Self-Healing Multiblock Copolypeptide Hydrogels via Polyion Complexation

Effect of ion distribution on stress relaxation in polyelectrolyte complex gels

Solutions of polyelectrolytes consisting of polycations and polyanions in equal proportions were studied in the present work. Due to the physical cross-links formed by the charged groups, physical gels were formed in such systems. The mechanical properties and structure of the obtained gels depending on the charge arrangement along the backbone and the dimensionless Bjerrum length λ were investigated. The response of the systems to a uniaxial affine deformation was studied first. It was found that the systems can be divided into three groups depending on the charge arrangement: showing an almost elastic response; showing a viscoelastic response with a very long relaxation time; and showing a weak viscoelastic response with a short relaxation time. Interestingly, no stable aggregates were formed in the systems with the charges located on spacers, probably because of the increased mobility of the charges in such systems. The obtained stress relaxation curves had different functional forms, indicating that the relaxation has at least two characteristic times, which are different for different systems. In order to understand the molecular nature of the observed mechanical response, the temporal evolution of the network structure of a system showing a viscoelastic response with a very long relaxation time was studied; the aggregates were found to be dynamic, which leads to the relaxation of the "subchains" conformation.

Block Sequence Effects on the Self-Assembly Behaviors of Polypeptide-Based Penta-Block Copolymer Hydrogels

Peptide-based hydrogels have great potential for applications in tissue engineering, drug delivery, and so on. We systematically synthesize, characterize, and investigate the self-assembly behaviors of a series of polypeptide-based penta-block copolymers by varying block sequences and lengths. The copolymers contain hydrophobic blocks of poly(γ-benzyl-l-glutamate) (PBG, Bx) and two kinds of hydrophilic blocks, poly(l-lysine) (PLL, Ky) and poly(ethylene glycol) (PEG, EG34), where x and y are the number of repeating units of each block, where PBG and PLL blocks have unique functions for nerve regeneration and cell adhesion. It shows that a sufficient length of the middle hydrophilic segment capped with hydrophobic end PBG blocks is required. They first self-assemble into flower-like micelles and sequentially form transparent hydrogels (as low as 2.3 wt %) with increased polymer concentration. The hydrogels contain a microscale porous structure, a desired property for tissue engineering to facilitate the access of nutrient flow for cell growth and drug delivery systems with high efficiency of drug storage. We hypothesize that the structure of Bx-Ky-EG34-Ky-Bx agglomerates is beyond micron size (transparent), while that of Ky-Bx-EG34-Bx-Ky is on the submicron scale (opaque). We establish a working strategy to synthesize a polypeptide-based block copolymer with a wide window of sol-gel transition. The study offers insight into rational polypeptide hydrogel design with specific morphology, exploring the novel materials as potential candidates for neural tissue engineering.

Advances, Applications, and Emerging Opportunities in Electrostatic Hydrogels

Polyelectrolyte complex (PEC) hydrogels, which self-assemble via complexation of oppositely charged block polymers, have recently risen to prominence owing to their unique characteristics such as hierarchical microstructure, tunable bulk properties, and the ability to precisely assimilate charged cargos (i.e., proteins and nucleic acids). Significant foundational research has delineated the structure-property relationship of PEC hydrogels for use in a wide range of applications. In this Perspective, we summarize key findings on the microstructure and bulk properties of PEC hydrogels and discuss how intrinsic and extrinsic factors can be tuned to create specifically tailored PEC hydrogels with desired properties. We highlight successful applications of PEC hydrogels while offering insight into strategies to overcome their shortcomings and elaborate on emerging opportunities in the field of electrostatic self-assemblies.

Facile topological transformation of ABA triblock copolymers into multisite, single-chain-folding and branched multiblock copolymers via sequential click coupling and anthracene chemistry

Telechelic PtBA-b-PSt-b-PtBA copolymers were designed to achieve on-demand topological transformation into multisite, single-chain-folding and branched multiblock copolymers via click/click-like reactions.

Direct N-substituted N-thiocarboxyanhydride polymerization towards polypeptoids bearing unprotected carboxyl groups

Synthesis of poly(α-amino acid)s bearing carboxyl groups is a critical pathway to prepare biomaterials to simulate functional proteins. The traditional approaches call for carboxyl-protected monomers to prevent degradation of monomers or wrong linkage. In this contribution, we synthesize N-carboxypentyl glycine N-thiocarboxyanhydride (CPG-NTA) and iminodiacetic acid N-thiocarboxyanhydride (IDA-NTA) without protection. Initiated by amines, CPG-NTA directly polymerizes into polyCPG bearing unprotected carboxyl groups with controlled molecular weight (2.8-9.3 kg mol-1) and low dispersities (1.08-1.12). Block and random copolymerizations of CPG-NTA with N-ethyl glycine N-thiocarboxyanhydride (NEG-NTA) demonstrate its versatile construction of complicated polypeptoids. On the contrary, IDA-NTA transforms amines into cyclic IDA dimer-capped species with carboxyl end group in decent yields (>89%) regio-selectively. Density functional theory calculation elucidates that IDA repeating unit is prone to cyclize to be the six-membered ring product with low ΔG. The polymer is a good adhesive reagent to various materials with adhesive strength of 33-229 kPa.

Polypeptide-based self-healing hydrogels: Design and biomedical applications

Self-healing hydrogels can heal themselves on the damaged sites, which opens up a fascinating way for enhancing lifetimes of materials. Polypeptide/poly(amino acid) is a class of polymers in which natural amino acid monomers or derivatives are linked by amide bonds with a stable and similar secondary structure as natural proteins (α-helix or β-fold). They have the advantages of nontoxicity, biodegradability, and low immunogenicity as well as easy modification. All these properties make polypeptides extremely suitable for the preparation of self-healing hydrogels for biomedical applications. In this review, we mainly focus on the progress in the fabrication strategies of polypeptide-based self-healing hydrogels and their biomedical applications in the recent 5 years. Various crosslinking methods for the preparation of polypeptide-based self-healing hydrogels are first introduced, including host-guest interactions, hydrogen bonding, electrostatic interactions, supramolecular self-assembly of β-sheets, and reversible covalent bonds of imine and hydrazone as well as molecular multi-interactions. Some representative biomedical applications of these self-healing hydrogels such as delivery system, tissue engineering, 3D-bioprinting, antibacterial and wound healing as well as bioadhesion and hemostasis are also summarized. Current challenges and perspectives in future for these "smart" hydrogels are proposed at the end . STATEMENT OF SIGNIFICANCE: Polypeptides with the advantages of nontoxicity, biodegradability, hydrophilicity and low immunogenicity, are extremely suitable for the preparation of self-healing hydrogels in biomedical applications. Recently, the researches of polypeptide-based self-healing hydrogel have drawn the great attentions for scientists and engineers. A review to summarize the recent progress in design and biomedical applications of these polypeptide-based self-healing hydrogels is highly needed. In this review, we mainly focus on the progress in fabrication strategies of polypeptide-based self-healing hydrogels and biomedical applications in recent five years and aim to draw the increased attention to the importance of these "smart" hydrogels, facilitating the advances in biomedical applications. We believe this work would draw interest from readers of Acta Biomaterialia.

Advances in Synthesis and Applications of Self-Healing Hydrogels

BACKGROUND

Hydrogels, a type of three-dimensional (3-D) crosslinked network of polymers containing a high water concentration, have been receiving increasing attention in recent years. Self-healing hydrogels, which can return to their original structure and function after physical damage, are especially attractive. Some self-healable hydrogels have several kinds of properties such as injectability, adhesiveness, and conductivity, which enable them to be used in the manufacturing of drug/cell delivery vehicles, glues, electronic devices, and so on.

MAIN BODY

This review will focus on the synthesis and applications of self-healing hydrogels. Their repair mechanisms and potential applications in pharmaceutical, biomedical, and other areas will be introduced.

CONCLUSION

Self-healing hydrogels are used in various fields because of their ability to recover. The prospect of self-healing hydrogels is promising, and they may be further developed for various applications.

Repairing Creep-Resistant and Kinetically Inert Hydrogels via Yeast Activity-Regulated Energy Dissipation

Energy dissipation, a ubiquitous process in biological systems, has been intensively studied and widely used to guide the transient assembly of natural or synthetic molecules, but very few examples of material transient healability controlled by this important process have been reported. Herein, we realize the healing of creep-resistant and kinetically inert polymer hydrogels that is driven by the respiration of baker's yeast (Saccharomyces cerevisiae) and spontaneous energy dissipation. The entire healing process can be simply controlled by a single variable: sucrose concentration. Due to the high activity and stability of yeast in the hydrogels, multiple local healing events become possible and healing of damaged hydrogels is also efficient after a long waiting time. All these results indicate that our yeast-containing polymer hydrogels are kinetically stable materials, which can be readily healable on demand.

Ring opening polymerization of α-amino acids: advances in synthesis, architecture and applications of polypeptides and their hybrids

This review provides a comprehensive overview of the latest advances in the synthesis, architectural design and biomedical applications of polypeptides and their hybrids.

Synthesis of multisegmented block copolymer by Friedel–Crafts hydroxyalkylation polymerization

Friedel–Crafts (FC) polycondensation of 1,4-dimethoxybenzene with 4-substituted benzaldehyde species was used to prepare telechelic oligomers and high-molar-mass multisegmented block copolymers.

Facile synthesis of helical multiblock copolypeptides: minimal side reactions with accelerated polymerization of N-carboxyanhydrides

Multiblock copolypeptides have attracted broad interests because their potential to form ordered structures and possess protein-mimetic functions. Controlled synthesis of multiblock copolypeptides through the sequential addition of N-carboxyanhydrides (NCAs), especially with the block number higher than five, however, is challenging and rarely reported due to competing side reactions during the polymerization process. Herein we report the unprecedented synthesis of block copolypeptides with up to 20 blocks, enabled by ultrafast polypeptide chain propagation in a water/chloroform emulsion system that outpaces side reactions and ensures high end-group fidelity. Well-defined multiblock copolypeptides with desired block numbers, block lengths, and block sequences as well as very low dispersity were readily attainable in a few hours. This method paves the way for the fast production of a large number of sequence-regulated multiblock copolypeptide materials, which may exhibit interesting assembly behaviors and biomedical applications.