Tag Archives: Fan Yang

Chameleon skin (nanomaterial made of gold nanoparticles) for robots

A June 17, 2020 news item on Nanowerk trumpets research into how robots might be able to sport chameleon-like skin one day,

A new film made of gold nanoparticles changes color in response to any type of movement. Its unprecedented qualities could allow robots to mimic chameleons and octopi — among other futuristic applications.

Unlike other materials that try to emulate nature’s color changers, this one can respond to any type of movement, like bending or twisting. Robots coated in it could enter spaces that might be dangerous or impossible for humans, and offer information just based on the way they look.

For example, a camouflaged robot could enter tough-to-access underwater crevices. If the robot changes color, biologists could learn about the pressures facing animals that live in these environments.

Although some other color-changing materials can also respond to motion, this one can be printed and programmed to display different, complex patterns that are difficult to replicate.

This video from the University of California at Riverside researchers shows the material in action (Note: It gets more interesting after the first 20 secs.),

A June 15, 2020 University of California at Riverside (UCR) news release (also on EurekAlert but published on June 17, 2020) by Jules Bernstein, which originated the news item, delves further,

Nanomaterials are simply materials that have been reduced to an extremely small scale — tens of nanometers in width and length, or, about the size of a virus. When materials like silver or gold become smaller, their colors will change depending on their size, shape, and the direction they face.

“In our case, we reduced gold to nano-sized rods. We knew that if we could make the rods point in a particular direction, we could control their color,” said chemistry professor Yadong Yin. “Facing one way, they might appear red. Move them 45 degrees, and they change to green.”

The problem facing the research team was how to take millions of gold nanorods floating in a liquid solution and get them all to point in the same direction to display a uniform color.

Their solution was to fuse smaller magnetic nanorods onto the larger gold ones. The two different-sized rods were encapsulated in a polymer shield, so that they would remain side by side. That way, the orientation of both rods could be controlled by magnets.

“Just like if you hold a magnet over a pile of needles, they all point in the same direction. That’s how we control the color,” Yin said.

Once the nanorods are dried into a thin film, their orientation is fixed in place and they no longer respond to magnets. “But, if the film is flexible, you can bend and rotate it, and will still see different colors as the orientation changes,” Yin said.

Other materials, like butterfly wings, are shiny and colorful at certain angles, and can also change color when viewed at other angles. However, those materials rely on precisely ordered microstructures, which are difficult and expensive to make for large areas. But this new film can be made to coat the surface of any sized object just as easily as applying spray paint on a house.

Though futuristic robots are an ultimate application of this film, it can be used in many other ways. UC Riverside chemist Zhiwei Li, the first author on this paper, explained that the film can be incorporated into checks or cash as an authentication feature. Under normal lighting, the film is gray, but when you put on sunglasses and look at it through polarized lenses, elaborate patterns can be seen. In addition, the color contrast of the film may change dramatically if you twist the film.

The applications, in fact, are only limited by the imagination. “Artists could use this technology to create fascinating paintings that are wildly different depending on the angle from which they are viewed,” Li said. “It would be wonderful to see how the science in our work could be combined with the beauty of art.”

Here’s a link to and a citation for the paper,

Coupling magnetic and plasmonic anisotropy in hybrid nanorods for mechanochromic responses by Zhiwei Li, Jianbo Jin, Fan Yang, Ningning Song & Yadong Yin. Nature Communications volume 11, Article number: 2883 (2020) DOI: https://doi.org/10.1038/s41467-020-16678-8 Published: 08 June 2020

This paper is open access.

Finding a way to prevent sunscreens from penetrating the skin

While nanosunscreens have been singled out for their possible impact on our health, the fact is many sunscreens contain dangerous ingredients penetrating the skin. A Dec. 14, 2015 news item on ScienceDaily describes some research into getting sunscreens to stay on the skin surface avoiding penetration,

A new sunscreen has been developed that encapsulates the UV-blocking compounds inside bio-adhesive nanoparticles, which adhere to the skin well, but do not penetrate beyond the skin’s surface. These properties resulted in highly effective UV protection in a mouse model, without the adverse effects observed with commercial sunscreens, including penetration into the bloodstream and generation of reactive oxygen species, which can damage DNA and lead to cancer.

A US National Institute of Biomedical Imaging and Bioengineering (NIBIB) Dec. 14, 2015 news release, which originated the news item, expands on the theme (Note: Links have been removed),

Commercial sunscreens use compounds that effectively filter out damaging UV light. However, there is concern that these agents have a variety of harmful effects due to penetration past the surface skin. For example, these products have been found in human breast tissue and urine and are known to disrupt the normal function of some hormones. Also, the exposure of the UV filters to light can produce toxic reactive oxygen species that are destructive to cells and tissues and can cause tumors through DNA damage.

“This work applies a novel bioengineering idea to a little known but significant health problem, adds Jessica Tucker, Ph.D., Director of the NIBIB Program in Delivery Systems and Devices for Drugs and Biologics. “While we are all familiar with the benefits of sunscreen, the potential toxicities from sunscreen due to penetration into the body and creation of DNA-damaging agents are not well known. Bioengineering sunscreen to inhibit penetration and keep any DNA-damaging compounds isolated in the nanoparticle and away from the skin is a great example of how a sophisticated technology can be used to solve a problem affecting the health of millions of people.”

Bioengineers and dermatologists at Yale University in New Haven, Connecticut combined their expertise in nanoparticle-based drug delivery and the molecular and cellular characteristics of the skin to address these potential health hazards of current commercial sunscreens.

The news release then goes on to provide some technical details,

The group encapsulated a commonly used sunscreen, padimate O (PO), inside a nanoparticle (a very small molecule often used to transport drugs and other agents into the body). PO is related to the better-known sunscreen PABA.

The bioadhesive nanoparticle containing the sunscreen PO was tested on pigs for penetration into the skin. A control group of pigs received the PO alone, not encapsulated in a nanoparticle. The PO penetrated beyond the surface layers of skin where it could potentially enter the bloodstream through blood vessels that are in the deeper skin layers. However, the PO inside the nanoparticle remained on the surface of the skin and did not penetrate into deeper layers.

Because the bioadhesive nanoparticles, or BNPs are larger than skin pores it was somewhat expected that they could not enter the body by that route. However, skin is full of hair follicles that are larger than BNPs and so could be a way for migration into the body. Surprisingly, BNPs did not pass through the hair follicle openings either. Tests indicated that the adhesive properties of the BNPs caused them to stick to the skin surface, unable to move through the hair follicles.

Further testing showed that the BNPs were water resistant and remained on the skin for a day or more, yet were easily removed by towel wiping. They also disappeared in several days through natural exfoliation of the surface skin.

BNPs enhance the effect of sunscreen

An important test was whether the BNP-encapsulated sunscreen retained its UV filtering properties. The researchers used a mouse model to test whether PO blocked sunburn when encapsulated in the BNPs. The BNP formulation successfully provided the same amount of UV protection as the commercial products applied directly to the skin of the hairless mouse model. Surprisingly, this was achieved even though the BNPs carried only a fraction (5%) of the amount of commercial sunblock applied to the mice.

Finally, the encapsulated sunscreen was tested for the formation of damaging oxygen-carrying molecules known as reactive oxygen species, (ROS) when exposed to UV light. The researchers hypothesized that any ROS created by the sunscreen’s interaction with UV would stay contained inside the BNP, unable to damage surrounding tissue. Following exposure to UV light, no damaging ROS were detected outside of the nanoparticle, indicating that any harmful agents that were formed remained inside of the nanoparticle, unable to make contact with the skin.

“We are extremely pleased with the properties and performance of our BNP formulation,” says senior author Mark Saltzman, Ph.D., Yale School of Engineering and Applied Science. “The sunscreen loaded BNPs combine the best properties of an effective sunscreen with a safety profile that alleviates the potential toxicities of the actual sunscreen product because it is encapsulated and literally never touches the skin.” Adds co-senior author, Michael Girardi, M.D. “Our nanoparticles performed as expected, however, these are preclinical findings. We are now in a position to assess the effects on human skin.”

So, all of this work has been done on animal models, which means that human clinical trials are the likely next step. As we wait, here’s a link to and a citation for this group’s paper,

A sunblock based on bioadhesive nanoparticles by Yang Deng, Asiri Ediriwickrema, Fan Yang, Julia Lewis, Michael Girardi, & W. Mark Saltzman. Nature Materials 14, 1278–1285 (2015) doi:10.1038/nmat4422 Published online 28 September 2015

This paper is behind a paywall.

Safer sunblock and bioadhesive nanoparticles from Yale University

The skin has a lot of protective barriers but it’s always possible to make something better so a sunblock that doesn’t penetrate the* skin at all seems like it might be a good thing. Interestingly, this new sunblock or sunscreen is enabled by nanoparticles but not the metallic nanoparticles found in what are sometimes called nanosunscreens. From a Sept. 29, 2015 news item on Nanowerk,

Researchers at Yale have developed a sunscreen that doesn’t penetrate the skin, eliminating serious health concerns associated with commercial sunscreens.

Most commercial sunblocks are good at preventing sunburn, but they can go below the skin’s surface and enter the bloodstream. As a result, they pose possible hormonal side effects and could even be promoting the kind of skin cancers they’re designed to prevent.

But researchers at Yale have developed a new sunblock, made with bioadhesive nanoparticles, that stays on the surface of the skin.

A Sept. 28, 2015 Yale University news release by William Weir, whch originated the news item, describes the research in more detail,

“We found that when we apply the sunblock to the skin, it doesn’t come off, and more importantly, it doesn’t penetrate any further into the skin,” said the paper’s senior author, Mark Saltzman, the Goizueta Foundation Professor of Biomedical Engineering. “Nanoparticles are large enough to keep from going through the skin’s surface, and our nanoparticles are so adhesive that they don’t even go into hair follicles, which are relatively open.”

Using mouse models, the researchers tested their sunblock against direct ultraviolet rays and their ability to cause sunburn. In this regard, even though it used a significantly smaller amount of the active ingredient than commercial sunscreens, the researchers’ formulation protected equally well against sunburn.

They also looked at an indirect — and much less studied — effect of UV light. When the active ingredients of sunscreen absorb UV light, a chemical change triggers the generation of oxygen-carrying molecules known as reactive oxygen species (ROS). If a sunscreen’s agents penetrate the skin, this chemical change could cause cellular damage, and potentially facilitate skin cancer.

“Commercial chemical sunblock is protective against the direct hazards of ultraviolet damage of DNA, but might not be against the indirect ones,” said co-author Michael Girardi, a professor of dermatology at Yale Medical School. “In fact, the indirect damage was worse when we used the commercial sunblock.”

Girardi, who specializes in skin cancer development and progression, said little research has been done on the ultimate effects of sunblock usage and the generation of ROS, “but obviously, there’s concern there.”

Previous studies have found traces of commercial sunscreen chemicals in users’ bloodstreams, urine, and breast milk. There is evidence that these chemicals cause disruptions with the endocrine system, such as blocking sex hormone receptors.

To test penetration levels, the researchers applied strips of adhesive tape to skin previously treated with sunscreen. The tape was then removed rapidly, along with a thin layer of skin. Repeating this procedure allowed the researchers to remove the majority of the outer skin layer, and measure how deep the chemicals had penetrated into the skin. Traces of the sunscreen chemical administered in a conventional way were found to have soaked deep within the skin. The Yale team’s sunblock came off entirely with the initial tape strips.

Tests also showed that a substantial amount of the Yale team’s sunscreen remained on the skin’s surface for days, even after exposure to water. When wiped repeatedly with a towel, the new sunblock was entirely removed. [emphasis mine]

To make the sunblock, the researchers developed a nanoparticle with a surface coating rich in aldehyde groups, which stick tenaciously to the outer skin layer. The nanoparticle’s hydrophilic layer essentially locks in the active ingredient, a hydrophobic chemical called padimate O.

Some sunscreen solutions that use larger particles of inorganic compounds, such as titanium dioxide or zinc oxide, also don’t penetrate the skin. For aesthetic reasons, though, these opaque sunscreen products aren’t very popular. By using a nanoparticle to encase padimate O, an organic chemical used in many commercial sunscreens, the Yale team’s sunblock is both transparent and stays out of the skin cells and bloodstream.

This seems a little confusing to me and I think clarification may be helpful. My understanding is that the metallic nanoparticles (nano titanium dioxide and nano zinc oxide) engineered for use in commercial sunscreens are also (in addition to the macroscale titanium dioxide and zinc oxide referred to in the Yale news release) too large to pass through the skin. At least that was the understanding in 2010 and I haven’t stumbled across any information that is contradictory. Here’s an excerpt from a July 20, 2010 posting where I featured portions of a debate between Georgia Miller (at that time representing Friends of the Earth) and Dr. Andrew Maynard (at that time director of the University of Michigan Risk Science Center and a longtime participant in the nanotechnology risk discussions),

Three of the scientists whose work was cited by FoE as proof that nanosunscreens are dangerous either posted directly or asked Andrew to post comments which clarified the situation with exquisite care,

Despite FoE’s implications that nanoparticles in sunscreens might cause cancer because they are photoactive, Peter Dobson points out that there are nanomaterials used in sunscreens that are designed not to be photoactive. Brian Gulson, who’s work on zinc skin penetration was cited by FoE, points out that his studies only show conclusively that zinc atoms or ions can pass through the skin, not that nanoparticles can pass through. He also notes that the amount of zinc penetration from zinc-based sunscreens is very much lower than the level of zinc people have in their body in the first place. Tilman Butz, who led one of the largest projects on nanoparticle penetration through skin to date, points out that – based on current understanding – the nanoparticles used in sunscreens are too large to penetrate through the skin.

However, there may be other ingredients which do pass through into the bloodstream and are concerning.

One other thing I’d like to note. Not being able to remove the sunscreen easily ( “When wiped repeatedly with a towel, the new sunblock was entirely removed.”) may prove to be a problem as we need Vitamin D, which is for the most part obtainable by sun exposure.

In any event, here’s a link to and a citation for the paper,

A sunblock based on bioadhesive nanoparticles by Yang Deng, Asiri Ediriwickrema, Fan Yang, Julia Lewis, Michael Girardi, & W. Mark Saltzman. Nature Materials (2015) doi:10.1038/nmat4422 Published online 28 September 2015

This paper is behind a paywall.

*’teh’ changed to ‘the’ on June 6, 2016.