Multi-purpose gel: From supramolecular envirogel to high-value applications

Dibenzylidene-D-sorbitol (DBS) has remained a well-known low molecular weight gelator of organic solvents for over 100 years. As such, it constitutes a very early example of supramolecular gels. It has found widespread applications such as personal care products and high-tech applications. Despite the versatility of DBS as an organogelator and industrial feedstock, none of its existing derivatives could gel water. Herein, functionalization of the aromatic ‘wings’ with various functionalities and their gelation profiles were described. None of the synthesized derivatives but DBS-COOH and DBS-CONHNH2 could undergo gelation in water. DBS-COOH formed a stable hydrogel by pH-switching while the DBS-CONHNH2 formed stable hydrogels across a wide range of pH values by a heat-cool cycle. CD spectroscopy and SEM were used to show that these functionalities control the aggregation mode of the parent DBS. DBS-COOH and DBS-CONHNH2 hydrogels demonstrated a significant uptake of dyes from model polluted water and hence we call them supramolecular envirogels. DBS-COOH demonstrated higher affinity towards methylene blue at ambient conditions but DBS-CONHNH2 demonstrated a pH-dependent selectivity towards various dyes. Lead, cadmium and mercury were significantly adsorbed by DBS-CONHNH2 .The maximum metal loading of 1:1 molar ratio was obtained at neutral ambient pH condition and 2:1 molar ratio at basic pH. The adsorption processes fit pseudo-second-order kinetic and the Langmuir isotherm models. DBS-CONHNH2 were used to recover precious metals from a model mine tailing with greater selectivity towards precious metals than earth-abundant metals. The adsorbed precious metals were reduced in situ to nanoparticulate form. Interestingly, the hydrogel–NPs exhibited higher conductance and electrocatalytic activities than bare gels and/or carbon electrodes. Solubility of the APIs in water was enhanced by forming complexes with the DBS-CONHNH2 while the mechanical stability and morphology of the native hydrogel was influenced by the presence of APIs. APIs were released under basic pH conditions in a controlled-manner

Self-assembled sorbitol-derived supramolecular hydrogels for the controlled encapsulation and release of active pharmaceutical ingredients

A simple supramolecular hydrogel based on 1,3:2,4-di(4-acylhydrazide)benzylidene sorbitol (DBS-CONHNH2), is able to extract acid-functionalised anti-inflammatory drugs via directed interactions with the self-assembled gel nanofibres. Two-component hydrogel-drug hybrid materials can be easily formed by mixing and exhibit pH-controlled drug release. This journal i

Covalent co-assembly between resilin-like polypeptide and peptide amphiphile into hydrogels with controlled nanostructure and improved mechanical properties

Covalent co-assembly holds great promise for the fabrication of hydrogels with controllable nanostructure, versatile chemical composition, and enhanced mechanical properties given its relative simplicity, high efficiency, and bond stability. This report describes our approach to designing functional multicomponent hydrogels based on photo-induced chemical interactions between an acrylamide-functionalized resilin-like polypeptide (RLP) and a peptide amphiphile (PA). Circular dichroism (CD) spectroscopy, electron microscopy, and amplitude sweep rheology were used to demonstrate that the co-assembled hydrogel systems acquired distinct structural conformations, tunable nanostructures, and enhanced elasticity in a PA concentration-dependent manner. We envisage the use of these materials in numerous biomedical applications such as controlled drug release systems, microfluidic devices, and scaffolds for tissue engineering

1,3:2,4-Dibenzylidene-d-sorbitol (DBS) and its derivatives-efficient, versatile and industrially-relevant low-molecular-weight gelators with over 100 years of history and a bright future

Dibenzylidene-d-sorbitol (DBS) has been a well-known low-molecular-weight gelator of organic solvents for over 100 years. As such, it constitutes a very early example of a supramolecular gel-a research field which has recently developed into one of intense interest. The ability of DBS to self-assemble into sample-spanning networks in numerous solvents is predicated upon its 'butterfly-like' structure, whereby the benzylidene groups constitute the 'wings' and the sorbitol backbone the 'body'-the two parts representing the molecular recognition motifs underpinning its gelation mechanism, with the nature of solvent playing a key role in controlling the precise assembly mode. This gelator has found widespread applications in areas as diverse as personal care products and polymer nucleation/clarification, and has considerable potential in applications such as dental composites, energy technology and liquid crystalline materials. Some derivatives of DBS have also been reported which offer the potential to expand the scope and range of applications of this family of gelators and endow the nansocale network with additional functionality. This review aims to explain current trends in DBS research, and provide insight into how by combining a long history of application, with modern methods of derivatisation and analysis, the future for this family of gelators is bright, with an increasing number of high-tech applications, from environmental remediation to tissue engineering, being within reach

Carboxylated-xyloglucan and peptide amphiphile co-assembly in wound healing

Hydrogel wound dressings can play critical roles in wound healing protecting the wound from trauma or contamination and providing an ideal environment to support the growth of endogenous cells and promote wound closure. This work presents a self-assembling hydrogel dressing that can assist the wound repair process mimicking the hierarchical structure of skin extracellular matrix. To this aim, the co-assembly behaviour of a carboxylated variant of xyloglucan (CXG) with a peptide amphiphile (PA-H3) has been investigated to generate hierarchical constructs with tuneable molecular composition, structure, and properties. Transmission electron microscopy and circular dichroism at a low concentration shows that CXG and PA-H3 co-assemble into nanofibres by hydrophobic and electrostatic interactions and further aggregate into nanofibre bundles and networks. At a higher concentration, CXG and PA-H3 yield hydrogels that have been characterized for their morphology by scanning electron microscopy and for the mechanical properties by small-amplitude oscillatory shear rheological measurements and compression tests at different CXG/PA-H3 ratios. A preliminary biological evaluation has been carried out both in vitro with HaCat cells and in vivo in a mouse model

Growth‐Factor Free Multicomponent Nanocomposite Hydrogels That Stimulate Bone Formation

Synthetic osteo‐promoting materials that are able to stimulate and accelerate bone formation without the addition of exogenous cells or growth factors represent a major opportunity for an aging world population. A co‐assembling system that integrates hyaluronic acid tyramine (HA‐Tyr), bioactive peptide amphiphiles (GHK‐Cu2+), and Laponite (Lap) to engineer hydrogels with physical, mechanical, and biomolecular signals that can be tuned to enhance bone regeneration is reported. The central design element of the multicomponent hydrogels is the integration of self‐assembly and enzyme‐mediated oxidative coupling to optimize structure and mechanical properties in combination with the incorporation of an osteo‐ and angio‐promoting segments to facilitate signaling. Spectroscopic techniques are used to confirm the interplay of orthogonal covalent and supramolecular interactions in multicomponent hydrogel formation. Furthermore, physico‐mechanical characterizations reveal that the multicomponent hydrogels exhibit improved compressive strength, stress relaxation profile, low swelling ratio, and retarded enzymatic degradation compared to the single component hydrogels. Applicability is validated in vitro using human mesenchymal stem cells and human umbilical vein endothelial cells, and in vivo using a rabbit maxillary sinus floor reconstruction model. Animals treated with the HA‐Tyr‐HA‐Tyr‐GHK‐Cu2+ hydrogels exhibit significantly enhanced bone formation relative to controls including the commercially available Bio‐Oss

An interfacial self-assembling bioink for the manufacturing of capillary-like structures with tuneable and anisotropic permeability

Self-assembling bioinks offer the possibility to biofabricate with molecular precision, hierarchical control, and biofunctionality. For this to become a reality with widespread impact, it is essential to engineer these ink systems ensuring reproducibility and providing suitable standardization. We have reported a self-assembling bioink based on disordered-to-ordered transitions of an elastin-like recombinamer (ELR) to co-assemble with graphene oxide (GO). Here, we establish reproducible processes, optimize printing parameters for its use as a bioink, describe new advantages that the self-assembling bioink can provide, and demonstrate how to fabricate novel structures with physiological relevance. We fabricate capillary-like structures with resolutions down to ~10 µm in diameter and ~2 µm thick tube walls and use both experimental and finite element analysis to characterize the printing conditions, underlying interfacial diffusion-reaction mechanism of assembly, printing fidelity, and material porosity and permeability. We demonstrate the capacity to modulate the pore size and tune the permeability of the resulting structures with and without human umbilical vascular endothelial cells (hUVECs). Finally, the potential of the ELR-GO bioink to enable supramolecular fabrication of biomimetic structures was demonstrated by printing tubes exhibiting walls with progressively different structure and permeability

De Novo Design of Functional Co-Assembling Organic-Inorganic Hydrogels for Hierarchical Mineralization and Neovascularization

Synthetic nanostructured materials incorporating both organic and inorganic components offer a unique, powerful and versatile class of materials for widespread applications due to the distinct, yet complementary, nature of the intrinsic properties of the different constituents. We report a supramolecular system based on synthetic nanoclay (Laponite™, Lap) and peptide amphiphiles (PAs, PAH3) rationally designed to co-assemble into nanostructured hydrogels with high structural integrity and a spectrum of bioactivities. Spectroscopic and scattering techniques and molecular dynamic simulation approaches were harnessedto confirm that PAH3 nanofibers electrostatically adsorbed and conformed to the surface of Lapnanodisks. Electron and atomic force microscopies also confirmed an increase in diameter and surface areaof PAH3nanofibers after co-assembly with Lap. Dynamic oscillatory rheology revealed that the co-assembled PAH3-Laphydrogels displayed high stiffness and robust self-healing behaviour while gas adsorption analysis confirmed a hierarchical and heterogeneous porosity. Furthermore, this distinctive structure within the three-dimensional matrix(3D) provided spatial confinement for the nucleation and hierarchical organization of high-aspect ratio hydroxyapatite nanorods into well-defined spherical clusters within the 3Dmatrix. Applicability of the organic-inorganic PAH3-Laphydrogels was assessed in vitrousing human bone marrow-derived stromal cells(hBMSCs) and ex vivousing a chick chorioallantoic membrane (CAM) assay. The results demonstrated that the organic-inorganic PAH3-Laphydrogels promote human skeletal cell proliferation and, upon mineralization, integrate with the CAM, are infiltrated by blood vessels, stimulate extracellular matrix production, and facilitate extensive mineral deposition relative to the controls

Applying low-molecular weight supramolecular gelators in an environmental setting – self-assembled gels as smart materials for pollutant removal

This review explores supramolecular gels as materials for environmental remediation. These soft materials are formed by self-assembling low-molecular-weight building blocks, which can be programmed with molecular-scale information by simple organic synthesis. The resulting gels often have nanoscale ‘solid-like’ networks which are sample-spanning within a ‘liquid-like’ solvent phase. There is intimate contact between the solvent and the gel nanostructure, which has a very high effective surface area as a result of its dimensions. As such, these materials have the ability to bring a solid-like phase into contact with liquids in an environmental setting. Such materials can therefore remediate unwanted pollutants from the environment including: immobilisation of oil spills, removal of dyes, extraction of heavy metals or toxic anions, and the detection or removal of chemical weapons. Controlling the interactions between the gel nanofibres and pollutants can lead to selective uptake and extraction. Furthermore, if suitably designed, such materials can be recyclable and environmentally benign, while the responsive and tunable nature of the self-assembled network offers significant advantages over other materials solutions to problems caused by pollution in an environmental setting