The Glitter of Carbon Nanostructures in Hybrid/Composite Hydrogels for Medicinal Use

Abstract

In recent years, we have witnessed to fast developments in the medicinal field of hydrogels containing various forms of integrated nanostructured carbon that adds interesting mechanical, thermal, and electronic properties. Besides key advances in tissue engineering (especially for conductive tissue, such as for the brain and the heart), there has been innovation also in the area of drug delivery on-demand, with engineered hydrogels capable of repeated response to light, thermal, or electric stimuli. This mini-review focusses on the most promising developments as applied to the gelation of protein/ peptide (including self-assembling amino acids and low-molecular-weight gelators), polysaccharide, and/or synthetic polymer components in medicine. The emerging field of graphene-only hydrogels is also briefly discussed, to give the reader a full flavor of the rising new paradigms in medicine that are made possible through the integration of nanostructured carbon (e.g., carbon nanotubes, nanohorns, nanodiamonds, fullerene, etc.). Nanocarbons are offering great opportunities to bring on a revolution in therapy that the modern medicinal chemist needs to master, to realise their full potential into powerful therapeutic solutions for the patient.

Luminescent supramolecular hydrogels from a tripeptide and nitrogen-doped carbon nanodots

“…The incorporation of carbon nanostructures into hydrogels is a useful approach to introduce additional properties to soft materials. In the case of self-assembling peptides, non-covalent π–π interactions between the nanocarbon and aromatic residues of the peptide offer a convenient means to bring the two components together into a supramolecular system [ 34 ]. This rationale could also be applied to NCNDs and the tripeptide D Leu-Phe-Phe, which were evaluated for co-assembly into hydrogels following a pH trigger from alkaline to neutral.…”

Numerical Simulations as Means for Tailoring Electrically Conductive Hydrogels towards Cartilage Tissue Engineering by Electrical Stimulation

“…This could be used to influence cellular ingrowth inside hydrogels and increase efficiency of initial cell seeding. Such high conductivities might only be reached by the use of, for example, highly conductive carbon nanotubes [ 20 ], reduced graphene oxide [ 21 , 24 ], or well-percolating doped conductive polymer networks made from, among others, polypyrrole or polyaniline [ 15 , 19 ].…”

“…The dopant changes the conductivity of the scaffold by adding or removing an electron from/to the polymer, which causes a lattice distortion inducing polarons that yield increased electric conductivity [ 19 ]. Carbon nanostructures can be integrated into the scaffold network and provide a pathway for the electric current [ 20 , 21 ]. The final electroactive hydrogel conductivity will be strongly dependent on the degree of percolation between the conductive fillers, purity and crystalinity of the conductive polymer, doping level, redox state of the conductive filler, diffusibility of and ion mobility in the final hydrogel, hydrogel porosity, and additional factors relevant for tuning the final hydrogel conductivity.…”

“…Biomaterials that served as scaffolds for cartilage tissue engineering (CTE) exemplarily included natural polysaccharides (alginate, agarose, chitosan) or constituents of the ECM (collagen, chondroitin sulfate, hyaluronic acid) as well as synthetic polymers (e.g., polyethylene glycol, polyacrylamide) [ 18 ]. Improved functionality can be reached by adding conductive polymers (polypyrrole, polyaniline) [ 16 , 19 ] or carbon nanostructures (graphene oxide, carbon nanotubes) [ 20 ] capable of enhancing the intrinsic hydrogel conductivity. When using conductive polymers, suitable dopants—for example, small salt ions (Cl − , NO 3 − ) or large polyelectrolyte molecules (e.g., sodium polystyrenesulfonate (PSS))—are a key ingredient for adjusting the conductivity of the hydrogel [ 15 , 19 ].…”

Mussel-Inspired Dopamine and Carbon Nanotube Leading to a Biocompatible Self-Rolling Conductive Hydrogel Film

“…The unique structure of CNTs, a hollow cylindrical carbon tube, provides a framework onto which functional molecules or polymers can be incorporated that is critical for biomedical applications [ 24 , 25 ]. CNTs have also been used in the development of carbon nanotube hybrid hydrogels for biomedical applications [ 26 , 27 ]. CNTs can be non-covalently coated by dopamine molecules via π-π stacking between the CNTs and the benzene rings of dopamine [ 28 , 29 ].…”