3D-printed dissolvable inserts for efficient and customizable fabrication of NMR transceiver coils

A Practical Guide to 3D Printing for Chemistry and Biology Laboratories

Three-dimensional (3D) printing promises a revolution in laboratory creativity by enabling rapid prototyping, broader availability of scientific apparatuses, and transformative scientific workflows. We believe all chemistry and biology laboratories should equip themselves with one or more 3D printers and a critical mass of scientists trained to operate them. This overview surveys the techniques, intricacies, and pitfalls associated with 3D printing of functional parts, including measurements, computer-aided design, slicing, limitations of 3D printing, troubleshooting, tips for tricky filaments, and 3D printer maintenance. A flow cells are essential tools in chemistry and biology laboratories, we discuss techniques relevant to the construction of watertight 3D-printed parts. Finally, we articulate a set of principles required for reporting 3D-printed innovations to improve the field's reproducibility and encourage iterative improvements by other scientists. Ideally, authors, peer reviewers, and editors will adopt these principles. We hope these protocols inspire a new generation of publications applying 3D printing in chemistry and biology-especially highly reproducible inventions with the requisite detail and associated documentation. Such reports will facilitate broad adoption and creative iteration of the most innovative designs, thus accelerating discovery in chemistry and biology. © 2024 The Author(s). Current Protocols published by Wiley Periodicals LLC.

A complete 3D-printed tool kit for Solid-State NMR sample and rotor handling

Solid state NMR (SSNMR) is a highly versatile and broadly applicable method for studying the structure and dynamics of biomolecules and materials. For scientists entering the field of SSNMR, the many quotidian activities required in the workflow to prepare samples for data collection can present a significant barrier to adoption. These steps include transfer of samples into rotors, marking the reflective surfaces for high sensitivity tachometer signal detection, inserting rotors into the magic-angle spinning (MAS) stator, achieving stable spinning, and removing and storing rotors to ensure reproducibility of data collection conditions. Even experienced spectroscopists experience occasional problems with these operations, and the cumulative probability of a delay to successful data collection is high enough to cause frequent disruptions to instrument schedules, particularly in the context of large facilities serving a diverse community of users. These problems are all amplified when utilizing rotors smaller than about 4 mm in diameter. Therefore, to improve the reliability and robustness of SSNMR sample preparation workflows, here we describe a set of tools for rotor packing, unpacking, tachometer marking, extraction and storage. Stereolithography 3D printing was employed as a cost-effective and convenient method for prototyping and manufacturing a full range of designs suitable for several types of probes and rotor geometries.

Design and optimization of THz coupling in zirconia MAS rotors for dynamic nuclear polarization NMR

We present 3D electromagnetic simulations of the coupling of a 250 GHz beam to the sample in a 380 MHz DNP NMR spectrometer. To obtain accurate results for magic angle spinning (MAS) geometries, we first measured the complex dielectric constants of zirconia, sapphire, and the sample matrix material (DNP juice) from room temperature down to cryogenic temperatures and from 220 to 325 GHz with a VNA and up to 1 THz with a THz TDS system. Simulations of the coupling to the sample were carried out with the ANSYS HFSS code as a function of the rotor wall material (zirconia or sapphire), the rotor wall thickness, and the THz beam focusing (lens or no lens). For a zirconia rotor, the B1 field in the sample was found to be strongly dependent on the rotor wall thickness, which is attributed to the high refractive index of zirconia. The optimum thickness of the wall is likely due to a transmission maximum but is offset from the thickness predicted by a simple calculation for a flat slab of the wall material. The B1 value was found to be larger for a sapphire rotor than for a zirconia rotor for all cases studied. The results found in this work provide new insights into the coupling of THz radiation to the sample and should lead to improved designs of future DNP NMR instrumentation.

Automated test apparatus for bench-testing the magnetic field homogeneity of NMR transceiver coils

We describe an automated hands-off bench testing method for measuring the magnetic field profile of transceiver coils for nuclear magnetic resonance (NMR). The scattering parameter (S-parameter) data is measured using a portable network analyzer, and the results are automatically exported to a computer for plotting and viewing. This assay dramatically reduces the time needed to measure the magnetic field (B1) homogeneity profile of a transceiver coil while also improving accuracy relative to manual operation. Here, we demonstrate the method on a saddle coil of a solution-state NMR probe in comparison to profiles obtained using NMR spectroscopy measurements. We also measure the axial and radial homogeneity of a variable-pitch solenoid.

New unifying metric for NMR/MRI probe evaluation based on optimized solenoid coil geometry

A three-dimensional numerical simulation of the magnetic field distribution and Bloch equations for arbitrary radio frequency (RF) coils is developed and compared against nuclear magnetic resonance (NMR) experimental results to evaluate the NMR signal intensity. Because NMR is inherently insensitive and its signal intensity is dependent on RF coil geometry, the investigation of RF coil geometry to maximize signal intensity for a given sample volume is important for improving the signal-to-noise ratio (SNR) and shortening the accumulation time. The developed simulation can optimize the RF coil geometry, specifically a single-layer solenoid coil with a constant winding pitch, and the result of the solenoid coil simulation serves as a new unifying metric for evaluating NMR/MRI probes. It is found that the most efficient sample aspect ratio (ratio of sample length to sample diameter) and pitch to wire diameter ratio for the highest signal intensity are around 2.2 and 1.65, respectively. Some discrepancies from the solenoid coil geometry ratios for higher signal intensity in previous studies can be explained by the difference in the gap between the inner diameter of the solenoid coil and the sample diameter. These results are confirmed through NMR signal intensity expressed in voltages with three approaches: 3D simulation, experiment, and estimation based on probe parameters. The simulated signal intensity shows a maximum error of approximately 5 % and an average error of 1 % when compared to the experimental results. This result suggests that the developed methods hold the potential for application in quantitative NMR (qNMR) without relying on standard reference materials. Finally, this study introduces a standardized geometry for the optimized solenoid coil for higher signal intensity and uses it to establish an evaluation metric called the signal-to-optimized-solenoid-signal ratio (3SR). The 3SR addresses the volume-dependence problem in conventional metrics like SNR and SNR per sample volume. It provides a standardized approach for the unified evaluation of all RF coils and probe designs, regardless of sample volume and measurement frequency. Therefore, 3SR can be utilized as a useful metric in the search for optimal coil geometry, while metrics such as SNR or SNR per sample volume are currently used for such purpose. This metric is expected to be useful for NMR/magnetic resonance imaging (MRI) users and developers.

Cryogenic-compatible spherical rotors and stators for magic angle spinning dynamic nuclear polarization

Cryogenic magic angle spinning (MAS) is a standard technique utilized for dynamic nuclear polarization (DNP) in solid-state nuclear magnetic resonance (NMR). Here we describe the optimization and implementation of a stator for cryogenic MAS with 9.5 mm diameter spherical rotors, allowing for DNP experiments on large sample volumes. Designs of the stator and rotor for cryogenic MAS build on recent advancements of MAS spheres and take a step further to incorporate sample insert and eject and a temperature-independent spinning stability of ± 1  Hz. At a field of 7 T and spinning at 2.0 kHz with a sample temperature of 105-107 K, DNP enhancements of 256 and 200 were observed for 124 and 223 µ L sample volumes, respectively, each consisting of 4 M 13 C, 15 N-labeled urea and 20 mM AMUPol in a glycerol-water glassy matrix.

3D-Printable centrifugal devices for biomolecular solid state NMR rotors

The advent of magic angle spinning (MAS) rates exceeding 100 kHz has facilitated the acquisition of 1H-detected solid-state NMR spectra of biomolecules with high resolution. However, challenges can arise when preparing rotors for these experiments, due to the physical properties of biomolecular solid samples and the small dimensions of the rotors. In this study, we have designed 3D-printable centrifugal devices that facilitate efficient and consistent packing of crystalline protein slurries or viscous phospholipids into 0.7 mm rotors. We demonstrate the efficacy of these packing devices using 1H-detected solid state NMR at 105 kHz. In addition to devices for 0.7 mm rotors, we have also developed devices for other frequently employed rotor sizes and styles. We have made all our designs openly accessible, and we encourage their usage and ongoing development as a shared effort within the solid state NMR community.

Performance of the cross-polarization experiment in conditions of radiofrequency field inhomogeneity and slow to ultrafast magic angle spinning (MAS)

In this paper, we provide an analytical description of the performance of the cross-polarization (CP) experiment, including linear ramps and adiabatic tangential sweeps, using effective Hamiltonians and simple rotations in 3D space. It is shown that radiofrequency field inhomogeneity induces a reduction in the transfer efficiency at increasing magic angle spinning (MAS) frequencies for both the ramp and the adiabatic CP experiments. The effect depends on the ratio of the dipolar coupling constant and the sample rotation frequency. In particular, our simulations show that for small dipolar couplings (1 kHz ) and ultrafast MAS (above 100 kHz ) the transfer efficiency is below 40 % when extended contact times up to 20 ms are used and relaxation losses are ignored. New recoupling and magnetization transfer techniques that are designed explicitly to account for inhomogeneous radiofrequency fields are needed.

High resolution solid-state NMR on the desktop

High-resolution low-field nuclear magnetic resonance (NMR) spectroscopy has found wide application for characterization of liquid compounds because of the low maintenance cost of modern permanent magnets. Solid-state NMR so far is limited to low-resolution measurements of static powders, because of the limited space available in this type of magnet. Magic-angle sample spinning and low-magnetic fields are an attractive combination to achieve high spectral resolution especially for paramagnetic solids. Here we show that magic angle spinning modules can be miniaturized using 3D printing techniques so that high-resolution solid-state NMR in permanent magnets becomes possible. The suggested conical rotor design was developed using finite element calculations and provides sample spinning frequencies higher than 20 kHz. The setup was tested on various diamagnetic and paramagnetic compounds including paramagnetic battery materials. The only comparable experiments in low-cost magnets known so far, had been done in the early times of magic angle spinning using electromagnets at much lower sample spinning frequency. Our results demonstrate that high-resolution low-field magic-angle-spinning NMR does not require expensive superconducting magnets and that high-resolution solid-state NMR spectra of paramagnetic compounds are feasible. Generally, this could introduce low-field solid-state NMR for abundant nuclei standard as a routine analytical tool.

One-Shot Resin 3D-Printed Stators for Low-Cost Fabrication of Magic-Angle Spinning NMR Probeheads

Additive manufacturing such as three-dimensional (3D)-printing has revolutionized the fast and low-cost fabrication of otherwise expensive NMR parts. High-resolution solid-state NMR spectroscopy demands rotating the sample at a specific angle (54.74°) inside a pneumatic turbine, which must be designed to achieve stable and high spinning speeds without mechanical friction. Moreover, instability of the sample rotation often leads to crashes, resulting in costly repairs. Producing these intricate parts requires traditional machining, which is time-consuming, costly, and relies on specialized labor. Herein, we show that 3D-printing can be used to fabricate the sample holder housing (stator) in one shot, while the radiofrequency (RF) solenoid was constructed using conventional materials available in electronics stores. The 3D-printed stator, equipped with a homemade RF coil, showed remarkable spinning stability, yielding high-quality NMR data. At a cost below 5 €, the 3D-printed stator represents a cost reduction of over 99% compared to repaired commercial stators, illustrating the potential of 3D-printing for mass-producing affordable magic-angle spinning stators.

In-house fabrication of 1.3 to 7 mm MAS drive caps using desktop 3D printers

The 3D-printing technology has emerged as a well-developed method to produce parts with considerably low cost and yet with high precision (<100 μm). Recent literature has shown that the 3D-printing technology can be exploited to fabricate a magic-angle spinning (MAS) system in solid-state nuclear magnetic resonance (NMR) spectroscopy. In particular, it was demonstrated that advanced industry-grade 3D printers could fabricate 3.2 mm MAS drive caps with intricate features, and the caps were shown to spin > 20 kHz. Here, we show that not only lab-affordable benchtop 3D printers can produce 3.2 mm drive caps with a similar quality as the commercialized version, but also smaller 2.5 mm and 1.3 mm MAS drive caps-despite a slight compromise in performance. All in-house fabricated drive caps (1.3 to 7 mm) can be consistently reproduced (>90 %) and achieve excellent spinning performances. In summary, the > 3.2 mm systems have similar performances as the commercial systems, while the 2.5- and 1.3-mm caps can spin up to 26 kHz ± 2 Hz, and 46 kHz ± 1 Hz, respectively. The low-cost and fast in-house fabrication of MAS drive caps allows easy prototyping of new MAS drive cap models and, possibly, new NMR applications. For instance, we have fabricated a 4 mm drive cap with a center hole that could allow better light penetration or sample insertion during MAS. Besides, an added groove design on the drive cap allows an airtight seal suitable for probing air- or moisture-sensitive materials. Moreover, the 3D-printed cap was shown to be robust for low-temperature MAS experiments at ∼ 100 K, making it suitable for DNP experiments.

Improving the sensitivity of MAS spheres using a 9.5 mm spherical shell with 219 μL sample volume spinning in a spherical solenoid coil

Spherical rotors in magic angle spinning (MAS) nuclear magnetic resonance (NMR) experiments have potential advantages relative to cylindrical rotors in terms of ease of fabrication, low risk of rotor crash, easy sample exchange, and better microwave access. However, one major disadvantage so far of spherical rotors is poor NMR filling factor due to the small sample volume and large cylindrical radiofrequency (RF) coil. Here we present a novel NMR coil geometry in the form of a spherical coil. The spherical coil best fits the spherical sample to maximize sensitivity, while also providing excellent RF homogeneity. We further improve NMR sensitivity by employing a spherical shell as the rotor, thereby maximizing sample volume (219 μL in this case of 9.5 mm outer diameter spheres). The spinning gas is supplied by a 3D-printed ring stator external to the coil, thereby introducing a simplified form of MAS stators. In this apparatus, the RF field generated along the coil axis is perpendicular to the external magnetic field, regardless of rotor orientation. We observe a linear increase in sensitivity with increasing sample volume. We also simulate the RF performance of spherical and cylindrical solenoid coils with constant or variable pitch for spherical and cylindrical rotors, respectively. The simulation results show that spherical solenoid coils generate comparable B₁ field intensities but have better homogeneity than cylindrical solenoid coils do.

A 3D Printer in the Lab: Not Only a Toy

Although 3D printers are becoming more common in households, they are still under-represented in many laboratories worldwide and regarded as toys rather than as laboratory equipment. This short review wants to change this conservative point of view. This mini-review focuses on fused deposition modeling printers and what happens after acquiring your first 3D printer. In short, these printers melt plastic filament and deposit it layer by layer to create the final object. They are getting cheaper and easier to use, and nowadays it is not difficult to find good 3D printers for less than €500. At such a price, a 3D printer is one, if not the most, versatile piece of equipment you can have in a laboratory.

3D-printed stators & drive caps for magic-angle spinning NMR

3D printing has evolved into an invaluable tool for rapid and cost-effective production of intricate parts. In this paper we describe 3D printing and other rapid prototyping methods to fabricate 3.2 mm stators and drive caps for use in magic angle spinning (MAS) NMR experiments. These components can be fabricated with the assistance of computer-aided design (CAD) software and at a fraction of the cost of commercial parts. Additionally, we show that the performance of these 3D printed stators and drive caps is comparable to commercially available systems and that they have significant advantages over their machined counterparts.

Stable magic angle spinning with Low-Cost 3D-Printed parts

A 3D-printed double-bearing magic angle spinning (MAS) system was developed with a home-built 4.0 mm MAS nuclear magnetic resonance (NMR) probe at 7 T. Various fused deposition modelling 3D printers were used to produce spinning modules of ignorable materials costs for rotors with a diameter of 7.0, 4.0, and 3.5 mm. High-performance MAS experiments on the 4.0 mm-diameter model using a pencil-type ceramic rotor and 3D-printed drive cap resulted in a high-resolution ¹H NMR signal of silicone grease. The 3.5 mm-diameter MAS system reached a spinning frequency of 23 kHz. Furthermore, 3D-printed inserts were designed for various rotor sizes which can isolate the sample from humidity for a duration of more than a week. Single crystal inserts for MAS rotors of commercial probes can readily be printed using two-color printers. Those developments enable customized low-cost MAS NMR for both adapting existing and manufacturing new probes, respectively.

Reimagining magnetic resonance instrumentation using open maker tools and hardware as protocol

Over the course of its history, the field of nuclear magnetic resonance spectroscopy has been characterized by alternating periods of intensive instrumentation development and rapid expansion into new chemical application areas. NMR is now both a mainstay of routine analysis for laboratories at all levels of education and research. On the other hand, new instrumentation and methodological advances promise expanded functionality in the future. At the core of this success is a community fundamentally dedicated to sharing ideas and collaborative advancements, as exemplified by the extensive remixing and repurposing of pulse sequences. Recent progress in modularity, automation, and 3D printing have reignited the tinkering spirit and demonstrate great promise to mature into a maker space that will enable similarly facile sharing of new applications and broader access to magnetic resonance.

3D printed sample tubes for solid-state NMR experiments

The availability of 3D printers and an assortment of polymers that can be fashioned into a wide variety of shapes provides opportunities to rethink the design and construction of probes for NMR spectroscopy. The direct interfacing of computer aided design (CAD) with precise 3D printing enables the simplification and optimization of probes through the rapid production of components. Here we demonstrate the use of 3D printing to fully integrate a permanent former for the radiofrequency (RF) coil with the sample chamber (equivalent to the sample tube). This simultaneously increases the sample volume and improves the filling factor within a fixed outer diameter (OD). It also reduces the space lost in dual coil arrangements where a high frequency resonator is positioned outside a solenoid coil tuned to one or more lower frequencies, making multiple-resonance experiments more efficient. The initial applications demonstrate the possibilities for future designs that reimagine the interface between resonators and the liquid, solid, and heterogeneous samples encountered in NMR studies of biomolecules, polymers, surfaces, and spectroscopy (MRS) and imaging (MRI) of biological organs and intact organisms.

3D-Printed Labware for High-Throughput Immobilization of Enzymes

In continuous flow biocatalysis, chemical transformations can occur under milder, greener, more scalable, and safer conditions than conventional organic synthesis. However, the method typically involves extensive screening to optimize each enzyme's immobilization on its solid support material. The task of weighing solids for large numbers of experiments poses a bottleneck for screening enzyme immobilization conditions. For example, screening conditions often require multiple replicates exploring different support chemistries, buffer compositions, and temperatures. Thus, we report 3D-printed labware designed to measure and handle solids in multichannel format and expedite screening of enzyme immobilization conditions. To demonstrate the generality of these advances, alkaline phosphatase, glucose dehydrogenase, and laccase were screened for immobilization efficiency on seven resins. The results illustrate the requirements for optimization of each enzyme's loading and resin choice for optimal catalytic performance. Here, 3D-printed labware can decrease the requirements for an experimentalist's time by >95%. The approach to rapid optimization of enzyme immobilization is applicable to any enzyme and many solid support resins. Furthermore, the reported devices deliver precise and accurate aliquots of essentially any granular solid material.