High-Performance Air-Stable n-Type Carbon Nanotube Transistors with Erbium Contacts

O ver the past few decades, the continued down-scaling of the physical dimensions of silicon field-effect transistors (FETs) has been the main drive for achieving higher device density while improving the transistor performance in complementary metalÀoxideÀ semiconductor (CMOS) circuits. One of the principle benefits of the conventional scaling trend, namely, reducing the power consumption per computation, has diminished in recent years. In particular, power management is increasingly becoming a major challenge because of the inability to further decrease the operating voltage without compromising the performance of silicon FETs. Incorporation of alternative channel materials with superior carrier transport properties, as presently conceived, is a favorable strategy for the semiconductor industry to complement or replace silicon FETs. Among the promising candidates, carbon nanotubes (CNTs) are predicted to offer the most energy-efficient solution for computation compared with other channel materials, 1 owing to their unique properties such as ultrathin body and ballistic carrier transport in the channel. ABSTRACT So far, realization of reproducible n-type carbon nanotube (CNT) transistors suitable for integrated digital applications has been a difficult task. In this work, hundreds of n-type CNT transistors from three different low work function metals ; erbium, lanthanum, and yttrium ; are studied and benchmarked against p-type devices with palladium contacts. The crucial role of metal type and deposition conditions is elucidated with respect to overall yield and performance of the n-type devices. It is found that high oxidation rates and sensitivity to deposition conditions are the major causes for the lower yield and large variation in performance of n-type CNT devices with low work function metal contacts. Considerable improvement in device yield is attained using erbium contacts evaporated at high deposition rates. Furthermore, the air-stability of our n-type transistors is studied in light of the extreme sensitivity of these metals to oxidation

Tryptophan and Kynurenine Enhances the Stemness and Osteogenic Differentiation of Bone Marrow-Derived Mesenchymal Stromal Cells In Vitro and In Vivo

Aging tissues present a progressive decline in homeostasis and regenerative capacities, which has been associated with degenerative changes in tissue-specific stem cells and stem cell niches. We hypothesized that amino acids could regulate the stem cell phenotype and differentiation ability of human bone marrow-derived mesenchymal stromal cells (hBMSCs). Thus, we performed a screening of 22 standard amino acids and found that D-tryptophan (10 mu M) increased the number of cells positive for the early stem cell marker SSEA-4, and the gene expression levels of OCT-4, NANOG, and SOX-2 in hBMSCs. Comparison between D- and L-tryptophan isomers showed that the latter presents a stronger effect in inducing the mRNA levels of Oct-4 and Nanog, and in increasing the osteogenic differentiation of hBMSCs. On the other hand, L-tryptophan suppressed adipogenesis. The migration and colony-forming ability of hBMSCs were also enhanced by L-tryptophan treatment. In vivo experiments delivering L-tryptophan (50 mg/kg/day) by intraperitoneal injections for three weeks confirmed that L-tryptophan significantly increased the percentage of cells positive for SSEA-4, mRNA levels of Nanog and Oct-4, and the migration and colony-forming ability of mouse BMSCs. L-kynurenine, a major metabolite of L-tryptophan, also induced similar effects of L-tryptophan in enhancing stemness and osteogenic differentiation of BMSCs in vitro and in vivo, possibly indicating the involvement of the kynurenine pathway as the downstream signaling of L-tryptophan. Finally, since BMSCs migrate to the wound healing site to promote bone healing, surgical defects of 1 mm in diameter were created in mouse femur to evaluate bone formation after two weeks of L-tryptophan or L-kynurenine injection. Both L-tryptophan and L-kynurenine accelerated bone healing compared to the PBS-injected control group. In summary, L-tryptophan enhanced the stemness and osteoblastic differentiation of BMSCs and may be used as an essential factor to maintain the stem cell properties and accelerate bone healing and/or prevent bone loss

Practical whole-tooth restoration utilizing autologous bioengineered tooth germ transplantation in a postnatal canine model

Whole-organ regeneration has great potential for the replacement of dysfunctional organs through the reconstruction of a fully functional bioengineered organ using three-dimensional cell manipulation in vitro. Recently, many basic studies of whole-tooth replacement using three-dimensional cell manipulation have been conducted in a mouse model. Further evidence of the practical application to human medicine is required to demonstrate tooth restoration by reconstructing bioengineered tooth germ using a postnatal large-animal model. Herein, we demonstrate functional tooth restoration through the autologous transplantation of bioengineered tooth germ in a postnatal canine model. The bioengineered tooth, which was reconstructed using permanent tooth germ cells, erupted into the jawbone after autologous transplantation and achieved physiological function equivalent to that of a natural tooth. This study represents a substantial advancement in whole-organ replacement therapy through the transplantation of bioengineered organ germ as a practical model for future clinical regenerative medicine

IMMUNOLOGICAL DIFFERENTIATION OF HUMAN TISSUE-NONSPECIFIC TYPE ALKALINE PHOSPHATASES BY A MONOCLONAL ANTIBODY TO THE ENZYME OF HUMAN OSTEOBLAST-LIKE CELLS

Monoclonal antibodies against alkaline phosphatase [ALP; ortho-phosphoric monoester phosphohydrolase, alkaline optimum, EC 3.1.3.1.] of cultured human osteoblast-like cells (HBC) were raised in mice. Immuno-reactions of tissue-nonspecific type ALP from human bone, dental pulp, liver and kidney as well as intestinal and placental types to the monoclonal antibodies were compared by a dot immunoassay and ELISA. One clone was able to recognize antigenic differences among tissue-nonspecific type ALPs in addition to intestinal and placental ALPs; it reacted favorably with ALPs from HBC, human bone, kidney and dental pulp, but not with human liver enzyme. Similarly, the antibody immunoreacted with bone-derived ALP but not with liver-derived enzyme present in human serum.The present monoclonal antibody preparation can be utilized in basic studies as well as in clinical laboratory tests to distinguish minor heterogeneity among human Al Ps

VOLUNTARY EXERCISE INCREASES OSTEOGENETIC ACTIVITY IN RAT BONES

The purpose of this study was to investigate the effect of voluntary exercise on osteoinductive activity in rat bone. Sprague-Dawley male and female rats were allowed to exercise freely by running on a treadmill or kept as controls without exercise for 53 days. Decalcified humeral diaphyses from experimental and control rats were implanted intraperitonealy into host rats and harvested after 33 days. A significant increase in bone formation was confirmed in the implanted bone matrices from the running group in comparison with those from control animals by soft X-ray photography and determination of alkaline phosphatase activity and mineral content. Alkaline phosphatase activity in bone and serum was increased by exercise in both male and female animals. The results suggest that osteoinductive activity in the bone was probably due to increased levels of bone morphogenetic protein following voluntary exercise