A group of researchers located in Australia at Monash University in Victoria are developing a process that could lead to self cleaning wool and silk. They have found a way to coat fibers with titanium dioxide nano-crystals, which break down food and dirt in sunlight. This team of academic researchers was led by Walid Daoud, an organic chemist and non-material's researcher have made natural fibers such as wool, silk, and hemp that will automatically remove food, grime, and even red-wine stains when exposed to sunlight. Apparently investigators are using sunlight as a complementary power resource to erase stains over these natural materials.

Monash University is not unique in developments with self-cleaning materials. Jeffrey Youngblood, engineering professor at Purdue University who is developing self-cleaning materials that repel oil said: 'When you burn something, you oxidize'; 'This titanium dioxide coating is just burning organic matter at room temperature in the presence of light'. Walid Daoud and his colleagues coat the fibers with an invisible and very thin layer of titanium dioxide nanoparticles. This titanium dioxide, which is also used in sunscreens, toothpaste, and paint, is a strong photocatalyst: in the presence of ultraviolet light and water vapor, it forms hydroxyl radicals, which oxidize, or decompose, organic matter. Moreover, Mr. Daoud says: 'these nanocrystals cannot decompose wool and are harmless to skin'. Also, the coating does not change the look and feel of the fabric.

In the case of professionals and workers who use clothes of clear colors such as white and need to remain clean all the time it could be a very interesting breakthrough. The titanium dioxide is also capable of destroying diverse pathogens such as bacteria when exposed to the presence of sunlight, by breaking down the cell walls of the microorganisms. The amazing result is that it should automatically make self-cleaning fabrics especially useful in hospitals and other medical settings. Daoud says that 'self-cleaning property will become a standard feature of future textiles and other commonly used materials to maintain hygiene and prevent the spreading of pathogenic infection, particularly since pathogenic microorganisms can survive on textile surfaces for up to three months'.

The future of the textiles will be ruled by this kind of technology applied to clothes through nanoparticles applications according to Daoud. He also argued that self-cleaning surely will become a standard feature not only in textiles but in other materials in order to maintain hygiene and prevent the spreading of pathogenic infection, particularly since pathogenic microorganisms can survive on textile surfaces for up to three month. However, the application of titanium dioxide to make self cleaning is a not a brand new technology.

For instance, in paints and window glass, titanium dioxide powder is applied as a transparent coating. Daoud and his team use nanocrystals of titanium dioxide in order to create self-cleaning wool. These nanocrystals are four to five nanometers in size. In previous experiments the researchers have made self-cleaning cotton through coating this material directly with these nanocrystals. But in the case of the wool, silk and hemp has proved more difficult. The fiber of these materials is made of a protein named 'keratin' which does not have any reactive chemical groups on its surface to bind with titanium dioxide.

THE NEXT STAGE IS GOING COMMERCIAL..
Talk about clothes which can be cleaned automatically when exposed to the sunlight is something many individual groups, companies and other group will consume in order to reduce costs of washing these items. Many wool manufacturer are planning to evaluate more in-depth this technology. Daoud Said: 'We are expecting that self-cleaning wools will be available in the general market within two years, once sufficient laboratory and industrial trials have been completed'.

Furthermore the greater importance of this technology is that the general population will have the possibility to limit considerably the use of water, chemicals and even energy, thanks to the advantage of this nanotechnology breakthrough. Rigorous industrial control is the most important step in the commercial development of these fabrics dedicated to self-cleaning technology. This also involves testing whether existing textile manufacturing equipment can be used appropriately and economically in their production.

By: Hector Nicolas Suero

Thin-film organic electronic devices are at the core of the fast growing plastic electronics industry that aims to deliver flexible, lightweight and cheap electronics products to consumers in many different shapes and forms such as disposable or wraparound displays, cheap identification tags, low cost solar cells and chemical and pressure sensitive sensors.

The performance of devices like organic light emitting diodes (OLEDs), flexible solar cells, or plastic electronics is sensitive to moisture because water and oxygen molecules seep past the protective plastic layer over time and degrade the organic materials which form the core of these products. To protect these sensitive devices, barrier technologies have been developed that protect them from environmental degradation. State-of-the-art barrier materials employ metal oxide (MOx) thin films, commonly from aluminum or silicon oxides, which provide excellent protection from atmospheric oxygen and water, but still suffer from two problem areas:
1) Defects such as pinholes, cracks and grain boundaries are common in thin oxide barrier films when fabricated onto plastic substrates. These defects cause a ‘pore effect’, where oxygen and water molecules are able to seep through and penetrate the plastic barrier. 2) MOx films are brittle, which can result in cracks upon repeated flexing.

A new study demonstrates a nanocomposite material that can initiate self-healing upon the influx of water through pores and cracks by delivering titanium dioxide nanoparticles to the defective site, which ultimately slows the rate of moisture diffusion to the reactive electronic device.

"The concept of self-healing has become a popular theme in the field of material science" Kenneth J. Balkus, Jr. tells Nanowerk. "While the idea of self-healing has been around for many years, recent studies on the autonomic healing of structural polymers has brought about a new wave of research." (We have reported on several recent activities in this area in previous Spotlights: Nanomaterial, heal thyself and Self-healing nanotechnology anticorrosion coatings as alternative to toxic chromium)
Balkus, a professor of chemistry at the University of Texas at Dallas, points out that, while these studies present a novel method for the autonomic healing of polymer matrices, the application of this strategy to self-healing metal oxides is not possible since the fundamental property of metal oxide thin films in permeation barriers that makes them appealing is their ability to exclude water and oxygen, a feat that polymeric healing cannot achieve.

"This challenge has led us to develop a method to encapsulate highly reactive materials in a polymer shell," says Harvey A. Liu, a student in Balkus's group and first author of a recent paper in Advanced Functional Materials that describes this work ("A Delivery System for Self-Healing Inorganic Films").
"Since the major source of device failure is the influx of moisture through stress-induced cracks, as well as through defects, we have developed a system that is not only physically responsive to flexing, but also chemically responsive to the influx of moisture," Liu describes the team's work. "In order to perform this action we have employed a water-degradable polymer, poly(lactic acid) (PLA), as the shell structure to encapsulate the healing agent, titanium tetrachloride. TiCl4 was chosen because of its rapid reactivity, volatility, and its ability to propagate repair without the introduction of a catalyst."

Liu explains how their proposed delivery system for healing agents works: "The permeation barrier consists of a metal oxide and a polymer. Integrated within the polymer layer are porous fibers composed of a water-degradable polymer encapsulating a reactive metal oxide precursor. The influx of atmospheric moisture through holes in the inorganic layer caused by stress-induced cracks or defects leads to the hydrolysis of the degradable polymer. The degradation of the polymer releases the metal oxide precursor, which diffuses into the crack and subsequently reacts with moisture to form a solid metal oxide to seal the crack."
Liu points out that their strategy does not solve the problem of cracking within the permeation barrier, but it does provide the potential for prolonging the effectiveness of the permeation barriers in excluding moisture, thus prolonging the lifetime of the organic electronic devices.

Interestingly, the technique developed by Balkus's team not only addresses self-healing of thin metal oxide films but can also be considered a method to store and release a highly reactive material in a biodegradable biocompatible polymer; something that could find uses in other areas, for instance drug delivery.
The team is currently exploring the use of new metal oxide precursors and attempts to extend this methodology to other types of films such as coatings for corrosion prevention.

By Michael Berger. Copyright 2008 Nanowerk LLC

This week Nature Nanotechnology journal reveals how scientists from the London Centre for Nanotechnology (LCN) at UCL are using a novel nanomechanical approach to investigate the workings of vancomycin, one of the few antibiotics that can be used to combat so-called ‘superbugs’, such as MRSA.

The researchers, led by Dr Rachel McKendry and Professor Gabriel Aeppli, developed ultra-sensitive probes capable of providing new insight into how antibiotics work, paving the way for the development of more effective new drugs.

“There has been an alarming growth in antibiotic-resistant hospital superbugs such as MRSA and vancomycin-resistant Enterococci (VRE),” said Dr McKendry. “This is a major global health problem and is driving the development of new technologies to investigate antibiotics and how they work.

“The cell wall of these bugs is weakened by the antibiotic, ultimately killing the bacteria,” she continued.

“Our research on cantilever sensors – tiny levers no wider than a human hair – suggests that the cell wall is disrupted by a combination of a local antibiotic and a polymer known as a mucopeptide binding together, and the spatial mechanical connectivity of these events.

“Investigating both these binding and mechanical influences on the cells’ structure could lead to the development of more powerful and effective antibiotics in future.”

During the study Dr McKendry, Joseph Ndieyira, Moyu Watari and co-workers used these cantilever arrays to examine the process that ordinarily takes place in the body when vancomycin binds itself to the surface of the bacteria.

They coated the cantilever array with polymers known as mucopeptides from bacterial cell walls and found that, as the antibiotic attaches itself it generates a surface stress on the bacteria, which can be detected by a tiny bending of the cantilever sensors.

The team suggests that this stress contributes to the disruption of the cell walls and the breakdown of the bacteria.

The interdisciplinary team went on to compare how vancomycin interacts with both non-resistant and resistant strains of bacteria. The ‘superbugs’ are resistant to antibiotics because of a simple mutation that deletes a single hydrogen bond from the structure of their cell walls.

This small change makes it approximately 1,000 times harder for the antibiotic to attach itself to the bug, leaving it much less able to disrupt the cells’ structure, and therefore therapeutically ineffective.

“This work at the LCN demonstrates the effectiveness of silicon-based cantilevers for drug screening applications,” says Professor Gabriel Aeppli, Director of the LCN.

“According to the Health Protection Agency, during 2007 there were around 7,000 cases of MRSA and more than a thousand cases of VRE in England alone. In recent decades the introduction of new antibiotics has slowed to a trickle but without effective new drugs the number of these fatal infections will increase.”

The research was funded by the EPSRC (Speculative Engineering Programme), the IRC in Nanotechnology (Cambridge, UCL and Bristol), the Royal Society and the BBSRC.