Sébastien Alix

In the realm of materials science and structural engineering, integrating sustainable development principles is crucial. This integration has led to the exploration of ecodesign, life cycle analysis, bio-based materials, and bioinspired designs. Bio-inspiration, particularly from plant structures, offers promising avenues for developing efficient and sustainable materials. Indeed, nature has developed plant systems capable of responding to mechanical stresses, particularly bending. This study focuses on designing a bio-inspired box beam using 3D printing technology and bio-based materials. Inspired by the internal structure of Typha leaves, the box beam is optimized for bending load with shear and transverse compression (under the supports). The materials used include polylactic acid and flax-reinforced polylactic acid, both shaped using additive manufacturing. Mechanical, thermal, and structural characterizations, along with finite element analysis, were conducted to validate the bio-inspired design. The results suggest that bioinspired structures, when combined with advanced manufacturing techniques like 3D printing, can achieve optimized mechanical properties while adhering to sustainability principles. Finite element simulations have allowed for the determination of the properties of the boxes by varying the geometry of the structure. It is thus possible to adjust the mechanical properties of the architectural structure according to the needs of the application.

The demand for patient-specific medicine is steadily increasing, particularly with the need for innovative materials capable not only of supporting tissue regeneration but also accelerating it. The aim of this study was to develop a new printable composite material exhibiting ductile behavior, in contrast to brittle failure, in order to support cell growth even under structural compromise. PBS was selected as a blending component with PLA due to its enhanced biocompatibility for bone tissue regeneration. Both neat PLA and the PLA/PBS blend were subsequently combined with BaTiO₃, processed into filaments, 3D printed, and subjected to mechanical testing. PLA-based composites demonstrated higher stiffness under compression, with up to a 6.5% increase in Young’s modulus compared to the blended samples. However, the incorporation of PBS resulted in a more ductile response, as evidenced by three-point bending tests, even at BaTiO₃ concentrations of 10 wt%. This improved ductility is expected to provide safer conditions for cell growth and enable elastic recovery following mechanical loading.

The demand for patient-specific medicine is growing, particularly with the need for innovative materials that can not only support tissue regeneration but also accelerate it. This study aimed to develop a new printable composite material exhibiting ductile behavior, as opposed to brittle failure, to support cell growth even in the event of structural compromise. PBS was selected in this study to be blended with PLA due to its higher biocompatibility for bone tissue regeneration[1]. Both neat PLA and the PLA/PBS blend were then mixed with BaTiO3, printed and tested by mechanical testing. PLA-based composites demonstrated higher stiffness under compression, with up to 6.5 % higher in Young’s Modulus compared to the blended samples. However, the incorporation of PBS resulted in a more ductile material, as evidenced by 3-point bending tests, even at BaTiO3 concentrations of 10 wt%. This ductility should provide safer conditions for cell growth and allow elastic recovery after mechanical loading.

The standard polylactic acid (PLA), as a biodegradable thermoplastic polymer, is commonly used in various industrial sectors, food, and medical fields. Unfortunately, it is characterized by a low elongation at break and low impact energy. In this study, a thermoplastic copolyester elastomer (TPCE) was added at different weight ratios to improve the impact resistance of PLA. DSC analysis revealed that the two polymers were immiscible. A good balance of impact resistance and rigidity was reached using the formulation that was composed of 80% PLA and 20% TPCE, with an elongation at break of 155% compared to 4% for neat PLA. This new formulation was selected to be tested in a fused filament fabrication process. The influence of the nozzle and bed temperatures as printing parameters on the mechanical and thermal properties was explored. Better impact resistance was observed with the increase in the two thermal printing parameters. The crystallinity degree was not influenced by the variation in the nozzle temperature. However, it was increased at higher bed temperatures. Tomographic observations showed an anisotropic distribution of the porosity, where it was mostly present between the adjacent printed filaments and it was reduced with the increase in the nozzle and bed temperatures.

Implanting scaffolds designed for the regeneration or the replacement of bone tissue damaged by diseases and injuries requires specially designed biomaterials that promote cell adhesion. However, the biodegradation rate of these scaffolds based on a single material is uniform. Four-dimensional printing appears to be a promising method to control this aspect by changing the shape and/or the intrinsic properties of 3D-printed objects under the influence of external stimuli. Two main classes of biomaterials and biocomposites based on biopolyesters, namely poly(lactic acid) (PLA) and poly(caprolactone) (PCL), were used in this study. Each of them was mixed with the inorganic filler hydroxyapatite (HA), which is a component of natural bone. The biocomposites and biomaterials were prepared using the melt extrusion process and then shaped using a 3D printer. Three-dimensional specimens showed a decrease in elongation at break and breaking strain due to variations of crystallinity. The crystallinity of irradiated samples increased slightly with irradiation and a new crystalline phase was observed in the case of the PLA. Four-dimensional printing of biomaterials using electron radiation shows great promise for bone tissue engineering based on biocomposite scaffolds and other medical applications.

Fused filament fabrication (FFF) has been used to create prototypes and functional parts for various applications using plastic filaments. It has also been extended to the use of continuous fibers for reinforcing thermoplastic polymers. This study aims to optimize the deposition design of a coextruded continuous carbon fiber (CCF) composite filament with a polyethylene terephthalate glycol‐modified (PETG) filament. The characterizations on the raw materials revealed that the matrix polymer in CCF composite filament had similar physicochemical properties as PETG, and carbon fibers were homogeneously distributed in CCF filament. The effect of raster orientation and shells number on the mechanical properties of non‐reinforced and coextruded CCF‐reinforced PETG was investigated. The highest mechanical properties were obtained at a raster orientation of 0° for both reinforced and non‐reinforced materials. With the increase of raster orientation, Young's modulus and ultimate tensile strength decreased. The presence of shells improved the tensile strength of non‐reinforced PETG. For composite samples printed with unreinforced shells, Young's modulus decreased due to decrease in fibers content, and elongation at break and ultimate tensile strength increased. Tomographic observations showed that the mechanical behavior of printed specimens depended on the anisotropy of porosity in printed specimens.