Magnetic resonance relaxometry bioreactor monitoring

Abstract

Systems and methods for obtaining real-time, continuous measurements of a sample of a biological cell culture through tubing of a bioreactor by using a magnetic resonance relaxometer (MRR) device. The system pumps samples through tubing of a bioreactor (which comprises a bioreactor vessel holding the biological cell culture and the tubing through which a sample may be pumped). A portion of this tubing is routed through the MRR device and measurements are performed using magnetic resonance without the samples every leaving the bioreactor. Specifically, the return signals produced by the media (for example, water) in which the sample exists are analyzed to make inferences about the cells in the sample. The samples are then pumped back into the bioreactor vessel and returned to the culture such that none of the cells are destroyed while the measurements are obtained.

Description

[0001] MAGNETIC RESONANCE RELAXOMETRY BIOREACTOR MONITORING

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to and benefit of U.S. Provisional Patent Application No. 63,606,559, filed December 5, 2023, which is incorporated herein by reference.

[0004] BACKGROUND

[0005] The manufacture of biological therapeutic products such as antibodies and viral vectors is a growing market, with a wide array of important medical applications. Many of these products are produced by bioreactor-based cultures of genetically engineered cells. One important example is the human embryonic kidney (HEK) cell culture, which is used to produce viral vectors for cell and gene therapies. During a culture, cell density measurements are used to monitor the growth and health of the cells. Unexpected and undesirable changes in pH, oxygen saturation, or available nutrients can cause rapid swings in cell density, and timely action is required to prevent a catastrophic failure of the cell culture. During normal operation of a bioreactor, the viable cell density (VCD) is a reasonable proxy for total biologic productivity, offering insight into the bioreactor efficiency and the overall success of the ongoing culture.

[0006] VCD is typically measured by removing a sample of cells from the bioreactor which are then analyzed with either cell counting or spectroscopy. Cell counting often involves either the addition of a stain to improve the signal-to-noise ratio or counting beads that are required to take absolute cell density measurements. This precludes the return of the cells to the bioreactor and creates a trade-off between the temporal resolution and the amount of culture that is lost. For example, the FLEX2 cell analyzer from Nova Biomedical, which is widely used for bioprocess monitoring, requires 400 pL per sample for cell density and viability measurements. Sample volumes in this range are inconsequential for large-volume bioreactors but unsuitable for regular measurements on small (<2 mL) research bioreactors which are widely used for process development. While modem systems can perform measurements with sample volumes below pL. the sample-to-sample variability increases 47 as the sampling size shrinks.

[0007] Raman spectroscopy, impedance based VCD estimation, and some specialized cell counting techniques have all been applied online for sample-free cell density measurements, but these techniques all require additional wetted hardware that must be cleaned or replaced between runs, increasing the cost and complexity of the bioreactor. Furthermore, changes in the flow dynamics of suspended cell cultures associated with the transitions between different types of tubing can cause cells to form clumps and die, creating clogs in the bioreactor tubing, which can cause the culture to fail. These practical obstacles make it difficult to use VCD as an input for real-time feedback control of the bioreactor, and traditional monitoring methods will struggle to identify problems quickly enough to allow corrective action before they cause the culture to fail.

[0008] BRIEF SUMMARY

[0009] In one aspect, a system for monitoring a bioreactor is provided. According to one or more embodiments, the system comprises a bioreactor vessel configured to contain a biological cell culture. The system also comprises a tube in fluid communication with the bioreactor vessel. The system also comprises a first pump configured to pump a sample of the biological cell culture through the tube. The system also comprises a magnetic resonance relaxometry (MRR) device configured to measure a relaxometry signal of water in the sample as the sample passes through the tube.

[0010] In another aspect, a method of measuring cell density in a bioreactor is provided. In one or more embodiments, the method comprises pumping, by a first pump, a sample of a culture of biological cells from a bioreactor vessel and through a tube in fluid communication with the bioreactor vessel. The method also comprises measuring, by a magnetic resonance relaxometry (MRR) device, a T2 relaxometry of water in the sample as the sample passes through the tube. The method also comprises determining a density of cells in the sample based on the relaxometry of the water in the sample.

[0011] In still another aspect, a magnetic resonance relaxometry (MRR) device for measuring cell density is provided. In one or more embodiments, the device comprises an insulating enclosure. The device also comprises a probe assembly configured to receive a portion of a tube of a bioreactor, wherein the tube is configured such that a sample of a biological cell culture of the bioreactor flows through the tube, and wherein the probe assembly is configured to be inserted into the insulating enclosure. The device also comprises one or more magnets disposed within the insulating enclosure and configured to produce a magnetic field through the sample in the portion of the tube.

[0012] BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The detailed description is set forth with reference to the accompanying drawings. The drawings are provided for purposes of illustration only and merely depict example embodiments of the disclosure. The drawings are provided to facilitate understanding of the disclosure and shall not be deemed to limit the breadth, scope, or applicability of the disclosure. In the drawings, the left-most digit(s) of a reference numeral may identify the drawing in which the reference numeral first appears. The use of the same reference numerals indicates similar, but not necessarily the same or identical components. However, different reference numerals may be used to identify similar components as well. Various embodiments may utilize elements or components other than those illustrated in the drawings, and some elements and / or components may not be present in various embodiments. The use of singular terminology to describe a component or element may depending on the context, encompass a plural number of such components or elements and vice versa.

[0014] FIG. 1 depicts a magnetic resonance relaxometry bioreactor monitoring system, in accordance with one or more example embodiments of the disclosure.

[0015] FIG. 2A depicts a cross-section of a MRR device, in accordance with one or more example embodiments of the disclosure.

[0016] FIG. 2B depicts the probe assembly of FIG. 2A, in accordance with one or more example embodiments of the disclosure.

[0017] FIG. 2C depicts the MRR device of FIG. 2A, in accordance with one or more example embodiments of the disclosure.

[0018] FIG. 3 depicts a block diagram of a relaxometer, in accordance with one or more example embodiments of the disclosure.

[0019] FIG. 4 depicts a flow diagram for signal processing of data captured by a magnetic resonance relaxometry bioreactor monitoring system, in accordance with one or more example embodiments of the disclosure.

[0020] FIGS. 5A-5B depict exemplary transmit and receive signals, in accordance with one or more example embodiments of the disclosure.

[0021] FIG. 6 depicts an example of magnetic resonance relaxometry, in accordance with one or more example embodiments of the disclosure.

[0022] FIGS. 7A-7B depict exemplary sample calibrations, in accordance with one or more example embodiments of the disclosure.

[0023] FIGS. 8A-8C exemplary cell density and R2 measurements for three different cell cultures, in accordance with one or more example embodiments of the disclosure.

[0024] FIG. 9 depicts an exemplary method for a magnetic resonance relaxometry bioreactor monitoring system, in accordance with one or more example embodiments of the disclosure.

[0025] FIG. 10 depicts an example computing device, in accordance with one or more example embodiments of the disclosure.

[0026] DETAILED DESCRIPTION

[0027] This disclosure relates to, among other things, magnetic resonance relaxometry (MRR) bioreactor monitoring. Specifically, described herein are systems and methods for obtaining real-time, continuous measurements (however, these measurements may also be discrete measurements as well) of a sample of a biological cell culture through tubing of a bioreactor by using a low-cost nuclear magnetic resonance (NMR) relaxometer. This approach is less invasive than conventional techniques because the cells and media (e.g., water, etc.) in which the cells exist are unaffected by the magnetic fields produced by the system.

[0028] Conventionally, cell density measurements are performed using cell counting techniques (for example, a camera captures images of cell samples that pass by the camera) or spectroscopy. However, these conventional approaches often involve removing samples from the bioreactor, which ultimately destroys the cells in the sample. Requiring the samples be removed from the bioreactor also adds time to the process, limiting the frequency at which measurements can be performed.

[0029] In contrast, the system described herein connects tubing to the bioreactor vessel housing the biological cell culture. The bioreactor vessel and the tubing together form the overall bioreactor because the cells can flow through the tubing without exposure to the external environment. The system pumps samples from the bioreactor vessel into and through the tubing, and the measurements are performed using magnetic resonance without the samples ever leaving the bioreactor (the closed loop including the bioreactor vessel and the tubing). The samples are then pumped back into the bioreactor vessel and returned to the biological cell culture. This system configuration allows for measurements to be performed without destroying any of the cells and at a greater frequency than if the samples were required to be removed from the bioreactor to obtain a measurement.

[0030] Magnetic resonance relaxometry measures the rate of decay of excited nuclear populations in a sample. Signals are received from the water in the aqueous media (predominately) of the sample as well as the water in the cells (smaller contribution). Iron and large molecules in the cells scatter the magnetization of the water and make the signal decay more quickly. For that reason, a higher cell density gives a faster decay of the signal.

[0031] In the system described herein, a sample is routed through the tubing to an MRR device that produces a static magnetic field, BO, which creates a small energy preference for nuclei with magnetization aligned in the same direction as the applied field. This creates a net sample magnetization parallel to BO that can be caused to precess around BO with the application of a small radio frequency magnetic field, Bl. This radio frequency magnetic field may be produced, for example, by a software-defined radio as described in further detail with respect to FIG. 3, however, the radio may also be a hardware-based radio as well. The radio frequency magnetic field may also be generated by any other type of software or hardware-based device. For example, 0.5 T may be used for BO and approximately 10 i-iT may be used for Bl. However, the value of BO can range from a few millitesla in experimental systems up to 12+ T in NMR magnets. This technique may be used at any of these field strengths, but the hardware may need to be tuned for these field strengths. Bl can be up to several mT but a reasonable range may include, for example, 1 to 500 microteslas.

[0032] Intracellular magnetic perturbers, such as paramagnetic iron and manganese (as nonlimiting examples), cause small disruptions to the magnetic fields within cells that drive a faster decay of the observable transverse magnetization of a sample of the bioreactor medium as the contributions from different protons lose coherence. The decay of the transverse magnetization, characterized by its time constant T2 and relaxation rate R2 = 1 / T2, is therefore strongly correlated to the number of cells within the sample. Relaxometry benefits from the natural abundance and high gyromagnetic ratio of the protons in water molecules, and each measurement is analogous to a “single pixel” MRI. However, although the goal of MRI is to produce images, relaxometry is a bulk measurement that provides quantitative information about small samples. Therefore, relaxometry measurements can be made with smaller and less expensive hardware, compared to that required for spectroscopy or MRI.

[0033] Previously, R2 measurements of drugs and vaccines have been used to detect the subtle chemical changes associated with the formation of protein aggregates, freezing, and exposure to oxygen in a purified sample that is free of cells or other background molecules. This approach has been demonstrated in line with protein biologies as a quality monitor for bioprocessing. In the purified or single-component samples in these earlier works, the R2 is sensitive to even subtle changes in the composition or chemical state of the sample. However, similar measurements would not be possible for fluids with significant molecular backgrounds such as cell culture supernatants.

[0034] It was surprisingly discovered that R2 is strongly correlated with the cellular ferric content, which has, in turn, been correlated with oxidative stress, senescence, and stem cell quality, making benchtop relaxometry with discrete cell samples a well-established quality assurance test. Since all cell lines contain relaxation agents like iron, direct relaxometry measurements on cell culture solutions (containing cells growing in the culture) show increased R2 for higher cell densities. This allows cell density measurements to generalize well to other cell types and culture setups.

[0035] There are some existing techniques described for NMR spectroscopy measurements of cultures of mammalian cells, tissue samples, algae, yeast, and chemicals. In some cases, the bioreactor itself is positioned inside the magnet and the entire culture is measured at once, but such an approach is not practical with production-scale bioreactors. Several other techniques describe using NMR spectroscopy with perfusion systems to monitor cell cultures. However, NMR spectroscopy is poorly suited for real-time monitoring because this process is relatively slow. The cell concentration in a given sample may be low so these NMR spectroscopy approaches require an extremely high-quality magnet (such as a superconducting magnet that is able to produce upwards of 10T and is shimmed to a homogeneity of approximately one part in a billion, for example).

[0036] In contrast with these existing techniques, the system described herein instead performs relaxometry measurements of the media (such as water or any other type of media) in which the cells exist, and these signals are used to infer information about the cells themselves. As one non-limiting example, the signals obtained from the media may be used to infer the cell density of the sample, however, any other type of information may also be inferred. The media is higher in abundance within a sample than the cells themselves so the measurements can be performed using a magnet that produces a much smaller static magnetic field and has a homogeneity of approximately 100 parts per million, for example (these numbers are only intended to provide an example distinction between the homogeneity of a superconducting magnet and the magnet used in the system described herein and are not intended to be limiting). These media-based relaxometry measurements are much faster than the existing NMR spectroscopy techniques, allowing meaningful measurements to be made continuously, compared to several minutes to an hour for traditional NMR spectroscopy. This is critical to quickly detect the changes within the culture.

[0037] In summary, the system advantageously allows for sample measurements to be continuously performed without having to remove any of the cells from the bioreactor by measuring signals from the media of the cells and using the data to make inferences about the cells themselves. The system is also configured to obtain measurements without requiring a magnet capable of producing strong magnetic fields. For example, the system descnbed herein may be configured to obtain measurements using magnets that produce a 0.5T magnetic field strength (however, other magnetic field strengths may also be used). These and several other advantages of the system are described in further detail below with respect to the figures.

[0038] Turning to the figures, FIG. 1 depicts a magnetic resonance relaxometry bioreactor monitoring system 100. In one or more embodiments, the system 100 comprises a bioreactor vessel 102. The bioreactor vessel 102 holds the biological cell culture being tested using the MRR device 116 as described herein. The biological cell culture may be provided within a media within the bioreactor vessel 102. For example, the media may be water, however, other types of media may also be used.

[0039] It may be generally undesirable to remove a sample of the biological cell culture from the bioreactor vessel 102 because the sample may then be exposed to the external environment and the sample may be destroyed or otherwise impacted. Accordingly, to allow a sample to be routed to the MRR device 116 for measurements, the system 100 may include tubing 106 that is provided in fluid communication with the bioreactor vessel 102. The interface between the tubing 106 and the bioreactor vessel 102 may be sufficiently sealed such that any samples that pass between the bioreactor vessel 102 and the tubing 106 are not exposed to the external environment. The tubing 106 is also sufficiently thick such that any sample that travels through the tubes 106 is also not exposed to the external environment. For example, the tubing 106 may be made of a Silicone material, however, the tubing 106 may also be made of any other material or combination of materials.

[0040] In one or more embodiments, the tubing 106 may include a first loop 108 and a second loop 110. The first loop 108 may comprise a cell retention device 114 that separates the cells of the sample of the biological culture and any media in which the cells exist. The cell retention device 114 may be a part of the perfusion bioreactor that is distinct from the MR monitoring. In these bioreactors, the product being produced may be secreted into the cell media, and it is desirable to be able to remove the product continuously while retaining the cells inside the bioreactor so that they can continue to produce the product. Accordingly, the cell retention device 114 separates the cells from the media so that the cells can be returned to the bioreactor and the media can be harvested for further processing and extraction of the product. In a perfusion setup like this, there may be other pumps that add new media in order to maintain the bioreactor volume and replenish the nutrients that the cells consume. In a batch culture (where the cells are grown in a closed flask with one volume of media and the entire culture is harvested after some time), MRR monitoring may have only one loop going out of and back into the flask with no cell retention device.

[0041] The second loop 110 may be a bypass loop from the first loop 108 and directs a sample into the MRR device 116 (that is, the second loop 110 travels through the MRR device 116), which obtains measurements from the sample (or more specifically, from the media in which the cells exist) as the sample passes through the MRR device 11 . That is, part of the sample flowing out of the bioreactor vessel 102 is diverted to a branch passing through MRR device 116 before being returned to the bioreactor vessel 102. In this manner, the MRR device 116 may obtain measurements as the sample flows through the tubing 106 such that the sample remains in the bioreactor (combination of the bioreactor vessel 102 and the tubing 106) and is not exposed to the external environment.

[0042] In one or more embodiments, the system 100 may also include one or more pumps to cause the samples to flow to and from the bioreactor vessel 102 and through the tubing 106. The one or more pumps may also be used to stop or slow the flow of media (and the sample included within the media) before a measurement is performed, however, the 100 system may also be configured such that the measurements may be performed while the one or more pumps are operating and the media and sample are flowing through the tubing 106. The one or more pumps may be controlled by a computing device, such as computing device 304, for example (or any other type of computing device capable of sending control instructions to the one or more pumps).

[0043] In the exemplary system configuration shown in FIG. 1, a first pump 109 is provided in the first loop 108 and a second pump I l l is provided in the second loop 110. The first pump 109 is configured to pump a sample from the bioreactor vessel 102 into the first loop 108, through the first loop 108, and back into the bioreactor vessel 102. Likewise, the second pump 111 is configured to re-direct a sample flowing through the first loop 108 into the second loop 110 such that the sample may then pass through the MRR device 116 such that measurements may be performed. The sample may then flow back into the first loop 108 and back into the bioreactor vessel 102. Although the system 100 shows two pumps, any other number of pumps may also be provided in the system 100 and such pumps may be provided at any other location within the system 100.

[0044] In one or more embodiments, the MRR device 116 comprises one or more magnets 118 that generate a static magnetic field to align the magnetic nuclei in the sample. When a sample is placed in the magnetic field, the spins of the nuclei align with or against the field. The MRR device then applies a brief radiofrequency (RF) pulse. This pulse excites the aligned spins, flipping them out of alignment with the magnetic field (the protons are now in an excited state). After the RF pulse is turned off, the nuclei begin to return to their original state (alignment with the magnetic field), a process called “relaxation.” This relaxation data may then be used to infer various properties of the sample.

[0045] The MRR device 116 may also comprise an insulating enclosure 117 that encloses the one or more magnets. The insulating enclosure 117 ensures that the temperature within the MRR device 116 is maintained at a constant value as the continuous sample measurements are performed over time. This is important because the magnetic field produced by the one or more magnets may be impacted by temperature. Therefore, the insulating enclosure 117 eliminates or removes the exposure of the one or more magnets to the changing ambient temperatures of the environment. The insulating enclosure 117 may be made of a foam material or any other type of material or combination of materials. One or more heating elements (such as resistive heating elements or any other elements configured to generate heat) may also be provided within the insulating enclosure 117 to further ensure that the temperature is maintained at a consistent value. Further details about the MRR device 116 are provided with respect to at least FIGS. 2A- 2C. The MRR device 116 may also comprise a probe assembly 120 that may be inserted into the insulating enclosure 117 within the magnetic field produced by the one or more magnets 118. The probe assembly 120 comprises a coil that is wound around the tubing 106 (for example, the second loop 110). The probe assembly 120 and the tubing 106 are inserted into the insulating enclosure 117 and within the magnetic field together. The probe assembly 120 may be connected to a relaxometer (such as relaxometer 300 described in further detail with respect to FIG. 3). For example, the probe assembly 120 may be connected to the relaxometer using a Bayonet Neill-Concelman (BNC) cable or any other type of wired or wireless connection. The relaxometer may be configured to generate signals to transmit through the probe assembly 120 and also receive return signals based on interactions between the transmitted signals and the sample flowing through the tubing 106 inside the MRR device 116.

[0046] FIGS. 2A-2C depict an exemplary MRR device 200. Specifically, FIG. 2A depicts a cross-section of the MRR device 200, FIG. 2B depicts the probe assembly of the MRR device 200, and FIG. 2C depicts a perspective view of the MRR device 200.

[0047] Beginning with FIG. 2A, in one or more embodiments, the MRR device 200 comprises one or more magnets 202. As indicated above, the one or more magnets 202 generate a static magnetic field to align the magnetic nuclei in a sample such that the relaxation times may then be measured to infer the properties of the sample. One advantage of the MRR device 200 described herein is that data may be obtained from a sample without the sample needing to be removed from the bioreactor (including the bioreactor vessel 102 and the tubing 106) and without requiring a homogeneous superconducting magnet (such a superconducting magnet would also require a complex and expensive cooling solution).

[0048] Within the one or more magnets 202 is a void 204 configured to receive a probe assembly 212 (which may be the same as, or similar to, probe assembly 120 shown in FIG. 1) of the MRR device 200. The probe assembly 212 comprises a coil 214 (for example, a solenoidal coil) and a tuning circuit 216 and is configured to receive a portion of the tubing (for example, the tubing 106 shown in FIG. 1) of the bioreactor. The coil 214 may be an enamel covered copper wire, for example, however, other materials may be used for the coil 214. The tuning circuit 216, for example, may comprise capacitor(s), with one for setting the resonance frequency and one for matching the input impedance. The probe assembly 212 may include a supporting structure 215 that is configured to receive the coil 214 and the tubing 218 in a position within the MRR device 200 within the one or more magnets 202.

[0049] The coil 214 may generate the excitation field and act as a detection coil for receiving the signals from the sample and the media in which the sample exists. The coil 214 may be tuned to resonant at a resonant frequency (for example, the Larmor frequency) of the sample to maximize sensitivity. The coil 214 may also be impedance matched to the impedance of the transmitter and receiver to facilitate power transfer. A high coil inductance may be desirable because the signal-to-noise ratio is proportional to the square root of the quality factor (Q), which is maximized by increasing inductance in the resonant circuit. The coil 214 may be in electrical communication with a relaxometer (for example, the relaxometer 300 shown in FIG. 3) that controls the radio frequency pulse produced by the coil 214 and also receives any return signals for analysis.

[0050] The probe assembly 212 is configured to produce a radio frequency magnetic field that is in the proper orientation and that is consistent across the size of a sample (for example, it may be desired to maintain the magnetic field consistently within a 0-5% variation across the size of the sample). The probe assembly 212 may be configured in such a way that the coil 214 may be wound around the tubing 218 and autoclaved with the tubing 218. After this is completed, then the coil 214 may be electrically connected to the remaining electric components in electrical communication with the probe assembly 212. As one non-limiting example, a screw terminal may be provided that is in electrical communication with the other electric components. The wiring of the coil may be connected to the screw terminal to complete the electrical connection with the other electronic components. This connection may also be accomplished in any other suitable manner. The completed assembly may then be inserted into the void 204 within the insulating enclosure 206 (as shown in FIG. 2C).

[0051] In one or more embodiments, MRR device 200 comprises an insulating enclosure 206 that encloses the one or more magnets. The insulating enclosure 206 also encloses the probe assembly 212 when the probe assembly 212 is inserted into the MRR device 200. The insulating enclosure 206 ensures that the temperature within the MRR device 200 is maintained at a constant value as the continuous sample measurements are performed over time. The insulating enclosure 206 may be made of a foam material or any other type of material or combination of materials.

[0052] Conventionally, a sample measurement system may need to be calibrated every time a sample is measured. Even if the calibrations are accurate, every time a re-calibration is performed, the measurements that are performed may be slightly different based on the calibration. If the measurements are performed frequently (e.g., every few minutes, continuously, etc.), then additional “jitter” or noise may be introduced into the data from the frequent calibrations that are performed. Additionally, the strength of the one or more magnets of the MRR device 200 may be impacted by temperature. Without the insulating enclosure 206, any changes in the ambient temperature of the environment in which the MRR device 200 exists (e.g., weather changes, air conditioning usage, etc.) would impact the magnetic field produced by the one or more magnets, necessitating the repeat calibrations. By providing the insulating enclosure 206, the temperature within the insulating enclosure 206 may be maintained consistently to within 1 / 1000th of a degree Celsius, for example. Accordingly, the MRR device 200 may be operated based on only one initial calibration (because the assumption is that the temperature will be maintained within the insulating enclosure 206 regardless of changes in the ambient temperature of the external environment.

[0053] In one or more embodiments, one or more heat generation elements may also be provided within the insulating enclosure 206. For example, the one or more heat generation elements 208 may be resistive heating elements or any other types of elements that may be used to increase the temperature within the insulating enclosure 206. The one or more heating elements 208 may be used in conjunction with the insulating enclosure 206 to ensure that the temperature within the insulating enclosure is maintained at the desired temperature.

[0054] In one or more embodiments, a second enclosure 212 may also be provided within the insulating enclosure 206 (between the insulating enclosure 206 and the one or more magnets). The second enclosure 212 serves to distribute heat generated by the one or more heating elements 208 evenly over the one or more magnets. For example, the second enclosure 212 may be made from an Aluminum or other type of metallic material (or any other type of material that is suitable for heat distribution). One or more temperature sensors may also be provided within the MRR device 200. The one or more temperature sensors may be configured to capture temperature data within the MRR device 218 and the operation of the one or more heating elements 208 may be dynamically performed based on this temperature data. For example, if the temperature data indicates that the temperature is below a desired temperature range (or is dropping at a certain rate), then the one or more heaters 208 may be automatically turned on by the system to increase the temperature within the insulating enclosure 206. Likewise, if the temperature data indicates that the temperature is above a desired temperature range (or is increasing at a certain rate), then the one or more heaters 208 may be automatically turned off by the system.

[0055] FIG. 3 depicts a block diagram for a relaxometer 300. Specifically, the block diagram illustrates some of the electrical and / or computing components that may be included in a system as described herein. As non-limiting examples, electrical and / or computing components used to facilitate the generation and transmission of a radio frequency signal to an MRR device to interact with a sample, receive a return signal from the sample, process the return signal, control any of the components of the system, and / or perform any other functions described herein in association with the MRR device and / or the larger system as a whole. The relaxometer 300 comprises a transmit side 301 including elements associated with the generation and / or transmission of a signal to the probe assembly 306, and a receiving side 303 including elements associated with receiving a return signal produced by the sample being measured.

[0056] In one or more embodiments, the relaxometer 300 may comprise a software-defined radio 302, which handles the synthesis and reception of the radio frequency pulses for obtaining measurements from samples. Specifically, a sample may be pumped through tubing 308 (which may be the same as, or similar to, the tubing 106 of FIG. 1, the tubing 211 of FIG. 2B, etc.) into the MRR device (not shown in FIG. 3) and measurements may be obtained from the sample within the MRR device. In a software-defined radio, some (or all) of the signal processing may be performed in software rather than by specialized hardware. The radio architecture may be reconfigured by updating the application software, which allows for rapid reconfiguration and experimentation. Additionally, because the signals within the system are stored in memory, it is possible to perform extended analyses on individual samples that may be cumbersome or impossible with physical hardware. However, while reference is made to a software-defined radio 302 herein, a hardware-based radio may also be used in place of the software-defined radio in some instances.

[0057] The relaxometer 300 may also comprise a probe assembly 306 (which may be the same as, or similar to, probe assembly 210 shown in FIGS. 2A-2C, probe assembly 120 shown in FIG. 1, or any other probe described herein) for interfacing with the sample, a Field Programmable Gate Array (FPGA) 310 (however, any other type of hardware and / or software component other than an FPGA may also be used) for sequencing the control of these and other elements of the system, and a computing device 304 (for example, a laptop or desktop computer, a server, etc.) for receiving and processing any of the return signals from the sample that passes through the receive side of the relaxometer 300. As shown in FIG. 2C, the probe assembly 306 and the tubing 308 may be inserted within the magnet (for example, one or more magnets 118, one or more magnets 202, etc.) disposed within an insulating enclosure. A transmit and receive switch 320 may also be used to protect the amplifiers in the receiver from the high-power transmit pulses. The specific configuration shown in FIG. 3 is merely exemplary and any other combination of different types of elements may be used. Additionally, while reference is made to software-defined elements, some or all of the relaxometer 300 may be hardware-based elements as well.

[0058] For echo times longer than a few hundred microseconds, diffusion of the water molecules in the sample may begin to impact the quality of the refocusing pulses, resulting in shorter-than-expected relaxation curves. To minimize the inter-echo times, the FPGA 310 may be synchronized with the software-defined radio 302. The FPGA 310 may time the operation of the pumps such that the pumps cease operation when the measurements are performed and resume operation after the measurement is obtained (however, the pumps may also continuously pump samples through the MRR device as well).

[0059] In some instances, the walls of the tubing 308 may also produce an NMR signal. This may be problematic given that the walls of the tubing 308 may be thick relative to the volume of the sample flowing through the tubing. The NMR signal produced by the tubing may be removed by increasing the gain of the radio, waiting for the signal to decay, and then only- reading the tail end where the signal from the tubing 308 has disappeared and only the signals from the cells and / or media in which the cells reside remain.

[0060] In some instances, a radio may not be capable of transmitting signals at frequencies below a specific threshold. As an example, the software-defined radio 302 may be incapable of transmitting or receiving at frequencies lower than 70MHz. However, the resonant frequency of a sample being measured may be even lower than this threshold frequency (as a non-limiting example, the resonant frequency of the sample may be approximately 20 MHz). Accordingly, the block diagram is shown as including additional elements that are used to shift signals generated by the radio down to the resonant frequency of the sample, and to shift signals returning to the radio up to a frequency suitable for the radio. However, these elements are not necessarily required and the electrical and / or computing elements included in the system may vary depending on the capabilities of the radio, the resonant frequency of the sample being measured, and various other factors. In some embodiments, all or some of the elements may be software-based elements, however, equivalent hardware-based components may also be used as well (or any combination of the two).

[0061] In one or more embodiments, at the transmitting side 301, the software-defined radio 302 may generate signals at a first frequency (or frequency range). As an example, the transmit frequency may be 140MHz, which is above the broadcast radio frequency band and therefore less likely to be subject to electromagnetic noise (however, any other frequency or frequency band may also be used). The relaxometer 300 also may include a signal generation element 322, which may be configured to generate a signal at the same or a different frequency than the software-defined radio 302. For example, the signal generation element 322 may be an oscillator that is configured to generate a 120MHz signal (however, any other type of signal generation element may also be used, including a software-defined signal generation element or a hardware-based signal generation device).

[0062] The specific frequency selected to be generated by the signal generation element 322 may depend on the frequency range of the software-defined radio 302 and the resonant frequency of the sample that is desired to be used with the probe assembly 306. In the example described herein, the resonant frequency of the sample is approximately 20MHz, however, the software-defined radio 302 may not be capable of generating signals at this frequency. To achieve the desired 20MHz, the signal generation element 322 generates the 120MHz signal such that the difference between the two signals (the 140MHz signal and the 120MHz signal) is the desired 20MHz. However, if the software-defined radio 302 were configured to transmit signals at 150MHz, then the signal generation element 322 would be configured to generate signals at 130MHz such that the difference between the two signals is still 20MHz.

[0063] At the transmit side, the signal from the signal generation element 322 passes through a splitter 324 (which may be a Wilkinson splitter or any other type of splitter). The signal generated by the software-defined radio 302 and the signal generation element 322 are received by the first mixer 314. The first mixer 314 (and the second mixer 326) may be configured to output frequencies at the sum and difference of the signals that are provided as inputs. In this example, the input signals are 140MHz and 120MHz. Accordingly, the outputs of the first mixer 314 in this example are a 20MHz signal (the difference between the inputs) and a 260MHz signal (the sum of the inputs). A bandpass filter 316 is provided after the first mixer 314 at the transmit side to remove the 260 MHz signal so that only the remaining 20MHz signal is provided to the probe assembly 306. An amplifier 318 may also be provided to amplify the transmitted signal before the signal reaches the probe assembly 306. For example, the signal may be amplified to 1W, however, any other signal amplification may be performed.

[0064] In one or more embodiments, a switch 320 may also be included to ensure that transmitted signals are not detected by the receiving side during transmission. The receiving side 303 may be sensitive to signals so the switch 320 may be configured to prevent signals from entering the receive side when signal transmission is being performed. Once the signals have been transmitted, the switch 320 may then be configured to allow signals to be detected by the receiving side 303 such that any signals returned from the sample may be received and analyzed.

[0065] In the receiving side 303 of the relaxometer 300, a signal that is received from the probe assembly 306 and the sample in the tubing 308 passes through one or more amplifiers (for example, amplifier 330, amplifier 334, and amplifier 336). In this exemplary configuration, each of the amplifiers may add approximately 30dB of gam to the received signal. However, any other number of amplifiers may be provided and the amplifiers may be configured to amplify the signal by any other amount. The bandpass filter 322 is also provided to remove any noise or undesired frequencies. The amplified signal is then received by the second mixer 326, The second mixer 326 also receives the signal generated by the signal generation element 322. Continuing the above example in which the signal is a 120MHz signal, the second mixer 326 produces output signals at 140MHz (the sum of the two input signals) and 100MHz (the difference between the two input signals). These two outputs are passed through passband filter 328, which then removes the 100MHz signal. It should be noted that all of these frequency values are merely exemplary and other frequencies may also be used.

[0066] FIG. 4 depicts a flow diagram 400 for signal processing of data captured by the MRR bioreactor monitoring system. That is, the operations shown in the flow diagram 400 may be performed on a return signal that is received from a sample. For example, these signal processing steps may be performed by the computing device 304 tasked with the analysis of any obtained measurements, however, the flow diagram 400 may also be performed by any other device and / or system with computing capabilities.

[0067] The flow diagram 400 begins with operation 402, which involves receiving a return signal from the radio (for example, the software-defined radio 302 of FIG. 3). The return signal may be the signal that is received from the sample at the probe assembly within the MRR device. At operation 404, the return signal is passed through a lowpass filter. The lowpass filter may remove environmental noise and thermal noise from the coil and the sample, for example. At operation 406, the resulting signal is frequency corrected. For example, the frequency correction may involve multiplying the signal by e27TVfAt operation 408, phase correction may be performed on the signal. For example, the phase correction may involve multiplying the signal by At operation 410, the echo amplitudes may be extracted from the signal. At operation 412, a least squares fit to a * e~b+ c may be performed. Finally, at operation 414, the resulting R2 signal may be processed to determine information about the cells in the sample.

[0068] It should be noted that the operations shown in the flow diagram 400 are merely exemplary and the signals may also be processed in any other suitable manner. Any filters may also be adjusted by fitting parameters after the fact. For example, if information about VCD estimation is desired, an additional filter can be added after the least squares fit, which removes noise but makes the measurements slower to respond to changes. If, on the other hand, leak detection is more important, this filter is left off, and the "a" value from the least squares fit may be monitored to identify air bubbles in the tubing.

[0069] FIGS. 5A-5B depict plots of exemplary transmit and receive signals. The second plot 502 shown in FIG. 5B is the transmitted signal and the first plot 500 shown in FIG. 5A is an example of a signal that is received from a sample based on the transmitted signal. In one or more embodiments, before capturing data, the system may cause any of the pumps to cease operations. The system may then send an instruction to the radio to transmit the RF pulses (as shown in FIG. 5B, for example). At the same time, the system may toggle the switch (for example, switch 320 shown in FIG. 3) so that the receiver is disconnected when a pulse is being transmitted. After the last pulse (usually about 3 seconds later), the system sends a command to the pump to resume pumping operations. As indicated above, the measurements may also be obtained while the pumps are operational and the sample is flowing through the MRR device.

[0070] FIG. 6 depicts an example of magnetic resonance relaxometry. The magnetization of a sample is caused to precess around a strong magnetic field. Over time, different populations within the sample spin slightly faster or slower depending on tiny variations in their magnetic environments. The result is a detectable decay in the amplitude of transverse magnetization, referred to as T2 decay.

[0071] FIGS. 7A-7B depict exemplary sample calibrations for two different biological cell cultures suspended in media (e.g., water or any other type of media). For example, a first plot 700 is shown for the first type of biological cell culture and a second plot 702 is shown for a second type of biological cell culture. 5 zL samples of each of the biological cell cultures may be prepared by diluting a single high-density sample with cell free media from the same sample. Each measurement may be repeated multiple times and the standard error is shown with error bars. Cell density may be correlated with R2 for both types of cells.

[0072] FIGS. 8A-8C exemplary cell density and R2 measurements for three different cell cultures (for example, a first plot 800 for a first cell culture, a second plot 802 for a second cell culture, and a third plot 804 for a third cell culture). Cell density and R2 measurements for three different HEK293 cell cultures. The relaxometry system may obtain R2 measurements periodically. The first plot 800 shows data associated with a scenario in which most of the cells were removed from the bioreactor on day four to simulate a harvest, and an antidumping agent (ACA) was added. On day eight, some cells were diverted into the harvest through the cell retention device, causing a loss of cells for several hours. On day 13, the stirrer that keeps the cells in suspension was disabled for an hour, causing a temporary drop in the cell density. The second plot 802 shows data associated with a scenario in which cells were removed on day seven and reintroduced on day eight. The third plot 804 shows data associated with a scenario in which cells were removed on day six.

[0073] FIG. 9 depicts an example method 900 for magnetic resonance relaxometry bioreactor monitoring. Some or all of the blocks of the process flows or methods in this disclosure may be performed in a distributed manner across any number of devices or systems (for example, radio 302, computing device 304, FPGA 310, etc.). The operations of the method 900 may be optional and may be performed in a different order.

[0074] At block 902 of the method 900, computer-executable instructions stored on a memory of a system or device may be executed to pump, by a first pump (for example, the first pump 109 and / or the second pump 111), a sample of a culture of biological cells from a bioreactor vessel (for example, bioreactor vessel 102) and through a tube (for example, tubing 106, tubing 218, etc.) in fluid communication with the bioreactor vessel.

[0075] At block 904 of the method 900, computer-executable instructions stored on a memory of a system or device may be executed to measure, by a magnetic resonance relaxometry (MRR) device (for example, MRR device 116, MRR device 200, etc.), a T2 relaxometry of water in the sample as the sample passes through the tube. However, the MRR device may also be configured to measure any other type of media other than water as well.

[0076] At block 906 of the method 900, computer-executable instructions stored on a memory of a system or device may be executed to determine a density of cells in the sample based on the relaxometry of the water in the sample.

[0077] FIG. 10 is a schematic block diagram of an illustrative computing device 1000 in accordance with one or more example embodiments of the disclosure. The computing device 1000 may include any suitable computing device capable of receiving and / or generating data including, but not limited to, a user device such as a smartphone, tablet, e-reader, wearable device, or the like; a desktop computer; a laptop computer; a content streaming device; a set-top box; or the like. The computing device 1000 may correspond to an illustrative device configuration for the devices of FIGS. 1-9 (such as the radio 302, computing device 304, FPGA 310, any other elements of an MRR device or a larger system as described herein with computing capabilities, etc.).

[0078] The computing device 1000 may be configured to communicate via one or more networks with one or more servers, search engines, user devices, or the like. In some embodiments, a single remote server or single group of remote servers may be configured to perform more than one type of content rating and / or machine learning functionality.

[0079] Example network(s) may include, but are not limited to, any one or more different types of communications networks such as, for example, cable networks, public networks (e.g., the Internet), private networks (e.g., frame-relay networks), wireless networks, cellular networks, telephone networks (e.g., a public switched telephone network), or any other suitable private or public packet-switched or circuit-switched networks. Further, such network(s) may have any suitable communication range associated therewith and may include, for example, global networks (e.g., the Internet), metropolitan area networks (MANs), wide area networks (WANs), local area networks (LANs), or personal area networks (PANs). In addition, such network(s) may include communication links and associated networking devices (e.g., link-layer switches, routers, etc.) for transmitting network traffic over any suitable type of medium including, but not limited to, coaxial cable, twisted-pair wire (e.g., twisted-pair copper wire), optical fiber, a hybrid fiber-coaxial (HFC) medium, a microwave medium, a radio frequency communication medium, a satellite communication medium, or any combination thereof.

[0080] In an illustrative configuration, the computing device 1000 may include one or more processors (processor(s)) 1002, one or more memory devices 1004 (generically referred to herein as memory 1004), one or more input / output (I / O) interface(s) 1006, one or more network interface(s) 1008, and data storage 1020. The computing device 1000 may further include one or more buses 1018 that functionally couple various components of the computing device 1000. The computing device 1000 may further include one or more antenna(e) 1034 that may include, without limitation, a cellular antenna for transmitting or receiving signals to / from a cellular network infrastructure, an antenna for transmitting or receiving Wi-Fi signals to / from an access point (AP), a Global Navigation Satellite System (GNSS) antenna for receiving GNSS signals from a GNSS satellite, a Bluetooth antenna for transmitting or receiving Bluetooth signals, a Near Field Communication (NFC) antenna for transmitting or receiving NFC signals, and so forth. These various components will be described in more detail hereinafter.

[0081] The bus(es) 1018 may include at least one of a system bus, a memory bus, an address bus, or a message bus, and may permit exchange of information (e.g., data (including computerexecutable code), signaling, etc.) between various components of the computing device 1000. The bus(es) 1018 may include, without limitation, a memory bus or a memory controller, a peripheral bus, an accelerated graphics port, and so forth. The bus(es) 1018 may be associated with any suitable bus architecture including, without limitation, an Industry Standard Architecture (ISA), a Micro Channel Architecture (MCA), an Enhanced ISA (EISA), a Video Electronics Standards Association (VESA) architecture, an Accelerated Graphics Port (AGP) architecture, a Peripheral Component Interconnects (PCI) architecture, a PCI-Express architecture, a Personal Computer Memory Card International Association (PCMCIA) architecture, a Universal Serial Bus (USB) architecture, and so forth.

[0082] The memory 1004 of the computing device 1000 may include volatile memory (memory that maintains its state when supplied with power) such as random access memory (RAM) and / or non-volatile memory (memory that maintains its state even when not supplied with power) such as read-only memory (ROM), flash memory, ferroelectric RAM (FRAM), and so forth. Persistent data storage, as that term is used herein, may include non-volatile memory. In certain example embodiments, volatile memory may enable faster read / write access than nonvolatile memory' . However, in certain other example embodiments, certain types of non-volatile memory (e.g., FRAM) may enable faster read / write access than certain types of volatile memory. In various implementations, the memory 1004 may include multiple different types of memory such as various types of static random access memory (SRAM), various types of dynamic random access memory (DRAM), various types of unalterable ROM, and / or writeable variants of ROM such as electrically erasable programmable read-only memory (EEPROM), flash memory, and so forth. The memory 1004 may include main memory as well as various forms of cache memory such as instruction cache(s), data cache(s), translation lookaside buffer(s) (TLBs), and so forth. Further, cache memory such as a data cache may be a multi-level cache organized as a hierarchy of one or more cache levels (LI, L2, etc.).

[0083] The data storage 1020 may include removable storage and / or non-removable storage including, but not limited to, magnetic storage, optical disk storage, and / or tape storage. The data storage 1020 may provide non-volatile storage of computer-executable instructions and other data. The memory 1004 and the data storage 1020, removable and / or non-removable, are examples of computer-readable storage media (CRSM) as that term is used herein.

[0084] The data storage 1020 may store computer-executable code, instructions, or the like that may be loadable into the memory 1004 and executable by the processor(s) 1002 to cause the processor(s) 1002 to perform or initiate various operations. The data storage 1020 may additionally store data that may be copied to memory 1004 for use by the processor(s) 1002 during the execution of the computer-executable instructions. Moreover, output data generated as a result of execution of the computer-executable instructions by the processor(s) 1002 may be stored initially in memory 1004, and may ultimately be copied to data storage 1020 for nonvolatile storage.

[0085] More specifically, the data storage 1020 may store one or more operating systems (O / S) 1022; one or more database management systems (DBMS) 1024; and one or more program module(s), applications, engines, computer-executable code, scripts, or the like such as, for example, one or more module(s) 1027. Any of the components depicted as being stored in data storage 1020 may include any combination of software, firmware, and / or hardware. The software and / or firmware may include computer-executable code, instructions, or the like that may be loaded into the memory 1004 for execution by one or more of the processor(s) 1002. Any of the components depicted as being stored in data storage 1020 may support functionality described in reference to correspondingly named components earlier in this disclosure.

[0086] The data storage 1020 may further store various types of data utilized by components of the computing device 1000. Any data storage in the data storage 1020 may be loaded into the memory 1004 for use by the processor(s) 1002 in executing computer-executable code. In addition, any data depicted as being stored in the data storage 1020 may potentially be stored in one or more datastore(s) and may be accessed via the DBMS 1024 and loaded in the memory 1004 for use by the processor(s) 1002 in executing computer-executable code. The datastore(s) may include, but are not limited to, databases (e.g., relational, object-oriented, etc.), file systems, flat files, distributed datastores in which data is stored on more than one node of a computer network, peer-to-peer network datastores, or the like. In FIG. 10, the datastore(s) may include any types of data described herein or otherwise.

[0087] The processor(s) 1002 may be configured to access the memory 1004 and execute computer-executable instructions loaded therein. For example, the processor(s) 1002 may be configured to execute computer-executable instructions of the various program module(s), applications, engines, or the like of the computing device 1000 to cause or facilitate various operations to be performed in accordance with one or more embodiments of the disclosure. The processor(s) 1002 may include any suitable processing unit capable of accepting data as input, processing the input data in accordance with stored computer-executable instructions, and generating output data. The processor(s) 1002 may include any type of suitable processing unit including, but not limited to, a central processing unit, a microprocessor, a Reduced Instruction Set Computer (RISC) microprocessor, a Complex Instruction Set Computer (CISC) microprocessor, a microcontroller, an Application Specific Integrated Circuit (ASIC), a Field- Programmable Gate Array (FPGA), a System-on-a-Chip (SoC), a digital signal processor (DSP), and so forth. Further, the processor(s) 1002 may have any suitable microarchitecture design that includes any number of constituent components such as, for example, registers, multiplexers, arithmetic logic units, cache controllers for controlling read / write operations to cache memory, branch predictors, or the like. The microarchitecture design of the processor(s) 1002 may be capable of supporting any of a variety of instruction sets.

[0088] Referring now to other illustrative components depicted as being stored in the data storage 1020, the O / S 1022 may be loaded from the data storage 1020 into the memory 1004 and may provide an interface between other application software executing on the computing device 1000 and hardware resources of the computing device 1000. More specifically, the O / S 1022 may include a set of computer-executable instructions for managing hardware resources of the computing device 1000 and for providing common services to other application programs (e.g., managing memory allocation among various application programs). In certain example embodiments, the O / S 1022 may control execution of the other program module(s) to dynamically enhance characters for content rendering. The O / S 1022 may include any operating system now known or which may be developed in the future including, but not limited to, any server operating system, any mainframe operating system, or any other proprietary or nonproprietary operating system. The DBMS 1024 may be loaded into the memory' 1004 and may support functionality for accessing, retrieving, storing, and / or manipulating data storaged in the memory 1004 and / or data storaged in the data storage 1020. The DBMS 1024 may use any of a variety of database models (e.g., relational model, object model, etc.) and may support any of a variety of query languages. The DBMS 1024 may access data represented in one or more data schemas and stored in any suitable data repository including, but not limited to, databases (e.g., relational, object-oriented, etc.), file systems, flat files, distributed datastores in which data is stored on more than one node of a computer network, peer-to-peer network datastores, or the like. In those example embodiments in which the computing device 1000 is a user device, the DBMS 1024 may be any suitable light-weight DBMS optimized for performance on a user device.

[0089] Referring now to other illustrative components of the computing device 1000, the input / output (I / O) interface(s) 1006 may facilitate the receipt of input information by the computing device 1000 from one or more I / O devices as well as the output of information from the computing device 1000 to the one or more I / O devices. The I / O devices may include any of a variety of components such as a display or display screen having a touch surface or touchscreen; an audio output device for producing sound, such as a speaker; an audio capture device, such as a microphone; an image and / or video capture device, such as a camera; a haptic unit; and so forth. Any of these components may be integrated into the computing device 1000 or may be separate. The I / O devices may further include, for example, any number of peripheral devices such as data storage devices, printing devices, and so forth.

[0090] The I / O interface(s) 1006 may also include an interface for an external peripheral device connection such as universal serial bus (USB), FireWire, Thunderbolt, Ethernet port or other connection protocol that may connect to one or more networks. The I / O interface(s) 1006 may also include a connection to one or more of the antenna(e) 1034 to connect to one or more networks via a wireless local area network (WLAN) (such as Wi-Fi) radio, Bluetooth, ZigBee, and / or a wireless network radio, such as a radio capable of communication with a wireless communication network such as a Long Term Evolution (LTE) network, WiMAX network, 3G network, ZigBee network, etc.

[0091] The computing device 1000 may further include one or more network interface(s) 1008 via which the computing device 1000 may communicate with any of a variety of other systems, platforms, networks, devices, and so forth. The network interface(s) 1008 may enable communication, for example, with one or more wireless routers, one or more host servers, one or more web servers, and the like via one or more of networks.

[0092] It should be appreciated that the program module(s), applications, computer-executable instructions, code, or the like depicted in FIG. 10 as being stored in the data storage 1020 are merely illustrative and not exhaustive and that processing described as being supported by any particular module may alternatively be distributed across multiple module(s) or performed by a different module. In addition, various program module(s), script(s), plug-in(s), Application Programming Interface(s) (API(s)), or any other suitable computer-executable code hosted locally on the computing device 1000, and / or hosted on other computing device(s) accessible via one or more networks, may be provided to support functionality provided by the program module(s), applications, or computer-executable code depicted in FIG. 10 and / or additional or alternate functionality. Further, functionality may be modularized differently such that processing described as being supported collectively by the collection of program module(s) depicted in FIG. 10 may be performed by a fewer or greater number of module(s), or functionality described as being supported by any particular module may be supported, at least in part, by another module. In addition, program module(s) that support the functionality described herein may form part of one or more applications executable across any number of systems or devices in accordance with any suitable computing model such as, for example, a client-server model, a peer-to-peer model, and so forth. In addition, any of the functionality described as being supported by any of the program module(s) depicted in FIG. 10 may be implemented, at least partially, in hardware and / or firmware across any number of devices.

[0093] It should further be appreciated that the computing device 1000 may include alternate and / or additional hardware, software, or firmware components beyond those described or depicted without departing from the scope of the disclosure. More particularly, it should be appreciated that software, firmware, or hardware components depicted as forming part of the computing device 1000 are merely illustrative and that some components may not be present or additional components may be provided in various embodiments. While various illustrative program module(s) have been depicted and described as software module(s) stored in data storage 1020, it should be appreciated that functionality described as being supported by the program module(s) may be enabled by any combination of hardware, software, and / or firmware. It should further be appreciated that each of the above-mentioned module(s) may, in various embodiments, represent a logical partitioning of supported functionality. This logical partitioning is depicted for ease of explanation of the functionality and may not be representative of the structure of software, hardware, and / or firmware for implementing the functionality. Accordingly, it should be appreciated that functionality described as being provided by a particular module may, in various embodiments, be provided at least in part by one or more other module(s). Further, one or more depicted module(s) may not be present in certain embodiments, while in other embodiments, additional module(s) not depicted may be present and may support at least a portion of the described functionality and / or additional functionality. Moreover, while certain module(s) may be depicted and described as sub-module(s) of another module, in certain embodiments, such module(s) may be provided as independent module(s) or as sub-module(s) of other module(s).

[0094] Program module(s), applications, or the like disclosed herein may include one or more software components including, for example, software objects, methods, data structures, or the like. Each such software component may include computer-executable instructions that, responsive to execution, cause at least a portion of the functionality described herein (e.g., one or more operations of the illustrative methods described herein) to be performed.

[0095] A software component may be coded in any of a variety of programming languages. An illustrative programming language may be a lower-level programming language such as an assembly language associated with a particular hardware architecture and / or operating system platform. A software component comprising assembly language instructions may require conversion into executable machine code by an assembler prior to execution by the hardware architecture and / or platform.

[0096] Another example programming language may be a higher-level programming language that may be portable across multiple architectures. A software component comprising higher- level programming language instructions may require conversion to an intermediate representation by an interpreter or a compiler prior to execution.

[0097] Other examples of programming languages include, but are not limited to, a macro language, a shell or command language, a job control language, a script language, a database query or search language, or a report writing language. In one or more example embodiments, a software component comprising instructions in one of the foregoing examples of programming languages may be executed directly by an operating system or other software component without having to be first transformed into another form.

[0098] A software component may be stored as a file or other data storage construct. Software components of a similar type or functionally related may be stored together such as, for example, in a particular directory, folder, or library. Software components may be static (e.g., pre-established or fixed) or dynamic (e g., created or modified at the time of execution).

[0099] Software components may invoke or be invoked by other software components through any of a wide variety of mechanisms. Invoked or invoking software components may comprise other custom-developed application software, operating system functionality (e.g., device drivers, data storage (e.g., file management) routines, other common routines and services, etc.), or third-party software components (e.g., middleware, encryption, or other security software, database management software, file transfer or other network communication software, mathematical or statistical software, image processing software, and format translation software).

[0100] Software components associated with a particular solution or system may reside and be executed on a single platform or may be distributed across multiple platforms. The multiple platforms may be associated with more than one hardware vendor, underlying chip technology, or operating system. Furthermore, software components associated with a particular solution or system may be initially written in one or more programming languages, but may invoke software components written in another programming language.

[0101] Computer-executable program instructions may be loaded onto a special-purpose computer or other particular machine, a processor, or other programmable data processing apparatus to produce a particular machine, such that execution of the instructions on the computer, processor, or other programmable data processing apparatus causes one or more functions or operations specified in the flow diagrams to be performed. These computer program instructions may also be stored in a computer-readable storage medium (CRSM) that upon execution may direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means that implement one or more functions or operations specified in the flow diagrams. The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational elements or steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process.

[0102] Additional types of CRSM that may be present in any of the devices described herein may include, but are not limited to, programmable random access memory' (PRAM), SRAM, DRAM, RAM, ROM, electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technology, compact disc read-only memory (CD-ROM), digital versatile disc (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the information and which can be accessed. Combinations of any of the above are also included within the scope of CRSM. Alternatively, computer-readable communication media (CRCM) may include computer-readable instructions, program module(s), or other data transmitted within a data signal, such as a carrier wave, or other transmission. However, as used herein, CRSM does not include CRCM.

[0103] Although embodiments have been described in language specific to structural features and / or methodological acts, it is to be understood that the disclosure is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as illustrative forms of implementing the embodiments. Conditional language, such as, among others, “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments could include, while other embodiments do not include, certain features, elements, and / or steps. Thus, such conditional language is not generally intended to imply that features, elements, and / or steps are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without user input or prompting, whether these features, elements, and / or steps are included or are to be performed in any particular embodiment.

[0104] Examples

[0105] The present invention is further illustrated by the following examples, which are not to be construed in any way as imposing limitations upon the scope thereof. On the contrary, it is to be clearly understood that resort may be had to various other aspects, embodiments, modifications, and equivalents thereof which, after reading the description herein, may suggest themselves to one of ordinary skill in the art without departing from the spirit of the present invention or the scope of the appended claims. Thus, other aspects of this invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein.

[0106] Materials and Methods

[0107] Cell Cultures. Two suspension-adapted, serum-free human embryonic kidney cell lines (HEK 293) were used to demonstrate the use of magnetic resonance relaxometry measurements in perfusion bioprocessing. A HEK293 cell line clonally selected for rAAV productivity was cultured with Peak expression medium. A HEK293 producer clone engineered to generate LV- CMV-GFP lentiviral vectors following the addition of cumate and coumermycin was cultured with Hycell-Transfx-H (Cytiva) supplemented with 4 mM L- 148 glutamine, surfactant Kolliphor Pl 88 0.1% v / v media, and 1% v / v penicillin-streptomycin. Both cell lines were cultured in a 125 mL shake culture flask with 50 rnL of volume. The cells were passaged every four days by seeding the cells with 0.4 x 106 cells / mL of density. Culture flasks were incubated on an orbital shaker spinning at 140 rpm, located in a cell culture incubator controlling the CO2 and temperature as 5.0% and 37°C, respectively. An IgG-producing CHO cell line was used for R2 calibration. The CHO cells were cultured with 4Cell Smart CHO Stock and Adaptation Medium in 125 mL shake culture flask with 50 mL of volume. The CHO cell culture flask was shaken at 170 rpm by an orbital shaker inside a cell culture incubator with 7% of CO2 and 37°C.

[0108] VCD-R2 Calibration. A 5 mL sample of HEK293 cells with a viable cell density of 1.2 x 107 cell / mL is first concentrated to 2.4 x 107 cell / mL when half of the HEK293 medium was removed through centrifugation at 100g for five minutes. Nine samples were prepared by mixing different fractions of the 2.4 x 107 cell / mL suspension and the now cell-free media from the previous step. Each sample was measured in a commercial 0.5 T 172 relaxometer, and the true cell densities were determined afterward using a cell culture analyzer. To confirm that the relationship between the cell density and sample R2 generalizes to other cell lines, this experiment was repeated with Chinese hamster ovary (CHO) cells, another important cell line in the field of biomanufacturing.

[0109] Cell Viability Calibration. Ten samples of HEK293 cells at different percent viabilities (0-90%) were prepared by mixing live cells with identical cells that were heat killed at 70°C for 10 minutes. Each sample was initially centrifuged at 300g for two minutes and 30 seconds to concentrate the cells, and then around 60 pL of the cell pellet was loaded into capillary tubes and centrifuged at 4000g for two minutes to remove as much supernatant as possible. Finally, the pellet in each capillary was measured in a benchtop relaxometry system. An additional sample of pure dead cells was resuspended after centrifugation at 4000g in a capillary tube and imaged to assess the integrity of the dead cells’ membranes after pelleting.

[0110] Bioreactor Setup. Samples for relaxometry measurements are typically contained in a glass capillary tube that is loaded into the system prior to the measurement and discarded afterward. For continuous monitoring, the system may combine a relaxometer with a magnet and probe assembly installed around the bioreactor’s tubing so that the sample never leaves the reactor or encounters the probe.

[0111] A 500 mL bioreactor from was connected to a series of peristaltic pumps that control the rate of nutrient addition and cell harvesting to maintain optimal nutrient and waste concentrations. The oxygen saturation was fixed at 60%, and the pH was fixed at 7.2. The relaxometer was connected to a branch of the tubing that connects the bioreactor to the microfluidic cell retention device, which sees a continuous flow of cells from the bioreactor. The cells were returned to the same tube in the first two cultures, while in the third culture they were returned to the retentate stream (in every case, they are pumped back into the bioreactor). The first culture uses HEK293 cells, while the second and third cultures use HEK293 cells. The true cell density and viability were measured once or twice daily using the cell culture analyzer. For the first bioreactor run, additional samples were removed each day and centrifuged to remove the media, and the R2 of the resulting pellet is measured offline. This makes it possible to monitor variation in the R2 caused by variation within the cells themselves rather than in the cell density.

[0112] Probe and Magnet Assembly. A uniform, static magnetic field over the sample detection volume is important for high-quality measurements, especially in this system, where no shimming coils are employed to increase uniformity. The proton resonant frequency depends linearly on BO, which may drift significantly with changes in the temperature of the room. While it is possible to calibrate the measurement frequency, each calibration is imperfect and results in some random variation around the resonant frequency. Because the relaxation measurement is affected by even small frequency errors, the system was calibrated only once at the beginning of the experiment, and the temperature of the magnet was held within 0.001 °C throughout the duration of the culture. This keeps temperature-induced variations in the measurement small enough to be insignificant and eliminates the noise created by random variations in the calibration. The magnet was a 0.5T model NMR permanent magnet, which was mounted within an aluminum box to eliminate any temperature gradient that might lead to magnetic field inhomogeneity. The f2 outside of this box was fitted with 10 small heaters, which were all driven by a large linear amplifier to maintain the magnet temperature at 25.5 °C for the duration of the experiment. The entire assembly was coated in insulating foam to further isolate it from room temperature. A solenoidal RF coil was tuned to generate the excitation field and act as a detection coil for receiving the NMR signal. The coil was tuned to resonate at the Larmor frequency of the sample to maximize sensitivity and matched to the 50 Q impedance of the transmitter and receiver to facilitate power transfer. A high coil inductance may be because the signal-to-noise ratio is proportional to the square root of the quality factor (Q), which is maximized by increasing inductance in the resonant circuit that comprises the probe. To guarantee that the addition of the monitoring system does not have any impact on the operation of the bioreactor, the coil was wound around the same silicone tubing used to connect different parts of the bioreactor together; 96% of the coil volume was filled with silicone, which produces a strong signal that overwhelms the signal from the cells and medium. Fortunately, because the silicone has a much shorter T2 (about 40 ms) than the water and cells, after the first 1000 echoes, the signal from the tubing is insignificant and can be ignored. The receiver amplifier gain was set for the best reception of the weaker water signal after the first thousand echoes, and as a result, the first part of each scan saturated the amplifiers in the receiver. Suppression of the silicone signal could also be achieved using the inversion recovery technique, but this might bias the multicomponent decay signal toward longer decay times from free media and lower the sensitivity to the cells.

[0113] Results and Discussion

[0114] Calibration and Offline Benchmarking. To establish the relationship between the cell density and R2 relaxation time, samples with controlled cell densities were measured in an offline benchtop relaxometer. FIGS. 7A-7B show a strong correlation between the cell density of samples and the sample R2 for both HEK293 and CHO cells. In general, the relationship between true cell density and the R2 is complex and strongly dependent on the pulse sequence parameters used to perform the measurement, the magnet, the media, and the cell type. At low cell densities and high intracellular iron concentrations, it may be possible to model the cells as highly magnetized spherical magnetic perturbers. However, most of the water within the cells at the beginning of a measurement may have diffused out of the cells in far less time than the duration of the experiment, and this suggests a significant contribution from interactions with intracellular macromolecules that is not captured by these simplified models, particularly at high cell densities.

[0115] While there are strong correlations between VCD and R2 for both cell ty pes, the R2 values for pure samples of the two types of cell growth medium may be different. In the benchtop system used for this experiment, the CHO cell medium had a cell-free R2 of 1.34 s-1, while the HEK cell medium had a cell-free R2 of 0.52 s-1. This could be caused by differences in the iron or oxygen content in the medium, or other properties such as viscosity. Because the relationships among cell density, media parameters, and bulk R2 are complex, changes to the media may be expected to change the relationship between R2 and cell density for the culture.

[0116] In practice, this is best addressed through careful calibration of the instrument on each cell type and medium used during culture. For the cultures described herein, where culture conditions change frequently between and even during bioreactor runs, relaxometry is the most useful as a qualitative measure of the cell growth rate. Furthermore, confounding factors that are actively controlled by the bioreactor system, such as dissolved oxygen, may not affect the trends in the data. In an industrial setting where the operating conditions are carefully controlled, it may be possible to measure the relationship between the relaxation time and cell density and use that consistently for the quantitative estimation of the cell density.

[0117] Online Culture Monitoring. Three independent HEK293 cultures were monitored with the online relaxometry system (FIGS. 8A-8C). In run one, the flow through the magnet was stopped for 10 seconds to allow measurements to be taken once every 10 min. In runs two and three, the measurement frequency was increased to once every two minutes. The raw relaxometry readings may be noisy due to the small fraction of the coil volume that is filled with cells and media and the electrically noisy environment of the laboratory. The raw data was digitally filtered by the computer to improve the accuracy of the cell density estimation at the expense of the response time of the relaxometry data. Multiple filters can be used simultaneously to allow for different observations. For example, the slowly changing cell density may be best characterized with low cutoff frequencies, while problems like cell clumping, bubbles, and catastrophic failure (such as the leak that ended Run two) can be detected in minutes without filtering. The R2 data quickly reflects many critical changes to the cultures. In run one, most of the cells were removed from the bioreactor on day four to simulate a harvest, and an antidumping agent (ACA) was added. On day eight, some cells were diverted into the harvest through the cell retention device, causing a loss of cells for several hours. On day 13, the stirrer that keeps the cells in suspension was disabled for an hour, causing a rapid but temporary drop in the cell density. In run two, cells were removed on day seven and reintroduced on day eight. In Run three, cells were removed on day six.

[0118] For run one, the raw relaxometry estimates over a period of one day had a standard deviation of 1.2 x 106 cells / mL, compared to 0.8 * 106 cells / mL for the cytometry measurements. Before filtering, the drop in cell density following the removal of the cells is apparent after only 10 minutes. With causal lowpass filtering to reduce the standard deviation of cell density measurements over one day to 0.7 x 106 cells / mL, this drop may be detectable after 40 minutes. The catastrophic leak that ended the second culture was initially detected within two minutes as anomalous readings by the system and confirmed by the absence of the water signal in the raw data from experiments after the leak. Anomalous readings between the beginning of day one and the beginning of day one in run three were caused by changes in the flow direction through the tubing leading to the magnet.

[0119] In both run one and run two, the relationship between VCD and R2 changes during the culture. At the beginning and end of each culture, there is disagreement between the ground truth measurements and the trend in the R2 data. At the beginning of run one, living cells formed clumps which reduced the per-cell contribution to R2 and caused the relaxometer to underestimate the true cell density. After the addition of ACA, the live cell clumps were dissociated, allowing these previously clumped cells to contribute independently to the R2 so that they are correctly reflected in the relaxometry data.

[0120] Changes in the cells and media during the culture are also potential contributors to variation in the relationship between R2 and cell density over time. For example, increases in the average cell size or the iron concentration of the media could increase the relaxation rate even if the cell number is fixed. Differences between the runs, even controlling for the cell number and media type, can be explained by differences in the specific cell type, the bioreactor setups and flow rates, and the position of the magnet and coil within the system.

[0121] The R2 rates of the pelleted cell samples removed from the bioreactor did not change significantly during Run one. This confirms that the measured R2 signal is mainly determined by the cell number or cell density.

[0122] Correlation with Cell Viability. While the largest contributor to changes in the R2 was the cell density, we expect the intrinsic R2 of the cells to vary subtly over the course of the culture in ways that correlate to changes in cells’ phenotype and offer insight into the culture that is not possible with optical cytometry or other cell characterization technologies.

[0123] To investigate the sensitivity of R2 to cell viability, samples of pelleted HEK293 cells were prepared with different proportions of heat-killed cells. There was a clear variation in the pellet R2 with the viability. This suggests that viability is a confounding factor in cell density measurements taken on a mixture of cells and media. At typical cell densities, the signal contribution from the intracellular media is low compared to that from the surrounding media and the resulting bulk R2 is decoupled from the intrinsic relaxation rate of the cells themselves. Importantly, the relaxation rates of pelleted cell samples are different from the relaxation rates of those same cells in suspension, since the reduced diffusion rate and highly complex structure of the cell pellet increase the relaxation rate of the pellet. Because the percent viability is held relatively constant in the perfusion bioreactor runs, the cell density measurements are largely unaffected.

[0124] It is possible that the disrupted membranes in dead cells cause them to be packed more tightly by the centrifuge, which could explain the shorter T2 times of the dead cells. However, the microscopic examination of the live and dead cells after centrifugation shows that both cell types still have visible membranes.

[0125] Example Embodiments

[0126] Embodiment 1. A system for monitoring a bioreactor, the system comprising: a bioreactor vessel configured to contain a biological cell culture; a tube in fluid communication with the bioreactor vessel; a first pump configured to pump a sample of the biological cell culture through the tube; and a magnetic resonance relaxometry (MRR) device configured to measure a relaxometry signal of water in the sample in the tube, for example as the sample flows through or is paused within the tube.

[0127] Embodiment 2. The system of embodiment 1, wherein the sy stem is configured to measure a density of cells in the sample based on the relaxometry signal.

[0128] Embodiment 3. The system of embodiment 1 or 2, wherein the tube is part of a bypass loop having an inlet and an outlet which are connected to a primary recirculation loop comprising a second pump.

[0129] Embodiment 4. The system of any one of embodiments 1 to 3, wherein the primary recirculation loop is in fluid communication with a cell retention device configured for separating cells and media.

[0130] Embodiment 5. The system of any one of embodiments 1 to 4, wherein the MRR device comprises a thermally insulating enclosure in which a magnet is disposed and configured to produce a magnetic field through the sample in a portion of the tube within the enclosure. Embodiment 6. The system of any one of embodiments 1 to 5, wherein the MRR device further comprises a heating element configured to maintain a selected temperature within the insulating enclosure.

[0131] Embodiment 7. The system of any one of embodiments 1 to 6, wherein the MRR device further comprises a probe assembly in electrical communication with a radio and disposed operably adjacent to the portion of the tube within the enclosure.

[0132] Embodiment 8. The system of any one of embodiments 1 to 7, wherein the system is configured to temporarily cease operation of the first pump during a measurement of the sample.

[0133] Embodiment 9. A method of measuring cell density in a bioreactor, the method comprising: pumping, by a first pump, a sample of a culture of biological cells from a bioreactor vessel and through a tube in fluid communication with the bioreactor vessel; measuring, by a magnetic resonance relaxometry (MRR) device, a T2 relaxometry of water in the sample in the tube, for example as the sample flows through or is paused within the tube; and determining a density of cells in the sample based on the relaxometry of the water in the sample.

[0134] Embodiment 10. The method of embodiment 9, wherein the MRR device comprises a thermally insulating enclosure in which one or more magnets are disposed, wherein the one or more magnets produce a magnetic field through the sample in a portion of the tube within the enclosure.

[0135] Embodiment 11. The method of embodiment 9 or 10, wherein the one or more magnets produce a OAT magnetic field.

[0136] Embodiment 12. The method of any one of embodiments 9 to 11, comprising activating a heating element disposed within the thermally insulating enclosure to maintain a selected temperature within the insulating enclosure.

[0137] Embodiment 13. The method of any one of embodiments 9 to 12, wherein measuring the T2 relaxometry of the sample within the tube further comprises temporarily ceasing operation of the first pump.

[0138] Embodiment 14. The method of any one of embodiments 9 to 13, further comprising: returning the sample from the tube back into the bioreactor vessel, for example via at least the first pump.

[0139] Embodiment 15. The method of any one of embodiments 9 to 14, wherein the tube is part of a bypass loop having an inlet and an outlet which are connected to a primary recirculation loop comprising a second pump.

[0140] Embodiment 16. The method of embodiment 15, wherein: the sample is pumped, via the first pump, from the bypass loop into the recirculation loop; and the sample is pumped, via the second pump, from the recirculation loop into the bioreactor vessel. Embodiment 17. A magnetic resonance relaxometry (MRR) device for measuring cell density, the device comprising: a thermally insulating enclosure; a probe assembly configured to receive a portion of a tube of a bioreactor, wherein the tube is configured such that a sample of a biological cell culture of the bioreactor flows through the tube, and wherein the probe assembly is configured to be inserted into the insulating enclosure; and one or more magnets disposed within the insulating enclosure and configured to produce a magnetic field through the sample in the portion of the tube.

[0141] Embodiment 18. The MRR device of any one of embodiments 1 to 17, further comprising: a heating element configured to maintain a selected temperature within the insulating enclosure.

[0142] Embodiment 19. The MRR device of any one of embodiments 1 to 18, further comprising: a second enclosure positioned between the magnet and the insulating enclosure, wherein the second enclosure is configured to distribute heat produced by the heating element evenly over the magnet. Embodiment 20. The MRR device of any one of embodiments 1 to 19, further comprising: a radio configured to generate a radio frequency signal and receive a return signal from the sample.

Claims

CLAIMSTHAT WHICH IS CLAIMED IS:

1. A system for monitoring a bioreactor, the system comprising: a bioreactor vessel configured to contain a biological cell culture; a tube in fluid communication with the bioreactor vessel; a first pump configured to pump a sample of the biological cell culture through the tube; and a magnetic resonance relaxometry (MRR) device configured to measure a relaxometry signal of water in the sample in the tube.

2. The system of claim 1, wherein the system is configured to measure a density of cells in the sample based on the relaxometry signal.

3. The system of claim 2, wherein the tube is part of a bypass loop having an inlet and an outlet which are connected to a primary recirculation loop comprising a second pump.

4. The system of claim 3, wherein the primary recirculation loop is in fluid communication with a cell retention device configured for separating cells and media.

5. The system of claim 1, wherein the MRR device comprises a thermally insulating enclosure in which a magnet is disposed and configured to produce a magnetic field through the sample in a portion of the tube within the enclosure.

6. The system of claim 5, wherein the MRR device further comprises a heating element configured to maintain a selected temperature within the insulating enclosure.

7. The system of claim 5, wherein the MRR device further comprises a probe assembly in electrical communication with a radio and disposed operably adjacent to the portion of the tube within the enclosure.

8. The system of any one of claims 1 to 7, wherein the system is configured to temporarily cease operation of the first pump during a measurement of the sample.

9. A method of measuring cell density in a bioreactor, the method comprising:pumping, by a first pump, a sample of a culture of biological cells from a bioreactor vessel and through a tube in fluid communication with the bioreactor vessel; measuring, by a magnetic resonance relaxometry (MRR) device, a T2 relaxometry of water in the sample in the tube; and determining a density of cells in the sample based on the relaxometry of the water in the sample.

10. The method of claim 9, wherein the MRR device comprises a thermally insulating enclosure in which one or more magnets are disposed, wherein the one or more magnets produce a magnetic field through the sample in a portion of the tube within the enclosure.

11. The method of claim 10, wherein the one or more magnets produce a 0.5T magnetic field.

12. The method of claim 10, comprising activating a heating element disposed within the thermally insulating enclosure to maintain a selected temperature within the insulating enclosure.

13. The method of claim 9, wherein measuring the T2 relaxometry of the sample within the tube further comprises temporarily ceasing operation of the first pump.

14. The method of claim 9, further comprising: returning the sample from the tube back into the bioreactor vessel.

15. The method of claim 9, wherein the tube is part of a bypass loop having an inlet and an outlet which are connected to a primary recirculation loop comprising a second pump.

16. The method of claim 15, wherein: the sample is pumped, via the first pump, from the bypass loop into the recirculation loop; and the sample is pumped, via the second pump, from the recirculation loop into the bioreactor vessel.

17. A magnetic resonance relaxometry (MRR) device for measuring cell densify, the device comprising: an insulating enclosure; a probe assembly configured to receive a portion of a tube of a bioreactor, wherein the tube is configured such that a sample of a biological cell culture of the bioreactor flows through the tube, and wherein the probe assembly is configured to be inserted into the insulating enclosure; and one or more magnets disposed within the insulating enclosure and configured to produce a magnetic field through the sample in the portion of the tube.

18. The MRR device of claim 17, further comprising: a heating element configured to maintain a selected temperature within the insulating enclosure.

19. The MRR device of claim 18, further comprising: a second enclosure positioned between the magnet and the insulating enclosure, wherein the second enclosure is configured to distribute heat produced by the heating element evenly over the magnet.

20. The MRR device of claim 17, further comprising: a radio configured to generate a radio frequency signal and receive a return signal from the sample.

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