Dipyridamole-loaded biodegradable PLA nanoplatforms as coatings for cardiovascular stents.

Cardiovascular stents are commonly used for the treatment of cardiovascular diseases that in developed societies are the most frequent causes of mortality and morbidity. In recent years, thorough research and development of drug-eluting stents has been done, with emphasis on coronary stenting to avoid the most common complication, in-stent thrombosis. Dipyridamole (DPM) is a medication that inhibits blood clot formation. Drug delivery nanoplatforms consisting of biodegradable polymers can be fabricated via electrospinning deposition, known for its cost-effective and versatile advantages, that produces fibrous scaffolds that are able to sustain and control drug release. A novel drug delivery nanosystem of polylactic acid fibrous scaffold loaded with the anti-platelet drug DPM was fabricated by electrospinning as coating for cardiovascular stents. The surface morphology and topography that were evaluated via atomic force microscopy, scanning electron microscopy and optical microscopy, were found to be good and suitable for tissue engineering. Contact angle measurements established the hydrophobic behavior of these fibrous nanoplatforms. Drug-release kinetics and degradation studies were conducted and revealed a sustained and controllable release of DPM, through this fibrous matrix over time. Finally, cytotoxicity studies took place to evaluate the cytocompatibility of the scaffold that confirmed its compatible behavior. The successful performance of this nanoplatform can lead to it being a valuable tool for atherosclerosis treatment.

Study of frozen low density lipoprotein particles by using nanotechnology.

OBJECTIVES: To investigate the impact of freezing in -80°C on the structure of isolated low density lipoproteins (LDLs), using nanotechnology, such as Atomic Force Microscopy (AFM). DESIGN AND METHODS: Blood EDTA plasma was obtained from healthy subject and used immediately to isolate LDL by sequential ultracentrifugation at 10°C in 55,000 rpm for 3h, using a Beckmann XL-90 ultracentrifuge (75Ti rotor), in the presence of KBr in PBS. LDLs were then diluted with PBS until final concentrations of 5 and 15 mg LDL/dl. After initial observation, samples were frozen in -80°C for two weeks and observed again after thawing. Experiments were performed in triplicate on two smooth and clean substrates of different hydrophobicity, glass (HOPG) and Si (c-Si). Statistical significance was set at 0.05. RESULTS: Macroscopically, LDL particles formed aggregations in a dendroid layout. There were no differences between images taken from both substrates (HOPG and c-Si). Frozen samples presented significantly smaller LDL particles, than fresh ones. In specific, mean diameter of LDL particle in the fresh LDL sample was 19.77 nm, ranging from 13.34 to 28.76 nm. The frozen LDL sample had a mean diameter of 5.2 nm, ranging from 2.0 to 8.0 nm, which was significantly different from the unfrozen. CONCLUSIONS: Atomic Force Microscopy showed that freezing of LDL causes alterations in their size.

Continuous transformations of C60 crystals: polymorphs, polymers, and the ideal strength of fullerites.

Application of pressure is a versatile method to tailor the properties of organic semiconductors. For example, it is known that high pressure can transform C60 face-centred-cubic (FCC) crystals to polymer structures with inter-molecular bonds. Here we use first-principles calculations to describe continuous crystalline transformation paths that include the FCC and polymer structures as distinct local energy minima. In addition to analysing the atomic-scale details of polymerization, we obtain the ideal strength of FCC-C60, identify metastable C60 crystalline polymorphs, and characterize their electronic properties-all key features for the performance of C60 crystals in organic electronic devices.

Bioelectronics meets nanomedicine for cardiovascular implants: PEDOT-based nanocoatings for tissue regeneration.

BACKGROUND: An exciting direction in nanomedicine would be to analyze how living cells respond to conducting polymers. Their application for tissue regeneration may advance the performance of drug eluting stents by addressing the delayed stent re-endothelialization and late stent thrombosis. METHODS: The suitability of poly (3, 4-ethylenedioxythiophene) (PEDOT) thin films for stents to promote cell adhesion and proliferation is tested in correlation with doping and physicochemical properties. PEDOT doped either with poly (styrenesulfonate) (PSS) or tosylate anion (TOS) was used for films' fabrication by spin coating and vapor phase polymerization respectively. PEGylation of PEDOT: TOS for reduced immunogenicity and biofunctionalization of PEDOT: PSS with RGD peptides for induced cell proliferation was further applied. Atomic Force Microscopy and Spectroscopic Ellipsometry were implemented for nanotopographical, structural, optical and conductivity measurements in parallel with wettability and protein adsorption studies. Direct and extract testing of cell viability and proliferation of L929 fibroblasts on PEDOT samples by MTT assay in line with SEM studies follow. RESULTS: All PEDOT thin films are cytocompatible and promote human serum albumin adsorption. PEDOT:TOS films were found superior regarding cell adhesion as compared to controls. Their nanotopography and hydrophilicity are significant factors that influence cytocompatibility. PEGylation of PEDOT:TOS increases their conductivity and hydrophilicity with similar results on cell viability with bare PEDOT:TOS. The biofunctionalized PEDOT:PSS thin films show enhanced cell proliferation. CONCLUSIONS: The application of PEDOT polymers has evolved as a new perspective to advance stents. GENERAL SIGNIFICANCE: In this work, nanomedicine involving nanotools and novel nanomaterials merges with bioelectronics to stimulate tissue regeneration for cardiovascular implants. This article is part of a Special Issue entitled Organic Bioelectronics - Novel Applications in Biomedicine.

Natural torsion in chiral single-wall carbon nanotubes.

Optimizations performed with two geometrical, molecular mechanical and density functional models show that the configuration of single-wall carbon nanotubes is slightly twisted with respect to that predicted by conventional techniques. Geometrical models are used to explain the effect by breaking of local symmetry of the equally distant neighbors in graphene in the course of rolling, which is minimized by torsion. The torsion angle is small, and decreases with nanotube diameter, being less than 1° Å(-1) for ultrathin tubes. Therefore this effect can be hard to observe in experiments. Still, we single out features in diffraction patterns which can distinguish between twisted and non-twisted configurations. In addition, torsion makes a blue shift in the radial breathing mode, which for thin tubes can be seen by Raman measurement. The effect is slightly strengthened at room temperature.

Thin film and interface properties during ZnO deposition onto high-barrier hybrid/PET flexible substrates.

The combination of transparent conductive oxides with high-barrier films deposited onto flexible polymeric substrates is of considerable importance in order to improve the efficiency, lifetime and stability of flexible electronic devices. In this work, ZnO thin films have been deposited onto high-barrier hybrid/PET flexible substrates by pulsed DC magnetron sputtering, at room temperature and by applying different power values on the target. The employment of in situ and real-time Vis-fUV (1.5-6.5 eV) spectroscopic ellipsometry allowed the investigation of the growth mechanisms of ZnO thin films as well as the modification procedure in the hybrid's surface. Island growth is dominant during the initial stages of deposition concerning low target power regime, whereas layer-by-layer deposition prevails at the high target power regime. The hybrid's modified layer of approximately 10nm was confirmed by the transmission electron microscopy measurements which additionally revealed a columnar structure of the film with a nanocrystalline morphology. The estimated size of the nanocrystals ( approximately 15 nm and above) was compatible with atomic force microscopy (AFM) measurements. Finally, the evolution of the optical parameters (energy gap and absorption peaks) of the ZnO films during the deposition was similar.

Role of N defects on thermally induced atomic-scale structural changes in transition-metal nitrides.

Transition-metal nitrides (TMN) have exceptional stability, which underlies their use in various applications. Here, we study the role of N point defects on the stability of prototype TMNs using first-principles calculations. We find that distinct regimes for TMN changes relate to specific atomic-scale mechanisms, namely, diffusion of N interstitials (I(N)), of I(N) pairs, and of N vacancies. The activation of these processes occurs sequentially as the temperature is raised in a range of several hundreds of degrees, accounting for observed TMN changes under widely different conditions.

Haemocompatibility of amorphous hydrogenated carbon thin films, optical properties and adsorption mechanisms of blood plasma proteins.

Haemocompatibility is one of the most important properties, together with the tissue compatibility and corrosion and wear resistance that determine the biocompatibility of the artificial implants. Carbon-based thin films, such as amorphous carbon (a-C) and amorphous hydrogenated diamond-like carbon (a-C:H or DLC) are considered as excellent candidates for use as biocompatible coatings on biomedical implants. The aim of this work is the comparative study of the haemocompatibility of the a-C:H thin films developed by magnetron sputtering under various deposition conditions, the development of a methodology in order to study the haemocompatibility of thin films, the optical properties of the adsorbed proteins (human serum albumin and fibrinogen) and their adsorption mechanisms. Haemocompatibility and the optical properties of a-C:H thin films and the adsorbed proteins were studied by spectroscopic ellipsometry (SE). The films grown under floating conditions performed better haemocompatibility compared with those deposited under application of bias voltage. In the range of vis-UV, proteins are transparent, while they present an absorption peak at higher energies, but except these characteristics, their optical functions are rather featureless. Adsorption mechanisms were studied through AFM technique too. AFM results are in accordance with those derived by SE. Combination of the two techniques gives us a more accurate description of protein adsorption mechanisms.

Early stages of human plasma proteins adsorption probed by Atomic Force Microscope.

Atomic Force Microscope (AFM) as a surface characterization technique has offered a great impulse in the advance of biocompatible materials. In this study AFM was implemented for the investigation of the early stages of adsorption of two human plasma proteins on titanium and hydrogenated carbon biocompatible thin films. The plasma proteins that were used were Human Serum Albumin and Fibrinogen, two of the most important proteins in human plasma. The concentration of the protein solutions was the same as that in human plasma. As the examined samples were soft, non-contact AFM mode was used to avoid their destruction. In order for the early stages of protein adsorption to be assessed, small incubation times were applied. AFM measurements in liquid buffer were also carried out, allowing the observation of the protein behaviour in an environment much closer to their native one. In addition, there was an assessment of the adsorption mechanism of the proteins on the above-mentioned biomaterials.