93 research outputs found
Effect of Nanoadditives on Bitumen Aging Resistance: A Critical Review
Starting from the eighties, the use of nanoadditives registered an increasing attention in the scientific and patent literature, especially for the case of polymeric nanocomposites. In the last decade, this involved bituminous materials, modified either with nanosized fillers or with polymeric nanocomposites. One of the expected benefits is an increased resistance of the binder to aging. After a short introduction underlining the uncertainties and risks of artefacts in aging tests, a review is given, focusing on the antiaging properties of layered silicates, which are by far the most important nanoadditives for bitumens. Together with layered silicates, other materials such as nanohydrated lime, nanosilica, and layered double hydroxides are mentioned. Preparation and characterization of the binary bitumen/layered silicate and ternary bitumen/layered silicate/polymer systems are described in order to individuate the aspects that influence the antiaging effect. Even if the available literature is quite abundant and unanimously confirms that nanoadditives may improve bitumen durability, there is a lack of studies clarifying the involved mechanisms. As it is for conventional fillers, it seems to be a combination of physical and chemical interactions. Nanoadditives with different chemistries, porosities, and interlayer spacings differently absorb the polar components from the bitumen, thus affecting their predisposition to oxidative aging
Azidated Ether-Butadiene-Ether Block Copolymers as Binders for Solid Propellants
Polymeric binders for solid propellants are usually based on hydroxyl-terminated polybutadiene (HTPB), which does not contribute to the overall energy output. Azidic polyethers represent an interesting alternative but may have poorer mechanical properties. Polybutadiene–polyether copolymers may combine the advantages of both. Four different ether-butadiene-ether triblock copolymers were prepared and azidated starting from halogenated and/or tosylated monomers using HTPB as initiator. The presence of the butadiene block complicates the azidation step and reduces the storage stability of the azidic polymer. Nevertheless, the procedure allows modifying the binder properties by varying the type and lengths of the energetic blocks
Synthesis of GAP and PAMMO Homopolymers from Mesylate Polymeric Precursors
In azidic binders for solid propellants, the N3 functionality is introduced by substitution of a halogen or tosyl group, but recently the mesyl group has been suggested as an alternative. The mesylate group has two advantages, mainly related to its small dimensions and low cost. Poly(glycidyl azide) and poly 3-azidomethyl-3-methyl oxetane were prepared by using both tosylate and mesylate precursors. The azidation kinetics were studied at three different temperatures while keeping all other operating parameters the same. The results confirmed the good potential of the mesylate precursors for the production of azidic binders
First in vivo MRI study on theranostic dendrimersomes
Amphiphilic Janus-dendrimers are able to self-assemble into nanosized vesicles named dendrimersomes.We recently
synthesized the 3,5-C12-EG-(OH)4 dendrimer that generates dendrimersomes with very promising safety
and stability profiles, that can be loaded with different contrast agents for in vivo imaging. In this contribution,
nanovesicles were loaded with both the Magnetic Resonance Imaging (MRI) reporter GdDOTAGA(C18)2 and
the glucocorticoid drug Prednisolone Phosphate (PLP), in order to test their effective potential as theranostic
nanocarriers on murine melanoma tumour models. The incorporation of GdDOTAGA(C18)2 into the membrane
resulted in dendrimersomes with a high longitudinal relaxivity (r1 = 39.1 mM−1 s−1, at 310 K and 40 MHz)
so that, after intravenous administration, T1-weighted MRI showed a consistent contrast enhancement in the tumour
area. Furthermore, the nanovesicles encapsulated PLP with good efficiency and displayed anti-tumour activity
both in vitro and in vivo, thus enabling their practical use for biomedical theranostic applications
Perforated red blood cells enable compressible and injectable hydrogels as therapeutic vehicles
Hydrogels engineered for medical use within the human body need to be
delivered in a minimally invasive fashion without altering their biochemical
and mechanical properties to maximize their therapeutic outcomes. In this
regard, key strategies applied for creating such medical hydrogels include
formulating precursor solutions that can be crosslinked in situ with physical
or chemical cues following their delivery or forming macroporous hydrogels at
sub-zero temperatures via cryogelation prior to their delivery. Here, we
present a new class of injectable composite materials with shape recovery
ability. The shape recovery is derived from the physical properties of red
blood cells (RBCs) that are first modified via hypotonic swelling and then
integrated into the hydrogel scaffolds before polymerization. The RBCs'
hypotonic swelling induces the formation of nanometer-sized pores on their cell
membranes, which enable fast liquid release under compression. The resulting
biocomposite hydrogel scaffolds display high deformability and shape-recovery
ability. The scaffolds can repeatedly compress up to ~87% of their original
volumes during injection and subsequent retraction through syringe needles of
different sizes; this cycle of injection and retraction can be repeated up to
ten times without causing any substantial mechanical damage to the scaffolds.
Our biocomposite material system and fabrication approach for injectable
materials will be foundational for the minimally invasive delivery of
drug-loaded scaffolds, tissue-engineered constructs, and personalized medical
platforms that could be administered to the human body with conventional
needle-syringe systems
Successful in vivo MRI tracking of MSCs labelled with Gadoteridol in a Spinal Cord Injury experimental model
In this study, murine Mesenchymal Stem Cells (MSCs) labeled with the clinically approved MRI agent Gadoteridol through a procedure based on the hypo-osmotic shock were successfully tracked in vivo in a murine model of Spinal Cord Injury (SCI). With respect to iso-osmotic incubations, the hypo-osmotic labeling significantly increased the Gd(3+) cellular uptake, and enhanced both the longitudinal relaxivity (r1) of the intracellular Gadoteridol and the Signal to Noise Ratio (SNR) measured on cell pellets, without altering the biological and functional profile of cells. A substantial T1 Contrast Enhancement after local transplantation of 3.0×10(5) labeled cells in SCI mice enabled to follow their migratory dynamics in vivo for about 10days, and treated animals recovered from the motor impairment caused by the injury, indicating unaltered therapeutic efficacy. Finally, analytical and histological data corroborated the imaging results, highlighting the opportunity to perform a precise and reliable monitoring of the cell-based therapy
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