Programmable living materials made with 3D printing methods and synthetic biology

There’s more than one ‘living’ material story here on this blog; it’s the plant cells that make this latest story different from the others. From a May 1, 2024 news item on phys.org, Note: A link has been removed,

Scientists are harnessing cells to make new types of materials that can grow, repair themselves and even respond to their environment. These solid “engineered living materials” are made by embedding cells in an inanimate matrix that’s formed in a desired shape. Now, researchers report in ACS Central Science that they have 3D printed a bioink containing plant cells that were then genetically modified, producing programmable materials. Applications could someday include biomanufacturing and sustainable construction.

Caption: After 24 days, the colors produced by plant cells in two different bioinks printed in this leaf-shaped engineered living material are clearly visible. Credit: Adapted from ACS Central Science 2024, DOI: 10.1021/acscentsci.4c00338

A May 1, 2024 American Chemical Society (ACS) news release (also on EurekAlert), which originated the news item, explains what makes this living material different,

Recently, researchers have been developing engineered living materials, primarily relying on bacterial and fungal cells as the live component. But the unique features of plant cells have stirred enthusiasm for their use in engineered plant living materials (EPLMs). However, the plant cell-based materials created to date have had fairly simple structures and limited functionality. Ziyi Yu, Zhengao Di and colleagues wanted to change that by making intricately shaped EPLMs containing genetically engineered plant cells with customizable behaviors and capabilities.

The researchers mixed tobacco plant cells with gelatin and hydrogel microparticles that contained Agrobacterium tumefaciens, a bacterium commonly used to transfer DNA segments into plant genomes. This bioink mixture was then 3D printed on a flat plate or inside a container filled with another gel to form shapes such as grids, snowflakes, leaves and spirals. Next, the hydrogel in the printed materials was cured with blue light, hardening the structures. During the ensuing 48 hours, the bacteria in the EPLMs transferred DNA to the growing tobacco cells. The materials were then washed with antibiotics to kill the bacteria. In the following weeks, as the plant cells grew and replicated in the EPLMs, they began producing proteins dictated by the transferred DNA.

In this proof-of-concept study, the transferred DNA enabled the tobacco plant cells to produce green fluorescent proteins or betalains — red or yellow plant pigments that are valued as natural colorants and dietary supplements. By printing a leaf-shaped EPLM with two different bioinks — one that created red pigment along the veins and the other a yellow pigment in the rest of the leaf — the researchers showed that their technique could produce complex, spatially controlled and multifunctional structures. Such EPLMs, which combine the traits of living organisms with the stability and durability of non-living substances, could find use as cellular factories to churn out plant metabolites or pharmaceutical proteins, or even in sustainable construction applications, according to the researchers.

The authors acknowledge funding from National Key Research and Development Program of China, the National Natural Science Foundation of China, the Natural Science Foundation of Jiangsu Province, and the State Key Laboratory of Materials-Oriented Chemical Engineering.

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

Advancing Engineered Plant Living Materials through Tobacco BY-2 Cell Growth and Transfection within Tailored Granular Hydrogel Scaffolds by Yujie Wang, Zhengao Di, Minglang Qin, Shenming Qu, Wenbo Zhong, Lingfeng Yuan, Jing Zhang, Julian M. Hibberd, and Ziyi Yu. ACS Cent. Sci. 2024, 10, 5, 1094–1104 DOI: https://doi.org/10.1021/acscentsci.4c00338 Publication Date:May 1, 2024 Copyright © 2024 The Authors. Published by American Chemical Society. This publication is licensed under CC-BY 4.0.

This paper is open access.

I think the last three years in particular have seen an upsurge of living materials stories (on this blog, at least). This one is a favourite of mine,

If you’re curious to see more, I suggest using the search term ‘living materials’.

Honey-containing nanoemulsion for topical delivery

This April 29, 2024 Xia & He Publishing press release is in fact the abstract for the paper,

Background and objectives

Honey is a viscous, hygroscopic liquid in nature. It has the ability to treat wounds, wrinkles, aging, and inflammation. This study’s objective was to create and characterize a nanoemulsion containing honey and evaluate its stability.

Methods

A pseudo-ternary phase diagram was retraced with several concentrations of the Smix, water, and liquid paraffin oil to formulate nanoemulsions containing honey. From the results of pre-formulation stability studies, formulation HNE-19, with a hydrophilic lipophilic balance value of 10, and a surfactant and oil ratio of 1:1, was selected as the most stable formulation. HNE-19 and base (B-19) were further subjected to thermodynamic studies of heating and cooling cycles and centrifugation. HNE-19 and its respective base B-19 were characterized for physical changes, droplet size analysis, pH measurements, turbidity, viscosity, and rheological parameters for a period of 90 days.

Results

Results showed that the nanoemulsion containing honey was clear and milky white. There was no evidence of phase separation in HNE-19 and B-19 after the thermodynamic study. The droplet size of fresh HNE-19 was 91.07 nm with a zeta potential of −38.5 mV. After three months, the droplet size and zeta potential were 197.06 nm and −32.5 mV respectively. The observed pH was between 5.8 and 6.7, which corresponds with the pH of the skin. HNE-19 showed non-Newtonian flow and pseudo-plastic behaviour.

Conclusions

A honey-loaded nanoemulsion (HNE-19) was successfully developed and characterized for stability. The nanoemulsion was thermodynamically stable. With the good rheology and stability of honey, the size of the nanodroplets was below 200 nm. Throughout the 90-day testing period, the nanoemulsion maintained normal pH values that corresponded to skin pH. The emulsion also showed non-Newtonian flow and pseudo-plastic behaviour, which are required for ideal topical formulation. In conclusion, stability studies and characterization showed that nanoemulsions containing honey are exceptional topical delivery formulations.

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

Development and Characterization of Honey-containing Nanoemulsion for Topical Delivery by Muneer Ahmad, Atif Ali, and Hira Khan. Journal of Exploratory Research in Pharmacology 2024 DOI: 10.14218/JERP.2023.00012 Copyright © 2024 Authors. This is an Open Access article distributed under the terms of the Creative Commons Attribution-Noncommercial 4.0 License (CC BY-NC 4.0), permitting all non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

This paper is open access.

Protecting your data from Apple is very hard

There has been a lot of talk about Tim Cook (Chief Executive Officer of Apple Inc.) and his policy for data privacy at Apple and his push for better consumer data privacy. For example, there’s this, from a June 10, 2022 article by Kif Leswing for CNBC,

Key Points

  • Apple CEO Tim Cook said in a letter to Congress that lawmakers should advance privacy legislation that’s currently being debated “as soon as possible.”
  • The bill would give consumers protections and rights dealing with how their data is used online, and would require that companies minimize the amount of data they collect on their users.
  • Apple has long positioned itself as the most privacy-focused company among its tech peers.

Apple has long positioned itself as the most privacy-focused company among its tech peers, and Cook regularly addresses the issue in speeches and meetings. Apple says that its commitment to privacy is a deeply held value by its employees, and often invokes the phrase “privacy is a fundamental human right.”

It’s also strategic for Apple’s hardware business. Legislation that regulates how much data companies collect or how it’s processed plays into Apple’s current privacy features, and could even give Apple a head start against competitors that would need to rebuild their systems to comply with the law.

More recently with rising concerns regarding artificial intelligence (AI), Apple has rushed to assure customers that their data is still private, from a May 10, 2024 article by Kyle Orland for Ars Technica, Note: Links have been removed,

Apple’s AI promise: “Your data is never stored or made accessible to Apple”

And publicly reviewable server code means experts can “verify this privacy promise.”

With most large language models being run on remote, cloud-based server farms, some users have been reluctant to share personally identifiable and/or private data with AI companies. In its WWDC [Apple’s World Wide Developers Conference] keynote today, Apple stressed that the new “Apple Intelligence” system it’s integrating into its products will use a new “Private Cloud Compute” to ensure any data processed on its cloud servers is protected in a transparent and verifiable way.

“You should not have to hand over all the details of your life to be warehoused and analyzed in someone’s AI cloud,” Apple Senior VP of Software Engineering Craig Federighi said.-

Part of what Apple calls “a brand new standard for privacy and AI” is achieved through on-device processing. Federighi said “many” of Apple’s generative AI models can run entirely on a device powered by an A17+ or M-series chips, eliminating the risk of sending your personal data to a remote server.

When a bigger, cloud-based model is needed to fulfill a generative AI request, though, Federighi stressed that it will “run on servers we’ve created especially using Apple silicon,” which allows for the use of security tools built into the Swift programming language. The Apple Intelligence system “sends only the data that’s relevant to completing your task” to those servers, Federighi said, rather than giving blanket access to the entirety of the contextual information the device has access to.

But you don’t just have to trust Apple on this score, Federighi claimed. That’s because the server code used by Private Cloud Compute will be publicly accessible, meaning that “independent experts can inspect the code that runs on these servers to verify this privacy promise.” The entire system has been set up cryptographically so that Apple devices “will refuse to talk to a server unless its software has been publicly logged for inspection.”

While the keynote speech was light on details [emphasis mine] for the moment, the focus on privacy during the presentation shows that Apple is at least prioritizing security concerns in its messaging [emphasis mine] as it wades into the generative AI space for the first time. We’ll see what security experts have to say [emphasis mine] when these servers and their code are made publicly available in the near future.

Orland’s caution/suspicion would seem warranted in light of some recent research from scientists in Finland. From an April 3, 2024 Aalto University press release (also on EurekAlert), Note: A link has been removed,

Privacy. That’s Apple,’ the slogan proclaims. New research from Aalto University begs to differ.

Study after study has shown how voluntary third-party apps erode people’s privacy. Now, for the first time, researchers at Aalto University have investigated the privacy settings of Apple’s default apps; the ones that are pretty much unavoidable on a new device, be it a computer, tablet or mobile phone. The researchers will present their findings in mid-May at the prestigious CHI conference [ACM CHI Conference on Human Factors in Computing Systems, May 11, 2024 – May 16, 2024 in Honolulu, Hawaii], and the peer-reviewed research paper is already available online.

‘We focused on apps that are an integral part of the platform and ecosystem. These apps are glued to the platform, and getting rid of them is virtually impossible,’ says Associate Professor Janne Lindqvist, head of the computer science department at Aalto.

The researchers studied eight apps: Safari, Siri, Family Sharing, iMessage, FaceTime, Location Services, Find My and Touch ID. They collected all publicly available privacy-related information on these apps, from technical documentation to privacy policies and user manuals.

The fragility of the privacy protections surprised even the researchers. [emphasis mine]

‘Due to the way the user interface is designed, users don’t know what is going on. For example, the user is given the option to enable or not enable Siri, Apple’s virtual assistant. But enabling only refers to whether you use Siri’s voice control. Siri collects data in the background from other apps you use, regardless of your choice, unless you understand how to go into the settings and specifically change that,’ says Lindqvist.

Participants weren’t able to stop data sharing in any of the apps

In practice, protecting privacy on an Apple device requires persistent and expert clicking on each app individually. Apple’s help falls short.

‘The online instructions for restricting data access are very complex and confusing, and the steps required are scattered in different places. There’s no clear direction on whether to go to the app settings, the central settings – or even both,’ says Amel Bourdoucen, a doctoral researcher at Aalto.

In addition, the instructions didn’t list all the necessary steps or explain how collected data is processed.

The researchers also demonstrated these problems experimentally. They interviewed users and asked them to try changing the settings.

‘It turned out that the participants weren’t able to prevent any of the apps from sharing their data with other applications or the service provider,’ Bourdoucen says.

Finding and adjusting privacy settings also took a lot of time. ‘When making adjustments, users don’t get feedback on whether they’ve succeeded. They then get lost along the way, go backwards in the process and scroll randomly, not knowing if they’ve done enough,’ Bourdoucen says.

In the end, Bourdoucen explains, the participants were able to take one or two steps in the right direction, but none succeeded in following the whole procedure to protect their privacy.

Running out of options

If preventing data sharing is difficult, what does Apple do with all that data? [emphasis mine]

It’s not possible to be sure based on public documents, but Lindqvist says it’s possible to conclude that the data will be used to train the artificial intelligence system behind Siri and to provide personalised user experiences, among other things. [emphasis mine]

Many users are used to seamless multi-device interaction, which makes it difficult to move back to a time of more limited data sharing. However, Apple could inform users much more clearly than it does today, says Lindqvist. The study lists a number of detailed suggestions to clarify privacy settings and improve guidelines.

For individual apps, Lindqvist says that the problem can be solved to some extent by opting for a third-party service. For example, some participants in the study had switched from Safari to Firefox.

Lindqvist can’t comment directly on how Google’s Android works in similar respects [emphasis mine], as no one has yet done a similar mapping of its apps. But past research on third-party apps does not suggest that Google is any more privacy-conscious than Apple [emphasis mine].

So what can be learned from all this – are users ultimately facing an almost impossible task?

‘Unfortunately, that’s one lesson,’ says Lindqvist.

I have found two copies of the researchers’ paper. There’s a PDF version on Aalto University’s website that bears this caution,

This is an electronic reprint of the original article.
This reprint may differ from the original in pagination and typographic detail.

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

Privacy of Default Apps in Apple’s Mobile Ecosystem by Amel Bourdoucen and Janne Lindqvist. CHI. ’24: Proceedings of the CHI Conference on Human Factors in Computing Systems May 2024 Article No.: 786 Pages 1–32 DOI: https://doi.org/10.1145/3613904.3642831 Published:11 May 2024

This paper is open access.

Books can be toxic (literally)

I do love word play although I am pushing it a bit with ‘book’, ‘literature’, and ‘literal’.

These poison books each contain heavy metals used to create striking colours [in] the 1800s. Source: Museums Victoria Photo: Rob French [downloaded from https://museumsvictoria.com.au/article/if-books-could-kill-poison-heavy-metal-and-literature/]

Mark Lorch’s, Professor of Science Communication and Chemistry at the University of Hull (UK), April 29, 2024 essay on The Conversation (h/t April 30, 2024 news item on phys.org) provides an interesting account of the dangers associated with literature, Note: Links have been removed,

In our modern society, we rarely consider books to be dangerous items. However, certain books contain elements so hazardous that they require scrutiny before being placed on the shelves of public libraries, bookstores or even private homes.

The Poisonous Book Project [also known as, Poison Book Project], a collaborative research project between Winterthur Museum, Garden & Library and the University of Delaware, is dedicated to cataloguing such books. Their concern is not with the content written on the pages, but with the physical components of the books themselves — specifically, the colours of the covers.

The project recently influenced the decision to remove two books from the French national library. The reason? Their vibrant green cloth covers raised suspicions of containing arsenic.

This concern is rooted in historical practices in bookbinding. During the 19th century, as books began to be mass produced, bookbinders transitioned from using expensive leather covers to more affordable cloth items. To attract readers, these cloth covers were often dyed in bright, eye-catching colours.

One popular pigment was Scheele’s green, named after Carl Wilhelm Scheele, a German-Swedish chemist who in 1775 discovered that a vivid green pigment could be produced from copper and arsenic. This dye was not only cheap to make, it was also more vibrant than the copper carbonate greens that had been used for over a century.

Scheele green eventually fell out of favour because it had a tendency to fade to black when it reacted with sulphur-based pollutants released from coal. But new dyes based on Scheele’s discovery, such as emerald and Paris green, proved to be much more durable. …

These pigments, however, had a significant drawback: they degraded easily, releasing poisonous and carcinogenic arsenic. The frequent reports of green candles poisoning children at Christmas parties, factory workers tasked with applying paint to ornaments convulsing and vomiting green water and warnings of poisonous ball dresses raised serious concerns about the safety of these green dyes.

Green isn’t the only colour to worry about, however. Red is also of concern. The brilliant red pigment vermilion was formed from the mineral cinnabar, also known as mercury sulfide. This was a popular source of red paint dating back thousands of years. There is even evidence that neolithic artists suffered from mercury poisoning. Vermilion red sometimes appears on the marbled patterns on the inside of book covers.

Yellow has also caught the eye of the poisonous book project. In this case, the culprit is lead chromate. The bright yellow of lead chromate was a favourite with painters, not least Vincent van Gogh, who used it extensively in his most famous series of paintings: Sunflowers. For the Victorian-era bookbinders, lead chromate allowed them to create a range of colours from greens (achieved by mixing chrome yellow with Prussian blue) to yellows, oranges and browns.

So what should you do if you come across a green cloth book from the 19th century? First, don’t be overly concerned. You would probably have to eat the entire book before you’d suffer from severe arsenic poisoning. However, casual exposure to copper acetoarsenite, the compound in the green pigment, can irritate the eyes, nose and throat.

It is more of a concern for folks who may regularly handle these books where frequent contact could result in more serious symptoms. Therefore, anyone who suspects they might be handling a Victorian-era book with an emerald green binding is advised to wear gloves and avoid touching their face. Then clean all surfaces afterwards.

If you have a bit of time, Lorch’s April 29, 2024 essay is fascinating. If you have more time, there’s the undated “If books could kill: poison, heavy metal and literature” article on the Museums Victoria (Australia) website,

Books are not usually thought of as hazardous objects, but you will want to be careful with these ones from the Melbourne Museum’s Rare Book Collection.

Poisonous heavy metals permeate their very fabric, and the last 150-odd years has done nothing to lessen their toxicity.

How did it happen though?

This is not some dastardly Name of the Rose-esque plot [a reference to Umberto Eco and his 1986 novel, The Name of the Rose] but rather a combination of fashion, vanity, and workers’ rights (or lack thereof) in the years following the Industrial Revolution.

And it has left a dangerous legacy for modern-day museums.

Lastly, you can find the Poison Book Project here.

Cotton gin waste and self-embedding silver nanoparticles

This work may lead to new uses for cotton waste products according to an April 10, 2024 news item on phys.org,

Cotton gin waste, also known as cotton gin trash, is a byproduct of the cotton ginning process and occurs when the cotton fibers are separated from the seed boll. For cotton gin waste, the treasure is its hidden potential to transform silver ions into silver nanoparticles and create a new hybrid material that could be used to add antimicrobial properties to consumer products, like aerogels, packaging, or composites.

An April 9, 2024 US Dept. of Agriculture (USDA) Agricultural Research Service (ARS) news release, which originated the news item, provides more detail, Note: Links have been removed,

Silver nanoparticles are highly sought-after products in the nanotechnology industry because of their antibacterial, antifungal, antiviral, electrical, and optical properties. These nanoparticles have an estimated global production of 500 tons per year and are widely applied to consumer goods such as textiles, coatings, paints, pigments, electronics, optics, and packaging.

In a study published in ACS Omega, researchers from the United States Department of Agriculture (USDA)’s Agricultural Research Service (ARS) revealed the ability of cotton gin waste to synthesize and generate silver nanoparticles in the presence of silver ions.

“Our method not only lets cotton gin waste act as chemical agents for producing silver nanoparticles, which makes it cost-effective and environmentally friendly but also enables embedding the nanoparticles within the cotton gin waste matrix,” said Sunghyun Nam, research engineer at ARS’s Cotton Chemistry and Utilization Research Unit in New Orleans. “By embedding them in the cotton gin waste, these materials acquire antimicrobial properties.”

Nam said the researchers used a simple heat treatment of cotton gin waste materials in water containing silver ions that produced silver nanoparticles without the need for additional chemical agents.

This finding is significant since making silver nanoparticles usually requires chemical agents which can be costly and pose environmental concerns. Embedding nanoparticles into a material can also be challenging.

Developing nanoparticle embedding technology is not new for Nam and her team. They previously developed washable antimicrobial wipes by using raw cotton fiber that produced silver nanoparticles inside the fiber. The embedded silver nanoparticles can continue to kill harmful bacteria wash after wash.

Large quantities of cotton gin waste are generated annually, and the cotton ginning industry is always seeking new sustainable processes that upcycle crop residue.

“Our research paves the way for new material applications of cotton gin waste that can protect against microbial contamination,” said Nam.

A provisional patent application on the self-embedding silver nanoparticle biomass waste compositions has recently been filed.

The Agricultural Research Service is the U.S. Department of Agriculture’s chief scientific in-house research agency. Daily, ARS focuses on solutions to agricultural problems affecting America. Each dollar invested in U.S. agricultural research results in $20 of economic impact.

Despite the date of the news release, this is a relatively old paper; here’s a link to and a citation,

Unveiling the Hidden Value of Cotton Gin Waste: Natural Synthesis and Hosting of Silver Nanoparticles by Sunghyun Nam*, Michael Easson, Jacobs H. Jordan, Zhongqi He, Hailin Zhang, Michael Santiago Cintrón, and SeChin Chang. ACS Omega 2023, 8, 34, 31281–31292 DOI: https://doi.org/10.1021/acsomega.3c03653 Publication Date: August 9, 2023 © 2023 The Authors. Published by American Chemical Society. This publication is licensed under CC-BY-NC-ND 4.0.

As you can see from the Creative Commons licence, this paper is open access.

Nanocellulose film and Kiragami hydrogels

A Kirigami pattern of the hydrogel (top) and the hydrogel swollen from dry state (bottom). (Image: NIMS) [downloaded from https://www.nanowerk.com/nanotechnology-news3/newsid=65005.php]

An April 11, 2024 news item on Nanowerk highlights research that combines kiragami with hydrogel production, Note 1: A link has been removed, Note 2: Kiragami is described in the excerpt after this one,

New options for making finely structured soft, flexible and expandable materials called hydrogels have been developed by researchers at Tokyo University of Agriculture and Technology (TUAT). Their work extends the emerging field of ‘kirigami hydrogels’, in which patterns are cut into a thin film allowing it to later swell into complex hydrogel structures.

An April 12, 2024 Tokyo University of Agriculture and Technology (TUAT) press release, which originated the news item, on JCN Newswire, Note: Distribution of press releases can be spread out over days (sometimes identical press releases are sent out twice, months apart),

Hydrogels have a network of water-attracting (hydrophilic) molecules, allowing their structure to swell substantially when exposed to water that becomes incorporated within the molecular network. Researchers Daisuke Nakagawa and Itsuo Hanasaki worked with an initially dry film composed of nanofibers of cellulose, the natural material that forms much of the structure of plant cell walls.

They used laser processing to cut structures into the film before water was added allowing the film to swell. The particular design of the Kirigami pattern works in such a way that the width increases when stretched in the longitudinal direction, which is called the auxetic property. This auxetic property emerges provided that the thickness grows sufficiently when the original thin film is wet.

“As Kirigami literally means the cut design of papers [emphasis mine], it was originally intended for thin sheet structures. On the other hand, our two-dimensional auxetic mechanism manifests when the thickness of the sheet is sufficient, and this three dimensionality of the hydrogel structure emerges by swelling when it is used. It is convenient to store it in the dry state before use, rather than keeping the same water content level of the hydrogel.” says Hanasaki. “Furthermore, the auxeticity is maintained during the cyclic loading that causes the adaptive deformation of the hydrogel to reach another structural state. It will be important for the design of intelligent materials.”

Potential applications for the adaptive hydrogels include soft components of robotic technologies, allowing them to respond flexibly when interacting with objects they are manipulating, for example. They might also be incorporated into soft switches and sensor components. Hydrogels are also being explored for medical applications, including tissue engineering, wound dressings, drug delivery systems and materials that can adapt flexibly to movement and growth. The advance in kirigami hydrogels achieved by the TUAT team significantly extends the options for future hydrogel applications.

“Keeping the designed characteristics while showing adaptivity to the environmental condition is advantageous for the development of multifunctionality,” Hanasaki concludes

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

Adaptive plasticity of auxetic Kirigami hydrogel fabricated from anisotropic swelling of cellulose nanofiber film by Daisuke Nakagawa & Itsuo Hanasaki. Science and Technology of Advanced Materials Volume 25, 2024 – Issue 1 Article: 2331959 DOI: https://doi.org/10.1080/14686996.2024.2331959 Published online: 02 Apr 2024

This is an open access paper.

Goldene, its single layer of gold atoms makes it a cousin to graphene (a single layer of carbon atoms)

An April 16, 2024 news item on ScienceDaily announces yet another addition to the world of 2D materials,

For the first time, scientists have managed to create sheets of gold only a single atom layer thick. The material has been termed goldene. According to researchers from Linköping University, Sweden, this has given the gold new properties that can make it suitable for use in applications such as carbon dioxide conversion, hydrogen production, and production of value-added chemicals. Their findings are published in the journal Nature Synthesis.

An April 16, 2024 Linköping University press release (also on EurekAlert), which originated the news item, describes the constraints the researchers faced and how they resolved the problem of how to create goldene,

Scientists have long tried to make single-atom-thick sheets of gold but failed because the metal’s tendency to lump together. But researchers from Linköping University have now succeeded thanks to a hundred-year-old method used by Japanese smiths.

“If you make a material extremely thin, something extraordinary happens – as with graphene. The same thing happens with gold. As you know, gold is usually a metal, but if single-atom-layer thick, the gold can become a semiconductor instead,” says Shun Kashiwaya, researcher at the Materials Design Division at Linköping University.

To create goldene, the researchers used a three-dimensional base material where gold is embedded between layers of titanium and carbon. But coming up with goldene proved to be a challenge. According to Lars Hultman, professor of thin film physics at Linköping University, part of the progress is due to serendipidy. 

“We had created the base material with completely different applications in mind. We started with an electrically conductive ceramics called titanium silicon carbide, where silicon is in thin layers. Then the idea was to coat the material with gold to make a contact. But when we exposed the component to high temperature, the silicon layer was replaced by gold inside the base material,” says Lars Hultman.

This phenomenon is called intercalation and what the researchers had discovered was titanium gold carbide. For several years, the researchers have had titanium gold carbide without knowing how the gold can be exfoliated or panned out, so to speak. 

By chance, Lars Hultman found a method that has been used in Japanese forging art for over a hundred years. It is called Murakami’s reagent, which etches away carbon residue and changes the colour of steel in knife making, for example. But it was not possible to use the exact same recipe as the smiths did. Shun Kashiwaya had to look at modifications:

“I tried different concentrations of Murakami’s reagent and different time spans for etching. One day, one week, one month, several months. What we noticed was that the lower the concentration and the longer the etching process, the better. But it still wasn’t enough,” he says.

The etching must also be carried out in the dark as cyanide develops in the reaction when it is struck by light, and it dissolves gold. The last step was to get the gold sheets stable. To prevent the exposed two-dimensional sheets from curling up, a surfactant was added. In this case, a long molecule that separates and stabilises the sheets, i.e. a tenside.

“The goldene sheets are in a solution, a bit like cornflakes in milk. Using a type of “sieve”, we can collect the gold and examine it using an electron microscope to confirm that we have succeeded. Which we have,” says Shun Kashiwaya.

The new properties of goldene are due to the fact that the gold has two free bonds when two-dimensional. Thanks to this, future applications could include carbon dioxide conversion, hydrogen-generating catalysis, selective production of value-added chemicals, hydrogen production, water purification, communication, and much more. Moreover, the amount of gold used in applications today can be much reduced.

The next step for the LiU researchers is to investigate whether it is possible to do the same with other noble metals and identify additional future applications.

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

Synthesis of goldene comprising single-atom layer gold by Shun Kashiwaya, Yuchen Shi, Jun Lu, Davide G. Sangiovanni, Grzegorz Greczynski, Martin Magnuson, Mike Andersson, Johanna Rosen & Lars Hultman. Nature Synthesis (2024) DOI: https://doi.org/10.1038/s44160-024-00518-4 Published: 16 April 2024

This paper is open access.

Three century long development of a scientific idea: body armor made from silk

Credit: Unsplash/CC0 Public Domain [downloaded from https://phys.org/news/2024-04-body-armor-silk-apparently-edge.html]

Lloyd Strickland’s (professor of Philosophy and Intellectual History, Manchester Metropolitan University) fascinating April 9, 2024 essay on The Conversation (h/t April 10, 2024 news item on phys.org) illustrates the long and winding road to scientific and technological discoveries, Note: Links have been removed,

Separate teams of Chinese and American scientists are reported to be developing body armour using the silk from genetically modified silkworms. The researchers modified the genes of silkworms to make them produce spider silk instead of their own silk.

Harnessing the properties of spider silk has been a longstanding aim because the material is as strong as steel, yet also highly elastic. However, the idea of using silk to make bulletproof vests is not a new idea. Instead, it goes back centuries.

The invention of the silk bulletproof vest is often credited to the American physician George Emory Goodfellow (1855–1910), following his observation that silk was impenetrable to bullets.

But the idea was in fact proposed more than two centuries earlier by the German polymath Gottfried Wilhelm Leibniz (1646–1716), best known as inventor of calculus and binary arithmetic. …

You’ll notice it’s almost two centuries between the idea being proposed and someone working out a way to make a silk bulletproof vest. First, Liebniz (from Strickland’s April 9, 2024 essay), Note: Links have been removed,

In one of these little-known writings, unassumingly entitled “Plan for a military manufacturing process”, Leibniz sought to identify a material suitable for making a lightweight, flexible, bulletproof fabric. He briefly considered metal wires, layered metal sheets, and layered “goldbeater’s skin”, which is a material made from ox intestine. However, he devoted most of his attention to silk.

Whereas Goodfellow had observed the impenetrability of silk by bullets, Leibniz never had. Instead, he thought silk was the most promising material for a bulletproof fabric due to being lightweight, flexible, and strong. “Of all the materials we use for fabrics, and which can be obtained in quantity, there is nothing firmer than a silk thread,” he wrote.

Noting that silk was never firmer than in the cocoon, “where the silk is still gathered in the way that nature produced it”, Leibniz proposed making a fabric formed of silkworm cocoons tightly pressed together with a little glue.

He realised that while such a sheet could not easily be pierced, due to the tightly-woven silk in the cocoons, it would be prone to tearing where one cocoon met the next. Thus, he inferred that a bullet would not make a hole in the fabric, but instead tear whatever cocoon it hit from the surrounding ones, and drive it into the body, similar to what Goodfellow would observe with the silk handkerchief two centuries later.

Leibniz’s solution to the tearing problem was to propose layering sheets of pressed silkworm cocoons on top of each other. He illustrated this with a rudimentary diagram of a row of circles stacked on top of one another in a lattice arrangement, where a small interstice is left between adjoining circles.

Layering cocoons in such a hexagonal packing arrangement ensures that the weak parts of one layer are covered by the strong parts of another. This way, the fabric would not tear or be pierced when hit by a bullet. The result, Leibniz claimed, would be a fabric suitable for covering almost the whole body, especially if it was made to be oversized, affording the wearer freedom of movement.

Leibniz never realised his proposal to create bulletproof clothing using silk.

Strickland’s April 9, 2024 essay offers more about how Goodfellow’s field observations led to the invention of the first silk bulletproof vest by a Catholic priest.

Scott Burton’s undated article for bodyarmornews.com on spider silk and bulletproof body armour offers information about current efforts by US and Chinese scientists to incorporate spider proteins by gene editing silkworms capable of producing enough hybrid silk for enhanced body armour.

A century later, what appears to be the latest breakthrough was announced in a September 24, 2023 news item on chinadaily.com (and noted in Burton’s article),

Chinese scientists have developed the first whole full-length spider silk fiber obtained from genetically-engineered silkworms, exhibiting a six-fold toughness when compared to a bulletproof vest.

The results pave the way for spider silk’s commercialization as a sustainable substitute for synthetic fibers, and it can be used in making surgical sutures and comfortable bulletproof vests, according to the study.

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

High-strength and ultra-tough whole spider silk fibers spun from transgenic silkworms by Junpeng Mi, Yizhong Zhou, Sanyuan Ma, Xingping Zhou, Shouying Xu, Yuchen Yang, Yuan Sun, Qingyou Xia, Hongnian Zhu, Suyang Wang, Luyang Tian, Qing Men. Matter Volume 6, ISSUE 10, P3661-3683, October 04, 2023 DOI: https://doi.org/10.1016/j.matt.2023.08.013 First published online: September 20, 2023

This paper is behind a paywall.