Self-regulatin materials with transient lifetimes via internal feedback in PH
Heuser, Thomas; Möller, Martin (Thesis advisor); Walther, Andreas (Thesis advisor)
Dissertation / PhD Thesis
Dissertation, RWTH Aachen University, 2017
The forthcoming generation of soft materials will be designed to autonomously adapt to their environment, in a way similar to living systems, in an active and self-regulating manner. While molecular engineering allows to program the spatial superstructures arising from soft matter building motifs, control over the time domain remains a major challenge. Within my thesis, I focus on the integration of preorchestrated temporal signatures into responsive self-assembling systems, to create adaptable and self-regulating materials. Within the last decade scientists widely mastered the spatial organization of complex and hierarchically ordered structures. In the simplest case, recognition between complementary building motifs, such as DNA base pairing, encodes the formation of the emerging super-structure. Classical responsiveness enables switching between separated equilibrium states upon external triggering and allows to induce assembly/disassembly processes on demand. The decisive step to conceive the next generation of bioinspired materials requires structuring under out-of-equilibrium conditions, to integrate lifelike characteristics, such as adaption, predefined lifetimes and autonomous self-regulation. In this work I present kinetic and biocatalytic strategies to program transient, preconfigured pH-profiles encoding the lifetimes of various pH-responsive self-assemblies. First I will showcase a general kinetic concept wherein temporal control is realized by combining a rapid promoter (base) and a slow hydrolyzing deactivator (acid) creating a transient alkaline pH-profile that controls the self-assembly response. Further, we refined this approach to include the feedback-driven biocatalytic conversion of urea into ammonia, which, concerted with an acidic buffer, results in time-controlled acidic pH-profiles. The system coupled to a peptide gelator enables temporal programming of hydrogel lifetimes depending on the concentration of the biocatalyst. Integration of our biocatalytic feedback system with a photonic gel based on a pH-sensitive block copolymer further facilitates self-regulating displays and pH-signal propagation. In the last part, both the promoting and deactivating pathway are substituted by biocatalytic feedback-controlled reactions, and I will present the transient formation of DNA-hydrogels preceded by an initial lag time. Though the fundamental objective of temporal control is similar for all approaches presented, they demonstrate different levels of complexity, from simple ester hydrolysis, towards feedback-regulated biocatalytic control, and finally comprising two antagonistic biocatalytic switches in the end.
- Department of Chemistry 
- Chair of Macromolecular Chemistry