Tag Archives: University of Amsterdam

They glow under stress: soft, living materials made with algae

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Caption: These soft, living materials glow in response to mechanical stress, such as compression, stretching or twisting. Credit: UC San Diego Jacobs School of Engineering

An October 20, 2023 news item on phys.org describes research into bioluminescent materials, Note: A link has been removed,

A team of researchers led by the University of California San Diego has developed soft yet durable materials that glow in response to mechanical stress, such as compression, stretching or twisting. The materials derive their luminescence from single-celled algae known as dinoflagellates.

The work, inspired by the bioluminescent waves observed during red tide events at San Diego’s beaches, was published Oct. 20 [2023] in Science Advances.

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An October 23, 2023 University of California at San Diego news release (also on EurekAlert but published October 20, 2023) by Liezel Labios, which originated the news item, delves further into the research,

An exciting feature of these materials is their inherent simplicity—they need no electronics, no external power source,” said study senior author Shengqiang Cai, a professor of mechanical and aerospace engineering at the UC San Diego Jacobs School of Engineering. “We demonstrate how we can harness the power of nature to directly convert mechanical stimuli into light emission.”

This study was a multi-disciplinary collaboration involving engineers and materials scientists in Cai’s lab, marine biologist Michael Latz at UC San Diego’s Scripps Institution of Oceanography, and physics professor Maziyar Jalaal at University of Amsterdam.

The primary ingredients of the bioluminescent materials are dinoflagellates and a seaweed-based polymer called alginate. These elements were mixed to form a solution, which was then processed with a 3D printer to create a diverse array of shapes, such as grids, spirals, spiderwebs, balls, blocks and pyramid-like structures. The 3D-printed structures were then cured as a final step.

When the materials are subjected to compression, stretching or twisting, the dinoflagellates within them respond by emitting light. This response mimics what happens in the ocean, when dinoflagellates produce flashes of light as part of a predator defense strategy. In tests, the materials glowed when the researchers pressed on them and traced patterns on their surface. The materials were even sensitive enough to glow under the weight of a foam ball rolling on their surface.

The greater the applied stress, the brighter the glow. The researchers were able to quantify this behavior and developed a mathematical model that can predict the intensity of the glow based on the magnitude of the mechanical stress applied.

The researchers also demonstrated techniques to make these materials resilient in various experimental conditions. To reinforce the materials so that they can bear substantial mechanical loads, a second polymer, poly(ethylene glycol) diacrylate, was added to the original blend. Also, coating the materials with a stretchy rubber-like polymer called Ecoflex provided protection in acidic and basic solutions. With this protective layer, the materials could even be stored in seawater for up to five months without losing their form or bioluminescent properties.

Another beneficial feature of these materials is their minimal maintenance requirements. To keep working, the dinoflagellates within the materials need periodic cycles of light and darkness. During the light phase, they photosynthesize to produce food and energy, which are then used in the dark phase to emit light when mechanical stress is applied. This behavior mirrors the natural processes at play when the dinoflagellates cause bioluminescence in the ocean during red tide events. 

“This current work demonstrates a simple method to combine living organisms with non-living components to fabricate novel materials that are self-sustaining and are sensitive to fundamental mechanical stimuli found in nature,” said study first author Chenghai Li, a mechanical and aerospace engineering Ph.D. candidate in Cai’s lab.

The researchers envision that these materials could potentially be used as mechanical sensors to gauge pressure, strain or stress. Other potential applications include soft robotics and biomedical devices that use light signals to perform treatment or controlled drug release.

However, there is much work to be done before these applications can be realized. The researchers are working on further improving and optimizing the materials.

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

Ultrasensitive and robust mechanoluminescent living composites by Chenghai Li, Nico Schramma, Zijun Wang, Nada F. Qari, Maziyar Jalaal, Michael I. Latz, and Shengqiang Cai. Science Advances 20 Oct 2023 Vol 9, Issue 42 DOI: 10.1126/sciadv.adi8643

This paper is open access.

Art masterpieces are turning into soap

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This piece of research has made a winding trek through the online science world. First it was featured in an April 20, 2017 American Chemical Society news release on EurekAlert,

A good art dealer can really clean up in today’s market, but not when some weird chemistry wreaks havoc on masterpieces. Art conservators started to notice microscopic pockmarks forming on the surfaces of treasured oil paintings that cause the images to look hazy. It turns out the marks are eruptions of paint caused, weirdly, by soap that forms via chemical reactions. Since you have no time to watch paint dry, we explain how paintings from Rembrandts to O’Keefes are threatened by their own compositions — and we don’t mean the imagery.

Here’s the video,

Interestingly, this seems to be based on a May 23, 2016 article by Sarah Everts for Chemical and Engineering News (an American Society publication) Note: Links have been removed,

When conservator Petria Noble first peered at Rembrandt’s “Anatomy Lesson of Dr. Nicolaes Tulp” under a microscope back in 1996, she was surprised to find pockmarks across the nearly 400-year-old painting’s surface.

Each tiny crater was just a few hundred micrometers in diameter, no wider than the period at the end of this sentence. The painting’s surface was entirely riddled with these curious structures, giving it “a dull, rather hazy, gritty surface,” Noble says.

A structure of lead nonanoate.

The crystal structures of metal soaps vary: Shown here is lead nonanoate, based on a structure solved by Cecil Dybowski at the University of Delaware and colleagues at the Metropolitan Museum of Art. Dashed lines are nearest oxygen neighbors.

This concerned Noble, who was tasked with cleaning the masterpiece with her then-colleague Jørgen Wadum at the Mauritshuis museum, the painting’s home in The Hague.

When Noble called physicist Jaap Boon, then at the Foundation for Fundamental Research on Matter in Amsterdam, to help figure out what was going on, the researchers unsuspectingly embarked on an investigation that would transform the art world’s understanding of aging paint.

More recently this ‘metal soaps in paintings’ story has made its way into a May 16, 2017 news item on phys.org,

An oil painting is not a permanent and unchangeable object, but undergoes a very slow change in the outer and inner structure. Metal soap formation is of great importance. Joen Hermans has managed to recreate the molecular structure of old oil paints: a big step towards better preservation of works of art. He graduated cum laude on Tuesday 9 May [2017] at the University of Amsterdam with NWO funding from the Science4Arts program.

A May 15, 2017 Netherlands Organization for Scientific Research (NWO) press release, which originated the phys.org news item, provides more information about Hermans’ work (albeit some of this is repetitive),

Johannes Vermeer, View of Delft, c. 1660 - 1661 (Mauritshuis, The Hague)Johannes Vermeer, View of Delft, c. 1660 – 1661 (Mauritshuis, The Hague)

Paint can fade, varnish can discolour and paintings can collect dust and dirt. Joen Hermans has examined the chemical processes behind ageing processes in paints. ‘While restorers do their best to repair any damages that have occurred, the fact remains that at present we do not know enough about the molecular structure of ageing oil paint and the chemical processes they undergo’, says Hermans. ‘This makes it difficult to predict with confidence how paints will react to restoration treatments or to changes in a painting’s environment.’

‘Sand grains’ In the red tiles of 'View of Delft' by Johannes Vermeer shows 'lead soap spheres' (Annelies van Loon, UvA/Mauritshuis)‘Sand grains’ In the red tiles of ‘View of Delft’ by Johannes Vermeer shows ‘lead soap spheres’ (Annelies van Loon, UvA/Mauritshuis)

Visible to the naked eye

Hermans explains that in its simplest form, oil paint is a mixture of pigment and drying oil, which forms the binding element. Colour pigments are often metal salts. ‘When the pigment and the drying oil are combined, an incredibly complicated chemical process begins’, says Hermans, ‘which continues for centuries’. The fatty acids in the oil form a polymer network when exposed to oxygen in the air. Meanwhile, metal ions react with the oil on the surface of the grains of pigment.

‘A common problem when conserving oil paintings is the formation of what are known as metal soaps’, Hermans continues. These are compounds of metal ions and fatty acids. The formation of metal soaps is linked to various ways in which paint deteriorates, as when it becomes increasingly brittle, transparent or forms a crust on the paint surface. Hermans: ‘You can see clumps of metal soap with the naked eye on some paintings, like Rembrandt’s Anatomy Lesson of Dr Nicolaes Tulp or Vermeer’s View of Delft’. Around 70 per cent of all oil paintings show signs of metal soap formation.’

Conserving valuable paintings

Hermans has studied in detail how metal soaps form. He began by defining the structure of metal soaps. One of the things he discovered was that the process that causes metal ions to move in the painting is crucial to the speed at which the painting ages. Hermans also managed to recreate the molecular structure of old oil paints, making it possible to simulate and study the behaviour of old paints without actually having to remove samples from Rembrandt’s Night Watch. Hermans hopes this knowledge will contribute towards a solid foundation for the conservation of valuable works of art.

I imagine this will make anyone who owns an oil painting or appreciates paintings in general pause for thought and the inclination to utter a short prayer for conservators to find a solution.

2-D melting and surfacing premelting of a single particle

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Scientists at the Hong Kong University of Science and Technology (HKUST) and the University of Amsterdam (in the Netherlands) have measured surface premelting with single particle resolution. From a March 15, 2016 HKUST news release on EurekAlert,

The surface of a solid often melts into a thin layer of liquid even below its melting point. Such surface premelting is prevalent in all classes of solids; for instance, two pieces of ice can fuse below 0°C because the premelted surface water becomes embedded inside the bulk at the contact point and thus freeze. Premelting facilitates crystal growth and is critical in metallurgy, geology, and meteorology such as glacier movement, frost heave, snowflake growth and skating. However, the causative factors of various premelting scenarios, and the effect of dimensionality on premelting are poorly understood due to the lack of microscopic measurements.

To this end, researchers from the Hong Kong University of Science and Technology (HKUST) and University of Amsterdam conducted a research where they were able to measure surface premelting with single-particle resolution for the first time by using novel colloidal crystals. They found that dimensionality is crucial to bulk melting and bulk solid-solid transitions, which strongly affect surface melting behaviors. To the surprise of the researchers, they found that a crystal with free surfaces (solid-vapor interface) melted homogenously from both surfaces and within the bulk, in contrast to the commonly assumed heterogeneous melting from surfaces. These observations would provide new challenges on premelting and melting theories.

The research team was led by associate professor of physics Yilong Han and graduate student Bo Li from HKUST. HKUST graduate students Feng Wang, Di Zhou, Yi Peng, and postdoctoral researcher Ran Ni from University of Amsterdam in Netherlands also participated in the research.

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Micrometer sized colloidal spheres in liquid suspensions have been used as powerful model systems for the studies of phase transitions because the thermal-motion trajectories of these “big atoms” can be directly visualized under an optical microscope. “Previous studies mainly used repulsive colloids, which cannot form stable solid-vapor interfaces,” said Han. “Here, we made a novel type colloid with temperature-sensitive attractions which can better mimic atoms, since all atoms have attractions, or otherwise they cannot condense into stable solid in air. We assembled these attractive spheres into large well-tunable two-dimensional colloidal crystals with free surfaces for the first time.

“This paves the way to study surface physics using colloidal model systems. Our first project along this direction is about surface premelting, which was poorly understood before. Surprisingly, we found that it is also related to bulk melting and solid-solid transitions,” Han added.

The team found that two-dimensional (2D) monolayer crystals premelted into a thin layer of liquid with a constant thickness, an exotic phenomenon known as incomplete blocked premelting. By contrast, the surface-liquid thickness of the two- or three-layer thin-film crystal increased to infinity as it approaches its melting point, i.e. a conventional complete premelting. Such blocked surface premelting has been occasionally observed, e.g. in ice and germanium, but lacks theoretical explanations.

“Here, we found that the premelting of the 2D crystal was triggered by an abrupt lattice dilation because the crystal can no longer provide enough attractions to surface particles after a drop in density.” Li said. “Before the surface liquid grew thick, the bulk crystal collapsed and melted due to mechanical instability. This provides a new simple mechanism for blocked premelting. The two-layer crystals are mechanically stable because particles have more neighbors. Thus they exhibit a conventional surface melting.”

As an abrupt dilation does not change the lattice symmetry, this is an isostructural solid-solid transition, which usually occurs in metallic and multiferroic materials. The colloidal system provides the first experimental observation of isostructural solid-solid transition at the single-particle level.

The mechanical instability induced a homogenous melting from within the crystal rather than heterogeneous melting from the surface. “We observed that the 2D melting is a first-order transition with a homogeneous proliferation of grain boundaries, which confirmed the grain-boundary-mediated 2D melting theory.” said Han. “First-order 2D melting has been observed in some molecular monolayers, but the theoretically predicted grain-boundary formation has not been observed before.”

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

Imaging the Homogeneous Nucleation During the Melting of Superheated Colloidal Crystals by Ziren Wang, Feng Wang, Yi Peng, Zhongyu Zheng, Yilong Han. Science  05 Oct 2012:
Vol. 338, Issue 6103, pp. 87-90 DOI: 10.1126/science.1224763

This paper is behind a paywall.