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Welcome to The Visible Embryo, a comprehensive educational resource on human development from conception to birth.

The Visible Embryo provides visual references for changes in fetal development throughout pregnancy and can be navigated via fetal development or maternal changes.

The National Institutes of Child Health and Human Development awarded Phase I and Phase II Small Business Innovative Research Grants to develop The Visible Embryo in 1993 as a first generation internet teaching tool consolidating human embryology teaching for first year medical students.

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The identification and understanding of genetic malfunction, inflammatory responses, and the progression in chronic disease, begins with a grounding in primary cellular and systemic functions manifested in the study of the early embryo.


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Pregnancy Timeline by SemestersFemale Reproductive SystemFertilizationThe Appearance of SomitesFirst TrimesterSecond TrimesterThird TrimesterFetal liver is producing blood cellsHead may position into pelvisBrain convolutions beginFull TermWhite fat begins to be madeWhite fat begins to be madeHead may position into pelvisImmune system beginningImmune system beginningPeriod of rapid brain growthBrain convolutions beginLungs begin to produce surfactantSensory brain waves begin to activateSensory brain waves begin to activateInner Ear Bones HardenBone marrow starts making blood cellsBone marrow starts making blood cellsBrown fat surrounds lymphatic systemFetal sexual organs visibleFinger and toe prints appearFinger and toe prints appearHeartbeat can be detectedHeartbeat can be detectedBasic Brain Structure in PlaceThe Appearance of SomitesFirst Detectable Brain WavesA Four Chambered HeartBeginning Cerebral HemispheresEnd of Embryonic PeriodEnd of Embryonic PeriodFirst Thin Layer of Skin AppearsThird TrimesterDevelopmental Timeline
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December 26, 2012--------News Archive Return to: News Alerts


A molecule made with a polynorbornene backbone can act as a lever to open a ring
embedded within the molecule 1000 times faster than a similar ring being tugged
at on a polybutadiene scaffold.







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'Molecular Levers' May Make Things Better

In a forced game of molecular tug-of war, some strings of atoms can act like a lever, accelerating reactions 1000 times faster than other molecules – opening up the possibilities of fabricating new materials

The discovery suggests that scientists could use these molecular levers to drive chemical and mechanical reactivity among atoms and ultimately engineer more efficient materials.


"We are interested in designing new, stress-responsive
materials, so we are trying to develop reactions that
are very slow normally but that can be
accelerated efficiently by force."


Steve Craig, chemist, research leader
Duke University


In recent experiments, Craig and his team found that a molecule made with a polynorbornene backbone can act as a lever to open a ring embedded within the molecule 1000 times faster than a similar ring being tugged at on a polybutadiene scaffold.

The results, which appear Dec. 23 in Nature Chemistry, suggest that a simple change in the backbone may affect how fast mechanically assisted reactions occur.

Scientists are interested in this type of molecular tug-of-war because many materials break down after repeated cycles of tugging, stress and other forces. "If we can channel usually destructive forces into constructive pathways, we could trigger reactions that make the material stronger when and where it is most useful," Craig said.


Researchers might then be able to extend a material's
lifetime, which in the long term affects applications ranging
from composite airplane frames to biomedical implants.


In the experiment, Craig, who is a professor and chair of the chemistry department, and his team used the equivalent of microscopic tweezers to grab onto two parts of atomic chains and pulled them so that they would break open, or react, in certain spots.


The team predicted that one molecule would react more
efficiently than the other but was surprised to find that the
force-induced rates differed by three orders of magnitude,
an amount that suggests that the polyn-orbornene
backbone can actually accelerate forced reactions
the way a crowbar enhances prying a nail from a wall.

Craig said changes to the molecular group undergoing
the reaction may have a much smaller effect than
changes to nearby, unreactive molecules
like those on the backbone.


It is also a good starting point to identify other molecular backbones that are easy to make and have the largest response to changes in nearby reactions, features Craig said might help in developing even better, more responsive materials.

The research was supported by the U.S. Army Research Laboratory, the Army Research Office and National Science Foundation.

Citation: "A Backbone Lever Arm Effect Enhances Polymer Mechanochemistry." (2012) Klukovich, H. et al. Nature Chemistry. AOP. DOI: 10.1038/NCHEM.1540

Original article: http://today.duke.edu/2012/12/craiglever