Nerve regeneration after injury is a critical medical issue. In previous work, we have developed an oligo(poly(ethylene glycol) fumarate) (OPF) hydrogel incorporated with positive charges as a promising nerve conduit. In this study, we introduced cross-linkable bonds to graphene oxide and carbon nanotube to obtain the functionalized graphene oxide acrylate (GOa) and carbon nanotube poly(ethylene glycol) acrylate (CNTpega). An electrically conductive hydrogel was then fabricated by covalently embedding GOa and CNTpega within OPF hydrogel through chemical cross-linking followed by in situ reduction of GOa in l-ascorbic acid solution. Positive charges were incorporated by 2-(methacryloyloxy)ethyltrimethylammonium chloride (MTAC) to obtain rGOaCNTpega-OPF-MTAC composite hydrogel with both surface charge and electrical conductivity. The distribution of CNTpega and GOa in the hydrogels was substantiated by transmission electron microscopy (TEM), and strengthened electrical conductivities were determined. Excellent biocompatibility was demonstrated for the carbon embedded composite hydrogels. Biological evaluation showed enhanced proliferation and spreading of PC12 cells on the conductive hydrogels. After induced differentiation using nerve growth factor (NGF), cells on the conductive hydrogels were effectively stimulated to have robust neurite development as observed by confocal microscope. A synergistic effect of electrical conductivity and positive charges on nerve cells was also observed in this study. Using a glass mold method, the composite hydrogel was successfully fabricated into conductive nerve conduits with surficial positive charges. These results suggest that rGOa-CNTpega-OPF-MTAC composite hydrogel holds great potential as conduits for neural tissue engineering.

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Two-dimensional (2D) materials have emerged as a new promising research topic for tissue engineering because of their ability to alter the surface properties of tissue scaffolds and thus improve their biocompatibility and cell affinity. Multiple 2D materials, such as graphene and graphene oxide (GO), have been widely reported to enhance cell adhesion and proliferation. Recently, a newly emerged black phosphorus (BP) 2D material has attracted attention in biomedical applications because of its unique mechanical and electrochemical characteristics. In this study, we investigated the synergistic effect of these two types of 2D materials on cell osteogenesis for bone tissue engineering. BP was first wrapped in negatively charged GO nanosheets, which were then adsorbed together onto positively charged poly­(propylene fumarate) three-dimensional (3D) scaffolds. The increased surface area provided by GO nanosheets would enhance cell attachment at the initial stage. In addition, slow oxidation of BP nanosheets wrapped within GO layers would generate a continuous release of phosphate, an important osteoblast differentiation facilitator designed to stimulate cell osteogenesis toward the new bone formation. Through the use of 3D confocal imaging, unique interactions between cells and BP nanosheets were observed, including a stretched cell shape and the development of filaments around the BP nanosheets, along with increased cell proliferation when compared with scaffolds incorporating only one of the 2D materials. Furthermore, the biomineralization of 3D scaffolds, as well as cellular osteogenic markers, was all measured and improved on scaffolds with both BP and GO nanosheets. All these results indicate that the incorporation of 2D BP and GO materials could effectively and synergistically stimulate cell proliferation and osteogenesis on 3D tissue scaffolds.

1 8 6 8 -1 9 2 7 ) P io n e e r s tu d e n t o f A m e r ic a n P e r m ia n a m m o n o id fa u n a s The strata of the Guadalupe Mountain region can be regarded as the classic Permian of North America. Over 80 years ago these rocks and their fossils were described in some detail, and the first comprehensive report on the marine Permian faunas of North America was based on specimens from the Guadalupe and the Delaware mountains. Further more, recent stratigraphic studies in this area have shown that the strata there are particularly significant; as they are transitional in nature, they enable us to correlate the typical marine fossiliferous Permian of the Southwest with contemporaneous beds that are nonfossiliferous. It is the purpose of this report to achieve an understanding of the ammonoid faunas of the Guadalupe Mountain area and to compare and relate these faunas with those found in the well-known Glass Mountain sequence.Naturally, it is impossible to ascertain the full significance of any fauna b y a study of specimens from a limited area, and the writers have therefore attempted to take advantage of the rather extensive collections at their disposal. All the Permian ammonoids that have resulted from the recent work of the United States Geological Survey in the Guadalupe Mountain area have been made available to the writers. Also, they have very large collections from the Glass Mountains, which add appreciably to the num ber of species known from there, and smaller collections from the Sierra Diablo and the Hueco, Finlay, and Chinati mountains of west Texas and from various localities in north-central Texas. Furthermore, the writers have been able to study essentially all the Permian ammonoids known from other localities in North America, including Coahuila, New Mexico, Kansas, Wyoming, British Columbia, and Greenland. Finally, they have representative collections from Sicily, the Ural region, the Salt Range, Timor, and Australia. Because of the world-wide importance of ammonoid zones, they are suggesting intercontinental correlations of Permian ammonoid-bearing beds.The great majority of the specimens on which this report is based were collected under the supervision of Philip B. King and were loaned to the writers for study through the courtesy of the United States Geological Survey. They were assembled in the field by George H . Girty, J. Brookes Knight, Philip B. King, and particularly H . C. Fountain. M r. Fountain devoted several months to this work, and any merit that this report may possess is primarily a result of his care and diligence. Also, Dr. Girty kindly loaned the type specimens which he illustrated and described in 1908. Professors Charles Schuchert and C. 0 . Dunbar sent the extensive INTRODUCTION AND ACKNOWLEDGMENTS 1 2 PE RM IA N AM MONOIDS O F GU ADALU PE M OU NTAIN REGION collections of Permian ammonoids in the Yale Peabody Museum from Texas, Coahuila, and Sicily; those from Texas and Coahuila, which were particularly helpful, were assembled in the field by R . E. King over a period o...

Chemically crosslinking GOa and CNTpega followed by in situ reduction fabricated a conductive rGOa–CNTpega–OPF hydrogel that strongly stimulated neurite growth.