Breathable 'second skin' to protect soldiers against biological and chemical threats

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Scientists have created a material that is highly breathable and protective from biological and chemical threats, an advance that promises to protect soldiers in under a decade.

Developed by a team at Lawrence Livermore National Laboratory in California, the material is said to be the first key component of future smart uniforms that will also respond to and protect from environmental chemical hazards. The research appears in Advanced Materials.

High breathability is a critical requirement for protective clothing to prevent heat-stress and exhaustion when military personnel are engaged in missions in contaminated environments. Current protective military uniforms are based on heavyweight full-barrier protection or permeable adsorptive protective attire that cannot meet the critical demand of simultaneous high comfort and protection, and provide a passive rather than active response to an environmental threat.

The LLNL team fabricated flexible polymeric membranes with aligned carbon nanotube (CNT) channels as moisture conductive pores.

"We demonstrated that these membranes provide rates of water vapour transport that surpass those of commercial breathable fabrics like GoreTex, even though the CNT pores are only a few nanometres wide," said Ngoc Bui, lead author of the paper.

To provide high breathability, the new composite material is said to take advantage of the transport properties of carbon nanotube pores. By quantifying the membrane permeability to water vapour, the team found that when a concentration gradient is used as driving force, CNT nanochannels can sustain gas-transport rates exceeding that of a well-known diffusion theory by more than one order of magnitude.

These membranes also provide protection from biological agents due to their very small pore size, which are less than 5nmwide. Biological threats like bacteria or viruses are much larger and typically over 10nm in size.

Tests demonstrated that the CNT membranes repelled Dengue virus from aqueous solutions during filtration tests, thereby confirming that LLNL-developed CNT membranes provide effective protection from biological threats by size exclusion rather than by preventing wetting. Furthermore, the results show that CNT pores combine high breathability and bio-protection in a single functional material.

Researchers Eric Meshot, left, and Ngoc Bui evaluate the uniformity of a carbon nanotube array covering the entire area of a 4-inch wafer [Photo by Julie Rusell/LLNL]
Researchers Eric Meshot, left, and Ngoc Bui evaluate the uniformity of a carbon nanotube array covering the entire area of a 4-inch wafer [Photo by Julie Rusell/LLNL][/figcaption>However, chemical agents are much smaller in size and require the membrane pores to be able to react to block the threat. To encode the membrane with a smart and dynamic response to small chemical hazards, LLNL scientists and collaborators are surface modifying these prototype carbon nanotube membranes with chemical-threat-responsive functional groups.

These functional groups will sense and block the threat. A second response scheme also is in development, which will exfoliate upon reaction with the chemical agent.

"The material will be like a smart second skin that responds to the environment," said Kuang Jen Wu, leader of the LLNL Biosecurity & Bionanosciences Group. "In this way, the fabric will be able to block chemical agents such as sulphur mustard [blister agent], GD and VX nerve agents, toxins such as staphylococcal enterotoxin and biological spores such as anthrax."

Current work is directed toward designing this multifunctional material to undergo a rapid transition from the breathable state to the protective state.

"These responsive membranes are expected to be particularly effective in mitigating a physiological burden because a less breathable but protective state can be actuated locally and only when needed," said Francesco Fornasiero, LLNL's principal investigator of the project.

The new uniforms could be deployed in less than 10 years.