EFTA01120562.pdf

An Electronic Second Skin Science Zhenqiang Ma Science 333, 830 (2011); DOI: 10.1126/science.1209094 kl AA AS This copy is for your personal, non-commercial use only. If you wish to distribute this article to others, you can order high-quality copies for your colleagues, clients, or customers by clicking here. Permission to republish or repurpose articles or portions of articles can be obtained by following the guidelines here. The following resources related to this article are available online at www.sciencemag.org (this infomation is current as of August 15, 2011): Downloaded from www.sciencemag.org on August 15. 2011 Updated information and services, including high-resolution figures, can be found in the online version of this article at: http://i.vww.sciencemag.org/content/333/6044/830.full.html A list of selected additional articles on the Science Web sites related to this article can be found at: http://www.sciencemag.org/content/333/6044/830.full.html#related This article cites 7 articles. 2 of which can be accessed free: http://www.sciencemag.org/content/333/6044/830.full.html#ref-list-1 This article appears in the following subject collections: Materials Science http://www.sciencemag.org/cgi/collection/mat sci Science (print ISSN 0036-8075: online ISSN 1095-9203) is published weekly, except the last week in December, by the American Association for the Advancement of Science, 1200 New York Avenue NW, Washington, DC 20005. Copyright 2011 by the American Association for the Advancement of Science; all rights reserved. The title Science is a registered trademark of AAAS. EFTA01120562 PERSPECTIVES for germ cell development, and the sex of male germ cells did not interfere with nor- The appearance and function of sperm the germ cells must match that of the soma mal spermatogenesis; when Sxl-expressing and egg are similar throughout the animal for proper gametogenesis to occur (2). A male germ cells were left in a male envi- kingdom, which suggests that the process key question facing researchers is how the ronment (testis), they produced sperm, as of germline sexual development may be germ line coordinates signals from the soma observed previously (9). Thus, Sr! cannot highly conserved. Thus, a better understand- with its own sex chromosome constitution to feminize a germ cell in all respects, because ing of how gennline sexual identity is reg- achieve proper sexual identity. a female germ cell is unable to make sperm ulated by the soma, and by the germ line's Hashiyama et at demonstrate that in in a male environment. own sex chromosome constitution, will have Drosophila, a gene named Sex lethal (Sxl) Compatibility between the germ line and far-reaching implications for our knowledge acts as a key switch in regulating gennline the soma is also an issue for mammalian of animal development and human fertility. sex determination. Expression of&I is suf- germ cells. In humans who are XXY (Kline- Hashiyama et al. have now brought us one ficient to allow germ cells with an XY geno- fetter's syndrome), the soma is male because step closer to this goal. type, which would normally be male, to pro- of the masculinizing influence of the Y chro- duce eggs when they are transplanted into mosome. However, the presence of two X References a female soma (ovary)—something that a chromosomes is incompatible with male 1. K. Hashiyama, Y. Hayashi, S. Kobayashi, SIWACe 333, 885 12011). male germ cell would normally never do. germline development and these individuals 2. S. M. Murray, S. Y. Yang, M. Van Doren, Cua. Opm. Cell There are several reasons why this work is are sterile; their testes have severely reduced Biol. 22, 722 (2010). Downloaded from www.sciencemag.org on August 15, 2011 exciting. First, Sxl expression is able to over- germline characteristics, including loss of 3. T. W. Chne, Dem Mot 72, 266 (1979). 4. M. Van Omen, A. L. Williamson, R. Lehman, Cum 8ml. come the incompatibility between a male premeiotic spermatogonia and spermatogo- 8, 243 (1998). germ line and a female soma. This offers nial stem cells (10). This defect is due to the 5. M. Steinmann-back% Development 117, 763 (1993). insight into how the two distinct inputs from number of X chromosomes in germ cells; any 6. 8. Grenadine, P. Santamana,1. Sanchez, Development the germ line and soma contribute to germ- foci of spermatogenesis observed in these 118, 813 (1993). 7. ). I.. Marsh, E. Wieschaus, Notate 272, 249119781. line sex determination. Second, the fact that patients are from germ cells that have lost one 8. 0. Bachiller, L. Sanchez, Oev. 8/of. 118, 379 (1986). Sr/ is sufficient to activate female germline X chromosome (11, 12). Germ cell defects 9. ). H. Hager, 1. W. Cline, 0evelopmen 124, 5033 (1997). identity is interesting given that it is also the are also seen in females with Turner's syn- 10. A. M. Wiksirbm, L Dunkel, Ham. Res 69,317 (2008). key switch gene in determining the sex ofthe drome, which is characterized by the pres- 11. R. B. Sourano et al., Hum. Remod. 24, 2353 (2009). 12. M. Bemire et d., Hum. Reproof. 17, 32 (2802). soma (3), yet it acts differently in the germ ence of only a single X chromosome (XO) 13. K. Reynaud Prof., felt Sten! 81.1112 (2004). line. Lastly, Hashiyama et at show that sex (13). Although recent studies have identified 14. N. Camara, C. Whinuerth, M. Van Doren, Can. Top. Dee. determination in the germ line occurs ear- signals by which the somatic gonad influ- Biol. 83, 6512038). 15. rn.trameink et of., Herat 436, 563 (2005). lier than was thought. Previous studies ences germline sex determination in mam- showed that germ cells exhibit sex-specific mals, how the sex chromosome constitution behaviors and gene expression at the time affects this process remains unknown. to.fizetscience.tz10282 they first associate with the somatic gonad (2). However, female-specific expression of Sr/ begins much earlier (1)—as soon as the MATERIALS SCIENCE germ cells are believed to generally activate zygotic transcription (4'). Thus, germ cells have a sexual identity even before they are influenced by sex-specific signals from the An Electronic Second Skin somatic gonad. Zhenqiang Ma This exciting work raises as many ques- tions as it answers. How is Sxl activated in Small, flexible devices that attach to the skin without adhesives or gels monitor physiological signals. female germ cells? Although Sr! expres- I sion in both the soma and the germ line is n clinical health monitoring, the diagnos- the electrode locations have to be constantly regulated by the number of X chromosomes tic machines that perform physiological moved around, interrupting monitoring. Clin- present, it appears that the way the cell's measurement and stimulation through ical physicians strongly desire more compact biochemical machinery "counts" X chro- skin are connected to patients with wires and even wireless health monitoring devices. mosomes in the germ line differs from the and cables. Such complicated wiring can be An electronic skin recently developed by way it counts them in the soma (5, 6). Fur- inconvenient and distressing for both patients Kim et at (1), reported on page 838 in this ther, what are Srts targets in the germ line? and physicians. For example, a patient who issue, will help solve these problems and Sr/ encodes an RNA binding protein; in the may have heart disease is usually required to allow monitoring to be simpler, more reliable, soma, it acts as a regulator of alternative wear a bulky monitor for a prolonged period and uninterrupted. These devices were made RNA splicing and translation, and controls (typically a month) in order to capture the through "transfer printing" fabrication pro- both sexual identity [by regulating trans- abnormal yet rare cardiac events. The cur- cesses that create flexible versions of high- former (rra)] and X chromosome dosage rent best electrodes are gel-coated adhesive performance semiconductors that are brittle compensation (by regulating male specific pads. Many people, particularly those who as bulk materials. lethal 2). However, neither of these key Sri have sensitive skins, will develop a rash, and The electronic skin concept was initially targets in the soma are important in the germ developed for applications in robotics (2-4). line (7, 8), indicating that Sri must regulate Robots could be provided with pressure sens- Department of Electrical and Computer Engineering, Uni- other, unknown factors there. Hashiyama versity of Wisconsin, Madison, WI 53706, USA. E-mail: ing ("touch") that would allow them to grip et at also found that activation of Sri in mamipenor.wisc.edu objects securely without damaging them (the 830 12 AUGUST 2011 VOL 333 SCIENCE www.sciencemag.org Published byAAAS EFTA01120563  PERSPECTIVES adequate adhesion with the natural skin. Special materials that are properly Strain gauges designed through accurate modeling were Transistors needed to achieve these properties. The sup- N port layer of the electronic skin is an elasto- meric (rubbery) polyester engineered to have mechanical properties well matched to those of natural skin. The circuitry part of the elec- tronic skin consists of two protection layers that sandwich a multifunctional middle layer (see the figure). With their equal thicknesses, Temperature sensors the protection layers develop opposite strains Photodetectors that cancel, so the middle circuit layer expe- riences little stress no matter which direction the device is bent. The middle layer consists of the metal, semiconductor, and insulator components needed for sensors, electronics, Downloaded from www.sciencemag.org on August 15, 2011 power supplies, and light-emitting compo- nents, all of which are in the serpentine shape that forms a stretchable net. The serpentine Po yester skin shapes allow the net to deform drastically Circuits and sensors Human skin with little effect on its functionality. This innovative design contains all of the neces- Information caught by film. A flexible electronic device attaches to the skin like a bandage tape and can be sary components in an ultrathin layer about used to acquire physiological information without bulky electrodes. Kim et at. developed an electronic skin the thickness of a human hair. in the form of a highly stretchable net, consisting of various sensors and electronics of serpentine shapes, The electronic skin designed by Kim et that is sandwiched between two protection layers of equal thickness. The device layer sits on a polyester layer at can be simply mounted onto or peeled off that was engineered with mechanical properties to match those of natural skin. natural skin in the same way as bandage tape. Physiological information has been collected "picking up an egg" problem). These elec- than that of conducting polymers (2, 3), is from heart, brain, and skeletal muscles with tronic skins, which mainly consist of pres- still much lower than that of doped silicon. a quality equivalent to that collected with sure-sensing materials and associated elec- With these types of materials, it is difficult bulky electrodes and hardware. Other forms tronic devices for pressure reading, might or impossible to achieve the performance of physiological information collection based also provide touch sense to prosthetic devices needed to amplify very weak signals acquired on the electronic skin are readily feasible such as artificial legs or arms. from natural skin. because they could use components that have One challenge for making these devices The electronic skin demonstrated by Kim more sophisticated functions. is that the transistors (and the semiconduc- et aL uses thin single-crystal silicon that has The transfer-printing fabrication tors in them) that amplify weak signals must superior flexibility and a mobility equivalent approach (6) has proved to be viable and be flexible in order to act like skin. The abil- to that of the silicon used in personal porta- low-cost in this demonstration, which will ity of transistors to amplify signals—their ble devices. The approach, a printing method greatly facilitate the practical clinical use gain—depends on the mobility of the charge developed previously by Rogers's group (6), of the electronic skin. Because of the higher carriers in their semiconductor under the gate could be called "inking and printing." A thin quality of the transferable thin silicon, wire- layer (or in their gated semiconductor layer). silicon layer is bonded to a silicon dioxide less communication directly from the elec- Doped single-crystalline silicon wafers are release layer. The silicon layer is cut into a tronic skin should be feasible, given recent used in most computer chips because of their lattice of micrometer-scale "chiplets,- and a demonstrations of this capability in other high carrier mobility, which allows opera- transfer stamp layer is then attached to the top devices (7). Other types of electronic skins tion with low applied voltage and low power. of the divided silicon. The transfer layer and with applications beyond physiology, such However, the wafers are brittle, so alterna- chiplets are then lifted and transferred to a as body heat harvesting and wearable radios, tive materials have been pursued. Some of flexible substrate. may also point to interesting directions for the candidate flexible semiconductors, such Attaching electronic skin to natural skin future work. as conducting polymers (2, 3), have much is more difficult than attaching it to robots lower carrier mobilities. The higher voltages or prosthetics. Natural skin is soft and del- References needed to use these materials as transistors icate and already has touch-sensing func- 1. 0.-H. Kim et of, Science 333, 838 (20111. 2. 1. 5omeya et at, Proc. Not!. Arad. so. tr.sA 101, 9966 may not be suitable for electronic skin that tions. The electronic skin that can be used (200O. makes direct contact with a patient's skin, and for physiological monitoring must have a 3. S. C. B. Manndetdet of., Nat. Mato. 9, 859 (2010). may quickly exhaust small power supplies. supporting layer with mechanical properties 4. Z. Fan a of Nano Left. 8, 20 (2008). 5. K. Takei et or.. Nat Mato. 9, 821(2010). Another approach is to convert brittle that match those of natural skin to avoid any 6. E. Menu& R. G. teuuo.1. k Rogers, Appt Phys. Lett 86, semiconductors into more flexible forms. discomfort resulting from long wearing. The 09350712005). For example, silicon and germanium are electronic skin must not be too thick, too 7. t. Sun ed.Small 6, 2553 (2010). highly flexible as nanowires (4, 5). However, rigid, too hard, or too heavy, but must have their carrier mobility, although much higher conformal contact, intimate integration, and 10.1126/Sibente.1209094 www.sciencemag.org SCIENCE VOL 333 12 AUGUST 2011 831 pubranedayams EFTA01120564