Characterization Of Cellular Structures Research Articles

An advanced method to design graded cylindrical scaffolds with versatile effective cross-sectional mechanical properties

The selection of the most-suited bone scaffold for a given clinical application is challenging, and has motivated numerous studies. They are mostly based on the characterization of cellular structures, generated from the three-dimensional repetition of a unit cell. However, the interest of circular graded bone scaffolds has been emphasized since they facilitate nutrient transport from the periphery to the core of the scaffold. In the present contribution, we present an advanced and versatile method to design graded circular porous 2D structures based on the conformal mapping of unit cells. We propose a method to generate 3D porous scaffolds by a multilayer repetition of the circular cross-section, resulting in tunable anisotropy depending on the clinical application. We then analyze the link between the porosities of the obtained structures and their effective elastic mechanical cross-sectional properties, making use of a novel and computationally efficient method allowing exhaustive parametric studies. The comparison of various conformal transformations and unit cell designs emphasizes the extent of mechanical properties and porosities that may be reached for a given constitutive material, including non-standard mechanical properties that open large perspectives towards the development of self-fitting scaffolds.

Dynamic deformation and failure process of quasi-closed-cell aluminum foam manufactured by direct foaming technique

The application of cellular structure for energy dissipation requires the investigation on the deformation and failure process of the foam under dynamic loading. In this study, the split-Hopkinson pressure bar technique with high speed video camera was used to directly observe the dynamic deformation in quasi-closed-cell aluminum foam fabricated by an in-house direct foaming methodology. The characterization of cellular structure was first performed on the developed aluminum foam, indicating that the cell size follows a log-normal distribution. The measurements revealed that the deformation mode varies with the strain rate. After that an experimentally validated X-ray micro-computed tomography based 3D finite element model of the as-fabricated specimen was established to predict the stress distribution and deformation history under impact loading, and correlated to the experimental observations to explore the deformation mechanisms. It was found that shear band is formed after peak stress. The dynamic deformation and failure process of the quasi-closed-cell aluminum foam result from the coexistence of cell wall bending and buckling, cell collapse and shear traction induced tearing breakage.

Characterization of additively manufactured cellular alumina dielectric structures

Additive manufacturing (AM, also known as 3D printing) can produce novel three-dimensional structures using low-loss dielectric materials. This enables the construction of dielectrics with complex shapes that enable innovative microwave applications such as resonators, filters, and metamaterial lenses. This paper addresses the production and characterization of cellular structures of various designed densities created with a low loss ceramic material, alumina (aluminum oxide), via vat photopolymerization. The permittivity of these printed structures is variable over roughly an octave, with a range of relative permittivites from 1.78 to 3.60, controlled via part geometry.

AFM studies of environmental effects on nanomechanical properties and cellular structure of human hair

Characterization of cellular structure and physical and mechanical properties of hair are essential to develop better cosmetic products and advance biological and cosmetic science. Although the morphology of the cellular structure of human hair has been traditionally investigated using scanning electron microscopy and transmission electron microscopy, these techniques provide limited capability to in situ study of the physical and mechanical properties of human hair in various environments. Atomic force microscopy (AFM) overcomes these problems and can be used for characterization in ambient conditions without requiring specific sample preparations and surface treatment. In this study, film thickness, adhesive forces and effective Young's modulus of various hair surfaces were measured at different environments (humidity and temperature) using force calibration plot technique with an AFM. Torsional resonance mode phase contrast images were also taken in order to characterize the morphology and cellular structure changes of human hair at different humidity. The correlation between the nanomechanical properties and the cellular structure of hair is discussed.