Biological tissues are frequently composed of macromolecular and low-molecular components, containing covalent and non-covalent crosslinks, and are assembled in a modular way exhibiting different hierarchy levels.1 Such hydrogel-like materials often exhibit hysteresis effects and non-linearity of their properties, which is essential to functions like adaptability and time-programming. 
This contribution will focus on chemical design of stimuli-responsive nanogels exhibiting no-covalent dynamic crosslinks based on host-guest complexes, ionic bonds or hydrogen bonds.2-9 The development of new synthesis methods that allow controlled integration of supramolecular functionalities into nanogels opens new ways to generate functional polymer materials and systems with unique functions like stimuli-responsiveness, re-shaping, and triggered disassembly. Stimuli-responsive aqueous nanogels containing degradable crosslinks based on the supramolecular host-guest complexes between β-cyclodextrin and cholesterol or ferrocene were synthesized.2,3 Nanogels functionalized with zwitterionic units contain two types of crosslinks: -covalent and ionic.4,5,6 Monodisperse colloidally stable nanogels with a high amount (> 30 mol-%) of zwitterionic groups were synthesized using W/O miniemulsion approach. High contents of zwitterionic groups in microgels led to the formation of dynamic reversible ionic crosslinks along with permanent covalent crosslinks generated by bisacrylamide. Obtained nanogels exhibit temperature-triggered swelling/deswelling behavior and co-existance of UCST- and LCST-type transitions in aqueous solutions. A new synthesis method to obtain aqueous supramolecular temperature-responsive nanogels using tannic acid as multifunctional physical cross-linker was developed recently.7,8 The precipitation polymerization of N-vinylcaprolactam in the presence of tannic acid leads to the formation of well-defined stimuli-responsive nanogels cross-linked by hydrogen bonds. We demonstrate that obtained nanogels exhibit reversible temperature-triggered swelling/deswelling and undergo pH-triggered degradation and re-shaping in aqueous solutions. Nanogels equipped with non-covalent crosslinks exhibit unique properties like on-demand degradation, controlled release of ions and small molecules and mechanical re-enforcement.9,10 

References:
[1] R. Eelkema, A. Pich, Advanced Materials 2019, 1906012. 
[2] D. Schmitz, A. Pich, Polymer Chemistry 2016, 7, 5687. 
[3] S.-H. Jung, S. Schneider, F. Plamper, A. Pich, Macromolecules 2020, 53, 1043-1053. 
[4] R. Schröder, W. Richtering, I. Potemkin, A. Pich, Macromolecules 2018, 51, 17, 6707-6716. 
[5] P. Saha, M. Kather, S. Banerjee, N. Singha, A. Pich, Eur. Polym. Journal 2019, 118, 195-204. 
[6] P. Saha, M. Santi, M. Frenken, A. Palanisamy, R. Ganguly, N. Singha, A. Pich, ACS Macro Letters 2020, 9, 895-901. 
[7] C. Molano, A. Pich, Macromolecular Rapid Communications 2018, 39, 1700808. 
[8] S. Jung, S. Bulut, L. P. B. Guerzoni, L. De Laporte, A. Pich, J Colloid Interface Science, 2022, 617, 409-421. 
[9] E. Izak-Nau, S. Braun, A. Pich, R. Göstl, Advanced Science, 2022, 2104004. 
[10] T. Kharandiuk, K. H. Tan, R. Göstl, A. Pich, Chemical Science 2022, 13, 11304.