Dynamic Heterogeneous Hydrogels with Cellulose Nanocrystals
by Heqin Huang
Date of Examination:2019-03-14
Date of issue:2019-04-08
Advisor:Prof. Dr. Kai Jr.-Zhang
Referee:Prof. Dr. Kai Jr.-Zhang
Referee:Prof. Dr. Philipp Vana
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Description:Doctoral thesis of Heqin Huang
Abstract
English
Most biological tissues are made out of hydrogels, which are three dimensionally (3D) crosslinked polymer chains in an aqueous microenvironment. Comparing with highly dynamic and heterogeneous natural hydrogels, such as muscle or cartilage, traditional synthetic hydrogels usually suffer from poor mechanical properties. Meanwhile, even the viscoelasticity of hydrogels is widely known, but it is lack of more sophisticated and more practical applications. In this study, cellulose nanocrystals (CNC) and surface-modified CNC introduce heterogeneity into synthetic hydrogels. By mimicking the dynamic heterogeneous structure in the natural hydrogels, a class of hydrogels was prepared with a heterogeneous crosslinking network based on the pre-organized dynamic CNC nano-crosslinkers. With the well-designed dynamic CNC-polymer interaction, the hydrogels not only got stiffened, but exhibited the improved tolerance to local defects. Furthermore, in a dually heterogeneous hydrogel, the necking phenomenon was observed and can be controlled by the active CNC nanocrosslinkers, which narrowed the mechanical difference of diverse hydrogel components and stabilized their shapes and mechanical behaviors as hybrids. In addition to the investigation about hydrogel mechanical properties, the liquid behaviors of dynamic heterogeneous hydrogels were utilized to fabricate polymer materials with programmable shapes and microstructures. We successfully integrated the efficacies of both dynamic and static liquid behaviors to construct structural birefringent materials. Thus, dynamic heterogeneous hydrogels can expand the liquid behavior-assisted materials fabrication into various 3D geometries without the limitation of fluid channels. Based on this study about dynamic heterogeneous hydrogels, we got deeper understanding of structure-performance relationship in hydrogel materials. In addition, the experiences and working mechanisms demonstrated with CNC can be further applied in the hydrogels with other nanostructures. This thesis is a cumulative work including 3 publications. All papers were published in peer-reviewed journals. The background, the objective of the study, results and discussion of these three publications and the conclusion are presented in Sections 1-4.
Keywords: Hydrogel; Polymer; Cellulose