Lateral Nanomechanics of Cartilage Aggrecan Macromolecules

To explore the role of the brush-like proteoglycan, aggrecan, in the shear behavior of cartilage tissue, we measured the lateral resistance to deformation of a monolayer of chemically end-attached cartilage aggrecan on a microcontact printed surface in aqueous NaCl solutions via lateral force microscopy. The effects of bath ionic strength (IS, 0.001–1.0 M) and lateral displacement rate (∼1–100 μm/s) were studied using probe tips functionalized with neutral hydroxyl-terminated self-assembled alkanethiol monolayers. Probe tips having two different end-radii (R ∼50 nm and 2.5 μm) enabled access to different length-scales of interactions (nano and micro). The measured lateral force was observed to depend linearly on the applied normal force, and the lateral force to normal force proportionality constant, μ, was calculated. The value μ increased (from 0.03 ± 0.01 to 0.11 ± 0.01) with increasing bath IS (0.001–1.0 M) for experiments using the microsized tip due to the larger compressive strain of aggrecan that resulted from increased IS at constant compressive force. With the nanosized tip, μ also increased with IS but by a smaller amount due to the fewer number of aggrecan involved in shear deformation. The variations in lateral force as a function of applied compressive strain ɛ(n) and changes in bath IS suggested that both electrostatic and nonelectrostatic interactions contributed significantly to the shear deformational behavior of the aggrecan layers. While lateral force did not vary with lateral displacement rate at low IS, where elastic-like electrostatic interactions between aggrecan dominated, lateral force increased significantly with displacement rate at physiological and higher IS, suggestive of additional viscoelastic and/or poroelastic interactions within the aggrecan layer. These data provide insights into molecular-level deformation of aggrecan macromolecules that are important to the understanding of cartilage behavior

Offshoring, Tasks, and the Skill-Wage Pattern

The paper investigates the relationship between offshoring, wages, and the ease with which individuals' tasks can be offshored. Our analysis relates to recent theoretical contributions arguing that there is only a loose relationship between the suitability of a task for offshoring and the associated skill level. Accordingly, wage effects of offshoring can be very heterogeneous within skill groups. We test this hypothesis by combining micro-level information on wages and demographic and workplace characteristics as well as occupational infor- mation relating to the degree of offshorability with industry-level data on offshoring. Our main results suggest that in partial equilibrium, wage effects of offshoring are fairly modest but far from homogeneous and depend significantly on the extent to which the respective task requires personal interaction or can be described as non-routine. When allowing for cross-industry movement of workers, i.e., looking at a situation closer to general equilibrium, the magnitude of the wage effects of offshoring becomes substantial. Low- and medium-skilled workers experience significant wage cuts due to offshoring which, however, again strongly depend on the degree of personal interaction and non-routine content

The China Syndrome: Local Labor Market Effects of Import Competition in the United States

We analyze the effect of rising Chinese import competition between 1990 and 2007 on local U.S. labor markets, exploiting cross-market variation in import exposure stemming from initial differences in industry specialization while instrumenting for imports using changes in Chinese imports by industry to other high-income countries. Rising exposure increases unemployment, lowers labor force participation, and reduces wages in local labor markets. Conservatively, it explains one-quarter of the contemporaneous aggregate decline in U.S. manufacturing employment. Transfer benefits payments for unemployment, disability, retirement, and healthcare also rise sharply in exposed labor markets