Piezoelectric nanoribbons for monitoring cellular deformations

Journal name:
Nature Nanotechnology
Volume:
7,
Pages:
587–593
Year published:
DOI:
doi:10.1038/nnano.2012.112
Received
Accepted
Published online

Abstract

Methods for probing mechanical responses of mammalian cells to electrical excitations can improve our understanding of cellular physiology and function1, 2, 3. The electrical response of neuronal cells to applied voltages has been studied in detail4, but less is known about their mechanical response to electrical excitations. Studies using atomic force microscopes (AFMs) have shown that mammalian cells exhibit voltage-induced mechanical deflections at nanometre scales5, 6, but AFM measurements can be invasive and difficult to multiplex. Here we show that mechanical deformations of neuronal cells in response to electrical excitations can be measured using piezoelectric PbZrxTi1-xO3 (PZT) nanoribbons, and we find that cells deflect by 1 nm when 120 mV is applied to the cell membrane. The measured cellular forces agree with a theoretical model in which depolarization caused by an applied voltage induces a change in membrane tension, which results in the cell altering its radius so that the pressure remains constant across the membrane5, 7. We also transfer arrays of PZT nanoribbons onto a silicone elastomer and measure mechanical deformations on a cow lung that mimics respiration. The PZT nanoribbons offer a minimally invasive and scalable platform for electromechanical biosensing.

At a glance

Figures

  1. Interfacing of PZT nanoribbons with cultured neuronal cells.
    Figure 1: Interfacing of PZT nanoribbons with cultured neuronal cells.

    a, Schematic of the piezoelectric nanoribbon device with cultured neuronal cells. The suspended nanoribbons record cellular mechanical deflections while the glass pipette (PPT) applies and records membrane potentials. b, SEM image of suspended PZT nanoribbons (scale bar, 5 µm). c, SEM image of a single PC12 cell directly interfaced with suspended PZT nanoribbons (scale bar, 15 µm).

  2. Biocompatibility of PZT nanoribbons with neuron-like cells.
    Figure 2: Biocompatibility of PZT nanoribbons with neuron-like cells.

    a, Phase-contrast images of healthy PC12 cells cultured on a standard cell culture dish, on a PZT surface, on PZT nanoribbons and on PZT nanobeams (left to right). Scale bars, 20 µm. b, Live/dead viability assay showing live (green) and dead (red) cells on PZT nanoribbons. Cells were cultured for 3 days (left) and 7 days (right). Scale bars, 30 µm. c, Percentage of healthy cells cultured on PZT nanoribbons (red columns) compared with cells cultured on a standard culture dish (blue columns) after 3 and 7 days. d, A typical electrophysiological voltage response (top) from the membranes of PC12 cells cultured on PZT nanoribbons when current pulses (bottom curves, redrawn from experimental data) are injected in current-clamp mode. The membrane voltage traces are triggered by the current pulse of the same colour. Each of the colours therefore represents a stimulated current and its corresponding membrane voltage.

  3. Quantifying the sensitivity of PZT nanoribbons.
    Figure 3: Quantifying the sensitivity of PZT nanoribbons.

    a, Schematic showing the experimental set-up. An AFM tip (grey) probes the centre of a PZT nanobeam (red). b, Piezoelectric signals generated in response to indentation by the AFM tip during scanning. Inset: tip exerting an indentation force. Scale bar, 50 µm. c, Graph showing that the piezoelectric nanoribbon signal depends on the applied force of the AFM tip. The solid line is a fit based on experimental data (points). Error bars arise from the variance in the spring constants of the AFM tips.

  4. Probing cellular mechanics using PZT nanoribbons.
    Figure 4: Probing cellular mechanics using PZT nanoribbons.

    a, Response of piezoelectric nanoribbons (blue) to cellular deformations evoked by an applied membrane voltage (green). Inset: optical image of the experiment (scale bar, 12 µm). b, Response of PZT nanoribbons (blue) to cellular deformations induced by spontaneous depolarization (green). Noise below a threshold of 2.2 mV has been removed for clarity. Inset: the experiment (scale bar, 12 µm). c, Relationship between imparted force and membrane potential. Red points represent experimental data. Error bars include errors from the fitting process of the AFM calibration and variance in the experimental data. The solid blue line is a theoretical calculation of the mechanical deformation force. d, Schematic of the theoretical model describing the force that the cell (blue circle) exerts on a PZT nanobeam (red line) following electrical excitation from a pipette (blue) on top of the cell. Left panel: the cell in a resting state (applied membrane voltage V = 0), with a cellular radius of R0. Right panel: the cell swells to a radius R in the excited state (V ≠ 0).

  5. Biointerfacing of PZT nanoribbons with multicellular cow lung tissue.
    Figure 5: Biointerfacing of PZT nanoribbons with multicellular cow lung tissue.

    a, SEM image of PZT nanoribbons following transfer onto a flexible PDMS substrate. Scale bar, 15 µm. b, Optical microscope image of PZT nanoribbons (thin vertical lines) and interdigitated gold electrodes (horizontal large yellow lines) on PDMS. Scale bar, 50 µm. c, Photograph of flexible PZT nanoribbon chip. d, Photograph of PZT nanoribbons on PDMS biointerfaced with cow lung tissue for sensing deformations during a mimicked respiration process. e, PZT/PDMS chip at rest on the cow lung. f, PZT/PDMS chip in a strained state during the mimicked respiration process. Scale bars, 1 cm (cf). g,h, PZT voltage (g) and current (h) signals associated with deformation of the cow lung during the respiration process.

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Author information

Affiliations

  1. Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544, USA

    • Thanh D. Nguyen &
    • Michael C. McAlpine
  2. Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544, USA

    • Nikhil Deshmukh,
    • Tal Kramer &
    • Michael J. Berry
  3. Broad Fellows Program, Division of Biology, California Institute of Technology, Pasadena, California 91125, USA

    • John M. Nagarah
  4. Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA

    • Prashant K. Purohit

Contributions

T.D.N., J.M.N. and M.C.M. devised the studies. T.D.N., N.D., J.M.N., M.J.B. and M.C.M. designed the experiments. T.D.N., N.D. and T.K. performed the experiments. P.K.P. developed the theoretical model. T.D.N., N.D., J.M.N., T.K., P.K.P., M.J.B. and M.C.M. wrote the paper.

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The authors declare no competing financial interests.

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