Puncture mechanics of soft solids

Fakhouri, Sami; Hutchens, Shelby B.; Crosby, Alfred J.

doi:10.1039/c5sm00230c

Cited by 64 publications

(82 citation statements)

References 31 publications

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“…3b). This observation is consistent with models of crack-initiated or energy-limited failure in compliant materials 33,34 , indicating the failure of the pia likely occurs via one of these modes. From this data, the force needed to puncture the brain could be directly calculated based on the size of the wire:…”

Section: Influence Of Microwire Diametersupporting

confidence: 87%

Ultra-sensitive measurement of brain penetration with microscale probes for brain machine interface considerations

Obaid

Hanna

et al. 2018

Preprint

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Microscale electrodes are rapidly becoming critical tools for neuroscience and brain-machine interfaces (BMIs) for their high spatial and temporal resolution. However, the mechanics of how devices on this scale insert into brain tissue is unknown, making it difficult to balance between larger probes with higher stiffness, or smaller probes with lower damage. Measurements have been experimentally challenging due to the large deformations, rapid events, and small forces involved. Here we modified a nanoindentation force measurement system to provide the first ultra-high resolution force, distance, and temporal recordings of brain penetration as a function of microwire diameter (7.5 µm to 100 µm) and tip geometry (flat, angled, and electrosharpened).Surprisingly, both penetration force and tissue compression scaled linearly with wire diameter, rather than cross-sectional area. Linear brain compression with wire diameter strongly suggest smaller probes will cause less tissue damage upon insertion, though unexpectedly no statistical difference was observed between angled and flat tipped probes. These first of their kind measurements provide a mechanical framework for designing effective microprobe geometries while limiting mechanical damage.

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Section: Influence Of Microwire Diametersupporting

confidence: 87%

Ultra-sensitive measurement of brain penetration with microscale probes for brain machine interface considerations

Obaid

Hanna

et al. 2018

Preprint

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“…The range of applications of the derived scaling goes far beyond the description of the elasto-buoyancy phenomenon. For instance, it can be directly checked that the recent indentation experiments performed on various types of compliant gels, by Fakhouri et al [15], are in quantitative agreement with our prediction, however their very naive model based on the neo-Hookean equation, misses the driving non-linearities.…”

Section: Discussionsupporting

confidence: 84%

“…What we report here is such a universality that is discovered in the large deformation behavior of ultra-soft gels. Soft solids undergoing huge deformations exhibit various fascinating and puzzling mechanical behaviors [4][5][6][7][8][9][10][11][12][13][14][15]. Our experimental protocol to study extra-large elastic deformations is remarkably simple, in that a heavy bead of stainless steel is gently deposited on the horizontal flat surface of a gel.…”

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confidence: 99%

Elastobuoyant Heavy Spheres: A Unique Way to Study Nonlinear Elasticity

et al. 2016

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Extra-large deformations in ultra-soft elastic materials are ubiquitous, yet systematic studies and methods to understand the mechanics of such huge strains are lacking. Here we investigate this complex problem systematically with a simple experiment: by introducing a heavy bead of radius a in an incompressible ultra-soft elastic medium. We find a scaling law for the penetration depth (δ) of the bead inside the softest gels as δ ∼ a 3/2 which is vindicated by an original asymptotic analytic model developed in this article. This model demonstrates that the observed relationship is precisely at the demarcating boundary of what would be required for the field variables to either diverge or converge. This correspondence between a unique mathematical prediction and the experimental observation ushers in new insights into the behavior of the deformations of strongly non-linear materials. 83.85.Cg,46.05.+b,83.80.Va Singularities are pervasive in various problems of linear continuum mechanics. In wetting, stress diverges at a moving contact line [1,2]; it diverges at the tip of a crack or even at a sharp point indenting a plane [3]. Understanding how such singularities can be tempered has often given rise to new physics invariably prompting us, on many occasions, to investigate a material phenomenon at a molecular dimension and then herald a way to bridge the near field with the far field behavior in a rather non-trivial manner. Nature, however, performs the difficult task herself and leaves her signature in a way that is independent of the constitutive property of a material, yet it belongs to a class of universality. What we report here is such a universality that is discovered in the large deformation behavior of ultra-soft gels. Soft solids undergoing huge deformations exhibit various fascinating and puzzling mechanical behaviors [4][5][6][7][8][9][10][11][12][13][14][15]. Our experimental protocol to study extra-large elastic deformations is remarkably simple, in that a heavy bead of stainless steel is gently deposited on the horizontal flat surface of a gel. The compliant gel is deformed by the load exerted by the heavy bead. It reaches a stable (elasto-buoyant) equilibrium position when the elastic force exerted by the surrounding gel balances its weight [14], within few tenths of a second. This experiment can be viewed as an elastic analog of the falling ball viscometry, in which the bead reaches a terminal sedimentation velocity resulting from the balance of the bead's weight and the viscous drag force [16]. In the limit of Hookean elasticity, an analogy with the Stokes equation (by replacing shear viscosity with shear modulus and velocity with depth of submersion, δ) [17] suggests that δ ∼ a 2 , a being the sphere radius. While for the higher modulus gels (Fig.1-a), such a relationship is more or less valid, for the softer ones, when the bead is totally engulfed by the gel and the deformations are very large ( Fig.1-b), it is observed that the depth scales with the bead's radius with an exponent of 3/2. This...

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“…The penetration process is initiated with crack nucleation at contact point of the device and this initial penetration force ( F c,0 ) is determined by the fracture nucleation energy ( Γ 0 ) of the organ. High tip sharpness or small radius of curvature ( R ) at the tip (thin pointed) of the device reduces the fracture process zone by focusing the applying force into a minuscule area, which minimizes the initial penetration force needed to overcome the fracture nucleation energy (Equation )60

F_{c, 0} ~ R {normalΓ}_{0}

…”

Section: Tissue Penetration Mechanics For Injectable Systemsmentioning

confidence: 99%

Injectable Biomedical Devices for Sensing and Stimulating Internal Body Organs

et al. 2020

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The rapid pace of progress in implantable electronics driven by novel technology has created devices with unconventional designs and features to reduce invasiveness and establish new sensing and stimulating techniques. Among the designs, injectable forms of biomedical electronics are explored for accurate and safe targeting of deep‐seated body organs. Here, the classes of biomedical electronics and tools that have high aspect ratio structures designed to be injected or inserted into internal organs for minimally invasive monitoring and therapy are reviewed. Compared with devices in bulky or planar formats, the long shaft‐like forms of implantable devices are easily placed in the organs with minimized outward protrusions via injection or insertion processes. Adding flexibility to the devices also enables effortless insertions through complex biological cavities, such as the cochlea, and enhances chronic reliability by complying with natural body movements, such as the heartbeat. Diverse types of such injectable implants developed for different organs are reviewed and the electronic, optoelectronic, piezoelectric, and microfluidic devices that enable stimulations and measurements of site‐specific regions in the body are discussed. Noninvasive penetration strategies to deliver the miniscule devices are also considered. Finally, the challenges and future directions associated with deep body biomedical electronics are explained.

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Puncture mechanics of soft solids

Cited by 64 publications

References 31 publications

Ultra-sensitive measurement of brain penetration with microscale probes for brain machine interface considerations

Ultra-sensitive measurement of brain penetration with microscale probes for brain machine interface considerations

Elastobuoyant Heavy Spheres: A Unique Way to Study Nonlinear Elasticity

Injectable Biomedical Devices for Sensing and Stimulating Internal Body Organs

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