Functional Bionanocomposite Fibers of Chitosan Filled with Cellulose Nanofibers Obtained by Gel Spinning.

Extremely high mechanical performance spun bionanocomposite fibers of chitosan (CHI), and cellulose nanofibers (CNFs) were successfully achieved by gel spinning of CHI aqueous viscous formulations filled with CNFs. The microstructural characterization of the fibers by X-ray diffraction revealed the crystallization of the CHI polymer chains into anhydrous chitosan allomorph. The spinning process combining acidic-basic-neutralization-stretching-drying steps allowed obtaining CHI/CNF composite fibers of high crystallinity, with enhanced effect at incorporating the CNFs. Chitosan crystallization seems to be promoted by the presence of cellulose nanofibers, serving as nucleation sites for the growing of CHI crystals. Moreover, the preferential orientation of both CNFs and CHI crystals along the spun fiber direction was revealed in the two-dimensional X-ray diffraction patterns. By increasing the CNF amount up to the optimum concentration of 0.4 wt % in the viscous CHI/CNF collodion, Young's modulus of the spun fibers significantly increased up to 8 GPa. Similarly, the stress at break and the yield stress drastically increased from 115 to 163 MPa, and from 67 to 119 MPa, respectively, by adding only 0.4 wt % of CNFs into a collodion solution containing 4 wt % of chitosan. The toughness of the CHI-based fibers thereby increased from 5 to 9 MJ.m-3. For higher CNFs contents like 0.5 wt %, the high mechanical performance of the CHI/CNF composite fibers was still observed, but with a slight worsening of the mechanical parameters, which may be related to a minor disruption of the CHI matrix hydrogel network constituting the collodion and gel fiber, as precursor state for the dry fiber formation. Finally, the rheological behavior observed for the different CHI/CNF viscous collodions and the obtained structural, thermal and mechanical properties results revealed an optimum matrix/filler compatibility and interface when adding 0.4 wt % of nanofibrillated cellulose (CNF) into 4 wt % CHI formulations, yielding functional bionanocomposite fibers of outstanding mechanical properties.

Plantar center of pressure and postural balance according to head anteposition / Centro de presión plantar y balance postural en función de la anteposición de cráneo

ABSTRACT Introduction: balance posture is noticeable in the variations occurring on the plantar center of pressure (COP) due to internal or external disorders. The objective of this study was to determine the limit of head anteposition in an antero-posterior direction to which a subject may be exposed to without significant modifications to plantar center of pressure and postural balance, conducting a pre-experimental study. Methods: a convenience sample of 30 healthy male subjects with aligned posture aged 20 to 25 years (22.6 ± 1.88) was selected. The following subjects were excluded: individuals taking drugs that affect posture and balance, who practiced intense physical activity 24 hours prior to the study or who suffered any disease of spine and lower extremities. The study complied with the Declaration of Helsinki and an informed consent was signed. To determine COP in orthostatic position, a force plate (Kistler model 9286BA) was used. Subjects were requested to take a bipedal position on the plate. A plumb line was placed over the tragus, in between subject and observer, recording oscillations for 30 seconds. The experiment was repeated by gradually inducing a head anteposition until reaching 5 centimeters. The Wilcoxon test was used to prove the null hypothesis. Results: the average displacement from the plantar center of pressure in orthostatic position per root mean square on the x-axis was 0,25170 and on the y-axis was 0,34987. With 1 cm of induced head antepopsition, the plantar center of pressure varied significantly to 0,23031 on the x-axis and 0,36576 on the y-axis. Conclusion: the minimum anterior displacement of skull significantly modifying the plantar center of pressure and postural balance is 1 cm.

RESUMEN. Introducción: el balance postural se evidencia en las variaciones que pueda sufrir el centro de presión plantar (COP) debido a disturbios internos o externos. El objetivo del presente trabajo consistió en determinar el límite de anteposición de cráneo, en un sentido antero-posterior, a que puede estar sometido un sujeto sin que se modifique significativamente el centro de presión plantar y el balance postural, para lo cual se realizó un estudio preexperimental. Métodos: se obtuvo una muestra por conveniencia conformada por 30 hombres sanos, posturalmente alineados, entre 20 y 25 años de edad (22,6±1,88). Se excluyeron los sujetos consumidores de medicamentos que afectan la postura y el balance, que practicaron actividad física intensa las 24 horas previas al estudio o que sufrían patologías de columna y miembros inferiores. Se siguió la declaración de Helsinki y se firmó un consentimiento informado. Para determinar el COP en posición ortostática se utilizó una plataforma de fuerza Kistler® modelo 9286BA. Se les solicitó a los sujetos adoptar una posición bípeda sobre la plataforma. Se ubicó una plomada por sobre el tragus, entre el sujeto y el observador, y se grabó la oscilación durante 30 segundos. El experimento se repitió al inducir progresivamente una anteposición de cráneo hasta alcanzar los 5 centímetros. Para contrastar la hipótesis nula se utilizó el test de Wilcoxon. Resultados: el promedio del desplazamiento del centro de presión plantar en posición ortostática, según la raíz media cuadrática en el eje x, fue de 0,25170 y en el eje y fue de 0,34987. Con 1 cm de anteposición de cabeza inducida, el centro de presión plantar varió significativamente a 0,23031 en el eje x y a 0,36576 en el eje y. Conclusión: el mínimo desplazamiento anterior de cráneo desde el cual se modifica significativamente el centro de presión plantar y el balance postural corresponde a 1 cm.