Molecular dynamics simulations of ultrathin free-standing layers made of melted (373.15–673.15 K) polyethylene chains, which exhibit a lower melting temperature (compared to the bulk value), were carried out to investigate the dominant pressure forces that shape the conformation of chains at the interfacial and bulk liquid regions. We investigated layer thicknesses, $t_L$, from the critical limit of mechanical stability up to lengths of tens of nm and found a normal distribution of bonds dominated by slightly stretched chains across the entire layer, even at large temperatures. In the bulk region, the contribution of bond vibrations to pressure was one order of magnitude larger than the contributions from interchain interactions, which changed from cohesive to noncohesive at larger temperatures just at a transition temperature that was found to be close to the experimentally derived onset temperature for thermal stability. The interchain interactions produced noncohesive interfacial regions at all temperatures in both directions (normal and lateral to the surface layer). Predictions for the value of the surface tension, $\gamma$, were consistent with experimental results and were independent of $t_L$. However, the real interfacial thickness—measured from the outermost part of the interface up to the point where $\gamma$ reached its maximum value—was found to be dependent on $t_L$, located at a distance of 62 Å from the Gibbs dividing surface in the largest layer studied (1568 chains or 313,600 bins); this was ~4 times the length of the interfacial thickness measured in the density profiles.

This paper presents a portable automated teardrop microinjection system as a practical solution for patients suffering from severe dry eye. The electronic device for the controlled and continuous injection of artificial tears is designed, assembled, and tested for performance and stability. It is controlled via Wi-Fi from an Android programmable device. Its design is based on the physicochemical properties of artificial tears, and with both production costs and portability in mind. The system was modeled according to the V methodology of the association for professional German engineers VDI 2206 standard. The microinjector handles a wide range of internal variables such as tears flow rate (0.13 to 60 μL/min), tears viscosity (up to 600 Pa·s), temperature (up to 60 °C), injected volume of tears, and time between consecutive injections. For evaluation purposes, a comprehensive set of experimental tests were carried out to the system, comparing the actually delivered amount of tears, flow rate, and prescribed time vs. programmed values, the error was ∼0.2% for commercially available artificial tears.

Multilayer heterostructures of [(BiFeO₃)_m/(SrTiO₃)_n]_p were synthesized on ITO-coated quartz substrates via pulsed laser deposition, with varying thickness ratios (r = n/m) and periodicities (p = 1–3). Structural, electrical, and piezoelectric properties were systematically investigated using X-ray diffraction, AFM, and PFM. The BiFeO₃ layers crystallized in a distorted rhombohedral phase (R3c), free of secondary phases. Compared to single-layer BiFeO₃ films, the multilayers exhibited markedly lower leakage current densities and enhanced piezoelectric response. Electrical conduction transitioned from space-charge-limited current at low fields (E < 100 kV/cm) to Fowler–Nordheim tunneling at high fields (E > 100 kV/cm). Optimal performance was achieved for r = 0.30, p = 1, with minimal leakage (J = 8.64 A/cm² at E = 400 kV/cm) and a peak piezoelectric coefficient (d₃₃ = 55.55 pm/V). The lowest coercive field (Ec = 238 kV/cm) occurred in the configuration r = 0.45, p = 3. Saturated hysteresis loops confirmed stable ferroelectric domains. These findings demonstrate that manipulating layer geometry in [(BiFeO₃)_m/(SrTiO₃)_n]_p stacks significantly enhances functional properties, offering a viable path toward efficient, lead-free piezoelectric nanodevices.

This article presents the experimental results of a series of analysis and validation tests carried out on a microinjection system designed to deliver artifitial tears to patients suffering of severe dry eye. The microinjector has the following characteristics: high efficiency and precision, user friendly, portable (8.5 × 4.5 × 2.5 cm) and low manufacturing and assembling costs. The microinjector overcomes many of the shortcomings inherent to the manual method drip, it has a syringe reservoir to keep and deliver the artifitial tears. An electronically driven plunger pushes the solution into a capillary that transfer it to the patient’s eyes. The programmed time to deliver the tears fluid is set by the ptient through a “C” program in an Android based device. The real delivering time differs slightly from the programmed one due to frictional effects between the plunger and the syringe walls. The validation tests had the objective to quantify the time difference between the programmed and real delivering times, using as artifitial tears the Lagricel Ofteno brand, whis is the most used in Mexico. Two differentiable tests were done, in one test the plunger was lubricated with silicon oil (Ardes brand) for its compararation with the case where no lubricant is used. All test were done with an operating flow rate range of 0.13 - 60 µL/min). The results show that the microinjection system has the ability to offer high performance and precision with ± 0.191 and ± 0.137 % average error respectively for non-lubricated vs. lubricated tests. The microinjection system can also be used for another compatible biomedical applications like chemotherapy, insulin administration, liquid drug delivery, among others adapting certain injection characteristics (flow rates and time).

The human knee synovial joint is considered one of the three joints having the higher damage or injury incidence, along with the hip and the ankle. Here, a 2D model of a knee synovial junction is presented, where the Condyle is modeled by a mobile circular wall, the condylar concave cavity by a larger circular wall, the Articular Cartilage with a porous medium, and the Synovial Fluid by a high viscosity Newtonian fluid. The model focuses in the study of the angular pressure distribution along the Synovial Fluid/Cartilage interface when the fluid zone undergoes a deformation in the direction of the symmetry axis due to simulated loads. The model equations were solved using FLUENT^® as a numerical tool for the study of biological systems, considering small deformations at the fluid zone, low deformation rates, high fluid viscosities, constant porous fractions and different initial thickness. The results show that the pressure decreases gradually from the center of the join to its ends. The maximum values obtained were in the order of 10⁹ for the dimensionless pressure (i.e. the total pressure with respect to dynamic pressure), these values correspond to 10³ Pa for the total pressure. The greater the fluid zone to cartilage thickness ratio the lower the maximum pressure. The numerical model was validated with an analytical model previously proposed by Jurczak in ( 2006 ).