A Pneumatic-based Mechanism for Inserting a Flexible Microprobe into the Brain

Insertion of flexible microprobes into the brain requires withstanding the compressive penetration force by the microprobes. To aid the insertion of the microprobes, most of the existing approaches employ pushing mechanisms to provide temporary stiffness increase for the microprobes to prevent buckling during insertion into the brain. However, increasing the microprobe stiffness may result in acute neural tissue damage during insertion. Moreover, any late or premature removal of the temporary stiffness after insertion may lead to further tissue damage due to brain micromotion, or inaccuracy in the microprobe positioning. In this study, a novel pneumatic-based insertion mechanism is proposed which simultaneously pulls and pushes a flexible microprobe towards the brain. As part of the brain penetration force in the proposed mechanism is supplied by the tensile force, the applied compressive force, which the microprobe must withstand during insertion, is lower compared to the existing approaches. Therefore, the microprobes with a critical buckling force less than the brain penetration force can be inserted into the brain without buckling. Since there is no need for temporary stiffness increment, the neural tissue damage during the microprobe insertion will be much lower compared to the existing insertion approaches. The pneumatic-based insertion mechanism is modelled analytically to investigate the effects of the microprobe configuration and the applied air pressure on the applied tensile and compressive forces to the microprobe. Next, finite element modelling is conducted, and its analysis results not only validate the analytical results but also confirm the efficiency of the mechanism.

Compression and Stretching of Confined Linear and Ring Polymers by Applying Force

We use Langevin dynamics to study the deformations of linear and ring polymers in different confinements by applying compression and stretching forces on their two sides. Our results show that the compression deformations are the results of an interplay among of polymer rigidity, degree of confinement, and force applied. When the applied force is beyond the threshold required for the buckling transition, the semiflexible chain under the strong confinement firstly buckles; then comes helical deformation. However, under the same force loading, the semiflexible chain under the weaker confinement exhibits buckling instability and shrinks from the folded ends/sides until it becomes three-folded structures. This happens because the strong confinement not only strongly reduces the buckling wavelength, but also increases the critical buckling force threshold. For the weakly confined polymers, in compression process, the flexible linear polymer collapses into condensed states under a small external force, whereas the ring polymer only shows slight shrinkage, due to the excluded volume interactions of two strands in the crowded states. These results are essential for understanding the deformations of the ring biomacromolecules and polymer chains in mechanical compression or driven transport.

Prediction of buckling force in hourglass-shaped specimens

It is important to avoid buckling during low-cycle fatigue testing. The buckling load is dependent on the specimen shape, material properties, and the testing machine. In the present investigation of hourglass-shaped specimens the importance of the diameter to radius of curvature is examined. Diameters of 5 and 7 mm are examined with a ratio of radius of curvature to diameter of 4, 6, and 8. The machine used is an Instron 8800 with elongated rods for a climate chamber. This leads to a reduced stiffness of the machine during compression testing. A finite element model (in Abaqus) is developed to identify the critical buckling force. For hourglass-shaped specimens, buckling means onset of sideways movement, without a drop in the applied load which is typical for conventional Euler buckling. The onset of sideways movement is identified experimentally by analysis of the data from extensometer and the load cell. This model is verified by experiments and fits within 0.6 to − 11% depending on the specimen diameter and diameter to radius of curvature ratio. The smallest deviations are obtained for the 7-mm-diameter specimen with deviation varying from 0.6 to − 3.3% between the model and the experiments. The current investigation is done with a commercially available hot rolled structural steel bar of Ø16 mm.

Optimisation of the Thin-Walled Composite Structures in Terms of Critical Buckling Force

The paper presents the optimisation of thin-walled composite structures on a representative sample of a thin-walled column made of carbon laminate with a channel section-type profile. The optimisation consisted of determining the configuration of laminate layers for which the tested structure has the greatest resistance to the loss of stability. The optimisation of the layer configuration was performed using two methods. The first method, divided into two stages to reduce the time, was to determine the optimum arrangement angle in each laminate layer using finite element methods (FEM). The second method employed artificial neural networks for predicting critical buckling force values and the creation of an optimisation tool. Artificial neural networks were combined into groups of networks, thereby improving the quality of the obtained results and simplifying the obtained neural networks. The results from computations were verified against the results obtained from the experiment. The optimisation was performed using ABAQUS® and STATISTICA® software.

Characterization of Spinal Needle Buckling Behavior

The use of large gauge (G) spinal anesthesia needles can increase complications due to buckling. The purpose of this study was to quantify the behavior of spinal needles in buckling using a repeatable laboratory model. A spinal anesthesia procedure and buckling complication was reproduced in vitro using a custom test fixture designed to match the boundary conditions of needle insertion as performed by an anesthesiologist and a uniaxial servohydraulic material testing machine (MTS, Eden Prairie, MN). Buckling tests were performed with 22 G Whitacre (Medline Industries, Inc., Northfield IL), SPROTTE® (Pajunk, Norcross, GA), and Gertie Marx (International Medical Development, Huntsville, UT) needles (n = 30) in a ballistics gelatin tissue surrogate (Clear Ballistics, Fort Smith, AR). In analyzing axial force results, critical buckling load results were 27.65 ± 0.92 N, signifying that needle fragility is not why buckling is challenging to detect. Force feedback during needle insertion increased linearly due to frictional forces from the tissue surrogate on the needle. The differential between the resultant insertion force and the critical buckling force is more important to the detection of needle buckling than the critical buckling force alone. A very small difference in these two forces could feel like expected resistance increase as the needle is further inserted into the multiple tissue layers. Comparison of the differential between the resultant insertion force and the critical buckling force should be considered when choosing a needle to best detect and prevent a buckling complication.

Buckling Analysis of Hetero-Junction Carbon Nanotubes

The buckling analysis of carbon nanotubes without and with hetero-junctions is described in this paper. The buckling behaviour was investigated by the finite element method and the carbon nanotubes were modelled as space frame structures. The results showed that the critical buckling force depends on the dimensions of carbon nanotubes. The critical buckling forces of hetero-junction carbon nanotubes are in range between critical buckling forces of carbon nanotubes of both used diameters with the same chiralities without hetero-junction.

Stability and vibrations control of a stepped beam using piezoelectric actuation

The objects of this studies are the stability and transversal vibrations of the system composed of three segments, where in the centre part of the system two piezoelectric patches are perfectly bonded to the top and bottom surface of the host beam. The system is kinematically loaded as a result of prescribed displacement of one or both end supports. For the analysis purposes three different beam end supports have been taken into consideration, which prevent longitudinal displacements i.e. clamped-clamped, clamped-pinned and pinned-pinned. This type of beam loading not only affect its natural vibration frequencies but also the system’s stability. By introducing the electric field to the piezo patches, depending on its vector direction, in-plane stretching or compressive residual force may be induced. Presented results show that piezo actuation can significantly modify both the critical buckling force and the vibration frequency.

About buckling calculus of straight bars on elastic environment by Transfer-Matrix Method (TMM) for dental implants

The paper presents a relatively simple and elegant analytical calculus of critical buckling force for a straight bar, one-end embedded and other end free, with an axial compression force F, using the Transfer-Matrix Method (TMM). The algorithm is based on the simplifications of the mathematical apparatus offered by Dirac and Heaviside’s functions and operators regarding effort density. The results obtained will be used in the study of dental implants. The implant was assimilated as a bar on elastic environment, one-end of bar embedded and other end free, with an axial compression force F at the free end, the bone being assimilated as an elastic environment.

Size-Dependent Postbuckling of Piezoelectric Microbeams Based on a Modified Couple Stress Theory

This paper aims to investigate the postbuckling behavior of piezoelectric microbeams (PMBs) using a modified couple stress theory (MCST) and a Euler–Bernoulli–von Kármán beam model. The critical buckling force, voltage and the deformation amplitude were calculated for the buckling of the axially compressed microbeams with a clamp–clamp boundary condition. It is found that the stiffness of microbeams considering the MCST is higher than that given by the classical model when the feature size decreases to the microscale. Moreover, the microscale size effect has a strong influence on the critical buckling loads and the amplitude of postbuckling deformation. This study brings an improved understanding of the postbuckling behavior of PMBs, and offers useful guidance for the design of piezobeam-based sensors, actuators and stretchable microelectronics.