Bovine serum albumin (BSA) is highly water soluble and binds drugs or inorganic substances noncovalently for their effective delivery to various affected areas of the body. Due to the well-defined structure of the protein, containing charged amino acids, albumin nanoparticles (NPs) may allow electrostatic adsorption of negatively or positively charged molecules, such that substantial amounts of drug can be incorporated within the particle, due to different albumin-binding sites. During the synthesis procedure, pH changes significantly. This variation modifies the net charge on the surface of the protein, varying the size and behavior of NPs as the drug delivery system. In this study, the synthesis of BSA NPs, by a desolvation process, was studied with salicylic acid (SA) as the active agent. SA and salicylates are components of various plants and have been used for medication with anti-inflammatory, antibacterial, and antifungal properties. However, when administered orally to adults (usual dose provided by the manufacturer), there is 50% decomposition of salicylates. Thus, there has been a search for some time to develop new systems to improve the bioavailability of SA and salicylates in the human body. Taking this into account, during synthesis, the pH was varied (5.4, 7.4, and 9) to evaluate its influence on the size and release of SA of the formed NPs. The samples were analyzed using field-emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared, zeta potential, and dynamic light scattering. Through fluorescence, it was possible to analyze the release of SA in vitro in phosphate-buffered saline solution. The results of chemical morphology characterization and in vitro release studies indicated the potential use of these NPs as drug carriers in biological systems requiring a fast release of SA.

No abstract

Melanins represent an important class of natural pigments present in plants and animals that are currently considered to be promising materials for applications in optic and electronic devices. Despite their interesting properties, some of the basic features of melanins are not satisfactorily understood, including the origin of their intrinsic paramagnetism. A number of experiments have been performed to investigate the electron spin resonance (ESR) response of melanin derivatives, but until now, there has been no consensus regarding the real structure of the paramagnetic centers involved. In this work, we have employed electronic structure calculations to evaluate the ESR parameters of distinct melanin monomers and dimers in order to identify the possible structures associated with unpaired spins in this biopolymer. The g-factors and hyperfine constants of the cationic, anionic and radicalar structures were investigated. The results confirm the existence of at least two distinct paramagnetic centers in melanin structure, identifying the chemical species associated with them and their roles in electrical conductivity.

The aim of this study was to develop a highly porous calcium‐containing chitosan scaffold suitable for dentin regeneration. A calcium hydroxide (Ca[OH]2) suspension was used to modulate the degree of porosity and chemical composition of chitosan scaffolds. The chitosan solution concentration and freezing protocol were adjusted to optimize the porous architecture using the phase‐separation technique. Scanning electron microscopy/energy‐dispersive spectroscopy demonstrated the fabrication of a highly porous calcium‐linked chitosan scaffold (CH‐Ca), with a well‐organized and interconnected porous network. Scaffolds were cross‐linked on glutaraldehyde (GA) vapor. Following a 28‐day incubation in water, cross‐linked CH scaffold had no changes on humid mass, and CH‐Ca featured a controlled degradability profile since the significant humid mass loss was observed only after 21 (26.0%) and 28 days (42.2%). Fourier‐transform infrared spectroscopy indicated the establishment of Schiff base on cross‐linked scaffolds, along with calcium complexation for CH‐Ca. Cross‐linked CH‐Ca scaffold featured a sustained Ca2+ release up to 21 days in a humid environment. This porous and stable architecture allowed for human dental pulp cells (HDPCs) to spread throughout the scaffold, with cells exhibiting a widely stretched cytoplasm; whereas, the cells seeded onto CH scaffold were organized in clusters. HDPCs seeded onto CH‐Ca featured significantly higher ALP activity, and gene expressions for ALP, Col1, DMP‐1, and DSPP in comparison to CH, leading to a significant 3.5 times increase in calcium‐rich matrix deposition. In sum, our findings suggest that CH‐Ca scaffolds are attractive candidates for creating a highly porous and bioactive substrate for dentin tissue engineering.

Melanins are promising materials for organic bioelectronics devices like transistors, sensors and batteries. In this study, the chemical structural changes of melanin synthesized, by the auto oxidation of L-DOPA, are analyzed for a new synthetic procedure that uses oxygen under pressure (4 to 8 atm). TEM, DLS, FTIR, NMR and XPS are use to characterize the material. Under oxygen pressure, melanin synthesis is accelerated, the polymer obtained is found to have structural differences most notably a higher number of carbonyl groups and different surface charges compared to conventional synthetic melanin. As a consequence it has higher homogeneity and it is soluble in water. To explain these findings a reaction mechanism is proposed based on current melanogenesis models.Keywords: Melanin, oxygen pressure, solubility, accelerated synthesis. E-mail address: joaovp281@gmail.comThis article is protected by copyright. All rights reserved.This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/pi.5185 Accepted Articleexample, thin films of synthetic melanin with good adherence and controllable thickness were made using layer-by-layer technique. It has also been reported that it is possible to obtain melanin films from electrochemical deposition methods, [8] An alternative to obtain good quality films is to modify the melanin structure preserving its main properties, but increasing its solubility or changing its aggregation state. The advantage of this approach is that all processing techniques used up to now for organic semiconducting polymers device production would be available for melanin. In addition, many routine advanced techniques dedicated to thin film or solution characterization could be used. In the last 15 years soluble melanin derivatives were synthesized using different functionalized groups. [14][15][16][17][18] In this study, we propose an alternative synthetic approach for a soluble melanin without any exotic functionalization using molecular oxygen under pressure. Molecular oxygen is considered an ideal oxidant in the context of "green chemistry"; it has low cost, is abundant and environmentally friendly, having thus academic and industrial interest. In addition the synthesis is found to be faster under oxygen pressure. EXPERIMENTALAll the commercially available chemicals were purchased from Acros or Sigma-Aldrich and were used without further purification. In what concerns reproducibility, more than 3 different syntheses were performed and similar optical and structural properties were obtained. Melanin synthesisThe synthesis of melanin was carried out using well-known procedures briefly described. [19] Initially 0.3 g of L-3,4-dihydroxyphenylalanine (L-DOPA) was dissolved in 60 mL of deionized water (Milli-Q), next 0.4 mL of ammonium hydroxide (NH 4 OH) is added, ...