Characterization and Evaluation of Composite Biomaterial Bioactive Glass-Polylactic Acid for Bone Tissue Engineering Applications.

The limitations associated with the clinical use of autographs and allografts are driving efforts to develop relevant and applicable biomaterial substitutes. In this research, 3D porous scaffolds composed of bioactive glass (BG) obtained through the sol-gel technique and polylactic acid (PLA) synthesized via lactic acid (LA) ring-opening polymerization were prepared by the gel-pressing technique. Two different weight compositions were evaluated, namely, BG70-PLA30 and BG30-PLA70. The structure and morphology of the resulting scaffolds were analysed by FTIR, XRD, SEM, and under ASTM F1635 standard characterizations. The results confirmed that BG promotes the formation of a hydroxy-carbonated apatite (HAp) layer on composites when immersed in simulated body fluid (SBF). Biodegradability evaluations were carried out according to the ISO 10993-13:2010 standard. In addition, electrochemical evaluations were performed in both Hank's and SBF solutions at 37 °C in order to analyse the degradation of the material. This evaluation allowed us to observe that both samples showed an activation mechanism in the early stages followed by pseudo-passivation due to physical bioactive glass characteristics, suggesting an improvement in the formation of the HAp nucleation. The described composites showed excellent resistance to degradation and outstanding suitability for bone tissue engineering applications.

Synthesis and characterization of a polymeric network made of polyethylene glycol and chitosan as a treatment with antibacterial properties for skin wounds.

Polyethylene glycol has been widely investigated for wound healing and dressing applications. Despite its advantages (i.e. great biocompatibility), polyethylene glycol lacks antibacterial activity. For this reason, semi-interpenetrated polymeric networks were prepared by combining a chemically cross-linked polyethylene glycol network with chitosan. The aim of this work was to identify the best amount of chitosan able to improve the antibacterial properties against Staphylococcus aureus. Briefly, the networks were synthesized by a sequential method, adding chitosan in different proportion to the polyethylene glycol. The antibacterial activity was tested following the MGA 0100 of the Pharmacopeia of the United States of Mexico. Fourier-transform infrared with attenuated total reflection spectroscopy, scanning electron microscopy and swelling behavior PBS at 37° C and room temperature were also performed to characterize the polymeric networks. The results showed that PC-2% was able to inhibit the bacterial growth of Staphylococcus aureus even more than Fosfomycin antibiotic. The networks showed cylindrical pores of different sizes (50-100 µm). The maximum swelling of all the networks was achieved in PBS at 37°C (>315%). Free hemoglobin and hemolysis assays were also evaluated to know the compatibility with erythrocytes. Human dermal fibroblasts were used to evaluate direct cytotoxicity. Therefore, the produced gels exerted interesting antibacterial activity and showed good biocompatibility properties.

STEM-HAADF electron microscopy analysis of the central dark line defect of human tooth enamel crystallites.

When human tooth enamel is observed with the Transmission Electron Microscope (TEM), a structural defect is registered in the central region of their nanometric grains or crystallites. This defect has been named as Central Dark Line (CDL) and its structure and function in the enamel structure have been unknown yet. In this work we present the TEM analysis to these crystallites using the High Angle Annular Dark Field (HAADF) technique. Our results suggest that the CDL region is the calcium richest part of the human tooth enamel crystallites.