Triggered detection and deposition: Toward the repair of microcracks

Developing methods to detect and repair damage in polymers is an active area of research. Many of the previously described methods suffer from the lack of long-term stability of the reagents, which are typically preincorporated into the polymer. Also, they tend to be specific to certain types of polymeric materials. In this paper, we describe a general method for detection and repair of cracks in polymers using a salt-triggered mechanism. The process consists of a polymer embedded with salt that works as a "reporter". Upon addition of a detection or healing agent, damaged areas in the polymer leach out salt, powering flows and activating the reagents in the fluid. Detection is possible with fluorescent quantum dots, which aggregate at the crack site. Repair is shown to occur through two different strategies. The first repair strategy involves high ionic strength triggered destabilization of oil-in-water emulsions, transporting polymerization agents, resulting in polymer deposition at the damage site. The second, more biocompatible strategy, involves using an enzyme, urease, and its catalytic hydrolysis of urea to deposit solid calcium carbonate in the crack. The solution of the detection or healing agent can be added "as needed" thereby overcoming the problem of reagent instability.