New Circuit Element The memristor could be useful for nonvolatile memory
Source: “The missing memristor found” R. Stanley Williams et al. Nature 453: 80-83
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Results:
Researchers at HP Labs have fabricated a
memristor, or memory resistor–a fundamental electronic device that had been
described theoretically but never produced until now. The amount of charge that
flows through the device can be changed by exposing it to an electrical
voltage. Applying a positive voltage lowers its resistance, and applying a
negative voltage increases it. Furthermore, the change in resistance is
proportional to the length of time the voltage is applied: the more the device
is charged, the more electricity it conducts. Once set, the resistance stays
the same until it’s reset.
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Why it
matters: Memristors could lead
to nonvolatile memory chips that store more data than flash memory. They
could also be used in processors designed to mimic aspects of the human brain.
In the brain, learning depends on changes in the strength of connections
between neurons. The memristor can be used to set the strength of connections
between transistors, achieving a similar effect. Chips using memristors could
be useful for face recognition and for controlling robot movement.
Methods:
The new memristors consist of two layers of
titanium dioxide sandwiched between two electrical contacts. One layer of
titanium dioxide is an insulator, blocking the flow of electrons from one
contact to the other. The other layer, which has fewer oxygen atoms than
titanium dioxide normally does, conducts electricity.
When a voltage is
applied, some of the oxygen ions move from the first layer into the oxygen-deficient
layer. That improves the conductivity of the first layer, allowing electrons
to pass through the memristor from one contact to the other.
Next
steps: Since Hewlett-Packard
doesn’t make memory chips, the technology will probably be licensed to
another company for product development. The HP researchers are working on a
prototype that combines transistors and memristors to form a brainlike chip.
Nano RNA Therapeutics Lipidlike materials improve delivery of RNA for
silencing gene expression
Source: “A combinatorial of lipid-like materials for delivery of RNAi therapeutics” Daniel G.
Anderson et al. Nature
Biotechnology 26: 561-569
Results:
By developing new techniques of chemical
synthesis, researchers at MIT and Alnylam
Pharmaceuticals in Cambridge,
MA, were able to quickly make
1,200 different lipidlike molecules that serve as building blocks for nanoscale
containers called liposomes. Some of the resulting liposomes proved effective
at introducing RNA into a variety of different cells in rodents and primates.
The RNA was able to block the action of certain genes and of microRNA, which
serves to regulate genes.
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Why it
matters: Silencing genes with
RNA–a technique known as RNA interference, or RNAi–is a potentially powerful
therapy for genetic diseases, viral infections, cancer, and even heart attacks,
but it’s been difficult to deliver RNA to cells, since the body’s immune system
breaks it down quickly. The new delivery agents skirt the body’s defenses.
Access to such a large
collection of lipidlike materials will allow scientists to better understand
how to design effective delivery nanoparticles. And the new synthesis methods
could help researchers find delivery agents that are even more effective, which
could increase the chances of success for RNA-based therapies, as well as other
drugs.
Methods:
The researchers developed a one-step process
for making molecules that resemble the lipids typically used for the commercial
manufacture of liposomes. Then they developed ways to screen the ability of
liposomes made from these molecules to deliver RNA directly to cells in a
petri dish and to living tissue in animals.
For in vivo tests, the
researchers added cholesterol and an ether called polyethylene glycol to their
molecules to help the liposomes avoid the body’s defenses.
Next
Steps: Researchers at MIT are
sorting through new molecules to find better delivery agents. They are testing
their potential for targeting a variety of diseases and for delivering
therapeutics other than RNA.