PSI - Issue 49

Nataliya Elenskaya et al. / Procedia Structural Integrity 49 (2023) 43–50 Author name / Structural Integrity Procedia 00 (2023) 000–000

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et al. 2019; Varma et al. 2020; Zheng et al. 2022). The scaffolds are fundamental component of tissue engineering, which supports attachment, proliferation, and differentiation of cells to form a new tissue. The composition and structural properties of the scaffold, including porosity and pore size, play a fundamental role in this process (Jodati et al. 2020). For instance, damage caused to bones may require the use of artificial structures - biocompatible implants such as endoprostheses, with osteosyntheses helping to restore the bone structure, integrity and morphology, its mechanical properties and functionality (Liu et al. 2020). Practical surgical bone reconstruction involves the integration of an implant in a form of a porous scaffold into the bone tissue. It is important that the body does not reject the implant, i.e., there should not be any pathological reactions from the tissue contacting with the implant. In addition, it is important that the implant is firmly fixed in the body and in a stable and long-term contact with the tissues. The active development of additive manufacturing (AM) technologies in recent years has led to their widespread use in biomedical applications. AM offers considerable opportunities for the production of customised medical implants, as the technology enables production of designs with a complex shape and internal architecture. With regard to tissue engineering, the advantages of AM are in its ability to replicate predetermined scaffold morphology, which can be personalised according to bone defects in each particular clinical case (Wang et al. 2016). Also, topological optimisation became a powerful digital tool in design of optimal structures and materials. The integration of these two technologies opens up a promising future for design and manufacture of biocompatible orthopaedic implants with desirable mechanical properties and minimal patient side effects in clinical use (Li et al. 2021). Scaffold materials are carefully selected for successful clinical applications: they must be biocompatible, bioactive and have sufficient in vivo mechanical strength (Shi et al. 2018a; Kanwar and Vijayavenkataraman 2021). Synthetic polymers are among main materials used in biomedicine, with their mechanical and biological properties, in particular their degradation rate, can be controlled and tuned (Helder et al. 1990; Jayaraman et al. 2015; Su et al. 2018; Wu et al. 2018). Among these materials, polylactide (polylactic acid, PLA) stands out for its controlled biodegradation, osseointegration, ability to induce bone-formation processes and high biocompatibility. The degradation of polymeric scaffolds is mainly due to a hydrolysis process that depends on several factors (Shui et al. 2019). This process leads to a reduction in molecular weight, mechanical properties and mass as well as volume shrinkage of the polymer (Göpferich 1996). It was shown that the rate of degradation was significantly influenced by the mechanical load applied to the scaffold, particularly in compression (Fan et al. 2008). In addition, the architecture of the scaffold itself should also be considered when studying degradation: it was demonstrated that the degradation process was also influenced by porosity of the scaffold (Zhang et al. 2013) and morphology of pores (Wu and Ding 2005). One approach to design a porous structure of bone scaffolds is based on triply periodic minimal surfaces (TPMS) (Yánez et al. 2018; Castro et al. 2019; Ma et al. 2020; Dong and Zhao 2021; Elenskaya and Tashkinov 2021a, b; Song et al. 2021; Yang et al. 2022; Elenskaya et al. 2022). Their internal morphology is defined by analytical mathematical expressions, allowing their resulting properties to be effectively controlled and tailored. Other undoubted advantages of such scaffolds include their high specific surface area and morphology, which provide biomorphic conditions suitable for good cells proliferation. The aim of this paper is to analyse the change in the effective mechanical properties of the unit cells of the TPMS-based scaffolds during degradation under compressive loading. The degradation results obtained from the two proposed modelling techniques – volume degradation (VD) and surface degradation (SD) – are compared for gyroid (G), diamond (D) and I-WP unit-cells.

Nomenclature D

diamond

FE

finite element

G gyroid I-WP wrapped-package PLA

polylactic acid, polylactide

SD surface degradation TPMS triply periodic minimal surfaces