Supramolecular stimuli-responsive microgels crosslinked by tannic acid

• Supramolekulare stimuli-responsive Mikrogele vernetzt mit Tanninsäure

Molano López, Astrid Catalina; Pich, Andrij (Thesis advisor); Richtering, Walter (Thesis advisor)

Aachen (2019)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2019

Abstract

After the era of revolutionary industrial developments, our society has reached the "green" period, in which the production of bioinspired materials is a prior ambition. Therefore, the understanding of biological processes at the molecular level opens up great possibilities and guides the evolutional path in modern science. Whether at the nanometric or at the macroscopic scale, the origin of living entities relies almost always on self-assembly and hierarchic organization between building blocks. These mechanisms and the role that biological units play herein are the inspiration in design of novel "smart" nanomaterials for bio- and medical applications. Additionally, the utilization of natural compounds in material science is also desired. Among the great variety of promising materials, polymers have showed remarkable biocompatible and responsive properties. In particular, polymeric colloidal networks, well-known as microgels, have been arousing enormous interest because of their stimuli-responsiveness and biocompatibility depending on their building units. Herein, not only the selected monomer, but also the crosslinking agent plays a decisive role, especially in view of supramolecular design. Supramolecular polymeric materials that allow adaptation, molecular recognition and triggered disassociation have been developed successfully within the last years. However, in terms of supramolecular microgels there are only few reports published, and all of them imply multistep procedures, as well as complex syntheses of supramolecular precursors. Based on all these facts, the main goal of this thesis was the design of bio-based supramolecular microgels with reversible crosslinks, and their utilization in bio-applications. In this work, I present a facile and optimized approach to produce supramolecular stimuli-responsive microgels composed of thermoresponsive and biocompatible poly(N-vinylcaprolactam) (PVCL) and the bioactive natural polyphenol tannic acid (TA). The ability of TA to form hydrogen bonds with polymeric compounds, allows its facile incorporation as a physical crosslinker within the microgel synthesis. Depending on the TA content, the microgel properties such as chemical composition, deformability, crosslinking density and dimension can be controlled. Moreover besides thermoresponsiveness, the PVCL/TA-microgels exhibit pH-sensitivity and can be degraded easily by pH-triggered disintegration of the non-covalent bonds. This feature, leads simultaneously to a controlled TA-release. Furthermore, the pH-dependent behavior of the microgels in combination with the complexant capacity of the incorporated TA guides to different interesting applications. The supramolecular polyphenolic PVCL-microgels were thus studied as attractive pH-responsive carriers for the transport of active components. Firstly, the nanomaterials were proposed as potential vehicles for the transport of metal ions (Fe3+). Herein, a controlled loading and release of the metal ions was successfully demonstrated. Moreover, the PVCL/TA-microgels were used as supramolecular containers for the incorporation of further phenolic derivatives, and encapsulation of antibacterial bioactive compounds. Here, the antibacterial activity of the multifunctional system was preliminary studied. The results obtained in this thesis confirmed not only that the developed microgel system is based on supramolecular assembly, but also that it offers an innovative, biocompatible and responsive compartment for the encapsulation of hydrophobic components in a water-based nanomaterial. This unique microgel represents an innovative biocompatible system that can be adapted to different applications and needs.