1,721,020 research outputs found
Termodinamica di complessi metallici con polimeri sintetici recanti residui di acido etilen-diammino-diacetico
No full text
Photochemical Modification of a Medical Grade Polyamide Using a Plasma-Based Pre-Treatment
No full textIntroduction: The surface modification of hydrophobic polymers (polyamide 12, PA12) offers a method to increase the hydrophilicity of the surfaces of polymeric medical devices. Plasma is a suitable technology but unfortunately, the modification is reversible, and the hydrophilicity decreases in short time. Otherwise, surface modification with photo-reactive chromophores, namely phenyl azide (PhAz), offers an alternative and irreversible method for the surface hydrophilization.
Methods: The aim of the present work was to combine plasma technology and the azide’s photo-reaction to increase the PA12 hydrophilicity. In the first process step, the polymer surface was activated using plasma reaction. Afterwards, a solution of PhAz was sprayed on the activated polymer surface. Finally, the samples were treated with ultraviolet light to trigger the chemical reaction between the polymer chemical groups and PhAz.
Results: Untreated, plasma-treated, and photo-modified polymers were compared in terms of wettability by means of the contact angle (CA) measurements (immediately, 1 week and a month from the reaction). The hydrophilicity increase of treated surfaces was estimated through “deltaCA”, the decreasing of CA compared to the untreated polymer. Plasma-treated samples were initially very hydrophilic, but hydrophilicity was significantly reduced after 1 week and almost completely lost after 1 month. PhAz-treated samples were significantly more hydrophilic if compared with untreated polymer and after 1-month deltaCA was unchanged. The samples produced by plasma activation followed by treatment with PhAz were very hydrophilic. Some hydrophilicity reduction occurred over time, but after 1 month “deltaCA” was stabilized and still considerably high.
Conclusions: The plasma-based pre-activation process was able to improve the PhAz surface process modification of PA12. Conceivably, new chemical groups generated by the plasma reaction can react with PhAz chromophores and increase the yield of the photochemical reaction, making the polymer surface more hydrophilic if compared with the other processes
Poly(amido-amine)s containing peptide nitrogens as potential binding sites for metal(II) ions
No full textSurface modification of polyamide 12 angioplasty balloons by photochemical reaction with an aromatic azide
No full textPolyamide 12 (PA12) is used in a variety of applications when low moisture absorption, good dimensional stability, and toughness are required. Polyamide 12 is one of the polymers most frequently employed to fabricate angioplasty balloon catheters; however, its high hydrophobicity and chemical inertness require the application of coatings to make its surface more hydrophilic and biocompatible. In this work, an alternative method, based on the photochemical reaction of PA12 with a hydrophilic aromatic azide, was developed. Static and dynamic contact angle measurements evidenced that the surface modification process was able to improve PA12 wettability and that the effects were retained even after 12 months from surface treatment. Polyamide 12 modification resulted in an increase of its surface free energy, as evaluated by the van Oss, Good, and Chaudhury method. X-ray photoelectron spectroscopy confirmed the presence of the aromatic azide on PA12 surface. Finally, compliance tests showed that the modification process did not reduce the mechanical performance of balloons
Amphoteric poly(amido-amine) polymers containing the N,N'-ethylenediaminediacetic acid moiety: stability of copper(II) and calcium(II) chelates
No full textThe thermodynamics of protonation and complexing ability with CuII and CaII ions of synthetic polyampholytes containing ethylenediamine-N,N′-diacetic acid residues is reported. The free and two cross-linked polymers, of poly(amido-amino) structure, have been studied in aqueous media (0.1 M NaCl and 25°C) mainly by potentiometry and solution calorimetry. Potentiometric and calorimetric titration curves have been fitted only with two basicity constants and two enthalpy changes, both relative to the protonation equilibria of the two amino nitrogens in each repeating unit. The first protonation step always revealed greater thermodynamic values owing to electrostatic and inductive effects. The metal ion equilibrium constant revealed only a single complex species of MIIL stoichiometry (where L2- is the repeating unit of the polymer in the ionized form) with a considerably higher log β value for CuII. The CuL species was present over a wide range of acidity (pH 2-12), while CaL formed appreciably only above pH 5. The enthalpy change (-ΔH°) of the CuII complex species was also considerably greater than that of CaII, suggesting a strong chemical bond in the former case in which d orbitals are utilized. Both cross-linked polymers retained the same ability to form metal complexes in the same pH range
Functionalization of medical device surfaces via photocatalytic reactions
No full textThe ability to tailor polymer surface properties has become a very important and challenging area of science. Most medical devices are constituted of polymeric materials, since they offer a great choice in terms of compromise between processability, properties, and cost. Different polymers are available, with specific mechanical properties and ease to process with known manufacturing technologies. The behavior of these materials with respect to blood, pharmacologic or physiologic solutions, different cells of the human body depends on the chemical structure of the polymer itself and on the conditions and technologies used to process it. Therefore, we focused our research on the development of a technique for modifying the surface properties of a balloon catheter without impacting on its main intended use properties nor on the production processes. Surface modification via photochemical reaction with aromatic azides was successfully performed and monitored by XPS and dynamic contact angle. Reactions of different types of aromatic azides have revealed that the new surface properties depend on the substituent groups present on their structures. The balloons modified according to the present experimental work, can be advantageously used in order to improve the balloon catheter performances in terms of lubricity and biocompatibility
Hydrophobically-modified PEG hydrogels with controllable hydrophilic/hydrophobic balance
Full text linkThis work reports on a novel method to synthesize hydrophobically-modified hydrogels by curing epoxy monomers with amines. The resulting networks contain hydrophilic poly(ethylene gly-col) (PEC) segments, poly(propylene glycol) (PPG) segments, and C18 alkyl segments. By varying the content of C18 segments, networks with different hydrophilic-lipophilic balance (HLB) are obtained. All networks show an amphiphilic behavior, swelling considerably both in organic solvents and in aqueous media. In the latter they display a thermosensitive behavior, which is highly affected by the network HLB and the pH of the solution. A decrease in HLB results in an Increment of the polymer weight content (wp) due to hydrophobic association. Furthermore, a reduction in HLB induces a remarkable increase in Initial modulus, elongation at break and tensile strength, especially when Wp becomes greater than about 10%. Low field nuclear magnetic resonance (LF-NMR) experiments evi- dence that, when HLB decreases, a sudden and considerable Increase in hydrogel heterogeneity takes place due to occurrence of extensive physical crosslinking. Available data suggest that in systems with wp ≳10% a continuous physical network superimposes to the pre-existing chemical network and leads to a sort of double network capable of considerably improving hydrogel toughness
- …
