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Non-toxic Insect-resistant Textiles for Military Clothing and Equipment

Description:

OBJECTIVE: Design and develop a novel, non-toxic, textile system for use in military clothing and equipment that will hinder arthropod-human contact and so reduce risk of exposure to insect-borne disease. DESCRIPTION: The most common means of avoiding insect bites or stings is through application of chemical formulations (insecticidal or repellent) to skin or clothing. Further measures undertaken on a broader scale will often include spraying or otherwise treating insect breeding areas with more potent insecticidal formulations. In the military, the current standard of protection for individuals required by the Department of Defense (DoD) is the DoD Insect Repellent System which consists of 1) a permethrin treated uniform; 2) DEET applied on exposed skin; and 3) proper wear of the military uniform [1]. The factory treated permethrin uniform was first issued to soldiers in July 2010, as the Flame-Resistant Army Combat Uniform, FR ACU-P (in both the Universal Camouflage Pattern and the OCP, Operation Enduring Freedom Camouflage Pattern, aka Multicam) which is made of a permethrin impregnated textile, in addition to the FR treatment. Future plans include issuance of the factory-treated non flame resistant Army Combat Uniform (ACU), most likely in 2013 [2]. Currently the ACU is required to be individually treated by the soldier or at the unit level, using the required permethrin application kit [3]. While effective, the DoD Insect Repellent System has several critical drawbacks. First, there is often a problem of compliance. When strictly adhering to the System, the soldier can expect excellent protection. However, surveys of troops redeploying from theatres of operation, as well as the rates of vector-borne diseases from recent operations, indicate that the use of any of the required protective measures, particularly the topical repellent, is low among service members [4]. In addition, there is a growing body of evidence that points to a rapidly developing biological resistance of the insect vector to existing insecticidal chemical formulations [5-8]. There is also significant concern regarding unintended harm to benign organisms: permethrin is a broad spectrum chemical, so in addition to eliminating the intended pest, it is also highly toxic to fish and aquatic life, honeybees and other insects, as well as to some mammals [9]. There are other environmental and ecological concerns. The permethrin treatments have a limited life span, and with normal wear and usage, as well as laundering of the ACU there will be loss of permethrin content, perhaps to the home environment as well as possible contamination into the wastewater stream from wash cycles. In addition, certain individuals, such as pregnant female soldiers or people with chemical sensitivities, may wish to avoid contact with permethrin treated fabrics. Finally, eventual disposal of the uniforms may raise the question of whether or not these textiles can safely be buried in landfills without further contamination of the ecosystem. There is a clear need to develop an alternative to permethrin treated textiles that can provide a safe, non-toxic method of protecting humans from contact with insect vectors to prevent the transmission of serious, debilitating diseases. However, the main challenge to finding such a solution is that the textile must be comfortable to wear in hot and humid climates. Any textile that is even moderately tightly woven or thick enough will prevent a mosquito from penetrating the clothing layer and reaching the skin of the target host. Fur on an animal host is highly effective at preventing insects from stinging or biting. But for the specific application of insect resistant clothing, the textile must meet thermophysiological requirements so that it will be tolerable to wear in the expected climate conditions. In summary, the requirements will be to develop and apply processing techniques or structural design to fabrics or fibers to be used in the production of textiles for soldier clothing or other personal use (bed nets, sleeping bags, tent materials etc.) that will hinder or prevent contact of the insect vector with human skin. The novel textile system may be based on a fabric coating or treatment that will thwart insect stings or bites, or a textile structure itself that will provide a physical barrier to insect attack. The method of protection must be via a mechanical or physical interference with the mode of insect attack, or other means of deterrence, for example, optical, electrostatic, acoustic, or other, so long as there is no deleterious effect of the protective mechanism on the human user. In addition, the clothing textiles must be comfortable to wear in warm and humid weather conditions, breathable, lightweight, and launderable, and all textiles should have no negative impact on the environment in terms of life cycle use or end of use disposal issues. Finally, the textile must be able to be produced in sufficient quantities for practical application to the clothing and equipment markets. PHASE I: Develop an initial design for an innovative textile or textile system that will prevent direct contact of the hematophagous organism (e.g. sandfly, blackfly, tsetse fly, bedbug, mosquito, tick, louse, mite, midge, or flea) with human skin. For baseline design concepts and evaluation of protective capability against insects, the mosquito will be used as the target pest. The design criteria for insect resistant textiles may be dependent on mosquito anatomy such as proboscis length and diameter [9], or mosquito sensory capabilities. The proposed textile must have unique characteristics such that it will function as a protective barrier, while still meeting thermophysiological requirements. These characteristics may include but are not limited to high fabric thickness, surface or near-surface impenetrability, or an ultra-smooth surface that make it difficult for the insect to maintain contact. The design criteria for insect resistant textiles will also be dependent on comfort parameters. For example, the textile must provide adequately sized pores that offer good air circulation but will hinder the insect from making direct contact with the skin [10]. To demonstrate proof of concept, produce 3-5 different textile systems and measure protective capability of the novel fabrics against live mosquitoes by using an in vitro bioassay system such as the Klun & Debboun module bioassay system [11] or an in vivo method using human volunteers which is based on ASTM 951-94 (2006),"Laboratory Testing of Non-Commercial Mosquito Repellent Formulations On the Skin"[12]. In general, in vivo bioassays are preferable to in vitro testing. Textiles must demonstrate a minimum of 70% bite protection by either method. Evaluate expected comfort parameters of the novel textiles through characterization of fabric swatches for thermal conductivity, moisture vapor transport, and tactile properties. Novel textiles produced for phase I should be in sufficient quantities to allow performance testing and comfort characterization. Phase I final report should include discussion of risk assessment regarding potential toxicity issues. The finished textiles should not present a health hazard and are expected to demonstrate compatibility with prolonged, direct skin contact when tested in Phase II. If there is sufficient historical use data, toxicity testing may not be required. For novel textiles, physical properties including weight, tearing strength, air permeability, and wicking should not vary by more than 10% from the current U.S. Army Combat Uniform (FR ACU or ACU) or current U.S. Army Combat Shirt (ACS) standards. Army Combat Uniform WEIGHT, oz/sq. yd. Min: 5.5 Max: 8.5 BREAKING STRENGTH, lbs (min) Warp: 100 Filling: 80 AIR PERMEABILITY, cu ft./min/sq. ft Min: 10.0 TEARING STRENGTH, lbs. (Min.) Dry Warp: 4.0 Filling: 4.0 DIMENSIONAL STABILITY; % (Max. after five wash cycles) 5.0 Army Combat Shirt WEIGHT (oz./sq. yd.) Min: 5.2 Max: 6.9 BURSTING STRENGTH, lbs Min: 35 AIR PERMEABILITY, cu.ft./min./sq. ft. Min: 30.0 WICKING, inches/hour (Length and Width) Min: 3.0 DIMENSIONAL STABILITY; % (Max. after five wash cycles) 9.0 Multi-functionality in the novel textile system is acceptable, for example insect resistance and flame resistance, or insect resistance and fragmentation protection. PHASE II: For textiles that performed well in Phase I both against live mosquitoes and for comfort testing, expand and refine the original design concept to enhance performance and comfort levels. Use human volunteer studies for evaluation of efficacy against insect bites, for example, the arm-in-cage method [13], as well as larger scale testing of textiles for comfort parameters, such as instrumented manikins. Provide a detailed plan for the scale-up of textile production so that sufficient quantities of materials can be produced using current (or other practicable manufacturing methods) by the clothing and individual equipment industry. Required Phase II deliverables will include 2-4 improved textile systems with additional materials for performance and comfort evaluation, as well as 2-4 examples of finished clothing using the improved materials. Textile properties and a detailed report of test results must be provided. Human toxicity will also need to be considered and the safety of the materials confirmed. If there is sufficient historical use data, toxicity testing may not be required. If toxicity testing is required this will be conducted in a two phase study: 1) an acute dermal irritation study and a skin sensitization study shall be conducted on laboratory animals, and 2) when the results of these studies indicate the cloth is not a sensitizer or irritant, a Repeat Insult Patch Test shall be performed in accordance with the Modified Draize Procedure [14]. If performed, toxicity test results should be included in the detailed report. PHASE III: Insect-resistant textiles produced for use in military clothing will have clear application to the commercial market as well. Vector borne disease is a world-wide problem of enormous scale and devastating impact, particularly in less developed countries. Protective textiles for use as bednets or clothing that use non-chemical methods are not vulnerable to issues of biological resistance, and could play a significant role in reducing prevalence of disease. For the domestic sports and athletic clothing market, insect resistant textiles may also provide a preferred alternative to chemically treated fabrics. REFERENCES: [1] U.S. Army Center for Health Promotion and Preventive Medicine, DoD Insect Repellent System, June 2007, http://phc.amedd.army.mil/PHC%20Resource%20Library/DODInsectRepellentSystemJustheFacts-June2007.pdf, accessed March 13, 2012. [2] Program Executive Office- Soldier, Flame Resistant Army Combat Uniform- Permethrin (FR ACU-P), https://peosoldier.army.mil/faqs/fracu.asp; accessed March 21, 2012. [3] Soldiers can still field treat their ACU"s with permethrin using the standard military clothing repellent products: aerosol spray (NSN 6840-01-278-1336) or Individual dynamic Absorption (IDA) kit (NSN 6840-01-345-0237). At the unit level, ACUs are treated with permethrin via DoD-certified applicators and a two-gallon sprayer (NSN 6840-01-334-2666). [4] Hemingway J, Hawkes NJ, McCarroll L, Ranson H, 2004. The molecular basis of insecticide resistance in mosquitoes. Insect Biochem Mol Biol 34: 653665. [5] Savedra-Rodriguez K, Strode C, Suarez AF, Salas IF, Ranson H, Hemingway J, Black WC IV, 2008. QTL mapping of genome regions controlling permethrin resistance in the mosquito Aedes aegypti. Genetics 180: 11371152. [6] Matowo, J., Kulkarni, M.A., Mosha, F.W., Oxborough, R.M., Kitau, J.A., Tenu, F. & Rowland, M. (2010). Biochemical basis of permethrin resistance in Anopheles arabiensis from Lower Moshi, northeastern Tanzania. Malaria Journal 9:193. [7] Betson M, Jawara M, Awolola S. Status of insecticide susceptibility in Anopheles gambiae s.l. from malaria surveillance sites in The Gambia. Malar J. 2009;8:187. [8] Toynton, K.; Luukinen, B.; Buhl, K.; Stone, D. 2009. Permethirn Technical Fact Sheet; National Pesticide Information Center, Oregon State University Extension Services. http://npic.orst.edu/factsheets/Permtech.pdf. [9] Ramasubramanian MK, Barham OM, Swaminathan V. Mechanics of a mosquito bite with applications to microneedle design. Bioinspir Biomim. 2008; 3:046001. [10] Collins, Lynda E.,"Non Chemical Insecticidal Textiles", Master Thesis submitted to North Carolina State University, Raleigh, NC 2008. [11] A. J. Klun et al., A new in vitro bioassay system for discovery of novel human-use mosquito repellents, J. Am. Mosq. Control Assoc., 21, 64, 2005. [12] American Society for Testing and Materials [ASTM] Laboratory Testing of Non-Commercial Mosquito Repellent Formulations On the Skin, ASTM-E951-94(2006). [13] U.S. Environmental Protection Agency, Office of Chemical Safety and Pollution Prevention (OCSPP), OCSPP Harmonized Test Guidelines, Series 810 - Product Performance Test Guidelines: OPPTS 810.3700: Insect Repellents to be Applied to Human Skin (July 2010), http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPPT-2009-0150-0011. [14] Repeat Insult Patch Test - Modified Draize Procedure; Principles and Methods of Toxicology, (fourth edition) A. Wallace Hayes (editor), pp 1057 - 1060, 2001. Copies are available online at http://www.taylorandfrancis.co.uk/ or from Taylor and Francis, 325 Chestnut Street, Philadelphia PA 19106.
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