Living Microstructures by Combining Laser Printing and Dynamic Covalent Exchange of Alkoxyamines

Two-photon lithography, also known as direct laser writing or 3D laser printing, allows to structure polymer networks in unprecedented definition and can generate interesting optical, mechanical and biomedical properties in the micro and nanoscale. The polymer networks applied usually relies on covalent bonds, lacking dynamic or living characteristics. Inclusion of dynamic and living characteristics to 3D laser printing microstructured polymer networks provides new and exciting possibilities to dynamically modify the molecular structure of the networks, such as crosslinking density or mesh sizes.[1] Such modifications at the molecular level strongly influence important characteristics, such as swelling degree or mechanical properties. For creating polymer network structures containing dynamic and living bonds, it is important to adopt the dynamic covalent chemistry to the radical chemistry applied in the laser printing process.<br/>Here, we include dynamic covalent bonds, based on nitroxide radicals, into the 3D laser printing microstructures. In our approach, dynamic alkoxyamine bonds form during the printing process via trapping of radical species by functionalized nitroxide radicals. The alkoxyamine bonds within the final microstructured polymer networks can afterwards be activated for nitroxide exchange reactions or nitroxide mediated polymerization, providing dynamic, adaptive and “living” properties to the microstructured networks. [2] [3] [4] [5]<br/>[1] 4D Printing at the Microscale C. Spiegel, M. Hippler, A. Münchinger, M. Bastmeyer, C. Barner-Kowollik, M. Wegener, E. Blasco<i> Adv. Funct. Mater.</i> <b>2020</b>, 30, 1907615.<br/>[2] Dynamic Covalent Polymer Networks via Combined Nitroxide Exchange Reaction and Nitroxide Mediated Polymerization Y. Jia, Y. Matt, Q. An, I. Wessely, H. Mutlu, P. Theato, S. Bräse, A. Llevot, <i>Polym. Chem.,</i> <b>2020</b>, 11, 2502.<br/>[3] Recycling and Self-Healing of Dynamic Covalent Polymer Networks with a Precisely Tuneable Crosslinking Degree Q. An, I. Wessely, Y. Matt, Z. Hassan, S. Bräse, M. Tsotsalas <i>Polym. Chem.</i> <b>2019</b>, 10, 672.<br/>[4] Self-Reporting Refoldable Fluorescent Single-Chain Nanoparticles<br/>T. Fischer, S. Spann, Q. An, B. Luy, M. Tsotsalas, J. Blinco, H. Mutlu, C. Barner-Kowollik<i> Chem. Sci.</i>, <b>2018</b>, 9, 4696.<br/>[5] Radical Exchange Reaction of Multi-Spin Isoindoline Nitroxides Followed by EPR Spectroscopy I. Wessely, V. Mugnaini, A. Bihlmeier, G. Jeschke, S. Bräse, M. Tsotsalas<br/><i>RSC Advances</i> <b>2016</b>, 6, 55715.