Polymer-supported membranes as models of the cell surface


Lipid-bilayer membranes supported on solid substrates are widely used as cell-surface models that connect biological and artificial materials. They can be placed either directly on solids or on ultrathin polymer supports that mimic the generic role of the extracellular matrix. The tools of modern genetic engineering and bioorganic chemistry make it possible to couple many types of biomolecule to supported membranes. This results in sophisticated interfaces that can be used to control, organize and study the properties and function of membranes and membrane-associated proteins. Particularly exciting opportunities arise when these systems are coupled with advanced semiconductor technology.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Supported membranes.
Figure 2: Electrophoretic accumulation.
Figure 3: Membrane patterning.
Figure 4: Membranes on beads.
Figure 5: Electrochemical detection schemes.
Figure 6: Membrane–semiconductor systems.


  1. 1

    Brian, A. A. & McConnell, H. M. Allogeneic stimulation of cytotoxic T cells by supported planar membranes. Proc. Natl Acad. Sci. USA 81, 6159–6163 ( 1984).

    ADS  CAS  PubMed  Google Scholar 

  2. 2

    Chan, P. et al. Influence of receptor lateral mobility on adhesion strengthening between membranes containing LFA-3 and CD2. J. Cell Biol. 10, 245–255 ( 1991).

    Google Scholar 

  3. 3

    Erb, E. -M., Tangemann, K., Bohrmann, B., Müller, B. & Engel, J. Integrin 4IIbM3 reconstituted into lipid bilayers is nonclustered in its activated state but clusters after fibrinogen binding. Biochemistry 36, 7395–7402 ( 1997).

    CAS  PubMed  Google Scholar 

  4. 4

    Kloboucek, A., Behrisch, A., Faix, J. & Sackmann, E. Adhesion-induced receptor segration and adhesion plaque formation: A model membrane study. Biophys. J. 77, 2311–2328 ( 1999).

    CAS  PubMed  PubMed Central  Google Scholar 

  5. 5

    Qi, S. Y., Groves, J. T. & Chakraborty, A. K. Synaptic pattern formation during cellular recognition. Proc. Natl Acad. Sci. USA 98, 6548–6553 ( 2001).

    ADS  CAS  PubMed  Google Scholar 

  6. 6

    Grakoui, A. et al. The immunological synapse: A molecular machine controlling T cell activation. Science 285, 221–227 ( 1999).

    CAS  PubMed  Google Scholar 

  7. 7

    , K. & McConnell, H. M. Supported phospholipid bilayers. Biophys. J. 47, 105–113 ( 1985).

  8. 8

    Groves, J. T. & Dustin, M. L. Supported planar bilayers in studies on immune cell adhesion and communication. J. Immunol. Meth. 278, 19–32 ( 2003).

    CAS  Google Scholar 

  9. 9

    Sackmann, E. Supported membranes: Scientific and practical applications. Science 271, 43–48 ( 1996).

    ADS  CAS  PubMed  Google Scholar 

  10. 10

    Groves, J. T. & Boxer, S. G. Micropattern formation in supported lipid membranes. Acc. Chem. Res. 35, 149–157 ( 2002).

    CAS  Google Scholar 

  11. 11

    Watts, T. H., Gaub, H. E. & McConnell, H. M. T-cell-mediated association of peptide antigen and major histocompatibility complex protein detected by energy-transfer in an evanescent wave-field. Nature 320, 179–181 ( 1986).

    ADS  CAS  PubMed  Google Scholar 

  12. 12

    Kalb, E., Frey, S. & Tamm, L. K. Formation of supported planar bilayers by fusion of vesicles to supported phospholipid monolayers. Biochim. Biophys. Acta 1103, 307–316 ( 1992).

    CAS  PubMed  Google Scholar 

  13. 13

    Bayerl, T. M. & Bloom, M. Physical-properties of single phospholipid-bilayers adsorbed to micro glass-beads — a new vesicular model system studied by H-2-nuclear magnetic-resonance. Biophys. J. 58, 357–362 ( 1990).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  14. 14

    Tatulian, S. A., Hinterdorfer, P., Baber, G. & Tamm, L. K. Influenza hemagglutinin assumes a tilted conformation during membrane-fusion as determined by attenuated total-reflection FTIR spectroscopy. EMBO J. 14, 5514–5523 ( 1995).

    CAS  PubMed  PubMed Central  Google Scholar 

  15. 15

    Terrettaz, S., Stora, T., Duschl, C. & Vogel, H. Protein-binding to supported lipid-membranes — Investigation of the cholera-toxin ganglioside interaction by simultaneous impedance spectroscopy and surface-plasmon resonance. Langmuir 9, 1361–1369 ( 1993).

    CAS  Google Scholar 

  16. 16

    Kjaer, K., Als-Nielsen, J., Helm, C. A., Laxhuber, L. A. & Mohwald, H. Ordering in lipid monolayers studied by synchrotron X-ray-diffraction and fluorescence microscopy. Phys. Rev. Lett. 58, 2224–2227 ( 1987).

    ADS  CAS  PubMed  Google Scholar 

  17. 17

    Johnson, S. J. et al. Structure of an adsorbed dimyristoylphosphatidylcholine bilayer measured with specular reflection of neutrons. Biophys. J. 59, 289–294 ( 1991).

    ADS  MathSciNet  CAS  PubMed  PubMed Central  Google Scholar 

  18. 18

    Kalb, E., Engel, J. & Tamm, L. K. Binding of proteins to specific target sites in membranes measured by total internal-reflection fluorescence microscopy. Biochemistry 29, 1607–1613 ( 1990).

    CAS  PubMed  Google Scholar 

  19. 19

    Bruinsma, R., Behrisch, A. & Sackmann, E. Adhesive switching of membranes: Experiment and theory. Phys. Rev. E 61, 4253–4267 ( 2000).

    ADS  CAS  Google Scholar 

  20. 20

    Sackmann, E. & Bruinsma, R. F. Cell adhesion as wetting transition? Chem. Phys. Chem. 3, 262–269 ( 2002).

    CAS  PubMed  Google Scholar 

  21. 21

    Wagner, M. L. & Tamm, L. K. Reconstituted syntaxin1A/SNAP25 interacts with negatively charged lipids as measured by lateral diffusion in planar supported bilayers. Biophys. J. 61, 266–275 ( 2001).

    Google Scholar 

  22. 22

    Sackmann, E. & Tanaka, M. Supported membranes on soft polymer cushions: Fabrication, characterization and applications. Trends Biotechnol. 18, 58–64 ( 2000).

    CAS  PubMed  Google Scholar 

  23. 23

    Knoll, W. et al. Functional tethered lipid bilayers. Rev. Mol. Biotechnol. 74, 137–158 ( 2000).

    CAS  Google Scholar 

  24. 24

    Koenig, B. W. et al. Neutron reflectivity and atomic force microscopy studies of a lipid bilayer in water adsorbed to the surface of a silicon single crystal. Langmuir 12, 1343–1350 ( 1996).

    CAS  Google Scholar 

  25. 25

    Lambacher, A. & Fromherz, P. Fluorescence interference-contrast microscopy on oxidized silicon using a monomolecular dye layer. Appl. Phys. A 63, 207–216 ( 1996).

    ADS  Google Scholar 

  26. 26

    Elender, G. & Sackmann, E. Wetting and dewetting of Si/SiO2-wafers by free and lipid-monolayer covered aqueous solutions under controlled humidity. J. Phys. II 4, 455–479 ( 1994).

    CAS  Google Scholar 

  27. 27

    Nissen, J., Gritsch, S., Wiegand, G. & Rädler, J. O. Wetting of phospholipid membranes on hydrophilic surfaces — concepts towards self-healing membranes. Eur. Phys. J. B 10, 335–344 ( 1999).

    ADS  CAS  Google Scholar 

  28. 28

    Tanaka, M. et al. Wetting and dewetting of extracellular matrix and glycocalix models. J. Phys. Cond. Matt. 17, S649S663 ( 2005).

    Google Scholar 

  29. 29

    Schaub, M., Wenz, G., Wegner, G., Stein, A. & Klemm, D. Ultrathin films of cellulose on silicon wafers. Adv. Mater. 5, 919–922 ( 1993).

    CAS  Google Scholar 

  30. 30

    Goennenwein, S., Tanaka, M., Hu, B., Moroder, L. & Sackmann, E. Functional incorporation of integrins into solid supported membranes on ultrathin films of cellulose: Impact on adhesion. Biophys. J. 85, 646–655 ( 2003).

    CAS  PubMed  PubMed Central  Google Scholar 

  31. 31

    Lang, H., Duschl, C. & Vogel, H. A new class of thiolipid for the attachment of lipid bilayers on gold surfaces. Langmuir 10, 197–210 ( 1994).

    CAS  Google Scholar 

  32. 32

    Cornell, B. A. et al. A biosensor that uses ion-channel switches. Nature 387, 580–583 ( 1997).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  33. 33

    Schiller, S. M., Naumann, R., Lovejoy, K., Kunz, H. & Knoll, W. Archaea analogue thiolipids for tethered bilayer lipid membranes on ultrasmooth gold surfaces. Angew. Chem. Int. Ed. Engl. 42, 208–211 ( 2003).

    CAS  PubMed  Google Scholar 

  34. 34

    Wagner, M. L. & Tamm, L. K. Tethered polymer-supported planar lipid bilayers for reconstitution of integral membrane proteins: Silane-polyethylenglycol-lipid as a cushion and covalent linker. Biophys. J. 79, 1400–1414 ( 2000).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  35. 35

    Bunjes, N. et al. Thiopeptide-supported lipid layers on solid substrates. Langmuir 13, 6188–6194 ( 1997).

    CAS  Google Scholar 

  36. 36

    Purrucker, O., Förtig, A., Jordan, R. & Tanaka, M. Supported membranes with well-defined polymer tethers — Incorporation of cell receptors. Chem. Phys. Chem. 5, 327–335 ( 2004).

    CAS  PubMed  Google Scholar 

  37. 37

    Purrucker, O., Förtig, A., Ludke, K., Jordan, R. & Tanaka, M. Confinement of transmembrane receptors in tunable stripe micropatterns. J. Am. Chem. Soc. 127, 1258–1264 ( 2005).

    CAS  PubMed  Google Scholar 

  38. 38

    Fischer, M., Bacher, A., Haase, I., Tristl, M. & Sackmann, E. Design of biofunctional assemblies on solids through recombinant bacterial protein lumazine synthase. Chem. Phys. Chem. 2, 623–627 ( 2001).

    CAS  PubMed  Google Scholar 

  39. 39

    Demè, B., Hess, D., Tristl, M., Lee, L. -T. & Sackmann, E. Binding of actin filaments to charged lipid monolayers: Film balance experiments combined with neutron reflectivity. Eur. Phys. J. E 2, 125–136 ( 2000).

    Google Scholar 

  40. 40

    Salafsky, J., Groves, J. T. & Boxer, S. G. Architecture and function of membrane proteins in planar supported bilayers: A study with photosyntehtic reaction centers. Biochemistry 35, 14773–14781 ( 1996).

    CAS  PubMed  Google Scholar 

  41. 41

    Tanaka, M., Kaufmann, S., Nissen, J. & Hochrein, M. Orientation selective immobilization of human erythrocyte membranes on ultrathin cellulose films. Phys. Chem. Chem. Phys. 3, 4091–4095 ( 2001).

    CAS  Google Scholar 

  42. 42

    Tanaka, M., Wong, A. P., Rehfeldt, F., Tutus, M. & Kaufmann, S. Selective deposition of native cell membranes on biocompatible micro-patterns. J. Am. Chem. Soc. 126, 3257–3260 ( 2004).

    CAS  PubMed  Google Scholar 

  43. 43

    Springer, T. A. Traffic signals on endothelium for lymphocyte recirculation and leukocyte emigration. Annu. Rev. Physiol. 57, 827–872 ( 1995).

    CAS  PubMed  PubMed Central  Google Scholar 

  44. 44

    Stelzle, M., Mielich, R. & Sackmann, E. Two-dimensional microelectrophoresis in supported lipid bilayers. Biophys. J. 63, 1346–1354 ( 1992).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  45. 45

    Groves, J. T., Boxer, S. G. & McConnell, H. M. Electric field-induced reorganization of two-component supportedbilayer membranes. Proc. Natl Acad. Sci. USA 25, 13390–13395 ( 1997).

    ADS  Google Scholar 

  46. 46

    Groves, J. T., Wulfing, C. & Boxer, S. G. Electrical manipulation of glycan phosphatidyl inositol tethered protein in planar supported bilayers. Biophys. J. 71, 2716–2723 ( 1996).

    CAS  PubMed  PubMed Central  Google Scholar 

  47. 47

    Olson, D. J. et al. Elecrophoresis of DNA adsorbed to a cationic supported bilayer. Langmuir 17, 7396–7401 ( 2001).

    CAS  Google Scholar 

  48. 48

    Yoshina-Ishii, C. & Boxer, S. G. Arrays of mobile tethered vesicles on supported lipid bilayers. J. Am. Chem. Soc. 125, 3696–3697 ( 2003).

    CAS  PubMed  Google Scholar 

  49. 49

    Merkel, R., Sackmann, E. & Evans, E. Molecular friction and epitactic coupling between monolayers in supported bilayers. J. Phys. (Paris) 50, 1535–1555 ( 1989).

    CAS  Google Scholar 

  50. 50

    Hillebrandt, H., Tanaka, M. & Sackmann, E. A novel membrane charge sensor: sensitive detection of surface charge at polymer/lipid composite films on indium-tin-oxide electrodes. J. Phys. Chem. B 106, 477–488 ( 2002).

    CAS  Google Scholar 

  51. 51

    McLaughlin, S. & Poo, M. M. The role of electro-osmosis in the electric-field-induced movement of charged macromolecules on the surfaces of cells. Biophys. J. 34, 85–93 ( 1981).

    CAS  PubMed  PubMed Central  Google Scholar 

  52. 52

    van Oudenaarden, A. & Boxer, S. G. Brownian ratchets: Molecular separations in lipid bilayers supported on patterned arrays. Science 285, 1046–1048 ( 1999).

    CAS  PubMed  Google Scholar 

  53. 53

    Groves, J. T., Ulman, N. & Boxer, S. G. Micropatterning fluid lipid bilayers on solid supports. Science 275, 651–653 ( 1997).

    CAS  PubMed  Google Scholar 

  54. 54

    Groves, J. T., Mahal, L. K. & Bertozzi, C. R. Control of cell adhesion and growth with micropatterned supported lipid membranes. Langmuir 17, 5129–5133 ( 2001).

    CAS  Google Scholar 

  55. 55

    Yang, T., Baryshnikova, O. K., Mao, H., Holden, M. A. & Cremer, P. S. Investigation of bivalent antibody binding on fluid-supported phospholipid bilayers: The effect of hapten density. J. Am. Chem. Soc. 125, 4779–4784 ( 2003).

    CAS  PubMed  Google Scholar 

  56. 56

    Morigaki, K., Baumgart, T., Offenhausser, A. & Knoll, W. Patterning solid-supported lipid bilayer membranes by lithographic polymerization of a diacetylene lipid. Ang. Chem. Inter. Ed. 40, 172–174 ( 2001).

    CAS  Google Scholar 

  57. 57

    Hovis, J. S. & Boxer, S. G. Patterning barriers to lateral diffusion in supported lipid bilayer membranes by blotting and stamping. Langmuir 16, 894–897 ( 2000).

    CAS  Google Scholar 

  58. 58

    Sapuri, A. R., Baksh, M. M. & Groves, J. T. Electrostatically targeted intermembrane lipid exchange with micropatterned supported membranes. Langmuir 19, 1606–1610 ( 2003).

    CAS  Google Scholar 

  59. 59

    Kung, L. A., Kam, L., Hovis, J. S. & Boxer, S. G. Patterning hybrid surfaces of proteins and supported lipid bilayers. Langmuir 16, 6773–6776 ( 2000).

    CAS  Google Scholar 

  60. 60

    Rehfeldt, F. & Tanaka, M. Hydration forces in ultrathin films of cellulose. Langmuir 19, 1467–1473 ( 2003).

    CAS  Google Scholar 

  61. 61

    Dean, C. et al. Neurexin mediates the assembly of presynaptic terminals. Nature Neurosci. 6, 708–716 ( 2003).

    CAS  PubMed  Google Scholar 

  62. 62

    Galneder, R. et al. Microelectrophoresis of a bilayer-coated silica bead in an optical trap: Application to enzymology. Biophys. J. 80, 2298–2309 ( 2001).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  63. 63

    Loidl-Stahlhofen, A., Kaufmann, S., Braunschweig, T. & Bayerl, T. M. The thermodynamic control of protein binding to lipid bilayers for protein chromatography. Nature Biotechnol. 14, 999–1002 ( 1996).

    CAS  Google Scholar 

  64. 64

    Baksh, M. M., Jaros, M. & Groves, J. T. Detection of molecular interactions at membrane surfaces through colloid phase transitions. Nature 427, 139–141 ( 2004).

    ADS  CAS  PubMed  Google Scholar 

  65. 65

    Jacobson, B. S. & Branton, D. Plasma membrane: rapid isolation and exposure of the cytoplasmic surface by use of positively charged beads. Science 195, 302–304 ( 1976).

    ADS  Google Scholar 

  66. 66

    Cohen, C. M., Kalish, D. I., Jacobson, B. S. & Branton, D. Membrane isolation on polylysine-coated beads. Plasma membrane from HeLa cells. J. Cell. Biol. 75, 119–134 ( 1977).

    CAS  PubMed  Google Scholar 

  67. 67

    Kaufmann, S. & Tanaka, M. Cell adhesion onto highly curved surfaces: One-step immobilization of human erythrocyte membranes on silica beads. Chem. Phys. Chem. 4, 699–704 ( 2003).

    CAS  PubMed  Google Scholar 

  68. 68

    Sakmann, B. & Neher, E., Single-channel Recording (Plenum, New York, 1985).

    Google Scholar 

  69. 69

    Fertig, N., Meyer, C., Blick, R. H., Trautmann, C. H. & Behrends, J. C. Microstructured glass chip for ion-channel electrophysiology. Phys. Rev. E 64, 040901 ( 2001).

    ADS  CAS  Google Scholar 

  70. 70

    Borisenko, V. et al. Simultaneous optical and electrical recording of single gramicidin channels. Biophys. J. 84, 612–622 ( 2003).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  71. 71

    Plant, A. L., Gueguetchkeri, M. & Yap, W. Supported phospholipid/alkanethiol biomimetic membranes — Insulating properties. Biophys. J. 67, 1126–1133 ( 1994).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  72. 72

    Steinem, C., Janshoff, A., Ulrich, W. -P., Sieber, M. & Galla, H. -J. Impedance analysis of supported lipid bilayer membranes: a scrutiny of different preparation techniques. Biochim. Biophys. Acta 1279, 169–180 ( 1996).

    PubMed  Google Scholar 

  73. 73

    Stenberg, M., Arwin, H. & Nilsson, A. Silicon-silicon dioxide as an electrode for electrical and ellipsometric measurements of adsorbed organic molecules. J. Colloid Interface Sci. 72, 255–264 ( 1979).

    ADS  CAS  Google Scholar 

  74. 74

    Hillebrandt, H., Wiegand, G., Tanaka, M. & Sackmann, E. High electric resistance polymer/lipid composite films on indium-tin-oxide electrodes. Langmuir 15, 8451–8459 ( 1999).

    CAS  Google Scholar 

  75. 75

    Gritsch, S., Nollert, P., Jähnig, F. & Sackmann, E. Impedance spectroscopy of porin and gramicidin pores reconstituted into supported lipid bilayers on indium-tin-oxide electrodes. Langmuir 14, 3118–3125 ( 1998).

    CAS  Google Scholar 

  76. 76

    Purrucker, O., Hillebrandt, H., Adlkofer, K. & Tanaka, M. Deposition of highly resistive lipid bilayer on silicon — silicon dioxide electrode and incorporation of gramicidin studied by ac impedance spectroscopy. Electrochim. Acta 47, 791 ( 2001).

    CAS  Google Scholar 

  77. 77

    Wiegand, G., Arribas-Layton, N., Hillebrandt, H., Sackmann, E. & Wagner, P. Electrical properties of supported lipid bilayer membranes. J. Phys. Chem. B 106, 4245–4254 ( 2002).

    CAS  Google Scholar 

  78. 78

    Wiegand, W., Neumaier, K. R. & Sackmann, E. Fast impedance spectroscopy: General aspects and performance study for single ion channel measurements. Rev. Sci. Instrum. 71, 2309–2320 ( 2000).

    ADS  CAS  Google Scholar 

  79. 79

    Fromherz, P., Offenhausser, A., Vetter, T. & Weis, J. A neuron-silicon junction — a Retzius cell of the leech on an insulated-gate field-effect transistor. Science 252, 1290–1293 ( 1991).

    ADS  CAS  PubMed  Google Scholar 

  80. 80

    Straub, B., Meyer, E. & Fromherz, P. Recombinant maxi-K channels on transistor, a prototype of iono-electronic interfacing. Nature Biotechnol. 19, 121–124 ( 2001).

    CAS  Google Scholar 

  81. 81

    Steinhoff, G., Purrucker, O., Tanaka, M., Stutzmann, M. & Eickhoff, M. AlxGa1-xN — A new material system for biosensors. Adv. Funct. Mater. 13, 841–846 ( 2003).

    CAS  Google Scholar 

  82. 82

    Steinhoff, G. et al. Recording of cell action potentials with AlGaN/GaN field-effect transistors. Appl. Phys. Lett. 86, 033901 ( 2005).

    ADS  Google Scholar 

  83. 83

    Ashkenasy, G., Cahen, D., Cohen, R., Shanzer, A. & Vilan, A. Molecular engineering of semiconductor surfaces and devices. Acc. Chem. Res. 35, 121–128 ( 2002).

    CAS  PubMed  Google Scholar 

  84. 84

    Luber, S. et al. Liquid phase sensors based on chemically functionalized GaAs/AlGaAs heterostructures. Physica E 21, 1111–1115 ( 2004).

    ADS  CAS  Google Scholar 

  85. 85

    Cui, Y., Wei, Q., Park, H. & Lieber, C. M. Nanowire nanosensors for highly sensitive and selective detection of biological and chemical species. Science 293, 1289–1292 ( 2001).

    ADS  CAS  PubMed  Google Scholar 

  86. 86

    Saffman, P. G. & Delbrück, M. Brownian motion in biological membranes. Proc. Natl Acad. Sci. USA 72, 3111–3113 ( 1975).

    ADS  CAS  PubMed  Google Scholar 

  87. 87

    Kühner, M., Tampé, R. & Sackmann, E. Lipid mono- and bilayer supported on polymer films: Composite polymer-lipid films on solid substrates. Biophys. J. 67, 217–226 ( 1994).

    ADS  PubMed  PubMed Central  Google Scholar 

Download references


We thank all our collaborators who contributed to this subject, including S. Kaufmann, O. Purrucker, F. Rehfeldt, A. Wong, M. Tutus, J. Hermann, S. Gönnenwein, M. Schneider, K. Adlkofer, H. Hillebrandt, G. Wiegand and S. Gritsch. We thank the groups of G. Wegner, R. Jordan, L. Moroder, M. Fischer, M. Tornow, M. Eickhoff, M. Stutzmann, G. Abstreiter and S. G. Boxer for fruitful collaborations and inspiring discussion. This work was supported through Deutsche Forschungs Gemeinschaft (DFG), National Science Foundation (NSF-MRSEC) and Fonds der Chemischen Industrie.

Author information



Corresponding author

Correspondence to Motomu Tanaka.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Additional information

Author Information Reprints and permissions information is available at npg.nature.com/reprintsandpermissions.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Tanaka, M., Sackmann, E. Polymer-supported membranes as models of the cell surface. Nature 437, 656–663 (2005). https://doi.org/10.1038/nature04164

Download citation

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing