Chunqiu Zhang

Culturing functional cartilage tissue under a novel bionic mechanical condition

Bioreactor, which is used for in vitro construction of tissue-engineered cartilage, has been extensively studied by researchers. The growth and development of articular cartilage tissue are affected by biomechanical and biochemical factors, especially mechanical condition. Kinds of mechanical conditions including compressive and shear force, fluid flow, hydrostatic pressure, and tissue deformation, were developed in the past years. However, most mechanical conditions of improved bioreactor involve only one or two external force, which is merely partial for engineering cartilage tissue. No bioreactor which can simulate a normal articular cartilage in terms of structure and function has been reported. Consequently, simulation of bionic mechanical environment of a normal articular cartilage is considered to be the optimal environment for culturing the functional articular cartilage in vitro. Based upon this purpose, we designed a rolling-compression loading bioreactor. It could provide cultures with multi-mechanical stimulations and sufficiently mimic the complex mechanical environment of a normal articular cartilage. We propose that this comprehensive rolling-compression loading bioreactor can enhance the cultivation of functional cartilage constructs in vitro.

Extracellular Matrix of Mechanically Stretched Cardiac Fibroblasts Improves Viability and Metabolic Activity of Ventricular Cells

Background: In heart, the extracellular matrix (ECM), produced by cardiac fibroblasts, is a potent regulator of heart,s function and growth, and provides a supportive scaffold for heart cells in vitro and in vivo. Cardiac fibroblasts are subjected to mechanical loading all the time in vivo. Therefore, the influences of mechanical loading on formation and bioactivity of cardiac fibroblasts, ECM should be investigated. Methods: Rat cardiac fibroblasts were cultured on silicone elastic membranes and stimulated with mechanical cyclic stretch. After removing the cells, the ECMs coated on the membranes were prepared, some ECMs were treated with heparinase II (GAG-lyase), then the collagen, glycosaminoglycan (GAG) and ECM proteins were assayed. Isolated neonatal rat ventricular cells were seeded on ECM-coated membranes, the viability and lactate dehydrogenase (LDH) activity of the cells after 1-7 days of culture was assayed. In addition, the ATPase activity and related protein level, glucose consumption ratio and lactic acid production ratio of the ventricular cells were analyzed by spectrophotometric methods and Western blot. Results: The cyclic stretch increased collagen and GAG levels of the ECMs, and elevated protein levels of collagen I and fibronectin. Compared with the ECMs produced by unstretched cardiac fibroblasts, the ECMs of mechanically stretched fibroblasts improved viability and LDH activity, elevated the Na+/K+-ATPase activity, sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) activity and SERCA 2a protein level, glucose consumption ratio and lactic acid production ratio of ventricular cells seeded on them. The treatment with heparinase II reduced GAG levels of these ECMs, and lowered these metabolism-related indices of ventricular cells cultured on the ECMs. Conclusions: Mechanical stretch promotes ECM formation of cardiac fibroblasts in vitro, the ECM of mechanically stretched cardiac fibroblasts improves metabolic activity of ventricular cells cultured in vitro, and the GAG of the ECMs is involved in regulating metabolic activity of ventricular cells.

On mechanical mechanism of damage evolution in articular cartilage

Superficial lesions of cartilage are the direct indication of osteoarthritis. To investigate the mechanical mechanism of cartilage with micro-defect under external loading, a new plain strain numerical model with micro-defect was proposed and damage evolution progression in cartilage over time has been simulated, the parameter were studied including load style, velocity of load and degree of damage. The new model consists of the hierarchical structure of cartilage and depth-dependent arched fibers. The numerical results have shown that not only damage of the cartilage altered the distribution of the stress but also matrix and fiber had distinct roles in affecting cartilage damage, and damage in either matrix or fiber could promote each other. It has been found that the superficial cracks in cartilage spread preferentially along the tangent direction of the fibers. It is the arched distribution form of fibers that affects the crack spread of cartilage, which has been verified by experiment. During the process of damage evolution, its extension direction and velocity varied constantly with the damage degree. The rolling load could cause larger stress and strain than sliding load. Strain values of the matrix initially increased and then decreased gradually with the increase of velocity, and velocity had a greater effect on matrix than fibers. Damage increased steadily before reaching 50%, sharply within 50 to 85%, and smoothly and slowly after 85%. The finding of the paper may help to understand the mechanical mechanism why the cracks in cartilage spread preferentially along the tangent direction of the fibers.

Depth and rate dependent mechanical behaviors for articular cartilage: experiments and theoretical predictions.

An optimized digital image correlation (DIC) technique was applied to investigate the depth-dependent mechanical properties of articular cartilage and simultaneously the depth-dependent nonlinear viscoelastic constitutive model of cartilage was proposed and validated. The creep tests were performed with different stress levels and it is found that the initial strain and instantaneous strain increase; however the creep compliance decreases with the increase of compressive stress. The depth-dependent creep strain of cartilage was obtained by analyzing the images acquired using the optimized DIC technique. Moreover the inhomogeneous creep compliance distributions within the tissues were determined at different creep time points. It is noted that both creep strain and creep compliance with different creep times decrease from cartilage surface to deep. The depth-dependent creep compliance increases with creep time and the increasing amplitude of creep compliance decreases along cartilage depth. The depth-dependent and stress rate dependent nonlinear stress and strain curves were obtained for articular cartilage through uniaxial compression tests. It is found that the Youngs modulus of cartilage increases obviously along cartilage depth from superficial layer to deep layer and the Youngs modulus of different layers for cartilage increases with the increase of stress rate. The Poissons ratio of cartilage increases along cartilage depth with given compressive strain and the Poissons ratio of different layers decreases with the increase of compressive strain. The depth-dependent nonlinear viscoelastic constitutive model was proposed and some creep data were applied to determine the parameters of the model. The depth-dependent compressive behaviors of cartilage were predicted by the model and the results show that there are good agreements between the experimental data and predictions.

A loading device suitable for studying mechanical response of bone cells in hard scaffolds.

Bone cells live in an environment heavily influenced by mechanical forces. Systematic study of cells mechanical responses has relied greatly on the in-vitro experiments due to complexity of internal environment of bone cells in vivo. A loading device suitable to hard scaffolds for studying mechanical responses of bone cells was made by using a kind of long-travel, high-load piezoelectric actuator. The device, which was precisely controlled by computer, and designed to work in an incubator at 37 degrees C and 100% humidity, can cause hard scaffolds with directly compressive strains with more magnitudes, frequency components, and waveforms, including bone physiologically mechanical state. The experiment using hard scaffolds indicates the device validity. The device represents a versatile model that will provide conditions for investigating the effects of mechanical responses on bone cells in 3D hard scaffolds in vitro. In addition, the preliminary biological test was performed by the application of the device. The results showed that the dynamic compression with the amplitude of 1000 microstrain, the frequency of 3 Hz, the duration of 3 min/day enhanced the osteoblastic proliferation and extracellular matrix compared with static conditions, and improved the cell distribution within scaffolds. The researches of 3D mechanical effects on bone cells just in hard scaffolds similar to that in cancellous bone can enhance the understanding of bone physiology in vivo. The direct, dynamic contact-loading of the device may provide an appropriate mechanical condition in bone tissue engineering culture.

Ratcheting behavior of articular cartilage under cyclic unconfined compression

The ratcheting deformation of articular cartilage can produce due to the repeated accumulations of compressive strain in cartilage. The aim of this study was to investigate the ratcheting behavior of articular cartilage under cyclic compression. A series of uniaxial cyclic compression tests were conducted for online soaked and unsoaked cartilage samples and the effects of stress variation and stress rate on ratcheting behavior of cartilage were investigated. It is found that the ratcheting strains of online soaked and unsoaked cartilage samples increase rapidly at initial stage and then show the slower increase with cyclic compression going on. On the contrary, the ratcheting strain rate decreases quickly at first and then exhibits a relatively stable and small value. Both the ratcheting strain and ratcheting strain rate increase with stress variation increasing or with stress rate decreasing. Simultaneously, the optimized digital image correlation (DIC) technique was applied to study the ratcheting behavior and Youngs modulus of different layers for cartilage under cyclic compression. It is found that the ratcheting behavior of cartilage is dependent on its depth. The ratcheting strain and its rate decrease through the depth of cartilage from surface to deep, whereas the Youngs modulus increases.

Depth-dependent strain fields of articular cartilage under rolling load by the optimized digital image correlation technique

It is significant to investigate the depth-dependent mechanical behaviors of articular cartilage under rolling load since considerable rolling occurs for cartilage joint in activities of daily living. In this study, the rolling experiments of articular cartilage were conducted by applying an optimized digital image correlation (DIC) technique for the first time and the depth-dependent normal strain and shear strain of cartilage were analyzed. It is found that the normal strain and shear strain values of different layers increase firstly and then decrease with rolling time, and they increase with increasing compressive strains. The normal strain and shear strain values decrease along cartilage depth with constant compressive strain. The normal strain values of different normalized depth decrease with increasing rolling rates. The shear strain values of superficial layer and middle layer decrease; however there are no major changes for the shear strain values of deep layer with increasing rolling rates. The normal strain values with different rolling time increase with increasing rolling numbers and the 30.6% increase in initial normal strain is observed from 1st to 99th cycle. The fitting relationship of the normal strain and normalized depth was obtained considering the effects of compressive strain and rolling rate and the fitting curves agree with the experimental results for cartilage very well.

The combination of icariin and constrained dynamic loading stimulation attenuates bone loss in ovariectomy-induced osteoporotic mice†

Osteoporosis is a disease characterized by low bone mass and progressive destruction of bone microstructure, resulting in increasing the risk of fracture. Icariin (ICA) as a phytoestrogen shows osteogenic effects, and the mechanical stimulation has been demonstrated the improving effect on osteoporosis. The objective of this study was to investigate the effect of ICA in combination with constrained dynamic loading (CDL) stimulation on osteoporosis in ovariectomized (OVX) mice. The serum hormone levels, bone turnover markers, trabecular architecture, ulnar biomechanical properties, and the expression of osteoblast‐related gene (alkaline phosphatase, ALP; osteocalcin, OCN; bone morphogenetic protein‐2, BMP‐2; Collagen I (α1), COL1; osteoprotegerin, OPG) and osteoclast‐related genes (receptor activators of NF‐κB ligand, RANKL; tartrate‐resistant acid phosphatase, TRAP) were analyzed. The results showed that ICA + CDL treatment could increase the osteocalcin (20.85%), estradiol levels (20.61%) and decrease the TRAP activity (26.27%) significantly than CDL treatment. The combined treatment attenuated bone loss and biomechanical decrease more than single use of CDL treatment. ICA + CDL treatment significantly up‐regulated the level of osteoblast‐related gene expression and down‐regulated the osteoclast‐related genes expression; moreover, the combined treatment increased the ratio of OPG/RANKL significantly compared to ICA (72.83%) or CDL (65.63%) treatment alone. The present study demonstrates that icariin in combination with constrained dynamic loading treatment may have a therapeutic advantage over constrained dynamic loading treatment alone for the treatment of osteoporosis, which would provide new evidence for the clinical treatment of osteoporosis.

Design of a New Multifunctional Wheelchair-bed

Currently, the aging of the population has become the world’s social problems. The increasing aging population and lots of disability, paralysis makes nursing care more difficult. Because of many elderly can not get timely care, the phenomenon that the elderly have chronic diseases has become more and more serious. It is important to research and develop new product which can help the elderly and the disabled for improving the quality of their life. This paper suggested a new type of multifunctional self-caring wheelchair-bed, which is combined with a wheelchair and a bed. The bed can realize the free conversion among user sitting, leg lifting and lie down, and also can implement the function of turning on sides. Particularly, the wheelchair can be easily separated from the bed and combined, so that patients and the elderly can move freely using it, and even it can be transformed into a standing type to satisfy the patient’s standing demand, and to a certain extent, carry out the purpose of rehabilitation.

Effects of creep and creep-recovery on ratcheting strain of articular cartilage under cyclic compression

Since the accumulations of ratcheting strain combined with creep deformation, which are produced in normal activities, can accelerate the fatigue damage of cartilage in joint, the creep-ratcheting and creep-recovery-ratcheting behaviors of articular cartilage are experimentally investigated under creep-fatigue loads. The effect of pre-creep on ratcheting behavior of cartilage was probed firstly and it is found that the initial ratcheting strain of cartilage presents the larger value (30% and 35%) due to its pre-creep deformation in spite of the short pre-creep time applied. With the increasing pre-creep time the ratcheting strain of sample increases while the ratcheting strain rate decreases. The effects of pre-creep and recovery on ratcheting behavior of cartilage were also investigated and it is noted that the strain of cartilage increases fast at first, decreases partly and then changes periodically with cyclic stress. The ratcheting strain evolutions of different layers are not coincident for cartilage sample after the pre-creep or pre-creep-recovery and the ratcheting strains of different layers with pre-creep are larger than them with pre-creep-recovery. Finally the creep-ratcheting strain of cartilage with different peak-holding time during cyclic compression was studied and it is found that the creep-ratcheting strain with peak-holding time is significantly greater than that without peak-holding time. The creep-ratcheting strain increases with increase of peak-holding time or stress amplitude, while it reduces with rising of stress rate. The creep-ratcheting behavior of cartilage is dependent on its depth. These findings point out that the accumulated deformations, including creep deformation and ratcheting deformation, can accelerate the cartilages damage.