Development of a three-dimensional cell culture system based on microfluidics for nuclear magnetic resonance and optical monitoring.

A new microfluidic cell culture device compatible with real-time nuclear magnetic resonance (NMR) is presented here. The intended application is the long-term monitoring of 3D cell cultures by several techniques. The system has been designed to fit inside commercially available NMR equipment to obtain maximum readout resolution when working with small samples. Moreover, the microfluidic device integrates a fibre-optic-based sensor to monitor parameters such as oxygen, pH, or temperature during NMR monitoring, and it also allows the use of optical microscopy techniques such as confocal fluorescence microscopy. This manuscript reports the initial trials culturing neurospheres inside the microchamber of this device and the preliminary images and spatially localised spectra obtained by NMR. The images show the presence of a necrotic area in the interior of the neurospheres, as is frequently observed in histological preparations; this phenomenon appears whenever the distance between the cells and fresh nutrients impairs the diffusion of oxygen. Moreover, the spectra acquired in a volume of 8 nl inside the neurosphereshow an accumulation of lactate and lipids, which are indicative of anoxic condi-tions. Additionally, a basis for general temperature control and monitoring and a graphical control software have been developed and are also described. The complete platform will allow biomedical assays of therapeutic agents to be performed in the early phases of therapeutic development. Thus, small quantities of drugs or advanced nanodevices may be studied long-term under simulated living conditions that mimic the flow and distribution of nutrient

Methods and microfabrication techniques for subnanoliter magnetic resonance spectroscopy

Nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR) and ferromagnetic resonance (FMR) spectroscopy can open up the possibility of studying many scientifically and biologically relevant samples at the µm and sub-µm scale. Examples of volume-limited systems include numerous species of microorganisms, mammalian zygotes, the majority of cells, proteins limited in growth, micro and nanostructured devices for the analysis of spin dynamics at the sub-µm scale. These volume-limited samples cannot be addressed by commercially available inductive spectrometers due to their constraint in sensitivity. It was previously proposed in our group that CMOS technology can be used to realize miniaturized high sensitivity inductive detection systems, having spin sensitivities at least two orders of magnitude greater than the commercially available spectrometers. During my PhD work, I developed methods and microfabrication techniques to perform NMR, EPR and FMR spectroscopy at the µm and sub-µm scale by using high sensitivity single chip CMOS detectors, previously proposed in our group. Microfluidic systems for the non-invasive handling of liquid samples and biological entities immersed in liquids are realized and integrated with the CMOS single chip NMR and EPR detectors. Microfluidic channels are fabricated via conventional microfabrication techniques and via two-photon polymerization, a 3D printing technique with a lateral resolution of 300 nm. The 3D printing technique is found to be an exceptional solution for NMR applications. Due to the flexibility in the design of the microfluidic systems, it is possible to reduce the magnetic field non-uniformieties with a consequent improval in spectral resolution. Spectral resolutions down to 0.007 ppm are reported for liquids having sample volumes of 100 pL. For the first time, NMR studies on intact biological entities submerged in liquid media of choice are performed, using 3D printed microfluidic systems. A spin sensitivity of 2.5·1013 spins/¿Hz is shown, sufficient to detect highly concentrated endogenous compounds in active volumes down to 100 pL with measurement times down to 3 h. EPR measurements on subnanoliter liquids and frozen solutions are reported, by the combination of commercially available capillaries and EPR single chip detectors. This is a first but important step towards the study of biological samples, whose paramagnetic ions have relaxation times too short to be measured at room temperature. Moreover, a novel method for the sensing of magnetic microbeads is presented, which is based on the detection of the change of susceptibility in FMR condition by the CMOS integrated detector. Due to the frequency and field dependence of the susceptibility, the detected variation is 20 times greater than the change in magnetization measured in static conditions by other approaches. The proposed detection scheme allows for single bead sensitivity over an active area of about 5·104 µm2. Lastly, sub-µm scale FMR detection capabilities of the single chip CMOS detector are shown by experiments on nanopatterned single permalloy (80% Ni - 20% Fe) and YIG (Yittrium Iron Garnet) dots. The combination of high sensitivity and large active area is seen as a considerable advantage with respect to other FMR detection methods, which suffer either from sensitivity or from reduced active area

Microfluidically Cryo-Cooled Planar Coils for Magnetic Resonance Imaging

High signal-to-noise ratio (SNR) is typically required for higher resolution and faster speed in magnetic resonance imaging (MRI). Planar microcoils as receiver probes in MRI systems offer the potential to be configured into array elements for fast imaging as well as to enable the imaging of extremely small objects. Microcoils, however, are thermal noise dominant and suffer limited SNR. Cryo-cooling for the microcoils can reduce the thermal noise, however conventional cryostats are not optimum for the microcoils because they typically use a thick vacuum gap to keep samples to be imaged to near room temperature during cryo-cooling. This vacuum gap is typically larger than the most sensitive region of the microcoils that defines the imaging depth, which is approximately the same as the diameters of the microcoils. Here microfluidic technology is utilized to locally cryo-cool the microcoils and minimize the thermal isolation gap so that the imaging surface is within the imaging depth of the microcoils. The first system consists of a planar microcoil with microfluidically cryo-cooling channels, a thin N2 gap and an imaging. The microcoil was locally cryo-cooled while maintaining the sample above 8°C. MR images using a 4.7 Tesla MRI system shows an average SNR enhancement of 1.47 fold. Second, the system has been further developed into a cryo-cooled microcoil system with inductive coupling to cryo-cool both the microcoil and the on-chip microfabricated resonating capacitor to further improve the Q improvement. Here inductive coupling was used to eliminate the physical connection between the microcoil and the tuning network so that a single cryocooling microfluidic channel could enclose both the microcoil and the capacitor with minimum loss in cooling capacity. Q improvement was 2.6 fold compared to a conventional microcoil with high-Q varactors and transmission line connection. Microfluidically tunable capacitors with the 653% tunability and Q of 1.3 fold higher compared to a conventional varactor have been developed and demonstrated as matching/tuning networks as a proof of concept. These developed microfluidically cryo-cooling system and tunable capacitors for improving SNR will potentially allow MR microcoils to have high-resolution images over small samples

Investigation of Cryo-Cooled Microcoils for MRI

When increasing magnetic resonance imaging (MRI) resolution into the micron scale, image signal-to-noise ratio (SNR) can be maintained by using small radiofrequency (RF) coils in close proximity to the sample being imaged. Micro-scale RF coils (microcoils) can be easily fabricated on chip and placed adjacent to a sample under test. However, the high series resistance of microcoils limits the SNR due to the thermal noise generated in the copper. Cryo-cooling is a potential technique to reduce thermal noise in microcoils, thereby recovering SNR. In this research, copper microcoils of two different geometries have been cryo-cooled using liquid nitrogen. Quality-factor (Q) measurements have been taken to quantify the reduction in resistance due to cryo-cooling. Image SNR has been compared between identical coils at room temperature and liquid nitrogen temperature. The relationship between the drop in series resistance and the increase in image SNR has been analyzed, and these measurements compared to theory. While cryo-cooling can bring about dramatic increases in SNR, the extremely low temperature of liquid nitrogen is incompatible with living tissue. In general, the useful imaging region of a coil is approximately as deep as the coil diameter, thus cryo-cooling of coils has been limited in the past to larger coils, such that the thickness of a conventional cryostat does not put the sample outside of the optimal imaging region. This research utilizes a scheme of microfluidic cooling (developed in the Texas A&M NanoBio Systems Lab), which greatly reduces the volume of liquid nitrogen required to cryo-cool the coil. Along with a small gas phase nitrogen gap, this eliminates the need for a bulky cryostat. This thesis includes a review of the existing literature on cryo-cooled coils for MRI, as well as a review of planar pair coils and spiral microcoils in MR applications. Our methods of fabricating and testing these coils are described, and the results explained and analyzed. An image SNR improvement factor of 1.47 was achieved after cryo-cooling of a single planar pair coil, and an improvement factor of 4 was achieved with spiral microcoils

Development and application of microtechnologies in the design and fabrication of cell culture biomimetic systems

“Lab-On-a-chip” systems have proved to be a promising tool in the field of biology. Currently, cell culture is performed massively on Petri dishes, which have traditionally been used in cell culture laboratories and tissue engineering. However, having proved to be a widely used tool until now, the scientific community has largely described the lack of correlation between the results obtained in the laboratory and the clinical results. This lack of connection between what has been studied in the laboratories and what has been observed in the clinic has led to the search for more advanced alternative tools that allow results to be obtained closer to reality. Thus, the use of microtechnologies in the field of biomedical engineering, presents itself as the perfect tool as an alternative to obsolete traditional media. Thanks to the low volumes of liquid it presents for its use, it also makes it an essential technology for the testing of drugs, new compounds and materials. By being able to more accurately reproduce the biomimetic environment of cell cultures and tissues, they make this technique fundamental as an intermediate step between basic in vitro laboratory tests and preclinical animal tests, resulting from this way in the best alternative for the reduction of both the use of animal models, as in times and costs. For a biomimetic system to be as such, it also needs another series of complementary devices for its better functioning. Micro-valves, micro pumps, flow sensors, O2 sensors, pH, CO2 are fundamental for the correct functioning andsophistication of biomimetic systems. This complexity, on the other hand, is often not perceived by the user since the miniaturization of all these components makes “Lab-On-a-Chip” systems smaller every day, despite numerous control components that can be incorporated.This thesis presents some examples of different microfluidic devices designed and manufactured through the use of microtechnologies, with all applications, focused on their use in biomimetic systems.<br /