Topology optimization on two-dimensional manifolds

Yongbo Deng, Zhenyu Liu, Jan G. Korvink

Computer Methods in Applied Mechanics and Engineering, 2020

This paper presents topology optimization on general two-dimensional manifolds for phenomena described by second-order partial differential equations, where the material interpolation is implemented by using the material distribution method. When a physical field is defined on a two-dimensional manifold, the material interpolation is implemented on a material parameter in the partial differential equation used to describe the distribution of the physical field. When the physical field is defined on a three-dimensional domain with its boundary conditions defined on a two-dimensional manifold corresponding a surface or an interface of this three-dimensional domain, the material density is used to formulate a mixed boundary condition of the partial differential equation for the physical field and implement the penalization between two different boundary types. Based on the homeomorphic property of two-dimensional manifolds, typical two-dimensional manifolds, e.g., sphere, torus, Möbius strip and Klein bottle, are included in the numerical tests, which are used to demonstrate this topology optimization approach for the design problems of fluidic mechanics, heat transfer and electromagnetics.

Glassy carbon microelectrodes minimize induced voltages, mechanical vibrations, and artifacts in magnetic resonance imaging

Surabhi Nimalkar, Erwin Fuhrer, Pedro Silva, Tri Nguyen, Martin Sereno, Sam Kassegne and Jan Korvink

Microsystems and Nanoengineering, 2019

The recent introduction of glassy carbon (GC) microstructures supported on flexible polymeric substrates has motivated the adoption of GC in a variety of implantable and wearable devices. Neural probes such as electrocorticography and penetrating shanks with GC microelectrode arrays used for neural signal recording and electrical stimulation are among the first beneficiaries of this technology. With the expected proliferation of these neural probes and potential clinical adoption, the magnetic resonance imaging (MRI) compatibility of GC microstructures needs to be established to help validate this potential in clinical settings. Here, we present GC microelectrodes and microstructures—fabricated through the carbon micro-electro-mechanical systems process and supported on flexible polymeric substrates—and carry out experimental measurements of induced vibrations, eddy currents, and artifacts. Through induced vibration, induced voltage, and MRI experiments and finite element modeling, we compared the performances of these GC microelectrodes against those of conventional thin-film platinum (Pt) microelectrodes and established that GC microelectrodes demonstrate superior magnetic resonance compatibility over standard metal thin-film microelectrodes. Specifically, we demonstrated that GC microelectrodes experienced no considerable vibration deflection amplitudes and minimal induced currents, while Pt microelectrodes had significantly larger currents. We also showed that because of their low magnetic susceptibility and lower conductivity, the GC microelectrodes caused almost no susceptibility shift artifacts and no eddy-current-induced artifacts compared to Pt microelectrodes. Taken together, the experimental, theoretical, and finite element modeling establish that GC microelectrodes exhibit significant MRI compatibility, hence demonstrating clear clinical advantages over current conventional thin-film materials, further opening avenues for wider adoption of GC microelectrodes in chronic clinical applications.

Lab-on-a-Disc and NMR – a strategic partnership

The Lab-on-a-Disc (LoaD) approach was conceived in the 1990s as a sub-class of the more generic µTAS (from MicroTotalAnalysingSystems). The µTAS concept was derived ~10 years earlier with the hope to make a complete chemical and, therefore, also biological analysis of all type of liquids in an integrated and automated way. The idea was to create a mini lab in a piece of glass or even plastic by using the shrinkage of all channels and components to obtain highly branched networks of unit operations that allow complex analyses. Most modern desktop analysis machines (like glucose or haemoglobin) are based in some sort on that idea. To move away from work benches with glasses and vials that are handled by highly trained personnel and replace them by microchannels and microchambers where one can perform simple diagnostics automatically, that triggered the idea to make laboratory diagnostic outside of clinics. If the analysis could be performed nearly semi-automatic outside of a clinic’s lab, would the patient still have to come to the clinic for initial tests? Saving the patient the long way to a real hospital, by placing a semi-automated diagnostic in the rural communities, is especially valuable in developing countries were this might take days. One obstacle in that endeavour was the need of precision pumps to drive the liquids through the channels and often also the usage of complex tubing, Lab-on-a-Disc circumvented the need of pumps by spinning the whole microfluidic chip and using the resulting centrifugal forces to drive the liquids. In the last two decades this led to a large variety of the diagnosable diseases using LoaDs.

The original idea of a (µ)TAS system to chemically completely analyse a liquid is and back in the 1980s already was performed much better by another technique – the NuclearMagneticResonance (NMR) Analysis. NMR is based on the modulation of an electromagnetic signal, by the content the liquid, allowing to get information directly from its molecular composition. Many atoms i.e. Hydrogen, when placed in a magnetic field and activated by an electromagnetic wave of a specific frequency, answer by sending back a signal of the same frequency (hence the name resonance). This signal is now not 100% at the same frequency but it is modulated slightly by the magnetic fields caused by the molecules present in the liquid. A spectral analysis of the signal in the frequency domain, therefore, shows characteristic peaks that are fingerprints of the molecules present in the liquid.

Since NMR can be seen as the real TAS system, can an integration of the two not lead to a true µTAS system, ignoring for now the little flaw that the NMR magnets are nearly 2 m high? Both systems use liquid analytes in fairly small quantities (µl to ml). Also, the rotation is beneficial for both, while it drives the LoaDs it is used in NMR to improve the signal quality in a technology called magic angle spinning. Automation in NMR is done via a carousel that loads the test tube sequentially into the machine, the handling of small plugs of sample is one of the key technologies in LoaD and could, therefore, improve the high throughput sample handling. The merging of these two very well-established technologies will allow to improve sample handling in NMR significantly while at the same time shrinking the needed sample volume.

MicroTAS 2019 Basel, Switzerland

Integration of Ex-vivo precision-cut liver slice (PCLS) culture with microfluidic NMR metabolomics

Seminar Abstract

Bishnubrata Patra(1), Manvendra Sharma(1), Ruby Karsten (2), Maciej Grajewski (2), Sabeth Verpoorte (2), and Marcel Utz (1)

1 School of Chemistry, University of Southampton, UK
2 School of Pharmacy, University of Groningen, The Netherlands

We present a novel microfluidic perfusion system for liver tissue slices that allows direct characterization of the perfusion fluid by micro nuclear magnetic resonance (NMR) spectroscopy and imaging. This system enables direct non-invasive observation of the metabolic processes on the liver slice in real time. Integration of a microfluidic system with high-performance NMR spectroscopy has been achieved with careful management of sensitivity and magnetic susceptibility effects to maintain spectral resolution. The system presented here combines excellent NMR
performance with the ability to sustain the PCLS over several hours of perfusion.

KEYWORDS: Tissue slice culture, Microfluidics, Metabolomics, NMR

Ex-vivo culture of tissue provides an alternative to animal models to study the effect of external factors like exposure to drugs, environmental changes, infection, and inflammation, requiring significantly less resources [1] and providing more detailed information. Observation of metabolism
by NMR is well established. We present a microfluidic perfusion culture system for PCLS that allows direct NMR observation of the metabolite composition of the perfusate after contact with the slice using a home made transmission-line NMR probe [2].

The NMR setup and the perfusion chip are shown in figure 1. The microfluidic device (figure 1E) with the PCLS is sandwiched between polydimethylsiloxane(PDMS) membranes and chip holders. Culture
medium is supplied with a syringe pump at a flow rate of 8 µl/min. Both oxygen and carbon dioxide are exchanged by diffusion through the PDMS membrane. The device containing PCLS is kept at physiological temperature bysupplying hot water from a water bath (figure 1C) through a micro pump ( figure 1B).

Murine PCLS were incubated in well plates at 37°C in 80% O2 and 5% CO2 after slicing. Their viability was ascertained by LDH leakage assay before the perfusion experiment at day 1. After 1-3 days of incubation, they were transferred into the perfusion system. NMR spectra were continuously
recorded for up to 5 hours of perfusion. Incremental NMR spectra obtained over the course of the perfusion demonstrates stability of the system over several hours (figure 3). The proton NMR spectrum in Figure 4, averaged over the duration of the experiment, gives an indication of the
quality of the spectral information. At least 20 different metabolites are clearly apparent from this spectrum; most prominently, glucose, alanine, glutamine, glutamate, valine, leucine, and isoleucine. A small lactate peak is visible t 1.32~ppm. After 5h of perfusion, viability of the slices was
verified using ATP content/ µg of protein assay.

These results demonstrate that PCLS can be kept viable in an NMR-compatible microfluidic system, while high-quality NMR data of the perfusate is extracted. This opens the way for further studies to explore the
metabolic activity of slices exposed to various external stimuli.

This research project is funded by the horizon 2020 Framework program of the European Union. The authors sincerely acknowledge the discussion with Prof. Peter Olinga regarding tissue slice culture.

[1] I. A. M. de Graaf, P. Olinga, M. H. de Jager, M. T. Merema, R. d Kanter, E. G. Van de Kerkhof, G. M. M Groothuis, Preparation and Incubation of Precision-Cut Liver and Intestinal Slices for Application in Drug
Metabolism and Toxicity Studies. Nature Protocols 2010, 5 (9), 1540-1551.
[2] M. Sharma, M. Utz, Modular Transmission Line Probes for Microfluidic Nuclear Magnetic Resonance Spectroscopy and Imaging. Journal of Magnetic Resonance 2019, 303, 75-81.

Electrified Lab-on-a-Disc

Poster Abstract

SaraĂ­ M. Torres Delgado, Jan G. Korvink1 and Dario Mager*

Karlsruhe Institute of Technology – IMT, Eggenstein – Leopoldshafen, 76344, Germany

Tec.Nano 2019

Over the last decade centrifugal microfluidic platforms have been of increasing interest for use in decentralized bioanalytical testing such as point-of-care diagnostics. This technology is particularly powerful due to the inherent ability to centrifuge samples like the ones required for blood processing. However, while the LoaD technique compared to LOC, has simplified basic operations such as valving, pumping, metering, mixing and sample preparation, solutions to other arising needs, such as the integration of (active) operations, or the readout of a bioassay result, has proven more challenging to achieve when the platform is under continuous rotation, a characteristic inherent to their working principle. As anyone can foresee, power and signal cables cannot be connected to a rotating system, because they will twist, entangled, and finally, disconnect or brake, hampering the integration of actuators and/or detectors into the system. These components are needed for a sensitive, reliable, time-independent, fast, direct and continuous interaction with the microfluidic disc while spinning and, thereby, enhancing the success of LoaD systems.

Hence, here we present the design and development of a low cost, compact and portable platform that co- rotates with the microfluidics disc, called the “electrified Lab-on-a-Disc (eLoaD) platform” which includes all modules necessary for it to be used in any diagnostic assay. Because it requires power, wireless energy transmission was introduced into the system. Hence, the platform was designed and fabricated to behave as a wireless power receiver compatible with the Qi standard, better known for its use in wireless charging of consumer electronic devices. Since most envisaged applications will require a control unit that provides enough computational power, a way to record data and real-time bidirectional communication between the user and the ongoing experiment, the platform comprises an Arduino microcontroller, an SD-Card and a Bluetooth module. The inclusion of those modules renders a flexible platform, easy to operate for most users with backgrounds ranging from biology to engineering and compatible with concurrently emerging trends and standard technologies.

As any laboratory that operates on basic and specialized equipment, the capabilities of the proposed system can be augmented by the addition of a second electronic board plug-compatible to the eLoaD. This additional board referred to as Application Disc in Fig. 1 contains the application-specific sensors and actuators. Such scheme leads to a higher degree of interaction and enables more sophisticated concepts to be implemented both in the control as well as in the readout. The performance of the platform was tested under several sensing and actuation experiments (1-3), some of which will be presented at the conference.

figure 1

Figure 1: Integration of the wireless centrifugal system into conventional LoaD systems. A commercially available Qi-compliant transmitter is inductively coupled to the eLoaD platform. This fully integrated platform can control sensors and actuators located on the Application Disc, which itself is simultaneously interacting with the microfluidics disc. The disposable microfluidic disc and the reusable Application Disc are typically designed for a particular application, whereas the eLoaD platform, which implements the control logic, power, and communication, is reused as a generic framework for all possible applications. Interfacing of the eLoaD platform is enabled by Bluetooth communication, here exemplary via an Android application program running on a portable device, and from a PC running e.g. a LabVIEW script.


(1) S. M. Torres Delgado et al., Lab Chip, vol. 16, no. 20, pp. 4002-4011, 2016.

(2) S. M. Torres Delgado et al., Biosensors and Bioelectronics, vol. 109, pp. 214 – 223, 2018.

A multi-purpose, rolled-up, double-helix resonator

Pedro F. Silva, Sarai M. Torres Delagado, Mazin Jouda, Dario Mager, Jan G. Korvink

Journal of Magnetic Resonance, 2019

Multilayer flexible substrates offer a means to combine high lateral precision and resolution with roll-up processes, allowing layer-based manufacturing to reach into the third dimension. Here we explore this combination to achieve an otherwise hard-to-manufacture resonator geometry: the double-helix. The use of commercial flexPCB technology enabled optimal winding connections and a versatile adjustment to various operation fields, sample volumes and resonance numbers. The sensitivity of the design is shown to greatly benefit from the fabrication method, though optimal electrical connections and several radially-wound windings, and was measured to outperform an equivalent solenoid despite the known geometrical disadvantage.

EUROISMAR 2019, Berlin, Germany

Monitoring Oxygen Levels in Microfluidic Devices using 19F NMR

Seminar Abstract

Sylwia Ostrowska (1)*, Bishnubrata Patra (1), Ciara Nelder (1), Manvendra Sharma (1), Marcel Utz (2)

  1. University of Southampton, 2. School of Chemistry, University of Southampton

We report an in-situ, non-invasive approach to quantify oxygen partial pressure in microfluidic lab-on-a-chip (LoC) devices. LoC systems provide a versatile platform to culture biological systems. As they allow a detailed control over the growth conditions, LoC devices are finding increasing applications in the culture of cells, tissues and other biological systems
[1]. Integrated microfluidic NMR spectroscopy [2] allows non-invasive monitoring of metabolic processes in such systems. Quantification of oxygen partial pressure would help ensuring stable growth conditions, and provide a convenient means to assess the viability of the cultured system. However, oxygen, one of the most important metabolites, cannot be quantified using either proton or carbon NMR spectroscopy. As is well known, the oxygen partial pressure can be determined by MRI in vivo by measuring the 19F spin-lattice relaxation time of perfluorinated agents [3]. Here, we show that the oxygen partial pressure in microfludic devices of 2.5 ÎĽl can be quantified using the 19F spin-lattice relaxation rate of perfluorinated tributylamine. The compound is added to the aquous perfusion medium in the form of micrometer-sized droplets. Our set up comprises a microfluidic device and a PDMS layer sandwiched between two 3D printed holders. The droplet emulsion is delivered via a syringe pump and carbogen is delivered through a separate channel. The semi- permeable PDMS layer acts as a diffusion bridge between the liquid and gas channels, allowing for oxygen to diffuse into the emulsion. T1 is obtained through standard inversion recovery experiments detected using a home-built transmission-line probe.[2] Due to the non-toxic nature of droplet emulsion, it can be easily incorporated into the perfusion fluid allowing for quantification of tissue oxygen levels.

References: [1] Gracz et al., Nature Cell Biology 17, 340–349, 2015. [2] M.Sharma, M.Utz, J.Mag.Res 303, 75-81, 2019. [3] R.Manson et al., Magnetic Resonance in Medicine 18, 71-79, 1991.

NMR hardware and micro-probes

Nuclear magnetic resonance (NMR) is an analysis technique which is widely used in physics, medicine and chemistry. As NMR is a non-invasive and non-destructive method, it is used to image soft tissue inside the human body in the form of Magnetic resonance imaging (MRI). Conventional liquid-state NMR spectroscopy is usually performed on 200-800 microliter sample in a 5-10 millimeter diameter tube. Although conventional NMR is successfully used for a variety of applications, many problems cannot be adequately addressed by it. For example, bodily fluids from small animals are usually available in much smaller quantities compared to the sample volumes required by conventional NMR.

Microfluidics is a well-established field for manipulation of small sample volumes in microliter to nanoliter range. Due to small sample volumes, physical conditions for a sample can be precisely controlled with minimum resources. NMR can be used to study these systems for various chemical or biological processes.

Microfluidic systems are usually planar in geometry as oppose to conventional NMR sample holders which are cylindrical in shape. To study microfluidic systems with NMR, new setups tailored to specific needs are required.

We have developed a platform that can study generic microfluidic setups with NMR. This new setup requires 100 times less sample volume compared to conventional liquid-state NMR. The sample is held in a planar microfluidic chip made from plastic materials. The microfluidic chip can be used as a passive sample holder or a flow can be induced to supply different liquids. Gases can be dissolved in liquids on the chip for chemical reaction or oxygen supply to biological systems. The temperature at the chip can be tightly controlled to study different physical conditions. As the chip is placed in the NMR detector all the systems can be studied in real-time in their native environment. The setup has already been used for various experiments including reaction monitoring, micro-imaging of mouse liver tissue slices, and metabolic studies of mammalian cells.

“Small is beautiful” in NMR

Jan G. Korvink, Neil MacKinnon, Vlad Badilita, Mazin Jouda

Journal of Magnetic Resonance, 2019

In this prospective paper we consider the opportunities and challenges of miniaturized nuclear magnetic resonance. As the title suggests, (irreverently borrowing from E.F. Schumacher’s famous book), miniaturized NMR will feature a few small windows of opportunity for the analyst. We look at what these are, speculate on some open opportunities, but also comment on the challenges to progress.

Ex vivo mouse model for the early detection of drug-induced cholestasis

Ruby E.H. Karsten, Nikolaas V.J.W. Krijnen, Maciej Grajewski, Elisabeth Verpoorte, Peter Olinga

Groningen Research Institute of Pharmacy, University of Groningen, Groningen, The Netherlands


SLAS Europe 2019

BelTox, Brussels 2019

Drug-induced cholestasis (DIC), an adverse drug reaction, has a complex disease mechanism with no good model for early detection in drug development.

We are developing an ex vivo mouse model based on precision-cut liver slices (mPCLS) to study DIC.  We incubate PCLS for 48h with glibenclamide (a cholestatic drug). Cholestasis is ascertained by comparing control slices to slices treated with drug, with and without an optimized bile acid (BA) mix. We studied mPCLS viability and gene expression of BA transporters.

Non-toxic glibenclamide concentrations led to greater gene expression of basolateral and canalicular bile export transporters, the latter with a higher increase in the presence of BA mix. This study is the first that relates gene expression data to early DIC development in mPCLS. Once optimized, mPCLS will be incubated in a microfluidic device to monitor DIC onset in real time. We will use this model to elucidate disease mechanisms and perform drug toxicity screening.

1.            de Graaf IAM, Olinga P, de Jager MH, Merema MT, de Kanter R, van de Kerkhof EG, e.a. Preparation and incubation of precision-cut liver and intestinal slices for application in drug metabolism and toxicity studies. Nat Protoc. september 2010;5(9):1540–51.