Browsing by Author "Utrera, Andres"

Now showing 1 - 4 of 4
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    An inverse fitting strategy to determine the constrained mixture model parameters: application in patient-specific aorta
    (2023) Navarrete, Alvaro; Utrera, Andres; Rivera, Eugenio; Latorre, Marcos; Celentano, Diego J.; Garcia-Herrera, Claudio M.
    The Constrained Mixture Model (CMM) is a novel approach to describe arterial wall mechanics, whose formulation is based on a referential physiological state. The CMM considers the arterial wall as a mixture of load-bearing constituents, each of them with characteristic mass fraction, material properties, and deposition stretch levels from its stress-free state to the in-vivo configuration. Although some reports of this model successfully assess its capabilities, they barely explore experimental approaches to model patient-specific scenarios. In this sense, we propose an iterative fitting procedure of numerical-experimental nature to determine material parameters and deposition stretch values. To this end, the model has been implemented in a finite element framework, and it is calibrated using reported experimental data of descending thoracic aorta. The main results obtained from the proposed procedure consist of a set of material parameters for each constituent. Moreover, a relationship between deposition stretches and residual strain measurements (opening angle and axial stretch) has been numerically proved, establishing a strong consistency between the model and experimental data.
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    Analysis of the geometrical influence of ring-opening samples on arterial circumferential residual stress reconstruction
    (2023) Inostroza, Matias; Utrera, Andres; Garcia-Herrera, Claudio M.; Rivera, Eugenio; Celentano, Diego J.; Herrera, Emilio A.
    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.
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    Biocompatible and bioactive PEG-Based resin development for additive manufacturing of hierarchical porous bone scaffolds
    (2023) Sarabia-Vallejos, Mauricio A.; Cerda-Iglesias, Felipe E.; Terraza, C. A.; Cohn-Inostroza, Nicolas A.; Utrera, Andres; Estrada, Manuel; Rodriguez-Hernandez, Juan; Gonzalez-Henriquez, Carmen M.
    Bone diseases can often result in patient bone fragility. Different bone problems include low bone density, osteoporosis, and other bone diseases. Such bone diseases, ailments, and malfunctions often require complex and expensive treatments. In this study, we synthesized a new type of DLP resin for 3D printing purposes based on poly(ethylene glycol diacrylate) (PEGDA) and acrylic acid (AAc). In addition, using a porogen within the photopolymerizable resin allowed us to fabricate hierarchical interconnected porous structures. These structures combine the pores resulting from the CAD design with those obtained by the lixiviation of the porogen. Finally, bioactive particles were added to the mixture to increase the material's biocompatibility, thus proving the strategy's potential to include active compounds for particular purposes. Our results demonstrate that including the photoabsorber, Orange G, considerably increases the printing precision and resolution of the synthesized resin, making it possible to obtain printed parts with intricate and complex geometries with high accuracy and definition. Nano-hydroxyapatite (nHA) inclusion significantly increases the material's biocompatibility and mechanical stiffness (similar to 47 % increase, from 5.47 MPa to 8.02 MPa).
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    Fabrication and Testing of Multi-Hierarchical Porous Scaffolds Designed for Bone Regeneration via Additive Manufacturing Processes
    (2022) Gonzalez-Henriquez, Carmen M.; Rodriguez-Umanzor, Fernando E.; Acuna-Ruiz, Nicolas F.; Vera-Rojas, Gloria E.; Terraza-Inostroza, Claudio; Cohn-Inostroza, Nicolas A.; Utrera, Andres; Sarabia-Vallejos, Mauricio A.; Rodriguez-Hernandez, Juan
    Bone implants or replacements are very scarce due to the low donor availability and the high rate of body rejection. For this reason, tissue engineering strategies have been developed as alternative solutions to this problem. This research sought to create a cellular scaffold with an intricate and complex network of interconnected pores and microchannels using salt leaching and additive manufacturing (3D printing) methods that mimic the hierarchical internal structure of the bone. A biocompatible hydrogel film (based on poly-ethylene glycol) was used to cover the surface of different polymeric scaffolds. This thin film was then exposed to various stimuli to spontaneously form wrinkled micropatterns, with the aim of increasing the contact area and the material's biocompatibility. The main innovation of this study was to include these wrinkled micropatterns on the surface of the scaffold by taking advantage of thin polymer film surface instabilities. On the other hand, salt and nano-hydroxyapatite (nHA) particles were included in the polymeric matrix to create a modified filament for 3D printing. The printed part was leached to eliminate porogen particles, leaving homogenously distributed pores on the structure. The pores have a mean size of 26.4 +/- 9.9 mu m, resulting in a global scaffold porosity of similar to 42% (including pores and microchannels). The presence of nHA particles, which display a homogeneous distribution according to the FE-SEM and EDX results, have a slight influence on the mechanical resistance of the material, but incredibly, despite being a bioactive compound for bone cells, did not show a significant increase in cell viability on the scaffold surface. However, the synergistic effect between the presence of the hydrogel and the pores on the material does produce an increase in cell viability compared to the control sample and the bare PCL material.