Recent Advances in Polymer Additive Engineering for Diagnostic and Therapeutic Hydrogels

Hydrogels are hydrophilic polymer materials that provide a wide range of physicochemical properties as well as are highly biocompatible. Biomedical researchers are adapting these materials for the ever-increasing range of design options and potential applications in diagnostics and therapeutics. Along with innovative hydrogel polymer backbone developments, designing polymer additives for these backbones has been a major contributor to the field, especially for expanding the functionality spectrum of hydrogels. For the past decade, researchers invented numerous hydrogel functionalities that emerge from the rational incorporation of additives such as nucleic acids, proteins, cells, and inorganic nanomaterials. Cases of successful commercialization of such functional hydrogels are being reported, thus driving more translational research with hydrogels. Among the many hydrogels, here we reviewed recently reported functional hydrogels incorporated with polymer additives. We focused on those that have potential in translational medicine applications which range from diagnostic sensors as well as assay and drug screening to therapeutic actuators as well as drug delivery and implant. We discussed the growing trend of facile point-of-care diagnostics and integrated smart platforms. Additionally, special emphasis was given to emerging bioinformatics functionalities stemming from the information technology field, such as DNA data storage and anti-counterfeiting strategies. We anticipate that these translational purpose-driven polymer additive research studies will continue to advance the field of functional hydrogel engineering.

Enzyme-Laden Bioactive Hydrogel for Biocatalytic Monitoring and Regulation

Enzymes, a class of highly efficient and specific catalysts in Nature, dictate a myriad of reactions that constitute various cascades in biological systems. There is growing evidence that many cellular reactions within metabolic pathways are catalyzed by matrix-associated multienzyme complexes, not via the free enzymes, verifying the vital effects of microenvironmental organization, which would reveal implications for the high efficiency, specificity, and regulation of metabolic pathways. The extracellular matrix (ECM), as the noncellular component, is composed of various proteins such as collagens, laminins, proteoglycans, and remodeling enzymes, playing the key role in tissue architecture and homeostasis. Hydrogels are defined as highly hydrated polymer materials and maintain structural integrity by physical and chemical force, which are thought of as the most suitable materials for matching the chemical, physical, and mechanical properties with natural ECM. As one specific type of soft and wet materials, hydrogels are suitable three-dimensional carriers to locally confine bioactive guests, such as enzymes, for molecular-level biological interactions. The efficient cascade catalysis can be realized by enzyme-laden hydrogels, which can potentially interact with cells and tissues by material-to-biology communication. In this Account, we present recent progress on the preparation of enzymatic bioactive hydrogels, including in situ coassembly, in situ cross-linking strategy, and in situ enzymatic radical polymerization technology, further promoting their applications on biomedical tissue engineering, biocatalytic health monitoring, and therapeutic research. First, we provide a brief introduction of the basic concept related to an enzymatic strategy in living systems and the importance of bioinspired enzyme-laden bioactive hydrogel systems. We discuss the difficulties of the fabrication of a bioactive hydrogel with a high catalytic efficiency, thereby providing the novel molecular design and regulation based on a noncovalent coassembly and in situ self-immobilization strategy to obtain the compartmentalized enzyme-laden structure. Then the applications of an enzyme-laden bioactive hydrogel for biocatalytic applications are discussed in detail. The enzyme-laden bioactive hydrogel can maintain the favorable perception and regulation behavior of enzymes with optimal enzymatic efficacy between this confined hydrogel network and a surrounding environment. A highlight to the advances in the responsively biocatalytic monitoring and regulation of bioactive hydrogel, including the enzymatic biomedical tissue engineering and health monitoring, enzymatic regulation of tumor reactive oxygen species and therapeutic research are given. Finally, the outlook of open challenges and future developments of this rapidly evolving field is provided. This Account with highlights of diverse enzyme-laden bioactive hydrogel systems not only provides interesting insights to understand the cascade enzymatic strategy of life but also inspires to broaden and enhance the molecular-level material design and bioapplications of existing enzymatic materials in chemistry, materials science, and biology.

Oxidoreductase-Initiated Radical Polymerizations to Design Hydrogels and Micro/Nanogels: Mechanism, Molding, and Applications

Due to their 3D cross-linked networks and tunable physicochemical properties, polymer hydrogels with different sizes are applied widely in tissue engineering, drug-delivery systems, pollution regulation, ionic conducting electrolytes, agricultural drought-resistance, cosmetics, and the food industry. Novel, environmentally friendly, and efficient oxidoreductase-initiated radical polymerizations to design hydrogels and micro/nanogels have gained increasing attention. Herein, the recent advances on the use of novel enzyme-initiated systems for hydrogel polymerization, including the mechanisms, and molding of polymeric and hybrid-polymeric networks are reviewed. Preliminary progress related to interfacial enzymatic polymerization for the generation of hybrid micro/nanogels is introduced as an emerging initiating approach. In addition, certain biological applications in tissue engineering, bioimaging, and therapy are demonstrated step by step. Finally, some perspectives on the safety profile of enzymatic formed hydrogels, new enzymatic systems, and potential theranostic applications are discussed.

Laccase-mediated formation of mesoporous silica nanoparticle based redox stimuli-responsive hybrid nanogels as a multifunctional nanotheranostic agent

In this work, we designed a new hybrid nanogel with redox responsive polymer gel shells and mesoporous silica nanoparticles (MSNs) cores via laccase-mediated radical polymerization. The successful coating of the responsive gel shells on the MSNs was confirmed by the morphology and increased diameters of the particles as determined by transmission electron microscopy (TEM) and dynamic light scattering (DLS). As observed by scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDS), the presence of the element S around the MSNs further confirmed the formation of the gel shell. When loaded with doxorubicin (DOX), these hybrid nanogels had a significantly higher cumulative DOX release in a reductive environment than that found under physiological conditions. The MSNs with mesoporous channels were loaded with perfluorohexane (PFH) for ultrasound imaging, which was enhanced by the presence of the elastic gel shells.