Mechanical Reinforcement of Hydrogels through Physical Crosslinks and Double Network Granular Architecture

Throughout nature, organisms fabricate a myriad of materials to sustain their lifestyle. Many of the soft materials are composed of water-swollen networks of organic molecules, so-called hydrogels. They generally contribute to the mechanical integrity of the organism, and act as scaffolds for living cells. The ability to fabricate synthetic hydrogels that mimic their natural counterparts would greatly benefit the biomedical field. In particular, synthetic hydrogels have the potential to revolutionize tissue engineering and to enable the fabrication of functional load-bearing soft implants. However, available hydrogels suffer from poor mechanical properties, as they are either too brittle or too soft. While great effort in the field of soft matter has been devoted to the development of hydrogels with improved mechanical properties, they are often not compatible with state-of-the art manufacturing techniques such as additive manufacturing.In this thesis, I present the mechanical reinforcement of hydrogels using two distinctive strategies, and demonstrate their potential as 3D printable materials. I first investigate the use of high functionality crosslinks in metal-coordinated hydrogels. I show that this crosslinking strategy greatly improves the solid-like mechanical properties of viscoelastic gels. I then present the use of hydrogel microparticles to fabricate double network granular hydrogels. I discovered that these materials exhibit an extraordinarily high strength and toughness. Furthermore, the jammed microparticle precursor ink enables the extrusion and 3D printing of this material. This allows the fabrication of hydrogels with locally varying compositions, which can be utilized for example to design stimuli responsive materials. I leverage the granular structure to design recyclable double network granular hydrogels. This is achieved by forming a percolating network that has reversible covalent bonds. I show that this method can be extended to the fabrication of degradable hard plastics. Finally, I conclude by presenting the key findings, and I present a few possible follow-up ideas to further develop the field of load-bearing hydrogels.