3D Printing of Living Structural Biocomposites
Inspired by nature, we introduce an energy-efficient process that takes advantage of the compartmentalization to fabricate porous CaCO3-based composites exclusively comprised of nature-derived materials whose compressive strength is similar to that of trabecular bones. To fabricate this unique material, we combine microgel-based granular inks that inherently can be 3D printed with the innate potential of engineered living materials to fabricate bacteria-induced biomineral composites. The resulting biomineral composites possess a porous trabecular structure that comprises up to 93 wt% CaCO3 and thereby can withstand pressures up to 3.5 MPa. This work is currently published in Materials Today, highlighted in this press release, and has been awarded the SCS DPCI PhD Student Award.
Additive Manufacturing of Porous Biominerals
Porous biominerals, such as trabecular bones and echinoderm skeletons, display a fascinating combination of mechanical properties and dexterity. Keys to this outstanding combination of properties are the well-defined structure of the minerals and the organic components over many orders of magnitudes. This work introduces a capsule-based ink that enables 3D printing of cm-sized biominerals possessing pores with diameters that can be controlled from 100 nm up to the mm length scale. This level of control is achieved by reversibly crosslinking pyrogallol-functionalized surfactants with Ca2+ ions at the surface of oil-in-water drops to convert them into viscoelastic capsules. These capsules are dispersed in a poly(vinyl alcohol) (PVA) solution before they are up-concentrated to yield a 3D printable ink. The 3D printed material is rigidified by mineralizing the capsule shells and firmly connecting adjacent capsules through mineral bridges. By tuning the mineralization conditions and porosity of the composite, we can adjust its mechanical properties to be similar to that of natural porous minerals such as human trabecular bones or the beaks of toucan birds. The tight control over the porous structure, mineral composition, and macroscopic 3D shape is achieved through an energy-efficient process that can be performed at room temperature under aqueous conditions. We foresee this process to open up new opportunities for the design of the next generation of strong and lightweight motile mineral-based composites. This work is now published in Advanced Functional Materials.
Reinforcing Hydrogels with In Situ Formed Amorphous CaCO3
Hydrogels have been gaining increasing attention in the biomedical field due to their good biocompatibility and tunable mechanical properties. However, traditional hydrogels are rarely used for load-bearing applications because of their limited stiffness and/or toughness. By contrast, nature utilizes minerals to reinforce hydrogel-like materials for load-bearing and protection purposes, such as cartilages in joints. Inspired by nature, the stiffness or toughness of synthetic hydrogels has been increased by forming minerals, such as CaCO3, within them. However, the hydrogel reinforcement achieved with CaCO3 remains limited due to the weak affinity between the minerals and the hydrogel matrix. To address this limitation, we form CaCO3 biominerals in situ within a model hydrogel, poly(acrylamide) (PAM), and systematically investigate the influence of the size, structure, and morphology of the reinforcing CaCO3 on the mechanical properties of the resulting hydrogels. We demonstrate that a percolating amorphous calcium carbonate (ACC) nano-structure forms in the presence of a sufficient quantity of Mg2+. This percolating ACC network strongly increases the toughness and stiffness of mineralized hydrogels. The stiffness of the hydrogel can be increased even more, by a factor of 50, when it is functionalized with moieties that have a high affinity to CaCO3, such as acrylic acid (AA). These fundamental insights on the structure-mechanical property relationship of CaCO3-functionalized hydrogels show the potential to tune the mechanical properties of mineralized hydrogels over a much wider range than what is currently possible. This work is now published in Biomaterials Science.
