Abstract
Material extrusion additive manufacturing (MEAM) is an advanced manufacturing method that produces parts via layer-wise addition of material. The potential of MEAM to prototype lattice structures is remarkable, but restrictions imposed by manufacturing processes lead to practical limits on the form and dimension of structures that can be produced. For this reason, such structures are mainly manufactured by selective laser melting. Here, the capabilities of fused filament fabrication (FFF) to produce custom-made lattice structures are explored by combining the 3D printing process, including computer-aided design (CAD), with the finite element method (FEM). First, we generated four types of 3D CAD scaffold models with different geometries (reticular, triangular, hexagonal, and wavy microstructures) and tunable unit cell sizes (1–5 mm), and then, we printed them using two nozzle diameters (i.e., 0.4 and 0.8 mm) in order to assess the printability limitation. The mechanical behavior of the above-mentioned lattice scaffolds was studied using FEM, combining compressive modulus (linear and nonlinear) and shear modulus. Using this approach, it was possible to print functional 3D polymer lattice structures with some discrepancies between nozzle diameters, which allowed us to elucidate critical parameters of printing in order to obtain printed that lattices (1) fully comply with FFF guidelines, (2) are capable of bearing different compressive loads, (3) possess tunable porosity, and (3) overcome surface quality and accuracy issues. In addition, these findings allowed us to develop 3D printed wrist brace orthosis made up of lattice structures, minimally invasive (4 mm of thick), lightweight (<20 g), and breathable (porosity >80%), to be used for the rehabilitation of patients with neuromuscular disease, rheumatoid arthritis, and beyond. Altogether, our findings addressed multiple challenges associated with the development of polymeric lattice scaffolds with FFF, offering a new tool for designing specific devices with tunable mechanical behavior and porosity.
Highlights
IntroductionControlled lattice architectures are seeing growing interest in different application fields, ranging from the manufacturing of lightweight orthosis [1,2,3], scaffolds for tissue engineering [4,5,6,7,8,9,10,11], implantable medical devices [12,13,14], stimuli-responsive softrobotics [15,16,17], and topology optimization for architectural structures [18]
This study aims to address the design complexity issues for lattice structures creation by Material extrusion additive manufacturing (MEAM), realizing a computer-aided design (CAD)/finite element method (FEM)-driven methodology that could be a useful tool for designers, materials scientists, and MEAM engineers who wish to apply complex structures for advanced designs, where the techniques described could be readily applied for specific applications, such as light-weighting orthosis, scaffolds for targeted tissues or
For triangular and hexagonal geometries, the scaffold consisted of 5 × 5 unit cell repetitions of layers, while the reticular and wavy scaffolds consisted of 5 × 5 cell unit repetitions of layers (Figure 1)
Summary
Controlled lattice architectures are seeing growing interest in different application fields, ranging from the manufacturing of lightweight orthosis [1,2,3], scaffolds for tissue engineering [4,5,6,7,8,9,10,11], implantable medical devices [12,13,14], stimuli-responsive softrobotics [15,16,17], and topology optimization for architectural structures [18]. As previously reported by Panetta and co-workers [27], such structures are mainly manufactured by selective laser sintering (SLS) or stereolithography (SLA) [28] since MEAM does not have the adequate resolution to precisely print microstructures. Limitations such as minimum cell size, thickness of walls/edges/faces, cell geometry, nozzle diameter, printing parameters, or porosity have not been fully evaluated. As highlighted by Silva et al, [28], albeit MEAM could seem inadequate compared to SLS and SLA for the production of lattice structures, it allows to use biocompatible and bioabsorbable polymers more suitable for biomedical applications, the feedstock is safer and easier to handle and does not require additional post-processing
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