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The idea of a needle and thread being used to sew up a wound makes me queasy, but sutures are a very routine and simple method of treating open wounds from an injury, surgery, or small procedure. The method of closing a wound with a needle and thread is thousands of years old. Although little has changed in the process, there have been several iterations of the material used for the suture including gold, human hair, metal thread, silk, and catgut. At the beginning of the 21st Century, synthetically manufactured, absorbable materials were introduced and quickly became the most popular material option.
New Suture Technology
The next generation of suture material was recently introduced in an article in the nanotechnology magazine called Small. The smart suture materials are electronic sutures, which contain ultrathin silicon sensors integrated on polymer or silk strips. The material can be threaded through needles, laced through skin and knotted without degrading the device. The sensors can measure temperature in the surrounding tissue. A higher temperature would indicate infection causing the micro-heaters to deliver heat to the wound, which is known to aid healing. A professor of materials science and engineering at the University of Illinois at Urbana-Champaign is the inventor of the smart sutures. Professor John Rogers also imagines that the sutures could be laden with devices that provide electrical stimulation or release drugs in a programmed way to heal wounds.
How Smart Sutures Are Made
The smart sutures are made from silicon-based devices that flex and stretch. The silicon membranes and gold electrode wires are just a few hundred nanometers thick and are patterned in a serpentine shape. The researchers first use chemicals to slice off an ultrathin film of silicon from a silicon wafer. A rubber stamp is used to lift off and transfer the nanomembranes to polymer or silk strips. Then they deposit metal electrodes and wires on top and encapsulate the entire device in an epoxy coating. A similar technology is used to create inflatable catheters and medical tattoos.
The smart sutures have the ability to sense the temperature of the surrounding tissue. There are two types of temperature sensors on the sutures. One is a silicon diode that shifts its current output with temperature. The other sensor is a platinum nanomembrane resistor which changes its resistance with temperature. The microheaters are simply gold filaments that heat up when current passes through them. The addition of a drug release system could be accommodated by coating the electrical threads with drug-infused polymers, which would release the chemicals when triggered by heat or an electrical pulse.
The materials used to make the sutures are safe for the body. Researchers said the most difficult part of creating this device was making the silicon flexible. Since silicon is brittle, the nanomembranes had to be made as thin as possible. The silicon needed to be laid out in a winding pattern for elasticity and placed in-between the top layer of epoxy and bottom polymer surface of the suture. "When you bend the entire construct, the top surface is in tension and the bottom is in compression, but at midpoint the strains are very small," said Rogers.
The new suture device may aid in the proper healing of open wounds by ensuring flexibility of the skin and preventing infection in the tissue.
Resources
Smart Sutures That Detect Infections
1. Kim, D.-H., Wang, S., Keum, H., Ghaffari, R., Kim, Y.-S., Tao, H., Panilaitis, B., Li, M., Kang, Z., Omenetto, F., Huang, Y. and Rogers, J. A. (2012), Thin, Flexible Sensors and Actuators as 'Instrumented' Surgical Sutures for Targeted Wound Monitoring and Therapy. Small. doi: 10.1002/smll.201200933
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Re: Smart Sutures Getting Hot
