Hydrogels are preferred materials for drug delivery due to their soft, elastomeric nature as well as their high water-retaining capability. The only problem is they have poor mechanical strength, but that can be improved by the incorporation of nanoparticles.

Nanohybrids — containing the composites of carbon nanotubes (CNT) — and polymeric hydrogels are considered as promising drug-delivery materials in recent research. These nanohybrids possess the properties of both CNTs and hydrogels with improved mechanical, physiochemical and biological properties.

The electrical conductivity of CNT could be useful in improving the cell growth. The impedance of polymer matrices is decreased, which could be helpful in the propagation of electrical signals in neural and cardiac muscles. The CNTs in nanohydrids could be also useful in improving dendrite elongation and cell adhesion in neural cells.

In a recent study, researchers observed that electrical stimulation conducted through the polymer/nanophase composites improved osteoblast functions, which could be responsible for chemical composition of bone's organic and inorganic phases. Also, the electrical stimulation on conducting matrix increased the neurotrophin release and nerve regeneration.

The CNT composites could also support the growth of cell types, such as skin fibroblasts and muscle myoblasts. The CNT surfaces can also be tailored with different polysachharides in order to change the hydrophilicity of the surface.

The amylase-tailored CNT surfaces, with exposed OH groups, improved cell adhesion and viability. The CNTs tailored with sulfonate and phosphate groups are promising candidates for bone scaffold. Furthermore, chitosan polysachharide is used to prepare composites of CNT-hydrogels. Incorporation of CNTs could increase the endurable force at complete breakdown of the hydrogel beads.

In another study, gellan gum hydrogels, impregnated with CNTs, were prepared to improve the electrical cell stimulation. Furthermore, in the presence of CNTs, molecularly-imprinted polymers were prepared by precipitation polymerization method for the electroresponsive release of diclofenac sodium salt drug.

Scientists have tried to reinforce polyvinyl alcohol (PVA) hydrogels with CNTs, where the composite material generated a better response in osteochondral defect repairing application. Growth rate was increased at the implant interface due to an increase in the concentration of calcium and phosphorous without any inflammation after 12 weeks.

In another study, the composite material, containing PVA and polyvinyl pyrolidone (PVP) was wrapped by multiwalled CNTs to improve the mechanical strength. Tensile strength was improved by 133 percent, and tear strength was improved by 63 percent. The composite MWCNT-PVP/PVA hydrogels have been known to be wear-resistant in the presence of PVP with different concentrations of MWCNTs.

The composite scaffolds — made of hydroxyapatite and collagen — showed a better mechanical performance and hierarchical porosity. These are considered as promising candidates for bone regenerative application. Incorporation of CNTs in polymeric hydrogels could improve the specific surface area, thermal stability and electrical conductivities, and could decrease the transition time.

In a 2011 study, MWCNTs were functionalized by ethylene glycol in order to increase the dispersion ability in poly(3,4-ethylenedioxythiophene)-poly(4-styrenesulfonate). The surface resistance and transmittance of the films were decreased with the number of coatings. Furthermore, polar solvents have been found to improve the electric and electrochemical properties.

In another study, a good-quality composite made of SWNTs, polypyrrole (PPy), and polyethylene glycol diacrylate (PEGDA) hydrogel was prepared by interfacial polymerization. The electrical conductivity of PPy/PEGDA hydrogel was increased nearly two times due to a higher content of PPy. The incorporation of SWNTs to PPy improved the mechanical and electrical properties of the composite, whereas the swelling ratio was found to be decreased.

In a recent study, electroresponsive hybrid composite with multiwalled CNT/polymethylacrylic acid (MWCNT/PMAA) was prepared, where controlled drug-release experiments in accordance with the external electric field availability were carried out under in vivo conditions. They also concluded that DNA hydrogels were promising materials for biomedical application.

Lastly, in a recent study, a DNA single-walled CNT hybrid hydrogel, with pH-responsive and strength tunable properties, was also prepared for biomedical application.

In summary, CNTs and hydrogel composites are two promising drug-delivery materials these days. These composites have the advantages of both hydrogels and polymers — i.e., biocompatibility, biodegradability, mechanical strength, and electromagnetic and magnetic behavior.