Micro-Pillar Mechanics

Journal of the Mechanical Behavior of Biomedical Materials (2020): Patterned Enteroscopy Balloon Design Factors Influence Tissue Anchoring

Anonymous — Sun, 23 Aug 2020 19:43:18 +0000

Journal of the Mechanical Behavior of Biomedical Materials (2020): Patterned Enteroscopy Balloon Design Factors Influence Tissue Anchoring Anonymous (not verified) Sun, 08/23/2020 - 13:43

Abstract: Balloon-assisted enteroscopy procedures allow visualization and intervention in the small intestine. These balloons anchor an endoscope and/or overtube to the small intestine, allowing endoscopists to plicate the small intestine over the overtube. This procedure can extend examination deeper into the small intestine than the length of the endoscope would allow with direct examination. However, procedures are often prolonged or incomplete due to balloon slippage. Enteroscopy balloons are pressure-limited to ensure patient safety and thus, improving anchoring without increasing pressure is essential. Patterning balloon exteriors with discrete features may enhance anchoring at the tissue-balloon interface. Here, the pattern design space is explored to determine factors that influence tissue anchoring. The anchoring ability of smooth versus balloons with patterned features is investigated by experimentally measuring a peak force required to induce slippage of an inflated balloon inside ex-vivo porcine small intestine. Stiffer materials, low aspect-ratio features, and pattern area/location on the balloons significantly increase peak force compared to smooth silicone balloons. Smooth latex balloons, used for standard enteroscopy, have the lowest peak force. This work demonstrates both a method to pattern curved surfaces and that a balloon with patterned features improves anchoring against a deformable, lubricated tissue interface.

Bowen, L.K., Johannes, K., Zuetell, E., Calahan, K., Edmundowicz, S.A., Long, R., Rentschler, M.E., “Patterned Enteroscopy Balloon Design Factors Influence Tissue Anchoring,” Journal of the Mechanical Behavior of Biomedical Materials. 111: 103966, 2020.

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Mechanics of Materials (2020): Friction Between a Plane Strain Circular Indenter and a Thick Poroelastic Substrate

Anonymous — Wed, 01 Jan 2020 03:30:15 +0000

Mechanics of Materials (2020): Friction Between a Plane Strain Circular Indenter and a Thick Poroelastic Substrate Anonymous (not verified) Tue, 12/31/2019 - 20:30

Abstract: This paper presents a computational study on the role of poroelasticity in gel friction. Motivated by recent experimental studies in the literature, we develop a plane strain finite element model to elucidate the contact mechanics between a circular indenter and a thick poroelastic substrate under both normal and shear loadings. Two cases are considered: i) steady state sliding under fixed normal displacements, and ii) relaxation under fixed normal and shear displacements. In steady state sliding, we find that a net friction force can arise even if no intrinsic adhesive or frictional interaction is implemented at the indenter/substrate interface. Such friction force exhibits a non-monotonic dependence on the sliding velocity and peaks at an intermediate velocity. Our model reveals that this friction force is induced by poroelastic diffusion in the gel substrate which can lead to considerable asymmetry in both the contact profile and contact pressure. In terms of relaxation, if the indenter/substrate interface is set to be frictionless, we find that the friction force induced by poroelasticity relaxes to zero with a characteristic time much faster than that of the normal force. When a finite friction coefficient is introduced at the interface, the normalized relaxation curve for the friction force approaches that for the normal force as the friction coefficient increases. These modeling results suggest that poroelasticity can be an important contributing mechanism for gel friction.

Qi, Y., Calahan, K.N., Rentschler, M.E., Long, R., “Friction Between a Plane Strain Circular Indenter and a Thick Poroelastic Substrate,” Mechanics of Materials. 142: 103303, 2020.

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Langmuir (2019): Three-Dimensional Microscale Imaging and Measurement of Soft Material Contact Interfaces Under Quasi-Static Normal Indentation and Shear

Anonymous — Fri, 12 Jul 2019 16:35:23 +0000

Langmuir (2019): Three-Dimensional Microscale Imaging and Measurement of Soft Material Contact Interfaces Under Quasi-Static Normal Indentation and Shear Anonymous (not verified) Fri, 07/12/2019 - 10:35

[video:https://youtu.be/vYKnGtwXVgg]

Abstract: Understanding the contact and friction of soft materials is vital for a wide variety of engineering applications including soft sealants and medical devices such as catheters and stents. While the mechanisms of friction between stiff materials have been extensively studied, the mechanisms of friction between soft materials are much less understood. Time dependent material responses, large deformations and fluid layers at the contact interface, common in soft materials, pose new challenges toward understanding friction of soft materials. This paper aims to characterize the three-dimensional (3D) contact interfaces in soft materials under large deformation and complex contact conditions. Specifically, we introduce a micro-indentation and visualization (MIV) system capable of investigating soft material contact interfaces with combined normal and shear loading. When combined with a laser scanning confocal microscope, the MIV system enables the acquisition of 3D image stacks of the deformed substrate and the indenter, under fixed normal and shear displacements. The 3D imaging data allows us to quantify the 3D contact profiles and correlate them with the applied normal and shear displacements. Using a spherical indenter and a hydrogel substrate as a model system, we demonstrate that the MIV system and the associated analysis techniques accurately measure the contact area under combined normal and shear loading. Although the limited speed of confocal scanning implies that this method is most suitable for quasi-static loading conditions, potential methods to increase the imaging speed and the corresponding trade-off in image resolution are discussed. The method presented here will be useful for future investigation of soft material contact and friction involving complex surface geometries.

Johannes, K.G., Calahan, K.N., Qi, Y., Long, R., Rentschler, M.E., “Three-Dimensional Microscale Imaging and Measurement of Soft Material Contact Interfaces Under Quasi-Static Normal Indentation and Shear,” Langmuir. 35: 10725-10733, 2019.

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Journal of the Mechanics and Physics of Solids (2019): Delamination of a Rigid Punch from an Elastic Substrate Under Normal and Shear Forces

Anonymous — Sat, 06 Oct 2018 18:04:07 +0000

Journal of the Mechanics and Physics of Solids (2019): Delamination of a Rigid Punch from an Elastic Substrate Under Normal and Shear Forces Anonymous (not verified) Sat, 10/06/2018 - 12:04

Abstract: Delamination of rigid objects from an elastic substrate with finite thickness is a fundamental problem underlying applications such as marine fouling release coatings or anti-icing coatings. Most existing theoretical studies assume that delamination is driven by forces normal to the substrate surface, while in practice the delamination force may also include shear components that are parallel to the substrate surface. In this work, we consider a model system where a rigid cylindrical punch is detached from an elastic substrate under normal force, shear force or both. Our focus is to determine the pull-off force and to reveal the delamination mechanics under various geometrical and loading conditions, specifically the substrate thickness and the position and angle of the delamination force. To gain theoretical insights, we first study a plane strain model where a long rigid strip is adhered to an elastic half-space, and obtain an analytical solution revealing how the pull-off force depends on the loading position and angle. Moreover, we develop a three-dimensional finite element model to simulate the delamination of a rigid cylindrical punch from an elastic substrate with finite thickness. Three delamination modes are identified from finite element results: Mode-I crack propagation, Mode-II crack propagation, and interface cavitation. For the first two modes, we obtain empirical formulas to calculate the pull-off force using adhesion energy, substrate modulus, contact radius and substrate thickness. We also find that the analytical solution derived from the plan strain model can serve as a qualitative guide to estimate the effect of loading position and angle on the pull-off force.

Sun, X., Yu, L., Rentschler, M.E., Wu, H., Long, R., "Delamination of a Rigid Punch from an Elastic Substrate Under Normal and Shear Forces," Journal of the Mechanics and Physics of Solids. 122: 141-160, 2019.

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Mechanics of Materials (2018): A Representative Volume Element Model for the Adhesion Between a Micro-Pillared Surface and a Compliant Substrate

Anonymous — Thu, 08 Feb 2018 16:15:56 +0000

Mechanics of Materials (2018): A Representative Volume Element Model for the Adhesion Between a Micro-Pillared Surface and a Compliant Substrate Anonymous (not verified) Thu, 02/08/2018 - 09:15

Abstract: A representative volume element (RVE) model was developed to understand how the adhesion response between an effectively rigid substrate with micro-pillar arrays and a compliant substrate is affected by the spacing and aspect ratio of pillars. A number of verification and validation steps were taken to ensure the RVE model was robust. We found that the pull-off force decreases when pillar spacing is small enough such that the local deformation within the compliant substrate around one pillar is affected by neighboring pillars. Additionally, pull-off force can increase dramatically if the compliant substrate makes contact with the back surface between pillars, which occurs when the pillar spacing is large and pillar aspect ratio is small. Our RVE model can provide useful insights and quantitative data for understanding the adhesive contact mechanics between micro-patterned surfaces and soft substrates.

Kern, M.D., Long, R. Rentschler, M.E., “A Representative Volume Element Model for the Adhesion between a Micro-Pillared Surface and a Compliant Substrate,” Mechanics of Materials. 119: 65-73, 2018.

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Langmuir (2017): Characterizing Adhesion between a Micro-Patterned Surface and a Soft Synthetic Tissue

Anonymous — Fri, 21 Apr 2017 20:21:51 +0000

Langmuir (2017): Characterizing Adhesion between a Micro-Patterned Surface and a Soft Synthetic Tissue Anonymous (not verified) Fri, 04/21/2017 - 14:21

[video:https://www.youtube.com/watch?v=nP3zeYif-6M]

Abstract: The work of adhesion and work of separation are characteristic properties of a contact interface that describe the amount of energy per unit area required to adhere or separate two contacting substrates, respectively. In this work, the authors present experimental and data analysis procedures that allow the contact interface between a soft synthetic tissue and a smooth or micropatterned poly(dimethylsiloxane) (PDMS) substrate to be characterized in terms of these characteristic parameters. Because of physical geometry limitations, the experimental contact geometry chosen for this study differs from conventional test geometries. Therefore, the authors used finite element modeling to develop correction factors specific to the experimental contact geometry used in this work. A work of adhesion was directly extracted from experimental data while the work of separation was estimated on the basis of experimental results. These values are compared to other theoretical calculations for validation. The results of this work indicate that the micropatterned PDMS substrate significantly decreases both the work of adhesion and work of separation as compared to a smooth PDMS substrate when in contact with a soft synthetic tissue substrate.

Kern, M., Qi, Y., Long, R., Rentschler, M.E., "Characterizing Adhesion between a Micro-Patterned Surface and a Soft Synthetic Tissue," Langmuir. 33(4): 854-864, 2017.

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IEEE/ASME Transactions on Mechatronics (2015): An Automated Traction Measurement Platform and Empirical Model for Evaluation of Rolling Micro-Patterned Wheels

Anonymous — Fri, 21 Apr 2017 20:20:51 +0000

IEEE/ASME Transactions on Mechatronics (2015): An Automated Traction Measurement Platform and Empirical Model for Evaluation of Rolling Micro-Patterned Wheels Anonymous (not verified) Fri, 04/21/2017 - 14:20

[video:https://youtu.be/eAP82kETW1Q]

Abstract: Colonoscopy is the leading preventative procedure for colorectal cancer. The traditional tool used for this procedure is an endoscope, which can cause patient discomfort, pain and fear of the procedure. There has been a movement to develop a robotic capsule colonoscope (RCC) in an attempt to mitigate these drawbacks and increase procedure popularity. An RCC is a capsule robot that propels itself through the colon as opposed to being pushed, like a traditional endoscope. In this study, an overview of an in vivo RCC is given, followed by the introduction of a mobility method for an RCC using micropatterned polydimethylsiloxane (PDMS). The design of a three degree-of-freedom automated traction measurement (ATM) platform for quantitative evaluation of the mobility method is presented. An empirical model for traction force as a function of slip ratio, robot speed, and weight for micropatterned PDMS on synthetic tissue is developed using data collected from the ATM platform. The model is then used to predict traction force at different slip ratios, speeds, and weights, and is verified experimentally. The average normalized root-mean-square error (NRMSE) between the empirical model and the data used to develop the model is 1.1% (min 0.0024%, max 4.2%). The average NRMSE between the traction force predicted by the model and the data used to verify the prediction is 1.8% (min 0.020%, max 8.6%). Understanding how model parameters influence tread performance will improve future RCC mobility systems and aid in the development of analytical models, leading to more optimal designs.

Sliker, L.J., Kern, M.D., Rentschler, M.E., "An Automated Traction Measurement Platform and Empirical Model for Evaluation of Rolling Micro-Patterned Wheels," IEEE/ASME Transactions on Mechatronics. 20(4): 1854-1862, 2015.

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Journal of Mechanical Behavior of Biomedical Materials (2014): Soft Material Adhesion Characterization for In vivo Locomotion of Robotic Capsule Endoscopes: Experimental and Modeling Results

Anonymous — Fri, 21 Apr 2017 20:19:46 +0000

Journal of Mechanical Behavior of Biomedical Materials (2014): Soft Material Adhesion Characterization for In vivo Locomotion of Robotic Capsule Endoscopes: Experimental and Modeling Results Anonymous (not verified) Fri, 04/21/2017 - 14:19

Abstract: The objective of this work is to validate an experimental method and nondimensional model for characterizing the normal adhesive response between a polyvinyl chloride based synthetic biological tissue substrate and a flat, cylindrical probe with a smooth polydimethylsiloxane (PDMS) surface. The adhesion response is a critical mobility design parameter of a Robotic Capsule Endoscope (RCE) using PDMS treads to provide mobility to travel through the gastrointestinal tract for diagnostic purposes. Three RCE design characteristics were chosen as input parameters for the normal adhesion testing: pre-load, dwell time and separation rate. These parameters relate to the RCE׳s cross sectional dimension, tread length, and tread speed, respectively. An inscribed central composite design (CCD) prescribed 34 different parameter configurations to be tested. The experimental adhesion response curves were nondimensionalized by the maximum stress and total displacement values for each test configuration and a mean nondimensional curve was defined with a maximum relative error of 5.6%. A mathematical model describing the adhesion behavior as a function of the maximum stress and total displacement was developed and verified. A nonlinear regression analysis was done on the maximum stress and total displacement parameters and equations were defined as a function of the RCE design parameters. The nondimensional adhesion model is able to predict the adhesion curve response of any test configuration with a mean R² value of 0.995. Eight additional CCD studies were performed to obtain a qualitative understanding of the impact of tread contact area and synthetic material substrate stiffness on the adhesion response. These results suggest that the nondimensionalization technique for analyzing the adhesion data is sufficient for all values of probe radius and substrate stiffness within the bounds tested. This method can now be used for RCE tread design optimization given a set of environmental conditions for device operation.

Kern, M., Ortega, J., Rentschler, M.E., "Soft Material Adhesion Characterization for In vivo Locomotion of Robotic Capsule Endoscopes: Experimental and Modeling Results," Journal of Mechanical Behavior of Biomedical Materials. 39: 257-269, 2014.

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Tribology Letters (2013): Preliminary Friction Force Measurements on Small Bowel Lumen when Eliminating Sled Edge Effects

Anonymous — Fri, 21 Apr 2017 20:16:09 +0000

Tribology Letters (2013): Preliminary Friction Force Measurements on Small Bowel Lumen when Eliminating Sled Edge Effects Anonymous (not verified) Fri, 04/21/2017 - 14:16

Abstract: This study aims to produce experimental results for the coefficient of friction (COF) between the small bowel lumen and an edgeless, translating sled. Friction was measured as a function of sled speed under in situ and in vitro conditions. The results indicate that by eliminating edge effects, the COF between a stainless steel sled and the inner surface of the small bowel lumen is decreased. The average COF for in situ testing was found to be slightly lower than in vitro tests. Friction increased with increasing velocity. The friction forces ranged from 0.013 to 0.08 N, and COF values ranged from 0.007 to 0.054 under these conditions.

Lyle, A.B., Terry, B.S., Schoen, J.A., Rentschler, M.E., "Preliminary Friction Force Measurements on Small Bowel Lumen when Eliminating Sled Edge Effects," Tribology Letters. 51(3): 377-383, 2013.

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Tribology International (2013): A Tribological Investigation of the Small Bowel Lumen Surface

Anonymous — Fri, 21 Apr 2017 20:15:16 +0000

Tribology International (2013): A Tribological Investigation of the Small Bowel Lumen Surface Anonymous (not verified) Fri, 04/21/2017 - 14:15

Abstract: Robotic capsule endoscopy (RCE), where a robotically controlled capsule endoscope is used to navigate the gastrointestinal tract, is a developing technology currently hindered by mobility challenges within the small bowel. This research seeks to engage the frictional characterization of the small bowel with a formally designed experiment which samples the variability within the porcine animal population while parameters such as engineering material, contact area and bowel region were varied. Friction force measurements were collected within an environmental chamber which closely simulates in vivo conditions. The results indicate that micro-patterned polydimethylsiloxane (PDMS) yields a statistically significantly higher coefficient of friction (COF) than stainless steel or polycarbonate. The effects of contact area and bowel region vary across the porcine animal population. The COF under these conditions ranged from 0.0004 to 0.018.

Lyle, A.B., Luftig, J.T., Rentschler, M.E., "A Tribological Investigation of the Small Bowel Lumen Surface," Tribology International. 62: 171-176, 2013.

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