Optothermally responsive nanocomposite generating mechanical forces for cells enabled by few-walled carbon nanotubes

We have designed and fabricated a nanocomposite substrate that can deliver spatially and temporally defined mechanical forces onto cells. This nanocomposite substrate comprises a 1.5-mm-thick near-infrared (NIR) mechanoresponsive bottom layer of few-walled carbon nanotubes (FWCNTs) that are uniformly distributed and covalently connected to thermally responsive poly(N-isopropylacrylamide) and an approximately 0.15-mm-thick cell-seeding top layer of collagen-functionalized poly(acrylic acid)-co-poly(N-isopropylacrylamide) that interpenetrates into the bottom layer. Covalent coupling of all the components and uniform distribution of FWCNTs lead to a large local mechanoresponse. As an example, 50% change in strain at the point of irradiation on the order of 0.05 Hz can be produced reversibly under NIR stimulation with 0.02 wt % FWCNTs. We have further demonstrated that the mechanical strain imposed by NIR stimulation can be transmitted onto cells. Human fetal hepatocytes change shape with no sign of detrimental effect on cell viability. To the best of our knowledge, this is the first demonstration of a nanocomposite platform that can generate fast and controlled mechanical force to actuate cells. Since the amplitude, location, and timing of force can be controlled remotely with NIR, the nanocomposite substrate offers the potential to provide accurately designed force sequences for tissue engineering.