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Plant root growth is often accompanied by circumnutative motion consisting of downward helical movement of the root tip. Previous studies indicate that circumnutations allow roots to avoid obstacles that would impede root growth, while other studies show that circumnutations can reduce the penetration resistance mobilised during root growth. Discrete-element modelling (DEM) simulations were performed on probes that employ circumnutation-inspired motion (CIM) to penetrate granular assemblies at shallow depths to evaluate the reduction in penetration resistance. These simulations investigate the effect of the ratio of tangential to vertical velocity of the circumnutative motion (i.e. relative velocity) and of the probe geometry (i.e. tip tilt angle and length). The results indicate that CIM penetration reduces the penetration force and work relative to non-rotational penetration (NRP) by changing the soil fabric and diffusing the force chains around the probe tip. However, the circumnutative motion leads to an increase in torque and associated rotational work. An optimal relative velocity and probe geometry exist for the simulated CIM probes, resulting in a smaller total work than that required for NRP. CIM penetration also mobilises smaller penetration forces and work than rotational penetration (i.e. with a straight tip), particularly at smaller relative velocities. The reduction in penetration forces induced by CIM could facilitate site investigation and monitoring activities.
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Cracking modes and force dynamics in the insertion of neural probes into hydrogel brain phantom
Abstract Objective. The insertion of penetrating neural probes into the brain is crucial for advancing neuroscience, yet it involves various inherent risks. Prototype probes are typically inserted into hydrogel-based brain phantoms and the mechanical responses are analyzed in order to inform the insertion mechanics duringin vivoimplantation. However, the underlying mechanism of the insertion dynamics of neural probes in hydrogel brain phantoms, particularly the phenomenon of cracking, remains insufficiently understood. This knowledge gap leads to misinterpretations and discrepancies when comparing results obtained from phantom studies to those observed under thein vivoconditions. This study aims to elucidate the impact of probe sharpness and dimensions on the cracking mechanisms and insertion dynamics characterized during the insertion of probes in hydrogel phantoms.Approach. The insertion of dummy probes with different shank shapes defined by the tip angle, width, and thickness is systematically studied. The insertion-induced cracks in the transparent hydrogel were accentuated by an immiscible dye, tracked byin situimaging, and the corresponding insertion force was recorded. Three-dimensional finite element analysis models were developed to obtain the contact stress between the probe tip and the phantom.Main results. The findings reveal a dual pattern: for sharp, slender probes, the insertion forces remain consistently low during the insertion process, owing to continuously propagating straight cracks that align with the insertion direction. In contrast, blunt, thick probes induce large forces that increase rapidly with escalating insertion depth, mainly due to the formation of branched crack with a conical cracking surface, and the subsequent internal compression. This interpretation challenges the traditional understanding that neglects the difference in the cracking modes and regards increased frictional force as the sole factor contributing to higher insertion forces. The critical probe sharpness factors separating straight and branched cracking is identified experimentally, and a preliminary explanation of the transition between the two cracking modes is derived from three-dimensional finite element analysis.Significance. This study presents, for the first time, the mechanism underlying two distinct cracking modes during the insertion of neural probes into hydrogel brain phantoms. The correlations between the cracking modes and the insertion force dynamics, as well as the effects of the probe sharpness were established, offering insights into the design of neural probes via phantom studies and informing future investigations into cracking phenomena in brain tissue during probe implantations.
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- PAR ID:
- 10594787
- Publisher / Repository:
- IOP Publishing Ltd
- Date Published:
- Journal Name:
- Journal of Neural Engineering
- Volume:
- 21
- Issue:
- 4
- ISSN:
- 1741-2560
- Page Range / eLocation ID:
- 046009
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1088/1741-2552/ad5937
