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

Abstract

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.

Figure 1

4.0 mm MAS stator: (A) Computer-assisted design (CAD) model (left) and sectional view of the 4.0 mm stator, highlighting the variable temperature (VT), bearing, and gas inlets (right); (B) 3D-printed 4.0 mm stator equipped with a homemade RF coil (left) and 3D-printed 4.0 mm stator retrofitted into the probehead (right).

Figure 2

MAS pneumatic spinning requirements. The bearing and drive gas pressures were measured as a function of the spin rate in both 3D-printed and commercial versions of the stator. The nominal spin rate was set to 12.0 kHz, and the rotor was spun in automatic mode, with bearing and drive pressures controlled by a MAS-2 Bruker unit. The same rotor, packed with ¹³C/¹⁵N Tyr·HCl, was used for both stators.

Figure 3

RF solenoid coil. (A) CAD model of a 4.0 mm RF coil; (B) homemade 4.0 mm RF coil.

Figure 4

Characterization of the in-house RF solenoid system. NMR spectra of ¹³C/¹⁵N-enriched Tyr·HCl were recorded at a field strength of 9.4 T and a MAS rate of 8.0 kHz. The 3D-printed stator and RF coil were retrofitted into a double-resonance Bruker MAS probe (blue lines). A commercial 4.0 mm Bruker triple-resonance MAS probe was used for comparison (orange lines). (A) ¹³C RF nutation plot. The irradiation offset was set to the carbonyl peak at 172.8 ppm. (B) ¹³C CPMAS NMR spectra, acquired in the same conditions.

Figure 5

2D ¹³C–¹³C DQ/SQ POST-C7 NMR spectrum of ¹³C/¹⁵N Tyr·HCl recorded at a field strength of 9.4 T. The spectrum was recorded using a MAS frequency of 8.0 kHz, 512 points were recorded for each t1 increment, and 32 scans per point were used. The recycle delay was set to 3 s. The total experimental time was ∼14 h; * depicts spinning side bands.