Helical and Bouligand Porous Scaffolds Fabricated by Dynamic Low Strength Magnetic Field Freeze Casting

Abstract

Porous Fe 3 O 4 scaffolds were fabricated while subject to a low (7.8 mT) magnetic field applied in helical and Bouligand motions using a custom-built triaxial nested Helmholtz coils-based freeze-casting setup. This setup allowed for the control of a dynamic, uniform low-strength magnetic field to align particles during the freezing process, resulting in the majority of lamellar walls aligning within ± 30°of the magnetic field direction and a decrease in porosity by up to 42%. Similar to how helical and Bouligand structures in nature promote impact resistance, these magnetic field motions produced structures with improved high strain rate mechanical properties. Strain at failure was increased by up to 2 times as cracks deflected to match the applied angles of rotation of the magnetic field.

Freeze Casting with Bioceramics for Bone Graft Substitutes

“…Intrinsic control methods can affect the global microstructure and porosity but tend to act uniformly, thus lacking the influence to enact localized alterations in the pore structure. Extrinsic controls, which are defined as those that act upon the freezing process through external influences [3], include the use of sacrificial templates [76][77][78], changes in the freezing direction [79], multi-step freezing [80], and the use of applied energized fields such as magnetic [67,81,82], electric [83][84][85], and ultrasonic fields [86][87][88]. Extrinsic control methods allow for more complex pore structures to be made, with hierarchical and localized anisotropy that can differ across multiple length scales and locations.…”

“…While there is a report on using magnetic fields to control iron (II, III) oxide (Fe 3 O 4 ) added to HA, Al 2 O 3 , ZrO 2 , and TiO 2 , the magnetic field had little influence on the bioceramics, instead the magnetic field caused distinct phase separation of the materials and Fe 3 O 4 [195]. As some bioinert ceramics such as TiO 2 are paramagnetic, applying strong magnetic fields to produce aligned pore structures could eventually prove useful in creating freeze-cast biomaterials [67,81]. Similarly, layered pore structures created through ultrasound freeze casting could mimic the laminar arrangement of osteons in bone [88].…”

Impact-resistant materials inspired by the mantis shrimp's dactyl club

“…79 Dynamically varying magnetic fields applied in conjunction with freezecasting can also be used to create helicoidal structures. 81,82 In this case, the ceramics are highly porous due to the formation of anisotropic ice crystals. 83 Finally, shear-driven alignment by brush painting of hydroxyapatite microfibers suspended in a sodium alginate hydrogel has been used to create Bouligand structures.…”

Superior Mechanical and Magnetic Performance of Highly Anisotropic Sendust‐Flake Composites Freeze Cast in a Uniform Magnetic Field

“…A novel and highly promising approach for the manufacture of low loss magnetic composites with highly aligned flakes is freeze‐casting. [ 11–19 ] Freeze casting, also termed ice‐templating, is based on the directional solidification of water‐based particle slurries. [ 20–24 ] Initially, the process was shown to produce highly aligned, nacre‐like microstructures with alumina platelets in a polymer binder.…”