Optimisation of 4D printed mortar-mini vascular networks (m-MVNs) for built heritage preservation

• m-MVNs offer an innovative self-healing solution for repaired lime mortar joints. • Iterative process: mechanical, visual, and waterproofing tests refined the final m-MVNs design. • Adaptive slicing, improved watertightness and performance. • m-MVNs embedded in lime mortar prisms did not affect flexural strength or stiffness, indicating compatibility. • m-MVNs ruptured at designed crack width, releasing healing agent effectively. As climate change increases risks to heritage buildings, enhancing repair methods for historic masonry is essential. This paper presents the design and optimisation process for the manufacturing of a novel self-healing technology—named mortar mini-vascular networks (m-MVNs)—intended for installation in mortar joints during joint repair. m-MVNs are Fused Deposition Modelling (FDM)-printed polymer units with interconnected channels designed to store and protect healing agents. When damage in the mortar joint exceeds a threshold, the m-MVNs rupture, releasing the healing agent to initiate the self-repair process. Engineered within a 4D printing framework, the m-MVNs were optimised through iterative design refinement to protect healing agents, with fracture properties ensuring activation under specific stress conditions. The final m-MVN design, manufactured using adaptive slicing from clear polylactide acid (PLA), achieved the best performance in terms of: i) geometrical regularity, ii) mechanical compatibility with hydraulic lime-based mortars, iii) quasi-isotropy, iv) and watertightness. This breakthrough paves the way for innovative self-healing solutions in heritage conservation.