Antimicrobial and Bioactive Silk Peptide Hybrid Hydrogel with a Heterogeneous Double Network Formed by Orthogonal Assembly

Gelation Dynamics, Formation Mechanism, Functionalization, and 3D Bioprinting of Silk Fibroin Hydrogel Materials for Biomedical Applications

Silk fibroin (SF), derived from silk cocoon fibers (Bombyx mori), is a natural protein polymer known for its biocompatibility, biodegradability, and sustainability. The protein can be processed into various material formats suitable for a range of applications. Among these, SF hydrogels are useful in the biomedical field, such as tissue engineering, due to the tailorable structures and properties achievable through tuning the gelation process. Therefore, the focus of this contribution is to comprehensively review and understand the formation, gelation mechanism, dynamic control, and functionalization of SF hydrogels. Unlike previous reviews, this work delves into understanding the strategies and mechanisms for tuning the gelation dynamics of SF from molecular assembly and crystallization points of view. Further, this review presents functionalization pathways and practical examples, such as for the 3D printing of SF hydrogels, to illustrate how these strategies, mechanisms, and pathways can be implemented in a specific application scenario. With these insights, researchers can gain a deeper understanding of how to manipulate or control the gelation process and the types of functionalization to achieve specific properties and features. This knowledge would further facilitate the development and application of SF hydrogel materials in various fields.

Metal Cross-Linked Supramolecular Gel Noodles: Structural Insights and Antibacterial Assessment

Achieving precise control over gelator alignment and morphology is crucial for crafting tailored materials and supramolecular structures with distinct properties. We successfully aligned the self-assembled micelles formed by a functionalized dipeptide 2NapFF into long 1-D "gel noodles" by cross-linking with divalent metal chlorides. We identify the most effective cross-linker for alignment, enhancing mechanical stability, and imparting functional properties. Our study shows that Group 2 metal ions are particularly suited for creating mechanically robust yet flexible gel noodles because of their ionic and nondirectional bonding with carboxylate groups. In contrast, the covalent nature and high directional bonds of d-block metal ions with carboxylates tend to disrupt the self-assembly of 2NapFF. Furthermore, the 2NapFF-Cu noodles demonstrated selective antibacterial activity, indicating that the potent antibacterial property of the copper(II) ion is preserved within the cross-linked system. By merging insights into molecular alignment, gel extrusion processing, and integrating specific functionalities, we illustrate how the versatility of dipeptide-based gels can be utilized in creating next-generation soft materials.

Manipulating supramolecular gels with surfactants: Interfacial and non-interfacial mechanisms

Gel is a class of self-supporting soft materials with applications in many fields. Fast, controllable gelation, micro/nano structure and suitable rheological properties are essential considerations for the design of gels for specific applications. Many methods can be used to control these parameters, among which the additive approach is convenient as it is a simple physical mixing process with significant advantages, such as avoidance of pH change and external energy fields (ultrasound, UV light and others). Although surfactants are widely used to control the formation of many materials, particularly nanomaterials, their effects on gelation are less known. This review summarizes the studies that utilized different surfactants to control the formation, structure, and properties of molecular and silk fibroin gels. The mechanisms of surfactants, which are interfacial and non-interfacial effects, are classified and discussed. Knowledge and technical gaps are identified, and perspectives for further research are outlined. This review is expected to inspire increasing research interest in using surfactants for designing/fabricating gels with desirable formation kinetics, structure, properties and functionalities.

One-Step Construction of Tryptophan-Derived Small Molecule Hydrogels for Antibacterial Materials

Amino acid-based hydrogels have received widespread attention because of their wide range of sources, biodegradability, and biocompatibility. Despite considerable progress, the development of such hydrogels has been limited by critical problems such as bacterial infection and complex preparation. Herein, by using the non-toxic gluconolactone (GDL) to adjust the pH of the solution to induce the rapid self-assembly of N-[(benzyloxy)carbonyl]-L-tryptophan (ZW) to form a three-dimensional (3D) gel network, we developed a stable and effective self-assembled small-molecule hydrogel. Characterization assays and molecular dynamics studies indicate that π-π stacking and hydrogen bonding are the main drivers of self-assembly between ZW molecules. In vitro experiments further confirmed this material's sustained release properties, low cytotoxicity, and excellent antibacterial activity, particularly against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. This study provides a different and innovative perspective for the further development of antibacterial materials based on amino acid derivatives.

Enhanced formation of bioactive and strong silk-bioglass hybrid materials through organic-inorganic mutual molecular nucleation induction and templating

Materials based on silk fibroin (SF) are important for many biomedical applications due to their excellent biocompatibility and tunable biodegradability. However, the insufficient mechanical strength and low bioactivity of these materials have limited their applications. For silk hydrogels, slow gelation is also a crucial problem. In this work, a simple approach is developed to address these challenging problems all at once. By mixing SF solution with bioglass (BG) sol, instant gelation of silk is induced, the storage modulus of the hydrogel and the compressive modulus of the aerogel are significantly enhanced. The formation of a complex of SF and tetraethyl orthosilicate (TEOS), either through hydrogen bonding or TEOS condensation on SF, facilitated the aggregation of SF and, on the other hand, created active sites for the condensation of TEOS and BG formation on the surface of silk nanofibrils. The resultant hybrid gels have much higher capacity for biomineralization, indicating their higher bioactivity, compared with the pristine silk gels. This organic (SF)-inorganic (BG) mutual nucleation induction and templating can be used for a general approach to produce bioactive silk materials of various formats not limited to gels and may also inspire the formation of other functional protein-BG hybrid materials.

Bio-inspired hydrogels with fibrous structure: A review on design and biomedical applications

Numerous tissues in the human body have fibrous structures, including the extracellular matrix, muscles, and heart, which perform critical biological functions and have exceptional mechanical strength. Due to their high-water content, softness, biocompatibility and elastic nature, hydrogels resemble biological tissues. Traditional hydrogels, on the other hand, have weak mechanical properties and lack tissue-like fibrous structures, limiting their potential applications. Thus, bio-inspired hydrogels with fibrous architectures have piqued the curiosity of biomedical researchers. Here, we review fabrication strategies for fibrous hydrogels and their recent progress in the biomedical fields of wound dressings, drug delivery, tissue engineering scaffolds and bioadhesives. Challenges and future perspectives are also discussed.