Spray-layer-by-layer assembly can more rapidly produce optical-quality multistack heterostructures.

Automated spray-layer-by-layer (LbL) assembly was used to create highly reflective structurally colored thin films with high reflectance at near-UV light wavelengths. Reflectance peaks were tuned by fabricating alternating stacks of high (TiO(2) nanoparticles) and low (SiO(2) nanoparticles) refractive index materials using a non-quarter-wave design. Spray-assembled multilayer heterostructures fabricated with up to 840 individual polymer or nanoparticle deposition steps presented similar roughness and refractive index values compared to Bragg stacks obtained via immersion LbL assembly. Such complex multilayer heterostructures, however, could be fabricated in significantly shorter times; the time required to deposit a complete bilayer was only about 90 s, compared to 36 min for the immersion assembly of the same system. Optimization of the experimental parameters was performed to achieve uniform coatings and relatively smooth interfaces and surfaces. We observed that the spraying times of the nanoparticle and polymer solutions are the main parameters that determine the thickness, optical properties, and uniformity of the assembled films. Ellipsometry, atomic force microscopy (AFM), UV-vis spectroscopy, and transmission electron microscopy (TEM) were used to characterize the samples. The nanoparticle thin films were iridescent and presented relatively narrow peaks of high reflectance (∼90%) at visible and near-UV wavelengths of light.

Preparation and characterization of ethanol-treated silk fibroin dense membranes for biomaterials application using waste silk fibers as raw material.

The possibility of producing valued devices from low cost natural resources is a subject of broad interest. The present study explores the preparation and characterization of silk fibroin dense membranes using waste silk fibers from textile processing. Morphology, crystallinity, thermal resistance and cytotoxicity of membranes as well as the changes on the secondary structure of silk fibroin were analyzed after undergoing treatment with ethanol. Membranes presented amorphous patterns as determined via X-ray diffraction. The secondary structure of silk fibroin on dense membranes was either random coil (silk I) or beta-sheet (silk II), before and after ethanol treatment, respectively. The sterilized membranes presented no cytotoxicity to endothelial cells during in vitro assays. This fact stresses the material potential to be used in the fabrication of biomaterials, as coatings of cardiovascular devices and as membranes for wound dressing or drug delivery systems.

Natural and prosthetic heart valve calcification: morphology and chemical composition characterization.

Calcification is the most common cause of damage and subsequent failure of heart valves. Although it is a common phenomenon, little is known about it, and less about the inorganic phase obtained from this type of calcification. This article describes the scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy and Ca K-edge X-ray absorption near edge structure (XANES) characterization performed in natural and bioprosthetic heart valves calcified in vivo (in comparison to in vitro-calcified valves). SEM micrographs indicated the presence of deposits of similar morphology, and XANES results indicate, at a molecular level, that the calcification mechanism of both types of valves are probably similar, resulting in formation of poorly crystalline hydroxyapatite deposits, with Ca/P ratios that increase with time, depending on the maturation state. These findings may contribute to the search for long-term efficient anticalcification treatments.

Layer-by-layer deposited chitosan/silk fibroin thin films with anisotropic nanofiber alignment.

Chitosan/silk fibroin multilayer thin films were assembled using layer-by-layer deposition. The resultant multilayer films contained nanofibers aligned parallel to the dipping direction. Fiber deposition and orientation was enabled uniquely by a judicious choice of solvent and drying conditions and layer-by-layer assembly with chitosan. The deposition of oriented nanofibers was found to be the result of a unique combination of layer-by-layer and Langmuir-Blodgett type processing. Fiber orientation was confirmed by fast Fourier transform (FFT) analysis of optical micrographs and atomic force microscopy (AFM). Bidirectional fiber alignment was realized by rotating the substrate between multilayer deposition steps. Infrared spectroscopy revealed that the silk fibroin adopted the silk II secondary structure in the deposited films. We anticipate that these anisotropic films are able to combine the biocompatibility of a natural polymer system with the mechanical strength of SF, two properties useful in many biological applications including scaffolds suitable for guiding cell attachment and spreading.

Lyophilized bovine pericardium treated with a phenethylamine-diepoxide as an alternative to preventing calcification of cardiovascular bioprosthesis: preliminary calcification results.

This study investigated the calcification process that occurred on chemically treated bovine pericardium substrata through tests with simulated body fluid solutions. The use of bovine pericardium bioprosthetic valves in heart valve surgery has a significant drawback due to the calcification processes. Thus, many routes such as chemical treatments in the substratum or the adoption of systemic therapies are considered in the literature with the intention to inhibit or to decelerate this process. The presented treatment using the two different phenetylamine-diepoxide solutions showed no effects on calcification experiments as showed by the tests. However, the lyophilized bovine pericardium samples, treated with both solutions, did not show any detectable phosphate deposits. The lyophilization of bovine pericardium before chemical treatments with cross-link agents as epoxy compounds may be an alternative to the conventional calcification prevention methods, but further investigations are recommended to check if the same behavior is found in all lyophilized systems.