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Nietupski CA, Moset Zupan A, Schutte SC. Impact of Cyclic Strain on Elastin Synthesis in a 3D Human Myometrial Culture Model. Tissue Eng Part C Methods 2024; 30:279-288. [PMID: 38943281 DOI: 10.1089/ten.tec.2024.0038] [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] [Indexed: 07/01/2024] Open
Abstract
The synthesis and assembly of mature, organized elastic fibers remains a limitation to the clinical use of many engineered tissue replacements. There is a critical need for a more in-depth understanding of elastogenesis regulation for the advancement of methods to induce and guide production of elastic matrix structures in engineered tissues that meet the structural and functional requirements of native tissue. The dramatic increase in elastic fibers through normal pregnancy has led us to explore the potential role of mechanical stretch in combination with pregnancy levels of the steroid hormones 17β-estradiol and progesterone on elastic fiber production by human uterine myometrial smooth muscle cells in a three-dimensional (3D) culture model. Opposed to a single strain regimen, we sought to better understand how the amplitude and frequency parameters of cyclic strain influence elastic fiber production in these myometrial tissue constructs (MTC). Mechanical stretch was applied to MTC at a range of strain amplitudes (5%, 10%, and 15% at 0.5 Hz frequency) and frequencies (0.1 Hz, 0.5 Hz, 1 Hz, and constant 0 Hz at 10% amplitude), with and without pregnancy-level hormones, for 6 days. MTC were assessed for cell proliferation, matrix elastin protein content, and expression of the main elastic fiber genes, tropoelastin (ELN) and fibrillin-1 (FBN1). Significant increases in elastin protein and ELN and FBN1 mRNA were produced from samples subjected to a 0.5 Hz, 10% strain regimen, as well as samples stretched at higher amplitude (15%, 0.5 Hz) and higher frequency (1 Hz, 10%); however, no significant effects because of third-trimester mimetic hormone treatment were determined. These results establish that a minimum level of strain is required to stimulate the synthesis of elastic fiber components in our culture model and show this response can be similarly enhanced by increasing either the amplitude or frequency parameter of applied strain. Further, our results demonstrate strain alone is sufficient to stimulate elastic fiber production and suggest hormones may not be a significant factor in regulating elastin synthesis. This 3D culture model will provide a useful tool to further investigate mechanisms underlying pregnancy-induced de novo elastic fiber synthesis and assembly by uterine smooth muscle cells.
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Affiliation(s)
- Carolyn A Nietupski
- Department of Biomedical Engineering, University of Cincinnati, Cincinnati, Ohio, USA
| | - Andreja Moset Zupan
- Department of Biomedical Engineering, University of Cincinnati, Cincinnati, Ohio, USA
| | - Stacey C Schutte
- Department of Biomedical Engineering, University of Cincinnati, Cincinnati, Ohio, USA
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2
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Bekedam FT, Smal R, Smit MC, Aman J, Vonk-Noordegraaf A, Bogaard HJ, Goumans MJ, De Man FS, Llucià-Valldeperas A. Mechanical stimulation of induced pluripotent stem derived cardiac fibroblasts. Sci Rep 2024; 14:9795. [PMID: 38684844 PMCID: PMC11058244 DOI: 10.1038/s41598-024-60102-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2023] [Accepted: 04/18/2024] [Indexed: 05/02/2024] Open
Abstract
Cardiac fibrosis contributes to the development of heart failure, and is the response of cardiac fibroblasts (CFs) to pressure or volume overload. Limiting factors in CFs research are the poor availability of human cells and the tendency of CFs to transdifferentiate into myofibroblasts when cultured in vitro. The possibility to generate CFs from induced pluripotent stem cells (iPSC), providing a nearly unlimited cell source, opens new possibilities. However, the behaviour of iPSC-CFs under mechanical stimulation has not been studied yet. Our study aimed to assess the behaviour of iPSC-CFs under mechanical stretch and pro-fibrotic conditions. First, we confirm that iPSC-CFs are comparable to primary CFs at gene, protein and functional level. Furthermore, iPSC-derived CFs adopt a pro-fibrotic response to transforming growth factor beta (TGF-β). In addition, mechanical stretch inhibits TGF-β-induced fibroblast activation in iPSC-CFs. Thus, the responsiveness to cytokines and mechanical stimulation of iPSC-CFs demonstrates they possess key characteristics of primary CFs and may be useful for disease modelling.
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Affiliation(s)
- Fjodor T Bekedam
- PHEniX Laboratory, Department of Pulmonary Medicine, Amsterdam UMC Location Vrije Universiteit Amsterdam, De Boelelaan 1117, Amsterdam, The Netherlands
- Amsterdam Cardiovascular Sciences, Pulmonary Hypertension and Thrombosis, Amsterdam, The Netherlands
| | - Rowan Smal
- PHEniX Laboratory, Department of Pulmonary Medicine, Amsterdam UMC Location Vrije Universiteit Amsterdam, De Boelelaan 1117, Amsterdam, The Netherlands
- Amsterdam Cardiovascular Sciences, Pulmonary Hypertension and Thrombosis, Amsterdam, The Netherlands
| | - Marisa C Smit
- PHEniX Laboratory, Department of Pulmonary Medicine, Amsterdam UMC Location Vrije Universiteit Amsterdam, De Boelelaan 1117, Amsterdam, The Netherlands
- Amsterdam Cardiovascular Sciences, Pulmonary Hypertension and Thrombosis, Amsterdam, The Netherlands
| | - Jurjan Aman
- PHEniX Laboratory, Department of Pulmonary Medicine, Amsterdam UMC Location Vrije Universiteit Amsterdam, De Boelelaan 1117, Amsterdam, The Netherlands
- Amsterdam Cardiovascular Sciences, Pulmonary Hypertension and Thrombosis, Amsterdam, The Netherlands
| | - Anton Vonk-Noordegraaf
- PHEniX Laboratory, Department of Pulmonary Medicine, Amsterdam UMC Location Vrije Universiteit Amsterdam, De Boelelaan 1117, Amsterdam, The Netherlands
- Amsterdam Cardiovascular Sciences, Pulmonary Hypertension and Thrombosis, Amsterdam, The Netherlands
| | - Harm Jan Bogaard
- PHEniX Laboratory, Department of Pulmonary Medicine, Amsterdam UMC Location Vrije Universiteit Amsterdam, De Boelelaan 1117, Amsterdam, The Netherlands
- Amsterdam Cardiovascular Sciences, Pulmonary Hypertension and Thrombosis, Amsterdam, The Netherlands
| | - Marie José Goumans
- Department of Cell and Chemical Biology, Leiden UMC, 2300 RC, Leiden, The Netherlands
| | - Frances S De Man
- PHEniX Laboratory, Department of Pulmonary Medicine, Amsterdam UMC Location Vrije Universiteit Amsterdam, De Boelelaan 1117, Amsterdam, The Netherlands.
- Amsterdam Cardiovascular Sciences, Pulmonary Hypertension and Thrombosis, Amsterdam, The Netherlands.
| | - Aida Llucià-Valldeperas
- PHEniX Laboratory, Department of Pulmonary Medicine, Amsterdam UMC Location Vrije Universiteit Amsterdam, De Boelelaan 1117, Amsterdam, The Netherlands.
- Amsterdam Cardiovascular Sciences, Pulmonary Hypertension and Thrombosis, Amsterdam, The Netherlands.
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Progressive daily hopping exercise improves running economy in amateur runners: a randomized and controlled trial. Sci Rep 2023; 13:4167. [PMID: 36914662 PMCID: PMC10011548 DOI: 10.1038/s41598-023-30798-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2022] [Accepted: 03/01/2023] [Indexed: 03/16/2023] Open
Abstract
This study investigated the effects of a daily plyometric hopping intervention on running economy (RE) in amateur runners. In a randomized, controlled trial, thirty-four amateur runners (29 ± 7 years, 27 males) were allocated to a control or a hopping exercise group. During the six-week study, the exercise group performed 5 min of double-legged hopping exercise daily. To progressively increase loading, the number of hopping bouts (10 s each) was steadily increased while break duration between sets was decreased. Pre- and post-intervention, RE, peak oxygen uptake (VO2peak), and respiratory exchange ratio (RER) were measured during 4-min stages at three running speeds (10, 12, and 14 km/h). ANCOVAs with baseline values and potential cofounders as cofactors were performed to identify differences between groups. ANCOVA revealed an effect of hopping on RE at 12 km/h (df = 1; F = 4.35; p < 0.05; η2 = 0.072) and 14 km/h (df = 1; F = 6.72; p < 0.05; η2 = 0.098), but not at 10 km/h (p > 0.05). Exercise did not affect VO2peak (p > 0.05), but increased RER at 12 km/h (df = 1; F = 4.26; p < 0.05; η2 = 0.059) and 14 km/h (df = 1; F = 36.73; p < 0.001; η2 = 0.520). No difference in RER was observed at 10 km/h (p > 0.05). Daily hopping exercise is effective in improving RE at high running speeds in amateurs and thus can be considered a feasible complementary training program.Clinical trial registration German Register of Clinical Trials (DRKS00017373).
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Coeyman SJ, Zhang Y, Baicu CF, Zile MR, Bradshaw AD, Richardson WJ. In vitro bioreactor for mechanical control and characterization of tissue constructs. J Biomech 2023; 147:111458. [PMID: 36682211 PMCID: PMC9946176 DOI: 10.1016/j.jbiomech.2023.111458] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2022] [Revised: 11/14/2022] [Accepted: 01/13/2023] [Indexed: 01/19/2023]
Abstract
Cardiac fibrosis is a key contributor to the onset and progression of heart failure and occurs from extracellular matrix accumulation via activated cardiac fibroblasts. Cardiac fibroblasts activate in response to mechanical stress and have been studied in the past by applying forces and deformations to three-dimensional, cell-seeded gels and tissue constructs in vitro. Unfortunately, previous stretching platforms have traditionally not enabled mechanical property assessment to be performed with an efficient throughput, thereby limiting the full potential of in vitro mechanobiology studies. We have developed a novel in vitro platform to study cell-populated tissue constructs under dynamic mechanical stimulation while also performing repeatable, non-destructive stress-strain tests in living constructs. Additionally, this platform can perform these tests across all constructs in a multi-well plate simultaneously, providing exciting potential for direct, functional readouts in future screening applications. In our pilot application, we showed that cyclically stretching cell-populated tissue constructs composed of murine cardiac fibroblasts within a 3D fibrin matrix leads to collagen accumulation and increased tissue stiffness over a three-day time course. Results of this study validate our platform's ability to apply mechanical loads to tissues while performing live mechanical analyses to observe cell-mediated tissue remodeling.
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Affiliation(s)
| | - Yuhua Zhang
- Gazes Cardiac Research Institute, Division of Cardiology, Department of Medicine, Medical University of South Carolina
| | - Catalin F. Baicu
- Gazes Cardiac Research Institute, Division of Cardiology, Department of Medicine, Medical University of South Carolina,,Ralph H. Johnson Department of Veterans Affairs Medical Center, Charleston, SC, USA
| | - Michael R. Zile
- Gazes Cardiac Research Institute, Division of Cardiology, Department of Medicine, Medical University of South Carolina,,Ralph H. Johnson Department of Veterans Affairs Medical Center, Charleston, SC, USA
| | - Amy D. Bradshaw
- Gazes Cardiac Research Institute, Division of Cardiology, Department of Medicine, Medical University of South Carolina,,Ralph H. Johnson Department of Veterans Affairs Medical Center, Charleston, SC, USA
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Fang X, Ni K, Guo J, Li Y, Zhou Y, Sheng H, Bu B, Luo M, Ouyang M, Deng L. FRET Visualization of Cyclic Stretch-Activated ERK via Calcium Channels Mechanosensation While Not Integrin β1 in Airway Smooth Muscle Cells. Front Cell Dev Biol 2022; 10:847852. [PMID: 35663392 PMCID: PMC9162487 DOI: 10.3389/fcell.2022.847852] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2022] [Accepted: 04/05/2022] [Indexed: 12/19/2022] Open
Abstract
Mechanical stretch is one type of common physiological activities such as during heart beating, lung breathing, blood flow through the vessels, and physical exercise. The mechanical stimulations regulate cellular functions and maintain body homeostasis. It still remains to further characterize the mechanical-biomechanical coupling mechanism. Here we applied fluorescence resonance energy transfer (FRET) technology to visualize ERK activity in airway smooth muscle (ASM) cells under cyclic stretch stimulation in airway smooth muscle (ASM) cells, and studied the mechanosensing pathway. FRET measurements showed apparent ERK activation by mechanical stretch, which was abolished by ERK inhibitor PD98059 pretreatment. Inhibition of extracellular Ca2+ influx reduced ERK activation, and selective inhibition of inositol 1,4,5-trisphosphate receptor (IP3R) Ca2+ channel or SERCA Ca2+ pump on endoplasmic reticulum (ER) blocked the activation. Chemical inhibition of the L-type or store-operated Ca2+ channels on plasma membrane, or inhibition of integrin β1 with siRNA had little effect on ERK activation. Disruption of actin cytoskeleton but not microtubule one inhibited the stretch-induced ERK activation. Furthermore, the ER IP3R-dependent ERK activation was not dependent on phospholipase C-IP3 signal, indicating possibly more mechanical mechanism for IP3R activation. It is concluded from our study that the mechanical stretch activated intracellular ERK signal in ASM cells through membrane Ca2+ channels mechanosensation but not integrin β1, which was mediated by actin cytoskeleton.
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Affiliation(s)
| | | | | | | | | | | | | | | | | | - Linhong Deng
- *Correspondence: Mingxing Ouyang, ; Linhong Deng,
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Rogers JD, Holmes JW, Saucerman JJ, Richardson WJ. Mechano-chemo signaling interactions modulate matrix production by cardiac fibroblasts. Matrix Biol Plus 2021; 10:100055. [PMID: 34195592 PMCID: PMC8233457 DOI: 10.1016/j.mbplus.2020.100055] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2020] [Revised: 11/23/2020] [Accepted: 11/23/2020] [Indexed: 01/20/2023] Open
Abstract
Extracellular matrix remodeling after myocardial infarction occurs in a dynamic environment in which local mechanical stresses and biochemical signaling species stimulate the accumulation of collagen-rich scar tissue. It is well-known that cardiac fibroblasts regulate post-infarction matrix turnover by secreting matrix proteins, proteases, and protease inhibitors in response to both biochemical stimuli and mechanical stretch, but how these stimuli act together to dictate cellular responses is still unclear. We developed a screen of cardiac fibroblast-secreted proteins in response to combinations of biochemical agonists and cyclic uniaxial stretch in order to elucidate the relationships between stretch, biochemical signaling, and cardiac matrix turnover. We found that stretch significantly synergized with biochemical agonists to inhibit the secretion of matrix metalloproteinases, with stretch either amplifying protease suppression by individual agonists or antagonizing agonist-driven upregulation of protease expression. Stretch also modulated fibroblast sensitivity towards biochemical agonists by either sensitizing cells towards agonists that suppress protease secretion or de-sensitizing cells towards agonists that upregulate protease secretion. These findings suggest that the mechanical environment can significantly alter fibrosis-related signaling in cardiac fibroblasts, suggesting caution when extrapolating in vitro data to predict effects of fibrosis-related cytokines in situations like myocardial infarction where mechanical stretch occurs.
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Affiliation(s)
- Jesse D. Rogers
- Department of Bioengineering, Clemson University, Clemson, SC, USA
| | - Jeffrey W. Holmes
- Departments of Biomedical Engineering, Medicine/Cardiovascular Disease, and Surgery/Cardiothoracic Surgery, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Jeffrey J. Saucerman
- Department of Biomedical Engineering and Robert M. Berne Cardiovascular Research Center, University of Virginia, Charlottesville, VA, USA
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Jin X, Rosenbohm J, Kim E, Esfahani AM, Seiffert-Sinha K, Wahl JK, Lim JY, Sinha AA, Yang R. Modulation of Mechanical Stress Mitigates Anti-Dsg3 Antibody-Induced Dissociation of Cell-Cell Adhesion. Adv Biol (Weinh) 2021; 5:e2000159. [PMID: 33724731 PMCID: PMC7993752 DOI: 10.1002/adbi.202000159] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2020] [Revised: 10/21/2020] [Indexed: 12/13/2022]
Abstract
It is becoming increasingly clear that mechanical stress in adhesive junctions plays a significant role in dictating the fate of cell-cell attachment under physiological conditions. Targeted disruption of cell-cell junctions leads to multiple pathological conditions, among them the life-threatening autoimmune blistering disease pemphigus vulgaris (PV). The dissociation of cell-cell junctions by autoantibodies is the hallmark of PV, however, the detailed mechanisms that result in tissue destruction remain unclear. Thus far, research and therapy in PV have focused primarily on immune mechanisms upstream of autoantibody binding, while the biophysical aspects of the cell-cell dissociation process leading to acantholysis are less well studied. In work aimed at illuminating the cellular consequences of autoantibody attachment, it is reported that externally applied mechanical stress mitigates antibody-induced monolayer fragmentation and inhibits p38 MAPK phosphorylation activated by anti-Dsg3 antibody. Further, it is demonstrated that mechanical stress applied externally to cell monolayers enhances cell contractility via RhoA activation and promotes the strengthening of cortical actin, which ultimately mitigates antibody-induced cell-cell dissociation. The study elevates understanding of the mechanism of acantholysis in PV and shifts the paradigm of PV disease development from a focus solely on immune pathways to highlight the key role of physical transformations at the target cell.
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Affiliation(s)
- Xiaowei Jin
- Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA
| | - Jordan Rosenbohm
- Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA
| | - Eunju Kim
- Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA
| | - Amir Monemian Esfahani
- Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA
| | | | - James K Wahl
- Department of Oral Biology, University of Nebraska Medical Center, Lincoln, NE, 68583, USA
| | - Jung Yul Lim
- Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA
- Mary and Dick Holland Regenerative Medicine Program, University of Nebraska Medical Center, Omaha, NE, 68198, USA
| | - Animesh A Sinha
- Department of Dermatology, University at Buffalo, Buffalo, NY, 14203, USA
| | - Ruiguo Yang
- Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA
- Mary and Dick Holland Regenerative Medicine Program, University of Nebraska Medical Center, Omaha, NE, 68198, USA
- Nebraska Center for Integrated Biomolecular Communication, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA
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Shi X, He L, Zhang SM, Luo J. Human iPS Cell-derived Tissue Engineered Vascular Graft: Recent Advances and Future Directions. Stem Cell Rev Rep 2020; 17:862-877. [PMID: 33230612 DOI: 10.1007/s12015-020-10091-w] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/19/2020] [Indexed: 12/19/2022]
Abstract
Tissue engineered vascular grafts (TEVGs) generated from human primary cells represent a promising vascular interventional therapy. However, generation and application of these TEVGs may be significantly hindered by the limited accessibility, finite expandability, donor-donor functional variation and immune-incompatibility of primary seed cells from donors. Alternatively, human induced pluripotent stem cells (hiPSCs) offer an infinite source to obtain functional vascular cells in large quantity and comparable quality for TEVG construction. To date, TEVGs (hiPSC-TEVGs) with significant mechanical strength and implantability have been generated using hiPSC-derived seed cells. Despite being in its incipient stage, this emerging field of hiPSC-TEVG research has achieved significant progress and presented promising future potential. Meanwhile, a series of challenges pertaining hiPSC differentiation, vascular tissue engineering technologies and future production and application await to be addressed. Herein, we have composed this review to introduce progress in TEVG generation using hiPSCs, summarize the current major challenges, and encapsulate the future directions of research on hiPSC-based TEVGs. Graphical abstract.
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Affiliation(s)
- Xiangyu Shi
- Department of Cardiovascular Medicine, The Second Xiangya Hospital, Central South University, Changsha, Hunan, 410011, China.,Yale Cardiovascular Research Center, Section of Cardiovascular Medicine, Department of Internal Medicine , Yale School of Medicine, 300 George Street, Room 752, New Haven, CT, 06511, USA
| | - Lile He
- Department of Cardiovascular Surgery, The Second Xiangya Hospital, Central South University, Changsha, Hunan, 410011, China
| | - Shang-Min Zhang
- Department of Pathology, Yale School of Medicine, 06520, New Haven, CT, USA
| | - Jiesi Luo
- Yale Cardiovascular Research Center, Section of Cardiovascular Medicine, Department of Internal Medicine , Yale School of Medicine, 300 George Street, Room 752, New Haven, CT, 06511, USA. .,Yale Stem Cell Center, 06520, New Haven, CT, USA.
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Hodge J, Quint C. Tissue engineered vessel from a biodegradable electrospun scaffold stimulated with mechanical stretch. Biomed Mater 2020; 15:055006. [DOI: 10.1088/1748-605x/ab8e98] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Lei Y, Goldblatt ZE, Billiar KL. Micromechanical Design Criteria for Tissue-Engineering Biomaterials. Biomater Sci 2020. [DOI: 10.1016/b978-0-12-816137-1.00083-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Lee PY, Liu YC, Wang MX, Hu JJ. Fibroblast-seeded collagen gels in response to dynamic equibiaxial mechanical stimuli: A biomechanical study. J Biomech 2018; 78:134-142. [PMID: 30107900 DOI: 10.1016/j.jbiomech.2018.07.030] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2018] [Revised: 07/18/2018] [Accepted: 07/20/2018] [Indexed: 02/03/2023]
Abstract
The remodeling of fibroblast-seeded collagen gels in response to dynamic mechanical stimuli was investigated by using a newly developed biaxial culture system capable of cyclically stretching planar soft tissues. Fibroblast-seeded collagen gels were subjected to three distinct dynamic mechanical conditions for six days: Cyclic Equibiaxial Stretching at two constant strain magnitudes (CES-7% and CES-20%), and Cyclic Equibiaxial Stretching with incrementally Increasing stain magnitude (ICES, 7% → 15% → 20% each for two days). The frequency of cyclic stretching was set at 1 Hz. At the end of culture, mechanical properties of the gels were examined by biaxial mechanical testing and checked again upon the removal of seeded cells. Collagen microstructure within the gels was illustrated by multiphoton microscopy. The mRNA levels of collagen type I and type III and fibronectin in the cells were examined by reverse transcription PCR. The protein expression of α-smooth muscle actin was detected by immunohistochemistry. We found that the gels cultured under cyclic stretching were stiffer than those cultured under static stretching. Particularly, the stiffness appeared to be significantly enhanced when the ICES was employed. The enhancement of mechanical properties by cyclic stretching appeared to persist upon cell removal, suggesting an irreversible remodeling of extracellular matrix. Second harmonic generation images showed that collagen fibers became thicker and more compact in the gels cultured under cyclic stretching, which may explain the mechanical findings. The mRNA expression of collagen type I in the cells of the ICES was significantly greater than that of the other groups except for the CES-20%. This study suggests that when cyclic stretching is to be used in engineering soft tissues, incrementally increasing strain magnitude may prove useful in the development of the tissue.
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Affiliation(s)
- Pei-Yuan Lee
- Department of Biomedical Engineering, National Cheng Kung University, Tainan, Taiwan; Department of Orthopedics Surgery, Show Chwan Memorial Hospital, Changhua, Taiwan
| | - Yen-Ching Liu
- Department of Mechanical Engineering, National Chiao Tung University, Hsinchu, Taiwan
| | - Mei-Xuan Wang
- Department of Biomedical Engineering, National Cheng Kung University, Tainan, Taiwan
| | - Jin-Jia Hu
- Department of Biomedical Engineering, National Cheng Kung University, Tainan, Taiwan; Medical Device Innovation Center, National Cheng Kung University, Tainan, Taiwan.
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