining respectively, followed by systematic image analysis. Regarding the severity of gliosis, no significant difference was observed in the vicinity of the different implant surfaces, however, the number of surviving neurons close to the nanostructured surface was higher than that of the microstructured ones. Our results imply that the functionality of implanted microelectrodes covered by Si nanopillars may lead to improved long-term recordings.

In Vivo Measurements With Robust Silicon-Based Multielectrode Arrays With Extreme Shaft Lengths

In this paper, manufacturing and in vivo testing of extreme-long Si-based neural microelectrode arrays are presented. Probes with different shaft lengths (15-70 mm) are formed by deep reactive ion etching and have been equipped with platinum electrodes of various configurations. In vivo measurements on rats indicate good mechanical stability, robust implantation, and targeting capability. High-quality signals have been recorded from different locations of the cerebrum of the rodents. The accompanied tissue damage is characterized by histology.

Tilted pillar array fabrication by the combination of proton beam writing and soft lithography for microfluidic cell capture: Part 1 Design and feasibility

Design, fabrication, integration, and feasibility test results of a novel microfluidic cell capture device is presented, exploiting the advantages of proton beam writing to make lithographic irradiations under multiple target tilting angles and UV lithography to easily reproduce large area structures. A cell capture device is demonstrated with a unique doubly tilted micropillar array design for cell manipulation in microfluidic applications. Tilting the pillars increased their functional surface, therefore, enhanced fluidic interaction when special bioaffinity coating was used, and improved fluid dynamic behavior regarding cell culture injection. The proposed microstructures were capable to support adequate distribution of body fluids, such as blood, spinal fluid, etc., between the inlet and outlet of the microfluidic sample reservoirs, offering advanced cell capture capability on the functionalized surfaces. The hydrodynamic characteristics of the microfluidic systems were tested with yeast cells (similar size as red blood cells) for efficient capture.

Surface Modification of PDMS Based Microfluidic Systems by Tensides

The material aspects of a polymer based microfluidic structure were characterised considering the compatibility of the system with bioanalytical applications. The polydimethylsiloxane (PDMS) based channel system is to be integrated in a full polymer photonic biosensor device developed within the European Union project P3SENS (FP7-ICT4-248304). This work is intended to define a modified material composition, which is appropriate to improve both the wettability and the non-specific protein binding characteristics of the PDMS significantly. Triton X-100 (Sigma-Aldrich) surfactant was added to the raw PDMS before polymerisation. The influence of the tenside was studied considering the polymerisation reaction, the surface characteristics and the functional applicability. To test the hydrodynamic behaviour and non-specific protein adsorption on the surfaces, phosphate buffered saline (PBS) solution and fluorescent labelled human serum albumin (HSA) was applied in a microfluidic capillary system.

Simultaneous in vivo recording of local brain temperature and electrophysiological signals with a novel neural probe

OBJECTIVE Temperature is an important factor for neural function both in normal and pathological states, nevertheless, simultaneous monitoring of local brain temperature and neuronal activity has not yet been undertaken. APPROACH In our work, we propose an implantable, calibrated multimodal biosensor that facilitates the complex investigation of thermal changes in both cortical and deep brain regions, which records multiunit activity of neuronal populations in mice. The fabricated neural probe contains four electrical recording sites and a platinum temperature sensor filament integrated on the same probe shaft within a distance of 30 µm from the closest recording site. The feasibility of the simultaneous functionality is presented in in vivo studies. The probe was tested in the thalamus of anesthetized mice while manipulating the core temperature of the animals. MAIN RESULTS We obtained multiunit and local field recordings along with measurement of local brain temperature with accuracy of 0.14 °C. Brain temperature generally followed core body temperature, but also showed superimposed fluctuations corresponding to epochs of increased local neural activity. With the application of higher currents, we increased the local temperature by several degrees without observable tissue damage between 34-39 °C. SIGNIFICANCE The proposed multifunctional tool is envisioned to broaden our knowledge on the role of the thermal modulation of neuronal activity in both cortical and deeper brain regions.

On the Fabrication Parameters of Buried Microchannels Integrated in In-Plane Silicon Microprobes

This paper aims the characterization of buried microchannels in silicon realized by deep reactive ion etching. The effects of dry etching parameters on the integrability into hollow microprobes are thoroughly investigated from both technological and functional aspects. Results are supposed to give physiology related probe designers a deeper insight into microfabrication-related issues.

Characterization of the end-of-range geometric effects in complex 3D silicon micro-components formed by proton beam writing

As a new alternative micromachining method to deep reactive ion etching (DRIE), the combination of proton beam writing (PBW) and porous silicon (PS) etching has proved to be a feasible technique to form crystalline silicon microstructures characterized by high aspect ratio and vertical sidewalls. However, the proposed use of the combined technology has been successfully applied to realize microfluidic MEMS components, whilst the undesired effects of ion scattering in the end-of-range (EOR) region are still under investigation. The widening geometry in the vicinity of the Bragg peak of the ion path limits the perfect functionality of the designed microstructures. In this work the effects of EOR volume on the realization of micro-components by PBW and subsequent PS etching are analysed by both experimental and simulation (MatLab, Comsol) methods. A MEMS process sequence, including the elimination of the widening at the bottom of the microstructures, is explained in detail. The elaborated technology provides the complete removal of the EOR volume without any necessary changes to the geometric design. As a result, the beneficial properties of the combined technique can be exploited more effectively and less compromise is needed during the development of complex 3D silicon microstructures.

Design, realisation and validation of microfluidic stochastic mixers integrable in bioanalytical systems using CFD modeling

In this work we present the design aspects of special microfluidic structures applicable to dilute and transport analyte solutions (such as whole blood) to the sensing area of biosensors. Our goal is to design and realise a reliable microfluidic system which is applicable for effective sample transport and can accomplish simple sample preparation functions such as mixing to ensure homogeneous concentration distribution of the species along the fluidic channel. The behaviour of different chaotic mixers were analysed by numerical modeling and experimentally to determine their efficiency. At first we used the concentration distribution method, however because of numerical diffusion this required higher mesh resolutions. Using the particle tracing method is more efficient according to the experimental results and requires lower computational effort. The microstructures were realised by micro-fabrication in polydimethylsiloxane (PDMS) and integrated into a real microfluidic transport system. The functional performance was verified by biological analyte.

In vitro and in vivo stability of black-platinum coatings on flexible, polymer microECoG arrays

OBJECTIVE Intracranial EEG (iEEG) or micro-electrocorticography (µECoG) microelectrodes offer high spatial resolution in recordings of neuronal activity from the exposed brain surface. Reliability of dielectric substrates and conductive materials of these devices are under intensive research in terms of functional stability in biological environments. APPROACH The aim of our study is to investigate the stability of electroplated platinum recording sites on 16-channel, 8 micron thick, polyimide based, flexible µECoG arrays implanted underneath the skull of rats. Scanning electron microscopy and electrochemical impedance spectroscopy was used to reveal changes in either surface morphology or interfacial characteristics. The effect of improved surface area (roughness factor  =  23  ±  0.12) on in vivo recording capability was characterized in both acute and chronic experiments. MAIN RESULTS Besides the expected reduction in thermal noise and enhancement in signal-to-noise ratio (up to 39.8), a slight increase in the electrical impedance of individual sites was observed, as a result of changes in the measured interfacial capacitance. In this paper, we also present technology processes and protocols in detail to use such implants without crack formation of the porous platinum surfaces. SIGNIFICANCE Our findings imply that black-platinum coating deposited on the recording sites of flexible microelectrodes (20 microns in diameter) provides a stable interface between tissue and device.