Zhonggang Feng

Measurements of the mechanical properties of contracted collagen gels populated with rat fibroblasts or cardiomyocytes

In this paper the mechanical properties of contracted collagen gels populated with rat fibroblasts or cardiomyocytes were investigated by means of uniaxial tensile testing. Rat type I collagen–Dulbeccos modified Eagles medium (DMEM) gels (each 2 ml in volume, 0.5 mg/ml collagen concentration) populated with different numbers of rat fibroblasts or cardiomyocytes were made in 31 × 17-mm wells cut in silicone rubber located in a 100-mm diameter plastic dish. Identically treated gels were incubated for 4 days floating in DMEM and then were subjected to uniaxial tensile testing. Rapid contraction occurred within the first 3 days for both the fibroblast and cardiomyocyte gels, but the cardiomyocyte gels consistently contracted to smaller sizes than the fibroblast gels for each number of cells used. The tension–strain curve of the contracted collagen gels demonstrated exponential behavior in the low stress region, followed by a linear section, and finally a maximum tension point, giving the ultimate strength of the gel tested. The cardiomyocyte gels had higher tension–strain curves than the fibroblast gels for each number of cells used. The tension relaxation and cyclic creep phenomena were observed in both kinds of gels, and these phenomena coincide with prior observations in collagen gels contracted by human fibroblasts. This experiment shows that type I collagen gels can be significantly contracted by rat fibroblasts or cardiomyocytes so as to achieve a certain mechanical strength. The contracted collagen structures made in these experiments have potential for developing tissue-engineered structures for cardiac muscle studies.

Construction of fibroblast–collagen gels with orientated fibrils induced by static or dynamic stress: toward the fabrication of small tendon grafts

As a step toward the fabrication of small tendon grafts, fibroblast–collagen gels were constructed with orientated fibrils induced by static or dynamic loading. Three groups of gel samples, each consisting of 1.0 × 106 fibroblasts and 2 mg type I collagen, were fabricated: freely contracted gels formed the control group; contraction-directed gels made up the static group (the gel contraction was directed perpendicular to an axis made by two anchors buried in the gels so that the constraint stress exerted by the two anchors was imposed on the gel); and for the dynamic group, a specific loading pattern (free contraction followed by cyclic stretching using a tensile bioreactor) was employed. Mechanical properties were evaluated by means of the uniaxial tension test. The gels of the static group had an ultimate stress of 350 ± 43.6 kPa and a material modulus of 548.8 ± 61.6 kPa, which were almost 5.2 times and 15.6 times, respectively, greater than those of the controls. The dynamic gels had an ultimate stress of 256.8 ± 80.7 kPa and a material modulus of 118.6 ± 23.5 kPa. These results show that the ultimate stress and material modulus of the static samples are much greater than those of the dynamic samples, which is the opposite of our expectations. Therefore, studies under other dynamic loading patterns and long-term culture are needed to clarify whether dynamic loading is superior to static loading.

Effect of cobalt on the liver glycogen content in the streptozotocin-induced diabetic rats.

Cobalt decreases blood glucose in diabetic rats but the mechanisms involved are unclear. To determine the contribution of glycogen metabolism to glycemia-lowering effect, glycogen contents of liver and muscle in the streptozotocin-induced diabetic rats were determined. The liver glycogen was depleted in diabetic rats. But when cobalt was administered to the rats, the glycogen returned to the level of healthy rats, concomitantly with the decrease in blood glucose. The cobalt treatment had no effect on the muscle glycogen in the diabetic rats. The tissue-specific responses of glycogen metabolism suggest the involvement of suppressed glucagon signaling due to cobalt treatment.

Direct quantification of gene expression using fluorescence correlation spectroscopy.

Among the methods for single molecule detection in the field of medicinal chemistry, the importance of fluorescence correlation spectroscopy (FCS) is growing. FCS has the advantage of permitting us to determine the number of fluorescent molecules and the diffusion constant dependent on the molecular weight without any physical separation process such as gel electrophoresis. Thus this method is appropriate for studies on the hybridization of fluorescence-labeled oligonucleotides with RNA or DNA as well as gene expression through translation of a target protein linked with green fluorescent protein. Indeed, several groups have employed FCS for evaluation of gene expression in different ways. Many investigators are particularly interested in using FCS to quantitatively analyze mRNA just after transcription in the living cell. Technical advances in FCS have broadened the research spectrum in medicinal chemistry since it can also be used to study SNPs and molecular interactions between transcription factors and promoter sequences, as well as gene expression in living cells.

Characterizing and modulating the mechanical properties of hydrogels from ventricular extracellular matrix

In order to differentiate pluripotent stem cells to cardiomyocytes, the most general method is to expose stem cells to various growth factors related to cardiogenesis. However, a novel method has been reported to induce cardiac differentiation of human ES cells without supplemental growth factors by culturing embryoid body of human ES cells in hybrid gels composed of cardiac extracellular matrix (ECM) and type I collagen. On the other hand, mechanical properties of scaffold is one of the critical cue for differentiation of stem cells. However, it has not been thoroughly investigated the mechanical properties of the scaffold made from cardiac ECM in view of this and other reports about the differentiation of stem cells into cardiomyocytes using cardiac ECM scaffold. In this study, we fabricated bio-hydrogels composed of goat ventricular extracellular matrix, and investigated the mechanical properties by means of uniaxial compression test. It showed that the ECM gels possess viscoelastic property. The elastic modulus K1 in modified non-linear Kelvin model is 9.5 Pa for these gels and K2 is 814.7 Pa. Moreover, we were able to improve the elastic moduli K1 and K2 up to 139.7 Pa and 2023.9 Pa, respectively, by chemical treatment using EDAC.

Black soybean extract reduces fatty acid contents in subcutaneous, but not in visceral adipose triglyceride in high-fat fed rats

Abstract It is known that black soybean (BS) extract, rich in polyphenols, has beneficial effects against obesity, inflammation and insulin resistance. However, detailed effects of BS on lipid metabolism have not been documented well. In the present study, we compared fatty acid composition in visceral and subcutaneous adipose tissues of high-fat fed (HFF) rats and BS administered HFF rats. Black soybean administration for 6 weeks influenced neither body nor adipose tissue weights, blood glucose, plasma insulin levels, or insulin sensitivity. However, BS reduced several saturated (C14:0 and C16:0), monounsaturated (C14:1n-5 and C18:1n-9) and n-6 polyunsaturated (C18:2n-6, C20:3n-6, C20:4n-6 and C22:4n-6) fatty acid contents in subcutaneous fat without any change in n-3 polyunsaturated fatty acid contents. No such effect was observed in fatty acid composition in visceral fat. Long-chain fatty acids are involved in regulation of inflammation. Therefore, those reduced fatty acids may be linked to the effects on suppressing inflammation.

Analysis of the contraction of fibroblast-collagen gels and the traction force of individual cells by a novel elementary structural model

Based on the experimental data of the contraction ratio of fibroblast-collagen gels with different initial collagen concentrations and cell numbers, we analyzed the traction force exerted by individual cells through a novel elementary structural model. We postulate that the mechanical mechanism of the gel contraction is mainly because that populated cells apply traction force to some of the surrounding collagen fibrils with such proper length potential to be pulled straight so as to be able to sustain the traction force; this traction induce the cells moving closely to each other and consequently compact the fibrillar network; the bending force of the fibrils in turn resists the movement. By employing fiber packing theory for random fibrillar networks and network alteration theory, the bending force of collagen fibrils was deduced. The traction force exerted by individual fibroblasts in the gels was balanced by the bending force and the resistance from interstitial fluid since inertial force can be neglected. The maximum traction force per cell under free floating condition is in the range of 0.27-9.02 nN depending on the initial collagen concentration and populated cell number. The most important outcome of this study is that the traction force of individual cells dynamically varies under different gel conditions, whereas the adhesion force between cell and individual fibrils is relatively converging and stable.

Influence of valve size on the hydrodynamic performance of the ATS valve

Cineradiography has revealed the presence of the “non-fully-open” phenomenon in patients with the ATS valve. Preliminary in vitro investigations have identified two contributing factors: the expanding space at the outlet of the valve, and the local flow in the pivot area. This further study was performed with the aim of elucidating these factors with respect to different sizes of the ATS valve. Three bileafet valves, ATS, CarboMedics (CM), and St. Jude Medical (SJM), with tissue annulus diameters of 25 and 29 mm, were studied. The hydrodynamic performance of the valves was tested at the mitral position of our own pulse duplicator. The opening angle was measured using a high-speed video camera. All the CM and SJM valves were able to open fully in these tests, whereas the 25-mm and 29-mm ATS valves opened to 75° and 82°, respectively, despite their design maximum of 85°. The ATS exhibited the smallest pressure drop of the 29-mm valves, and the SJM the smallest of the 25-mm valves. The incomplete opening of the ATS valve might be explained by the ability of its leaflets to align themselves with the divergent outlet flow, due to its unique open-pivot design. Such a feature would also exhibit a low pressure drop, as seen in the 29-mm valve. The smaller opening angle in the 25-mm valve, however, could be caused by the additional pivot-flow, which might cause greater deviation of the leaflets in the smaller valve, resulting in a higher relative pressure drop.

Contribution of voltage-dependent ion channels to subthreshold resonance

Subthreshold resonance has been observed in many excitatory/inhibitory neurons in the brain and it is suggested that such resonance phenomena play an important role in behavioral or perceptual functions in animals. Various voltage-dependent channels are thought to be involved in the generation of these resonance oscillations. For a compartmental neuron model with Ca2+-dependent K+ channel and low-threshold Ca2+ channel, conductance-based channel dynamics are linearized around equilibrium states and a neuron model can be treated as an equivalent RLC electric circuit, which indicates that the subthreshold resonance may be attributable to inductive properties of voltage-dependent channels. By computer simulation, we examine how parameters of these voltage-dependent channels, such as an equilibrium potential and the amplitude, effect to generate a subthreshold resonance.

Stress relaxation and stress-strain characteristics of porcine amniotic membrane

BACKGROUND Recently, amniotic membrane (AM) as scaffold is accumulating much more attention in tissue engineering. It is well-known that the mechanical properties of the scaffold inevitably affect the biological process of the incorporated cells. OBJECTIVE This study investigates the stress relaxation and stress-strain characteristics of AM, which have not been sufficiently elucidated before. METHODS Porcine AM samples were prepared at four different AM regions and at three different directions. Ramp-and-hold and stretch-to-rupture tests were conducted on a uniaxial tensile apparatus. A nonlinear viscoelastic model with two relaxation coefficients is proposed to fit the ramp-and-hold data. Rupture strain, rupture stress, and elastic modulus of the linear portion of the stress-strain curve are used to characterize the strength properties of the AM. RESULTS Sample direction has no significant effect on the mechanical properties of the AM. Samples at the ventral region has the maximum rupture strength and elastic modulus, respectively, 2.29±0.99MPa and 6.26±2.69MPa. The average of the relaxation coefficient for the fast and slow relaxation phases are 12.8±4.4s and 37.0±7.7s, respectively. CONCLUSIONS AM is a mechanically isotropic and heterogeneous material. The nonlinear viscoelastic model is suitable to model the AM viscoelasticity and potential for other biological tissues.