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P Panizza

Publications and source records attributed to P Panizza.

At least 19 recordsLinked to original sources
PubMed2006

Selection of two-phase flow patterns at a simple junction in microfluidic devices.

We study the behavior of a confined stream made of two immiscible fluids when it reaches a T junction. Two flow patterns are witnessed: the stream is either directed in only one sidearm, yielding a preferential flow pathway for the dispersed phase, or splits between both. We show that the selection of these patterns is not triggered by the shape of the junction nor by capillary effects, but results from confinement. It can be anticipated in terms of the hydrodynamic properties of the flow. A simple model yielding universal behavior in terms of the relevant adimensional parameters of the problem is presented and discussed.

Journal Article↗
PubMed2006

Study and formation of vesicle systems with low polydispersity index by ultrasound method.

The formation of liposomes with low polydispersity index by application of ultrasounds was investigated considering methodology specifications such as sonication time and sonication power. Phosphatidylcholine (PC) liposomes were formed by the evaporation-hydration method. The vesicles were sonicated using several sonication conditions. The liposomes were then characterized by dynamic light scattering (DLS) and freeze-fracture electron microscopy (FFEM). Correlation functions from DLS were treated by cumulants method and GENDIST to obtain the mean radius and polydispersity index. These calculations allowed to fix an optimal sonication time (3000 s) and a useful interval of ultrasound power between 39 and 91 W. DLS and FFEM results confirmed that vesicle size, lamellarity and the polydispersity index decreased with the increase of sonication power. Thus, we propose a systematic method to form liposomes in which the physical characteristics of the vesicles may be controlled as a function of sonication time and power.

Chemical Phenomena↗
PubMed2006

Structural steady states and relaxation oscillations in a two-phase fluid under shear flow: experiments and phenomenological model.

By means of several rheophysics techniques, we report on an extensive study of the couplings between flow and microstructures in a two-phase fluid made of lamellar (L(alpha)) and sponge (L(3)) phases. Depending on the nature of the imposed dynamical parameter (stress or shear rate) and on the experimental conditions (brine salinity or temperature), we observe several different structural steady states consisting of either multilamellar droplets (with or without a long range order) or elongated (L(3)) phase domains. Two different astonishing phenomena, shear-induced phase inversion and relaxation oscillations, are observed. We show that (i) phase inversion is related to a shear-induced topological change between monodisperse multilamellar droplets and elongated structures and (ii) droplet size relaxation oscillations result from a shear-induced change of the surface tension between both coexisting (L(alpha)) and (L(3)) phases. To explain these relaxation oscillations, we present a phenomenological model and compare its numerical predictions to our experimental results.

Journal Article↗
PubMed2005

Smart control of monodisperse Stöber silica particles: effect of reactant addition rate on growth process.

Control over the synthesis of monodisperse silica particles up to mesoscopic scale is generally made difficult due to intrinsic limitation to submicrometric dimensions and secondary nucleation in seeded experiments. To investigate this issue and overcome these difficulties, we have implemented single step processing by quantifying the effects of the progressive addition of a diluted tetraethyl orthosilicate solution in ethanol on the size and monodispersity of silica particles. Contrary to particles grown in seeded polymerization, monodisperse particles with size up to 2 microm were synthesized. Moreover, the particles exhibit a final diameter (d(f)), which varies with V(-1/3) over more than 2 orders of magnitude in rate of addition (V). On the basis of a kinetic study in the presence of addition showing that particle growth is limited by the diffusion of monomer species, we developed a diffusion-limited growth model to theoretically explain the observed d(f)(V) behavior and quantitatively retrieve the measured amplitude and exponent. Using a single parameter procedure, we can therefore predict and generate in the room temperature range, monodisperse particles of a targeted size by simply adjusting the rate of addition.

Journal Article↗
PubMed2004

Can a droplet break up under flow without elongating? Fragmentation of smectic monodisperse droplets.

We study the fragmentation under shear flow of smectic monodisperse droplets at high volume fraction. Using small angle light scattering and optical microscopy, we reveal the existence of a break-up mechanism for which the droplets burst into daughter droplets of the same size. Surprisingly, this fragmentation process, which is strain controlled and occurs homogeneously in the cell, does not require any transient elongation of the droplets. Systematic experiments as a function of the initial droplet size and the applied shear rate show that the rupture is triggered by an instability of the inner droplet structure.

Journal Article↗
PubMed2004

Shear-induced formation of vesicles in membrane phases: kinetics and size selection mechanisms, elasticity versus surface tension.

Multilamellar vesicles can be formed upon shearing lamellar phases (L(alpha)) and phase-separated lamellar-sponge (L(alpha)/L(3)) mixtures. In the first case, the vesicle volume fraction is always 100% and the vesicle size is monitored by elasticity ("onion textures"). In the second system the vesicle volume fraction can be tuned from 0 to 100% and the mean size results from a balance between capillary and viscous forces ("Taylor droplets"). However, despite these differences, in both systems we show that the formation of vesicles is a strain-controlled process monitored by a universal primary buckling instability of the lamellae.

Dioctyl Sulfosuccinic Acid↗
PubMed2003

Formation and properties of mini-emulsions formed by microemulsions dilution.

Mini-emulsions have been formed in quaternary systems water/hexanol/sodium dodecyl sulfate/decane by dilution of a microemulsion with an excess of water. We have investigated systematically the effect of composition variables in the droplet size and Ostwald Ripening rate. This droplet size has been investigated by using dynamic light scattering of samples submitted to further dilution in water. According to the dynamic light scattering results, the initial droplet size depends on the initial microemulsion water content, the larger the initial water concentration, the smaller the initial droplet size. This is probably related to the structure of the initial phase. The rate of Ostwald Ripening depends on the final surfactant concentration as expected for differences in interfacial tension. At high surfactant and dispersed phase contents, instability due to flocculation has been observed. Other experiments in which a fifth component (a more hydrophobic oil) was added to slow down Ostwald Ripening showed an initial droplet size increasing comparable to the systems without additive but after a relatively long time of approximately 2 h, a decrease was observed.

Journal Article↗
PubMed2002

Instability of a lamellar phase under shear flow: formation of multilamellar vesicles.

The formation of closed-compact multilamellar vesicles (referred to in the literature as the "onion texture") obtained upon shearing lamellar phases is studied using small-angle light scattering and cross-polarized microscopy. By varying the shear rate gamma;, the gap cell D, and the smectic distance d, we show that: (i) the formation of this structure occurs homogeneously in the cell at a well-defined wave vector q(i), via a strain-controlled process, and (ii) the value of q(i) varies as (dgamma;/D)(1/3). These results strongly suggest that formation of multilamellar vesicles may be monitored by an undulation (buckling) instability of the membranes, as expected from theory.

Alkanes↗
PubMed2002

The Italian multi-centre project on evaluation of MRI and other imaging modalities in early detection of breast cancer in subjects at high genetic risk.

This report presents the preliminary results of the first phase (21 months) of a multi-centre, non-randomised, prospective study, aimed at evaluating the effectiveness of contrast-enhanced magnetic resonance imaging (MRI), X-ray mammography (XM) and ultrasound (US) in early diagnosis of breast cancer (BC) in subjects at high genetic risk. This Italian national trial (coordinated by the Istituto Superiore di Sanità, Rome) so far recruited 105 women (mean age 46.0 years; median age 51.0; age range 25-77 years), who were either proven BRCA1 or BRCA2 mutation carriers or had a 1 in 2 probability of being carriers (40/105 with a previous personal history of BC). Eight cases of breast carcinomas were detected in the trial (mean age 55.3 years, median age 52.5; age range 35-70 years; five with previous personal history of BC). All trial-detected BC cases (8/8) were identified by MRI, while XM and US correctly classified only one. MRI had one false positive case, XM and US none. Seven "MRI-only" detected cancers (4 invasive, 3 in situ) occurred in both pre- (n = 2) and post-menopausal (n = 5) women. With respect to the current XM screening programmes addressed to women in the age range 50-69 years, the global incidence of BC in the trial (7.6%) was over ten-fold higher. The cost per "MRI-only" detected cancer in this particular category of subjects at high genetic risk was substantially lower than that of an XM-detected cancer in the general women population. These preliminary results confirmed that MRI is a very useful tool to screen subjects at high genetic risk for breast carcinoma, not only in pre-, but also in post-menopausal age, with a low probability of false positive cases.

Adult↗
PubMed2002

Usefulness of breast MRI in a patient with genetic risk.

We describe an interesting case-report represented by a patient carrying BRCA1 mutation, recruited for the study "Multicenter evaluation of Magnetic Resonance Imaging (MRI) in early diagnosis and prevention of breast cancer in high risk population", diagnosed with breast cancer on the basis of MRI findings but not with conventional mammography and ultrasound (US). She was already affected at 53 years of age by a multifocal Ductal Infiltrating Carcinoma (DIC) in the left breast; then, she had an axillary and sovraclavear nodal recurrence of the disease, three years after the initial diagnosis. Since other relatives were affected by breast cancer (mother, sister and niece) and two arose at early age (< 40 years), BRCA1 mutational analysis was offered to the patient, identifying a nonsense mutation on the exon 13. Furthermore, this patient was recruited to study contralateral breast and at the second round, two little foci, suspicious of malignancy, were identified only with MRI, but not with mammography and ultrasonography. The final diagnosis was multifocal Ductal Carcinoma in situ (DCIS); the major focus measured 3 mm. In our patient MRI has shown a major sensitivity with respect to conventional radiology and US and has provided a very early diagnosis in this woman at genetic risk.

Biopsy, Needle↗
PubMed2001

Conductivity of an inverse lyotropic lamellar phase under shear flow.

We report conductivity measurements on solutions of closed compact monodisperse multilamellar vesicles (the so-called "onion texture") formed by shearing an inverse lyotropic lamellar L(alpha) phase. The conductivity measured in different directions as a function of the applied shear rate reveals a small anisotropy of the onion structure due to the existence of free oriented membranes. The results are analyzed in terms of a simple model that allows one to deduce the conductivity tensor of the L(alpha) phase itself and the proportion of free oriented membranes. The variation of these two parameters is measured along a dilution line and discussed. The high value of the conductivity perpendicular to the layers with respect to that of solvent suggests the existence of a mechanism of ionic transport through the insulating solvent.

Journal Article↗
PubMed2001

Ribbon phase in a phase-separated lyotropic lamellar-sponge mixture under shear flow.

We report the effect of shear flow on a phase-separated system composed of lyotropic lamellar (L(alpha)) and sponge (L3) phases in a mixture of brine, surfactant, and cosurfactant. Optical microscopy, small-angle light, and x-ray scattering measurements are consistent with the existence of a steady state made of multilamellar ribbon-like structures aligned in the flow direction. At high shear rates, these ribbon-like structures become unstable and break up into monodisperse droplets resulting in a shear-thickening transition.

Biophysical Phenomena↗
PubMed2000

Shear-induced structural transitions in newtonian non-newtonian two-phase flow

We show the existence under shear flow of steady states in a two-phase region of a brine-surfactant system in which lyotropic dilute lamellar (non-Newtonian) and sponge (Newtonian) phases are coexisting. At high shear rates and low sponge phase-volume fractions, we report on the existence of a dynamic transition corresponding to the formation of a colloidal crystal of multilamellar vesicles (or "onions") immersed in the sponge matrix. As the sponge phase-volume fraction increases, this transition exhibits a hysteresis loop leading to a structural bistability of the two-phase flow. Contrary to single phase lamellar systems where it is always 100%, the onion volume fraction can be monitored continuously from 0 to 100 %.

Journal Article↗
PubMed2000

[The current state of the diagnostics of breast diseases in Lombardy].

PURPOSE: The SIRM study group for senology in Lombardy set the following goals: to quantify the number of radiologist working in public radiology centers and in private credited hospitals in Lombardy; to quantify the number of radiologists working in diagnostic senology and the mean time they devote to this field; to survey the diagnostic equipment used for senology purposes and check its adequacy. MATERIAL AND METHODS: We considered 58 centers of senology diagnostic imaging in the radiology departments of general hospitals in 8 Lombardy provinces. First we evaluated the screening programs for early breast cancer detection carried out with clinical mammography. All data were evaluated with reference to female residents aged 40 to 69, to the average adherence rates reported in the literature, to the protocols adopted in different centers relative to the examination frequency. Mammography was always associated with a physical examination and then the patient was submitted to radiological investigations to make the final diagnosis. The form we used for data report is summarized in Table I. RESULTS: In the centers for diagnostic senology we surveyed in 1998, in all 182,724 mammograms, 58,686 breast US examinations and 7,097 needle biopsies for cytology or microhistology were performed; 35.5% of the female population which should have been screened actually underwent the examination and 32.6% of them was also submitted to breast US, while 3.88% underwent FNAB. Sixty-three mammographic units and 62 US units were operated by 152 radiologists. An average 2,900 radiographic investigations per mammographic unit were performed yearly. Each radiologist reported an average 1,202 mammograms a year. Refer to the tables for detailed data reporting by province. Thirty-six per cent of radiologists presently reads more than 1,500 breast examinations a year. The radiologists working in diagnostic imaging in senology devote an average 20% of their working time to this field. As for the technical adequacy of mammographic and US equipment relative to some reference levels reported in detail in the paper, only 42% of the former and 48% of the latter were up to standards. DISCUSSION AND CONCLUSIONS: Despite the massive work done in the field of senology, the estimated needs of the female population have not been met yet, given the increased demand for senologic examinations and women's growing awareness of the need of early breast cancer diagnosis. The answer to this problem lies in a political health care policy that should promote the current clinical programs increasing both instrumental and human resources. Alternatively screening programs could be planned on a regional basis, with the pro of reaching a larger female population and that of a more homogeneous methodological approach. Our data indicate that breast cancer detection is best achieved with clinical and screening tools: the former can be easily promoted in a short time and could thus make our first goal, while the latter, which is more complex, could be implemented later. Thus, a growing clinical activity could make a very good basis for high quality breast screening programs. Finally, it is necessary to guarantee high quality standards for equipment, methods and training of medical and nonmedical staff.

Adult↗
PubMed1999

[Therapeutic and prophylactic role of mesalazine (5-ASA) in symptomatic diverticular disease of the large intestine. 4 year follow-up results].

In order to evaluate the efficacy and tolerability of mesalazine (5-ASA) in the prophylaxis of symptomatic relapses, of major complications and of microhemorrhagic phenomena in diverticular disease of the large intestine (MDC), prospective clinical study was conducted on patients with light-moderate symptomatic MDC under treatment with sulbactam-ampicillin 1.5 g/12 h i.m. and rifaximine 400 mg/12 h per os for 7 days. Follow-up period of 5 years with seriated checkups and laboratory and instrumentation controls. End points are represented by the relapse on inflammation and/or by the occurrence of major complications. On enrollment, 166 patients were randomized to receive mesalazine (Pentacol tablets--SOFAR S.p.A.) 400 mg b.i.d. per os for 8 weeks (81 patients; group M) or no supplementary treatment (85 patients; group C). After 4 years of follow-up, 44 patients dropped out of the study (9 because of major complications, 3 for massive hemorrhage, and 32 drop outs). Symptomatic relapses occurred in 51 patients (12 M; 39 C), while minor diverticular hemorrhages occurred in 43 patients (12 M; 31 C), with an estimated probability of remaining free respectively from symptomatic relapse (p=0.00005) and from microhemorrhagic phenomena (p=0.001) decisively in favor of the group treated with mesalazine. The duration of abdominal pain due to diverticolitis was also shorter in patients of group M (p=0.0002), while the incidence of major complications and side effects was comparable in the two groups. In conclusion, supplementary treatment with mesalazine in patients affected with MDC--at a follow-up limited to 48 months--proved to be well tolerated and effective in reducing the frequency of symptomatic relapses and microhemorrhagic phenomena and in reducing the duration of abdominal pain.

English Abstract↗
PubMed1998

MR state of the art.

Magnetic resonance imaging is undergoing continual and progressive evolution. To make a high quality examination, some requirements are mandatory, such as high spatial and contrast resolution to identify lesions and high temporal resolution to characterize them. We review the most important new magnetic resonance technologies, both those which are already available and used in clinical practice and those which are still to be developed. We analyze such technologic and methodolgic features as magnetic field strength, gradients, surface coils, echoplanar imaging, fat suppression techniques and magnetization transfer, contrast agents, automatic injectors, image postprocessing, computer assisted diagnosis, magnetic resonance-guided biopsy and spectroscopy. All these factors are in continuous evolution and new technologies anticipate, in the near future, faster examinations with very high spatial and contrast resolution, with magnetic resonance-guided cytologic and histologic aspiration biopsies, as well as spectroscopic studies of previously identified lesions. To perform a correct, state-of-the-art magnetic resonance examination of the breast, we need high strength gradients with high slew rate and bilateral coils. Finally, we discuss new technologies and methods which will increase the accuracy of magnetic resonance studies of the breast, improving image quality and decreasing execution time. Thus, magnetic resonance spectroscopy, allowing in vivo biochemical tissue analysis, seems to have high potentials; even though they are still difficult to define, the technique is sure to have major diagnostic impact also in monitoring the results to different treatments.

Biopsy↗