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Chittajallu SNSH, Gururani H, Tse KM, Rath SN, Basu S, Chinthapenta V. Investigation of microstructural failure in the human cornea through fracture tests. Sci Rep 2023; 13:13876. [PMID: 37620375 PMCID: PMC10449857 DOI: 10.1038/s41598-023-40286-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2023] [Accepted: 08/08/2023] [Indexed: 08/26/2023] Open
Abstract
Fracture toughness of the human cornea is one of the critical parameters in suture-involved corneal surgeries and the development of bioengineered mimetics of the human cornea. The present article systematically studied the fracture characteristics of the human cornea to evaluate its resistance to tear in the opening (Mode-I) and trouser tear mode (Mode-III). Tear experiments reveal the dependency of the fracture behavior on the notch size and its location created in the corneal specimens. The findings indicate lamellar tear and collagen fiber pull-out as a failure mechanism in trouser tear and opening mode tests, respectively. Experimental results have shown a localized variation of tear behavior in trouser tear mode and indicated an increasing resistance to tear from the corneal center to the periphery. This article demonstrated the complications of evaluating fracture toughness in opening mode and showed that the limbus was weaker than the cornea and sclera against tearing. The overall outcomes of the present study help in designing experiments to understand the toughness of the diseased tissues, understanding the effect of the suturing location and donor placement, and creating numerical models to study parameters affecting corneal replacement surgery.
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Affiliation(s)
- Sai Naga Sri Harsha Chittajallu
- Department of Mechanical and Aerospace Engineering, Indian Institute of Technology Hyderabad (IIT Hyderabad), Hyderabad, India
- Department of Mechanical and Product Design Engineering, Swinburne University of Technology, Melbourne, Australia
- Centre for Technology Innovation, LV Prasad Eye Institute, Hyderabad, India
| | - Himanshu Gururani
- Department of Mechanical and Aerospace Engineering, Indian Institute of Technology Hyderabad (IIT Hyderabad), Hyderabad, India
| | - Kwong Ming Tse
- Department of Mechanical and Product Design Engineering, Swinburne University of Technology, Melbourne, Australia
| | - Subha Narayan Rath
- Department of Biomedical Engineering, Indian Institute of Technology Hyderabad, Hyderabad, India
| | - Sayan Basu
- Prof. Brien Holden Eye Research Centre, LV Prasad Eye Institute, Hyderabad, India
| | - Viswanath Chinthapenta
- Department of Mechanical and Aerospace Engineering, Indian Institute of Technology Hyderabad (IIT Hyderabad), Hyderabad, India.
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2
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Picu R, Jin S. Toughness of Network Materials: Structural Parameters Controlling Damage Accumulation. JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 2023; 172:105176. [PMID: 36582492 PMCID: PMC9794194 DOI: 10.1016/j.jmps.2022.105176] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Many materials have a network of fibers as their main structural component and are referred to as network materials. Their strength and toughness are important in both engineering and biology. In this work we consider stochastic model fiber networks without pre-existing cracks and study their rupture mechanism. These materials soften as the crosslinks or fibers fail and exhibit either brittle failure immediately after the peak stress, or a more gradual, ductile rupture in the post peak regime. We observe that ductile failure takes place at constant energy release rate defined in the absence of pre-existing cracks as the strain derivative of the specific energy released. The network parameters controlling the energy release rate are identified and discussed in relation to the Lake-Thomas theory which applies to crack growth situations. We also observe a ductile to brittle failure transition as the network becomes more affine and relate the embrittlement to the reduction of mechanical heterogeneity of the network. Further, we confirm previous reports that the network strength scales linearly with the bond strength and with the crosslink density. The present results extend the Lake-Thomas theory to networks without pre-existing cracks which fail by the gradual accumulation of distributed damage and contribute to the development of a physical picture of failure in stochastic network materials.
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Affiliation(s)
- R.C. Picu
- Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180
| | - S. Jin
- Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180
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3
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How the Nonwoven Polymer Volume Microstructure Is Transformed under Tension in an Aqueous Environment. Polymers (Basel) 2022; 14:polym14173526. [PMID: 36080601 PMCID: PMC9460304 DOI: 10.3390/polym14173526] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2022] [Revised: 08/24/2022] [Accepted: 08/26/2022] [Indexed: 11/27/2022] Open
Abstract
The fibrous porous structure of polymers can mimic the extracellular matrix of the native tissue, therefore such polymers have a good potential for use in regenerative medicine. Organs and tissues within the body exhibit different mechanical properties depending on their functionality, thus artificial scaffolds should have mechanical behaviors similar to the extracellular matrix in conditions like living organisms, primarily in aqueous media. Several methods have been investigated in aquatic environments, including noninvasive techniques based on ultrasonic focused beams for biological objectives. In this study we explored the tensile behavior of poly(L-lactide) nonwoven polymer scaffolds using high-frequency ultrasound microscopy combined with a horizontal testing machine, which provided a visualization of the reorganization and transformation of the dynamic volume microstructure. The mechanisms of unwinding, elongation, orientation, and deformation of polymer fibers under uniaxial tension were revealed. We observed an association between the lined plastic deformation from 100 to 400% and the formation of multiple necks in the fibers, which caused stress relaxation and significant rarefaction of the fibrous microstructure. It was shown that both peaks on the stress–strain curve corresponded to the microstructure of aligned fibers in terms of initial diameter and thinning fibers. We discuss the possible influence of these microstructure transformations on cell behavior.
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4
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Lai CSE, Leyva-Aranda V, Kong VH, Lopez-Silva TL, Farsheed AC, Cristobal CD, Swain JWR, Lee HK, Hartgerink JD. A Combined Conduit-Bioactive Hydrogel Approach for Regeneration of Transected Sciatic Nerves. ACS APPLIED BIO MATERIALS 2022; 5:10.1021/acsabm.2c00132. [PMID: 35446025 PMCID: PMC11097895 DOI: 10.1021/acsabm.2c00132] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Transected peripheral nerve injury (PNI) affects the quality of life of patients, which leads to socioeconomic burden. Despite the existence of autografts and commercially available nerve guidance conduits (NGCs), the complexity of peripheral nerve regeneration requires further research in bioengineered NGCs to improve surgical outcomes. In this work, we introduce multidomain peptide (MDP) hydrogels, as intraluminal fillers, into electrospun poly(ε-caprolactone) (PCL) conduits to bridge 10 mm rat sciatic nerve defects. The efficacy of treatment groups was evaluated by electromyography and gait analysis to determine their electrical and motor recovery. We then studied the samples' histomorphometry with immunofluorescence staining and automatic axon counting/measurement software. Comparison with negative control group shows that PCL conduits filled with an anionic MDP may improve functional recovery 16 weeks postoperation, displaying higher amplitude of compound muscle action potential, greater gastrocnemius muscle weight retention, and earlier occurrence of flexion contracture. In contrast, PCL conduits filled with a cationic MDP showed the least degree of myelination and poor functional recovery. This phenomenon may be attributed to MDPs' difference in degradation time. Electrospun PCL conduits filled with an anionic MDP may become an attractive tissue engineering strategy for treating transected PNI when supplemented with other bioactive modifications.
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Affiliation(s)
- Cheuk Sun Edwin Lai
- Department of Bioengineering, Rice University, Houston, Texas 77005, United States
| | | | - Victoria H Kong
- Department of Bioengineering, Rice University, Houston, Texas 77005, United States
| | - Tania L Lopez-Silva
- Department of Chemistry, Rice University, Houston, Texas 77005, United States
| | - Adam C Farsheed
- Department of Bioengineering, Rice University, Houston, Texas 77005, United States
| | - Carlo D Cristobal
- Integrative Program in Molecular and Biomedical Sciences, Baylor College of Medicine, Houston, Texas 77030, United States
| | - Joseph W R Swain
- Department of Chemistry, Rice University, Houston, Texas 77005, United States
| | - Hyun Kyoung Lee
- Integrative Program in Molecular and Biomedical Sciences, Baylor College of Medicine, Houston, Texas 77030, United States
- Department of Pediatrics, Jan and Dan Duncan Neurological Research Institute, Texas Children's Hospital, Houston, Texas 77030, United States
| | - Jeffrey D Hartgerink
- Department of Bioengineering, Rice University, Houston, Texas 77005, United States
- Department of Chemistry, Rice University, Houston, Texas 77005, United States
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5
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Alsmairat O, Barakat N. Characterizing the Effect of Adding Boron Nitride Nanotubes on the Mechanical Properties of Electrospun Polymer Nanocomposite Microfibers Mesh. MATERIALS (BASEL, SWITZERLAND) 2022; 15:1634. [PMID: 35268874 PMCID: PMC8911170 DOI: 10.3390/ma15051634] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/04/2022] [Revised: 02/11/2022] [Accepted: 02/15/2022] [Indexed: 02/04/2023]
Abstract
Electrospun fibrous meshes have a variety of applications such as filtration, drug delivery, energy storage, and engineered tissues due to their high surface area to mass ratio. Therefore, understanding the mechanical properties of these continuously evolving meshes is critical to expand and improve their performance. In this study, the effect of adding Boron Nitride Nanotube (BNNT) to Polymethylmethacrylate (PMMA) composite meshes on the mechanical properties of the polymer is studied. Electrospinning is used to fabricate microfiber meshes of PMMA and BNNT-PMMA. The fabricated meshes are tested experimentally with a uniaxial tensile tester. In addition, a theoretical model is introduced to investigate the effect of the number of fibers and the diameter of fiber inside the mesh on Young's Modulus and Tensile Strength of the PMMA mesh. By adding 0.5% BNNT to the PMMA, Young's Modulus and Tensile Strength of the PMMA mesh improved by 62.4% and 9.3%, respectively. Furthermore, simulated results show enhanced mesh properties when increasing the number of fibers and the single fiber diameter inside the mesh. The findings of this study help in understanding the mechanical properties of the nanocomposite electrospun meshes which expands and improves its utilization in different applications.
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Affiliation(s)
- Ohood Alsmairat
- Department of Mechanical Engineering, The University of Texas at Tyler, 3900 University Blvd., Tyler, TX 75799, USA;
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6
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Elkhouly H, Mamdouh W, El-Korashy DI. Electrospun nano-fibrous bilayer scaffold prepared from polycaprolactone/gelatin and bioactive glass for bone tissue engineering. JOURNAL OF MATERIALS SCIENCE. MATERIALS IN MEDICINE 2021; 32:111. [PMID: 34453628 PMCID: PMC8403125 DOI: 10.1007/s10856-021-06588-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/13/2020] [Accepted: 07/20/2021] [Indexed: 06/13/2023]
Abstract
This work is focused on integrating nanotechnology with bone tissue engineering (BTE) to fabricate a bilayer scaffold with enhanced biological, physical and mechanical properties, using polycaprolactone (PCL) and gelatin (Gt) as the base nanofibrous layer, followed by the deposition of a bioactive glass (BG) nanofibrous layer via the electrospinning technique. Electrospun scaffolds were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy. Surface area and porosity were evaluated using the nitrogen adsorption method and mercury intrusion porosimetry. Moreover, scaffold swelling rate, degradation rate and in vitro bioactivity were examined in simulated body fluid (SBF) for up to 14 days. Mechanical properties of the prepared scaffolds were evaluated. Cell cytotoxicity was assessed using MRC-5 cells. Analyses showed successful formation of bead-free uniform fibers and the incorporation of BG nanoparticles within fibers. The bilayer scaffold showed enhanced surface area and total pore volume in comparison to the composite single layer scaffold. Moreover, a hydroxyapatite-like layer with a Ca/P molar ratio of 1.4 was formed after 14 days of immersion in SBF. Furthermore, its swelling and degradation rates were significantly higher than those of pure PCL scaffold. The bilayer's tensile strength was four times higher than that of PCL/Gt scaffold with greatly enhanced elongation. Cytotoxicity test revealed the bilayer's biocompatibility. Overall analyses showed that the incorporation of BG within a bilayer scaffold enhances the scaffold's properties in comparison to those of a composite single layer scaffold, and offers potential avenues for development in the field of BTE.
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Affiliation(s)
- Hend Elkhouly
- Biomaterials Department, Faculty of Dentistry, Ain Shams University, Organization of African Unity St., El-Qobba Bridge, Al Waili, Cairo, 11566, Egypt
| | - Wael Mamdouh
- Department of Chemistry, School of Sciences and Engineering, The American University in Cairo (AUC), AUC Avenue, P.O. Box 74, New Cairo, 11835, Egypt.
| | - Dalia I El-Korashy
- Biomaterials Department, Faculty of Dentistry, Ain Shams University, Organization of African Unity St., El-Qobba Bridge, Al Waili, Cairo, 11566, Egypt
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7
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Bansal S, Peloquin JM, Keah NM, O'Reilly OC, Elliott DM, Mauck RL, Zgonis MH. Structure, function, and defect tolerance with maturation of the radial tie fiber network in the knee meniscus. J Orthop Res 2020; 38:2709-2720. [PMID: 32301519 PMCID: PMC7572531 DOI: 10.1002/jor.24697] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/07/2019] [Revised: 04/03/2020] [Accepted: 04/11/2020] [Indexed: 02/04/2023]
Abstract
The knee menisci are comprised of two orthogonal collagenous networks-circumferential and radial-that combine to enable efficient load bearing by the tissue in adults. Here, we assessed how the structural and functional characteristics of these networks developed over the course of skeletal maturation and determined the role of these fiber networks in defect tolerance with tissue injury. Imaging of the radial tie fiber (RTF) collagen structure in medial bovine menisci from fetal, juvenile, and adult specimens showed increasing heterogeneity, anisotropy, thickness, and density with skeletal development. The mechanical analysis showed that the tensile modulus in the radial direction did not change with skeletal development, though the resilience (in the radial direction) increased and the tolerance to defects in the circumferential direction decreased, in adult compared to fetal tissues. This loss of defect tolerance correlated with increased order in the RTF network in adult tissue. These data provide new insights into the role of the radial fiber network in meniscus function, will lead to improved clinical decision-making in the presence of a tear and may improve engineering efforts to reproduce this critical load-bearing structure in the knee.
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Affiliation(s)
- Sonia Bansal
- Department of Orthopaedic Surgery, McKay Orthopaedic Research Laboratory, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
- Department of Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania
- Translational Musculoskeletal Research Center, Corporal Michael J Crescenz Veterans Administration Medical Center, Philadelphia, Pennsylvania
| | - John M Peloquin
- Department of Biomedical Engineering, University of Delaware, Newark, Delaware
| | - Niobra M Keah
- Department of Orthopaedic Surgery, McKay Orthopaedic Research Laboratory, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
- Translational Musculoskeletal Research Center, Corporal Michael J Crescenz Veterans Administration Medical Center, Philadelphia, Pennsylvania
| | - Olivia C O'Reilly
- Department of Orthopaedic Surgery, McKay Orthopaedic Research Laboratory, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
- Translational Musculoskeletal Research Center, Corporal Michael J Crescenz Veterans Administration Medical Center, Philadelphia, Pennsylvania
| | - Dawn M Elliott
- Department of Biomedical Engineering, University of Delaware, Newark, Delaware
| | - Robert L Mauck
- Department of Orthopaedic Surgery, McKay Orthopaedic Research Laboratory, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
- Department of Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania
- Translational Musculoskeletal Research Center, Corporal Michael J Crescenz Veterans Administration Medical Center, Philadelphia, Pennsylvania
| | - Miltiadis H Zgonis
- Department of Orthopaedic Surgery, McKay Orthopaedic Research Laboratory, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
- Translational Musculoskeletal Research Center, Corporal Michael J Crescenz Veterans Administration Medical Center, Philadelphia, Pennsylvania
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8
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9
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Yoshida K, Jayyosi C, Lee N, Mahendroo M, Myers KM. Mechanics of cervical remodelling: insights from rodent models of pregnancy. Interface Focus 2019; 9:20190026. [PMID: 31485313 PMCID: PMC6710664 DOI: 10.1098/rsfs.2019.0026] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/28/2019] [Indexed: 01/01/2023] Open
Abstract
The uterine cervix undergoes a complex remodelling process during pregnancy, characterized by dramatic changes in both extracellular matrix (ECM) structure and mechanical properties. Understanding the cervical remodelling process in a term or preterm birth will aid efforts for the prevention of preterm births (PTBs), which currently affect 14.8 million babies annually worldwide. Animal models of pregnancy, particularly rodents, continue to provide valuable insights into the cervical remodelling process, through the study of changes in ECM structure and mechanical properties at defined gestation time points. Currently, there is a lack of a collective, quantitative framework to relate the complex, nonlinear mechanical behaviour of the rodent cervix to changes in ECM structure. This review aims to fill this gap in knowledge by outlining the current understanding of cervical remodelling during pregnancy in rodent models in the context of solid biomechanics. Here we highlight the collective contribution of multiple mechanical studies which give evidence that cervical softening coincides with known ECM changes throughout pregnancy. Taken together, mechanical tests on tissue from pregnant rodents reveal the cervix's remarkable ability to soften dramatically during gestation to allow for a compliant tissue that can withstand damage and can dissipate mechanical loads.
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Affiliation(s)
- Kyoko Yoshida
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Charles Jayyosi
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Nicole Lee
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Mala Mahendroo
- Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Kristin M. Myers
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
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10
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Bircher K, Ehret AE, Spiess D, Ehrbar M, Simões-Wüst AP, Ochsenbein-Kölble N, Zimmermann R, Mazza E. On the defect tolerance of fetal membranes. Interface Focus 2019; 9:20190010. [PMID: 31485307 DOI: 10.1098/rsfs.2019.0010] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/15/2019] [Indexed: 11/12/2022] Open
Abstract
A series of mechanical experiments were performed to quantify the strength and fracture toughness of human amnion and chorion. The experiments were complemented with computational investigations using a 'hybrid' model that includes an explicit representation of the collagen fibre network of amnion. Despite its much smaller thickness, amnion is shown to be stiffer, stronger and tougher than chorion, and thus to determine the mechanical response of fetal membranes, with respect to both, deformation and fracture behaviour. Data from uniaxial tension and fracture tests were used to inform and validate the computational model, which was then applied to rationalize measurements of the tear resistance of tissue samples containing crack-like defects. Experiments and computations show that the strength of amnion is not significantly reduced by defects smaller than 1 mm, but the crack size induced by perforations for amniocentesis and fetal membrane suturing during fetal surgery might be larger than this value. In line with previous experimental observations, the computational model predicts a very narrow near field at the crack tip of amnion, due to localized fibre alignment and collagen compaction. This mechanism shields the tissue from the defect and strongly reduces the interaction of multiple adjacent cracks. These findings were confirmed through corresponding experiments, showing that no interaction is expected for multiple sutures for an inter-suture distance larger than 1 mm and 3 mm for amnion and chorion, respectively. The experimental procedures and numerical models applied in the present study might be used to optimize needle and/or staple dimensions and inter-suture distance, and thus to reduce the risk of iatrogenic preterm premature rupture of the membranes from amniocentesis, fetoscopic and open prenatal surgery.
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Affiliation(s)
- Kevin Bircher
- ETH Zurich, Institute for Mechanical Systems, 8092 Zurich, Switzerland
| | - Alexander E Ehret
- ETH Zurich, Institute for Mechanical Systems, 8092 Zurich, Switzerland.,Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland
| | - Deborah Spiess
- Department of Obstetrics, University Hospital Zurich, 8091 Zurich, Switzerland
| | - Martin Ehrbar
- Department of Obstetrics, University Hospital Zurich, 8091 Zurich, Switzerland
| | | | | | - Roland Zimmermann
- Department of Obstetrics, University Hospital Zurich, 8091 Zurich, Switzerland
| | - Edoardo Mazza
- ETH Zurich, Institute for Mechanical Systems, 8092 Zurich, Switzerland.,Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland
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11
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Koh CT, Tonsomboon K, Oyen ML. Fracture toughness of human amniotic membranes. Interface Focus 2019; 9:20190012. [PMID: 31485308 DOI: 10.1098/rsfs.2019.0012] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/20/2019] [Indexed: 01/23/2023] Open
Abstract
Amnion is a membrane that surrounds and structurally protects the developing fetus during pregnancy. The rupture of amniotic membranes prior to both normal and preterm deliveries involves stretch forces acting on a biochemically triggered weak zone of the membranes. Fracture toughness is an important mechanical property describing how the membranes containing a defect resist fracture, but this property has never been investigated in amniotic membranes. In this work, the fracture toughness of many samples cut from four pieces of amniotic membrane from different mothers was examined by uniaxial and pure shear (mode I) fracture tests. The measurement was checked for dependence on the sample geometry and notch length. Results from the uniaxial tensile test show J-shaped stress-strain curves and confirm that the amniotic membrane is a nonlinear material. The measured fracture toughness of four amniotic membranes ranged from 0.96 ± 0.11 to 1.83 ± 0.18 kJ m-2. Despite considering the effect of the presence of the defect on mechanical property measurement, similar fracture behaviour was observed for pre-notched and unnotched specimens, indicating that the membranes were extremely tolerant to defects. This defect-tolerant characteristic provides insight into the understanding of fetal membrane rupture.
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Affiliation(s)
- Ching Theng Koh
- Department of Engineering, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ, UK.,Faculty of Mechanical and Manufacturing Engineering, Universiti Tun Hussein Onn Malaysia, 81310 Parit Raja, Johor, Malaysia
| | - Khaow Tonsomboon
- Department of Engineering, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ, UK
| | - Michelle L Oyen
- Department of Engineering, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ, UK
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12
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Deogekar S, Yan Z, Picu RC. Random Fiber Networks With Superior Properties Through Network Topology Control. JOURNAL OF APPLIED MECHANICS 2019; 86:81010-NaN. [PMID: 31666750 PMCID: PMC6694714 DOI: 10.1115/1.4043828] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2019] [Revised: 05/02/2019] [Accepted: 05/03/2019] [Indexed: 05/22/2023]
Abstract
In this work, we study the effect of network architecture on the nonlinear elastic behavior and strength of athermal random fiber networks of cellular type. We introduce a topology modification of Poisson-Voronoi (PV) networks with convex cells, leading to networks with stochastic nonconvex cells. Geometric measures are developed to characterize this new class of nonconvex Voronoi (NCV) networks. These are softer than the reference PV networks at the same nominal network parameters such as density, cross-link density, fiber diameter, and connectivity number. Their response is linear elastic over a broad range of strains, unlike PV networks that exhibit a gradual increase of the tangent stiffness starting from small strains. NCV networks exhibit much smaller Poisson contraction than any network of same nominal parameters. Interestingly, the strength of NCV networks increases continuously with an increasing degree of nonconvexity of the cells. These exceptional properties render this class of networks of interest in a variety of applications, such as tissue scaffolds, nonwovens, and protective clothing.
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Affiliation(s)
- S Deogekar
- Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180 e-mail:
| | - Z Yan
- Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180 e-mail:
| | - R C Picu
- Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180 e-mail:
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13
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Abstract
Fracture toughness characterizes the ability of a material to maintain a certain level of strength despite the presence of a macroscopic crack. Understanding this tolerance for defects in soft collagenous tissues (SCT) has high relevance for assessing the risks of fracture after cutting, perforation or suturing. Here we investigate the peculiar toughening mechanisms of SCT through dedicated experiments and multi-scale simulations, showing that classical concepts of fracture mechanics are inadequate to quantify and explain the high defect tolerance of these materials. Our results demonstrate that SCT strength is only modestly reduced by defects as large as several millimeters. This defect tolerance is achieved despite a very narrow process zone at the crack tip and even for a network of brittle fibrils. The fracture mechanics concept of tearing energy fails in predicting failure at such defects, and its magnitude is shown to depend on the chemical potential of the liquid environment.
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14
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McGuire JA, Abramowitch SD, Maiti S, De Vita R. Swine Vagina Under Planar Biaxial Loads: An Investigation of Large Deformations and Tears. J Biomech Eng 2019; 141:2720658. [DOI: 10.1115/1.4042437] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2018] [Indexed: 12/26/2022]
Abstract
Vaginal tears are very common and can lead to severe complications such as hemorrhaging, fecal incontinence, urinary incontinence, and dyspareunia. Despite the implications of vaginal tears on women's health, there are currently no experimental studies on the tear behavior of vaginal tissue. In this study, planar equi-biaxial tests on square specimens of vaginal tissue, with sides oriented along the longitudinal direction (LD) and circumferential direction (CD), were conducted using swine as animal model. Three groups of specimens were mechanically tested: the NT group (n = 9), which had no pre-imposed tear, the longitudinal tear (LT) group (n = 9), and the circumferential tear (CT) group (n = 9), which had central pre-imposed elliptically shaped tears with major axes oriented in the LD and the CD, respectively. Through video recording during testing, axial strains were measured for the NT group using the digital image correlation (DIC) technique and axial displacements of hook clamps were measured for the NT, LT, and CT groups in the LD and CD. The swine vaginal tissue was found to be highly nonlinear and somewhat anisotropic. Up to normalized axial hook displacements of 1.15, no tears were observed to propagate, suggesting that the vagina has a high resistance to further tearing once a tear has occurred. However, in response to biaxial loading, the size of the tears for the CT group increased significantly more than the size of the tears for the LT group (p = 0.003). The microstructural organization of the vagina is likely the culprit for its tear resistance and orientation-dependent tear behavior. Further knowledge on the structure–function relationship of the vagina is needed to guide the development of new methods for preventing the severe complications of tearing.
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Affiliation(s)
- Jeffrey A. McGuire
- STRETCH Lab, Department of Biomedical Engineering and Mechanics, Virginia Tech, Blacksburg, VA 24061 e-mail:
| | - Steven D. Abramowitch
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15261 e-mail:
| | - Spandan Maiti
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15261 e-mail:
| | - Raffaella De Vita
- STRETCH Lab, Department of Biomedical Engineering and Mechanics, Virginia Tech, Blacksburg, VA 24061 e-mail:
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15
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Dhume RY, Shih ED, Barocas VH. Multiscale model of fatigue of collagen gels. Biomech Model Mechanobiol 2019; 18:175-187. [PMID: 30151813 PMCID: PMC6367047 DOI: 10.1007/s10237-018-1075-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2018] [Accepted: 08/20/2018] [Indexed: 12/24/2022]
Abstract
Fatigue as a mode of failure becomes increasingly relevant with age in tissues that experience repeated fluctuations in loading. While there has been a growing focus on the mechanics of networks of collagen fibers, which are recognized as the predominant mechanical components of soft tissues, the network's fatigue behavior has received less attention. Specifically, it must be asked (1) how the fatigue of networks differs from that of its component fibers, and (2) whether this difference in fatigue behaviors is affected by changes in the network's architecture. In the present study, we simulated cyclic uniaxial loading of Voronoi networks to model fatigue experiments performed on reconstituted collagen gels. Collagen gels were cast into dog-bone shape molds and were tested on a uniaxial machine under a tension-tension cyclic loading protocol. Simulations were performed on networks modeled as trusses of, on average, 600 nonlinear elastic fibers connected at freely rotating pin-joints. We also simulated fatigue failure of Delaunay, and Erdős-Rényi networks, in addition to Voronoi networks, to compare fatigue behavior among different architectures. The uneven distribution of stresses within the fibers of the unstructured networks resulted in all three network geometries being more endurant than a single fiber or a regular lattice under cyclic loading. Among the different network geometries, for low to moderate external loads, the Delaunay networks showed the best fatigue behavior, while at higher loads, the Voronoi networks performed better.
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Affiliation(s)
- Rohit Y. Dhume
- Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455,
| | - Elizabeth D. Shih
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455,
| | - Victor H. Barocas
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455,
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16
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Planz V, Seif S, Atchison JS, Vukosavljevic B, Sparenberg L, Kroner E, Windbergs M. Three-dimensional hierarchical cultivation of human skin cells on bio-adaptive hybrid fibers. Integr Biol (Camb) 2017; 8:775-84. [PMID: 27241237 DOI: 10.1039/c6ib00080k] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
The human skin comprises a complex multi-scale layered structure with hierarchical organization of different cells within the extracellular matrix (ECM). This supportive fiber-reinforced structure provides a dynamically changing microenvironment with specific topographical, mechanical and biochemical cell recognition sites to facilitate cell attachment and proliferation. Current advances in developing artificial matrices for cultivation of human cells concentrate on surface functionalizing of biocompatible materials with different biomolecules like growth factors to enhance cell attachment. However, an often neglected aspect for efficient modulation of cell-matrix interactions is posed by the mechanical characteristics of such artificial matrices. To address this issue, we fabricated biocompatible hybrid fibers simulating the complex biomechanical characteristics of native ECM in human skin. Subsequently, we analyzed interactions of such fibers with human skin cells focusing on the identification of key fiber characteristics for optimized cell-matrix interactions. We successfully identified the mediating effect of bio-adaptive elasto-plastic stiffness paired with hydrophilic surface properties as key factors for cell attachment and proliferation, thus elucidating the synergistic role of these parameters to induce cellular responses. Co-cultivation of fibroblasts and keratinocytes on such fiber mats representing the specific cells in dermis and epidermis resulted in a hierarchical organization of dermal and epidermal tissue layers. In addition, terminal differentiation of keratinocytes at the air interface was observed. These findings provide valuable new insights into cell behaviour in three-dimensional structures and cell-material interactions which can be used for rational development of bio-inspired functional materials for advanced biomedical applications.
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Affiliation(s)
- Viktoria Planz
- Department of Biopharmaceutics and Pharmaceutical Technology, Saarland University, Campus Building A 4.1, 66123 Saarbrücken, Germany.
| | - Salem Seif
- Department of Biopharmaceutics and Pharmaceutical Technology, Saarland University, Campus Building A 4.1, 66123 Saarbrücken, Germany. and PharmBioTec GmbH, Science Park 1, 66123 Saarbrücken, Germany
| | - Jennifer S Atchison
- INM - Leibniz Institute for New Materials, Campus Building D 2.2, 66123 Saarbrücken, Germany
| | - Branko Vukosavljevic
- Helmholtz Centre for Infection Research (HZI) and Helmholtz Institute for Pharmaceutical Research Saarland (HIPS), Department of Drug Delivery (DDEL), Campus Building E 8.1, 66123 Saarbrücken, Germany
| | - Lisa Sparenberg
- Department of Biopharmaceutics and Pharmaceutical Technology, Saarland University, Campus Building A 4.1, 66123 Saarbrücken, Germany.
| | - Elmar Kroner
- INM - Leibniz Institute for New Materials, Campus Building D 2.2, 66123 Saarbrücken, Germany
| | - Maike Windbergs
- Department of Biopharmaceutics and Pharmaceutical Technology, Saarland University, Campus Building A 4.1, 66123 Saarbrücken, Germany. and PharmBioTec GmbH, Science Park 1, 66123 Saarbrücken, Germany and Helmholtz Centre for Infection Research (HZI) and Helmholtz Institute for Pharmaceutical Research Saarland (HIPS), Department of Drug Delivery (DDEL), Campus Building E 8.1, 66123 Saarbrücken, Germany
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17
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Assessing stiffness of nanofibres in bacterial cellulose hydrogels: Numerical-experimental framework. MATERIALS SCIENCE & ENGINEERING. C, MATERIALS FOR BIOLOGICAL APPLICATIONS 2017; 77:9-18. [DOI: 10.1016/j.msec.2017.03.231] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2016] [Accepted: 03/25/2017] [Indexed: 11/18/2022]
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18
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Kumar P, Vasita R. Understanding the relation between structural and mechanical properties of electrospun fiber mesh through uniaxial tensile testing. J Appl Polym Sci 2017. [DOI: 10.1002/app.45012] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Prasoon Kumar
- Department of Mechanical Engineering; IIT Bombay; Powai, Mumbai Maharashtra 400076 India
| | - Rajesh Vasita
- School of Life Sciences; Central University of Gujarat; Gandhinagar 382030 India
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19
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Tonsomboon K, Butcher AL, Oyen ML. Strong and tough nanofibrous hydrogel composites based on biomimetic principles. MATERIALS SCIENCE & ENGINEERING. C, MATERIALS FOR BIOLOGICAL APPLICATIONS 2017; 72:220-227. [DOI: 10.1016/j.msec.2016.11.025] [Citation(s) in RCA: 61] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/2016] [Revised: 10/13/2016] [Accepted: 11/07/2016] [Indexed: 10/20/2022]
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20
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Systematic mechanical evaluation of electrospun gelatin meshes. J Mech Behav Biomed Mater 2017; 69:412-419. [PMID: 28208112 DOI: 10.1016/j.jmbbm.2017.02.007] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Revised: 11/17/2016] [Accepted: 02/06/2017] [Indexed: 01/18/2023]
Abstract
Electrospinning is a simple and efficient process for producing sub-micron fibres. However, the process has many variables, and their effects on the non-woven mesh of fibres is complex. In particular, the effects on the mechanical properties of the fibre meshes are poorly understood. This paper conducts a parametric study, where the concentration and bloom strength of the gelatin solutions are varied, while all electrospinning process parameters are held constant. The effects on the fibrous meshes are monitored using scanning electron microscopy and mechanical testing under uniaxial tension. Mesh mechanical properties are relatively consistent, despite changes to the solutions, demonstrating the robustness of electrospinning. The gel strength of the solution is shown to have a statistically significant effect on the morphology, stiffness and strength of the meshes, while the fibre diameter has surprisingly little influence on the stiffness of the meshes. This experimental finding is supported by finite element analysis, demonstrating that the stiffness of the meshes is controlled by the volume fraction, rather than fibre diameter. Our results demonstrate the importance of understanding how electrospinning parameters influence the pore size of the meshes, as controlling fibre diameter alone is insufficient for consistent mechanical properties.
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Abstract
Damage to soft tissues in the human body has been investigated for applications in healthcare, sports, and biomedical engineering. This paper reviews and classifies damage models for soft tissues to summarize achievements, identify new directions, and facilitate finite element analysis. The main ideas of damage modeling methods are illustrated and interpreted. A few key issues related to damage models, such as experimental data curve-fitting, computational effort, connection between damage and fractures/cracks, damage model applications, and fracture/crack extension simulation, are discussed. Several new challenges in the field are identified and outlined. This review can be useful for developing more advanced damage models and extending damage modeling methods to a variety of soft tissues.
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Affiliation(s)
- Wenguang Li
- School of Engineering, University of Glasgow, Glasgow, G12 8QQ UK
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22
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Gao X, Kuśmierczyk P, Shi Z, Liu C, Yang G, Sevostianov I, Silberschmidt VV. Through-thickness stress relaxation in bacterial cellulose hydrogel. J Mech Behav Biomed Mater 2016; 59:90-98. [DOI: 10.1016/j.jmbbm.2015.12.021] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2015] [Revised: 12/15/2015] [Accepted: 12/17/2015] [Indexed: 10/22/2022]
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23
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Mauri A, Hopf R, Ehret AE, Picu CR, Mazza E. A discrete network model to represent the deformation behavior of human amnion. J Mech Behav Biomed Mater 2016; 58:45-56. [DOI: 10.1016/j.jmbbm.2015.11.009] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2015] [Revised: 10/16/2015] [Accepted: 11/11/2015] [Indexed: 11/16/2022]
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24
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Guessasma S, Oyen M. Virtual design of electrospun-like gelatin scaffolds: the effect of three-dimensional fibre orientation on elasticity behaviour. SOFT MATTER 2016; 12:602-613. [PMID: 26508563 DOI: 10.1039/c5sm02342d] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Remarkable mechanical performance of biological tissues is explained by a hierarchical fibrous structure. Designing materials that have similar properties is challenging because of the need to assess complex deformation mechanisms. In order to shed more light on architectural possibilities of biopolymer fibrous networks, we propose a numerical study that relates the fibre arrangement to the elastic modulus of a gelatin scaffold obtained using electrospinning. The adopted approach is based on the virtual designing of scaffolds using all possible combinations of Euler angles that define fibre orientations including preferable alignment. The generated networks are converted into a finite element model and the predicted elastic behaviour is examined. Predictions show that the fibre alignment achieved experimentally in biopolymer fibrous networks is for most of the fibres exhibiting an orthotropic behaviour. Some particular combinations of Euler angles allow transverse isotropic architectures while only limited cases are isotropic. A large sensitivity of Young's moduli to Euler angles is achieved describing multiple scenarios of independent anisotropic behaviours. An anisotropy ratio of the elastic behaviour is suggested based on a suitable combination of elastic moduli. Such a ratio exhibits a wide variation depending on individual and coupled effects of Euler angles. The finite element model predicts 2D, 3D and 4D maps representing all possible configurations of fibre alignment and their consequences on elastic behaviour. The predicted fibre orientation representing the observed anisotropic behaviour of electrospun gelatin networks demonstrates unbalanced contributions of in-plane and out-of plane fibres for a large range of processing conditions.
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Affiliation(s)
- S Guessasma
- INRA, Research Unit BIA UR1268, Rue Geraudiere, F-44316 Nantes, France.
| | - M Oyen
- Department of Engineering, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ, UK
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25
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Peloquin JM, Elliott DM. A comparison of stress in cracked fibrous tissue specimens with varied crack location, loading, and orientation using finite element analysis. J Mech Behav Biomed Mater 2015; 57:260-8. [PMID: 26741533 DOI: 10.1016/j.jmbbm.2015.12.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2015] [Revised: 11/26/2015] [Accepted: 12/03/2015] [Indexed: 12/01/2022]
Abstract
Cracks in fibrous soft tissue, such as intervertebral disc annulus fibrosus and knee meniscus, cause pain and compromise joint mechanics. A crack concentrates stress at its tip, making further failure and crack extension (fracture) more likely. Ex vivo mechanical testing is an important tool for studying the loading conditions required for crack extension, but prior work has shown that it is difficult to reproduce crack extension. Most prior work used edge crack specimens in uniaxial tension, with the crack 90° to the edge of the specimen. This configuration does not necessarily represent the loading conditions that cause in vivo crack extension. To find a potentially better choice for experiments aiming to reproduce crack extension, we used finite element analysis to compare, in factorial combination, (1) center crack vs. edge crack location, (2) biaxial vs. uniaxial loading, and (3) crack-fiber angles ranging from 0° to 90°. The simulated material was annulus fibrosus fibrocartilage with a single fiber family. We hypothesized that one of the simulated test cases would produce a stronger stress concentration than the commonly used uniaxially loaded 90° crack-fiber angle edge crack case. Stress concentrations were compared between cases in terms of fiber-parallel stress (representing risk of fiber rupture), fiber-perpendicular stress (representing risk of matrix rupture), and fiber shear stress (representing risk of fiber sliding). Fiber-perpendicular stress and fiber shear stress concentrations were greatest in edge crack specimens (of any crack-fiber angle) and center crack specimens with a 90° crack-fiber angle. However, unless the crack is parallel to the fiber direction, these stress components alone are insufficient to cause crack opening and extension. Fiber-parallel stress concentrations were greatest in center crack specimens with a 45° crack-fiber angle, either biaxially or uniaxially loaded. We therefore recommend that the 45° center crack case be tried in future experiments intended to study crack extension by fiber rupture.
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Affiliation(s)
| | - Dawn M Elliott
- University of Delaware, 150 Academy St, 161 Colburn Lab, Newark, DE 19716, USA.
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26
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Koh CT, Low CY, Yusof YB. Structure-property Relationship of Bio-Inspired Fibrous Materials. ACTA ACUST UNITED AC 2015. [DOI: 10.1016/j.procs.2015.12.278] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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27
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Butcher AL, Offeddu GS, Oyen ML. Nanofibrous hydrogel composites as mechanically robust tissue engineering scaffolds. Trends Biotechnol 2014; 32:564-570. [DOI: 10.1016/j.tibtech.2014.09.001] [Citation(s) in RCA: 81] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2014] [Revised: 09/01/2014] [Accepted: 09/04/2014] [Indexed: 10/24/2022]
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28
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Strange DGT, Tonsomboon K, Oyen ML. Mechanical behaviour of electrospun fibre-reinforced hydrogels. JOURNAL OF MATERIALS SCIENCE. MATERIALS IN MEDICINE 2014; 25:681-690. [PMID: 24408274 DOI: 10.1007/s10856-013-5123-y] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/08/2013] [Accepted: 12/11/2013] [Indexed: 06/03/2023]
Abstract
Mechanically robust and biomimicking scaffolds are needed for structural engineering of tissues such as the intervertebral disc, which are prone to failure and incapable of natural healing. Here, the formation of thick, randomly aligned polycaprolactone electrospun fibre structures infiltrated with alginate is reported. The composites are characterised using both indentation and tensile testing and demonstrate substantially different tensile and compressive moduli. The composites are mechanically robust and exhibit large strains-to-failure, exhibiting toughening mechanisms observed in other composite material systems. The method presented here provides a way to create large-scale biomimetic scaffolds that more closely mimic the composite structure of natural tissue, with tuneable tensile and compressive properties via the fibre and matrix phases, respectively.
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Affiliation(s)
- Daniel G T Strange
- Engineering Department, Cambridge University, Trumpington St., Cambridge, CB2 1PZ, UK
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29
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Tonsomboon K, Koh CT, Oyen ML. Time-dependent fracture toughness of cornea. J Mech Behav Biomed Mater 2014; 34:116-23. [PMID: 24566382 DOI: 10.1016/j.jmbbm.2014.01.015] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2013] [Revised: 01/13/2014] [Accepted: 01/21/2014] [Indexed: 10/25/2022]
Abstract
The fracture and time-dependent properties of cornea are very important for the development of corneal scaffolds and prostheses. However, there has been no systematic study of cornea fracture; time-dependent behavior of cornea has never been investigated in a fracture context. In this work, fracture toughness of cornea was characterized by trouser tear tests, and time-dependent properties of cornea were examined by stress-relaxation and uniaxial tensile tests. Control experiments were performed on a photoelastic rubber sheet. Corneal fracture resistance was found to be strain-rate dependent, with values ranging from 3.39±0.57 to 5.40±0.48kJm(-2) over strain rates from 3 to 300mmmin(-1). Results from stress-relaxation tests confirmed that cornea is a nonlinear viscoelastic material. The cornea behaved closer to a viscous fluid at small strain but became relatively more elastic at larger strain. Although cornea properties are greatly dependent on time, the stress-strain responses of cornea were found to be insensitive to the strain rate when subjected to tensile loading.
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Affiliation(s)
- Khaow Tonsomboon
- Cambridge University Engineering Department, Trumpington Street, Cambridge CB2 1PZ, UK
| | - Ching Theng Koh
- Cambridge University Engineering Department, Trumpington Street, Cambridge CB2 1PZ, UK
| | - Michelle L Oyen
- Cambridge University Engineering Department, Trumpington Street, Cambridge CB2 1PZ, UK.
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