New Scientist – Ayusman Sen of Pennsylvania State University in University Park and his colleagues have created the self-propelling microspiders using spheres less than a micrometre wide. Each sphere is made up of two halves – one hemisphere is gold, the other silica – and looks like a gold-and-silver Christmas bauble.
Sen hopes to develop versions of these tiny aquatic spiders that run on chemicals readily available in the body, such as glucose. In the future, more sophisticated microspiders attached to nanobots that detect chemicals secreted by damaged tissue could swim through the bloodstream, weaving a medical glue to help heal tears in vessel walls. Decorated with other micromachines and enzymes, they could swim through the circulatory system scouting out tumours, scouring plaque from vessel walls and helping the immune system battle infections .
The microspider represents a “new model of micromachines based on chemistry”, says Joseph Wang, a nanoengineer at the University of California, San Diego, in La Jolla. “It’s the first example of a micromotor that works on polymerisation. The concept is preliminary, but when it is improved it could be very powerful.
Polymer-powered! A polymerization reaction is used to power the first micromotor outside biological systems. The motor employs a form of Grubbs’ catalyst asymmetrically bound to gold–silica Janus microspheres (see picture). These motors show increased diffusion of up to 70 % when placed in solutions of the monomer. The motors also exhibit chemotaxis when placed in a monomer gradient.