Functional Gels from Natural Nanomaterials

Significance 

Gels are entangled networks where a fluid is physically confined, yielding a material with a unique soft-solid behavior. Evidenced by widespread applications: ranging from simple food additives and drug carriers, to intricate smart materials and soft robotics, these materials have evolved academically into the backbone of many research studies. Gels possess properties that enable their application as molecular receptors, absorbing chemical species from solution or air. To further improve on their applicability, functional units can be installed inside the gel’s structure. During this endeavor, chemically or physically, reversible, responsive, and selective absorption processes can occur. Regardless, supramolecular approaches to embed functional moieties within gels remain rare. To overcome this pitfall, several researchers have proposed the use of cellulose nanocrystals (CNCs), colloidal suspensions modified with inorganic or organic salts, to assemble cellulose-based hydrogels.

Simply put, cellulose nanocrystals spontaneously assemble into gels when mixed with a polyionic organic or inorganic salt. Unfortunately, not much has been reported on this ion-induced gelation strategy to create functional CNC gels with organic host molecules. To bridge this gap, researchers from the University of British Columbia in Canada: Dongjie Zhang (graduate student), Dr. Miguel A. Soto (postdoctoral fellow), Dr. Lev Lewis and led by Professor Mark MacLachlan, in collaboration with Dr. Wadood Hamad at the Bioproducts Innovation Centre of Excellence, FPInnovations developed a novel approach to create CNC-based materials that contain functional ions. Their work is currently published in the research journal, Angewandte Chemie.

The researchers envisioned ionic macrocycles driving gelation of CNCs to generate materials with embedded host molecules. To pursue their concept, the team selected the rigid tetracationic macrocycle, cyclobis(paraquat-p-phenylene) (CBPQT4+), as the functional ion. Technically, their approach involved mixing of an aqueous suspension of sodium neutralized cellulose nanocrystals with [CBPQT]Cl4 in solution. The enhancement of the gel stiffness with increasing host concentration was confirmed through rheological studies of the CNC-CBPQT4+ systems.

The authors reported that addition of [CBPQT]Cl4 to CNCs caused gelation and embedded an active host inside the material. Moreover, the team established that the fabricated CNC gels could reversibly absorb guest molecules from solution then undergo molecular recognition processes that created colorful host–guest complexes. The researchers even implemented the aforementioned materials in gel chromatography (for guest exchange and separation), and as elements to encode 2- and 3-dimensional patterns, where they anchored well.

In summary, the Canadian scientists employed a supramolecular ion-induced strategy to produce CNC-CBPQT4+ gels with a cationic host embedded in a cellulose nanocrystal matrix, a supramolecular process that does not require tedious synthesis.  Remarkably, the reported gels could function as receptors to absorb guest species from solution to subsequently undergo reversible assembly of host–guest complexes in their interior. In a statement to Advances in Engineering, Professor Mark MacLachlan, the lead author emphasized that they anticipated their facile, yet robust, gel fabrication strategy will have important applications particularly when creating new functional materials. “These materials could be excellent for developing sensors or sequestering contaminants from the environment,” he added.

Functional Gels from Natural Nanomaterials - Advances in Engineering

About the author

Mark MacLachlan is a Professor of Chemistry at the University of British Columbia and holds the Canada Research Chair in Supramolecular Materials. He received his B.Sc. degree in honours chemistry (1995; UBC) and Ph.D. degree (1999; Toronto) in inorganic materials chemistry. After an NSERC Postdoctoral Fellowship at M.I.T., Mark began his independent career at UBC in 2001. His research interests span supramolecular chemistry, nanomaterials, mesoporous materials, photonic structures, and biopolymers. Mark’s most notable contributions have been in the area of cellulose nanocrystals, where he has used them to construct new photonic materials. He has received a Humboldt Fellowship for Experienced Researchers (2009-2010), an E. W. R. Steacie Memorial Fellowship (2012-2014), and the Award for Excellence in Materials Chemistry of the Canadian Society of Chemistry (2015). Mark is a Fellow of the Royal Society of Canada and the Royal Society of Chemistry (UK).

About the author

Miguel A. Soto completed his B.Sc. (industrial chemistry) and Ph.D. degrees in Mexico City, at the National Autonomous University of Mexico (UNAM) and the Center for Research and Advanced Studies (Cinvestav), respectively. Soon after defending his Ph.D. (2017), he moved to the University of British Columbia to join the MacLachlan group as a postdoctoral researcher where he develops new systems combining materials science and supramolecular chemistry. His research interests span from physical/chemical sensors to water remediation technologies and photoluminescent materials.

About the author

Dongjie Zhang was born in a small county called Rongcheng (now called Xiong’an, new district since 2017). She completed her B.Sc. degree in 2014 and started her Ph.D. degree at the same institution: Harbin Institute of Technology, in China, where she currently undertakes varied research projects at the intersection of polymer science and engineering. In October 2018, she joined the MacLachlan group as an international visiting student and investigated the gelation properties of cellulose nanocrystals and their incorporation into stimuli-responsive gels.

About the author

Wadood Y. Hamad has expertise in materials science and nanotechnology with over 20 years of experience in academic research, material design, and industrial implementation. He is Lead Scientist and Research Manager of the Transformation and Interfaces Group within the Bioproducts Innovation Centre of Excellence at FPInnovations, and Adjunct Professor at the Department of Chemistry, University of British Columbia. His work has led to over 25 families of patented applications and over 120 peer-reviewed book chapters, scientific papers and authoritative reviews. He authored two seminal monographs, Cellulosic Materials: Fibers, Networks and Composites (Kluwer Academic, 2002) and Cellulose Nanocrystals: Properties, Production and Applications (Wiley, 2017).

About the author

Lev Lewis received his PhD in Chemistry from the University of British Columbia in 2019. He studied the gelation of cellulose nanocrystals to form colloidal gels under the supervision of Prof. Mark MacLachlan. He now works as a Scientist at STEMCELL Technologies Inc. focusing on magnetic nanoparticle synthesis and stability for cell separation applications.

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Reference

D. Zhang, Miguel A. Soto, L. Lewis, W. Y. Hamad, M. J. MacLachlan. Host-Guest Chemistry Within Cellulose Nanocrystal Gel Receptors. Angewandte Chemie International Edition 2020, volume 59, page 4705 – 4710.

Go To Angewandte Chemie International Edition

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