A food additive is finding an alternative use in electrically-conducting hydrogels with potential in tissue engineering.

Marc in het Panhuis and Cameron Ferris at the University of Wollongong, Australia, used gellan gum, a common additive in yogurts, jellies and toothpaste, to prepare a scaffold that jellifies at body temperature. The researchers say that the gel's formation under mild and physiological conditions suggests medical applications. For example, cell-doped gels could be developed as injectable scaffolds to repair tissues non-invasively, such as heart or muscle.

The team investigated cell growth on their gellan gum gel. 'Because it's a hydrogel, we can mould it into any shape we like,' says in het Panhuis. To demonstrate this, the researchers used vinyl records as a template, spreading the gel in a thin film on the surface to create a subtly ridged pattern. When the team added cells to the gel, the cells adhered in valleys within the pattern, demonstrating that they could be prompted to grow in a desired arrangement. 

Cells grow readily on hydrogel surfaces moulded using vinyl records

The researchers also added highly conducting carbon nanotube fillers to their gellan gum gels and investigated how electrical signals propagated through the composites. The duo found that the nanotubes form an interconnected network within the hydrogel, which aids conductivity. 

Phillip Messersmith, an authority on biomaterials for tissue engineering at Northwestern University, Evanston, US, points out that whilst there are many examples of carbon nanotubes in hydrogels, 'the electrical conductivity measurement is a nice accomplishment.'

'Electrical stimulation of cells is one of the cues used by the human body,' says in het Panhuis, explaining his motivation for developing the conducting gels. 'It is used to trigger wound healing and many other biological functions.' However, the researchers avoided patterning cells on the gels containing carbon nanotubes due to the intense speculation surrounding their biocompatibility. 'Now that we've made the materials, a major challenge is to look at the electrical stimulation of cells using common materials other than carbon nanotubes,' says in het Panhuis. 

Mark Bradley, an expert in biomaterials at the University of Edinburgh, UK, says that it would also be interesting for the researchers to look at other cell types. 'If you take stem cells, for example, and apply an electrical stimulus, they can be directed to differentiate in a specific direction,' he adds, suggesting that the study could have widespread implications in many other fields of biomaterials research.

Lois Alexander

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