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81.
Development and validation of a bioreactor for physical stimulation of engineered cartilage 总被引:1,自引:0,他引:1
A bioreactor has been developed to apply different regimes of physical stimulation to tissue specimens under highly controlled conditions. The computer-controlled device exposes specimens to compressive deformation at various strains and frequencies, measures the load applied to each sample and allows simultaneous medium stirring at different velocities. Validation tests confirmed the accuracy of the system in (i) its displacement (errors averaged 0.072+/-0.051 microm), and in (ii) setting the contact with the samples utilizing micrometer screws coupled to plungers (errors averaged 1.74+/-0.36% for samples of 1.60-3.18 mm thickness), thus ensuring accurate compressive deformation. The developed bioreactor, which represents an advance in the technology for physical stimulation of tissue specimens, is currently used to apply compressive deformation and hydrodynamic forces to human chondrocytes cultured in biodegradable polymer scaffolds, with the goals of (i) engineering functional grafts for the repair of cartilage defects (ii). 相似文献
82.
Oscillating perfusion of cell suspensions through three-dimensional scaffolds enhances cell seeding efficiency and uniformity 总被引:13,自引:0,他引:13
We developed a bioreactor for automated cell seeding of three-dimensional scaffolds by continuous perfusion of a cell suspension through the scaffold pores in oscillating directions. Using quantitative biochemical and image analysis techniques, we then evaluated the efficiency and uniformity of perfusion seeding of Polyactive foams as compared to conventional static and spinner flask methods. Finally, we assessed the efficacy of the perfusion seeding technique for different scaffolds and cell types. Perfusion seeding of chondrocytes into Polyactive foams resulted in "viable cell seeding efficiencies," defined as the percentages of initially loaded cells that were seeded and remained viable, that were significantly higher (75 +/- 6%) than those by static (57% +/- 5%) and spinner flask seeding (55% +/- 8%). In addition, as compared to static and spinner flask methods, cells seeded by perfusion were respectively 2.6-fold and 3.8-fold more uniformly distributed and formed more homogeneously sized cell clusters. Chondrocytes seeded by perfusion into Hyaff-11 nonwoven meshes were 26% and 63%, respectively, more uniformly distributed than following static and spinner flask seeding. Bone marrow stromal cells seeded by perfusion into ChronOS porous ceramics were homogeneously distributed throughout the scaffold volume, while following the static method, cells were found only near the top surface of the ceramic. In summary, we demonstrated that our cell seeding perfusion bioreactor generated constructs with remarkably uniform cell distributions at high efficiencies, and was effective for a variety of scaffolds and different mesenchymal cell types. 相似文献
83.
Skirnisdottir S Hreggvidsson GO Holst O Kristjansson JK 《Extremophiles : life under extreme conditions》2001,5(1):45-51
Thermophilic, faculatatively mixotrophic sulfur-oxidizing bacteria were isolated from a sulfide-rich, neutral hot spring in Iceland. The strain, IT-7254, used thiosulfate and elemental sulfur as electron donors, oxygen and nitrate as electron acceptors, and acetate and other organic compounds as carbon sources. After a few days of growth in the presence of thiosulfate, this strain formed sulfur globules. Comparison of intracellular enzymes and heme proteins of heterotrophically and mixotrophically grown cells showed some differences. The new isolate belonged to Thermus scotoductus because the small subunit (SSU) rRNA gene sequence analysis showed 98.6% sequence similarity and 84% DNA:DNA reassociation to Thermus scotoductus NMX2 A. 1. It is also close to Thermus antranikianii HN3-7, with 98.3% and 79% SSU rRNA sequence similarity and DNA:DNA reassociation, respectively. It was also found that both Thermus NMX2 A.1 and T. antranikianii HN3-7 were able to oxidize thiosulfate but that the T. scotoductus type strain SE-1 was not. This is the first report of Thermus strains that are capable of mixotrophic growth with sulfur oxidation. 相似文献
84.
Real-time quantitative RT-PCR analysis of human bone marrow stromal cells during osteogenic differentiation in vitro 总被引:18,自引:0,他引:18
Frank O Heim M Jakob M Barbero A Schäfer D Bendik I Dick W Heberer M Martin I 《Journal of cellular biochemistry》2002,85(4):737-746
We developed and used real-time RT-PCR assays to investigate how the expression of typical osteoblast-related genes by human bone marrow stromal cells (BMSC) is regulated by (i) the culture time in medium inducing osteogenic differentiation and (ii) the previous expansion in medium enhancing cell osteogenic commitment. BMSC from six healthy donors were expanded in medium without (CTR) or with fibroblast growth factor-2 and dexamethasone (FGF/Dex; these factors are known to increase BMSC osteogenic commitment) and further cultivated for up to 20 days with ascorbic acid, beta-glycerophosphate and dexamethasone (these factors are typically used to induce BMSC osteogenic differentiation). Despite a high variability in the gene expression levels among different individuals, we identified the following statistically significant patterns. The mRNA levels of bone morphogenetic protein-2 (BMP-2), bone sialo protein-II (BSP), osteopontin (OP) and to a lower extent cbfa-1 increased with culture time in osteogenic medium (OM), both in CTR- and FGF/Dex-expanded BMSC, unlike levels of alkaline phosphatase, collagen type I, osteocalcin, and osteonectin. After 20 days culture in OM, BMP-2, BSP, and OP were more expressed in FGF/Dex than in CTR-expanded BMSC (mRNA levels were, respectively, 9.5-, 14.9-, and 5.8-fold higher), unlike all the other investigated genes. Analysis of single-colony-derived strains of BMSC further revealed that after 20 days culture in OM, only a subset of FGF/Dex-expanded clones expressed higher mRNA levels of BMP-2, BSP, and OP than CTR-expanded clones. In conclusion, we provide evidence that mRNA levels of BMP-2, BSP, and OP, quantified using real-time RT-PCR, can be used as markers to monitor the extent of BMSC osteogenic differentiation in vitro; using those markers, we further demonstrated that only a few subpopulations of BMSC display enhanced osteogenic differentiation following FGF/Dex expansion. 相似文献
85.
Bacterivorous protists are known to induce changes in bacterial community composition (BCC). We hypothesized that changes
in BCC could be related quantitatively to a measure of grazing: the ratio of bacterial mortality to growth rate. To test this
hypothesis, we analyzed time-course changes in BCC, protistan grazing rate, and bacterial production from 3 in situ studies conducted in a freshwater reservoir and three laboratory studies. In the field experiments, samples were manipulated
to yield different levels of protistan bacterivory and incubated in dialysis bags. Laboratory investigations were continuous
cultivation studies in which different bacterivorous protists were added to bacterial communities. BCC was assessed using
4–6 different rRNA-targeted oligonucleotide probes for community analysis. Change in BCC (Δ BCC) was estimated as the sum
of changes in the proportions of the two phylogenetic groups that showed the largest shifts. Analysis of a set of 22 estimates
of shifts in the ratio of grazing to production rate over periods of 48–72 h and Δ BCC showed that Δ BCC was positively and
tightly correlated (r
2 = 0.784) with shifts in the ratio of grazing mortality to cell production. While the nature of a shift in BCC is unpredictable,
the magnitude of the change can be related to changes in the balance between bacterial production and protistan grazing.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
86.
Canal construction destroys the barrier between major European invasion lineages of the zebra mussel 总被引:4,自引:0,他引:4
Müller JC Hidde D Seitz A 《Proceedings. Biological sciences / The Royal Society》2002,269(1496):1139-1142
Since the mid-1980s the zebra mussel, Dreissena polymorpha, Pallas 1771, has become the protagonist of a spectacular freshwater invasion in North America due to its large economic and biological impact. Several genetic studies on American populations have failed to detect any large-scale geographical patterns. In western Europe, where D. polymorpha has been a classical invader from the Pontocaspian since the early 19th century, the situation is strikingly different. Here, we show with genetic markers that two major western European invasion lineages with lowered genetic variability within and among populations can be discriminated. These two invasion lineages correspond with two separate navigable waterways to western Europe. We found a rapid and asymmetrical genetic interchange of the two invasion lines after the construction of the Main-Danube canal in 1992, which interconnected the two waterways across the main watershed. 相似文献
87.
Tougaard J 《Biological cybernetics》2002,87(2):79-90
Stochastic resonance is a phenomenon in which the performance of certain non-linear detectors can be enhanced by the addition
of appropriate levels of random noise. Signal detection theory offers a powerful tool for analysing this type of system, through
an ability to separate detection processes into reception and classification, with the former generally being linear and the
latter always non-linear. Through appropriate measures of signal detectability it is possible to decide whether a local improvement
in detection via stochastic resonance occurs due to the non-linear effects of the classification process. In this case, improvement
of detection through the addition of noise can never improve detection beyond that of a corresponding adaptive system. Signal
detection and stochastic resonance is investigated in several integrate-and-fire neuron models. It is demonstrated that the
stochastic resonance observed in spiking models is caused by non-linear properties of the spike-generation process itself.
The true detectability of the signal, as seen by the receiver part of the spiking neuron (the integrator part), decreases
monotonically with input noise level for all signal and noise intensities.
Received: 3 April 2001 / Accepted in revised form: 8 March 2002 相似文献
88.
Andreas Niemeitz Ralf Kreutzfeldt Manfred Schartl Jakob Parzefall Ingo Schlupp 《Acta ethologica》2002,5(1):45-49
The Tamesí molly, Poecilia latipunctata, has a very limited biogeographical range in northeast Mexico. This area is nested within the ranges of the Atlantic molly,
Poecilia mexicana, and the unisexual Amazon molly, Poecilia formosa. Based on morphology, especially fin shape, the Tamesí molly has been considered to be a "short-fin" molly. We describe the
courtship sequence of P. latipunctata. The courtship clearly places the species into the clade of "long-fin" mollies, a finding that corroborates earlier studies
based on nuclear DNA and mitochondrial DNA. All three species live together in certain habitats. This renders P. latipunctata a potential host species for the sperm-dependent, unisexual Amazon molly. Using behavioural tests, we demonstrate that P. latipunctata males actually copulate with Amazon mollies, despite a pronounced preference for conspecific females. In laboratory experiments
P. latipunctata males are capable of triggering embryogenesis in P. formosa females. Field observations support the hypothesis that P. latipunctata is a third host species for P. formosa, indicating that the Amazon molly effectively exploits all available host species for its gynogenetic mode of reproduction.
Electronic Publication 相似文献
89.
Using optical tweezers and single particle tracking, we have revealed the motion of a single protein, the lambda-receptor, in the outer membrane of living Escherichia coli bacteria. We genetically modified the lambda-receptor placing a biotin on an extracellular site of the receptor in vivo. The efficiency of this in vivo biotinylation is very low, thus enabling the attachment of a streptavidin-coated bead binding specifically to a single biotinylated lambda-receptor. The bead was used as a handle for the optical tweezers and as a marker for the single particle tracking routine. We propose a model that allows extraction of the motion of the protein from measurements of the mobility of the bead-molecule complex; these results are equally applicable to analyze bead-protein complexes in other membrane systems. Within a domain of radius approximately 25 nm, the receptor diffuses with a diffusion constant of (1.5 +/- 1.0) x 10(-9) cm(2)/s and sits in a harmonic potential as if it were tethered by an elastic spring of spring constant of ~1.0 x 10(-2) pN/nm to the bacterial membrane. The purpose of the protein motion might be to facilitate transport of maltodextrins through the outer bacterial membrane. 相似文献
90.
Transcriptome changes during intestinal cell differentiation 总被引:4,自引:0,他引:4