Polyelectrolyte microgels with controlled number and distribution of charges : from synthesis to application
- Polyelektrolytische Mikrogele mit kontrollierter Anzahl und Verteilung von Ladungen: Von Synthese bis zur Anwendung
Xu, Wenjing; Pich, Andrij (Thesis advisor); Richtering, Walter (Thesis advisor)
Dissertation / PhD Thesis
Dissertation, RWTH Aachen University, 2020
Research in microgels focuses more than ever on mastering increasingly complex molecular structures and superstructure assemblies. The studies aim at novel properties, multiple responsiveness, and targeted application in different fields. In this work, I introduce charged microgels with complex architectures and defined localization of different ionizable groups. The challenge is to synthesize polyampholyte microgels with ionizable groups of opposite charges, and the production of surface-modified polyelectrolyte microgels of superior colloidal stability which respond to pH and temperature changes for defined application as drug carriers for biological guest molecules and as building blocks to assemble polyampholyte superstructures. As the control over the charge distribution of the acidic and basic moieties within the microgel network is crucial not only for the fundamental research but also plays an important role in the interaction with guest molecules, polyampholyte microgels with controlled architectures and defined localization of ionizable groups (random, core-shell, and Janus-like) were synthesized by modified precipitation polymerization. A new facile and straightforward approach to produce Janus-like polyampholyte microgels was proposed based on the coacervation process of oppositely charged precursor particles under a specific mixing time. In addition, surface modified polyelectrolyte core-shell microgels with functional GMA (Glycidyl methacrylate) groups located only on the surface of the microgels were synthesized via two-step precipitation polymerization with a delayed GMA addition. Polyelectrolyte microgels have been used as carriers for the transport and protection of guest molecules for decades due to their response to pH changes. So far, studies exposed that the interaction between the polyelectrolyte microgels and oppositely charged guest molecules are strongly dependent on the type of charges within the microgel as well as the kind of guest molecules. However, other factors such as the distribution of opposite charged ionizable groups and the structural formation alone or in combination have not been discussed. Therefore, investigation on the interaction of different pre-synthesized charged microgel carriers (polyampholyte microgels and surface modified polyelectrolyte microgels) with biological guest molecules of a different kind (protein and peptide) were accomplished. The effect of the charge distribution and the structural design of the microgels as well as the change of the environment (pH of the surroundings) on the uptake and release procedure was revealed. A striking discovery was made showing that the distribution of ionizable groups in polyampholyte microgels (random and core-shell) as well as the surface modification of the polyelectrolyte core-shell microgels with fuctional GMA groups controls the interactions with the captured proteins from entrapment and “levitation” to accelerated release. Furthermore, polyampholyte colloidal superstructures using polyampholyte and polyelectrolyte microgels as efficient building blocks was introduced. Regarding their temperature and pH responsiveness, polyampholyte colloidal superstructures with unique properties was designed. In specific, polyampholyte hydrogels via additional physical crosslinking with tannic acid under a dense state, and polyampholyte assemblies via the self-assembly process of two opposite charged microgels was synthesized. The formation of the polyampholyte superstructures were confirmed by means of different techniques. Both superstructures will not only open a new pathway for the fundamental research on studies of gel-based superstructures but are also promising candidates for wound healing or as functional materials that enable multiple loading and release of guest molecules which can be applied in the biomedical entity.