67 research outputs found
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Orienting lignocellulosic fibers by means of a magnetic field
Controlling the orientation and spatial distribution of
discontinuous fibers in composite materials enables product
properties to be tailored to anticipated use. Electric
fields are already (albeit rarely) used to affect alignment
in lignocellulosic (LC) fiber composites. The use of
magnetic fields has not, however, been suggested or
explored; this is apparently because LC fibers are
essentially non-magnetic. The approach may offer, however,
some considerable advantages, as long as ferromagnetism may
be imparted to the fibers.
In the present research several fiber modification
processes were considered and two, electroless nickel
plating and spray application of a coating containing nickel
in suspension, were investigated in more depth. The latter
was chosen to render highly engineered, elongated wood
particles responsive to magnetic fields. Individual treated
particles were suspended in viscous, newtonian silicone
fluids and their rotation under the influence of a
controlled magnetic field was video recorded.
The magnetic torque on the particle was, under the
above conditions, directly proportional to the fluid
viscosity, to the particle's angular velocity and to a
characteristic shape constant. The maximum of the specific
magnetic torque (magnetic torque divided by the shape
constant) was found to reflect the influence of field
strength and particle Ni-treatment on rotation. Results
were scaled to an arbitrarily chosen viscosity for
comparison.
The dependencies of the magnetic torque found in the
present research compare with those theoretically predicted
for ellipsoidal and cylindrical bodies. For field strengths
ranging from 0.07T to 0.15T (below magnetic saturation) the
magnetic torque increased almost linearly with increasing
field strength. Magnetic torque was also found to increase
nearly linearly with increasing bulk Ni-concentration (5g/kg
- 50g/kg).
Rotational motion was sometimes impeded at low field
strengths and this was attributed to a permanent magnetic
moment obtained by the particle. A coercive field strength
of 7600A/m supported this hypothesis. Judiciously switched
field polarity increased magnetic torque at small alignment
angles.
The present research indicates that orienting LC fibers
with magnetic fields is possible and promising. To study
dynamics of fiber motion in low viscosity fluids, such as
air, a different experimental method is necessary; however,
dependencies of the magnetic torque found in the present
study still hold true
Interaction of Proteins with a Planar Poly(acrylic acid) Brush: Analysis by Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D)
We describe the preparation of a poly(acrylic acid) (PAA) brush, polymerized by atom transfer radical polymerization (ATRP) of tert-butyl acrylate (tBA) and subsequent acid hydrolysis, on the flat gold surfaces of quartz-crystal microbalance (QCM) crystals. The PAA brushes were characterized by Fourier transform infrared (FT-IR) spectroscopy, ellipsometry and water contact angle analysis. The interaction of the PAA brushes with human serum albumin (HSA) was studied for a range of ionic strengths and pH conditions by quartz-crystal microbalance with dissipation monitoring (QCM-D). The quantitative analysis showed a strong adsorption of protein molecules onto the PAA brush. By increasing the ionic strength, we were able to release a fraction of the initially bound HSA molecules. This finding highlights the importance of counterions in the polyelectrolyte-mediated protein adsorption/desorption. A comparison with recent calorimetric studies related to the binding of HSA to polyelectrolytes allowed us to fully analyze the QCM data based on the results of the thermodynamic analysis of the binding process
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Large-Scale microRNA Expression Profiling Identifies Putative Retinal miRNA-mRNA Signaling Pathways Underlying Form-Deprivation Myopia in Mice
Development of myopia is associated with large-scale changes in ocular tissue gene expression. Although differential expression of coding genes underlying development of myopia has been a subject of intense investigation, the role of non-coding genes such as microRNAs in the development of myopia is largely unknown. In this study, we explored myopia-associated miRNA expression profiles in the retina and sclera of C57Bl/6J mice with experimentally induced myopia using microarray technology. We found a total of 53 differentially expressed miRNAs in the retina and no differences in miRNA expression in the sclera of C57BL/6J mice after 10 days of visual form deprivation, which induced -6.93 ± 2.44 D (p < 0.000001, n = 12) of myopia. We also identified their putative mRNA targets among mRNAs found to be differentially expressed in myopic retina and potential signaling pathways involved in the development of form-deprivation myopia using miRNA-mRNA interaction network analysis. Analysis of myopia-associated signaling pathways revealed that myopic response to visual form deprivation in the retina is regulated by a small number of highly integrated signaling pathways. Our findings highlighted that changes in microRNA expression are involved in the regulation of refractive eye development and predicted how they may be involved in the development of myopia by regulating retinal gene expression
Peptide-PEG Amphiphiles as Cytophobic Coatings for Mammalian and Bacterial Cells
SummaryAmphiphilic macromolecules containing a polystyrene-adherent peptide domain and a cell-repellent poly(ethylene glycol) domain were designed, synthesized, and evaluated as a cytophobic surface coating. Such cytophobic, or cell-repellent, coatings are of interest for varied medical and biotechnological applications. The composition of the polystyrene binding peptide domain was identified using an M13 phage display library. ELISA and atomic force spectroscopy were used to evaluate the binding affinity of the amphiphile peptide domain to polystyrene. When coated onto polystyrene, the amphiphile reduced cell adhesion of two distinct mammalian cell lines and pathogenic Staphylococcus aureus strains
Mechanical Properties and Gene Expression of Chondrocytes on Micropatterned Substrates Following Dedifferentiation in Monolayer
Chondrocytes in articular cartilage normally exhibit high expression of collagen II and aggrecan but rapidly dedifferentiate to a fibroblastic phenotype if passaged in culture. Previous studies have suggested that the loss of chondrocyte phenotype is associated with changes in the structure of the F-actin cytoskeleton, which also controls cell mechanical properties. In this study, we examined how dedifferentiation in monolayer influences the mechanical properties of chondrocytes isolated from different zones of articular cartilage. Atomic force microscopy was used to measure the mechanical properties of superficial and middle/deep zone chondrocytes as they underwent serial passaging and subsequent growth on fibronectin-coated, micropatterned self-assembled monolayers (MSAMs) that restored a rounded cell shape in 2D culture. Chondrocytes exhibited significant increases in elastic and viscoelastic moduli with dedifferentiation in culture. These changes were only partially ameliorated by the restoration of a rounded shape on micropatterned surfaces. Furthermore, intrinsic zonal differences in cell mechanical properties were rapidly lost with passage. These findings indicate that cell mechanical properties may provide additional measures of phenotypic expression of chondrocytes as they undergo dedifferentiation and possibly redifferentiation in culture
Altered Trabecular Bone Structure and Delayed Cartilage Degeneration in the Knees of Collagen VI Null Mice
Mutation or loss of collagen VI has been linked to a variety of musculoskeletal abnormalities, particularly muscular dystrophies, tissue ossification and/or fibrosis, and hip osteoarthritis. However, the role of collagen VI in bone and cartilage structure and function in the knee is unknown. In this study, we examined the role of collagen VI in the morphology and physical properties of bone and cartilage in the knee joint of Col6a1−/− mice by micro-computed tomography (microCT), histology, atomic force microscopy (AFM), and scanning microphotolysis (SCAMP). Col6a1−/− mice showed significant differences in trabecular bone structure, with lower bone volume, connectivity density, trabecular number, and trabecular thickness but higher structure model index and trabecular separation compared to Col6a1+/+ mice. Subchondral bone thickness and mineral content increased significantly with age in Col6a1+/+ mice, but not in Col6a1−/− mice. Col6a1−/− mice had lower cartilage degradation scores, but developed early, severe osteophytes compared to Col6a1+/+mice. In both groups, cartilage roughness increased with age, but neither the frictional coefficient nor compressive modulus of the cartilage changed with age or genotype, as measured by AFM. Cartilage diffusivity, measured via SCAMP, varied minimally with age or genotype. The absence of type VI collagen has profound effects on knee joint structure and morphometry, yet minimal influences on the physical properties of the cartilage. Together with previous studies showing accelerated hip osteoarthritis in Col6a1−/− mice, these findings suggest different roles for collagen VI at different sites in the body, consistent with clinical data
Orienting Lignocellulosic Fibers and Particles by Means of a Magnetic Field
Fiber and particle alignment in composite materials may be used to tailor material and object properties to specific performance requirements. The present research demonstrates that alignment of ferromagnetically modified slender wood particles in magnetic fields is feasible. Magnetic torque, which causes rotation, increases linearly with the amount of magnetic material on particle surfaces. Below magnetic saturation, magnetic torque increases with increasing strength of the applied field; closer to magnetic saturation, torque becomes less dependent on the applied field strength. Magnetic torque maxima occur at field-to-particle axis angles above 45°. Polarity switches of the applied magnetic field increase particle rotation rates and may counter permanent magnetization, which otherwise tends to impede full particle alignment
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