Realization of advanced bio-interactive electronic devices requires mechanically compliant sensors with the ability to detect extremely large strain. Here, we design a new multifunctional carbon nanotube (CNT) based capacitive strain sensors which can detect strains up to 300% with excellent durability even after thousands of cycles. The CNT-based strain gauge devices exhibit deterministic and linear capacitive response throughout the whole strain range with a gauge factor very close to the predicted value (strictly 1), representing the highest sensitivity value. The strain tests reveal the presented strain gauge with excellent dynamic sensing ability without overshoot or relaxation, and ultrafast response at sub-second scale. Coupling these superior sensing capabilities to the high transparency, physical robustness and flexibility, we believe the designed stretchable multifunctional CNT-based strain gauge may have various potential applications in human friendly and wearable smart electronics, subsequently demonstrated by our prototypical data glove and respiration monitor.R ecent developments in flexible and stretchable electronics, either through structural consideration or by exploring novel materials 1,2 , have imparted otherwise rigid and brittle electronic devices mechanical compliance and bio-compatibility, paving the way for energy-efficient, lightweight, portable, wearable and even implantable electronics 3 . Examples include stretchable and large area display that can undergo complex deformations 4 , bio-inspired material and structural designs that enable bionic functions 5 , and printable sensory system capable of detecting planar strains, normal pressure, temperature, light, moisture and chemical/biological species 6 . Multifunctional sensors, in particular, with sensing abilities akin to or beyond those of human skin 6-12 , are essential for applications such as interactive electronics 13 , structural health monitoring 14 , smart clothing 15 , robotic systems with advanced sensing capabilities 16 , human motion detection 8 and so on. Among the various types of sensors, strain gauge is one of the most important smart sensors, which have been widely used in the measurements of strain, acceleration and tension, as well as structural health monitoring. Conventional strain gauges, made of metal foils, register resistance changes under tensile strains. Actually, mechanical compliance and large strain range (?5%), obviously not the case of metal foils, are required to meet the demands of wearable electronics 15 , human motion detection 8 and interactive robots 17 . Although mercury-in-rubber strain gauge has been used in the biological measurements for decades 18 , the maximum strain limit and toxicity of mercury still block their practically wide applications. In addition, the combination of conformability and optical transparency will facilitate intelligent electronics and self-powered robot where strain sensors are integrated with optoelectronic devices and direct observation through the devices is ne...

The potential to differentiate human embryonic stem cells (hESCs) in vitro to provide an unlimited source of human hepatocytes for use in biomedical research, drug discovery, and the treatment of liver diseases holds great promise. Here we describe a three-stage process for the efficient and reproducible differentiation of hESCs to hepatocytes by priming hESCs towards definitive endoderm with activin A and sodium butyrate prior to further differentiation to hepatocytes with dimethyl sulfoxide, followed by maturation with hepatocyte growth factor and oncostatin M. We have demonstrated that differentiation of hESCs in this process recapitulates liver development in vivo: following initial differentiation, hESCs transiently express characteristic markers of the primitive streak mesendoderm before turning to the markers of the definitive endoderm; with further differentiation, expression of hepatocyte progenitor cell markers and mature hepatocyte markers emerged sequentially. Furthermore, we have provided evidence that the hESCderived hepatocytes are able to carry out a range of hepatocyte functions: storage of glycogen, and generation and secretion of plasma proteins. More importantly, the hESC-derived hepatocytes express several members of cytochrome P450 isozymes, and these P450 isozymes are capable of converting the substrates to metabolites and respond to the chemical stimulation. Our results have provided evidence that hESCs can be differentiated efficiently in vitro to functional hepatocytes, which may be useful as an in vitro system for toxicity screening in drug discovery. STEM CELLS 2008;26:894 -902 Disclosure of potential conflicts of interest is found at the end of this article.

In the mammalian model of sex determination, embryos are considered to be sexually indifferent until the transient action of a sex-determining gene initiates gonadal differentiation. Although this model is thought to apply to all vertebrates, this has yet to be established. We have examined three lateral gynandromorph chickens with the aim of investigating the nature of the sex-determining mechanism in birds. These studies demonstrated that gynandromorph birds are genuine male:female chimeras, and suggested that male and female avian somatic cells may have an inherent sex identity. To test this hypothesis, we transplanted presumptive mesoderm between embryos of reciprocal sexes to generate embryos containing male:female chimeric gonads. In contrast to the outcome for mammalian mixed-sex chimeras, in chicken mixed-sex chimeras the donor cells were excluded from the functional structures of the host gonad. Most strikingly, in an instance where female tissue was transplanted into a male host, donor cells contributing to the developing testis retained a female identity and expressed a marker of female function. Our study demonstrates that avian somatic cells possess an inherent sex identity and that, in birds, sexual differentiation is substantively cell autonomous.