Publications

Based on our continuous R&D efforts and the participation in outstanding publicly funded projects, our customers, project partners and ourselves have been able to generate a considerable list of publications.

BioFluidiX' dispensing technologies and workstations enable a broad range of new applications, ranging from protein cristallization to fabrication of proton exchange membranes for polymer electrolyte fuel cells.

But not only our standard products are enabling academia to research new scientific approaches. BioFluidix is also able to provide solutions tailored to the scientific needs of research institutes, like a SAXS-player, or a centrifugal microfluidic screening platform for protein structure analysis based on small angle x-ray scattering.

2017 | Cytocompatibility testing of hydrogels toward bioprinting of mesenchymal stem cells | L. Benning et al | Society For Biomaterials | EN

Cytocompatibility testing of hydrogels toward bioprinting of mesenchymal stem cells

L. Benning et al.
First published: 22 August 2017
Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/jbm.a.36179

Abstract:
Mesenchymal stem cells (MSCs) represent a very attractive cell source for tissue engineering applications aiming at the generation of artificial bone substitutes. The use of three-dimensional bioprinting technologies has the potential to improve the classical tissue engineering approach because bioprinting will allow the generation of hydrogel scaffolds with high spatial control of MSC allocation within the bioprinted construct. In this study, we have performed direct comparisons between commercially available hydrogels in the context of their cytocompatibility toward MSCs and their physicochemical parameters with the aim to identify the most suitable hydrogel for drop-on-demand (DoD) printing of MSCs. In this context, we examined matrigel, fibrin, collagen, gelatin, and gelatin/alginate at various hydrogel concentrations. Matrigel, fibrin, collagen, and gelatin were able to support cell viability, but the latter showed a limited potential to promote MSC proliferation. We concentrated our study on fibrin and collagen hydrogels and investigated the effect of hydroxyapatite (HA) inclusion. The inclusion of HA enhanced proliferation and osteogenic differentiation of MSCs and prevented degradation of fibrin in vitro. According to viscosity and storage moduli measurements, HA-blends displayed physicochemical characteristics suitable for DoD printing. In bioprinting experiments, we confirmed that fibrin and collagen and their respective HA-blends represent excellent hydrogels for DoD-based printing as evidenced by high survival rates of printed MSCs. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3231–3241, 2017.

2017 | Open microfluidic gel electrophoresis: Rapid and low cost separation and analysis of DNA at the nanoliter scale | L. Gutzweiler, et al | Electrophoresis | EN

Open microfluidic gel electrophoresis: Rapid and low cost separation and analysis of DNA at the nanoliter scale

L. Gutzweiler, et al.
Electrophoresis
Volume 38, Issue 13-14 July 2017
Pages 1764–1770

Abstract:
Gel electrophoresis is one of the most applied and standardized tools for separation and analysis of macromolecules and their fragments in academic research and in industry. In this work we present a novel approach for conducting on-demand electrophoretic separations of DNA molecules in open microfluidic (OM) systems on planar polymer substrates. The approach combines advantages of slab gel, capillary- and chip-based methods offering low consumable costs (<0.1$) circumventing cost-intensive microfluidic chip fabrication, short process times (5 min per analysis) and high sensitivity (4 ng/μL dsDNA) combined with reasonable resolution (17 bases). The open microfluidic separation system comprises two opposing reservoirs of 2–4 μL in volume, a semi-contact written gel line acting as separation channel interconnecting the reservoirs and sample injected into the line via non-contact droplet dispensing and thus enabling the precise control of the injection plug and sample concentration. Evaporation is prevented by covering aqueous structures with PCR-grade mineral oil while maintaining surface temperature at 15°C. The liquid gel line exhibits a semi-circular cross section of adaptable width (∼200–600 μm) and height (∼30–80 μm) as well as a typical length of 15–55 mm. Layout of such liquid structures is adaptable on-demand not requiring time consuming and repetitive fabrication steps. The approach was successfully demonstrated by the separation of a standard label-free DNA ladder (100–1000 bp) at 100 V/cm via in-line staining and laser induced fluorescent end-point detection using an automated prototype.

2017 | Large scale production and controlled deposition of single HUVEC spheroids for bioprinting applications | L. Gutzweiler, et al | Biofabrication | EN

Large scale production and controlled deposition of single HUVEC spheroids for bioprinting applications

L. Gutzweiler, et al.
Biofabrication, Volume 9, Number 2, June 2017

Abstract:
We present (1) a fast and automated method for large scale production of HUVEC spheroids based on the hanging drop method and (2) a novel method for well-controlled lateral deposition of single spheroids by drop-on-demand printing. Large scale spheroid production is achieved via printing 1536 droplets of HUVEC cell suspension having a volume of 1 μl each within 3 min at a pitch of 2.3 mm within an array of 48 × 32 droplets onto a flat substrate. Printing efficiencies between 97.9% and 100% and plating efficiencies between 87.3% and 100% were achieved. Harvested spheroids (consisting of approx. 250 HUVECs each) appear uniform in size and shape. After incubation and harvesting, the spheroids are deposited individually in user-defined patterns onto hydrogels using an automated drop-on-demand dispenser setup. Controlled by an image detection algorithm focusing the dispenser nozzle, droplets containing exactly one spheroid are printed onto a substrate, while all other droplets are discarded. Using this approach an array of 6 × 3 HUVEC spheroids with intermediate distances of 500 μm embedded in fibrin was generated. Successful progress of spheroid sprouting and merging of neighboring sprouts was observed during the first 72 h of incubation indicating a good viability of the deposited spheroids.

2017 | A new and highly sensitive TLC method to measure hypericin using chemiluminescence | A. Lotz, et al | Journal of Liquid Chromatography & Related Technologies | EN

A new and highly sensitive TLC method to measure hypericin using chemiluminescence

A. Lotz, et al.
Journal of Liquid Chromatography & Related Technologies
Volume 40, 2017 - Issue 5-6: Thin-Layer Chromatography
Pages 287-291

Abstract:
Hypericin is a polyphenolic compound belonging to the group of polyphenols and is the active constituents of Hypericum perforatum (Saint John’s wort). We present a new high-performance thin-layer chromatography (HPTLC) method to measure a large number of hypericin extracts using chemiluminescence. On a 10 × 10 cm HPTLC plate (LiChrospher® Merck, 1.05586), more than 40 tracks can be simultaneously quantified using a piezoelectric application system (pipeJet) which can apply 56 nL of a methanolic hypericin extract contactless with high precision. For separation, a solvent mixture of ethyl acetate, water, formic acid, methyl tert-butyl ether, and cyclohexane (180 + 14 + 14 + 80 + 30, v/v) was used. The Rf-value of hypericin is 0.27. The method presented is specific for hypericin and offers a limit of quantification of 690 pg hypericin per band.

2017 | Simple fabrication of 12 μm thin nanocomposite fuel cell membranes by direct electrospinning and printing | M. Breitwieser, et al | Journal of Power Sources | EN

Simple fabrication of 12 μm thin nanocomposite fuel cell membranes by direct electrospinning and printing

M. Breitwieser, et al.
Journal of Power Sources
Volume 337, 1 January 2017
Pages 137-144

Abstract:
Direct membrane deposition (DMD) was recently introduced as a novel polymer electrolyte membrane fabrication method. Here, this approach is extended to fabricate 12 μm thin nanocomposite fuel cell membranes. Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofibers are directly electrospun onto gas diffusion electrodes. By inkjet-printing Nafion ionomer dispersion into the pore space of PVDF-HFP nanofiber mats, composite membranes of 12 μm thickness were fabricated. At 120 °C and 35% relative humidity, stoichiometric 1.5/2.5 H2/air flow and atmospheric pressure, the power density of the DMD fuel cell (0.19 W cm-2), was about 1.7 times higher than that of the reference fuel cell (0.11 W cm-2) with Nafion HP membrane and identical catalyst. A lower ionic resistance and, especially at 120 °C, a reduced charge transfer resistance is found compared to the Nafion HP membrane. A 100 h accelerated stress test revealed a voltage decay of below 0.8 mV h-1, which is in the range of literature values for significantly thicker reinforced membranes. Finally, this novel fabrication approach enables new degrees of freedom in the design of complex composite membranes. The presented combination of scalable deposition techniques has the potential to simplify and thus reduce cost of composite membrane fabrication at a larger scale.

2016 | Automated harvesting and processing of protein crystals through laser photoablation | U. Zander, et al | Acta Crystallographica Section D | EN

Simple fabrication of 12 μm thin nanocomposite fuel cell membranes by direct electrospinning and printing

U. Zander, et al.
Acta Crystallographica Section D
Structural Biology
ISSN: 2059-7983
Volume 72 Part 4 April 2016
Pages 454-466

Abstract:
Currently, macromolecular crystallography projects often require the use of highly automated facilities for crystallization and X-ray data collection. However, crystal harvesting and processing largely depend on manual operations. Here, a series of new methods are presented based on the use of a low X-ray-background film as a crystallization support and a photoablation laser that enable the automation of major operations required for the preparation of crystals for X-ray diffraction experiments. In this approach, the controlled removal of the mother liquor before crystal mounting simplifies the cryocooling process, in many cases eliminating the use of cryoprotectant agents, while crystal-soaking experiments are performed through diffusion, precluding the need for repeated sample-recovery and transfer operations. Moreover, the high-precision laser enables new mounting strategies that are not accessible through other methods. This approach bridges an important gap in automation and can contribute to expanding the capabilities of modern macromolecular crystallography facilities.

2016 | Semi-contact-writing of polymer molds for prototyping PDMS chips with low surface roughness, sharp edges and locally varying channel heights | L. Gutzweiler, et al | Journal of Micromechanics and Microengineering | EN

Semi-contact-writing of polymer molds for prototyping PDMS chips with low surface roughness, sharp edges and locally varying channel heights

L. Gutzweiler, et al.
Journal of Micromechanics and Microengineering
Volume 26, Number 4

Abstract:
Microfluidic systems fabricated in polydimethylsiloxane (PDMS) enable a broad variety of applications and are widespread in the field of Lab-on-a-Chip. Here we demonstrate semi-contact-writing, a novel method for fabrication of polymer based molds for casting microfluidic PDMS chips in a highly flexible, time and cost-efficient manner. The method is related to direct-writing of an aqueous polymer solution on a planar glass substrate and substitutes conventional, time- and cost-consuming UV-lithography. This technique facilitates on-demand prototyping in a low-cost manner and is therefore ideally suited for rapid chip layout iterations. No cleanroom facilities and less expertise are required. Fabrication time from scratch to ready-to-use PDMS-chip is less than 5 h. This polymer writing method enables structure widths down to 140 μm and controllable structure heights ranging from 5.5 μm for writing single layers up to 98 μm by stacking. As a unique property, freely selectable height variations across a substrate can be achieved by application of local stacking. Furthermore, the molds exhibit low surface roughness (R a   =  24 nm, R RMS  =  28 nm) and high fidelity edge sharpness. We validated the method by fabrication of molds to cast PDMS chips for droplet based flow-through PCR with single-cell sensitivity.

2016 | The smaller, the better? The size effect of alginate beads carrying plant growth-promoting bacteria for seed coating | Teresa Berninger, et al | Journal of Microencapsulation | EN

The smaller, the better? The size effect of alginate beads carrying plant growth-promoting bacteria for seed coating

Teresa Berninger, et al.
Journal of Microencapsulation
Micro and Nano Carriers
Volume 33, 2016 - Issue 2
Pages 127-136

Abstract:
A range of lab-scale methods for encapsulation of plant growth-promoting bacteria in alginate beads intended for seed coating was evaluated: contact-spotting, extrusion through syringe with/without vibration, ejection by robotic liquid handler, extrusion by centrifugal force and commercial devices (nanodispenser, aerodynamically assisted jetting, encapsulator). Two methods were selected based on throughput (encapsulator: 1.5–5 mL/min; syringe with subsequent pulverisation: 5 mL/min). Four bead sizes (55 ± 39 μm, 104 ± 23 μm, 188 ± 16 μm and 336 ± 20 μm after lyophilisation) were produced. Bacterial viability, release, bead morphology, seed surface coverage and attrition were investigated. Release from the smallest bead size was approximately 10 times higher than from the largest. Seed surface coverage was highest (69 ± 3%) when alginate beads produced with nozzle size 80 μm were applied. Pulverised macro-beads are an alternative option, if high throughput is top priority.

2015 | Improved Pt-utilization efficiency of low Pt-loading PEM fuel cell electrodes using direct membrane deposition | M. Breitwieser, et al | Electrochemistry Communications | EN

Improved Pt-utilization efficiency of low Pt-loading PEM fuel cell electrodes using direct membrane deposition

M. Breitwieser, et al.
Electrochemistry Communications
Volume 60, November 2015
Pages 168-171

Abstract:
Direct membrane deposition was used to produce record platinum catalyst utilization efficiency polymer electrolyte membrane fuel cells. The novel membrane fabrication technique was applied to gas diffusion electrodes with low Pt-loadings of 0.102 and 0.029 mg/cm2. Under oxygen atmosphere and 300 kPaabs total pressure, 88 kW/gPt cathodic catalyst utilization efficiency with a symmetrical Pt-loading of 0.029 mg/cm2 on the anode and cathode side was achieved. This is 2.3 times higher than the Pt-utilization efficiency of a reference fuel cell prepared using a commercial Nafion N-211 membrane and identical catalyst layers, emphasizing that the improvement is purely attributable to the novel membrane fabrication technique. This value represents the highest Pt-utilization efficiency reported in literature. The results strongly motivate the application of employing direct membrane deposition techniques to prepare low resistance polymer electrolyte thin films in order to compensate for kinetic losses introduced when using low catalyst loadings.

2015 | Direct deposition of proton exchange membranes enabling high performance hydrogen fuel cells | M. Klingele, et al | J. Mater. Chem. A | EN

Direct deposition of proton exchange membranes enabling high performance hydrogen fuel cells

M. Klingele, et al.
J. Mater. Chem. A ,2015, 3, 11239

Abstract:
We apply drop-on-demand inkjet printing to fabricate proton exchange membranes for polymer electrolyte fuel cells. This completely substitutes the commonly used membrane foil. A Nafion® dispersion is deposited directly onto the catalyst layers of anode and cathode gas diffusion electrodes, and the two electrodes are pressed together with the membrane layers facing each other. Fuel cells constructed utilizing this method reveal a thin overall membrane thickness of 8–25 μm and a good adhesion of membrane and catalyst layers. This results in a membrane ionic resistance of only 12.7 mΩ cm2 without compromising hydrogen crossover, which was determined to be less than 2 mA cm−2. We achieve a cell power density exceeding 4 W cm−2 with pure oxygen as cathode fuel, which, to our knowledge, is the highest reported power density with a Nafion® membrane hydrogen fuel cell. The membrane shows a stable performance over the entire range of reactant gas humidification from 0 to 100% relative humidity. Power densities exceeding 1.0 W cm−2 are achieved under dry operation with air as cathode fuel. A 576 hour combined mechanical and chemical accelerated stress test reveals no significant degradation in terms of hydrogen crossover, indicating a promising lifetime of the membrane.

2014 | Improving surface properties by laser-based drying, gelation, and densification of printed sol–gel coatings | Dominik Hawelka, et al | Journal of Coatings Technology and Research | EN

Improving surface properties by laser-based drying, gelation, and densification of printed sol–gel coatings

Dominik Hawelka, et al
Journal of Coatings Technology and Research
January 2014, Volume 11, Issue 1, pp 3–10

Abstract:
In this article, an innovative laser-based inline-capable coating process for the production of highly wear resistant coatings is presented. A zirconia-based sol–gel material is applied onto hardened and tempered steel substrates by a PipeJet-based printing process and spin-coating. Green films with a thickness of 100–200 nm are produced. Drying, gelation, and transformation of the green films into mechanically resistant wear protection coatings is done by laser treatments. Due to the precise temporal and spatial controllability of the diode laser radiation it is possible to generate temperatures >1000°C, required for the crystallization of the films, as well as to minimize the thermal load of the substrate. The formation of a tetragonal ZrO2 phase within the films is achieved by the laser treatment. According to finite-element calculations the temperature penetration depth of temperatures >150°C (thermal stability of the substrate around 180°C) is reduced to 20–100 μm by using pulsed diode laser radiation. The evolution of the layer thickness as well as chemical and morphological coating properties is investigated by white light interferometry, Fourier transform infrared spectroscopy, and grazing-incidence XRD measurements.

2013 | On-demand electrophoretic separation of DNA in written gel lines on planar substrates | Laurent Tanguy, et al | Solid-State Sensors, Actuators and Microsystems | EN

On-demand electrophoretic separation of DNA in written gel lines on planar substrates

Laurent Tanguy, et al
Solid-State Sensors, Actuators and Microsystems
2013 Transducers & Eurosensors XXVII
Date of Conference: 16-20 June 2013

Abstract:
We report a new approach to perform on-demand electrophoretic separation of DNA. In contrast to standard chip-based capillary electrophoresis in micromachined glass chips, we apply a planar polyimide substrate, write 200 μm wide gel lines bridging two Pt-electrodes and inject 500 pl sample volumes in non-contact manner. The gel is covered with mineral oil to inhibit evaporation. Subsequently, an electrical field is applied for 80 s and the separation of the DNA molecules (56 bp-Cy5 and 112 bp-Cy5, 10 μM) is successfully demonstrated.

2012 | SAXS-LABDISK: A centrifugal microfluidic screening platform for protein structure analysis | F. Schwemmer, et al | µTAS Conference Paper | EN

SAXS-LABDISK: A centrifugal microfluidic screening platform for protein structure analysis

F. Schwemmer, et al.
µTAS 2012, Conference Paper

Abstract:
A small angle x-ray scattering (SAXS) screening platform for fully automated protein structure analysis based on a centrifugal microfluidic LabDisk is presented. Protein sample (2 μl), dilution buffer (3 μl), and screening solution (3 μl) are split into 40 nl aliquots each (CVs < 5.5%), recombined in predefined ratios to 20 samples of 240 nl and mixed. On-Disk analysis can then be performed in a SAXS beamline. Up to 7 different screenings can be performed in parallel on one disk. For the first time, the SAXS-LabDisk will enable routine SAXS screening of minute protein volumes.

2012 | Droplet break-up with negative momentum Fluid Dynamics Videos | L. Tanguy, et al | ARXIV Fluid Dynamics | EN

Droplet break-up with negative momentum Fluid Dynamics Videos

L. Tanguy, et al.
eprint arXiv:1210.4078, Publication and video

Link to droplet break up with negative momentum video

Abstract:
The ejection of liquid droplets from a nozzle is highly important for physics of fluid. The Weber number describes how much kinetic energy is needed to overcome the surface tension and create a free-flying droplet. According to literature Weber numbers above 12 assure the creation and safe break up of a liquid droplet. However, even when this number goes down below 8, it is still possible to observe droplet break-up but sometimes with particular effects. We present here a fluid dynamics video showing experimental results and CFD simulations for droplet break-up at low Weber number where the droplet is generated with negative momentum. Such droplet generation is characterized by the droplet breaking up and then returning back into the nozzle. This is due to the fact that during the droplet formation the surface tension begins to slow down the flow velocity inside the droplet and then finally inverts the flow direction, while the droplet tail still breaks off from the nozzle. Thus after the break up the droplet momentum is oriented toward the nozzle. It is therefore possible to observe the droplet returning into the bulk fluid. High-speed images of this particular phenomenon are shown and simulation results are presented to illustrate the break up dynamics and the local velocities in the droplet.

2012 | Towards a “Sample-In, Answer-Out” Point-of-Care Platform for Nucleic Acid Extraction and Amplification: Using an HPV E6/E7 mRNA Model System | Anja Gulliksen, et al | Journal of Oncology | EN

Towards a “Sample-In, Answer-Out” Point-of-Care Platform for Nucleic Acid Extraction and Amplification: Using an HPV E6/E7 mRNA Model System

Anja Gulliksen, et al
Journal of Oncology
Volume 2012 (2012), Article ID 905024

Abstract:
The paper presents the development of a “proof-of-principle” hands-free and self-contained diagnostic platform for detection of human papillomavirus (HPV) E6/E7 mRNA in clinical specimens. The automated platform performs chip-based sample preconcentration, nucleic acid extraction, amplification, and real-time fluorescent detection with minimal user interfacing. It consists of two modular prototypes, one for sample preparation and one for amplification and detection; however, a common interface is available to facilitate later integration into one single module. Nucleic acid extracts from cervical cytology specimens extracted on the sample preparation chip were tested using the PreTect HPV-Proofer and achieved an overall detection rate for HPV across all dilutions of 50%–85.7%. A subset of 6 clinical samples extracted on the sample preparation chip module was chosen for complete validation on the NASBA chip module. For 4 of the samples, a 100% amplification for HPV 16 or 33 was obtained at the 1 : 10 dilution for microfluidic channels that filled correctly. The modules of a “sample-in, answer-out” diagnostic platform have been demonstrated from clinical sample input through sample preparation, amplification and final detection.

2011 | Inkjet-like printing of single-cells | Azmi Yusof, et al | Lab on a Chip | EN

Inkjet-like printing of single-cells

Azmi Yusof, et al
Lab on a Chip
Issue 14, 2011

Abstract:
Cell sorting and separation techniques are essential tools for cell biology research and for many diagnostic and therapeutic applications. For many of these applications, it is imperative that heterogeneous populations of cells are segregated according to their cell type and that individual cells can be isolated and analysed. We present a novel technique to isolate single cells encapsulated in a picolitre sized droplet that are then deposited by inkjet-like printing at defined locations for downstream genomic analysis. The single-cell-manipulator (SCM) developed for this purpose consists of a dispenser chip to print cells contained in a free flying droplet, a computer vision system to detect single-cells inside the dispenser chip prior to printing, and appropriate automation equipment to print single-cells onto defined locations on a substrate. This technique is spatially dynamic, enabling cell printing on a wide range of commonly used substrates such as microscope slides, membranes and microtiter plates. Demonstration experiments performed using the SCM resulted in a printing efficiency of 87% for polystyrene microbeads of 10 μm size. When the SCM was applied to a cervical cancer cell line (HeLa), a printing efficiency of 87% was observed and a post-SCM cell viability rate of 75% was achieved.

2010 | Dye-based coatings for hydrophobic valves and their application to polymer labs-on-a-chip | L. Riegger, et al | Journal of Micromechanics and Microengineering | EN

Dye-based coatings for hydrophobic valves and their application to polymer labs-on-a-chip

L. Riegger, et al
Journal of Micromechanics and Microengineering,
Volume 20, Number 4

Abstract:
We provide a method for the selective surface patterning of microfluidic chips with hydrophobic fluoropolymers which is demonstrated by the fabrication of hydrophobic valves via dispensing. It enables efficient optical quality control for the surface patterning thus permitting the low-cost production of highly reproducible hydrophobic valves. Specifically, different dyes for fluoropolymers enabling visual quality control (QC) are investigated, and two fluoropolymer-solvent-dye solutions based on fluorescent quantum dots (QD) and carbon black (CB) are presented in detail. The latter creates superhydrophobic surfaces on arbitrary substrates, e.g. chips made from cyclic olefin copolymer (COC, water contact angle = 157.9°), provides good visibility for the visual QC in polymer labs-on-a-chip and increases the burst pressures of the hydrophobic valves. Finally, an application is presented which aims at the on-chip amplification of mRNA based on defined flow control by hydrophobic valves is presented. Here, the optimization based on QC in combination with the Teflon-CB coating improves the burst pressure reproducibility from 14.5% down to 6.1% compared to Teflon-coated valves.

2009 | A capacitive sensor for non-contact nanoliter droplet detection | A. Ernst, et al | Sensors and Actuators A: Physical | EN

A capacitive sensor for non-contact nanoliter droplet detection

A. Ernst, et al
Sensors and Actuators A: Physical
Volume 153, Issue 1, 25 June 2009
Pages 57-63

Abstract:
This paper reports on a sensor for the detection of microdroplets in flight. The presented sensor is based on a capacitive principle, which allows for non-contact monitoring of a complete droplet dispensing process. In the presented experiments the change in capacity caused by liquid droplets in the range of a few nanoliters passing through the electric field of the sensor is studied. From the capacitive change the droplet presence can be deduced with a reliability of 100%, which means that every single droplet dispensed within the experiments caused a significant signal change. In addition, the sensor signal is sensitive to the droplet's volume V, dielectric constant ɛr (epsilon) and velocity . It turns out that every specific droplet exhibits a characteristic “fingerprint” signal depending on these parameters. Especially the droplet volume correlates very well with the peak value of the extracted signal. Therefore, the calibrated sensor is able to determine the volume of dispensed droplets in the range from 20 to 65 nl with a resolution of less than 2 nl. Furthermore, the printed circuit board (PCB) technology applied for fabrication of the sensor enables a very cost efficient and flexible realisation of the whole sensor unit. The non-contact capacitive principle prevents contamination and loss of media. Therefore, the proposed approach is well suited for high precision droplet presence detection and low cost online monitoring of liquid volumes in microdispensing processes for various applications.

2008 | Contact-Free Dispensing of Living Cells in Nanoliter Droplets | S. Lutz, et al | EN

Contact-Free Dispensing of Living Cells in Nanoliter Droplets

S. Lutz, et al

Abstract:
We present a novel method for automated dispensing of living cells in nanoliter range droplets using a disposable pipette tip combined with an elastic polymer tube. After introduction of an unmetered suspension of cells into a reservoir connected to the pipette tip, a tuneable volume of 10 - 80 nL of cells suspension is issued in a non-contact procedure. Droplet ejection is enabled by a piezostack driven piston squeezing the tube at a defined position. We achieve a reproducibility of the printed cell culture medium volumes better than 5% and survival rate of the cells of 97% directly after dispensing. In addition we demonstrated good culturability and cell differentiation in order to consider potential long term effects of the dispensing process that could harness the cells.

2004 | PipeJet: A Simple Disposable Dispenser for the Nano- and Microliter Range | W. Streule, et al | JALA | EN

PipeJet: A Simple Disposable Dispenser for the Nano- and Microliter Range

W. Streule, et al.
2004 Journal of the Association for Laboratory Automation (JALA), Band: 9, Number: 5
Pages 300 - 306

Abstract:
This paper reports on a simple, disposable non-contact dispenser for the nano- and microliter range. In contrast to other known dispensers manufactured by silicon micromachining the new device simply consists of an elastic polymer tube with a circular cross section. Actuation is done by a piezostack driven piston, squeezing
the tube at a defined position near the open end by a significant fraction of the cross section. In contrast to drop-on-demand devices based on an acoustic actuation principle, the squeezing of the tube leads to a significant mechanical displacement of the liquid. Our experiments tested a large number of media in the viscosity range from 1 to 27 mPas. Some of our experiments tested up to approximately 2,000 mPas. Frequency characteristics showed an independent dosage volume for water up to a frequency of 15 Hz for tubes with an inner diameter of approximately 200 µm. Standard deviation within 1,000shots resulted in an excellent CV (standard deviation/dosage volume) of less than 2% of the dosage volume.Using tubes with an inner diameter of approximately 1,000 µm and a print frequency of 340 Hz, a flow rate of less than or equal to 143 µL/s could be reached. Beyond the possibility to dispense pure liquids, emulsion paints with particles that have a diameter of approximately 40µm have also been printed successfully.