Eugenio Rivera

This study reports the development and characterization of hierarchical electrospun scaffolds based on poly (L-lactic acid) (PLA) and polyacrylonitrile (PAN) reinforced with calcium oxide (CaO) nanoparticles (18.5 ± 4.7 nm) for skin regeneration. Six configurations, including two five-layer multilayer systems (PLA/PAN/CaO and PAN/PLA/CaO), were evaluated to determine how composition and deposition sequence influence physicochemical, mechanical, and biological performance. FT-IR, XRD and DSC confirmed the successful integration of CaO, while thermal analysis evidenced an effect of chain mobility and interfacial interactions within multilayer systems. Cross-sectional SEM revealed the presence of both fibers with continuous interfaces. Nitrogen adsorption showed that CaO significantly increased the specific surface area (e.g., from 4.6 m²/g in neat PLA to 21.65 m²/g in PLA/CaO), with type IV isotherms indicating mesoporosity. Wettability assays demonstrated reduced contact angle in PLA (from 126.3° to 91.8°) and sequence-dependent surface properties in multilayers. Tensile testing confirmed that the multilayer architecture bridged the mechanical gap between compliant PLA and high-strength PAN, yielding intermediate moduli (~10–11 MPa) and balanced toughness. Antibacterial assays against S. aureus and E. coli showed that CaO significantly reduced bacterial viability, with PLA/PAN/CaO achieving the highest inhibition (up to 37.1%). In vitro HaCaT assays and in vivo implantation in BALB/c mice confirmed high cytocompatibility and biocompatibility. These findings demonstrate that multilayer electrospinning of PLA/PAN/CaO enables the design of structurally integrated, bioactive, and mechanically balanced scaffolds for advanced wound healing and dermal repair.

La caracterización biomecánica del esófago es esencial para comprender su función y explorar alternativas terapéuticas ante daño o disfunción. En este estudio se evaluó la respuesta mecánica pasiva del esófago de corderos recién nacidos, con énfasis en los efectos de la melatonina. Las muestras se dividieron en dos grupos: control y tratados con melatonina. Se realizaron ensayos de tracción uniaxial in vitro en direcciones longitudinal y circunferencial, observándose un comportamiento anisótropo, típico de tejidos blandos. A partir de las curvas esfuerzo-alargamiento se extrajeron parámetros mecánicos comparables entre grupos. La respuesta global fue ajustada mediante modelos constitutivos hiperelásticos, adecuados para tejidos reforzados con fibras. Simulaciones numéricas y análisis estadísticos permitieron describir el comportamiento mecánico en ambos grupos. Aunque no se identificaron diferencias significativas entre tratamientos, los resultados constituyen una base útil para futuras investigaciones sobre el impacto de fármacos en la biomecánica esofágica y su aplicación en ingeniería de tejidos.

This study aims to assess the efficacy of melatonin in mitigating the adverse effects of hypobaric hypoxia on the cardiovascular system of neonatal lambs (30 days old). Two groups were considered for this purpose: (i) Melatonin-treated group (N = 5) and (ii) Control group (N = 6) without treatment. All subjects were exposed to hypobaric hypoxia during gestation and perinatal periods, with melatonin administered after birth. The study focused on the carotid artery, a known predictor of cardiovascular risk. Biomechanical tests, morphometric, and histological measurements were conducted, and a numerical model was developed based on the biomechanical data. Key findings showed remodeling effects: Firstly, a realignment of collagen fibers towards a longitudinal direction was observed with melatonin treatment, similar to non-hypoxic arteries. Second, changes in residual stress and ex-vivo luminal radius were noted, aiming to reduce wall stress and increase vascular resistance. These changes indicate an antihypertensive response, reducing the effects of increased blood pressure and flow due to hypobaric hypoxia. This study demonstrates that biomechanical and histomorphometric methodologies effectively assess the beneficial effects of melatonin treatment under hypobaric hypoxia exposure.

One of the purposes of tissue engineering is to offer therapeutic alternatives to treat various esophagus-related diseases. To develop viable esophageal replacements that are both mechanically and biologically compatible and to assess the impact of pharmacological treatments on esophageal tissue at the macro- and micro-structural levels, it is crucial to understand the biomechanical properties of the esophagus. In this study, we analyzed esophageal tissue samples from nine newborn lambs. Subjects were randomly separated into a control group (n = 5) and a melatonin-treated group (n = 4). The passive mechanical response of the esophagus was studied by performing in-vitro uniaxial tensile tests along longitudinal and circumferential directions. Samples were classified into three types: internal tissue (mucosa and submucosa layers), external tissue (external muscular layer), and integrated tissue (comprising all layers). Uniaxial stress versus stretch curves of each classification were used to determine mechanical properties that were statistically analyzed. Moreover, average experimental results were used to calibrate an anisotropic hyperelastic model. Stress-stretch curves from uniaxial tests showed a highly anisotropic behavior, with a higher stiffness along the longitudinal direction and internal tissue exhibiting the highest stiffness. To contrast the results obtained from mechanical testing, histological analysis of esophagus samples was carried out. Microstructural components were quantified and morphological measurements of the main zones were performed. No significant differences were found at the macro- and microstructural levels of the tissue, indicating that the supply of low doses of melatonin does not alter the biomechanical properties of the esophagus.

This work consists of analyzing the impact of geometrical features (thickness and curvature) on the estimation of circumferential residual stresses in arteries. For this purpose, a specific sample of lamb abdominal artery is chosen for analysis and, through computational tools based on Python libraries, the stress-free geometry is captured after the ring opening test. Numerical simulations are then used to reconstruct the sample in order to estimate the circumferential residual stresses. Then, four stress-free geometry models are analyzed: an ideal geometry, i.e., constant curvature and thickness; a constant curvature and variable thickness geometry; a variable curvature and constant thickness geometry; and a variable curvature and thickness geometry. The numerical results show that models perform well from a geometric point of view, where the most different feature was the closed outer perimeter that differs about 14% from the closed real sample. As far as residual stress is concerned, differences up to 198% were found in more realistic models taking a constant curvature and thickness model as reference. Thus, the analysis of a realistic geometry with highly variable curvature and thickness can introduce, compared to an idealized geometry, significant differences in the estimation of residual stresses. This could indicate that the characterization of arterial residual stresses is not sufficient when considering only the opening angle and, therefore, it is also necessary to incorporate more geometrical variables.

In this work, we propose a reliable and stable procedure to characterize anisotropic hyperelastic materials. For this purpose, a metaheuristic optimization method known as evolutionary strategies is used. The advantage of this technique with respect to traditional methods used for non-linear optimization, such as the Levenberg–Marquardt Method, is that this metaheuristic algorithm is oriented to the global optimization of a problem, is independent of gradients and allows to solve problems with constraints. These features are essential when characterizing hyperelastic materials that have non-linearities and are conditioned to regions of stability. To characterize the mechanical behavior of the arteries analyzed in this work, the anisotropic hyperelastic models of Holzapfel–Gasser–Ogden and Gasser–Holzapfel–Ogden are used. An important point of the analysis is that these models may present a non-physical behavior: this drawback is overcome by defining a new criterion of stabilization in conjunction with the evolutionary strategies. Finally, the finite element simulations are used in conjunction with the evolutionary strategies to characterize experimental data of the artery pressurization test, ensuring that the parameters obtained are stable and representative of the material response.

The present study involves experiments and modelling aimed at characterizing the passive structural mechanical behavior of the chronic hypoxic lamb thoracic aorta, whose gestation, birth and postnatal period were carried at high altitude (3600 masl). To this end, the mechanical response was studied via tensile and pressurization tests. The tensile and pressurization tests measurements were used simultaneously to calibrate the material parameters of the Gasser–Holzapfel–Ogden (GHO) hyperelasctic anisotropic constitutive model through an analytical-numerical optimization procedure solved with an evolutionary strategy that guarantees a stable response of the model. The model and procedure of calibration adequately adjust to the material behavior in a wide deformation range with an appropriate physical description. The results of this study predict the mechanical response of the lamb thoracic aorta under generalized loading states like those that can occur in physiological conditions and/or in systemic arterial hypertension. Finally, the novel use of the evolutionary strategy, together with the set of experiments and tools used in this study, provide a robust alternative to validate biomechanical characterizations.

RESUMEN Para evaluar de manera fidedigna el riesgo de ruptura de la aorta – junto a los índices de peligrosidad de enfermedades cardiovasculares u otras condiciones extremas y los efectos de posibles tratamientos – se requiere conocer los mecanismos de daño que conducen a ésta. En este trabajo, se caracteriza el daño mecánico del tejido aórtico en condición de hipoxia, analizando numéricamente su respuesta al ser sujeto a un estado de presurización similar al inducido por un ensayo de acopado hidráulico. El comportamiento mecánico de la pared aórtica, se describe mediante un modelo de material hiperelástico con dos direcciones de isotropía transversal y un modelo de daño isótropo; ambos calibrados experimentalmente, a partir de resultados de ensayos de tracción uniaxial previamente reportados, realizados a muestras de aorta torácica de corderos expuestos a hipoxia hipobárica crónica. Se estudia un grupo tratado con melatonina, en contraste a un grupo control. Una vez calibrado el modelo constitutivo, se evalúa su desempeño en la simulación numérica del ensayo de acopado hidráulico, en la cual se analiza la respuesta cuasi-estática de una estructura – en forma de cuarto de disco, fijada en el perímetro curvo – solicitada fuera de su plano por una presión o fuerza por unidad de superficie, permanentemente normal al área de carga. Los datos experimentales y los resultados de las simulaciones numéricas indican, que un tratamiento con melatonina reduce rigidez de la aorta. Adicionalmente, las presiones asociadas al inicio del daño entregadas por la simulación del ensayo son compatibles con una condición de hipertensión arterial.