A collaboration between Harvard University and the University of Waterloo has produced a carbon nanotube-reinforced scaffold for growing cardiomyocytes — heart muscle cells — in the lab.

The scaffold is based on gelatin that has been functionalized with methacrylate groups that are cross-linked with UV light. This material, called GelMA, can be formed into very specific shapes using microfabrication techniques, but the resulting hydrogels still lack the electrical conductivity, mechanical strength and nanofibrous structure found in native heart tissues. “Traditionally, making a gel stronger requires making the pores smaller,” says Xiaowu (Shirley) Tang, a physical chemist at the University of Waterloo. “This means the cells will be too constrained.”

The team coated carbon nanotubes with GelMA, forming gelatinous fibres 20 to 30 nanometres in diameter. These were then cross-linked to make a scaffold permeated by a web-likestructure of conductive carbon. The strength — as measured by compression tests — was three times higher than GelMA, and the electrical conductivity improved as well. Neonatal rat cardiomyocytes grown on the scaffolds secreted more connective proteins and were better organized than those grown on GelMA alone. They also started beating sooner and faster, with average rates approaching 60 beats per minute. The research is published in ACS Nano.

The improved properties could help grow replacement cardiac tissues for damaged hearts, but they still have a way to go before they can fully match the properties of native heart tissue. Meanwhile, the team has other applications in mind like growing cardiomyocytes to use as muscle-like actuators in bio-mechanical robots. “This is a hugely fun playground for scientists and engineers,” says Tang.