3D-printed bioinspired spicules: Strengthening and toughening via stereolithography.

Recently, the replication of biological microstructures has garnered significant attention due to their superior flexural strength and toughness, coupled with lightweight structures. Among the most intriguing biological microstructures renowned for their flexural strength are those found in the Euplectella Aspergillum (EA) marine sponges. The remarkable strength of this sponge is attributed to its complex microstructure, which consists of concentric cylindrical layers known as spicules with organic interlayers. These features effectively impede large crack propagation, imparting extraordinary mechanical properties. However, there have been limited studies aimed at mimicking the spicule microstructure. In this study, structures inspired by spicules were designed and fabricated using the stereolithography (SLA) 3D printing technique. The mechanical properties of concentric cylindrical structures (CCSs) inspired by the spicule microstructure were evaluated, considering factors such as the wall thickness of the cylinders, the number of layers, and core diameter, all of which significantly affect the mechanical response. These results were compared with those obtained from solid rods used as solid samples. The findings indicated that CCSs with five layers or fewer exhibited a flexural strength close to or higher than that of solid rods. Particularly, samples with 4 and 5 cylindrical layers displayed architecture similar to natural spicules. Moreover, in all CCSs, the absorbed energy was at least 3-4 times higher than solid rods. Conversely, CCSs with a cylinder wall thickness of 0.65 mm exhibited a more brittle behavior under the 3-point bending test than those with 0.35 mm and 0.5 mm wall thicknesses. CCSs demonstrated greater resistance to failure, displaying different crack propagation patterns and shear stress distributions under the bending test compared to solid rods. These results underscore that replicating the structure of spicules and producing structures with concentric cylindrical layers can transform a brittle structure into a more flexible one, particularly in load-bearing applications.

Encapsulation of bioactives within electrosprayed κ-carrageenan nanoparticles.

In this study, an electrospray synthesis approach was utilized in which a solution mixture of a sensitive bioactive agent, d-limonene (DL, R-(+)-Limonene), and a nature-inspired polymer, κ-carrageenan (κC) was applied to design DL-κC nanoparticles (NPs) in a one step process. The engineered DL-κC NPs displayed spherical morphology and the maximum encapsulation efficiency of NPs was about 97 % by altering the mass ratio of DL to κC. The developed DL-κC NPs showed a pH-dependent release manner in vitro. Both photostability and thermostability of DL were promoted by increasing the κC concentration, and >85 % of the original DL could be preserved following 120 min of UV-light exposure in the NPs with 0.5 % κC. The results demonstrated that electrosprayed κC NPs are promising candidates for the design of high-loading pH-sensitive NPs for encapsulation of highly sensitive bioactive agents.