Stimuli-Responsive and Self-Healing Nanocomposite Hydrogels Based on Reversible and Dynamic Crosslinks
Creators: Wu, Meng
Publisher: name: University of Alberta Library
Year: 2022

<p>Hydrogels, due to their soft and water abundant natures, highly resemble human skins and tissues and thereby have attracted extensive attention in recent years. Functional hydrogels showing responsiveness to various stimuli such as pH, temperature, strain and pressure are promising for a wide range of biomedical and electrical applications. However, traditional hydrogels crosslinked via permanent covalent bonds are generally weak, brittle and lack of functionalities. Incorporation of reversible and dynamic crosslinks into hydrogel networks can effectively improve their mechanical performances, introduce multiple responsiveness, and endow the hydrogels with self-healing capability. On the other hand, introduction of stiff nanomaterials into hydrogel matrix is an effective approach towards strong and functional gel materials. The combination of the nanofillers and appropriate interfacial reversible and dynamic interactions provides a promising method for the fabrication of high-performance multifunctional hydrogels to meet the increasing needs of modern materials. In this thesis, a review on hydrogels based on reversible and dynamic crosslinks, stimuli-responsive and self-healing functions, and nanocomposite hydrogels was presented first followed by three original research projects on developing nanocomposite hydrogels with stimuli sensitivity and self-healing property based on reversible interactions for biomedical and electrical applications.<br>
Injectable, self-healing and pH-responsive hydrogels are great intelligent drug delivery vehicles for controlled and localized therapeutic release. Hydrogels that show pH-sensitive behaviors in mildly acidic range are ideal to be used for the treatment of regions showing local acidosis like tumors, wounds and infections. In the first project, we present a facile preparation of an injectable, self-healing and super-sensitive pH-responsive nanocomposite hydrogel based on Schiff base reactions between aldehyde-functionalized polymers and amine-modified silica nanoparticles. The hydrogel shows fast gelation, injectability and rapid self-healing capability. Moreover, the hydrogel demonstrates excellent stability under neutral physiological conditions while a sharp gel-sol transition induced by faintly acidic environment. The pH-responsiveness of the hydrogel is ultra-sensitive, where the mechanical properties, hydrolytic degradation and drug release behaviors can alter significantly when subjected to a slight pH change of 0.2. The novel injectable, self-healing and sensitive pH-responsive hydrogel serves as a promising candidate as localized drug carriers with controlled delivery capability triggered by acidosis, holding great promise for cancer therapy, wound healing and infection treatment.<br><br>
Conductive hydrogels are of great significance for soft electronic devices. In the second project, we have developed a novel hydrogel ionic conductor by integrating nanofiller reinforcement with micelle cross-linking. The hydrogel was facilely prepared via one-pot polymerization of acrylamide and an amino-functionalized monomer in the presence of carbon nanotubes, aldehyde-modified F127 and LiCl. The dynamic chemical and physical interactions of the cross-linked network offers the hydrogel with a wide spectrum of properties, including excellent stretchability, toughness, exceptional elasticity, resistance to damage by sharp materials, self-healing property and high conductivity. In addition, the hydrogel demonstrated cooling-induced whitening optical behavior. When exploited as a strain and pressure sensor to monitor diverse human motions, the prepared hydrogel sensor showed excellent sensitivity and reliability. The hydrogel was further integrated with an eye mask to monitor human sleep and showed high reliability for the detection of rapid eye movement (REM) sleep. This work provides new insights into the fabrication of multifunctional, smart and conductive materials, holding great promise for a broad range of applications like wearable sensors, artificial skins, and soft robotics.<br>
In the third project, we have developed an ionic conductive nanocomposite hydrogel with ultra-stretchability and intelligent sensing functions. By leveraging the dynamic feature of multiple intermolecular interactions, polymer/carbon nanotube networks with excellent mechanical performances (i.e., tensile strength, stretchability and toughness up to 1.09 MPa, 4075% and 12.8 MJ/m3, respectively) were achieved. Additionally, the hydrogel is soft, elastic, transparent and self-healing. The rational combination of the mechanical and electrical properties renders the as-prepared hydrogel with excellent sensing performances and cycling stability, and therefore enables it to perform as a sensory unit of a complete platform for the recognition of some complicated human behaviors. Specifically, with the integration of machine learning module, the hydrogel-based platform exhibits great recognition accuracies to human handwriting motions from single letters to words and phrases after proper training. The combination of superior mechanical performances and intelligent sensing functions within this hydrogel-based ionic skin unlocks its potential as the intelligent human-device interface, which promotes the application of artificial intelligence in customized electronic devices.</p>