Light can exert forces on small dielectric objects. A tightly focused beam of light can trap micron-sized objects, such as latex beads. This “optical trapping” principle has found many applications in Chemistry, Physics and Biology. It has found its most prominent use in Biophysics, because it allows the manipulation (like with a tweezers) of single biomolecules. As discussed above, the “optical tweezers” have been used to measure the elasticity of single DNA molecules and the forces induced by molecular motors such as kinesin that generate the forces in living cells.
Using laser light to manipulate microscopic objects has broad applications in material research, biology, and biochemistry. The principle of optical tweezers is based on gradient force of a single tightly-focused laser beam. This gradient light force can trap particles as large as 100 μm and as small as an individual atom. Manipulation and control of dielectric spheres and living cells have all been achieved in laboratories around the world.
The need for blood substitutes has been around for centuries. The first successful blood transfusion was recorded in 1667, though consistently successful transfusions were not possible until the early 1900s when the four blood types were discovered and understood. Transfusions were soon in routine, but then during WWII blood shortages began to be a problem. During the Vietnam War the shortages, coupled with improved chemical knowledge spurred people to begin looking for a synthetic blood. Blood substitution falls into two categories: volume replacement and oxygenation replacement. The second amounts to replacing red blood cells so that oxygen can be transported throughout the body. Oxygenation substitutes also come in two kinds: perfluorocarbon based and hemoglobin based. Perfluorocarbon based oxygenation began with liquid breathing where Leland Clark was able to keep mice alive while breathing liquid that was oxygen rich. The damage to the lungs that occurred by cycling liquid in and out ultimately made this impractical. However, it did show that enough oxygen could be dissolved in a liquid to sustain life. Problems of solubility in water (because perfluorocarbon is an oil like substance) made further work necessary before it could be used as a blood substitute. To solve this problem emulsifying agents such as egg yolk phospholipids and triglycerides were used. This made the perfluorocarbon more water soluble so that it could mesh with blood better. After some unsuccessful attempts in the 1980s and 1990s to conduct clinical trials on this class of blood substitute there have been further improvements. A product known as Oxygent has shown promise and is currently in clinical trials. It has been licensed in China, Europe, and Canada. On the US market Oxycyte is in clinical trials. Some problems that occur with these products include: limited shelf life, side effects of headaches, fever, chills and nausea, and finally the time it takes to get the blood substitute out of the system.