Cobalt-Cross-Linked, Redox-Responsive Spy Network Protein Hydrogels

Stimuli-responsive peptide hydrogels for biomedical applications

Stimuli-responsive hydrogels can respond to external stimuli with a change in the network structure and thus have potential application in drug release, intelligent sensing, and scaffold construction. Peptides possess robust supramolecular self-assembly ability, enabling spontaneous formation of nanostructures through supramolecular interactions and subsequently hydrogels. Therefore, peptide-based stimuli-responsive hydrogels have been widely explored as smart soft materials for biomedical applications in the last decade. Herein, we present a review article on design strategies and research progress of peptide hydrogels as stimuli-responsive materials in the field of biomedicine. The latest design and development of peptide hydrogels with responsive behaviors to stimuli are first presented. The following part provides a systematic overview of the functions and applications of stimuli-responsive peptide hydrogels in tissue engineering, drug delivery, wound healing, antimicrobial treatment, 3D cell culture, biosensors, etc. Finally, the remaining challenges and future prospects of stimuli-responsive peptide hydrogels are proposed. It is believed that this review will contribute to the rational design and development of stimuli-responsive peptide hydrogels toward biomedical applications.

Catcher/Tag Toolbox: Biomolecular Click-Reactions For Protein Engineering Beyond Genetics

Manipulating protein architectures beyond genetic control has attracted widespread attention. Catcher/Tag systems enable highly specific conjugation of proteins in vivo and in vitro via an isopeptide-bond. They provide efficient, robust, and irreversible strategies for protein conjugation and are simple yet powerful tools for a variety of applications in enzyme industry, vaccines, biomaterials, and cellular applications. Here we summarize recent development of the Catcher/Tag toolbox with a particular emphasis on the design of Catcher/Tag pairs targeted for specific applications. We cover the current limitations of the Catcher/Tag systems and discuss the pH sensitivity of the reactions. Finally, we conclude some of the future directions in the development of this versatile protein conjugation method and envision that improved control over inducing the ligation reaction will further broaden the range of applications.

Stimuli-Responsive Protein Hydrogels: Their Design, Properties, and Biomedical Applications

Protein-based hydrogels are considered ideal biomaterials due to their high biocompatibility, diverse structure, and their improved bioactivity and biodegradability. However, it remains challenging to mimic the native extracellular matrices that can dynamically respond to environmental stimuli. The combination of stimuli-responsive functionalities with engineered protein hydrogels has facilitated the development of new smart hydrogels with tunable biomechanics and biological properties that are triggered by cyto-compatible stimuli. This review summarizes the recent advancements of responsive hydrogels prepared from engineered proteins and integrated with physical, chemical or biological responsive moieties. We underscore the design principles and fabrication approaches of responsive protein hydrogels, and their biomedical applications in disease treatment, drug delivery, and tissue engineering are briefly discussed. Finally, the current challenges and future perspectives in this field are highlighted.

Synthetic biology-guided design and biosynthesis of protein polymers for delivery

Vehicles derived from genetically engineered protein polymers have gained momentum in the field of biomedical engineering due to their unique designability, remarkable biocompatibility and excellent biodegradability. However, the design and production of these protein polymers with on-demand sequences and supramolecular architectures remain underexplored, particularly from a synthetic biology perspective. In this review, we summarize the state-of-the art strategies for constructing the highly repetitive genes encoding the protein polymers, and highlight the advanced approaches for metabolically engineering expression hosts towards high-level biosynthesis of the target protein polymers. Finally, we showcase the typical protein polymers utilized to fabricate delivery vehicles.

Orchestrating Chemical and Physical Cross-Linking in Protein Hydrogels to Regulate Embryonic Stem Cell Growth

Protein hydrogels are ideal candidates for next-generation biomaterials due to their genetically programmable properties. Herein, we report an entirely protein-based hydrogel as an artificial extracellular matrix (ECM) for regulating the embryonic stem cell growth. A synergy between chemical and physical cross-linking was achieved in one step by SpyTag/SpyCatcher reaction and P zipper association at 37 °C. The hydrogels' stress relaxation behaviors can be tuned across a broad spectrum by single-point mutation on a P zipper. It has been found that faster relaxation can promote the growth of HeLa tumor spheroids and embryonic stem cells, and mechanical regulation of embryonic stem cells occurs via retention of the cells at the G1 phase. The results highlight the promise of genetically encoded protein materials as a platform of artificial ECM for understanding and controlling the complex cell-matrix interactions in a 3D cell culture.

Modulation of hydrogel networks by metal ions

Self-assembling hydrogels are receiving great attention for both biomedical and technological applications. Self-assembly of protein/peptides as well as organic molecules is commonly induced in response to external triggers such as changes of temperature, concentration, or pH. An interesting strategy to modulate the morphology and mechanical properties of the gels implies the use of metal ions, where coordination bonds regulate the dynamic cross-linking in the construction of hydrogels, and coordination geometries, catalytic, and redox properties of metal ions play crucial roles. This review aims to discuss recent insights into the supramolecular assembly of hydrogels involving metal ions, with a focus on self-assembling peptides, as well as applications of metallogels in biomedical fields including tissue engineering, sensing, wound healing, and drug delivery.

Photoredox-Mediated Designing and Regulating Metal-Coordinate Hydrogels for Programmable Soft 3D-Printed Actuators

Metal-organic coordination is widely applied for designing responsive polymers and soft devices. But it is still a challenge to prepare redox-responsive actuators with complicated structures, limiting their advanced applications in material and engineering fields. Here, we report a photoredox-mediated designing and regulating strategy to fabricate metal-coordinate hydrogels with the catalysis of Ru(II)/Co(III) under visible-light irradiation in seconds. Meanwhile, multiple polymer networks are formed and penetrated by each other, enabling as-prepared hydrogels excellent mechanical properties and toughness. This rapid, one-step, and controllable process is highly compatible with standard photography and printing techniques to make hierarchical 2D/3D structures. Importantly, the oxidization decomposition of Co(III) benefits the formation of cobalt cation-based redox-responsive networks, which have the potential for designing shape-memory materials and actuators by the regulation of Co^3+/2+ states via tuning redox environmental conditions. As a proof-of-concept, a programmable air-driven actuator is successfully demonstrated to control cargo capturing/releasing by designing complicated, asymmetric structures and optimizing their performance with the combination of a typical extrusion 3D printing approach. In this Letter, we report a simple and general metal-organic coordination strategy for designing high-performance actuators, which shows promising applications in smart soft devices and electronics.

Physical and Chemical Factors Influencing the Printability of Hydrogel-based Extrusion Bioinks

Bioprinting researchers agree that "printability" is a key characteristic for bioink development, but neither the meaning of the term nor the best way to experimentally measure it has been established. Furthermore, little is known with respect to the underlying mechanisms which determine a bioink's printability. A thorough understanding of these mechanisms is key to the intentional design of new bioinks. For the purposes of this review, the domain of printability is defined as the bioink requirements which are unique to bioprinting and occur during the printing process. Within this domain, the different aspects of printability and the factors which influence them are reviewed. The extrudability, filament classification, shape fidelity, and printing accuracy of bioinks are examined in detail with respect to their rheological properties, chemical structure, and printing parameters. These relationships are discussed and areas where further research is needed, are identified. This review serves to aid the bioink development process, which will continue to play a major role in the successes and failures of bioprinting, tissue engineering, and regenerative medicine going forward.

Injectable, photoresponsive hydrogels for delivering neuroprotective proteins enabled by metal-directed protein assembly

Axon regeneration constitutes a fundamental challenge for regenerative neurobiology, which necessitates the use of tailor-made biomaterials for controllable delivery of cells and biomolecules. An increasingly popular approach for creating these materials is to directly assemble engineered proteins into high-order structures, a process that often relies on sophisticated protein chemistry. Here, we present a simple approach for creating injectable, photoresponsive hydrogels via metal-directed assembly of His6-tagged proteins. The B12-dependent photoreceptor protein CarHC can complex with transition metal ions through an amino-terminal His6-tag, which can further undergo a sol-gel transition upon addition of AdoB12, leading to the formation of hydrogels with marked injectability and photodegradability. The inducible phase transitions further enabled facile encapsulation and release of cells and proteins. Injecting the Zn2+-coordinated gels decorated with leukemia inhibitory factor into injured mouse optic nerves led to prolonged cellular signaling and enhanced axon regeneration. This study illustrates a powerful strategy for designing injectable biomaterials.

Tagging and catching: rapid isolation and efficient labeling of organelles using the covalent Spy-System in planta

BACKGROUND

Up-to-now, several biochemical methods have been developed to allow specific organelle isolation from plant tissues. These procedures are often time consuming, require substantial amounts of plant material, have low yield or do not result in pure organelle fractions. Moreover, barely a protocol allows rapid and flexible isolation of different subcellular compartments. The recently published SpySystem enables the in vitro and in vivo covalent linkage between proteins and protein complexes. Here we describe the use of this system to tag and purify plant organelles.

RESULTS

We developed a simple and specific method to in vivo tag and visualize, as well as isolate organelles of interest from crude plant extracts. This was achieved by expressing the covalent split-isopeptide interaction system, consisting of SpyTag and SpyCatcher, in Nicotiana benthamiana leaves. The functionality of the SpySystem in planta, combined with downstream applications, was proven. Using organelle-specific membrane anchor sequences to program the sub-cellular localization of the SpyTag peptide, we could tag the outer envelope of chloroplasts and mitochondria. By co-expression of a cytosolic, soluble eGFP-SpyCatcher fusion protein, we could demonstrate intermolecular isopeptide formation in planta and proper organelle targeting of the SpyTag peptides to the respective organelles. For one-step organelle purification, recombinantly expressed SpyCatcher protein was immobilized on magnetic microbeads via covalent thiol-etherification. To isolate tagged organelles, crude plant filtrates were mixed with SpyCatcher-coated beads which allowed isolation of SpyTag-labelled chloroplasts and mitochondria. The isolated organelles were intact, showed high yield and hardly contaminants and can be subsequently used for further molecular or biochemical analysis.

CONCLUSION

The SpySystem can be used to in planta label subcellular structures, which enables the one-step purification of organelles from crude plant extracts. The beauty of the system is that it works as a covalent toolbox. Labeling of different organelles with individual tags under control of cell-specific and/or inducible promoter sequences will allow the rapid organelle and cell-type specific purification. Simultaneous labeling of different organelles with specific Tag/Catcher combinations will enable simultaneous isolation of different organelles from one plant extract in future experiments.

A review on recent advances in polymer and peptide hydrogels

In this review, we focus on the very recent developments on the use of the stimuli responsive properties of polymer hydrogels for targeted drug delivery, tissue engineering, and biosensing utilizing their different optoelectronic properties. Besides, the stimuli-responsive hydrogels, the conducting polymer hydrogels are discussed, with specific attention to the energy generation and storage behavior of the xerogel derived from the hydrogel. The electronic and ionic conducting gels have been discussed that have applications in various electronic devices, e.g., organic field effect transistors, soft robotics, ionic skins, and sensors. The properties of polymer hybrid gels containing carbon nanomaterials have been exemplified here giving attention to applications in supercapacitors, dye sensitized solar cells, photocurrent switching, etc. Recent trends in the properties and applications of some natural polymer gels to produce thermal and acoustic insulating materials, drug delivery vehicles, self-healing material, tissue engineering, etc., are discussed. Besides the polymer gels, peptide gels of different dipeptides, tripeptides, oligopeptides, polypeptides, cyclic peptides, etc., are discussed, giving attention mainly to biosensing, bioimaging, and drug delivery applications. The properties of peptide-based hybrid hydrogels with polymers, nanoparticles, nucleotides, fullerene, etc., are discussed, giving specific attention to drug delivery, cell culture, bio-sensing, and bioimaging properties. Thus, the present review delineates, in short, the preparation, properties, and applications of different polymer and peptide hydrogels prepared in the past few years.

Decorating protein hydrogels reversibly enables dynamic presentation and release of functional protein ligands on protein hydrogels

Utilizing protein fragment reconstitution, we demonstrate the reversible and repeatable functionalization of protein hydrogels.