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Park JS, Kim J, Lee A, Kim HY. Snap-through inversion of elastic shells swelling via solvent diffusion. SOFT MATTER 2023; 19:8213-8220. [PMID: 37859545 DOI: 10.1039/d3sm01020a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/21/2023]
Abstract
Snap-through buckling instability of elastic shells can provide a variety of biological and artificial mechanical systems with an efficient strategy to generate rapid and powerful actuation. However, snapping spherical shells studied to date have typically been shallow and thus are dominantly prone to axisymmetric inversions. Here, we study diffusion-swelling stimulated snap-through inversion of bilayer shells of a wide range of depth to cover non-axisymmetric as well as axisymmetric modes. We first establish an analytical model of strain energy stored in axisymmetrically swelling shells, in order to predict the snap-through conditions based on energy minimization. Confirming that the strain energy can indicate the critical conditions for snap-through, we compare the conditions of axisymmetric and non-axisymmetric snap-through inversion using both experiments and numerical simulations. We find that differentially swelling bilayer shells snap-through with a time-lagged but increased energy release during inversion when buckled non-axisymmetrically rather than axisymmetrically.
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Affiliation(s)
- Ji-Sung Park
- Department of Mechanical Engineering, Seoul National University, Seoul 08826, Korea.
| | - Junseong Kim
- Department of Mechanical Engineering, Seoul National University, Seoul 08826, Korea.
| | - Anna Lee
- Department of Mechanical Engineering, Pohang University of Science and Technology, Pohang 37673, Korea
| | - Ho-Young Kim
- Department of Mechanical Engineering, Seoul National University, Seoul 08826, Korea.
- Institute of Advanced Machines and Design, Seoul National University, Seoul 08826, Korea
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2
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Abstract
Thermal actuation is a common actuation method for soft robots. However, a major limitation is the relatively slow actuation speed. Here we report significant increase in the actuation speed of a bimorph thermal actuator by harnessing the snap-through instability. The actuator is made of silver nanowire/polydimethylsiloxane composite. The snap-through instability is enabled by simply applying an offset displacement to part of the actuator structure. The effects of thermal conductivity of the composite, offset displacement, and actuation frequency on the actuator speed are investigated using both experiments and finite element analysis. The actuator yields a bending speed as high as 28.7 cm-1/s, 10 times that without the snap-through instability. A fast crawling robot with locomotion speed of 1.04 body length per second and a biomimetic Venus flytrap were demonstrated to illustrate the promising potential of the fast bimorph thermal actuators for soft robotic applications.
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Affiliation(s)
- Shuang Wu
- Department of Mechanical and Aerospace Engineering and North Carolina State University, Raleigh, North Carolina, USA
| | - Gregory Langston Baker
- Department of Mechanical and Aerospace Engineering and North Carolina State University, Raleigh, North Carolina, USA
| | - Jie Yin
- Department of Mechanical and Aerospace Engineering and North Carolina State University, Raleigh, North Carolina, USA
| | - Yong Zhu
- Department of Mechanical and Aerospace Engineering and North Carolina State University, Raleigh, North Carolina, USA.,Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, USA.,Joint Department of Biomedical Engineering, University of North Carolina-Chapel Hill and NC State University, Chapel Hill, North Carolina, USA
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3
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Wu D, He L. Study on the Mechanism of Elastic Instability Caused by Natural Growth in Orthotropic Material. MATERIALS (BASEL, SWITZERLAND) 2022; 15:7059. [PMID: 36295124 PMCID: PMC9605602 DOI: 10.3390/ma15207059] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/17/2022] [Revised: 10/03/2022] [Accepted: 10/06/2022] [Indexed: 06/16/2023]
Abstract
Compared to synthetic materials, naturally grown biological materials have more specific behavioral patterns and life connotations in their morphological evolution over millions of years of environmental evolution on Earth. In this paper, we investigate the physical mechanisms and manifestations of out-of-plane deformation instability. Firstly, the origin of the instability phenomenon caused by the growth of the leaf is introduced. Leaf instability problems are modeled using rectangular thin plates. Secondly, the variation in the critical intrinsic strain with the principal shear modulus is obtained by numerical solution. The post-buckling behavior of the growth instability is further analyzed by general static analysis, and we obtain the phase diagram of morphogenesis of thin plant organs as functions of the principal shear modulus and off-axis angle. The research results enhance the understanding of the mechanism of elastic instability caused by natural growth in orthotropic materials.
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4
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Stein-Montalvo L, Lee JH, Yang Y, Landesberg M, Park HS, Holmes DP. Efficient snap-through of spherical caps by applying a localized curvature stimulus. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2022; 45:3. [PMID: 35024982 DOI: 10.1140/epje/s10189-021-00156-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2021] [Accepted: 12/16/2021] [Indexed: 06/14/2023]
Abstract
In bistable actuators and other engineered devices, a homogeneous stimulus (e.g., mechanical, chemical, thermal, or magnetic) is often applied to an entire shell to initiate a snap-through instability. In this work, we demonstrate that restricting the active area to the shell boundary allows for a large reduction in its size, thereby decreasing the energy input required to actuate the shell. To do so, we combine theory with 1D finite element simulations of spherical caps with a non-homogeneous distribution of stimulus-responsive material. We rely on the effective curvature stimulus, i.e., the natural curvature induced by the non-mechanical stimulus, which ensures that our results are entirely stimulus-agnostic. To validate our numerics and demonstrate this generality, we also perform two sets of experiments, wherein we use residual swelling of bilayer silicone elastomers-a process that mimics differential growth-as well as a magneto-elastomer to induce curvatures that cause snap-through. Our results elucidate the underlying mechanics, offering an intuitive route to optimal design for efficient snap-through.
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Affiliation(s)
- Lucia Stein-Montalvo
- Department of Mechanical Engineering, Boston University, Boston, USA
- Department of Civil and Environmental Engineering, Princeton University, Princeton, USA
| | - Jeong-Ho Lee
- Department of Mechanical Engineering, Boston University, Boston, USA
| | - Yi Yang
- Department of Mechanical Engineering, Boston University, Boston, USA
- Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, USA
| | - Melanie Landesberg
- Department of Mechanical Engineering, Boston University, Boston, USA
- Yale University, New Haven, USA
| | - Harold S Park
- Department of Mechanical Engineering, Boston University, Boston, USA
| | - Douglas P Holmes
- Department of Mechanical Engineering, Boston University, Boston, USA.
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5
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Abstract
Mechanical mechanisms have been used to process information for millennia, with famous examples ranging from the Antikythera mechanism of the Ancient Greeks to the analytical machines of Charles Babbage. More recently, electronic forms of computation and information processing have overtaken these mechanical forms, owing to better potential for miniaturization and integration. However, several unconventional computing approaches have recently been introduced, which blend ideas of information processing, materials science and robotics. This has raised the possibility of new mechanical computing systems that augment traditional electronic computing by interacting with and adapting to their environment. Here we discuss the use of mechanical mechanisms, and associated nonlinearities, as a means of processing information, with a view towards a framework in which adaptable materials and structures act as a distributed information processing network, even enabling information processing to be viewed as a material property, alongside traditional material properties such as strength and stiffness. We focus on approaches to abstract digital logic in mechanical systems, discuss how these systems differ from traditional electronic computing, and highlight the challenges and opportunities that they present.
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6
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Shen B, Erol O, Fang L, Kang SH. Programming the time into 3D printing: current advances and future directions in 4D printing. ACTA ACUST UNITED AC 2020. [DOI: 10.1088/2399-7532/ab54ea] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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7
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Ali S, Baloch AM. Overview of Sustainable Plant Growth and Differentiation and the Role of Hormones in Controlling Growth and Development of Plants Under Various Stresses. Recent Pat Food Nutr Agric 2019; 11:105-114. [PMID: 31215383 DOI: 10.2174/2212798410666190619104712] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2018] [Revised: 10/18/2018] [Accepted: 11/19/2018] [Indexed: 12/15/2022]
Abstract
Plant development is different from animals by many fundamental aspects; as they have immobilized cells, a rigid cell wall, and the large central vacuole. Plant growth and cell division are restricted to the specific area of the shoot and root called meristems. Plants have the ability to carry out differentiation, dedifferentiation and redifferentiation. In plants, the growth and differentiation processes are controlled by hormonal and genetic factors. Phytohormones can exert independent/ dependent actions on plant growth and development. A pool of stem cells is placed at the niche of the apex meristem, which is the source of self-renewal of the cell system and its maintenance to provide cells to differentiated tissues. A complex interaction network between hormones and other factors maintains a balance between cell division and differentiation. Auxins promote the growth, gibberellins' function in seed germination, cytokinin's influence on cell division and delay leaf senescence; abscisic acid promotes the stomatal closure and bud dormancy, while salicylic acid promotes resistance against different diseases. Plants are often exposed to different abiotic and biotic stresses, for example, heat, cold, drought, salinity etc., whereas biotic stress arises mainly from fungi, bacteria, insect, etc. Phytohormones play a critical role in well-developed mechanisms that help to perceive the stress signal and enable the plant's optimal growth response. In this review, we studied both the intrinsic and extrinsic factors which govern growth and differentiation of plants under normal and stress condition. This review also deals with genetic modifications occurring in the cell and cell signaling during growth and differentiation.
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Affiliation(s)
- Shahid Ali
- College of Life Science, Northeast Forestry University, Harbin, Heilongjiang 150040, China
| | - Abdul Majeed Baloch
- Department of Horticulture, Sindh Agriculture University Hyderabad, Pakistan
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9
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Jiang Y, Korpas LM, Raney JR. Bifurcation-based embodied logic and autonomous actuation. Nat Commun 2019; 10:128. [PMID: 30631058 PMCID: PMC6328580 DOI: 10.1038/s41467-018-08055-3] [Citation(s) in RCA: 56] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2018] [Accepted: 12/12/2018] [Indexed: 11/09/2022] Open
Abstract
Many plants autonomously change morphology and function in response to environmental stimuli or sequences of stimuli. In contrast with the electronically-integrated sensors, actuators, and microprocessors in traditional mechatronic systems, natural systems embody these sensing, actuation, and control functions within their compositional and structural features. Inspired by nature, we embody logic in autonomous systems to enable them to respond to multiple stimuli. Using 3D printable fibrous composites, we fabricate structures with geometries near bifurcation points associated with a transition between bistability and monostability. When suitable stimuli are present, the materials swell anisotropically. This forces a key geometric parameter to pass through a bifurcation, triggering rapid and large-amplitude self-actuation. The actuation time can be programmed by varying structural parameters (from 0.6 to 108 s for millimeter-scale structures). We demonstrate this bioinspired control strategy with examples that respond to their environment according to their embodied logic, without electronics, external control, or tethering.
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Affiliation(s)
- Yijie Jiang
- Department of Mechanical Engineering and Applied Mechanics, 220 S 33rd St., University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - Lucia M Korpas
- Department of Mechanical Engineering and Applied Mechanics, 220 S 33rd St., University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - Jordan R Raney
- Department of Mechanical Engineering and Applied Mechanics, 220 S 33rd St., University of Pennsylvania, Philadelphia, PA, 19104, USA.
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10
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Huang C, Wang Z, Quinn D, Suresh S, Hsia KJ. Differential growth and shape formation in plant organs. Proc Natl Acad Sci U S A 2018; 115:12359-12364. [PMID: 30455311 PMCID: PMC6298086 DOI: 10.1073/pnas.1811296115] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Morphogenesis is a phenomenon by which a wide variety of functional organs are formed in biological systems. In plants, morphogenesis is primarily driven by differential growth of tissues. Much effort has been devoted to identifying the role of genetic and biomolecular pathways in regulating cell division and cell expansion and in influencing shape formation in plant organs. However, general principles dictating how differential growth controls the formation of complex 3D shapes in plant leaves and flower petals remain largely unknown. Through quantitative measurements on live plant organs and detailed finite-element simulations, we show how the morphology of a growing leaf is determined by both the maximum value and the spatial distribution of growth strain. With this understanding, we develop a broad scientific framework for a morphological phase diagram that is capable of rationalizing four configurations commonly found in plant organs: twisting, helical twisting, saddle bending, and edge waving. We demonstrate the robustness of these findings and analyses by recourse to synthetic reproduction of all four configurations using controlled polymerization of a hydrogel. Our study points to potential approaches to innovative geometrical design and actuation in such applications as building architecture, soft robotics and flexible electronics.
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Affiliation(s)
- Changjin Huang
- Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
| | - Zilu Wang
- Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
| | - David Quinn
- Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
| | - Subra Suresh
- Nanyang Technological University, 639798 Singapore, Republic of Singapore;
| | - K Jimmy Hsia
- Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213;
- Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
- School of Mechanical and Aerospace Engineering, Nanyang Technological University, 639798 Singapore, Republic of Singapore
- School of Chemical and Biomedical Engineering, Nanyang Technological University, 639798 Singapore, Republic of Singapore
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11
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Liang Z, Liu Y, Zhang F, Ai Y, Liang Q. Dehydration-triggered shape morphing based on asymmetric bubble hydrogel microfibers. SOFT MATTER 2018; 14:6623-6626. [PMID: 29938287 DOI: 10.1039/c8sm00984h] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Inspired by nature, scientists have been engaged in developing deformable artificial systems. Here, we propose an innovative method to realize controllable deformations using asymmetric bubble hydrogel microfibers produced by microfluidic cascaded coaxial devices. Asymmetric geometries, coupled with the mismatched shrinkage ratio, contribute to deformations upon dehydration. The dynamic process can be controlled by regulating bubble sizes, distances and packing modes. Various 4D structures have been constructed. Combined with the 3D printing technique, this proof-of-concept study may open new avenues for bio-engineering and beyond.
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Affiliation(s)
- Zhe Liang
- MOE Key Laboratory Bioorganic Phosphorous Chemistry & Chemical Biology, Beijing Key Laboratory of Microanalytical Methods & Instrumentation, Department of Chemistry, Tsinghua University, Beijing, 100084, China.
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12
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Abdullah AM, Li X, Braun PV, Rogers JA, Hsia KJ. Self-Folded Gripper-Like Architectures from Stimuli-Responsive Bilayers. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:e1801669. [PMID: 29921009 DOI: 10.1002/adma.201801669] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2018] [Revised: 04/20/2018] [Indexed: 06/08/2023]
Abstract
Self-folding microgrippers are an emerging class of smart structures that have widespread applications in medicine and micro/nanomanipulation. To achieve their functionalities, these architectures rely on spatially patterned hinges to transform into 3D configurations in response to an external stimulus. Incorporating hinges into the devices requires the processing of multiple layers which eventually increases the fabrication costs and actuation complexities. The goal of this work is to demonstrate that it is possible to achieve gripper-like configurations in an on-demand manner from simple planar bilayers that do not require hinges for their actuation. Finite element modeling of bilayers is performed to understand the mechanics behind their stimuli-responsive shape transformation behavior. The model predictions are then experimentally validated and axisymmetric gripper-like shapes are realized using millimeter-scale poly(dimethylsiloxane) bilayers that undergo differential swelling in organic solvents. Owing to the nature of the computational scheme which is independent of length scales and material properties, the guidelines reported here would be applicable to a diverse array of gripping systems and functional devices. Thus, this work not only demonstrates a simple route to fabricate functional microgrippers but also contributes to self-assembly in general.
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Affiliation(s)
- Arif M Abdullah
- Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Xiuling Li
- Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Paul V Braun
- Department of Materials Science and Engineering, Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - John A Rogers
- Center for Bio-Integrated Electronics, Departments of Materials Science and Engineering, Biomedical Engineering, Chemistry,, Mechanical Engineering, Electrical Engineering and Computer Science, and Neurological Surgery, Simpson Querrey Institute for Nano/Biotechnology, McCormick School of Engineering, Feinberg School of Medicine, Northwestern University, Evanston, IL, 60208, USA
| | - K Jimmy Hsia
- Departments of Mechanical Engineering and Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA, 15213, USA
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13
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Pezzulla M, Stoop N, Steranka MP, Bade AJ, Holmes DP. Curvature-Induced Instabilities of Shells. PHYSICAL REVIEW LETTERS 2018; 120:048002. [PMID: 29437411 DOI: 10.1103/physrevlett.120.048002] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2017] [Revised: 12/05/2017] [Indexed: 06/08/2023]
Abstract
Induced by proteins within the cell membrane or by differential growth, heating, or swelling, spontaneous curvatures can drastically affect the morphology of thin bodies and induce mechanical instabilities. Yet, the interaction of spontaneous curvature and geometric frustration in curved shells remains poorly understood. Via a combination of precision experiments on elastomeric spherical shells, simulations, and theory, we show how a spontaneous curvature induces a rotational symmetry-breaking buckling as well as a snapping instability reminiscent of the Venus fly trap closure mechanism. The instabilities, and their dependence on geometry, are rationalized by reducing the spontaneous curvature to an effective mechanical load. This formulation reveals a combined pressurelike term in the bulk and a torquelike term in the boundary, allowing scaling predictions for the instabilities that are in excellent agreement with experiments and simulations. Moreover, the effective pressure analogy suggests a curvature-induced subcritical buckling in closed shells. We determine the critical buckling curvature via a linear stability analysis that accounts for the combination of residual membrane and bending stresses. The prominent role of geometry in our findings suggests the applicability of the results over a wide range of scales.
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Affiliation(s)
- Matteo Pezzulla
- Department of Mechanical Engineering, Boston University, Boston, Massachusetts 02215, USA
| | - Norbert Stoop
- Department of Mathematics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Mark P Steranka
- Department of Mechanical Engineering, Boston University, Boston, Massachusetts 02215, USA
| | - Abdikhalaq J Bade
- Department of Mechanical Engineering, Boston University, Boston, Massachusetts 02215, USA
| | - Douglas P Holmes
- Department of Mechanical Engineering, Boston University, Boston, Massachusetts 02215, USA
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14
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Controlled molecular self-assembly of complex three-dimensional structures in soft materials. Proc Natl Acad Sci U S A 2017; 115:70-74. [PMID: 29255037 PMCID: PMC5776829 DOI: 10.1073/pnas.1717912115] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Many applications in tissue engineering, flexible electronics, and soft robotics call for approaches that are capable of producing complex 3D architectures in soft materials. Here we present a method using molecular self-assembly to generate hydrogel-based 3D architectures that resembles the appealing features of the bottom-up process in morphogenesis of living tissues. Our strategy effectively utilizes the three essential components dictating living tissue morphogenesis to produce complex 3D architectures: modulation of local chemistry, material transport, and mechanics, which can be engineered by controlling the local distribution of polymerization inhibitor (i.e., oxygen), diffusion of monomers/cross-linkers through the porous structures of cross-linked polymer network, and mechanical constraints, respectively. We show that oxygen plays a role in hydrogel polymerization which is mechanistically similar to the role of growth factors in tissue growth, and the continued growth of hydrogel enabled by diffusion of monomers/cross-linkers into the porous hydrogel similar to the mechanisms of tissue growth enabled by material transport. The capability and versatility of our strategy are demonstrated through biomimetics of tissue morphogenesis for both plants and animals, and its application to generate other complex 3D architectures. Our technique opens avenues to studying many growth phenomena found in nature and generating complex 3D structures to benefit diverse applications.
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15
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Hubbard AM, Mailen RW, Zikry MA, Dickey MD, Genzer J. Controllable curvature from planar polymer sheets in response to light. SOFT MATTER 2017; 13:2299-2308. [PMID: 28233884 DOI: 10.1039/c7sm00088j] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The ability to change shape and control curvature in 3D structures starting from planar sheets can aid in assembly and add functionality to an object. Herein, we convert planar sheets of shape memory polymers (SMPs) into 3D objects with controllable curvature by dictating where the sheets shrink. Ink patterned on the surface of the sheet absorbs infrared (IR) light, resulting in localized heating, and the material shrinks locally wherever the temperature exceeds the activation temperature, Ta. We introduce two different mechanisms for controlling curvature within SMP sheets. The 'direct' mechanism uses localized shrinkage to induce curvature only in regions patterned with ink. The 'indirect' mechanism uses localized shrinkage in regions patterned with ink to induce curvature in neighboring regions without ink through a balance of internal stresses. Finite element analysis predicts the final shape of the polymer sheets with excellent qualitative agreement with experimental studies. Results from this study show that curvature can be controlled by the distribution and darkness of the ink pattern on the polymer sheet. Additionally, we utilize the direct and indirect curvature mechanisms to demonstrate the formation and actuation of gripper devices, which represent the potential utility of this approach.
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Affiliation(s)
- Amber M Hubbard
- Department of Chemical and Biomolecular Engineering, NC State University, Campus Box 7905, Raleigh, NC 27695-7905, USA.
| | - Russell W Mailen
- Department of Mechanical and Aerospace Engineering, NC State University, Campus Box 7910, Raleigh, NC 27695-7910, USA
| | - Mohammed A Zikry
- Department of Mechanical and Aerospace Engineering, NC State University, Campus Box 7910, Raleigh, NC 27695-7910, USA
| | - Michael D Dickey
- Department of Chemical and Biomolecular Engineering, NC State University, Campus Box 7905, Raleigh, NC 27695-7905, USA.
| | - Jan Genzer
- Department of Chemical and Biomolecular Engineering, NC State University, Campus Box 7905, Raleigh, NC 27695-7905, USA.
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