Wenhao Cai | ALES Graduate Seminar

Event details: A graduate exam seminar is a presentation of the student’s final research project for their degree. This is an ALES PhD Final Exam Seminar by Wenhao Cai. This seminar is open to the general public to attend.

Zoom Link: https://ualberta-ca.zoom.us/j/98697739556?pwd=yXk3bwV5fbbYmJ2aipaYoqrFd6an8l.1  

PhD with Dr. Lingyun Chen       

Thesis Topic: Development of Molecular Design Approaches for New and Improved Functional Properties of Protein-Based Hydrogels and Exploring Their Potentials in Food and Electronic Applications

Abstract:

Proteins are natural, renewable, and biodegradable macromolecules with great potential as building blocks for sustainable hydrogel materials. Their intrinsic biocompatibility and nutritional value make them especially attractive for food and biomedical applications. However, many plant proteins, particularly from pulses like pea, suffer from weak gelation properties due to their low cysteine content and limited ability to form strong intermolecular crosslinks. This challenge restricts their broader application as structuring agents in food systems and beyond. The overall objective of this thesis was to develop molecular design strategies for protein-based hydrogels with new and improved functional properties and to explore their potential in food and electronic applications. The approaches focused on green, physically driven methods compatible with biodegradability and food safety.

The initial work aims to address the weak gelling ability of pea protein, largely attributed to its low cysteine content and limited capacity for strong crosslinks. To overcome this while maintaining food safety and clean-label status, physical strategies were considered. Instead of using native protein, heat-induced pea protein aggregates were employed to prepare the gels, owing to their enhanced surface hydrophobicity and structural rearrangement, which facilitate network formation. These aggregates were subsequently complexed with κ-carrageenan, a food-grade polysaccharide known for its strong gelling properties. This approach produced food-grade gels with impressive mechanical strength (~14.15 kPa) at low protein (7.5%) and carrageenan (0.5%) levels, comparable to or exceeding the strength of whey protein isolate gels at similar concentrations. TEM and FTIR analyses revealed that hydrophobic regions on the aggregates effectively interacted with carrageenan, forming a fine-pored, interconnected network. This tight crosslinking enabled phase separation and contributed directly to gel strength. Practically, this strategy offers the food industry a sustainable, plant-based alternative to animal-derived gelling agents. The resulting textures meet consumer demands for natural, clean-label ingredients and support applications in vegan meats and dairy alternatives.

Inspired by biological interactions, the second part of the study focused on designing a biodegradable hydrogel electrolyte from gelatin and β-cyclodextrin-grafted chitosan for zinc-ion battery applications, addressing the limitations of current liquid electrolytes such as flammability, leakage and pollution. Supramolecular host–guest chemistry between the hydrophobic cavity of β-cyclodextrin and aromatic residues in gelatin (e.g., tyrosine, phenylalanine) produced strong gels with tensile strength (~1.49 MPa) and stretchability (>400%). These properties, combined with dynamic ionic crosslinking and electron-donating groups (amino, hydroxyl, carboxyl), enabled uniform Zn²⁺ ion transport and suppressed dendrite growth, which is a common issue that limits battery lifespan. The hydrogel achieved high ionic conductivity (~24.9 mS·cm⁻¹), comparable to liquid electrolytes, and enabled over 1200 hours of stable cycling. Composed entirely of biodegradable, biocompatible materials, the hydrogel degraded ~85% within 28 days in soil. This electrolyte improved battery safety and reduced environmental impact, offering a sustainable alternative to conventional systems.

Building on these design principles, the final study developed a multifunctional hydrogel for wearable electronics, where biocompatibility, flexibility, and sustainability are essential. A physically crosslinked gelatin/β-cyclodextrin-chitosan organohydrogel was prepared for strain-sensing applications. Multiple reversible non-covalent interactions, hydrogen bonding, ionic interactions, and host–guest complexes, created a robust, dynamic network without synthetic polymers. The organohydrogel showed high elasticity (~410%) and self-healing ability (~85% recovery after damage), with stable performance from –20°C to 37°C. As a strain sensor, it accurately tracked human motions, from facial expressions to joint bending, and delivered consistent electrical signals over 600 cycles. Its comfort and biocompatibility make it well-suited for use in wearable health monitors and interactive devices.

Collectively, this research introduced physical and chemical strategies to enable hydrogels with enhanced strength, elasticity, conductivity, and self-healing, while preserving biodegradability and biocompatibility. These improved functions expand the use of food proteins in both edible systems (e.g., meat substitutes, gelled snacks) and non-food applications (e.g., hydrogel electrolytes, wearable sensors). The work advances understanding of how molecular-level interactions, such as aggregate morphology, protein–polysaccharide binding, and supramolecular crosslinking, influence bulk hydrogel properties. It also offers practical guidance for creating fully bio-based, clean-label alternatives to synthetic polymers. Demonstrating that gelatin and pea protein based hydrogels can match the performance of synthetic materials in both edible and electronic applications, thus providing viable, scalable, and sustainable solutions for industries seeking to reduce reliance on petroleum-based materials.