Tag Archives: mechanical properties

Curing Cancer: a Giant Problem with a Nano- Solution

What if scientists could treat cancer without the extreme side effects of chemotherapy? Could scientists create a tiny way to cure a giant health crisis? Nanoparticle drug delivery systems could be the answer to our prayers.

Image of nanoparticles (small red circles) in a rat brain that has a tumor (green string-like material)
Nano-particles (red) in rat brain with tumor (green). Image taken from Washington Post.

Almost everyone knows a friend or family member who has had cancer and suffered through chemotherapy to recover. Currently, chemotherapy for treating cancer causes extreme side effects. For years, scientists have been researching methods to mitigate the adverse effects of treating cancers with the hope of one day creating a cure.

Delivering therapeutic drugs via nanoparticles (NP) are currently used in some FDA approved cancer treatments. Nanoparticles are extremely small–on the scale of the cells in our body. This is even smaller than a strand of hair on your head. Their size makes them ideal candidates for transporting drugs to tumors without damaging healthy tissue . In theory, NPs could hold drugs inside them, travel through our blood (ignoring healthy cells) and deposit the drugs right into the tumor.  However, there is a lot of research and improvements to be made before NPs can live up to their full potential. One of the largest unknowns in the study of NPs is their mechanical properties and how these properties interact with the body.

How does our body automatically know how to function without us telling it? Our body has biological sensors which govern our bodily functions in response to the world around us. For example, to prevent unwanted particles that may enter our bloodstream from getting to our brain or lungs, we have filters (like the spleen) that prevent them from passing through. Blood cells are soft, so they can squeeze through biological filters that dirt or stiffer blood cells could not pass through. To reach cancer cells, NPs must pass through these filters.

Stiffness is a mechanical property that measures how much an object moves when it is pushed on. Greater stiffness corresponds to larger applied forces.  For example, a piece of wood is stiff but a pillow is soft because it is easier to dent a pillow than to dent wood. To deliver NPs to the tumor through blood, the NPs have to get through the biological filters as they flow through the blood.

Image of blood cells squeezing through cell walls. Imagine a trying to push a pillow through a narrow opening. The blood cells (pillow) deform to pass through.
Blood cells squeeze through spleen walls, which acts as a filter for foreign objects in the bloodstream. Image taken from Zhang, et. al.

To allow passage through these filters, the NP’s mechanical properties must mimic blood. Scientists have performed tests on NPs with various stiffnesses and found that the soft NPs (like blood) were more likely to be allowed through the biological filters, whereas the stiffer (harder) NPs were blocked. If the NPs are blocked, they cannot travel through the blood streams to reach the tumor and are thus ineffective in treating the diseased cells.

The NPs (represented by the red circles) travel further into the tumor (blue and irregular shaped) than the stiff NPs do, allowing for more effective drug delivery. Image adapted from Hui, et. al.

Furthermore, soft NPs have been shown to penetrate deeper into tumor cells. The soft NPs can deform, allowing them to maneuver through the gaps between tumor cells (intercellular spaces). The deeper the NPs travel into the tumor, the more effective the drug treatment will be in attacking cancerous cells.

Nanoparticles hold the potential to revolutionize cancer treatment and prevention. By optimizing the mechanical properties of NPs, they could automatically release drugs in the presence of the tumors in response to their biological environment without delivering drugs to other cells. Further development of nanoparticle drug delivery methods may one day lead to a cure that will save loved ones’ lives. 

What Makes and Breaks the World’s Tallest Trees

Trees have the potential to be the largest organisms on Earth. The world’s tallest tree, dubbed Hyperion, is 380 ft tall and weighs over 1,600,000 lbs. Compared this to the world’s largest animal, a particularly massive blue whale which was 100 ft long and weighed 380,000 lbs, the simply massive size of this tree should be obvious. And unlike a whale, a tree is much less likely collapse and crush itself under its own weight. Trees need to be tall, even if doing so consumes a lot of resources, in order to compete for sunlight. So what lets trees get this big, and what limits their height?

A diagram showing a space shuttle, which when prepared to launch is less than half the height of Hyperion, General Sherman, a wider but slightly shorter tree of a different family sequoia, a blue whale that is much shorter than either tree, and the statue of liberty, whose torch barely comes close to the shorter of the two trees
Comparison diagram of the World’s largest trees – Sequoia Tree Comparison Chart, Sequoias

There are two primary rules that govern tree sizes. The first is mechanics, the way the trunk of the tree is built and how it responds to weight. The wood of the biggest trees has a very high strength to weight ratio, which enables a tree to carry its own massive weight without collapsing. The layout and structure of this wood is analyzed at length in the journal by M. Ramage, but in summary, tall trees have internal cells called tracheids. These tiny circular tubes are 2-4 mm long and around 30 μm wide and provide support to the tree and allow water to flow throughout it, without adding as much weight. 

an image showing the tracheid cell structure of wood, many small cylinders stacked on top of each other.
A section of the annual ring of a conifer- M. Ramage’s The wood from the trees: The use of timber in construction and Dr. Krzysztof Wicher.

The high strength to weight ratio of wood allows trees to support themselves at incredible heights. Using B. Blonder’s research about the scaling of trees, it can be shown that trees are so strong and yet comparatively light weight that a tree would not actually collapse under its own weight until it was almost 15 Empire State Buildings tall. Obviously no tree is this tall, meaning some other factors must limit their height, but the incredible strength of wood should now be clear!

A diagram showing the decreasing size of pine needle branch segments. They decrease dramatically as height increases.
Leaf samples taken from the same type of tree with the height they were taken from listed adjacently in meters, – G. Koch’s The limits of tree height

The second primary rule that governs tree size is hydraulics, and it restricts the height a tree can reach. Hydraulics defines a tree’s ability to move water from its roots to its upper leaves in order to perform photosynthesis. The taller a tree gets, the more difficult this process becomes until the tree becomes incapable of growing any taller. G. Koch’s article, The Limits to Tree Height, explores how this hydraulic system works and how it restricts the heights a tree can reach. Xylem, tiny internal pipes that run from the roots to the tops of the tree, and carry water in a long continuous column this whole length. The longer this column becomes, the more difficult it is to maintain and the greater suction pressure that occurs at the highest leaves. Koch studied how properties in leaves changed the higher up they could be found, determining that the efficiency of Photosynthesis decreased, the pressure at the end of the xylem increased, and the size of leaves decreased. At great heights, the status of leaves seemed remarkably similar to those of a tree undergoing a severe drought.

 

Koch determined that these changes with height would eventually hit a maximum limit which they could not exceed, a limit that was determined to occur between 122-130 meters. So while the efficient properties of wood allow trees to reach incredible heights, their restricted ability to move water limits just how tall they can grow.

Sources and Further Reading:

  • Ramage M., Burridge H., Busse-Wicher M., et al. The wood from trees: The use of timber in construction. Renewable and Sustainable Energy Reviews 68, 333-359 (2017)
  • Blonder B. The size of trees: exploring biological scaling (2010)
  • Koch, G., Sillett, S., Jennings, G. et al. The limits to tree height. Nature 428, 851–854 (2004)

Can we 3D print our own skin?

Can you imagine a world where amputees receive replacement limbs which are able to detect temperature and pressure like an actual limb? How about a world where when you get a cut, you can 3D print some of your own skin to patch the wound?

To the average citizen, this might seem like something out of a science fiction movie. To researchers at the Graz University of Technology, the Wake Forest School of Medicine, and the Universidad Carlos III de Madrid, this is a reality that they are helping bring ever closer. Both of these scenarios are discussed in a recent article by Mark Crawford, who investigated the recent breakthroughs in 3D printing human skin and creating sense-sensitive artificial skin.

photograph of an arm reaching into the sky to feel the rain in the palm of their hand
photo by Alex Wong on Unsplash

At the Graz University of Technology, researchers are working on creating an artificial skin that can sense temperature, humidity, and pressure. Currently, artificial skins can measure one sense at best, but with the use of the nanoscale sensors that these researchers are developing, sensing all three at once could be possible. This is achieved through the materials that the nanosensors are created out of: a smart polymer core and a piezoelectric shell. The smart polymer core can detect humidity and temperature through expansion, and the piezoelectric shell detects pressure through an electric signal that is created when pressure is applied. With this technology, prosthetics could be made which could allow the wearer to retain some of their lost senses.

At the Wake Forest School of Medicine, researchers have created a handheld 3D printer which produces human skin. This device could be used to replace skin grafts, as it can apply layers of skin directly onto the wound. Through the use of bioink, this handheld printer can create different types of skin cells. After scanning the wound to see what layers of tissue have been disrupted, it can print the appropriate skin needed to correct the injury.

Photograph of the 3D skin printer created at the Universidad Carlos III de Madrid, which is still in its prototype phase.
modified from Crawford, ASME January 2019

At the Universidad Carlos III de Madrid, researchers are also 3D printing human skin using bioink. They are creating both allogenic and autologous skin to create the optimal skin, which is a combination of the patient’s own cells and cells created from a stock. Although they have managed to print functioning skin in its natural layered state, it is tricky to create the cells in such a way that they do not deteriorate.

It is also tricky to correctly deposit the product. To illustrate, more research needs to be done on the mechanical properties of artificial skin before it could be used on humans. The artificial skin must be able to stretch and react to tension in a similar manner to the real skin it will be connected to. Additionally, researchers must figure out how to safely send the signals the artificial skin is detecting to the brain.

Overall, both advancing artificial skins and 3D printing human skins could largely impact humanity. Even though we have yet to use these skins on people, they are already being used in industries, such as L’Oreal, to limit testing on humans and animals. Already, these skins are being used on robots, as seen in this video, to help prepare the skin for human transplant:

 

Interested in seeing more? Check out some more articles on the advancement of artificial skin from Caltech and Time.