Editorial to the Special Issue—“Recent Advances in Self-Assembled Peptides”

Peptide self-assembly is an interdisciplinary research area involving chemistry, life science, and materials science [...].

spherical counterparts [4]. The work has practical implications on controlling monocyte recruitment associated with cancer progression. The results also provide important guidance on designing PAMs with desired physical characteristic to suit specific needs for biological applications.
Self-assembling peptide hydrogels have shown great promise as an injectable multi-functional scaffold for drug delivery and tissue regeneration. Kumar et al. presented a nice summary of the current status of the progress and obstacle in the development and translation of peptide-hydrogel therapy in treating peripheral artery disease (PAD) [5]. The unmet medical needs can be potentially overcome by rational design of material scaffolds that allow for sustained angiogenic effect, de novo formation of microvasculature and neovasculature development.
Liquid-liquid phase separation (LLPS) is commonly observed in natural proteins, leading to non-fibrillar self-assembly. Considering many of the cell compartments are liquids that form by phase separation from the cytoplasm, the study of self-assembling peptides in association with LLPS has tremendous biological significance. Luo et al. reviewed the self-assembling process of Fused in Sarcoma (FUS), which is a DNA/RNA binding protein and in association with a variety of neurodegenerative diseases [6]. The review nicely summarizes both the aggregation and LLPS of FUS and their relationship with the pathology of diseases.
Polyelectrolyte complexes (PECs) are a result of liquid-liquid phase separation upon interaction between oppositely charged macromolecules. PECs from self-assembling peptides are an emerging area for the design of supramolecular nanomaterials. Leon et al. demonstrated a rational design approach to create PECs formed by an alternating sequenced d-and l-chiral patterns of charged and hydrophobic residues [7]. An important finding is that both the overall hydrophobicity and hydrophobic pattern play important roles on PECs formation and their properties. In addition to its fundamental significance with regard to PECs formation, rational design and patterning of the hydrophobic domain play key roles in effective encapsulation of a variety of therapeutic molecules with different hydrophobicity and charges.
Biophysical and biochemical assay are extremely crucial for the characterization and elucidation of the hierarchical structures of complex self-assembling systems. For example, self-assembled amyloid-β oligomers (AβOs) are implicated as neurotoxins to cause Alzheimer's disease (AD) and the toxicity may be dependent on their quaternary structure. However, the polymorphic nature of AβO and their low abundance present significant challenges in accurate assessment of their structure-activity-function correlation. Doran et al. reported a simple yet effective biochemical assay to separate the distinct morphologies, quantify their relative abundance and ascertain their structures in comparison with a recombinant Aβ(M1-40) [8]. This method is highly promising to facilitate further functional characterization and biological activity of AβO and help establish a detailed understanding of AβO-mediated neurotoxicity.
These contributions aim to provide some of the current and future trends in the development of self-assembling peptide materials and effective tools to characterize these materials. We hope this special issue helps illustrate the fundamental design principle in self-assembling peptides and promote future research on the design, characterization, and translation of this technology to address unmet clinical needs.

Conflicts of Interest:
The author declares no conflict of interest.