Sacrificial Bonds in Collagen Contribute to Bone Strength
- PDF / 1,220,042 Bytes
- 1 Pages / 612 x 792 pts (letter) Page_size
- 78 Downloads / 279 Views
constructs. The purpose of these devices is to achieve a variety of structural configurations on the nanometer scale, thus paving the way for nanorobotics. By inserting DNA “set” strands that select the state of the device and “fuel” strands that remove the set strands to return the device to an unspecified state, into individual molecule pairs, the scientists fabricated a sequence-dependent rotary DNA device that operates in a four-step cycle. In the January 3 issue of Nature, the scientists reported that they used paranemic crossover (PX) DNA, a four-strand molecule in which two double helices are joined by the crossing over of strands everywhere that the strands come together. The scientists produced a half-turn rotation by converting them into JX2 molecule pairs that lack two of the crossovers present in the PX structure. “Set” strands refer to the strands that position the state of the device in the PX conformation. The “fuel” strand refers to the strand that is complementary to the entire length of the set strand and will pair with it. The scientists alternated additions and removals of fuel and set strands, holding the solution at 20°C for 60 min through each stage of the four-step cycle. Nondenaturing gel electrophoresis and atomic force microscopy verified the formation and interconversion of the PX DNA and its topoisomer JX2 DNA. The researchers report motions up to 35 nm.
Sacrificial Bonds in Collagen Contribute to Bone Strength With the use of atomic force microscopy (AFM), scientists at the University of California—Santa Barbara have revealed that sacrificial bonds in collagen may be partially responsible for the toughness of bone. Collagen is a protein that serves as a structural component of a variety of tissues including bone, tendon, and skin. Using a purified cow tendon as a sample, the scientists stressed the collagen, discovering that the protein contains sacrificial bonds that rupture when stretched, then reform. Graduate student James B. Thompson said, “These sacrificial bonds provide a mechanism for dissipating mechanical energy in collagen molecules. The time scale required for sacrificial bonds to reform in collagen correlates to the time needed for bone to recover from microscopic indentations.” Besides stretching the collagen from bones (AFM pulling using force probes with spring constants of 50 pN nm-1), the scientists made small indentations in the femur of a rat (AFM indentation with
MRS BULLETIN/MARCH 2002
spring constants of ~50 N m-1), discovering that the bone returns to its original shape in ~30 s. They needed a stiffer force probe to indent a bone than to stretch a collagen molecule. As reported in the December 13 issue of Nature, the researchers noted that the sacrificial bonds found within or between collagen molecules in their samples were similar to those found in abalone shell. Thompson said it is too early to tell what impact this study will have on human health and how the study might affect technology or medicine.
Carbon Nanotube Electrodes May Increase Storage of Li-
Data Loading...
