Synthesis and Application of Trehalose Materials

Trehalose is a naturally occurring, nonreducing disaccharide that is widely used in the biopharmaceutical, food, and cosmetic industries due to its stabilizing and cryoprotective properties. Over the years, scientists have developed methodologies to synthesize linear polymers with trehalose units either in the polymer backbone or as pendant groups. These macromolecules provide unique properties and characteristics, which often outperform trehalose itself. Additionally, numerous reports have focused on the synthesis and formulation of materials based on trehalose, such as nanoparticles, hydrogels, and thermoset networks. Among many applications, these polymers and materials have been used as protein stabilizers, as gene delivery systems, and to prevent amyloid aggregate formation. In this Perspective, recent developments in the synthesis and application of trehalose-based linear polymers, hydrogels, and nanomaterials are discussed, with a focus on utilization in the biomedical field.

Trehalose-Rich, Degradable Hydrogels Designed for Trehalose Release under Physiologically Relevant Conditions

Trehalose, a natural disaccharide, is primarily known for its ability to protect proteins from inactivation and denaturation caused by a variety of stress conditions. Furthermore, over the past few years, it has emerged as a promising therapeutic candidate for treatment of neurodegenerative diseases. Herein, we examine the attachment of trehalose to polymers for release under selected physiologically relevant conditions. The proposed strategies are evaluated specifically using hydrogels undergoing simultaneous degradation during trehalose release. These materials are fabricated via copolymerization of the appropriate acrylamide-type monomers with polymerizable trehalose esters or benzylidene acetals. This provides trehalose release in a slightly alkaline (i.e., pH 7.4) or mildly acidic (i.e., pH 5.0) environment, respectively. Using this method materials containing up to 51.7 wt% of trehalose are obtained. The presented results provide a solid basis for future studies on polymeric materials intended for trehalose release in biological systems.

Nonviral Gene Delivery with Cationic Glycopolymers

The field of gene therapy, which aims to treat patients by modulating gene expression, has come to fruition and has landed several landmark FDA approvals. Most gene therapies currently rely on viral vectors to deliver nucleic acid cargo into cells, but there is significant interest in moving toward chemical-based methods, such as polymer-based vectors, due to their low cost, immunocompatibility, and tunability. The full potential of polymer-based delivery systems has yet to be realized, however, because most polymeric transfection reagents are either too inefficient or too toxic for use in the clinic. In this Account, we describe developments in carbohydrate-based cationic polymers, termed glycopolymers, for enhanced nonviral gene delivery. As ubiquitous components of biological systems, carbohydrates are a rich class of compounds that can be harnessed to improve the biocompatibility of non-native polymers, such as linear polyamines used for promoting transfection. Reineke et al. developed a new class of carbohydrate-based polymers called poly(glycoamidoamine)s (PGAAs) by step-growth polymerization of linear monosaccharides with linear ethyleneamines. These glycopolymers were shown to be both efficient and biocompatible transfection reagents. Systematic modifications of the structural components of the PGAA system revealed structure-activity relationships important to its function, including its ability to degrade in situ. Expanding upon the development of step-growth glycopolymers, monosaccharides, such as glucose, were functionalized as vinyl-based monomers for the formation of diblock copolymers via radical addition-fragmentation chain-transfer (RAFT) polymerization. Upon complexation with plasmid DNA, the glucose-containing block creates a hydrophilic shell that promotes colloidal stability as effectively as PEG functionalization. An N-acetyl-d-galactosamine variant of this diblock polymer yields colloidally stable particles that show increased receptor-mediated uptake by liver hepatocytes in vitro and promotes liver targeting in mice. Finally, the disaccharide trehalose was incorporated into polycationic structures using both step-growth and RAFT techniques. It was shown that these trehalose-based copolymers imparted increased colloidal stability and yielded plasmid and siRNA polyplexes that resist aggregation upon lyophilization and reconstitution in water. The aforementioned series of glycopolymers use carbohydrates to promote effective and safe delivery of nucleic acid cargo into a variety of human cells types by promoting vehicle degradation, tissue-targeting, colloidal stabilization, and stability toward lyophilization to extend shelf life. Work is currently underway to translate the use of glycopolymers for safe and efficient delivery of nucleic acid cargo for gene therapy and gene editing applications.

Biosynthetic Polymers as Functional Materials

The synthesis of functional polymers encoded with biomolecules has been an extensive area of research for decades. As such, a diverse toolbox of polymerization techniques and bioconjugation methods has been developed. The greatest impact of this work has been in biomedicine and biotechnology, where fully synthetic and naturally derived biomolecules are used cooperatively. Despite significant improvements in biocompatible and functionally diverse polymers, our success in the field is constrained by recognized limitations in polymer architecture control, structural dynamics, and biostabilization. This Perspective discusses the current status of functional biosynthetic polymers and highlights innovative strategies reported within the past five years that have made great strides in overcoming the aforementioned barriers.