Extrusion-based 3D printing and characterisation of biodegradable porous iron-akermanite composite scaffolds

Abstract

The increase in the average human lifespan and the higher prevalence of extreme sports communities in the current society has led to an unfortunate increase in bone defect and fracture cases. Consequently, there is a growing demand for bone fracture therapy and technology. In the case of orthopaedic implants, research has been gradually inclining towards designing biodegradable, biologically integrative porous scaffolds, capable of providing a healthy environment for optimal bone regeneration. Moreover, by mimicking the interconnected porous structures of the natural bone matrix, these implants allow the flow of blood, oxygen and nutrients that are essential in the healing and maintenance of healthy osseous tissue. The gradual dissolution of the structure deems it a non-permanent implant, ultimately completely replaced by natural bone tissue. Pure Fe can offer suitable mechanical properties to support the applied loads of habitual human activities, however, it exhibits too slow biodegradation rates and fails to display satisfactory bone integrative characteristics. Fe-based bioceramic composites are reported to offer biocompatibility, biodegradation and mechanical properties ideal for bone substitution applications. Currently, additively manufactured (AM) Fe-bioceramic composites are one of the most promising material classes for biodegradable scaffold implants. This thesis investigates the extrusion-based AM Fe-akermanite (5 to 15 vol%) composite scaffolds. The fabrication method involved 3D printing printable Fe-akermanite inks followed by heat treatment in an inert environment. Static in vitro immersion testing was conducted to evaluate the degradation characteristics of the scaffolds. Furthermore, the as-sintered and degraded scaffolds were subjected to uniaxial compression testing to determine how the mechanical properties vary as the scaffold degrades. Cytotoxicity evaluations of the scaffolds were also conducted in the form of indirect and direct preosteoblast seeding and culture procedures. The addition of akermanite hastened the degradation rate, with the Fe-15 (vol%) akermanite scaffolds displaying the fastest degradation and most rapid formation of corrosion products containing bone-forming elements, e.g., Ca and P. The yield strength of the scaffolds decreased with increased akermanite content however remained within a suitable range even after degradation. Furthermore, the akermanite addition did not induce a shift towards brittle-like material behaviour. The scaffolds containing 15 vol% akermanite displayed superior cytocompatibility with preosteoblast cells. Therefore, Fe- akermanite composites exhibit great potential for use in biodegradable orthopaedic scaffold applications, with Fe-15 (vol%) akermanite displaying the most promising results.