Polymer mechanochemistry harnesses mechanical force to trigger chemical transformations in polymers and those functional groups are called mechanophores. Traditionally, polymer mechanochemistry relies on 20 kHz ultrasound (US) to activate mechanophores. However, low-frequency US exhibits inherent biocompatibility limitations. Moreover, in biological applications, the spatial resolution achievable with a single low frequency transducer is compromised, as resolution is inversely proportional to the applied US frequency. High frequency US has been employed to activate mechanophores in a number of applications. However, activating covalently linked mechanophores typically requires very high pressure/power density or prolonged burst durations. In these examples, polymer materials were first treated with US, then transferred to cell solutions for cellular experiments. Direct, in situ US treatment of cells and polymer samples remains largely unexplored.

We developed two polymer platforms that are responsive to high‑frequency ultrasound. One exploits piezoelectric polymers; the other uses tailored polymer architectures to pre‑stretch chains before ultrasound exposure. Piezoelectric materials are solids in which mechanical deformation generates an electrical potential because of the aligned dipoles shifts under stress induced charge separation inside the materials. In this context, we used zwitterionic and polyelectrolyte brushes with large side chain dipole moment grown by surface‑initiated polymerization and discovered pyro‑ and piezoelectric behavior in these soft layers, which we attribute to non‑uniform segment density and asymmetric counterion distribution. Second, we use surface‑initiated polymerizations to prepare densely grafted polymer brushes with mechanophores at the brush–substrate interface and exploit swelling‑induced chain stretching to enhance mechanophore activation under clinically relevant high‑frequency ultrasound. Pre‑stretching lowers the activation energy, enabling activation with relatively weak ultrasound. In this work, mechanophores at the brush–substrate interface on silica nanoparticles are stretched upon swelling in a good solvent (water), which accelerates mechanochemical activation of an azo mechanophore, generating reactive oxygen species that selectively kill cancer cells in vitro and in vivo. In a further example, mechanophores are embedded in microbubble shells, an alternative polymer architecture that enhances mechanophore activation. The internal gas pressure tunes membrane stress, and disulfide mechanophore activation increases with shell membrane stress, with higher stress yielding faster activation under high‑frequency ultrasound. Together, these studies deepen the mechanistic understanding of polymer mechanochemistry and establish new strategies for precise spatiotemporal mechanophore activation and ultrasound‑triggered drug delivery.

Jian Wang received his B.Sc. from Jilin University, in 2012 under the supervision of Prof. Hui Na and Prof. Chengji Zhao. After that, he became a master student under the guidance of Professor Yapei Wang at Renmin University of China. In 2015, he joined Professor H.-A Klok’s group in EPFL, Switzerland as a Ph.D. student. In 2021, he was awarded a Thesis Distinction 8% award at EPFL and won two prestigious mobility fellowships from the Swiss National Science Foundation to support his postdoctoral research in Prof. Jeffery S. Moore’s group from UIUC. His postdoctoral research is focused on the development of biomedical ultrasound responsive motifs that are incorporated into nanoparticle polymer brushes interface for mechano-dynamic therapy. Working in collaboration with colleagues in Nuclear, Plasma and Radiological Engineering, he has also developed a solution phase plasma electrochemistry as a new tool for organic synthesis. He is now an independent group leader in DWI-Leibniz Institute for Interactive Materials in Germany, a PI of the Leibniz ScienceCampus "ACTISONO" and has won the Alicat University grant 2025. 

Jian Wang's research focuses on the fascinating intersection of interface chemistry and functional materials, exploring innovative approaches to material design and synthesis. His work encompasses several key areas: plasma-liquid synthesis and advanced functional materials.

1. Plasma electrochemistry: He is pioneering the use of plasma-liquid techniques as a novel strategy for organic small molecule synthesis. He investigates how plasma-liquid interactions can facilitate the synthesis of small molecules, potentially offering more efficient and environmentally friendly synthesis routes. The success of this plasma-liquid synthesis route will open up new possibilities in the field of polymer recycling and upcycling, potentially leading to more efficient and sustainable methods for reprocessing and repurposing polymers.

2. Advanced functional materials: He also delves into the fundamental aspects of interface chemistry to design advanced functional polymer materials at the interfaces including piezoelectric materials and antibiofouling materials. He aims to combine the characteristics of these materials to design a general controlled release system that can aid in cancer or gene therapy.

Selected publications: 

1. Wang, J.; Zhao, S.; Yi, J.; Sun, Y.; Agrawal, M.; Oelze, M. L.; Li, K.*; Moore, J. S.*; Chen, Y.-S.* Injectable Mechanophore Nanoparticles for Deep-Tissue Mechanochemical Dynamic Therapy. ACS Nano 2024, 18 (38), 25997-26010 https://pubs.acs.org/doi/abs/10.1021/acsnano.4c04090 

2. Wang, J.; Hu, F.; Sant, S.; Chu, K.; Riemer, L.; Damjanovic, D.; Kilbey Ii, S. M.; Klok, H.-A.* Pyroelectric Polyelectrolyte Brushes. Adv. Mater. 2024, 36 (14), 2307038.

https://onlinelibrary.wiley.com/doi/epdf/10.1002/adma.202307038

3. Wang, J.; Üner, N. B.; Dubowsky, S. E.; Confer, M. P.; Bhargava, R.; Sun, Y.; Zhou, Y.; Sankaran, R. M.*; Moore, J. S.* Plasma Electrochemistry for Carbon–Carbon Bond Formation via Pinacol Coupling. J. Am. Chem. Soc. 2023, 145 (19), 10470-10474. https://pubs.acs.org/doi/full/10.1021/jacs.3c01779 

4. Wang, J.; Gao, X.; Boarino, A.; Célerse, F.; Corminboeuf, C.; Klok, H.-A.* Mechanical Acceleration of Ester Bond Hydrolysis in Polymers. Macromolecules 2022, 55 (22), 10145-10152. https://pubs.acs.org/doi/abs/10.1021/acs.macromol.2c01789

5. Wang, J.; Klok, H.-A.* Swelling-Induced Chain Stretching Enhances Hydrolytic Degrafting of Hydrophobic Polymer Brushes in Organic Media. Angew. Chem., Int. Ed. 2019, 58 (29), 9989-9993. https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.201904436