No abstract

such as drug release, contact lenses, or super absorbents. The introduction of new tough hydrogel systems with enhanced toughness (10 2 -10 4 J m −2 ) [2] and extended elongation at break (>500%) inaugurated new potential applications for hydrogels that never existed before. Thanks to their improved mechanical performance, tough hydrogels can now be considered as suitable material candidates for soft robotics, [3] stretchable electronics, [4,5] structural scaffolds, [6] and load-bearing substrates. [7] Many of these applications, however, rely on constructs with anisotropic properties and highly engineered 3D geometries made of multiple materials. Hence, to fully realize the potential of tough hydrogels in these rapidly advancing areas, they will ideally need to be compatible with a variety of fabrication techniques.The toughening mechanism of tough hydrogels varies between different systems, but most often relies on the introduction of an additional energy dissipating process at the molecular level. [8] For instance, the toughness in double-network hydrogels [9] originates from the magnified energy dissipation process occurring via chain session in one polymer network, while the second polymer network prevents the dissociation of the hydrogel. [10,11] Similarly, in hybrid ionically-chemically crosslinked hydrogels, [12] the source of toughness is the dissociation of ionic bonds in one polymer network while another network holds the hydrogel intact. To create such finely tuned Conventional tough hydrogels offer enhanced mechanical properties and high toughness. Their application scope however is limited by their lack of processability. Here, a new porous tough hydrogel system is introduced which is processable via gel fiber spinning and 3D printing. The tough hydrogels are produced by rehydrating processable organogels developed by induced phase separation between two linear polymer chains capable of intermolecular hydrogen bonding. Through a slow sol-gel phase separation, highly porous gel networks made of hydrogen bonded polymer chains is formed. These organogels can be easily transformed to 3D printed multimaterial constructs or gel fibers, and after rehydration produce highly robust hydrogel structures. Although such hydrogels are highly porous and contain large amount of water, their strength can reach as high as 2000 kPa, with high elongation at break (≈900%), and tunable moduli ranging from 250 to 2000 kPa. The hydrogels have fracture energies larger than cartilage and demonstrate excellent load recovery because of their renewable hydrogen bond crosslinks. Furthermore, the hydrogels exhibit excellent hemocompatibility and in vitro biocompatibility. Such hydrogels can further expand the application of tough hydrogels and may serve as a model to explore the toughening mechanism of hydrogen bonded hybrid, tough hydrogel systems.Hydrogels are defined as crosslinked polymer networks swollen with water. Traditionally, single network, chemically or physically crosslinked hydrogels suffer from low fracture energie...

Current heart valve replacements lack durability and sustained performance, especially in paediatric patients. In part, these problems may be attributed to the materials chosen for these constructs, but an important contributing factor is the design of the valve, as this dictates haemodynamic performance and impacts leaflet stresses which may accelerate structural valve deterioration. Most current era bioprosthetic valves adhere to a fundamental design where flat leaflets are supported by stent posts, secured to a sewing ring. This overall design strategy is effective, but functionality and durability may be improved by incorporating features of the native valve geometry. This paper presents a novel workflow for developing and analysing bioinspired valve designs computationally. The leaflet curvature was defined using a mathematical equation that was derived from the 3D model of a native sheep pulmonary valve obtained via micro-computed tomography. Finite Element Analysis was used to screen the various valve designs proposed in this study by assessing the effect of leaflet thickness, Young's modulus, and height/curvature on snap-through, Geometric Orifice Area (GOA) and the stress in the leaflets. This workflow demonstrated benefits for valve designs with leaflet thicknesses between 0.1-0.3 mm, Young's moduli less than 50 MPa, and elongated leaflets with greater curvatures. The proposed workflow brings substantial efficiency gains, minimising manufacturing and animal testing during iterative improvements, and offers a bridge between in vitro and more complex in silico studies in the future.