AbstractsBiology & Animal Science

Functionalized hydrogel systems for molecular sensing and transport

by Chunjie Zhang

Institution: University of Illinois – Urbana-Champaign
Department: 0130
Degree: PhD
Year: 2015
Keywords: hydrogel
Record ID: 2058304
Full text PDF: http://hdl.handle.net/2142/73065


Hydrogels are a unique class of materials. The combination of many outstanding properties, including responsiveness, elasticity, transparency, porosity, high water content, biocompatibility, and the ability to immobilize functional species makes hydrogels attractive multifunctional materials for a broad range of applications. This dissertation focuses on modulating hydrogel properties for applications in molecular sensing and transport. There are two focus areas under the hydrogel theme within this dissertation. The first area is focused on the design, synthesis, and characterization of hydrogel glucose sensor materials with a liner fast response, small hysteresis and good stability under simulated physiological conditions. The first step was to study the interactions of glucose with phenylboronic acid (PBA) which is the glucose sensing functionality inside hydrogels. We find that (i) linear and slow responses are observed on hydrogels containing PBAs of low reactivity to glucose, (ii) linear and slow responses are coupled, (iii) the intramolecular ring formed in such PBAs is responsible for the low reactivity, (iv) PBAs of low pKa generally lead to low sensitivity, (v) hydrogels containing PBAs without intramolecular ring show fast and nonlinear response, (vi) nonlinear and fast responses are coupled, (vii) 1:1 and 2:1 PBA-glucose complexes exist universally in PBA-modified hydrogels and their coexistence leads to the nonlinear response. Based on these observations, a linear and fast sensor design is developed by tailoring the binding of nonlinear PBAs with glucose. A volume resetting agent is incorporated into the PBA-modified hydrogels to crosslink the PBA moieties and shrink the hydrogel volume in the absence of glucose. When glucose is present, the crosslinks are displaced into 1:1 PBA-glucose complexes, leading to a linear volume expansion. The coexistence of 1:1 and 2:1 PBA-glucose complexes during glucose sensing is largely eliminated. The sensor performance in terms of sensitivity, dynamic range, kinetics, hysteresis and stability is evaluated under simulated physiological conditions. The structure-property correlation of the sensor material is studied to allow customizing the sensor performance for different applications. The second primary area of this dissertation focuses on developing autonomic hydrogel materials that can manipulate molecular transport without external input. To anisotropically move molecules, enthalpy gradients are incorporated into the hydrogel. The molecules of interest undergo a downhill movement to lower enthalpy locations in the hydrogel, enabling the spatial iii control of molecular transport, even when such directed transport leads to the concentration of molecules. The enthalpy of molecules are essentially from interactions with the chemical gradients built inside the hydrogel medium. The chemical gradients are fabricated by localized chemical modification of hydrogels. The diffusion of reactive species inside hydrogel enables a gradual variation in the hydrogel chemical…