Tunable Photonic Structures via Photomechanical Actuation

Project Information

PHOTOTUNE

Grant agreement ID: 679646

DOI

10.3030/679646

Project closed

EC signature date 6 April 2016

Start date 1 May 2016

End date 30 April 2021

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 486 400,00

EU contribution

€ 1 486 400,00

Coordinated by

TAMPEREEN KORKEAKOULUSAATIO SR
Finland

Periodic Reporting for period 4 - PHOTOTUNE (Tunable Photonic Structures via Photomechanical Actuation)

Reporting period: 2020-11-01 to 2021-04-30

Summary of the context and overall objectives of the project

Light is a powerful tool in remote, reversible control over the properties of materials. Through photochemical switching or photothermal heating, one can photomodulate the color, refractive index, mechanical properties, or macroscopic shape/dimensions of soft polymeric materials, the latter known as photomechanics. Herein, we aim at intertwining photomechanics and photonics, by harnessing light-induced macroscopic shape changes to control the optical properties of functional systems. We will develop tunable feedback elements and photomechanically controlled nanostructured surfaces, and use them to devise tunable lasers and optical sensing, respectively. Beyond these specific examples, our general goal is to create a new light-based toolbox not only for tunable optical components and sensing platforms, but outreaching also to various different fields such as biomaterials science and soft robotics.

Within the PHOTOTUNE project, we have successfully demonstrated both phototunable lasing and active plasmonics. We have also devised a new method, based on photoswitchable molecules, for optical humidity sensing. The method was developed within an ERC Proof of Concept project (OPTOSENSE, Decision number 789788) and has also attracted further commercialization funding, targeting spin-off next year. Two further proof of concept projects will be applied from the next calls for light-reconfigurable cell-growth platforms and for pixelated printing of diffractive elements on photosensitive polymer substrates. Hence, in addition to scientific success (detailed later on), the project has been successful also from a more applied perspective. Scientifically, the most important results have been obtained in the field of (bioinspired) light-driven soft robotics, a topic that thanks to the PHOTOTUNE project has raised to the very center of our group’s research activities.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The PHOTOTUNE project has resulted in 29 scientific articles that have already gathered ca. 1300 citations. These include, e.g. 4xNature Communications, 5xAdvanced Materials, 1xPNAS, 1xChemical Science, among others. At least six additional PHOTOTUNE-associated publications will be submitted in the becoming months. Our activities have spanned from organic synthesis and materials engineering all the way to soft-matter photonics and soft robotics. The breadth of activities shows up also in the team composition, which throughout the project period has comprised both physicists and chemists. Our works have gained lots of publicity in popular science media (e.g. C&EN, New Scientist, Popular Science, Photonics Media, …) as well as in general newspapers (e.g. USA Today, Daily Mail, in addition to local newspapers and radio interviews).

The most important project outcomes, from the perspective of scientific impact (1.), commercialization (2.) and future openings (3. & 4.) are given below:

1. LIGHT ROBOTICS. We have mainly focused on novel bioinspired photoactuation schemes, demonstrating light-driven materials that are autonomous [Nat. Commun. 2017, 8, 15546], self-regulating [Adv. Mater. 2017, 29, 1701814], programmable [Nat. Commun. 2018, 9, 4148], multi-responsive [Adv. Mater. 2019, 31, 1805985], and capable of advanced functionalities such as swimming [PNAS 2020, 117, 5125], self-oscillation [Nat. Commun. 2019, 10, 5057] and even mimicking simplified forms of learning [Matter 2020, 2, 194].

2. OPTICAL HUMIDITY SENSING. This work started from pure fundamental science but eventually it turned out as the most significant outcome of the project in terms of photonic applications. The fundamental observation [ACS Macro Lett. 2018, 7, 381], based on humidity-dependent photoswitching of polymer thin films, was first developed into a proof of concept device within the ERC PoC funding framework [OPTOSENSE, Agreement No. 789788], which with funding from Business Finland is now being further developed towards profitable business, by a team consisting of both scientists and business developers.

3. PHOTONIC PRINTING. We have developed a device which allows photo-induced inscription/printing of diffractive patterns onto azobenzene-containing thin films with precision that has not been previously achievable. The technique allows us to obtain full-color diffractive images, superpose several holographic structures on top of each other, and inscribe waveguides onto azopolymer films. What's more, all these structures can be erased (either thermally or with light irradiation) and re-written at will, and if needed, used as master gratings and replicated into other polymers such as PDMS. We see great potential in the technique we have developed in e.g. AR/VR technologies and plan to further develop and utilise in it the months and years to come.

4. LIGHT-RECONFIGURABLE CELL-CULTURE PLATFORM. We have shown that similar photosensitive films used in 3. can also be used to control collective migration of epithelial cells and align neuronal axons. This provides an unprecedented reconfigurable tool for cell biologists in creating dynamic platforms for cell culture. Interfacing light-responsive materials with cell biology will be among the key future directions we target in the future.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

We have progressed beyond the state of the art in many fields. Herein, I would like to highlight two conceptually new photoactcator designs and two new openings related to soft-matter photonics.

1. In 2017, we demonstrated the “optical flytrap” – photomechanical actuator that “makes decisions” [Nat. Commun 2017, 8, 15546]. By integrating optical fiber and photomechanical actuator, we were able to devise an autonomous actuator whose light response is based on optical feedback it receives from the environment. Alike Venus flytrap, the device only closes when receiving the feedback (from an object that scatters or reflects light), providing means to distinguish between objects, manipulate them, and releasing them at will.

2. In 2018, we published our work on synergistic photoactuator, allowing us to program the photomechanical response of polymer sheets [Nat. Commun. 2018, 9, 4148]. We used photochemical actuation for shape programming and photoinduced heating for shape morphing, to obtain light-reconfigurable shape deformations that for the first time synergistically combine both photochemical and photothermal actuation schemes.

3. Our work on photoswitching-based optical humidity sensor presents a new way to measure relative humidity from the environment [ACS Macro Lett. 2018, 7, 381]. The concept is based on integrating photoswitchable molecules into polymer matrices. With proper molecular design, the photoswitching kinetics of the molecules depends exponentially on environmental humidity, providing an excellent basis for device applications with features that are non-existent in present humidity sensors. The commercial potential of our concept as identified also by the ERC Proof of Concept funding framework (OPTOSENSE, Agreement No. 789788) and Business Finland Research to Business funding framework, within which we presently further develop the optical humidity sensor.

4. In late 2020 we published a paper on combined digital holographic microscopy and laser-interference lithography of photosensitive thin polymer films, a device that was built within our group for two years [Sci. Rep. 2020, 10, 19642]. This device is one of a kind in the whole world, and it allows inscription of diffractive structures onto photoswitchable films with precision that has not been previously possible. This device will be valuable not only scientifically, allowing us to further our efforts in tunable lasing and plasmonic structures, but it also opens up new routes for photonic printing and rapid prototyping.

The project ended in April 2021 but several research results, especially related to tunable plasmonics and tunable lasing are still to be published. Hence, in addition to the 29 publications reported for the paper, there will be at least 6 more papers still to be published.

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