7,843 research outputs found
Synthesis of bio-based thermoplastic polyurethane elastomers containing isosorbide and polycarbonate diol and their biocompatible properties.
A new family of highly elastic polyurethanes (PUs) partially based on renewable isosorbide were prepared by reacting hexamethylene diisocyanate with a various ratios of isosorbide and polycarbonate diol 2000 (PCD) via a one-step bulk condensation polymerization without catalyst. The influence of the isorsorbide/PCD ratio on the properties of the PU was evaluated. The successful synthesis of the PUs was confirmed by Fourier transform-infrared spectroscopy and (1)H nuclear magnetic resonance. The resulting PUs showed high number-average molecular weights ranging from 56,320 to 126,000 g mol(-1) and tunable Tg values from -34 to -38℃. The thermal properties were determined by differential scanning calorimetry and thermogravimetric analysis. The PU films were flexible with breaking strains from 955% to 1795% at from 13.5 to 54.2 MPa tensile stress. All the PUs had 0.9-2.8% weight lost over 4 weeks and continual slow weight loss of 1.1-3.6% was observed within 8 weeks. Although the cells showed a slight lower rate of proliferation than that of the tissue culture polystyrene as a control, the PU films were considered to be cytocompatible and nontoxic. These thermoplastic PUs were soft, flexible and biocompatible polymers, which open up a range of opportunities for soft tissue augmentation and regeneration
Bioresponsive matrices in drug delivery
For years, the field of drug delivery has focused on (1) controlling the release of a therapeutic and (2) targeting the therapeutic to a specific cell type. These research endeavors have concentrated mainly on the development of new degradable polymers and molecule-labeled drug delivery vehicles. Recent interest in biomaterials that respond to their environment have opened new methods to trigger the release of drugs and localize the therapeutic within a particular site. These novel biomaterials, usually termed "smart" or "intelligent", are able to deliver a therapeutic agent based on either environmental cues or a remote stimulus. Stimuli-responsive materials could potentially elicit a therapeutically effective dose without adverse side effects. Polymers responding to different stimuli, such as pH, light, temperature, ultrasound, magnetism, or biomolecules have been investigated as potential drug delivery vehicles. This review describes the most recent advances in "smart" drug delivery systems that respond to one or multiple stimuli
Vertical current induced domain wall motion in MgO-based magnetic tunnel junction with low current densities
Shifting electrically a magnetic domain wall (DW) by the spin transfer
mechanism is one of the future ways foreseen for the switching of spintronic
memories or registers. The classical geometries where the current is injected
in the plane of the magnetic layers suffer from a poor efficiency of the
intrinsic torques acting on the DWs. A way to circumvent this problem is to use
vertical current injection. In that case, theoretical calculations attribute
the microscopic origin of DW displacements to the out-of-plane (field-like)
spin transfer torque. Here we report experiments in which we controllably
displace a DW in the planar electrode of a magnetic tunnel junction by vertical
current injection. Our measurements confirm the major role of the out-of-plane
spin torque for DW motion, and allow to quantify this term precisely. The
involved current densities are about 100 times smaller than the one commonly
observed with in-plane currents. Step by step resistance switching of the
magnetic tunnel junction opens a new way for the realization of spintronic
memristive devices
General Form of the Color Potential Produced by Color Charges of the Quark
Constant electric charge satisfies the continuity equation where is the current density of the electron.
However, the Yang-Mills color current density of the quark
satisfies the equation which is not a continuity
equation () which implies that a color charge
of the quark is not constant but it is time dependent where
are color indices. In this paper we derive general form of color
potential produced by color charges of the quark. We find that the general form
of the color potential produced by the color charges of the quark at rest is
given by \Phi^a(x) =A_0^a(t,{\bf x}) =\frac{q^b(t-\frac{r}{c})}{r}\[\frac{{\rm
exp}[g\int dr \frac{Q(t-\frac{r}{c})}{r}] -1}{g \int dr
\frac{Q(t-\frac{r}{c})}{r}}\]_{ab} where integration is an indefinite
integration, ~~ , ~~, ~~ is the retarded time, ~~ is the speed
of light, ~~ is the position of the quark at the retarded
time and the repeated color indices (=1,2,...8) are summed. For constant
color charge we reproduce the Coulomb-like potential
which is consistent with the Maxwell theory where
constant electric charge produces the Coulomb potential
.Comment: Final version, two more sections added, 45 pages latex, accepted for
publication in JHE
Micro-Electro-Mechanical-Systems (MEMS) and Fluid Flows
The micromachining technology that emerged in the late 1980s can provide micron-sized sensors and actuators. These micro transducers are able to be integrated with signal conditioning and processing circuitry to form micro-electro-mechanical-systems (MEMS) that can perform real-time distributed control. This capability opens up a new territory for flow control research. On the other hand, surface effects dominate the fluid flowing through these miniature mechanical devices because of the large surface-to-volume ratio in micron-scale configurations. We need to reexamine the surface forces in the momentum equation. Owing to their smallness, gas flows experience large Knudsen numbers, and therefore boundary conditions need to be modified. Besides being an enabling technology, MEMS also provide many challenges for fundamental flow-science research
Pupillometry evaluation of melanopsin retinal ganglion cell function and sleep-wake activity in pre-symptomatic Alzheimer's disease
BACKGROUND:
Melanopsin-expressing retinal ganglion cells (mRGCs), intrinsically photosensitive RGCs, mediate the light-based pupil response and the light entrainment of the body's circadian rhythms through their connection to the pretectal nucleus and hypothalamus, respectively. Increased awareness of circadian rhythm dysfunction in neurological conditions including Alzheimer's disease (AD), has led to a wave of research focusing on the role of mRGCs in these diseases. Postmortem retinal analyses in AD patients demonstrated a significant loss of mRGCs, and in vivo measurements of mRGC function with chromatic pupillometry may be a potential biomarker for early diagnosis and progression of AD.
METHODS:
We performed a prospective case-control study in 20 cognitively healthy study participants: 10 individuals with pre-symptomatic AD pathology (pre-AD), identified by the presence of abnormal levels of amyloid \u3b242 and total Tau proteins in the cerebrospinal fluid, and 10 age-matched controls with normal CSF amyloid \u3b242 and Tau levels. To evaluate mRGC function, we used a standardized protocol of chromatic pupillometry on a Ganzfeld system using red (640 nm) and blue (450 nm) light stimuli and measured the pupillary light response (PLR). Non-invasive wrist actigraphy and standardized sleep questionnaires were also completed to evaluate rest-activity circadian rhythm.
RESULTS:
Our results did not demonstrate a significant difference of the PLR between pre-AD and controls but showed a variability of the PLR in the pre-AD group compared with controls on chromatic pupillometry. Wrist actigraphy showed variable sleep-wake patterns and irregular circadian rhythms in the pre-AD group compared with controls.
CONCLUSIONS:
The variability seen in measurements of mRGC function and sleep-wake cycle in the pre-AD group suggests that mRGC dysfunction occurs in the pre-symptomatic AD stages, preceding cognitive decline. Future longitudinal studies following progression of these participants can help in elucidating the relationship between mRGCs and circadian rhythm dysfunction in AD
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Bioresponsive matrices in drug delivery
For years, the field of drug delivery has focused on (1) controlling the release of a therapeutic and (2) targeting the therapeutic to a specific cell type. These research endeavors have concentrated mainly on the development of new degradable polymers and molecule-labeled drug delivery vehicles. Recent interest in biomaterials that respond to their environment have opened new methods to trigger the release of drugs and localize the therapeutic within a particular site. These novel biomaterials, usually termed "smart" or "intelligent", are able to deliver a therapeutic agent based on either environmental cues or a remote stimulus. Stimuli-responsive materials could potentially elicit a therapeutically effective dose without adverse side effects. Polymers responding to different stimuli, such as pH, light, temperature, ultrasound, magnetism, or biomolecules have been investigated as potential drug delivery vehicles. This review describes the most recent advances in "smart" drug delivery systems that respond to one or multiple stimuli.Engineering and Applied Science
Surface topography of hydroxyapatite affects ROS17/2.8 cells response
Hydroxyapatite (HA) has been used in orthopedic, dental, and maxillofacial surgery as a bone substitute.
The aim of this investigation was to study the effect of surface topography produced by the presence of microporosity on cell response, evaluating: cell attachment, cell morphology, cell proliferation, total protein content, and alkaline phosphatase (ALP) activity. HA discs with different percentages of microporosity (< 5%, 15%, and 30%) were confected by means of the combination of uniaxial powder pressing and different sintering conditions. ROS17/2.8 cells were cultured
on HA discs. For the evaluation of attachment, cells were cultured for two hours. Cell morphology was evaluated
after seven days. After seven and fourteen days, cell proliferation, total protein content, and ALP activity were measured. Data were compared by means of ANOVA and Duncan’s multiple range test, when appropriate. Cell attachment (p = 0.11) and total protein content (p = 0.31) were not affected by surface topography. Proliferation after 7 and 14 days (p = 0.0007 and p = 0.003, respectively), and ALP activity (p = 0.0007) were both significantly decreased by the most irregular surface (HA30). These results suggest that initial cell events were not affected by surface topography, while surfaces with more regular topography, as those present in HA with 15% or less of microporosity, favored intermediary and final events such as cell proliferation and ALP activity
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