196,098 research outputs found
Investigation on the thermal gelation of Chitosan/β-Glycerophosphate solutions
No full textThis work deals with the effect of temperature on the thermal-gelation process of water solutions containing
chitosan β-glycerolphosphate disodium salt hydrate. In particular, the attention is focused on the role played by
temperature on the gel final properties, a very important aspect in the frame of drug delivery systems. The study
was performed by combining rheology and low field nuclear magnetic resonance, two approaches that revealed
to be highly synergic as they can detect different aspects of the developing polymeric network. This study
indicates that 30 °C represent a sort of threshold for both the gelation kinetics and the gel final properties.
Indeed, above this temperature, gelation kinetics was rapid and yielded to a strong gel. On the contrary, a slow
kinetics and a final weak gel occurred below 30 °C. Finally, rheology and low field NMR allowed, independently,
evaluating the time evolution of the network mesh size upon gelation
Current and future status of blood flow tracers
No full textMyocardial perfusion imaging is important for
the management of patients with suspected or known
coronary artery disease. Nuclear cardiology is the most
widely used noninvasive approach for the assessment of
myocardial perfusion. The available single-photon emission
CT (SPECT) flow agents are characterized by a rapid
myocardial extraction and by a cardiac uptake proportional
to blood flow. In addition, different positron emission
tomography (PET) tracers may be used for the absolute
quantitative measurement of myocardial blood flow and
coronary flow reserve. However, the available SPECT and
PET tracers for myocardial perfusion imaging have some limitations that must be considered to maximize their
clinical applications and there is still a well-recognized
need for the development of new perfusion tracers with
more ideal properties. This review illustrates the current
status and the future perspectives of blood flow tracers for
SPECT and PET myocardial perfusion imaging
Mechanistic Understanding of Degradation in Bioerodible Polyanhydrides: Consequences for Drug Delivery
No full textWater diffusion in glassy polymers and their silica hybrids: an analysis of state of water molecules and of the effect of tensile stress
No full textIn-situ, time-resolved FTIR spectroscopy along with gravimetric anal. were used to study water sorption and transport in several glassy polymeric matrixes, characterized by different levels of interaction with water, and on polymer-silica hybrids. The polymers include tetraglycidyl-4,4'-diaminodiphenylmethane epoxy, cured with either 4,4'-diaminodiphenylsulfone or hexahydrophthalic anhydride; polyimide of pyromellitic dianhydride and oxydianiline (PMDA-ODA); and the hybrids of silica (from TEOS and g-glycidyloxypropyltrimethoxysilane) and the polyimide. The time-resolved FTIR technique was coupled to a dynamical-mech. analyzer to gather information on the water sorption kinetics and thermodn. in a polymer sample submitted to stretching deformation and load. Results were modeled by coupling the mass balance and momentum balance, using a theor. approach developed for elastic matrixes and low sorbed amts. by Larche and Cahn
Mechanistic Understanding of Degradation in Bioerodible Polyanhydrides: Consequences for Drug Delivery
No full textSol-gel transition of aqueous chitosan-ßglycerophosphate solutions
No full textHydrogels represent reliable systems for the delivery of drugs, including those based on nucleic acids. Indeed, hydrogel nature, structure, and response to physiological or external stimuli strongly influence the delivery mechanisms of entrapped active molecules, making hydrogel very attractive for many pharmacological and biomedical applications. In this study, the attention was focused on a thermo-gelling hydrogel, composed of chitosan/β-glycero-phosphate, which can be injected in situ and induced to gelify at physiological pH and temperature. Particular care was devoted to study the effect of temperature on the gelation kinetics and on the gel final properties, two very important aspects in the light of clinical applications.
The rheological characterization (temperature and frequency sweep test) evidenced the important effect of temperature (15°C ≤ T ≤ 47°C), on both the gelation kinetics and the gel final properties. In particular, we found that similar slow gelation kinetics and weak gels occurred below 30°C while similar faster gelation kinetics and stronger gels took place for T ≥ 30°C. This result was confirmed by means of a Low Field NMR (LF-NMR) characterization. Interestingly, it was possible evaluating, by means of rheology and LF-NMR, the time evolution of the polymeric network mesh size upon gelation. Thus, the importance of rheology in a socially relevant field (drug delivery) is eviden
Automated segmentation and measurement of global white matter lesion volume in patients with multiple sclerosis.
No full textA fully automated magnetic resonance (MR) segmentation method for identification and volume measurement of demyelinated white matter has been developed. Spin-echo MR brain scans were performed in 38 patients with multiple sclerosis (MS) and in 46 healthy subjects. Segmentation of normal tissues and white matter lesions (WML) was obtained, based on their relaxation rates and proton density maps. For WML identification, additional criteria included three-dimensional (3D) lesion shape and surrounding tissue composition. Segmented images were generated, and normal brain tissues and WML volumes were obtained. Sensitivity, specificity, and reproducibility of the method were calculated, using the WML identified by two neuroradiologists as the gold standard. The average volume of 'abnormal' white matter in normal subjects (false positive) was 0.11 ml (range 0-0.59 ml). In MS patients the average WML volume was 31.0 ml (range 1.1-132.5 ml), with a sensitivity of 87.3%. In the reproducibility study, the mean SD of WML volumes was 2.9 ml. The procedure appears suitable for monitoring disease changes over time
Assessment of scanner performance and normalization of estimated relaxation rate values.
No full textMorphological imaging of thymic disorders
No full textThe thymus is a bilobed lymphoid organ the morphology of which varies considerably with age as a result of a process of fatty infiltration occurring after puberty. Although several diseases can arise in the thymic parenchyma, including germ cell and neuroendocrine tumours, primitive epithelial neoplasms (thymomas) are the most common neoplasms and account for almost 10% of mediastinal masses. Thymomas are usually benign but can be locally invasive. Up to 30% of patients with a thymoma have myasthenia gravis, which is more commonly associated with thymic hyperplasia. The latter results in a symmetric diffuse enlargement of the thymus. However, thymic hyperplasia can be histologically found in up to 50% of normal-sized thymuses on computed tomography (CT). CT is much more accurate in detecting thymomas than it is in detecting thymic hyperplasia, although CT findings may be unspecific. CT can be exhaustive in the case of an encapsulated thymoma (65% of all thymomas), which appear as a solid homogeneous mass with a slight contrast enhancement and a well-defined surrounding fat plane. These tumours rarely recur after surgery. CT can also accurately detect a spread through the capsule into the adjacent mediastinal fat, which characterizes invasive thymomas (35%). These, however, are best evaluated by magnetic resonance imaging (MRI). On T1-weighted MR scans the thymus is well delineated against the mediastinal fat, whereas marked inhomogeneity of the signal may appear on T2-weighted images as a result of areas of cystic degeneration in the tumour mass. The superior contrast resolution of MRI and the multiplanar images that can be produced with it are well suited for documenting the mediastinal spread of invasive thymomas. MRI depicts accurately pleural and/or pericardial implants as well as the involvement of great vessels, offering considerable aid in the planning of surgery
Implementation of stimulated Raman losses and stimulated Raman gain microscopy using three femtosecond laser sources
No full textStimulated Raman scattering microscopy allows vibrational contrast mechanism for imaging with high spectral and spatial resolution along with three-dimensional sectioning. In this paper, the implementation of a Stimulated Raman Scattering microscope (SRSM), obtained by the integration of a femtosecond SRS spectroscopy set-up with an optical microscope equipped with a scanning unit, is described. Femtosecond Stimulated Raman Scattering microscope is equipped with three femtosecond laser sources:a Ti:Sapphire (Ti:Sa), a synchronized optical parametric oscillator (SOPO) and a frequency converters for ultrafast lasers, i.e. a second harmonic generator optimized for the SOPO. The proposed implementation allows to cover all the regions of Raman spectra, taking advantage of two different laser combinations. The first, Ti:Sa and SHG laser combination can cover in SRL modality the fingerprint region (500 - 1700 cm(-1)) and the silent region. The second, Ti:Sa and OPO, can cover the C-H region or O-H region (2800 - 3200 cm(-1)) in SRG modality. In order to demonstrate its successful realization Stimulated Raman Gain (SRG) and Stimulated Raman Losses (SRL) images of polystyrene beads are reported and discussed
- …
