MIT engineers have conceived pliable, 3-D-printed mesh materials whose flexibility and toughness can emulate and support softer tissues such as muscles and tendons. They are able to customize structures in each mesh, and anticipate that the tough but stretchy fabric-like material could be used as personalized, wearable supports, including ankle or knee braces, and even implantable devices that better match to a person’s body.

Inspired by fabrics and collagen

The flexible meshes were inspired by fabrics and collagen, the protein in the body composing the connective tissues. Sebastian Pattinson, a postdoc at MIT, created wavy patterns which he 3D-printed utilizing thermoplastic polyutherine. He then conceived a mesh configuration which is stretchy, strong, and pliable like fabric.

3-D meshes are conceived to be lightweight and confortable, similar to fabric and textiles. Credit: Felice Frankel, MIT, Fair Use.

In order to test the material, the team printed long strips of mesh and attached them on the outside of the ankle of healthy volunteers. They used an ankle stiffness measurement robot named Anklebot to examine as to how the mesh affected movement in different directions.

They observed that the material increased the ankle’s stiffness during inversion, a common cause of injury, but had no effect to movement in other directions. The researchers also conceived a knee brace that conforms to a patient’s knee even as it bends and a glove that conforms to the wearer’s knuckles in order to prevent involuntary grasping following a stroke.

It’s all about the layers

With traditional 3-D printing, a material is printed through a heated nozzle (layer by layer). When heated polymer is thrusted, it bonds with the layer beneath it. Pattinson figured that, once he printed a first layer, if he elevated the print nozzle slightly, the material leaving the nozzle would take a bit longer to land on the layer below, giving the material time to cool. Consequently, it would be less sticky. By printing a mesh pattern this way, Pattinson was able to create layers that, instead of being completely bonded, were free to move relative to each other. He demonstrated such using a multilayer mesh that covered and conformed to the shape of a golf ball.

Moreover, the team designed meshes that incorporated auxetic structures (patterns that become larger when you pull on them). Case in point, they were successful printing meshes, the middle of which were composed of structures that, when stretched, became wider rather than contracting as regular mesh would. Such property could be useful for supporting curved surfaces of the body (the knee comes to mind).

“There’s potential to make all sorts of devices that interface with the human body, Surgical meshes, orthoses, even cardiovascular devices like stents — you can imagine all potentially benefiting from the kinds of structures we show.” Pattinson concluded.