Chemical cocktail in skin summons disease-spreading mosquitoes

Mosquitoes that spread Zika, dengue and yellow fever are guided toward their victims by a scent from human skin. The exact composition of that scent has not been identified until now.

A UC Riverside-led team discovered that the combination of carbon dioxide plus two chemicals, 2-ketoglutaric and lactic acids, elicits a scent that causes a mosquito to locate and land on its victim. This chemical cocktail also encourages probing, the use of piercing mouthparts to find blood.

This chemical mixture appears to specifically attract female Aedes aegypti mosquitoes, vectors of Zika as well as chikungunya, dengue, and yellow fever viruses. This mosquito originated in Africa, but has spread to tropical and subtropical regions worldwide, including the U.S.

This new research finding, and how the team discovered it, is detailed in the journal Scientific Reports. "Though others have identified compounds that attract mosquitoes, many of them don't elicit a strong, rapid effect. This one does," said Ring Cardé, UCR entomologist.

Mosquitoes use a variety of cues to locate their victims, including carbon dioxide, sight, temperature, and humidity. However, Cardé's recent research shows skin odors are even more important for pinpointing a biting site.

"We demonstrated that mosquitoes land on visually indistinct targets imbued with these two odors, and these targets aren't associated with heat or moisture," Cardé said. "That leaves skin odor as the key guiding factor."

Given the significance of odor in helping mosquitoes successfully feed on humans, Cardé wanted to discover the exact chemicals that make our scent so potent for the insects. Part of the equation, lactic acid, was identified as one chemical element in the odor cocktail as long ago as 1968.

Since then, several studies have identified that carbon dioxide combined with ammonia, and other chemicals produced by humans also attract these mosquitoes. However, Cardé, who has studied mosquitoes for 26 years, felt these other chemicals were not strong attractants.

"I suspected there was something undiscovered about the chemistry of odors luring the yellow fever mosquito," Cardé said. "I wanted to nail down the exact blend."

Methods that chemists typically use to identify these chemicals would not have worked for 2-ketoglutaric acid, Cardé said. Gas chromatography, which separates chemicals by their molecular weight and polarity, would have missed this acid.

"I think that these chemicals may not have been found before because of the complexity of the human odor profile and the minute amounts of these compounds present in sweat," said chemist Jan Bello, formerly of UCR and now with insect pest control company Provivi.

Searching for mosquito attractors, Cardé turned to Bello, who extracted compounds from the sweat in his own feet. He filled his socks with glass beads and walked around with the beads in his socks for four hours per odor collection.

"Wearing the beads felt almost like a massage, like squeezing stress balls full of sand, but with your feet," said Bello. 'The most frustrating part of doing it for a long time is that they would get stuck in between your toes, so it would be uncomfortable after a while."

The inconvenience was worth the investment. Bello isolated chemicals from the sweat deposited on the sock beads and observed the mosquitoes' response to those chemicals. In this way, the most active combination emerged.

Future studies are planned to determine whether the same compound is effective for any other mosquitoes, and why there is such variation in how individuals are apt to be bitten. "Some are more attractive than others to these mosquitoes, but no one's yet established why this is so," Cardé said.

Though this discovery may not lead to insights for the development of new repellants, the research team is hopeful their discovery can be used to attract, trap, and potentially kill disease-spreading mosquitoes.

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Scientists craft living human skin for robots

From action heroes to villainous assassins, biohybrid robots made of both living and artificial materials have been at the center of many sci-fi fantasies, inspiring today's robotic innovations. It's still a long way until human-like robots walk among us in our daily lives, but scientists from Japan are bringing us one step closer by crafting living human skin on robots. The method developed, presented June 9 in the journal Matter, not only gave a robotic finger skin-like texture, but also water-repellent and self-healing functions.

"The finger looks slightly 'sweaty' straight out of the culture medium," says first author Shoji Takeuchi, a professor at the University of Tokyo, Japan. "Since the finger is driven by an electric motor, it is also interesting to hear the clicking sounds of the motor in harmony with a finger that looks just like a real one."

Looking "real" like a human is one of the top priorities for humanoid robots that are often tasked to interact with humans in healthcare and service industries. A human-like appearance can improve communication efficiency and evoke likability. While current silicone skin made for robots can mimic human appearance, it falls short when it comes to delicate textures like wrinkles and lacks skin-specific functions. Attempts at fabricating living skin sheets to cover robots have also had limited success, since it's challenging to conform them to dynamic objects with uneven surfaces.

"With that method, you have to have the hands of a skilled artisan who can cut and tailor the skin sheets," says Takeuchi. "To efficiently cover surfaces with skin cells, we established a tissue molding method to directly mold skin tissue around the robot, which resulted in a seamless skin coverage on a robotic finger."

To craft the skin, the team first submerged the robotic finger in a cylinder filled with a solution of collagen and human dermal fibroblasts, the two main components that make up the skin's connective tissues. Takeuchi says the study's success lies within the natural shrinking tendency of this collagen and fibroblast mixture, which shrank and tightly conformed to the finger. Like paint primers, this layer provided a uniform foundation for the next coat of cells -- human epidermal keratinocytes -- to stick to. These cells make up 90% of the outermost layer of skin, giving the robot a skin-like texture and moisture-retaining barrier properties.

The crafted skin had enough strength and elasticity to bear the dynamic movements as the robotic finger curled and stretched. The outermost layer was thick enough to be lifted with tweezers and repelled water, which provides various advantages in performing specific tasks like handling electrostatically charged tiny polystyrene foam, a material often used in packaging. When wounded, the crafted skin could even self-heal like humans' with the help of a collagen bandage, which gradually morphed into the skin and withstood repeated joint movements.

"We are surprised by how well the skin tissue conforms to the robot's surface," says Takeuchi. "But this work is just the first step toward creating robots covered with living skin." The developed skin is much weaker than natural skin and can't survive long without constant nutrient supply and waste removal. Next, Takeuchi and his team plan to address those issues and incorporate more sophisticated functional structures within the skin, such as sensory neurons, hair follicles, nails, and sweat glands.

Read more at Science Daily

Electronic skin: Physicist develops multisensory hybrid material

The "smart skin" developed by Anna Maria Coclite is very similar to human skin. It senses pressure, humidity and temperature simultaneously and produces electronic signals. More sensitive robots or more intelligent prostheses are thus conceivable.

The skin is the largest sensory organ and at the same time the protective coat of the human being. It "feels" several sensory inputs at the same time and reports information about humidity, temperature and pressure to the brain. For Anna Maria Coclite, a material with such multisensory properties is "a kind of 'holy grail' in the technology of intelligent artificial materials. In particular, robotics and smart prosthetics would benefit from a better integrated, more precise sensing system similar to human skin." The ERC grant winner and researcher at the Institute of Solid State Physics at TU Graz has succeeded in developing the three-in-one hybrid material "smart skin" for the next generation of artificial, electronic skin using a novel process. The result of this pioneering research has now been published in the journal Advanced Materials Technologies.

As delicate as a fingertip

For almost six years, the team worked on the development of smart skin as part of Coclite's ERC project Smart Core. With 2,000 individual sensors per square millimetre, the hybrid material is even more sensitive than a human fingertip. Each of these sensors consists of a unique combination of materials: an smart polymer in the form of a hydrogel inside and a shell of piezoelectric zinc oxide. Coclite explains: "The hydrogel can absorb water and thus expands upon changes in humidity and temperature. In doing so, it exerts pressure on the piezoelectric zinc oxide, which responds to this and all other mechanical stresses with an electrical signal." The result is a wafer-thin material that reacts simultaneously to force, moisture and temperature with extremely high spatial resolution and emits corresponding electronic signals. "The first artificial skin samples are six micrometres thin, or 0.006 millimetres. But it could be even thinner," says Anna Maria Coclite. In comparison, the human epidermis is 0.03 to 2 millimetres thick. The human skin perceives things from a size of about one square millimetre. The smart skin has a resolution that is a thousand times smaller and can register objects that are too small for human skin (such as microorganisms).

Material processing at the nanoscale

The individual sensor layers are very thin and at the same time equipped with sensor elements covering the entire surface. This was possible in a worldwide unique process for which the researchers combined three known methods from physical chemistry for the first time: a chemical vapour deposition for the hydrogel material, an atomic layer deposition for the zinc oxide and nanoprint lithography for the polymer template. The lithographic preparation of the polymer template was the responsibility of the research group "Hybrid electronics and structuring" headed by Barbara Stadlober. The group is part of Joanneum Research's Materials Institute based in Weiz.

Several fields of application are now opening up for the skin-like hybrid material. In healthcare, for example, the sensor material could independently detect microorganisms and report them accordingly. Also conceivable are prostheses that give the wearer information about temperature or humidity, or robots that can perceive their environment more sensitively. On the path to application,smart skin scores with a decisive advantage: the sensory nanorods -- the "smart core" of the material -- are produced using a vapor-based manufacturing process. This process is already well established in production plants for integrated circuits, for example. The production of smart skin can thus be easily scaled and implemented in existing production lines.

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