Acta of bioengineering and biomechanics最新文献

Purpose: This study aimed to develop an energy-absorbing structure for bicycle helmets to minimize head injuries caused by collisions. The research team explored three geometric structures produced through additive methods and compares their energy absorption properties with a standard bicycle helmet made of Expanded Polystyrene (EPS) foam.

Methods: The study prepared samples of three geometric structures (a ball, a honeycomb and a conical shape) and a fragment of a bicycle helmet made of EPS foam with the same overall dimensions. Laboratory tests were conducted using a pneumatic hammer, piston compressor, anvil, triaxial accelerometer and data processing systems. Three crash tests were performed for each type of structure, and the anvil's maximum acceleration and stopping distance after the crash were analyzed.

Results: The study found that the energy absorption properties of the Polylactic Acid (PLA) material printed with the incremental method were comparable or better than those of the EPS material used in helmets. The geometric structure of the energy-absorbing material played a crucial role in its effectiveness. The most promising results were obtained for the ball samples.

Conclusions: The study concluded that further research on energy-absorbing structures made using the Fused Deposition Modeling (FDM) method could be useful in the production of bicycle helmets. The results show that the geometric structure of the energy-absorbing material is a crucial factor in its effectiveness. The findings suggest that the ballshaped structure made with PLA material printed using the incremental method could be a promising design for bicycle helmets to minimize head injuries caused by collisions.

Purpose: The aim of the study was to assess static postural stability under fatigue in subjects with chronic ankle instability - "copers" in comparison with healthy controls.

Methods: We conducted a prospective study on a group of 60 young, physically active subjects, divided into 3 groups: I - 14 subjects with unilateral ankle instability, II - 15 subjects with bilateral ankle instability, III - 31 healthy subjects, without ankle instability. The fatigue trial was based on modified Short-Term Fatigue Protocol. Static stabilography was performed with the use of HUR platform.

Results: showed an increase in the value of COP trace length after fatigue test in study population I. The level of COP trace length Z before fatigue was significantly lower than after fatigue. Subjects from study population I had higher levels of COP trace length Z in comparison with the control group. The main effect for the group also proved to be significant. Study population I had higher levels of COP trace length Z in comparison with the control group. For the measurement after fatigue, there was significant difference only between the study population I and the control group.

Conclusions: The incidence of structural ankle instability was not correlated with functional instability. Subjects with ankle instability, or "copers", had good functional levels, enabling them to perform sports activities. "Copers" had weakened proprioception in static stabilography tests. Short and intense fatigue protocol weakened the ability to maintain balance in static stabilography test with eyes closed.

Purpose: Abnormal iris mechanical properties have been considered to be an important cause of pupillary-block and angle-closure glaucoma. In this research, viscoelasticity, anisotropy and location-dependence of mechanical properties of rabbit iris were investigated using uniaxial tensile test.

Methods: Iris strips were taken along three directions: inner-circumferential direction (ICD), outer-circumferential direction (OCD) and radial direction (RD), respectively. Quasi-static tensile tests and stress-relaxation tests were applied on the iris strips. Then, the stress-stretch data was fitted with third order Ogden model; the stress-relaxation data was fitted with the third order Prony series model. Through comparing the tangent modulus and relaxation limit of the strips from different directions and locations, the viscoelasticity, anisotropy and location-dependence of mechanical properties of rabbit iris were explored.

Results: The tangent moduli of iris at the stretch of 1.05 along ICD, OCD, and RD were 3.2 ± 1.4 kPa, 4.2 ± 2.6 kPa, 1.5 ± 0.8 kPa, respectively. Iris strips in ICD and OCD were found to have almost the same stress-relaxation behavior, and both relaxed slower than iris strips in RD.

Conclusions: The mechanical properties of the iris were typically nonlinear, viscoelastic, anisotropic and location-dependent. The stress growth rate of the circumferential direction iris strip is significantly lower than that of RD and the stress-relaxation rate is significantly higher than that of the RD. That is, the iris is more prone to deformation in RD and the stress-retention ability after deformation in RD is weak, which is consistent with the fact that the iris bombe more likely happens in RD in vivo. The results of this study may also help us to establish a more accurate finite element model to simulate the flow field of humor aqueous and find the key factor of pupillary-block.