Any child can confirm that ants are not delicate creatures. Their size makes it difficult for us to grab an ant without harming it. Unless you happen to be an Entomologist, wrangling with an ant may not fall into your general activities. However, if for some reason you have to pick or hold something as small or smaller, a micro-tentacle would be the best way to go.
Traditional tweezers are no good when grasping tiny delicate objects such as blood vessels. The process can be painstaking as putting a little too much pressure might crush the object – deciding how much pressure is adequate may also be difficult to gage.
At the Iowa State University, scientists have developed a micro-tentacle or a miniature coiling tentacle, which is just suited for holding tiny objects such as an ant, without causing it any harm. According to the researchers, such micro-scale soft-robots hold a lot of promise as safe handlers for delicate micro-objects. However, to adopt them for wider applications requires easily fabricated micro-actuators of great efficiency.
The micro-actuator for the miniature coiling tentacle developed by the researchers at the Iowa State University is actually a pneumatic actuator based on an elastomeric micro-tube. It is a highly deformable, long and thin micro-tube, based on a new technique called direct peeling. While building the semi-analytical model for shape engineering, scientists use them in combination, amplifying the pneumatically driven bending of the micro-tube into inward spiraling multi-turns.
The result is a micro-tentacle with a grabbing force of nearly 0.78 mN and a final radius as small as 185 µm. That makes it ideally suitable for non-damaging manipulations capable of handling fragile micro-objects. With this spiraling micro-tentacle based grabbing modality, scientists have given the field of soft-robotics several new concepts such as direct peeling, micro-tube shape engineering and the elastomeric micro-tube fabrication technique.
Applications such as vivo biomedical manipulations are increasingly turning to elastomer-based soft-robots for handling delicate objects. Although a lot of headway has been achieved for their micro-scale miniaturization, finding suitable and efficient actuators has remained a difficult task so far. Tentacle actuators composed of polydimethylsiloxane or PDMS elastomers are the answer.
Researchers dip a rod-shaped cylindrical template in a bath containing liquid PDMS. The PDMS clings to the template as researchers pull it out of the bath. They leave the PDMS-coated template in a horizontal position for curing. Most of the gelling elastomer collects on the underside of the template, because gravity pulls it down. That makes the coating on the top much thinner than at the bottom.
When the PDMS sets to a soft and rubbery consistency, it is peeled off the template. That results in a hollow micro-tube, with an uneven wall that is thicker on one side and thinner on the other. Scientists then plug one end of the tube. When they pump air in through the other end, the tube as a whole coils towards on its thinner side and the higher air pressure makes it stiffen. For accentuating the coil formation, scientists add a lump of PDMS to the base of the micro-tube on the outside of the thinner side.
