Bulk metallic glasses for biomedical applications

The selection criteria for biomaterials include the material’s properties and biocompatibility, and the ability to fabricate the desired shapes. Bulk metallic glasses (BMGs) are relative newcomers in the field of biomaterials but they exhibit an excellent combination of properties and processing capabilities desired for versatile implant applications. To further evaluate the suitability of BMGs for biomedical applications, we analyzed the biological responses they elicited in vitro and in vivo. The BMGs promoted cell adhesion and growth in vitro and induced improved foreign body responses in vivo suggesting their potential use as biomaterials. Because of the BMGs’ flexible chemistry, atomic structure, and surface topography, they offer a unique opportunity to fabricate complex implants and devices with a desirable biological response from a material with superior properties over currently used metallic biomaterials.     

BMP signaling plays a role in visceral endoderm differentiation and cavitation in the early mouse embryo

At E4.0 the inner cell mass of the mouse blastocyst consists of a core of embryonic ectoderm cells surrounded by an outer layer of primitive (extraembryonic) endoderm, which subsequently gives rise to both visceral endoderm and parietal endoderm. Shortly after blastocyst implantation, the solid mass of ectoderm cells is converted by a process known as cavitation into a pseudostratified columnar epithelium surrounding a central cavity. We have previously used two cell lines, which form embryoid bodies that do (PSA1) or do not (S2) cavitate, as an in vitro model system for studying the mechanism of cavitation in the early embryo. We provided evidence that cavitation is the result of both programmed cell death and selective cell survival, and that the process depends on signals from visceral endoderm (Coucouvanis, E. and Martin, G. R. (1995) Cell 83, 279-287). Here we show that Bmp2 and Bmp4 are expressed in PSA1 embryoid bodies and embryos at the stages when visceral endoderm differentiation and cavitation are occurring, and that blocking BMP signaling via expression of a transgene encoding a dominant negative mutant form of BMP receptor IB inhibits expression of the visceral endoderm marker, Hnf4, and prevents cavitation in PSA1 embryoid bodies. Furthermore, we show that addition of BMP protein to cultures of S2 embryoid bodies induces expression of Hnf4 and other visceral endoderm markers and also cavitation. Taken together, these data indicate that BMP signaling is both capable of promoting, and required for differentiation of, visceral endoderm and cavitation of embryoid bodies. Based on these and other data, we propose a model for the role of BMP signaling during peri-implantation stages of mouse embryo development.     

A construction set for multimedia applications

The authors describe an interface system called Athena Muse. Muse is an experiment kit for the construction of multimedia learning environments. Learning environments developed with Muse offer a diverse set of complementary interaction techniques, styles, and devices. An interface developer can choose from four representation approaches: directed graphs, multidimensional spatial frameworks, declarative constraints, and procedural languages     

Theory of initially twisted, composite, thin-walled beams

An asymptotically correct theory for initially twisted, thin-walled, composite beams has been constructed by the variational asymptotic method. The strain energy of the original, three-dimensional structure is first rigorously reduced to be a two-dimensional energy expressed in terms of shell strains. Then the two-dimensional strain energy is further reduced to be expressed in terms of the classical beam strain measures. The resulting theory is a classical beam model approximating the three-dimensional energy through the first-order of the initial twist. Consistent use of small parameters that are intrinsic to the problem allows a natural derivation for all thin-walled beams within a common framework, regardless of whether the section is open, closed, or strip-like. Several examples are studied using the present theory and the results are compared with a general cross-sectional analysis, VABS, and other published results.     

Fate of C-triclocarban in biosolids-amended soils

Triclocarban (TCC) is an antibacterial compound commonly detected in biosolids at parts-per-million concentrations. Approximately half of the biosolids produced in the United States are land-applied, resulting in a systematic release of TCC into the soil environment. The extent of biosolids-borne TCC environmental transport and potential human/ecological exposures will be greatly affected by its bioavailability and the rate of degradation in amended soils. To investigate these factors, radiolabeled TCC (¹⁴C-TCC) was incorporated into anaerobically digested biosolids, amended to two soils, and incubated under aerobic conditions. The evolution of ¹⁴CO2 (biodegradation) and changes in chemical extractability (bioavailability) was measured over time. Water extractable TCC over the study period was low and significantly decreased over the first 3 weeks of the study (from 14% to 4% in a fine sand soil and from 3 to < 1% in a silty clay loam soil). Mineralization (i.e. ultimate degradation), as measured by evolution of ¹⁴CO₂, was < 4% over 7.5 months. Methanol extracts of the amended soils were analyzed by radiolabel thin-layer chromatography (RAD-TLC), but no intermediate degradation products were detected. Approximately 20% and 50% of the radioactivity in the amended fine sand and silty clay loam soils, respectively, was converted to bound residue as measured by solids combustion. These results indicate that biosolids-borne TCC becomes less bioavailable over time and biodegrades at a very slow rate.