Exploring the Hierarchical Structure and Alignment of Wood Cellulose Fibers for Bioinspired Anisotropic Polymeric Composites.

Materials found in nature have their properties tuned by the chemical composition and hierarchical organization of their structures. Wood is one example of natural material which has properties tuned by its multi-scale hierarchical organization. The cellulose microfibril angle is critical for physical and mechanical properties of wood. On the other hand, polymeric composites containing fibrillar additives, like cellulose fibers, are widespread and have exceptional mechanical properties, which enable them to be used as structural materials. However, obtaining polymer composites with well-aligned cellulose fibers is a challenging task. This work aims to explore the hierarchical structure and alignment of cellulose fibers from wood in polymeric composites with anisotropic mechanical properties, inspired by what trees naturally do. In this sense, cellulosic material from wood was analyzed on a multi-scale; impregnation with polyethylene and densification were performed to form composites; and their mechanical properties were correlated with fiber angles in composite specimens. Moreover, polymer addition to the cellulosic backbone has tremendously increased the material resistance to wetting and chemical oxidation.

Evaluation of the sintering temperature on the mechanical behavior of ß-tricalcium phosphate/calcium silicate scaffolds obtained by gelcasting method.

Scaffolds have been studied during the last decades as an alternative method to repair tissues. They are porous structures that act as a substrate for cellular growth, proliferation and differentiation. In this study, scaffolds of ß-tricalcium phosphate with calcium silicate fibers were prepared by gel casting method in order to be characterized and validated as a better choice for bone tissue treatment. Gel-casting led to scaffolds with high porosity (84%) and pores sizes varying from 160 to 500 µm, which is an important factor for the neovascularization of the growing tissue. Biocompatible and bioactive calcium silicate fibers, which can be successfully produced by molten salt method, were added into the scaffolds as a manner to improve its mechanical resistance and bioactivity. The addition of 5 wt% of calcium silicate fibers associated with a higher sintering temperature (1300 °C) increased by 64.6% the compressive strength of the scaffold and it has also led to the formation of a dense and uniform apatite layer after biomineralization assessment.

Bionanocomposite foams based on the assembly of starch and alginate with sepiolite fibrous clay.

Bionanocomposite foams based on alginate, potato starch and the microfibrous clay mineral sepiolite as reinforcing filler were prepared by lyophilization. Spectroscopic techniques were applied in order to assess the interaction mechanism established between the inorganic fibers and the polysaccharide chains, which is established between the hydroxyl groups in the polysaccharide chains and the silanol groups at the external surface of the sepiolite fibers. The textural properties studied by means of mercury intrusion porosimetry, FE-SEM and X-ray microtomography, revealed a decrease in porosity as the sepiolite content increased. Mechanical properties were also determined for the studied foams, showing an increase in compression moduli from 7.3MPa in the foam without sepiolite to 29MPa in foams containing 10% starch, 40% sepiolite and 50% alginate. Horizontal burning tests were carried out for a preliminary evaluation of the role of the inorganic fibers on the fire resistance properties of the bionanocomposite foams, revealing that bionanocomposite foams with sepiolite content >25% behave as auto-extinguishable materials. Post-synthesis cross-linking with CaCl2 was carried out in some of these samples, leading to an increase in the compression modulus up to 40MPa for the optimal composition.

Hierarchical structures of ß-TCP/45S5 bioglass hybrid scaffolds prepared by gelcasting.

This paper investigates the microstructure and the mechanical properties of ß-tricalcium phosphate (ß-TCP) three-dimensional (3D) porous materials reinforced with 45S5 bioactive glass (BG). ß-TCP and ß-TCP/x%-BG scaffolds with interconnected pores networks, suitable for bone regeneration, were fabricated by gel-casting method. Mechanical properties, porosity, and morphological characteristics were evaluated by compressive strength test, scanning electron microscopy (SEM) and X-ray microtomography analysis, whereas the structures were fully explored by XRD, and Raman spectroscopy. To the best of our knowledge, this is the first time where the mechanism for understanding the effect of bioglass on the mechanical properties and microstruture of ß-TCP/45S5-BG scaffolds has been systematically studied. The findings showed that ionic product lixiviated from 45S5 bioactive glass, rich in silicon species and sodium ion, catalyzes a phase transition from ß-TCP to Si-TCP by replacement of phosphorus for silicon and contributes to the improvement of scaffolds mechanical properties. The compressive strength of ß-TCP/5%-BG and ß-TCP/7.5%-BG was improved around 200% in comparison to pure ß-TCP. Osteoblast-like cells (MG 63) were exposed to the materials for 24h through the use of medium conditioned by ß-tricalcium phosphate/bioactive glass. Cell viability was measured by MTT assay in the cells and the data obtained were submitted to ANOVA, Tukey׳s multiple comparison (p<0.05). The ß-TCP/7.5-BG promoted an increase of cell proliferation. The results suggest that compositions and processing method studied may provide appropriate materials for tissue engineering.