Increasing tensile properties and collagen content is a recognized need in articular cartilage tissue engineering. This study tested the hypothesis that multiple applications of chondroitinase ABC (C-ABC), a glycosaminoglycan (GAG) degrading enzyme, could increase construct tensile properties in a scaffold-less approach for articular cartilage tissue engineering. Developing constructs were treated with C-ABC at 2 weeks, 4 weeks, or both 2 and 4 weeks. At 4 and 6 weeks, construct sulfated GAG composition, collagen composition, and compressive and tensile biomechanical properties were assessed, along with immunohistochemistry (IHC) for collagens type I, II, and VI, and the proteoglycan decorin. At 6 weeks, the tensile modulus and ultimate tensile strength of the group treated at both 2 and 4 weeks were significantly increased over controls by 78% and 64%, reaching values of 3.4 and 1.4 MPa, respectively. Collagen concentration also increased 43%. Further, groups treated at either 2 weeks or 4 weeks alone also had increased tensile stiffness compared to controls. Surprisingly, though GAG was depleted in the treated groups, by 6 weeks there were no significant differences in compressive stiffness. IHC showed abundant collagen type II and VI in all groups, with no collagen type I. Further, decorin staining was reduced following C-ABC treatment, but returned during subsequent culture. The results support the use of C-ABC in cartilage tissue engineering for increasing tensile properties.

We have used resonant Raman scattering spectroscopy to fully analyze the relative abundances of different (n,m) species in single-walled carbon nanotube samples that are metallically enriched by density gradient ultracentrifugation. Strikingly, the data clearly show that our density gradient ultracentrifugation process enriches the metallic fractions in armchair and near-armchair species. We observe that armchair carbon nanotubes constitute more than 50% of each (2n + m) family.

We performed detailed photoluminescence ͑PL͒ spectroscopy studies of three different types of singlewalled carbon nanotubes ͑SWNTs͒ by using samples that contain essentially only one chiral type of SWNT, ͑6,5͒, ͑7,5͒, or ͑10,5͒. The observed PL spectra unambiguously show the existence of an emission sideband at ϳ140 meV below the lowest singlet excitonic ͑E 11 ͒ level, whose identity and origin are now under debate. We find that the energy separation between the E 11 level and the sideband is independent of the SWNT diameter within our experimental certainty. Based on this, we ascribe the origin of the observed sideband to coupling between K-point phonons and dipole-forbidden dark excitons, as recently suggested based on the measurement of ͑6,5͒ SWNTs.

ABSTRACT:The colors of suspended metallic colloidal particles are determined by their size-dependent plasma resonance, while those of semiconducting colloidal particles are determined by their size-dependent band gap. Here, we present a novel case for armchair carbon nanotubes, suspended in aqueous medium, for which the color depends on their sizedependent excitonic resonance, even though the individual particles are metallic. We observe distinct colors of a series of armchair-enriched nanotube suspensions, highlighting the unique coloration mechanism of these one-dimensional metals.The size-dependent colors of suspended colloidal particles have fascinated researchers, engineers, and artists for centuries. While quantum confinement always plays a fundamental role, the coloration mechanism can differ depending on whether the particles are metallic or semiconducting. For metallic nanoparticles, their colors are determined by the freecarrier plasma resonance whose frequency depends on the electron density as well as the particle size and shape. 1 For semiconducting nanoparticles, the key parameter is the sizedependent fundamental band gap, i.e., the separation between the top of the valence band (HOMO) and the bottom of the conduction band (LUMO), which sensitively changes with quantum confinement, i.e., size. 2 Here, we present a novel case for armchair single-walled carbon nanotubes (SWCNTs), suspended in aqueous medium, for which the origin of their color depends on the interband excitonic resonance even though the individual particles are gapless, i.e., metallic. Armchair nanotubes enjoy a rather special status among the SWCNT family. The structure of each member, or species, of the family is uniquely specified by a pair of integers, (n,m), resulting in different species possessing different diameters, chiral angles, and electronic types (semiconducting or metallic). 3 Armchair SWCNTs are characterized by the simple relation n = m, i.e., (n,n), and they are known to be the only truly gapless species with excellent electrical properties, exhibiting ballistic conduction even at room temperature. 4 At the same time, their one-dimensional characteristics combined with their linear band dispersions have attracted much fundamental interest for exploring many-body phenomena. 5 However, systematic studies of macroscopic ensembles of armchair nanotubes have been impossible due to the coexistence of different (n,m) species of nanotubes in asgrown samples.Recent years have seen impressive progress in post-growth separation of SWCNTs using a variety of methods. One of the most successful methods has been density gradient ultracentrifugation (DGU), 6-10 which can sort out different species of SWCNTs in bulk quantities according to their diameters, chiralities, and electronic types, enabling studies of (n,m)-dependent properties using standard macroscopic characterization measurements. In a recent report, 10 we provided unambiguous evidence of bulk enrichment of armchair nanotubes through DGU by utilizing wavelength-dependen...

Ovarian vein thrombophlebitis should be considered in patients with abdominal pain, fever, and evidence of venous stasis, even if they are lacking typical risk factors of pregnancy or surgery.