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Mechanical Environment (mechanical + environment)
Selected AbstractsCharacterization of a Novel Fiber Composite Material for Mechanotransduction Research of Fibrous Connective TissuesADVANCED FUNCTIONAL MATERIALS, Issue 5 2010Hazel R. C. Screen Abstract Mechanotransduction is the fundamental process by which cells detect and respond to their mechanical environment, and is critical for tissue homeostasis. Understanding mechanotransduction mechanisms will provide insights into disease processes and injuries, and may support novel tissue engineering research. Although there has been extensive research in mechanotransduction, many pathways remain unclear, due to the complexity of the signaling mechanisms and loading environments involved. This study describes the development of a novel hydrogel-based fiber composite material for investigating mechanotransduction in fibrous tissues. By encapsulating poly(2-hydroxyethyl methacrylate) rods in a bulk poly(ethylene glycol) matrix, it aims to create a micromechanical environment more representative of that seen in vivo. Results demonstrated that collagen-coated rods enable localized cell attachment, and cells are successfully cultured for one week within the composite. Mechanical analysis of the composite indicates that gross mechanical properties and local strain environments could be manipulated by altering the fabrication process. Allowing diffusion between the rods and surrounding matrix creates an interpenetrating network whereby the relationships between shear and tension are altered. Increasing diffusion enhances the shear bond strength between rods and matrix and the levels of local tension along the rods. Preliminary investigation into fibroblast mechanotransduction illustrates that the fiber composite upregulates collagen I expression, the main protein in fibrous tissues, in response to cyclic tensile strains when compared to less complex 2D and 3D environments. In summary, the ability to create and manipulate a strain environment surrounding the fibers, where combined tensile and shear forces uniquely impact cell functions, is demonstrated. [source] Inside Front Cover: A Unique Microcracking Process Associated with the Inelastic Deformation of Haversian Bone (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 1 2009Mater. Human cortical bone is capable of adapting to the mechanical environment through dynamic remodeling of the Haversian systems. The presence of Haversian canals, however, also introduces stress concentration and could have detrimental effects on the fracture resistance of bone. How is the hierarchical structure in bone designed to alleviate such stress concentrations? On page 57, Vincent Ebacher and Rizhi Wang report a unique and stable microcracking process accompanying the inelastic deformation of Haversian bone. The results lead to the critical role of the well-organized bone lamellae surrounding each Haversian canal. [source] In vivo mechanical condition plays an important role for appearance of cartilage tissue in ES cell transplanted jointJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 1 2008Masaaki Nakajima Abstract The objective of this study was to evaluate the effects of the mechanical environment on the formation of cartilage tissue in transplanted embryonic stem (ES) cells. Full-thickness osteochondral defects were created on the patella groove of SD rats, and ES cells (CCE ES cells obtained from 129/Sv/Ev mice and Green ES FM260 ES cells obtained from 129SV [D3] - Tg [NCAG-EGFP] CZ,001,FM260Osb mice) were transplanted into the defects embedded in collagen gel. The animals were randomly divided into either the joint-free group (JF group) or the joint-immobilized group (JI group) for 3 weeks after a week postoperatively. The results showed that cartilage-like tissue formed in the defects of the JF group whereas large teratomatous masses developed in the defects of the JI group. Some parts of the cartilage-like tissue and the teratomatous masses were positively stained with immunostain for GFP when the Green ES FM260 ES cells were transplanted. It is suggested that the environment plays an important role for ES cells in the process of repairing cartilage tissue in vivo. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:10,17, 2008 [source] Intact fibula improves fracture healing in a rat tibia osteotomy modelJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 2 2005Sandra J. Shefelbine Abstract Rat tibia fractures are often used in fracture healing studies. Usually the fracture is stabilized with an intramedullary pin, which provides bending stiffness, but little torsional stiffness. The objective of this research was to determine the in vitro torsional rigidity of an osteotomized tibia with and without the fibula, and to determine if this difference influences the healing process in vivo. In vitro eleven rat tibias received an osteotomy, were stabilized with an intramedullary pin, and were tested in internal rotation to determine the torsional rigidity. The fibula was then manually broken and the torsional rigidity measured again. In vivo 18 rats received a tibial osteotomy, eight of which had an additional fractured fibula. After three weeks, the rats were sacrificed and the tibias were analyzed. Bone density in the fracture callus was measured with qCT. Bending rigidity and maximum breaking moment were determined in three-point bending. In vitro testing demonstrated that the torsional rigidity with an intact fibula was nearly two times higher than when the fibula was fractured. Though the torsional rigidity was still small in comparison with an intact bone, it resulted in a significantly different healing process in vivo. Rats with intact fibulas had significantly higher bone mineral density, bending rigidity, and maximum breaking moment compared to rats with a fractured fibula. These results indicate that torsional stability considerably affects the healing process. In a fracture model, it is critical to characterize the mechanical environment of the fracture. © 2004 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved. [source] Cellular and molecular characterization of a murine non-union modelJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 5 2004P. Choi Abstract Purpose. We have developed a method to study the molecular and cellular events underlying delayed skeletal repair in a model that utilizes distraction osteogenesis. Methods. The clinical states of delayed union and non-union were reproduced in this murine model by altering distraction parameters such as the inclusion and exclusion of a latency phase and variations in the rate and rhythm of distraction. Radiographic, cellular, and molecular analyses were performed on the distraction tissues. Results. Eliminating the latency period delayed bony union, but did not appreciably alter the extent of platelet endothelial cell adhesion marker (PECAM) immunostaining. Following elimination of a latency phase and a threefold increase in the rate of distraction, there was a further delay in bone regeneration and a higher rate of non-union (60%). Instead of bone, the distraction gap was comprised of adipose or fibrous tissue. Once again, despite the rigorous distraction protocol, we detected equivalent PECAM staining within the distraction gap. In a minority of cases, cartilage and osseous tissues occupied the distraction gap likely by a prolonged process of endochondral ossification. Conclusions. Here, we have altered the mechanical environment in such a way to reproducibly create delays in skeletal regeneration. These delays in skeletal tissue regeneration appear to develop even in the presence of endothelial cells, which suggests that mechanisms other than a disruption to the vascular network can account for some cases of non-union. © 2004 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved. [source] Induction of a neoarthrosis by precisely controlled motion in an experimental mid-femoral defectJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 3 2002Dennis M. Cullinane Bone regeneration during fracture healing has been demonstrated repeatedly, yet the regeneration of articular cartilage and joints has not yet been achieved. It has been recognized however that the mechanical environment during fracture healing can be correlated to the contributions of either the endochondral or intramembranous processes of bone formation, and to resultant tissue architecture. Using this information, the goal of this study was to test the hypothesis that induced motion can directly regulate osteogenic and chondrogenic tissue formation in a rat mid-femoral bone defect and thereby influence the anatomical result. Sixteen male Sprague Dawley rats (400 ± 20 g) underwent production of a mid-diaphyseal, non-critical sized 3.0 mm segmental femoral defect with rigid external fixation using a custom designed four pin fixator. One group of eight animals represented the controls and underwent surgery and constant rigid fixation. In the treatment group the custom external fixator was used to introduce daily interfragmentary bending strain in the eight treatment animals (12°s angular excursion), with a hypothetical symmetrical bending load centered within the gap. The eight animals in the treatment group received motion at 1.0 Hz, for 10 min a day, with a 3 days on, one day off loading protocol for the first two weeks, and 2 days on, one day off for the remaining three weeks. Data collection included histological and immunohistological identification of tissue types, and mean collagen fiber angles and angular conformity between individual fibers in superficial, intermediate, and deep zones within the cartilage. These parameters were compared between the treatment group, rat knee articular cartilage, and the control group as a structural outcome assessment. After 35 days the control animals demonstrated varying degrees of osseous union of the defect with some animals showing partial union. In every individual within the mechanical treatment group the defect completely failed to unite. Bony arcades developed in the experimental group, capping the termini of the bone segments on both sides of the defect in four out of six animals completing the study. These new structures were typically covered with cartilage, as identified by specific histological staining for Type II collagen and proteoglycans. The distribution of collagen within analogous superficial, intermediate, and deep zones of the newly formed cartilage tissue demonstrated preferred fiber angles consistent with those seen in articular cartilage. Although not resulting in complete joint development, these neoarthroses show that the induced motion selectively controlled the formation of cartilage and bone during fracture repair, and that it can be specifically directed. They further demonstrate that the spatial organization of molecular components within the newly formed tissue, at both microanatomical and gross levels, are influenced by their local mechanical environment, confirming previous theoretical models. © 2002 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved. [source] Molecular aspects of healing in stabilized and non-stabilized fracturesJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 1 2001A. X. Le Bone formation is a continuous process that is initiated during fetal development and persists in adults in the form of bone regeneration and remodeling. These latter two aspects of bone formation are clearly influenced by the mechanical environment. In this study we tested the hypothesis that alterations in the mechanical environment regulate the program of mesenchymal cell differentiation, and thus the formation of a cartilage or bony callus, at the site of injury. As a first step in testing this hypothesis we produced stabilized and non-stabilized tibial fractures in a mouse model, then used molecular and cellular methods to examine the stage of healing. Using the "molecular map" of the fracture callus, we divided our analyzes into three phases of fracture healing: the inflammatory or initial phase of healing, the soft callus or intermediate stage, and the hard callus stage. Our results show that indian hedgehog(ihh), which regulates aspects of chondrocyte maturation during fetal and early postnatal skeletogenesis, was expressed earlier in an non-stabilized fracture callus as compared to a stabilized callus, ihh persisted in the non-stabilized fracture whereas its expression was down-regulated in the stabilized bone. IHH exerts its effects on chondrocyte maturation through a feedback loop that may involve bone morphogenetic protein 6 [bmp6; (S. Pathi, J.B. Rutenberg, R.L. Johnson, A. Vortkamp, Developmental Biology 209 (1999) 239,253)] and the transcription factor gli3, bmp6 and gli3 were re-induced in domain adjacent to the ihh -positive cells during the soft and hard callus stages of healing. Thus, stabilizing the fracture, which circumvents or decreases the cartilaginous phase of bone repair, correlates with a decrease in ihh signaling in the fracture callus. Collectively, our results illustrate that the ihh signaling pathway participates in fracture repair, and that the mechanical environment affects the temporal induction of ihh, bmp6 and gli3. These data support the hypothesis that mechanical influences affect mesenchymal cell differentiation to bone. © 2001 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved. [source] Functional adaptation of the femoral head to voluntary exerciseTHE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 7 2006Jeffrey H. Plochocki Abstract The functional adaptation of limb joints during postnatal ontogeny is necessary to maintain proper joint function. Joint form is modified primarily through differential rates of articular cartilage proliferation across articular surfaces during endochondral growth. This process is hypothesized to be mechanically regulated by the magnitude and orientation of stresses in the articular cartilage. However, the adaptation of limb joint morphology to the mechanical environment is poorly understood. We investigate the effects of voluntary exercise on femoral head morphology in 7-week-old female mice of the inbred strain C57BL/6J. The mice were divided into a control group and a group treated with voluntary access to an activity wheel for the duration of the 4-week study. Histomorphometric comparisons of chondral and osseous joint tissue of the proximal femur were made between control and exercise treatment groups. We find that exercised mice have significantly thicker articular cartilage with greater chondral tissue area and cellularity. Exercised mice also exhibit significantly greater bone tissue area and longer and flatter subchondral surfaces. No significant difference is found in the curvature of the articular cartilage or the length of the chondral articular surface between groups. These data suggest that a complex mechanistic relationship exists between joint stress and joint form. Joint tissue response to loading is multifaceted, involving both size and shape changes. Our data support the hypothesis that joint growth is ontogenetically plastic. Mechanical loading significantly influences chondral and subchondral tissue proliferation to provide greater support against increased mechanical loading. Anat Rec Part A, 288A:776,781, 2006 © 2006 Wiley-Liss, Inc. [source] Developmental and osteoarthritic changes in Col6a1 -knockout mice: Biomechanics of type VI collagen in the cartilage pericellular matrixARTHRITIS & RHEUMATISM, Issue 3 2009Leonidas G. Alexopoulos Objective Chondrocytes, the sole cell type in articular cartilage, maintain the extracellular matrix (ECM) through a homeostatic balance of anabolic and catabolic activities that are influenced by genetic factors, soluble mediators, and biophysical factors such as mechanical stress. Chondrocytes are encapsulated by a narrow tissue region termed the "pericellular matrix" (PCM), which in normal cartilage is defined by the exclusive presence of type VI collagen. Because the PCM completely surrounds each cell, it has been hypothesized that it serves as a filter or transducer for biochemical and/or biomechanical signals from the cartilage ECM. The present study was undertaken to investigate whether lack of type VI collagen may affect the development and biomechanical function of the PCM and alter the mechanical environment of chondrocytes during joint loading. Methods Col6a1,/, mice, which lack type VI collagen in their organs, were generated for use in these studies. At ages 1, 3, 6, and 11 months, bone mineral density (BMD) was measured, and osteoarthritic (OA) and developmental changes in the femoral head were evaluated histomorphometrically. Mechanical properties of articular cartilage from the hip joints of 1-month-old Col6a1,/,, Col6a1+/,, and Col6a1+/+ mice were assessed using an electromechanical test system, and mechanical properties of the PCM were measured using the micropipette aspiration technique. Results In Col6a1,/, and Col6a1+/, mice the PCM was structurally intact, but exhibited significantly reduced mechanical properties as compared with wild-type controls. With age, Col6a1,/, mice showed accelerated development of OA joint degeneration, as well as other musculoskeletal abnormalities such as delayed secondary ossification and reduced BMD. Conclusion These findings suggest that type VI collagen has an important role in regulating the physiology of the synovial joint and provide indirect evidence that alterations in the mechanical environment of chondrocytes, due to either loss of PCM properties or Col6a1,/, -derived joint laxity, can lead to progression of OA. [source] Design and characterization of a modified T-flask bioreactor for continuous monitoring of engineered tissue stiffnessBIOTECHNOLOGY PROGRESS, Issue 3 2010Richard A. Lasher Abstract Controlling environmental conditions, such as mechanical stimuli, is critical for directing cells into functional tissue. This study reports on the development of a bioreactor capable of controlling the mechanical environment and continuously measuring force-displacement in engineered tissue. The bioreactor was built from off the shelf components, modified off the shelf components, and easily reproducible custom built parts to facilitate ease of setup, reproducibility and experimental flexibility. A T-flask was modified to allow for four tissue samples, mechanical actuation via a LabView controlled stepper motor and transduction of force from inside the T-flask to an external sensor. In vitro bench top testing with instrumentation springs and tissue culture experiments were performed to validate system performance. Force sensors were highly linear (R2 > 0.998) and able to maintain force readings for extended periods of time. Tissue culture experiments involved cyclic loading of polyurethane scaffolds seeded with and without (control) human foreskin fibroblasts for 8 h/day for 14 days. After supplementation with TGF-,, tissue constructs showed an increase in stiffness between consecutive days and from the acellular controls. These experiments confirmed the ability of the bioreactor to distinguish experimental groups and monitor tissue stiffness during tissue development. © 2010 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] Fluid Mechanics, Cell Distribution, and Environment in Cell Cube BioreactorsBIOTECHNOLOGY PROGRESS, Issue 1 2003John G. Auni Cultivation of MRC-5 cells and attenuated hepatitis A virus (HAV) for the production of VAQTA, an inactivated HAV vaccine ( 1), is performed in the Cell Cube reactor, a laminar flow fixed-bed bioreactor with an unusual diamond-shaped, diverging-converging flow geometry. These disposable bioreactors have found some popularity for the production of cells and gene therapy vectors at intermediate scales of operation ( 2, 3). Early testing of the Cell Cube revealed that the fluid mechanical environment played a significant role in nonuniform cell distribution patterns generated during the cell growth phase. Specifically, the reactor geometry and manufacturing artifacts, in combination with certain inoculum practices and circulation flow rates, can create cell growth behavior that is not simply explained. Via experimentation and computational fluid dynamics simulations we can account for practically all of the observed cell growth behavior, which appears to be due to a complex mixture of flow distribution, particle deposition under gravity, fluid shear, and possibly nutritional microenvironment. [source] Functional characterization of TRPV4 as an osmotically sensitive ion channel in porcine articular chondrocytesARTHRITIS & RHEUMATISM, Issue 10 2009Mimi N. Phan Objective Transient receptor potential vanilloid 4 (TRPV4) is a Ca2+ -permeable channel that can be gated by tonicity (osmolarity) and mechanical stimuli. Chondrocytes, the cells in cartilage, respond to their osmotic and mechanical environments; however, the molecular basis of this signal transduction is not fully understood. This study was undertaken to demonstrate the presence and functionality of TRPV4 in chondrocytes. Methods TRPV4 protein expression was measured by immunolabeling and Western blotting. In response to TRPV4 agonist/antagonists, osmotic stress, and interleukin-1 (IL-1), changes in Ca2+ signaling, cell volume, and prostaglandin E2 (PGE2) production were measured in porcine chondrocytes using fluorescence microscopy, light microscopy, or immunoassay, respectively. Results TRPV4 was expressed abundantly at the RNA and protein levels. Exposure to 4,-phorbol 12,13-didecanoate (4,PDD), a TRPV4 activator, caused Ca2+ signaling in chondrocytes, which was blocked by the selective TRPV4 antagonist, GSK205. Blocking TRPV4 diminished the chondrocytes' response to hypo-osmotic stress, reducing the fraction of Ca2+ responsive cells, the regulatory volume decrease, and PGE2 production. Ca2+ signaling was inhibited by removal of extracellular Ca2+ or depletion of intracellular stores. Specific activation of TRPV4 restored the defective regulatory volume decrease caused by IL-1. Chemical disruption of the primary cilium eliminated Ca2+ signaling in response to either 4,PDD or hypo-osmotic stress. Conclusion Our findings indicate that TRPV4 is present in articular chondrocytes, and chondrocyte response to hypo-osmotic stress is mediated by this channel, which involves both an extracellular Ca2+ and intracellular Ca2+ release. TRPV4 may also be involved in modulating the production or influence of proinflammatory molecules in response to osmotic stress. [source] | ||||||||||