On the Mechanism of Self-Assembly by a Hydrogel-Forming Peptide

Self-assembling peptide-based hydrogels are a class of tunable soft materials that have been shown to be highly useful for a number of biomedical applications. The dynamic formation of the supramolecular fibrils that compose these materials has heretofore remained poorly characterized. A better understanding of this process would provide important insights into the behavior of these systems and could aid in the rational design of new peptide hydrogels. Here, we report the determination of the microscopic steps that underpin the self-assembly of a hydrogel-forming peptide, SgI_37-49. Using theoretical models of linear polymerization to analyze the kinetic self-assembly data, we show that SgI_37-49 fibril formation is driven by fibril-catalyzed secondary nucleation and that all the microscopic processes involved in SgI_37-49 self-assembly display an enzyme-like saturation behavior. Moreover, this analysis allows us to quantify the rates of the underlying processes at different peptide concentrations and to calculate the time evolution of these reaction rates over the time course of self-assembly. We demonstrate here a new mechanistic approach for the study of self-assembling hydrogel-forming peptides, which is complementary to commonly used materials science characterization techniques.

Synthetic peptide hydrogels as 3D scaffolds for tissue engineering

The regeneration of tissues and organs poses an immense challenge due to the extreme complexity in the research work involved. Despite the tissue engineering approach being considered as a promising strategy for more than two decades, a key issue impeding its progress is the lack of ideal scaffold materials. Nature-inspired synthetic peptide hydrogels are inherently biocompatible, and its high resemblance to extracellular matrix makes peptide hydrogels suitable 3D scaffold materials. This review covers the important aspects of peptide hydrogels as 3D scaffolds, including mechanical properties, biodegradability and bioactivity, and the current approaches in creating matrices with optimized features. Many of these scaffolds contain peptide sequences that are widely reported for tissue repair and regeneration and these peptide sequences will also be discussed. Furthermore, 3D biofabrication strategies of synthetic peptide hydrogels and the recent advances of peptide hydrogels in tissue engineering will also be described to reflect the current trend in the field. In the final section, we will present the future outlook in the design and development of peptide-based hydrogels for translational tissue engineering applications.

Controlling the properties and self-assembly of helical nanofibrils by engineering zinc-binding β-hairpin peptides

This work illustrates a series of novel peptides that have the capability to bind Zn2+ ions and to produce fibrillar structures. The location and the type of the residues along the peptide sequence can determine the nature of the fibril. This work presents a proof-of-concept milestone for designing peptides with different properties to produce diverse materials.

Design, characterization and evaluation of β-hairpin peptide hydrogels as a support for osteoblast cell growth and bovine lactoferrin delivery

The use of peptide hydrogels is of growing interest in bone regeneration. Self-assembling peptides form hydrogels and can be used as injectable drug delivery matrices. Injected into the defect site, they can gel in situ, and release factors that aid bone growth. We report on the design, synthesis and characterization of three β-hairpin peptide hydrogels, and on their osteoblast cytocompatibility as well as delivery of the lactoferrin glycoprotein, a bone anabolic factor. Osteoblasts cultured in hydrogels of the peptide with sequence NH₂-Leu-His-Leu-His-Leu-Lys-Leu-Lys-Val-dPro-Pro-Thr-Lys-Leu-Lys-Leu-His-Leu-His-Leu-Arg-Gly-Asp-Ser-CONH₂ (H4LMAX-RGDS) increased the osteoblast cell number and the cells appeared healthy after seven days. Furthermore, we showed that H4LMAX-RGDS was capable of releasing up to 60% of lactoferrin (pre-encapsulated in the gel) over five days while retaining the rest of the glycoprotein. Thus, H4LMAX-RGDS hydrogels are cytocompatible with primary osteoblasts and capable of delivering bio-active lactoferrin that increases osteoblast cell number.

Self-assembling peptide H4LMAX-RGDS hydrogels, designed to enhance bone regeneration, are cytocompatible and capable of delivering the bone anabolic factor lactoferrin to increase osteoblast cell number.

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

Although assembly of recombinant proteins by SpyTag/SpyCatcher chemistry has proven to be a versatile approach for creating bioactive hydrogels, the resulting Spy networks often exhibit weak mechanics due to the poor efficiency of interchain cross-linking. Here we leverage metal/ligand (i.e., cobalt/His6-tag) coordination interactions to modulate the bulk mechanics of the protein networks. The drastic difference between the Co²⁺ and Co³⁺ complexes in thermodynamic and kinetic properties enabled us to regulate the materials' properties and to immobilize and release recombinant proteins in a redox-dependent manner. The resulting hydrogels are capable of not only supporting cell growth and proliferation, but also influencing specific cell signaling via immobilized growth factors such as leukemia inhibitory factor (LIF). The integrated use of stimuli-responsive metal coordination and SpyTag/SpyCatcher chemistry opens up a new dimension for designing bioactive protein materials.

The physical basis of fabrication of amyloid-based hydrogels by lysozyme

Schematic of heating- and cooling-induced transitions between HEWL states, and the subsequent formation of the hydrogel.