Multi-layer 3D printed dipeptide-based low molecular weight gels

Self-assembly of heterochiral, aliphatic dipeptides with Leu

This work describes the self-assembly behavior of heterochiral, aliphatic dipeptides, l-Leu-d-Xaa (Xaa = Ala, Val, Ile, Leu), in green solvents such as acetonitrile (MeCN) and buffered water at neutral pH. Interestingly, water plays a structuring role because at 1% v/v, it enables dipeptide self-assembly in MeCN to yield organogels, which then undergo transition towards crystals. Other organic solvents and oils were tested for gelation, and metastable gels were formed in tetrahydrofuran, although at high peptide concentration (80 mM). Single-crystal X-ray diffraction revealed the dipeptides' supramolecular packing modes in amphipathic layers, as opposed to water channels reported for the homochiral Leu-Leu, or hydrophobic columns reported for homochiral Leu-Val and Leu-Ile.

Supramolecular gels - a panorama of low-molecular-weight gelators from ancient origins to next-generation technologies

Supramolecular gels, self-assembled from low-molecular-weight gelators (LMWGs), have a long history and a bright future. This review provides an overview of these materials, from their use in lubrication and personal care in the ancient world, through to next-generation technologies. In academic terms, colloid scientists in the 19th and early 20th centuries first understood such gels as being physically assembled as a result of weak interactions, combining a solid-like network having a degree of crystalline order with a highly mobile liquid-like phase. During the 20th century, industrial scientists began using these materials in new applications in the polymer, oil and food industries. The advent of supramolecular chemistry in the late 20th century, with its focus on non-covalent interactions and controlled self-assembly, saw the horizons for these materials shifted significantly beyond their historic rheological applications, expanding their potential. The ability to tune the LMWG chemical structure, manipulate hierarchical assembly, develop multi-component systems, and introduce new types of responsive and interactive behaviour, has been transformative. Furthermore, the dynamics of these materials are increasingly understood, creating metastable gels and transiently-fueled systems. New approaches to shaping and patterning gels are providing a unique opportunity for more sophisticated uses. These supramolecular advances are increasingly underpinning and informing next-generation applications - from drug delivery and regenerative medicine to environmental remediation and sustainable energy. In summary, this article presents a panorama over the field of supramolecular gels, emphasising how both academic and industrial scientists are building on the past, and engaging new fundamental insights and innovative concepts to open up exciting horizons for their future use.

Cysteine-Silver-Polymer Systems for the Preparation of Hydrogels and Films with Potential Applications in Regenerative Medicine

Herein, the problem concerning the poorer mechanical properties of gels based on low molecular weight gelators (LMWGs)-L-cysteine and silver nitrate-was solved by the addition of various polymers-polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP) and polyethylene glycol (PEG)-to the initial cysteine-silver sol (CSS). The physicochemical methods of analysis-viscosimetry, UV spectroscopy, DLS, and SEM-identified that cysteine-silver hydrogels (CSG) based on PVA possess the best rheological properties and porous microstructure (the average pore size is 2-10 µm) compared to gels without the polymer or with PVP or PEG. Such gels are able to form cysteine-silver cryogels (CSC) and then porous cysteine-silver films (CSF) with an average pore size of 10-20 µm and good mechanical, swelling, and adhesion to skin characteristics as long as the structure of CSS particles remains stable. In vitro experiments have shown that hydrogels are non-toxic to normal human fibroblast cells. The obtained materials could potentially be applied to regenerative medicine.

Effect of molar ratio and concentration on the rheological properties of two-component supramolecular hydrogels: tuning of the morphological and drug releasing behaviour

Self-assembled supramolecular hydrogels offer great potential as biomaterials and drug delivery systems. Specifically, peptide-based multicomponent hydrogels are promising materials due to their advantage that their mechanical and physical properties can be tuned to enhance their functionalities and broaden their applications. Herein, we report two-component assembly and formation of hydrogels containing inexpensive complementary anionic, BUVV-OH (A), and cationic, KFFC12 (B), peptide amphiphiles. Individually, neither of these components formed a hydrogel, while mixtures with compositions 1 : 1, 1 : 2, and 2 : 1 (molar ratio) as A : B show hydrogel formation (Milli-Q water, at pH = 6.79). These hydrogels displayed a good shear-thinning behaviour with different mechanical stabilities and nano-fibrous network structures. The 1 : 1 hydrogel shows good cell viability for human embryonic kidney (HEK-293) cells and CHO cells indicating its non-cytotoxicity. The biocompatible, thixotropic 1 : 1 hydrogel with a nanofiber network structure shows the highest mechanical strength with a storage modulus of 3.4 × 103 Pa. The hydrogel is able to encapsulate drugs including antibiotics amoxicillin and rifampicin, and anticancer drug doxorubicin, and it exhibits sustainable release of 76%, 70%, and 81% respectively in vitro after 3 days. The other two mixtures (composition 1 : 2 and 2 : 1) are unable to form a hydrogel when they are loaded with these drugs. Interestingly, it is noticed that with an increase in concentration, the mechanical strength of a 1 : 1 hydrogel is significantly enhanced, showing potential that may act as a scaffold for tissue engineering. The two-component gel offers tunable mechanical properties, thixotropy, injectability, and biocompatibility and has great potential as a scaffold for sustained drug release and tissue engineering.

Wet-spinning multi-component low-molecular-weight gelators to print synergistic soft materials

Two different low-molecular-weight gelators (LMWGs) have been 3D-printed as filaments by wet-spininng. When the two LMWGs are simultaneously wet-spun, the co-assembled hybrid gel filaments combine the individual properties of the two gelators (dynamic pH response and in-situ metal nanoparticle formation) in synergistic ways, creating gel objects with new properties.