1,720,983 research outputs found
Isothermal and non-isothermal polymerization of methyl methacrylate in presence of multiple initiators
No full textMethyl methacrylate (MMA) polymerization is a diffusion-controlled reaction, characterized by a strong gel effect, which may cause uncontrolled heat generation and the thermal runaway of the process. For applications to industrial polymerization, kinetic control is particularly important and difficult to achieve due to the interplay between heat development and diffusional control occurring during polymerization. Sustaining the polymerization reaction (i.e. enhancing heat exchange) is a promising strategy to control MMA polymerization kinetics. In particular, different initiators triggering polymerization at different times can be used, thus reducing the possibility of thermal runaway by engineering temperature history and initiator nature/concentrations. There are few models accounting for the presence of multiple initiators and non-isothermal conditions. Therefore, a new, simple semi-empirical model, relating degree of conversion and polymerization rate to time and temperature, was developed. To validate the model, DSC tests were performed in isothermal and non-isothermal conditions, thus deriving the heat developed during polymerization. Model parameters were calculated from isothermal DSC experiments, and the model was predictive of monomer conversion in non-isothermal conditions in presence of single initiators and the mixture of them. Results indicate that. by varying formulation parameters (temperature history and initiator concentrations), polymerization kinetics may be optimized
Nanoparticle-Integrated Hydrogels as Multifunctional Composite Materials for Biomedical Applications
No full textThis review focuses on the most recent developments in the field of nanocomposite hydrogels intended for biomedical applications. Nanocomposite hydrogels are hydrated polymeric networks with a physically or covalently crosslinked three-dimensional (3D) structure swollen with water, in the presence of nanoparticles or nanostructures. A wide array of nanomaterials (polymeric, carbon-based, metallic, ceramic) can be incorporated within the hydrogel network to obtain reinforced nanocomposite hydrogels. Nanocomposites represent a new class of materials with properties absent in the individual components. In particular, the incorporation of nanomaterials within a polymeric hydrogel network is an attractive approach to tailor the mechanical properties of the hydrogels and/or to provide the nanocomposite with responsiveness to external stimuli
Stimuli-responsive chitosan/poly (N-isopropylacrylamide) semi-interpenetrating polymer networks: effect of pH and temperature on their rheological and swelling properties
No full textThe aim of this work was to synthesize semi-interpenetrating polymer networks (semi-IPNs) by free radical polymerization of N-isopropylacrylamide [poly (NIPAAm)], in the presence of chitosan (CHI), and to study the effect of pH and temperature changes on their rheological and swelling properties. The semi-IPNs are thermally stable up to about 400 °C and the presence of CHI increases the thermal degradation rate compared to bare poly (NIPAAm). The prepared systems presents a well-defined porosity and proved to be non-toxic, in vitro, on human embryonic skin fibroblast, thus offering appropriate support for cell proliferation. The semi-IPNs present, at physiological pH, swelling degrees well below those of the pure poly (NIPAAm). Differently, at acidic pH, the CHI macromolecules are protonated and become much more permeable to the diffusion of water giving a swelling degree that approaches that of bare poly (NIPAAm). The viscoelastic moduli of the semi-IPNs increase as a function of pH while the LCST remain unchanged. Moreover, the semi-IPNs viscoelastic moduli increase with the increase of CHI content and, in particular, the difference between the elastic modulus before and after the sol/gel transition is higher for the semi-IPN than for bare poly (NIPAAm) just at about physiological conditions. © 2016, Springer Science+Business Media New York
Effect of Composition of Lung Biomimetic Niche on the Mesenchymal Stem Cell Differentiation toward Alveolar Type II Pneumocytes
No full text: Pulmonary niche dynamically orchestrates the signals, such as proliferation or differentiation of mesenchymal stem cells (MSCs), which allows inducing tissue repair. Lung niche includes extracellular matrix (ECM), comprising hyaluronic acid (HA) and collagen (COLL), and several types of MSCs. Impaired ECM, in lung pathologies, makes the promising therapies based on MSCs ineffective, as it results in a reduced attachment and homing of MSCs, precluding their differentiation and viability. To overcome this problem, in this study a pulmonary biomimetic niche based on HA and COLL hydrogel is developed, with the specific aim to elucidate the role of COLL and HA/COLL semi-interpenetrating polymer networks (SIPNs) in directing the differentiation of MSCs into Alveolar Type II (ATII) cells. The effect of low (L), medium (M), and high (H) molecular weight (MW) HA is investigated, both like structural component of the SIPNs hydrogel and like trophic factor in cell culture media solution. HA in the culture media significantly improves surfactant protein (SP)-C expression (≈2 ng mL-1 ), without showing difference in the MW tested, compared to control only (≈1 ng mL-1 ). Furthermore, LMWHA/COLL hydrogel promotes the SPC expression (approximately two times) compared to COLL, MMWHA/COLL, and HMWHA/COLL hydrogels
Mechanical behavior of bioactive poly(ethylene glycol) diacrylate matrices for biomedical application
No full textDesign of Electrospayed non-spherical poly (L-lactide-coglicolide) microdevices for sustained drug delivery
No full textPolymer chains entanglements in organic solvents can be considered key parameter in formation of non-spherical beads when electrospraying is employed. The shape of micro/nanometric drug delivery systems, plays a major role since it can affect circulation, extravasation, distribution and clearance in vivo of the devices. In this frame, we investigated the influence of polymer processing parameters for the design of polylactic-co-glycolic acid (PLGA) non-spherical microdevices (nSMDs) loaded with triamcinolone acetonide (TrA) prepared by electrospraying technique through a one-step process. In particular, we verified that the formation of non spherical MDs is related to the presence of entanglements among polymer chains to select the optimal solution to be sprayed. Meanwhile, the addition of TrA, a sparingly water soluble corticosteroid, did not substantially affect the particle morphology in terms of size, size distribution and circularity at all the tested drug loadings. Furthermore, the drug could be released for a prolonged period, with controlled and reproducible kinetics for over 3 weeks. The mathematical modeling of release profiles highlighted that release is mainly driven by degradation, at a higher extent in the case of low drug loading
Spontaneous Arrangement of a Tumor Targeting Hyaluronic Acid Shell on Irinotecan Loaded PLGA Nanoparticles
No full textThe arrangement of tumor targeting hyaluronic acid (HA) moieties on irinotecan (IRIN)-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) has been directed by means of a gradient of lipophilicity between the oil and water phases of the emulsion used to produce the NPs. PLGA constitutes the NP bulk while HA is superficially exposed, with amphiphilic poloxamers acting as a bridge between PLGA and HA. Differential scanning calorimetry, zeta potential analyses and ELISA tests were employed to support the hypothesis of polymer assembly in NP formulations. The presence of flexible HA chains on NP surface enhances NP size stability over time due to an enhanced electrostatic repulsion between NPs and a higher degree of hydration. IRIN in vitro release kinetics can be sustained up to 7-13 days. In vitro biologic studies indicated that HA-containing NPs were more toxic than bare PLGA NPs against CD44-overexpressing breast carcinoma cells (HS578T), therefore indicating their ability to target CD44 receptor
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