Robot use all sorts of clever techniques to climb: we've seen magnets, grippers, gecko feet, electrostatics, and even supersonic jets of air. It's sort of surprising, then, that the idea of using the most stereotypically sticky thing in the universe to climb has been (more or less) ignored until now. Yes, this robot sticks to surfaces with glue.
Technically, what this robot uses is hot-melt adhesive, or HMA. This is the stuff that comes out of hot glue guns, and it goes from a solid to a sticky liquid when it's passed through a heating element. As it cools, it solidifies again. The robot uses this property to temporarily bond its limbs to a vertical surface one by one and hoist itself up, unsticking itself as it goes by re-heating the blobs of glue that it sets down:
By now, you've probably spotted several issues that this robot has to deal with: first, it's very, very slow, since it has to wait for the adhesive to cure every time it takes a step, a 90 second process. And second, totally it leaves a trail of sticky little glue spots along every surface that it climbs, making its usefulness questionable in many (if not most) environments.
So yes, a few things need to be addressed, but this technique has a bunch of upsides, too. The biggest one is that glue, being glue, sticks to just about anything. It doesn't have to be especially rough, especially smooth, or especially magnetic, which makes it more versatile than than the current generation of just about every other robot adhesion system that I can think of off the top of my head.
Also, the hot melt adhesive can support a lot of weight, and it can do it completely passively: you don't need to expend energy once the adhesive sets to keep from falling. The bonding strength of the HMA in its solid state is such that a four square centimeter little patch can hold a staggering 60 kilograms, easily enough to hold this robot plus a fairly gigantic payload, most of which is likely going to have to consist of extra sticks of glue.
"A Climbing Robot Based on Hot Melt Adhesion," by Marc Osswald and Fumiya Iida from the Bio-Inspired Robotics Laboratory at ETH Zurich, was presented at the IEEE International Conference on Intelligent Robots and Systems in San Francisco last month.