04 Aug 2006
The human eye has inspired researchers who are developing a self-focusing artificial lens.
Researchers at the University of Winsconsin-Madison, US , have developed an artificial microlens that can focus without the need for external control. According to the team, the self-focusing lens could be used in imaging, displays and medical diagnostics (Nature 442 551).
"Our lens is unique since it autonomously refocuses without an external control system that uses sensors and feedback systems to tune the focal length," Hongrui Jiang, the lead researcher, told optics.org. "We were inspired by the human eye, in which the ciliary muscles adjust the focusing of the pupil."
The key feature of the microlens are stimuli-responsive hydrogels, which "sense" the environment and provide the actuation force needed to adjust the curvature of a liquid lens. Hydrogels are polymers that can be tuned to respond to different kinds of stimuli, such as acidity and temperature.
In this case, the liquid lens consisted of a water droplet in an aperture that is covered with a film of oil. The curved water-oil interface acts as a lens with a focal length that depends on its curvature. As the hydrogels expand and contract in response to variations in temperature or acidity, they can be used to automatically adjust the focal length of the liquid lens.
The team says that the lens system is easy and cheap to make and can be constructed on a variety of surfaces. It is also versatile in terms of the lens' shape, which can also be cylindrical.
According to Jiang, the lenses have applications in medical diagnostics and lab-on-chip technologies, as well as being used as simple sensors that give a direct optical output, a visible image or light intensity.
"Flexible, versatile micro-imaging systems are required in medical diagnostics," he said. "In addition, the lens could advance lab-on-a-chip technologies, where bench-top analysis systems need to be shrunk onto tiny chips for faster, cheaper analysis."
Although the lens was designed to respond to changes in temperature and acidity, other hydrogels could be used for response to different stimuli such as light, electric fields and the presence of antigens. "The 'smart' attribute of the lens is versatile since it can be extended to a wide range of chemical, biological or physical parameters by simply patterning the right hydrogel," said Jiang.