Biological machines such as human and animal bodies are quite incredible. Your body seamlessly incorporates materials as different as muscle, bone, and tendons into an integrated whole. Now Texas A&M researchers think they can imitate nature using polymer networks that have a tunable stiffness. As a bonus, similar to biological devices, the material spontaneously self-heals.
The trick relies on the Diels-Alder reaction which is a cycloaddition reaction of a conjugated diene to an alkene. Diels-Alder-based polymers or DAPs will bond together even when they have different physical characteristics and they undergo a reversible reaction to heat which offers shape-memory and healing capability.
The polymer takes the form of a liquid, and a Makerbot Replicator 2X fitted with a custom syringe system did the printing. Different syringes with different materials were put in during layer changes. Different polymer crosslinkers produce different physical properties in the cured polymer.
From what we can tell, this is probably not ready for prime time yet. But it does show that we still have a lot to learn on the best materials to use for creating 3D objects via additive manufacturing. We spend a lot of time thinking about 3D printing materials. While we used to do a lot of ABS, PLA is more in vogue, today.