The Mechanics of Bioinspired Stiff-to-Compliant Multi-Material 3D-Printed Interfaces

Complex interfaces that involve a combination of stiff and compliant materials are widely prevalent in nature. This combination creates a superior assemblage with strength and toughness. When combining two different materials with large stiffness variations, an interfacial stress concentration is created, decreasing the structural integrity and making the structure more prone to failure. However, nature frequently combines two dissimilar materials with different properties. Additive manufacturing (AM) and 3D printing have revolutionized our engineering capabilities concerning the combination of stiff and compliant materials. The emergence of multi-material 3D-printing technologies has allowed the design of complex interfaces with combined strength and toughness, which is often challenging to achieve in homogeneous materials. Herein, we combined commercial 3D-printed stiff (PETG) and compliant (TPU) polymers using simple and bioinspired interfaces using a fused deposition modeling (FDM) printer and characterized the mechanical behaviors of the interfaces. Furthermore, we examined how the different structural parameters, such as the printing resolution (RES) and horizontal overlap distance (HOD), affect the mechanical properties. We found that the bioinspired interfaces significantly increased the strain, toughness, and tensile modulus compared with the simple interface. Furthermore, the more refined printing resolution elevated the yield stress, while the increased overlap distance mostly elevated the strain and toughness. Additionally, 3D printing allows the fabrication of other complex designs in the stiff and compliant material interface, allowing various tailor-designed and bioinspired interfaces. The importance of these bioinspired interfaces can be manifested in the biomedical and robotic fields and through interface combinations

Unique Collagen Fibers for Biomedical Applications

The challenge to develop grafts for tissue regeneration lies in the need to obtain a scaffold that will promote cell growth in order to form new tissue at a trauma-damaged site. Scaffolds also need to provide compatible mechanical properties that will support the new tissue and facilitate the desired physiological activity. Here, we used natural materials to develop a bio-composite made of unique collagen embedded in an alginate hydrogel material. The collagen fibers used to create the building blocks exhibited a unique hyper-elastic behavior similar to that of natural human tissue. The prominent mechanical properties, along with the support of cell adhesion affects cell shape and supports their proliferation, consequently facilitating the formation of a new tissue-like structure. The current study elaborates on these unique collagen fibers, focusing on their structure and biocompatibility, in an in vitro model. The findings suggest it as a highly appropriate material for biomedical applications. The promising in vitro results indicate that the distinctive collagen fibers could serve as a scaffold that can be adapted for tissue regeneration, in support of healing processes, along with maintaining tissue mechanical properties for the new regenerate tissue formation