Multiscale topology optimisation with nonparametric microstructures using three-dimensional convolutional neural network (3D-CNN) models

Additive manufacturing enables the fabrication of parts with complex geometries, thereby opening up the design space from part scale to microarchitecture scale. By optimising the structure in the expanded design space, structural performance can be improved. Topology optimisation is commonly used as the tool to optimise the structures according to specific application requirements. However, multiscale topology optimisation can be computationally expensive and with limited choices in microscale structures. Therefore, we propose a surrogate model based on three-dimensional convolutional neural networks (3D-CNN) to model the effective elasticity tensor and its gradients for general voxel-based nonparametric microstructures. The proposed 3D-CNN-based surrogate model greatly extends the flexibility over existing surrogate-based methods which can only be applied in relatively simple parametric microstructures. Given the microscale structure, the proposed 3D-CNN-based model can effectively predict its material properties. Furthermore, being able to estimate the gradient of the material properties with respect to microscale structure changes makes the proposed 3D-CNN-based surrogate readily adaptive to existing multiscale topology optimisation frameworks. Through extensive simulations, by comparing with both SIMP and existing surrogate-based methods, we demonstrate the advantages of the proposed 3D-CNN-based surrogate model

A Review of Post-Processing Technologies in Additive Manufacturing

10.3390/jmmp5020038Journal of Manufacturing and Materials Processing5238-3

Selective Laser Sintering of Porous Silica Enabled by Carbon Additive

The aim of this study is to investigate the possibility of a freeform fabrication of porous ceramic parts through selective laser sintering (SLS). SLS was proposed to manufacture ceramic green parts because this additive manufacturing technique can be used to fabricate three-dimensional objects directly without a mold, and the technique has the capability of generating porous ceramics with controlled porosity. However, ceramic printing has not yet fully achieved its 3D fabrication capabilities without using polymer binder. Except for the limitations of high melting point, brittleness, and low thermal shock resistance from ceramic material properties, the key obstacle lies in the very poor absorptivity of oxide ceramics to fiber laser, which is widely installed in commercial SLS equipment. An alternative solution to overcome the poor laser absorptivity via improving material compositions is presented in this study. The positive effect of carbon additive on the absorptivity of silica powder to fiber laser is discussed. To investigate the capabilities of the SLS process, 3D porous silica structures were successfully prepared and characterized

Achieving High Porosity in Scaffold Building Using Electrohydrodynamic Jetting 3D Printing

Electrohydrodynamic Jetting (E-Jetting) printing is a promising microfabrication technology for its unique capability of generating and controlling fine fibers at nanometer/micrometer level. Its capability of building highly oriented scaffold makes it superior for some bio-medical applications. The porosity of E-jeted scaffold is essential in order to provide an environment mimicking the functional cells living environment. This paper analyzes fiber diameter and fiber adjacent gap, and proposes an ideal process to build scaffolds with controllable porosity and precisely oriented fibers.Published versio

Fabrication of Polycaprolactone Scaffolds Using an E-Jet 3D Printing System

The electrohydrodynamic jetting (or E-jetting) 3D printing system developed in-house is used as a fiber-based fabrication approach which applies electrical voltage between a nozzle and a substrate to deposit fibers onto the substrate layer by layer. PCL (polycaprolactone) is chosen as biomaterial of scaffolds because of its bio-compatibility and bio-degradability. This study focused on the fiber characteristics impacted by two main parameters, solution dispensing feed rate and plotting speed, to optimize filament diameter, filament formation and stability. Scaffolds fabricated with 70wt% PCL with size of 30×30mm and pore size of 300×300µm were investigated and characterized.Published versio

Biomimetic Janus film fabricated via cryogenic electrospinning for gastrointestinal mucosa repair

Substantial mucosa defects in gastrointestinal tracts are difficult to repair, causing high mortality. Existing artificial mucosa studies overlooked the natural surface texture and the paracrine action between epithelial cells and fibroblasts, leading to an incomplete repair of the mucosa. Here, a Janus film with an exterior surface having a ridge-like texture and an interior flat surface to mimic the anatomical pattern of natural mucosa in digestive tracts is obtained through cryogenic electrospinning (e-spinning). Inspired by the natural mucosa surface textures, biopolymer nanofiber assemblies are employed to replicate the micro-ridges of the exterior layer of mucosa, while the flat surface mimics the morphology of the inferior layer. Hence, the exterior surface of Janus film bolsters epithelial cells' proliferation through the macro pores between fiber assemblies and the nanopores on fibers. In addition, the Janus film realizes a bilayer epithelium/lamina propria reconstruction by culturing epithelial cells and fibroblasts on different sides of the Janus film. Moreover, the Janus film assists the paracrine action between epithelial cells and fibroblasts while insulating their direct contact, an essential mimicry of the natural counterpart. In summary, it is proved that the Janus film will be a promising repair solution for mucosa defects in digestive tracts