Biobased phononic materials (BPM) – biophoNonics

Our preliminary results are the first demonstration that BPM can be engineered and controlled by manipulating plant phenotype. In this project, we improved surface acoustic wave detection (SAW) by implementing laser-ultrasonic techniques in which we generate sound with ultrashort laser pulses. This approach allows simplified on-chip evaluation of BPMs. Using insights from plant biology, we have refined our control of the phononic features by modulating topology (geometry, periodicity of the cell walls) and mechanical properties (adhesion, anisotropy) of the plant tissues. We have simulated all these effects with numerical tools, allowing a deeper understanding of the phonon behavior and the underlying biological mechanisms supporting unusual wave propagation. We have also investigated the impact of this type of materials on the socio-ecological metabolism in which they could be incorporated, extending the approach to the “materials of the Anthropocene” and thus raising awareness in diverse other communities.

In terms of instrumentation, we have implemented several detection schemes for SAWs, including TG that was initially not planned. Today, this technique is a hallmark of phononic studies in plants and is a unique implementation in France. We have also implemented SBS and, through the support of the CNRS, we are now developing this technique further using stimulated approaches and transferring this tool to the ILMtech platform. The combination of TG and Brillouin technologies should support many new projects in the field of BPM.
We have developed FE and analytical modelling, image analysis techniques and inverse problems that allow identifying the phononics features of BPM. In particular, we have observed the influence of adhesion on the formation of gaps, and the influence of various drugs on the gap behavior. In future, many applications will follow from these findings.
Finally we have demonstrated the ability to probe Arabidopsis roots in which we have observed a radial symmetry in the mechanical properties at the cellular level. Using mechanical stretching, we are now investigating the ability to control phononics features in these samples.

In terms of philosophical reflection, the results were significant both methodologically (how to study an object that does not yet fully exist, and describe the interactions between disciplines around it) and conceptually (with the concepts of “bio-hijack” and “material hijacking”). We also broadened the reflection to the question of the metabolism of materials between nature and society in the Anthropocene. This enabled us to bring together a small international and interdisciplinary community, to initiate new collaborations and enable awareness in a large diversity of communities and cultures.
The project was slowed down by the long-term impact of COVID on the organization of research, by structural reorganisation within the ILM that left us without an operating environment (moving, loss of thermal regulation) for a long period of time, and the resignation of non permanent researchers contracted on this project due to their recruitment as permanent researchers in other labs (which is also an important positive impact of the project). As a consequence, the human resources were fragmented and not aligned with the extended duration of the project. This situation impacted all aspects of the project. Despite these difficulties, we have obtained important results that advance the research in the field of BPMs. In particular, we have established TG and BLS as hallmarks of phononic studies in plants. We have identified the ability to control phononic features (including gaps and band folding) notably with adhesion. We have implemented new models based on Arabidopsis roots where we can tune mechanics with mechanical stretching. All in all, this project represents an important contribution to the field and should be continued via different follow-up projects that have already been initiated.

We are now evaluating the impact of stretching on cellular mechanics and its impact on phononic features. For this research we have secured additional fundings for a PhD fellowship (bourse ministérielle) and equipment (MITI large spectre du son). The ANR project has also allowed reaching new partners in plant Biology on these aspects.
Regarding the control of phononics parameters, we have identified the important contribution of adhesion. While this has held us back for a while because it took time to fully grasp its influence, it is today the main parameter in our strategy to design biobased phononic materials. We are currently studying the ability to tune adhesion to engineer waveguides, and take advantage of the band folding. This is done in the context of a follow-up ANR project.
Editorial work on the book is underway, giving rise to fruitful Franco-German exchanges with the cluster of excellence Matters of Activity at Humboldt University Berlin with a view to future collaborations. The launch of the books series Materials, Technology & Society Nexus at Word Scientific will lead to the publication of a book on “materials and time”, and on “materials and intelligence” in the coming years.

During the project we have published 2 papers that discuss harnessing adhesion to engineer metasurfaces. Other publications leveraging the anisotropy and periodicity are being written. Importantly, we have also organized a conference on living the biodesign and bioeconomy of “materials in the Anthropocene” that gathered the main actors of the field in physics, philosophy and economy. A collective book is being edited on this topic.