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Smart photonic materials

The world population is estimated to reach 9.8 billion by 2050. Ensuring an adequate food supply for such a large number of people would be challenging enough for agriculture. But climate change is putting even more pressure on farmers, agricultural companies, and crop scientists to protect plants from the effects of weather and pests, and to maximize crop productivity.


Today’s options are limited. Plants are shielded with foil and sheltered in greenhouses, and their growth is enhanced by cost-intensive methods such as the installation of artificial light. In order to effectively manage the challenges of feeding the world, we created a solution that is capable of fine-tuning the sunlight spectrum to the precise needs of the plants, thereby accelerating growth and increasing yields.


MERCK KGAA, Darmstadt, Germany Researchers are developing various Photonics based solution to meet this challenge.  Photonic solutions have the power to fine-tune sunlight spectra by means of a fluorescent carrier nanostructure  suitable for the needs of plants. Their innovative technology performs two functions at once. The photonic material blocks overly intense, harmful UV radiation. At the same time, it amplifies specific radiation primarily in the red or far-red region of the light spectrum, which favors key developmental responses in plants that accelerate crop growth.


Researchers have been also developing photonics based smart materials. The concept of smart materials and structures is the idea of mechanical, electrical and civil engineering structures which can react or adapt their characteristics according to signals received from embedded sensors. Such structures must be able to provide detailed information on their internal status during the manufacturing stage, and continuous indications of their physical state in real time, later in service.


You have to be better informed In order to get smarter decisions. Sensors can provide that information. Optical fiber sensors are able to withstand extreme temperatures, pressure, humidity, chemicals, and can to be embedded where it is impractical to run direct wiring or in locations unsafe for humans.


Tufts University develop new smart materials  that twist, bend and move controlled by light alone, reported in March 2021

Researchers at Tufts University School of Engineering have created light-activated composite devices able to execute precise, visible movements and form complex three-dimensional shapes without the need for wires or other actuating materials or energy sources. The design combines programmable photonic crystals with an elastomeric composite that can be engineered at the macro and nano scale to respond to illumination.


The research provides new avenues for the development of smart light-driven systems such as high-efficiency, self-aligning solar cells that automatically follow the sun’s direction and angle of light, light-actuated microfluidic valves or soft robots that move with light on demand. A “photonic sunflower,” whose petals curl towards and away from illumination and which tracks the path and angle of the light, demonstrates the technology in a paper that appears March 12th, 2021 in Nature Communications.


Color results from the absorption and reflection of light. Behind every flash of an iridescent butterfly wing or opal gemstone lie complex interactions in which natural photonic crystals embedded in the wing or stone absorb light of specific frequencies and reflect others. The angle at which the light meets the crystalline surface can affect which wavelengths are absorbed and the heat that is generated from that absorbed energy.


The photonic material designed by the Tufts team joins two layers: an opal-like film made of silk fibroin doped with gold nanoparticles (AuNPs), forming photonic crystals, and an underlying substrate of polydimethylsiloxane (PDMS), a silicon-based polymer. In addition to remarkable flexibility, durability, and optical properties, silk fibroin is unusual in having a negative coefficient of thermal expansion (CTE), meaning that it contracts when heated and expands when cooled. PDMS, in contrast, has a high CTE and expands rapidly when heated. As a result, when the novel material is exposed to light, one layer heats up much more rapidly than the other, so the material bends as one side expands and the other contracts or expands more slowly.


“With our approach, we can pattern these opal-like films at multiple scales to design the way they absorb and reflect light. When the light moves and the quantity of energy that’s absorbed changes, the material folds and moves differently as a function of its relative position to that light,” said Fiorenzo Omenetto, corresponding author of the study and the Frank C. Doble Professor of Engineering at Tufts.


Whereas most optomechanical devices that convert light to movement involve complex and energy-intensive fabrication or setups, “We are able to achieve exquisite control of light-energy conversion and generate ‘macro motion’ of these materials without the need for any electricity or wires,” Omenetto said.


The researchers programmed the photonic crystal films by applying stencils and then exposing them to water vapor to generate specific patterns. The pattern of surface water altered the wavelength of absorbed and reflected light from the film, thus causing the material to bend, fold and twist in different ways, depending on the geometry of the pattern, when exposed to laser light.


The authors demonstrated in their study a “photonic sunflower,” with integrated solar cells in the bilayer film so that the cells tracked the light source. The photonic sunflower kept the angle between the solar cells and the laser beam nearly constant, maximizing the cells’ efficiency as the light moved. The system would work as well with white light as it does with laser light. Such wireless, light-responsive, heliotropic (sun-following) systems could potentially enhance light-to-energy conversion efficiency for the solar power industry. The team’s demonstrations of the material also included a butterfly whose wings opened and closed in response to light and a self-folding box.


Smart Photonic Materials (SPM) research team Tampere University, Finland

Smart Photonic Materials (SPM) research team works at the interface between chemistry, physics, and materials engineering. We are interested in developing functional and stimuli-responsive materials based on polymers and liquid crystals, with particular focus on light-controllable systems. Our activities are centered around functional supramolecular systems and soft-matter photonics. For further information, see the



Artificial iris that functions the same way as the human eye, reported in 2017

The iris in the human eye is a tissue that regulates the amount of light coming into the eye by changing the size of the pupil. This way, the retina always receives the correct amount of light, ensuring a high-quality vision event. Controlling the amount of incoming light is just as important to imaging applications, such as cameras. However, these applications require complicated control circuitry and light detection schemes to adjust the amount of incoming light and produce high-quality pictures. The Smart Photonic Materials research group from the Tampere University of Technology (TUT) has developed a solution for this problem: an artificial iris that acts like the human eye.


“An autonomous iris that can independently adjust its shape and the size of its aperture in response to the amount of incoming light is a new innovation in the field of light-deformable materials,” says head of the research group, Academy Researcher, Associate Professor (tenure track) Arri Priimägi from TUT’s Laboratory of Chemistry and Bioengineering.


TUT’s researchers developed the iris in collaboration with Dr Piotr Wasylczyk from the University of Warsaw and Dr Radosław Kaczmarek from Wrocław Medical University. The artificial iris was manufactured from light-sensitive liquid crystal elastomer. Its manufacture utilised the so-called photoalignment technology that is also used in some contemporary mobile phone displays. “The artificial iris looks a little bit like a contact lens, and its centre opens and closes according to the amount of light that hits it,” Priimägi says.


Applications in ophthalmology?

According to Priimägi, what makes this invention significant is the device’s ability to function autonomously, free from power sources or external light detection systems. “This research was inspired by Dr Kaczmarek, who is an ophthalmologist and foresees potential use for a self-regulating iris-like device in the treatment of iris defects. The road to practical applications is long, but our next goal is to make the iris function also in aqueous environment. Another important goal will be to increase the sensitivity of the device in order to make it react to smaller changes in the amount of incoming light. These developments will be the next steps towards possible biomedical applications,” Priimägi says.


As the head of the research group, Priimägi expresses his thanks to group members Postdoctoral Researcher Hao Zeng and Doctoral StudentOwies Wani for their important contributions to the success of the artificial iris research. The project is also anticipated to launch a long-term collaboration with Dr Wasylczyk on soft robotics and light-actuable materials.


Earlier this spring, the Smart Photonic Materials group published a paper in the Nature Communications journal concerning a light-driven polymer gripper, resembling in function the Venus flytrap plant, that can independently recognise different objects and select the desired ones among them. The research opens new venues in the development of soft micro-robots. The ERC-funded artificial iris research was published on 7 June 2017 in the esteemed Advanced Materials journal. The research is available online.

Military applications

Military have large demand for smart materials and devices including smart self-repair, smart clothing such as cloaking suits, and adaptive hull structures for ships. Morphing aircraft are multi-role aircraft that change their external shape substantially to adapt to a changing mission environment during flight.


Chameleon inspires smart skin, reported in sep 2019

Chameleons’ color-changing camouflage arises from photonic crystals embedded in their skin. By tensing or relaxing their skin, the reptiles can change the space between the crystals and generate different colors to blend into their surroundings. Scientists have tried to copy this structure by embedding photonic crystals in hydrogels, but these materials typically need dramatic deformations to change color, which can strain the materials. Chameleons, on the other hand, change color through subtle movements.


That prompted Emory University’s Khalid Salaita and colleagues to study time-lapse images of chameleon skin in action. They noticed that only a fraction of the reptiles’ skin cells contain photonic crystals, and the rest are colorless. They reasoned that these colorless cells accommodate the strain that occurs as the photonic crystals move to change the chameleon’s color. Inspired by this, the researchers created arrays of photonic crystals in a hydrogel and then embedded those arrays in a second, colorless hydrogel that acts as a supporting layer (ACS Nano 2019, DOI: 10.1021/acsnano.9b04231). The resulting material shifts from yellow to green in sunlight, which could be useful for camouflage and anticounterfeiting applications.

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