Performance of triply periodic minimal surface lattice structures under compressive loading for tissue engineering applications

Abstract

Triply Periodic Minimal Surfaces have been a major research topic in the field of tissue engineering. The interest stems from their theorized ability to serve as functional tissue scaffolds. Tissue scaffolds need to fulfil certain criteria for successful integration. It is important for the scaffold to possess similar mechanical properties to the surrounding tissue where the scaffolds would be implanted to avoid stress shielding. This article discusses the evaluation of the compressive mechanical properties of four types of TPMS lattice structures which are the Primitive, Diamond, Gyroid, and I-WP lattices. Each of the lattices were tested under two relative densities. The first set of relative densities ranged between 29% - 30%. The second set was comprised of relative densities ranging between 48% - 53%. The compressive properties studied were the compressive modulus, compressive strength and yield strain to determine which of the lattices possess the most favourable mechanical performance. The comparison of the lattices also featured a Cubic lattice structure to determine whether TPMS lattices perform better under compression than the Cubic lattice structure. A comparison was then performed between the obtained mechanical properties of the lattices and some of the known mechanical properties of several human tissue types. The study revealed that under both the tested relative densities, the Cubic lattice illustrated the highest mechanical performance while the I-WP lattice demonstrated the lowest mechanical properties for both relative densities. Additionally, it was seen that the Primitive, Diamond, Gyroid, and I-WP lattices with lower relative density resemble the mechanical properties of bone tendons and Cancellous bone. Lastly, an error analysis was performed on the relative density of the manufactured lattices to determine the suitability of the Fused Deposition Modelling (FDM) method for manufacture of functional tissue scaffold and the mechanical properties were compared to existing literature. The mechanical properties of the lattices agreed with the published literature. FDM proved to be suitable for manufacturing the lattices though improvements must be made for optimum results. Improvements can be integrated through usage of a smaller nozzle diameter or by adjusting the printing settings such as the nozzle speed or temperature.