Italy: Studying Properties & Geometry of Scaffold-Like Structures for Tissue Engineering

Italian authors Claudia Pagano, Lara Rebaioli, Francesco Baldi, and Irene Fassi explore the unique details of creating scaffold-like structures in the recently published ‘Mechanical behavior of scaffold-like structures: Research of relationships between properties and geometry.’ In this study, the focus is on scaffold geometry and stability, and how mechanical properties are affected.

Scaffolds today are used in a wide range of tissue regeneration and engineering applications, serving as porous structures based on networks promoting the growth of human tissue. The researchers realized for this study that it was critical to confirm the relationship between stiffness and strength and the size of samples in ‘polymeric parts’ structured like scaffolds. PLA ‘scaffold-like samples’ were printed and tested for tensile strength, slicing the 3D models in Simplify3D using a Sharebot NG 3D printer. Samples were printed to include ten replicates for each height of 6, 12, 18, and 24mm.

a) Model of the structure geometry b) specimen examples

Each of the specimens was evaluated regarding density, porosity, and mass.

Picture of the compression test set-up

Loading curves for each specimen demonstrated:

• First region (R1) – load increases linearly
• Second region (R2) – characterized by abrupt reduction of slope
• Third region (R3) – just beyond the knee

“By analogy with the behavior of cellular materials, and by considering the compression direction and the specific 3D structure, it is likely that: in the linear elastic region R1, the load is mostly borne by the material in the filament junctions of the adjacent layers; at the knee (R2), the plastic collapse of the structure occurs, based on localized yielding phenomena of the constituent polymer; in R3, the porous structure undergoes a progressive accumulation of plastic deformation and the filaments crash together, resulting in an evident distortion of the specimen.”

a) relative stiffness b) relative strength

The authors also note that because of the polymer strength offering more influence, ‘with respect to stiffness,’ that element should be taken into account when selecting material to build a structure; in fact—and of course this makes sense in any construction project—a comprehensive knowledge is critical to the success of any design and consequent structure that is created later.

“In case the mechanical behavior of a typical scaffold structure could be described by referring to properties intrinsic to the system (independent on the geometry/size) the structure could be treated as an effective ‘3D material,’ and the scaffold design could be easily produced and its performance predicted,” concluded the researchers.

“Several parallelepiped-shaped specimens with different sizes have been fabricated and their mechanical stiffness and strength measured by compression tests. The results have showed that the porosity degree controls the stiffness and strength of the 3D structure. Only the strength, taken as the stress at failure, is intrinsic to the examined structure (thus behaving as a ‘3D material’ concerning the mechanical strength), whereas for the stiffness, a specimen size dependence has been observed. The polymer properties have a stronger influence on the 3D structure strength rather than on its elastic response.”

The successful fabrication of scaffolds is becoming more important to research today—and to patient-specific treatment in areas such as bone replacement, mesh reinforcements, and classic tissue engineering.

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