The doctoral thesis is devoted to the development and comprehensive study of porous titanium/hydroxyapatite interpenetrating phase composites produced through an innovative processing method. The developed approach combines superior control of the topological distribution of constitutes, i.e., the structural titanium (Ti) scaffold and the osteoconductive calcium deficient hydroxyapatite (CDHA) foam, with a complex network of open pores. The composites were processed using a novel sequence consisting of an additive manufacturing material-extrusion-based technique, robocating, followed by in situ foam hardening at physiological temperature.
The first part of the thesis focuses on enabling robocasting as a viable additive manufacturing route for Ti components. Critical challenges related to binder removal and contamination were addressed thorough development and optimisation of ink formulation and debinding process. This work established a robust foundation for producing chemically pure, structurally stable Ti scaffolds via robocasting.
The next part of the thesis elucidated the influence of sintering conditions on the microstructure and mechanical behaviour of Ti scaffolds. By systematically varying sintering temperature and dwell time, clear correlations were established between densification, grain growth, pore morphology, and mechanical properties. Importantly, this work demonstrated that microstructural tailoring through thermal treatment provides an additional degree of control beyond architectural design, enabling the mechanical properties of Ti scaffolds to be tuned to values compatible with a host bone. These findings confirmed that robocast Ti scaffolds can be engineered to mitigate stress shielding while retaining sufficient load-bearing capacity and fatigue resistance.
Considering that mechanical compatibility alone is insufficient for optimal bone regeneration, the thesis subsequently addressed the biological limitations of metallic scaffolds. Calcium phosphate cements based on alpha tricalcium phosphate (α-TCP) were investigated as self-hardening, osteogenic materials capable to transform into hydroxyapatite under physiological conditions. The results revealed that the mechanical properties of resulting CDHA defined by crystalline morphology, which is in turn can be tailored by adjusting α-TCP particle size and setting temperature.
The apex of the thesis integrated these parallel studies into a single composite material concept: porous Ti/CDHA interpenetrating phase composites fabricated entirely through low-temperature biomimetic processing. The resulting composites exhibited continuous three-dimensional networks of Ti, CDHA, and pores, retained chemical purity without forming secondary phases, and demonstrated enhanced stiffness, strength, energy absorption, and damage tolerance compared to bare Ti scaffolds. At the same time, the foamed CDHA phase provided a highly interconnected concave pore network that supported cell adhesion and proliferation, thereby introducing biological functionality directly into the bulk material rather than relying on surface modification alone.