366 research outputs found
Effects of Orthogonal Rotating Electric Fields on Electrospinning Process
Electrospinning is a nanotechnology process whereby an external electric
field is used to accelerate and stretch a charged polymer jet, so as to produce
fibers with nanoscale diameters. In quest of a further reduction in the cross
section of electrified jets hence of a better control on the morphology of the
resulting electrospun fibers, we explore the effects of an external rotating
electric field orthogonal to the jet direction. Through extensive particle
simulations, it is shown that by a proper tuning of the electric field
amplitude and frequency, a reduction of up to a in the aforementioned
radius can be obtained, thereby opening new perspectives in the design of
future ultra-thin electrospun fibres. Applications can be envisaged in the
fields of nanophotonic components as well as for designing new and improved
filtration materials.Comment: 22 pages, 8 figure
3D printing of optical materials: an investigation of the microscopic properties
3D printing technologies are currently enabling the fabrication of objects
with complex architectures and tailored properties. In such framework, the
production of 3D optical structures, which are typically based on optical
transparent matrices, optionally doped with active molecular compounds and
nanoparticles, is still limited by the poor uniformity of the printed
structures. Both bulk inhomogeneities and surface roughness of the printed
structures can negatively affect the propagation of light in 3D printed optical
components. Here we investigate photopolymerization-based printing processes by
laser confocal microscopy. The experimental method we developed allows the
printing process to be investigated in-situ, with microscale spatial
resolution, and in real-time. The modelling of the photo-polymerization
kinetics allows the different polymerization regimes to be investigated and the
influence of process variables to be rationalized. In addition, the origin of
the factors limiting light propagation in printed materials are rationalized,
with the aim of envisaging effective experimental strategies to improve optical
properties of printed materials.Comment: 8 pages, 3 figure
Surface-enhanced Raman spectroscopy in 3D electrospun nanofiber mats coated with gold nanorods
Nanofibers functionalized by metal nanostructures and particles are exploited
as effective flexible substrates for SERS analysis. Their complex
three-dimensional structure may provide Raman signals enhanced by orders of
magnitude compared to untextured surfaces. Understanding the origin of such
improved performances is therefore very important for pushing nanofiber-based
analytical technologies to their upper limit. Here we report on polymer
nanofiber mats which can be exploited as substrates for enhancing the Raman
spectra of adsorbed probe molecules. The increased surface area and the
scattering of light in the nanofibrous system are individually analyzed as
mechanisms to enhance Raman scattering. The deposition of gold nanorods on the
fibers further amplifies Raman signals due to SERS. This study suggests that
Raman signals can be finely tuned in intensity and effectively enhanced in
nanofiber mats and arrays by properly tailoring the architecture, composition,
and light-scattering properties of the complex networks of filaments.Comment: 29 pages, 9 figures, 1 Tabl
Maneuvering the Migration and Differentiation of Stem Cells with Electrospun Nanofibers
Electrospun nanofibers have been extensively explored as a class of scaffolding materials for tissue regeneration, because of their unique capability to mimic some features and functions of the extracellular matrix, including the fibrous morphology and mechanical properties, and to a certain extent the chemical/biological cues. This work reviews recent progress in applying electrospun nanofibers to direct the migration of stem cells and control their differentiation into specific phenotypes. First, the physicochemical properties that make electrospun nanofibers well-suited as a supporting material to expand stem cells by controlling their migration and differentiation are introduced. Then various systems are analyzed in conjunction with mesenchymal, neuronal, and embryonic stem cells, as well as induced pluripotent stem cells. Finally, some perspectives on the challenges and future opportunities in combining electrospun nanofibers with stem cells are offered to address clinical issues
Anisotropic conjugated polymer chain conformation tailors the energy migration in nanofibers
Conjugated polymers are complex multi-chromophore systems, with emission
properties strongly dependent on the electronic energy transfer through active
sub-units. Although the packing of the conjugated chains in the solid state is
known to be a key factor to tailor the electronic energy transfer and the
resulting optical properties, most of the current solution-based processing
methods do not allow for effectively controlling the molecular order, thus
making the full unveiling of energy transfer mechanisms very complex. Here we
report on conjugated polymer fibers with tailored internal molecular order,
leading to a significant enhancement of the emission quantum yield. Steady
state and femtosecond time-resolved polarized spectroscopies evidence that
excitation is directed toward those chromophores oriented along the fiber axis,
on a typical timescale of picoseconds. These aligned and more extended
chromophores, resulting from the high stretching rate and electric field
applied during the fiber spinning process, lead to improved emission
properties. Conjugated polymer fibers are relevant to develop optoelectronic
plastic devices with enhanced and anisotropic properties.Comment: 43 pages, 15 figures, 1 table in Journal of the American Chemical
Society, (2016
Advances in Medical Applications of Additive Manufacturing
In the past few decades, additive manufacturing (AM) has been developed and applied as a cost-effective and versatile technique for the fabrication of geometrically complex objects in the medical industry. In this review, we discuss current advances of AM in medical applications for the generation of pharmaceuticals, medical implants, and medical devices. Oral and transdermal drugs can be fabricated by a variety of AM technologies. Different types of hard and soft clinical implants have also been realized by AM, with the goal of producing tissue-engineered constructs. In addition, medical devices used for diagnostics and treatment of various pathological conditions have been developed. The growing body of research on AM reveals its great potential in medical applications. The goal of this review is to highlight the usefulness and elucidate the current limitations of AM applications in the medical field
Non-local cooperative atomic motions that govern dissipation in amorphous tantala unveiled by dynamical mechanical spectroscopy
The mechanisms governing mechanical dissipation in amorphous tantala are studied at microscopic scale via Molecular Dynamics simulations, namely by mechanical spectroscopy in a wide range of temperature and frequency. We find that dissipation is associated with irreversible atomic rearrangements with a sharp cooperative character, involving tens to hundreds of atoms arranged in spatially extended clusters of polyhedra. Remarkably, at low temperature we observe an excess of plastically rearranging oxygen atoms which correlates with the experimental peak in the macroscopic mechanical losses. A detailed structural analysis reveals preferential connections of the irreversibly rearranging polyhedra, corresponding to edge and face sharing. These results might lead to microscopically informed design rules for reducing mechanical losses in relevant materials for structural, optical, and sensing applications
Control of photon transport properties in nanocomposite nanowires
Active nanowires and nanofibers can be realized by the electric-field induced
stretching of polymer solutions with sufficient molecular entanglements. The
resulting nanomaterials are attracting an increasing attention in view of their
application in a wide variety of fields, including optoelectronics, photonics,
energy harvesting, nanoelectronics, and microelectromechanical systems.
Realizing nanocomposite nanofibers is especially interesting in this respect.
In particular, methods suitable for embedding inorganic nanocrystals in
electrified jets and then in active fiber systems allow for controlling
light-scattering and refractive index properties in the realized fibrous
materials. We here report on the design, realization, and morphological and
spectroscopic characterization of new species of active, composite nanowires
and nanofibers for nanophotonics. We focus on the properties of
light-confinement and photon transport along the nanowire longitudinal axis,
and on how these depend on nanoparticle incorporation. Optical losses
mechanisms and their influence on device design and performances are also
presented and discussed.Comment: 7 pages, 3 figures, 29 references. Invited contribution. Copyright
(2016) Society of Photo Optical Instrumentation Engineers. One print or
electronic copy may be made for personal use only. Systematic reproduction
and distribution, duplication of any material in this paper for a fee or for
commercial purposes, or modification of the content of the paper are
prohibite
Polydimethylsiloxane-LiNbO3 surface acoustic wave micropump devices for fluid control into microchannels.
This paper presents prototypical microfluidic devices made by hybrid microchannels based on piezoelectric LiNbO3 and polydimethylsiloxane. This system enables withdrawing micropumping by acoustic radiation in microchannels. The withdrawing configuration, integrated on chip, is here quantitatively investigated for the first time, and found to be related to the formation and coalescence dynamics of droplets within the microchannel, primed by surface acoustic waves. The growth dynamics of droplets is governed by the water diffusion on LiNbO3, determining the advancement of the fluid front. Observed velocities are up to 2.6 mm s−1 for 30 dBm signals applied to the interdigital transducer, corresponding to tens of nl s−1, and the micropumping dynamics is described by a model taking into account an acoustic power exponentially decaying upon travelling along the microchannel. This straighforward and flexible micropumping approach is particularly promising for the withdrawing of liquids in lab-on-chip devices performing cycling transport of fluids and biochemical reactions
Threading Through Macrocycles Enhances the Performance of Carbon Nanotubes as Polymer Fillers
In this work we study the reinforcement of polymers by mechanically
interlocked derivatives of single-walled carbon nanotubes (SWNTs). We compare
the mechanical properties of fibers made of polymers and of composites with
pristine single-walled carbon nanotubes (SWNTs), mechanically interlocked
derivatives of SWNTs (MINTs) and the corresponding supramolecular models.
Improvements of both Young's modulus and tensile strength of up to 200 % were
observed for the polystyrene-MINTs samples with an optimized loading of just
0.01 wt.%, while the supramolecular models with identical chemical composition
and loading showed negligible or even detrimental influence. This behavior is
found for three different types of SWNTs and two types of macrocycles.
Molecular dynamics simulations show that the polymer adopts an elongated
conformation parallel to the SWNT when interacting with MINT fillers,
irrespective of the macrocycle chemical nature, whereas a more globular
structure is taken upon facing with either pristine SWNTs or supramolecular
models. The MINT composite architecture thus leads to a more efficient
exploitation of the axial properties of the SWNTs and of the polymer chain at
the interface, in agreement with experimental results. Our findings demonstrate
that the mechanical bond imparts distinctive advantageous properties to SWNT
derivatives as polymer fillers.Comment: 39 pages, 19 figure
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