RESUMEN
Poly(lactic-co-glycolic acid) (PLGA) and poly(caprolactone-co-glycolic acid) (PCLGA) solutions were electrospun into membranes with tailored fiber diameter of 1.8 µm. This particular fiber diameter was tuned depending on the used co-polymer by adjusting the electrospinning parameters that mainly influence the fiber diameter. The greatest setting of the fiber diameter was achieved by varying the polymer solution parameters (polymer concentration, solvents and solvents ratio). PLGA was adequately electrospun with 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), whereas PCLGA required a polar solvent (such as chloroform) with a lower dielectric constant. Moreover, due to the amorphous morphology of PCLGA, pyridine as salt had to be added to the starting solution to increase its conductivity and make it electrospinnable. Indeed, the electrospinning of this co-polymer presents notable difficulties due to its amorphous structure. Interestingly, PCLGA, having a higher glycolic acid molar fraction than commonly electrospun co-polymers (caprolactone:glycolic acid ratio of 45:55 instead of 90:10), could be successfully electrospun, which has not been reported to date. To an accurate setting of fiber diameter, the voltage and the distance from needle to collector were varied. Finally, the study of the surface tension, conductivity and viscosity of the polymer solutions allowed to correlate these particular characteristics of the solutions with the electrospinning variables so that prior knowledge of them enables predicting the required processing conditions.
RESUMEN
In this study, hemp seed oil was reacted with maleic anhydride in an ene reaction to obtain maleinized hemp seed oil (MHO). The use of MHO as a plasticizer and compatibilizer has been studied for polylactic acid (PLA) and thermoplastic starch (TPS) blends (80/20, respectively). By mechanical, thermal and morphological characterizations, the addition of MHO provides a dual effect, acting as plasticizer and compatibilizer between these two partially miscible biopolymers. The addition of MHO up to 7.5 phr (parts by weight of MHO per hundred parts of PLA and TPS) revealed a noticeable increase in the ductile properties, reaching an elongation at break 155% higher than the PLA/TPS blend. Furthermore, contrary to what has been observed with maleinized oils such as linseed oil, the thermal properties do not decrease significantly as a result of the plasticizing effect, due to the compatibilizing behavior of the MHO and the natural antioxidants present in the oil. Finally, a disintegration test was carried out in aerobic conditions at 58 °C, for 24 days, to demonstrate that the incorporation of the MHO, although causing a slight delay, does not impair the biodegradability of the blend, obtaining total degradation in 24 days.
RESUMEN
OBJECTIVES: The aim of this study was to determine whether the most physically active adolescents have better lower limb control. METHODS: 31 high school students (12 males and 19 females) participated in this study. The Anterior Knee Pain Scale was used to find any cases of knee pain. Only subjects with high scores were selected, to exclude those with knee pain or lower limb injuries. Single Leg Squat and Tuck Jump Assessment were used to evaluate movements with two cameras in a two-dimensional assessment. The IPAQ Questionnaire was used to score the physical activity and to classify it into MET total, MET moderate activity, MET vigorous activity and MET walking. These scores were related to knee angle at landing, age and body mass index by self-organizing maps analysis. RESULTS: The subjects were classified into 4 clusters and the descriptive statistics of the different clusters were determined to find any differences. The subjects in cluster 3 were classified as those with the highest risk factors of suffering lower limb musculoskeletal disorders or knee pain, even though injuries do not only depend on quality of movement. Physical activity was not related to healthy movements during jump and single leg squat. CONCLUSION: Physical activity alone cannot be an indicator of good quality lower limb movement, as the knee valgus angle plays a determining role, as it could also depend on neuromuscular control and anatomical characteristics. The analytical method described in the study could be used by physical education teachers to detect potential risk factors for musculoskeletal problems in the lower limbs, especially in the knees.