Additive Manufacturing of Bioinspired Mineral-Based Composites

Biominerals are used by natural organisms for example as structural supports and optical sensors. They are produced from a limited number of elements and under ambient conditions. Nevertheless, they often possess excellent mechanical properties and sometimes even display multifunctionality. The secret of using brittle constituents to achieve superior mechanical properties such as high toughness in biological materials lies in their locally varying compositions and well-defined hierarchical structures. This level of control over a similar length scale range is challenging to achieve in synthetic materials. The inferior structural and compositional control can be attributed to the difference in processing between biological and synthetic materials. Nature often produces biominerals from well-defined, compartmentalized building blocks through a bottom-up assembly. By contrast, synthetic mineral-based composites are most frequently produced in bulk. New processes for synthetic materials that combine various assembly techniques might offer the potential to capture the structural and compositional intricacies and thereby achieve extraordinary mechanical properties and adaptivity that are similar to those of biological systems. In my thesis, I introduce inks that can be 3D printed and mineralized to build mineral-based composites possessing well-defined multiscale structures and reinforced mechanical properties by combining different bioinspired fabrication processes. I first investigate the use of emulsion-templating and localized mineralization to 3D print porous mineral-based composites. I show that the porous structure and mineral composition can be adjusted to achieve mechanical properties that are close to those of porous biominerals in nature. I then introduce a second polymer to functionalize the porous mineralized matrix. The osmosis-driven swelling and dehydration of the polymer are exploited to reversibly stiffen and strengthen the composite. The mechanical properties of these materials can be dynamically adjusted by changing the composition of the polymer inclusions and the structure of the matrix. I demonstrate the potential of using the osmosis-driven mechanical reinforcement to construct soft actuators. I conclude the thesis by presenting key findings and a few possible future perspectives in advancing the field of mechanically strong, multifunctional and adaptive mineral-based composites. In summary, I combine several manufacturing techniques to fabricate mineral-based materials whose structure is well-defined over up to six orders of magnitudes. The mechanical properties of the material, especially the stiffness, can be reversibly increased up to three-fold by employing the osmosis process. I envisage this contribution of features to benefit the sustainable processing of high-performance mineral-based composites and hydrogels that have the potential to be used in a wide variety of applications.