Multifunctional Hydrogels Integrated with Reversible Noncovalent Interactions for Bioengineering and Sensing Applications
Creators: Peng, Xuwen
Publisher: name: University of Alberta Library
Year: 2023

<p>Hydrogels bear a close resemblance to human tissues and thus have been extensively employed for a broad range of applications in recent years. Intelligent hydrogels that can respond to diverse stimuli, such as pH, temperature, ionic strength, strain and stress, hold great promise for a variety of biological engineering and sensing applications. Nevertheless, weak mechanical properties and narrow functionality have limited the application of traditional hydrogels generally based on permanent covalent bonds. Incorporating reversible noncovalent interactions within hydrogel networks is an effective approach that lifts those restrictions. In the context of the growing demand for bioengineering and sensing applications, it is of great significance yet remains a challenge to integrate multifunctionalities such as mechanical robustness, self-healing properties, stimuli-responsiveness and conductivity into one hydrogel through the introduction of reversible interactions, functional components and well-designed structures. In this thesis, a review of multifunctional hydrogels, non-covalent interactions and corresponding hydrogels, and bioengineering and sensing applications of hydrogels is presented first, followed by three original research projects investigating the integrated multifunctional hydrogels for different potential biomedical and electrical sensing applications. <br>
Hydrogels with good stretchability, high adhesiveness, sensitive electrical responsiveness, biocompatible and antibacterial features are exceptionally desirable materials for various biomedical and sensing applications. In the first project, we fabricated a highly stretchable, moldable, self-healing and antibacterial hydrogel with electrical responsiveness by introducing dynamic noncovalent interactions, i.e., hydrogen-bonding among hydroxyl groups of poly (vinyl alcohol) (PVA), carboxyl moieties of poly (methyl vinyl ether-alt-maleic acid) (PMVEMA), and the catechol groups in tannic acid (TA). The prepared PPTA hydrogel shows a wide spectrum of desirable properties, including fast gelation, excellent and adjustable mechanical properties (true stress at break and fracture strain up to ~7 MPa and ∼2300%, respectively), self-healing and remolding abilities, robust adhesion to diverse substrates, antimicrobial activity to both Escherichia coli and staphylococcus aureus bacteria, and stability under a broad range of pH environments (pH 1−10). Moreover, this hydrogel demonstrates good sensitivity for monitoring strain, pressure and human motions. Therefore, this hydrogen-bonding-driven, multifunctional hydrogel with facile fabrication and flexible modification provides an exciting paradigm for biosensing and bioengineering applications.<br>
Hydrogels combining both conductive capability and robust mechanical properties hold great promise in wearable soft electronics. In the second project, we fabricated a multifunctional hydrogel for strain sensing applications. By incorporating a conductive polymer network Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT: PSS) into the PVA/ poly (acrylic acid) (PAA) double network (DN) hydrogel, this PEDOT: PSS@PVA/PAA hydrogel system presents good stretchability, high toughness and fatigue resistance. Besides the improvement of mechanical properties, the multiple hydrogen bonding interactions also endow the hydrogel with self-healing properties and strong adhesion to various substrates. Moreover, the hydrogel shows high electrical sensitivity (Gauge Factor from 2.21 to 3.82) to strains, which enables it to sense different types of motions (e.g., stretching, compressing, bending, etc.). Precise detections of many subtle human motions including pulse and vocal cord vibration were achieved. This work provides new insights into the development of multifunctional conductive hydrogels for wearable sensors, electronic skin, and other bioelectrical engineering applications.<br>
Multifunctional hydrogels that respond to bio-related stimuli hold significant promise for smart drug delivery systems. In the third project, a pH-responsive microgel-embedded hydrogel with adhesiveness and robust mechanical properties was developed as a dual drug delivery system for wound-healing. The polyacrylamide (PAAm)/ chitosan (CS) semi-interpenetrating (semi-IPN) hydrogel exhibits excellent stretchability, compressibility and elasticity. Meanwhile, this hydrogel can tightly adhere to various surfaces of porcine tissues and subduct the mismatch between hydrogel and tissue interfaces. Moreover, by incorporating poly (N-isopropylacrylamide-co-acrylic acid) (PNIPAAm-AAc) based microgel particles, the hybrid hydrogel system can be used for dual drug delivery of both bovine serum albumin (BSA, model protein) and Sulfamethoxazole (SMZ) in a pH-responsive manner. Compared with traditional oral, injection and smear medications, this integrated microparticle-based drug delivery system shows advantages such as high drug loading efficiency (more than 80%), controllable drug releasing behaviors and sustained drug releasing duration (over 48h), which have the potential for applications of smart wound dressing materials in biomedical engineering.<br>
This thesis work develops three multifunctional hydrogels based on various non-covalent interactions for applications in bioengineering and sensing. This work broadens the application of hydrogels in some bioengineering areas and provides new insights for developing novel, intelligent, wearable electronics for sensing applications.</p>