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TY  - THES
AU  - He, Siyang
TI  - Photo- and mechano-responsive PNIPAM and PVCL microgels
PB  - RWTH Aachen University
VL  - Dissertation
CY  - Aachen
M1  - RWTH-2025-00522
SP  - 1 Online-Ressource : Illustrationen
PY  - 2024
N1  - Veröffentlicht auf dem Publikationsserver der RWTH Aachen University 2025
N1  - Dissertation, RWTH Aachen University, 2024
AB  - Responsive microgels, particularly those based on poly(N-isopropylacrylamide) (PNIPAM) and poly(N-vinylcaprolactam) (PVCL), have received significant attention across diverse disciplines. Their inherent thermoresponsive nature, coupled with biocompatibility, positions them as promising candidates for targeted drug delivery systems. Moreover, owing to their unique physical characteristics such as their behavior at interfaces, they have emerged as intriguing subjects for investigation in the field of atomic force microscopy (AFM) and super-resolution microscopy. This thesis explores the development of photoresponsive microgels based on PNIPAM and PVCL, which accordingly exhibit switchable physical properties. These microgels, incorporating the photoresponsive unit diarylethene (DAE) into their networks, undergo photoswitching upon exposure to UV or vis irradiation, leading to alterations in their size and network properties. The interactions of these microgels with human HEK293T cells are investigated to assess their cellular toxicity and interactions with cells. Simultaneously, the study reveals that DAE-crosslinked PVCL microgels exhibit a variable volume phase transition temperature (VPTT) when photoswitching the DAE unit. This phenomenon induces changes in the size and swelling state of the microgels. Upon UV irradiation, the ring-closing process of the DAE unit lowers the VPTT of the microgels, causing them to collapse. Consequently, the microgels become more resistant to mechanical forces in solution, such as those in the sonication process induced by the implosion of cavitation bubbles. By combining the stimuli of light and mechanical force to modulate the swelling states and degradation of microgels, this mechanical cloaking system enables the creation of a responsive system requiring multiple stimuli at a topological level. Furthermore, to deepen our understanding of the internal structure and mechanical properties of microgels, a dual-fluorescent benzothiadiazole (BTD)-based mechanophore was integrated into PVCL microgel networks. With super-resolution fluorescence microscopy (SRFM), the efficacy of this mechanophore was investigated using both STED microscopy and dSTORM microscopy techniques. Additionally, a protocol employing fluorescence lifetime imaging microscopy (FLIM) was developed to discriminate activated BTD from potential artifacts in the confocal laser scanning microscopy (CLSM) imaging. Finally, to enable localized activation and imaging of individual microgels, a novel approach combining AFM with SRFM was proposed, and a newly engineered force-gated fluorescent dye was designed to facilitate this objective. The preliminary findings from these investigations are elaborated upon in this thesis, intended to shed light on the intricate behavior of microgels under mechanical stimuli.
LB  - PUB:(DE-HGF)11
DO  - DOI:10.18154/RWTH-2025-00522
UR  - https://publications.rwth-aachen.de/record/1002424
ER  -