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Adaptable ‘skin’

Hydrogel changes wet suit’s water flow for better protection

Divers may one day have a wet suit that automatically adapts to prevailing environmental and operational conditions for improved thermal protection.

The new wet suit uses “SmartSkin,” a patent-pending technology that represents a disruptive technological advance in wet suit fabrics. SmartSkin works by adjusting the permeability of the fabric’s inner layer through the action of a thermally-sensitive polymer hydrogel.

The gel transforms the suit into a thermally-activated flow control system, which permits increased flow of water through the wet suit material when the diver is warm, but expands to cut off flow when the diver’s skin temperature drops below a preset threshold temperature. The effect is regulation of skin temperature in a wide range of diving conditions.

The product, funded through the Small Business Innovative Research program, is a joint development effort between Midé Technology Corporation of Medford, Mass., the U.S. Special Operations Command of MacDill Air Force Base, Fla., and the U.S. Navy Clothing and Textile Research Facility, an installation partner at the U.S. Army Soldier Systems Center (Natick).

“The Special Operations Forces were interested in exploring technologies to protect surface swimmers from cold water exposure,” said Cleveland Heath, a textile technologist at the Navy facility. “The ultimate goal of the project was to create an ensemble for operations in extreme environments capable of transitioning from a water to land environment with no external power. They knew we had a hydro-environmental simulator and submersible instrumented thermal manikin, capable of quantifying the benefits of any technological advancements for in-water applications, so approaching the Navy was a logical choice to fulfill their need.”

A dry suit offers divers the best protection in cold water by totally encapsulating the wearer and maintaining an insulative air layer, but it is bulky and requires skilled use.

A semi-dry suit offers the next best level of protection by using rubber seals at the neck, wrists and ankles. Unfortunately, the seals tend to be tight and uncomfortable and, because these suits are so good at preventing flushing, divers often overheat in warmer conditions.

Although traditional wet suits protect at a lower level, they tend to be more comfortable because they lack tight seals. In addition to the insulation value provided by the base material, these suits offer thermal protection by limiting flushing through close fit over the entire body.

SmartSkin suit
It looks like an ordinary wet suit, but the SmartSkin suit protects the user under a wider range of water temperatures.

Mimicking the contours of the body to ensure close fit is difficult, meaning that gaps and voids, particularly in areas of drastic shape change such as joints, are unavoidable. Motion causes the volume of these cavities to change and the suit acts like a pump. The flushing of water through the suit results in a continuous loss of body heat through forced convection, a mechanism that is responsible for up to 60 percent of the total heat loss.

“It is here that the opportunity exists to improve the fundamental function of the ordinary wetsuit,” said Marco Serra, senior engineer and project lead at Midé Technology Corporation. “If the rate at which water flushes through the suit can be controlled, the temperature of the diver can be regulated.”

With SmartSkin, the hydrogel absorbs water and expands, reducing the permeability of the inner foam layer. This creates a seal, trapping the heated water layer inside the suit and making it difficult for additional water to flush through.

“The beauty of the system is that if the trapped water becomes too warm and the diver begins to overheat, the system reverses—water is expelled from the hydrogel, the foam reduces thickness and the flushing exchange begins again, thereby cooling the wearer,” Heath said.

Heath is the contracting officer’s technical representative for the project. He said Midé’s original goal was to increase thermal protection as the composite fabric became thicker with decreased water temperature.

After Heath suggested that Midé explore using the hydrogel as a mechanism to control flushing, Midé identified the results of a laboratory study that confirmed this was the way to go. Initial laboratory experiments were conducted, demonstrating that water flow could be regulated using the novel technology in this application. Consequently, Midé developed the SmartSkin composite fabric into its current form.

The resulting SmartSkin suit looks like a conventional wet suit. The outer skin, which provides structural integrity, is made of closed-cell neoprene foam typical of wet suits. The inner layer contains the active material.

Although much of the suit is still made in the same way as ordinary wet suits, portions use the composite SmartSkin fabric, which is strategically placed in the torso, forearms and calves to control water movement within the suit.

In October 2001, Midé compared the performance of a SmartSkin prototype suit to that of a conventional suit using the Navy facility’s submersible, instrumented manikin. Since the concept relies on water flushing through the suit, tests were done using the facility’s wave generator.

In this test Midé successfully demonstrated SmartSkin’s ability to alter the thermal protection capabilities of the suit and adapt to environmental conditions.

“Manikin testing quantified the results to prove the concept before we could recommend an optimum configuration for user testing,” Heath said. “We tested suits with no hydrogel, all hydrogel and partial hydrogel. Using partial hydrogel to strategically control the flushing gave us the desired results with the minimum use of hydrogel-laden foam.”

NCTRF's hydro-environmental simulator
NCTRF’s hydro-environmental simulator performs instrumented tests on a thermal manikin wearing the SmartSkin suit. The facility is capable of quantifying the benefits of any technological advancements for in-water applications.

When tested in warm water, the two suits offered nearly the same protection. However, in cold water, SmartSkin provided a 70 percent improvement. As a result of the manikin data, Midé envisions being able to significantly reduce the thickness of the outer layer of neoprene, thereby improving mobility and reducing garment weight.

The hydrogel for the SmartSkin prototype tested on the manikin was engineered for freshwater. Since the gels react differently depending on the surrounding environment, a second saltwater version of the hydrogel was subsequently produced. Indications in the laboratory have confirmed that the saltwater hydrogel behaves as well as the original prototype hydrogel, according to Heath.

“SmartSkin suits allow surface swimmers and divers to operate in a wider range of temperatures without having to possess a range of suit thicknesses,” Serra said. “Divers and surfers in particular would find it helpful, although we would be looking at designs optimized for each application to take specific needs into account. The two activities are very different, and it is important to recognize that when designing the product.”

Other potential markets include the Navy shipboard community and commercial fishermen, where the technology could be adapted to survival suits for accidental immersion. Midé is seeking funding to move to the program’s final phase of commercialization and explore further application possibilities.

“Although we remain cautiously optimistic, there’s enough interest from the user-community to recommend follow-up funding to further the technology, and certainly an opportunity for recreational use in a market which has not seen a realistic technological advancement in many years,” Heath said.

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