by Keyword: Geometry
Raymond, Y, Lehmann, C, Thorel, E, Benitez, R, Riveiro, A, Pou, J, Manzanares, MC, Franch, J, Canal, C, Ginebra, MP, (2022). 3D printing with star-shaped strands: A new approach to enhance in vivo bone regeneration Biomaterials Advances 137, 212807
Concave surfaces have shown to promote bone regeneration in vivo. However, bone scaffolds obtained by direct ink writing, one of the most promising approaches for the fabrication of personalized bone grafts, consist mostly of convex surfaces, since they are obtained by microextrusion of cylindrical strands. By modifying the geometry of the nozzle, it is possible to print 3D structures composed of non-cylindrical strands and favor the presence of concave surfaces. In this work, we compare the in vivo performance of 3D-printed calcium phosphate scaffolds with either conventional cylindrical strands or star-shaped strands, in a rabbit femoral condyle model. Mono cortical defects, drilled in contralateral positions, are randomly grafted with the two scaffold configurations, with identical composition. The samples are explanted eight weeks post-surgery and assessed by ??-CT and resin embedded histological observations. The results reveal that the scaffolds containing star-shaped strands have better osteoconductive properties, guiding the newly formed bone faster towards the core of the scaffolds, and enhance bone regeneration, although the increase is not statistically significant (p > 0.05). This new approach represents a turning point towards the optimization of pore shape in 3D-printed bone grafts, further boosting the possibilities that direct ink writing technology offers for patient-specific applications.
JTD Keywords: 3d printing, Architecture, Biomimetic calcium phosphate, Bone regeneration, Calcium-phosphate scaffolds, Geometry, Growth, Implants, In vivo, Induction, Microporosity, Osteoinduction, Pore architecture, Scaffold, Surfaces, Tissue
Beltrán G, Navajas D, García-Aznar JM, (2022). Mechanical modeling of lung alveoli: From macroscopic behaviour to cell mechano-sensing at microscopic level Journal Of The Mechanical Behavior Of Biomedical Materials 126, 105043
The mechanical signals sensed by the alveolar cells through the changes in the local matrix stiffness of the extracellular matrix (ECM) are determinant for regulating cellular functions. Therefore, the study of the mechanical response of lung tissue becomes a fundamental aspect in order to further understand the mechanosensing signals perceived by the cells in the alveoli. This study is focused on the development of a finite element (FE) model of a decellularized rat lung tissue strip, which reproduces accurately the mechanical behaviour observed in the experiments by means of a tensile test. For simulating the complex structure of the lung parenchyma, which consists of a heterogeneous and non-uniform network of thin-walled alveoli, a 3D model based on a Voronoi tessellation is developed. This Voronoi-based model is considered very suitable for recreating the geometry of cellular materials with randomly distributed polygons like in the lung tissue. The material model used in the mechanical simulations of the lung tissue was characterized experimentally by means of AFM tests in order to evaluate the lung tissue stiffness on the micro scale. Thus, in this study, the micro (AFM test) and the macro scale (tensile test) mechanical behaviour are linked through the mechanical simulation with the 3D FE model based on Voronoi tessellation. Finally, a micro-mechanical FE-based model is generated from the Voronoi diagram for studying the stiffness sensed by the alveolar cells in function of two independent factors: the stretch level of the lung tissue and the geometrical position of the cells on the extracellular matrix (ECM), distinguishing between pneumocyte type I and type II. We conclude that the position of the cells within the alveolus has a great influence on the local stiffness perceived by the cells. Alveolar cells located at the corners of the alveolus, mainly type II pneumocytes, perceive a much higher stiffness than those located in the flat areas of the alveoli, which correspond to type I pneumocytes. However, the high stiffness, due to the macroscopic lung tissue stretch, affects both cells in a very similar form, thus no significant differences between them have been observed. © 2021 The Authors
JTD Keywords: rat, scaffolds, stiffness, Afm, Animal cell, Animal experiment, Animal model, Animal tissue, Article, Biological organs, Cell function, Cells, Computational geometry, Cytology, Extracellular matrices, Extracellular matrix, Extracellular-matrix, Geometry, High stiffness, Human, Lung alveolus cell type 1, Lung alveolus cell type 2, Lung parenchyma, Lung tissue, Male, Mechanical behavior, Mechanical modeling, Mechanical simulations, Mechanosensing, Model-based opc, Nonhuman, Physical model, Rat, Rigidity, Stiffness, Stiffness matrix, Tensile testing, Thin walled structures, Three dimensional finite element analysis, Tissue, Type ii, Voronoi tessellations
Raymond Y, Thorel E, Liversain M, Riveiro A, Pou J, Ginebra MP, (2021). 3D printing non-cylindrical strands: Morphological and structural implications Additive Manufacturing 46,
Conventional direct ink writing uses circular nozzles and, therefore, results in cylindrical strands. 3D printing with non-circular nozzles adds new degrees of freedom to this versatile technology, and allows obtaining structures with higher specific surface area or even introducing concave surfaces in the printed architecture. This is an enticing prospect for countless applications, including tissue engineering, chemical reaction catalysts, water evaporators and electrochemical energy storage devices. Despite this, it has been hardly explored by the 3D-printing community. Herein, we develop for the first time 3D printed structures with complex filament section morphologies using a custom-made modular nozzle and a self-setting ceramic ink. The fast elastic recovery of the ink allows obtaining good shape fidelity in the printed filaments, permitting the creation of intricate surfaces with up to 30% concavity and increasing up to 2.5 times the specific surface area compared to cylindrical strands. The use of non-circular nozzles introduces some specific constraints in the printing process. The geometry of the nozzle determines the stable printing directions, and nozzle orientation becomes a critical parameter to achieve a stable printing. Strand torsion, a phenomenon that remains unnoticed with circular nozzles, may result in relevant changes in the geometrical features of the printed structures.
JTD Keywords: calcium phosphate, ceramic, ceramics, flow, geometry, microextrusion, robocasting, Calcium phosphate, Ceramic, Direct ink writing, Microextrusion, Robocasting, Scaffolds
Vaca, R., Aranda, J., (2014). Approximating coupler curves using strip trees Advanced Numerical Methods II 11th World Congress on Computational Mechanics (WCCM XI) 5th European Conference on Computational Mechanics (ECCM V) 6th European Conference on Computational Fluid Dynamics (ECFD VI) , CIMNE (Barcelona, Spain) , 1-2
For the mechanisms considered under the title linkages, coupler curve is the path traced by one of the point on the coupler link considered as an output of the mechanism which is joined to a fixed link. The equation of the coupler curve generated can be obtained solving a set of equations which describes distance constancy between all points of a mechanism and this coupler curve is the eliminant of these equations. The proposal to this work is to approximate coupler curves using strip trees.
JTD Keywords: Coupler curves, Strip tress, Distance geometry, Affine arithmetics, Planar linkages