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. 

Staying airborne: How bird wings are built for aerodynamic and efficient flight

Flight is a concept that has, until relatively recently in history, eluded humanity. However, birds have been successfully flying for approximately 130 million years, proving themselves to be a physical marvel of the natural world. And while our means of flight have historically been crude in design and performance, nature provides an elegant, efficient solution to get creatures off of the ground. Rüppell’s griffon vultures have been recorded flying as high as 37,000 ft, while some species of shorebirds have been recorded flying as far as from Alaska to New Zealand over eight days without stopping. But how exactly do birds seem to effortlessly overcome gravity so effectively? And perhaps more importantly, how might we apply these answers to improve manmade aircraft?

Morphology

Obviously, the exact aerodynamics and physical characteristics of birds will vary from species to species, but there are still underlying similarities that enable birds to fly. A bird’s wing consists of a shoulder, elbow, and wrist joint which establish the wing’s basic shape and allow a range of motion. Covering the wing are structures called primary, secondary, and coverts, which are all groups of feathers that provide lift and stabilize flight. Feathers consist of flexible fibers attached to a center shaft, called the rachis. Overtime, the rachis will become damaged from fatigue and large instances of stress. As a result, birds will molt and regrow their feathers on a regular basis. 

A diagram of the structure of a bird wing
Picture by marcosbseguren on Wikimedia Commons

Generally, a bird’s body will be adapted to either gliding flight, in which the wings flap very infrequently, or active flight, in which the wings flap nearly constantly. For gliding birds, such as the ocean dwelling albatross, the wings will extend far away from the body, and prioritize both wing and feather surface area over flexibility. Additionally, these wings will have a thick leading edge, and will be much straighter. However for fast, agile birds, such as falcons, the opposite is true. Consequently, agility is sacrificed for energy efficiency. In both cases, the rachis will change shape and rigidity, becoming larger and stiffer for gliding flight and smaller and more flexible for agile flight. 

Aerodynamics

One of the most unique aerodynamic characteristics of birds is that nearly all of their lift and thrust is exclusively generated by their wings, as opposed to aircraft that implement both wings and engines. This provides, among other things, near instantaneous control of both flight direction and speed. In other words, this gives birds an advantage when hunting, escaping from predators, and maneuvering through a landscape. 

To aid in the generation of thrust and lift during flight, birds will change their wing shape through a process called active morphing. During flight, the wing will be bent inwards and twisted up during the upstroke, and extended and straightened during the downstroke. As a result, this minimizes drag while maximizing thrust and, consequently, energy efficiency. This can aid in anything from traveling farther distances to hunting prey.

An osprey folding its wings in while catching a fish
Photo by Paul VanDerWerf on Wikimedia Commons

Applications

Initially, these principles may seem difficult to realistically utilize in aircraft. After all, we are limited by the materials available and the size that aircraft must reach. However, small steps could be taken to improve the energy efficiency and responsiveness of aircraft. For example, wing shape, material flexibility, surface finish, and moving joints could all be explored. In fact, research at MIT is currently being conducted on flexible wings made of scale-like modular structures. If experiments like this are successful, it could show that aircraft designs inspired by nature may be the future of the world of aeronautics.

Innovative plant: How does the dandelion drift its seeds?

How far do you think a dandelion seed can drift from its base plant?

The Common Dandelion (Taraxacum officinale) primarily relies on wind flow to scatter its seeds. The dandelion seed has a fluffy structure that enables it to hold the most prolonged wind-based dispersal record. Commonly the seeds land 2 meters away from their mother plant. Still, in windy, dry weather favored by the dandelion, the seeds can fly up to 30 kilometers and even far (150 kilometers in some conditions). The vital point in this extraordinary adventure of the dandelion is flying with a constant velocity and having a short descent time, which means it should stay stable in the air for a relatively long time.

A study tried to illuminate the mystery behind the dandelion seeds’ ability to stay aloft in the air. Researchers attempted to mimic the dandelion flight using similarly structured silicon disks in a wind tunnel that simulated the airflow around the pappus. Pappus, the flying seed of the dandelion, consists of radially oriented filaments, each interacting with other adjacent ones, resulting in a reduction in the airflow. They compared the flight of natural seeds collected from one plant with several silicon disks with different porosities.

Dandelion seeds and silicon disks in wind tunnel
Wind tunnel experiment, modified from Cathal Cummins & et al. 2018
vortex ring above pappus
Pappus & separated vortex ring, modified from Madeleine Seale & et al. 2019

Their results showed that when pappus separates into the air,  it forms an air bubble detached from its surface above it. This air bubble, known as a vortex, is unique to the dandelion seed. When the pappus is released in the air, it takes some time to reach a steady point, in which the vortex becomes symmetrical. An important feature affecting this symmetry is the porosity of the pappus, defined by the number of filaments and their dimension in each pappus— generally, the more the porosity, the steadier the flight. The best porosity for a stable vortex ring is greater than 84.97%, and the vortex ring begins to separate as the porosity falls below 77.42%. The experiment also indicated that the vortex is axisymmetric in low velocities, but it begins to lose its symmetry as the Reynolds increases.

Pappus with water drops on it
Pappus in moisture, photo by enfantnocta

This phenomenal plant has evolved techniques for mass germination, even in the absence of wind! Pappus’s hairy structure enables it to attach to an animal’s skin and soil particles, assuring the dandelion to have enough seed dispersion during the flowering season. More interestingly, the dandelion is known to have an informed dispersal in response to environmental fluctuations. When the plant experiences root herbivory, it intensifies the seed dispersal. The flight distance may vary from meters to kilometers to assure good germination in the absence of threatening conditions. Imagine a rainy day; the moist weather condition makes the pappus’ bristles come close together, reducing the possibility of separating from the plant. The moisture makes the current spot a suitable choice to stay. So even the detached seeds prefer to fall close to their base plant. 

It worth mentioning that this remarkable plant also inspired areas of science. In their study of Mars exploration, researchers presented a primary model of a dandelion-inspired rover. Considering the harsh environmental condition on Mars, other excavators find the wind flow as an obstacle that results in damaged parts and incomplete missions. In contrast, the new dandelion-shaped rovers use the wind flow as an accelerating point to explore locations on Mars that other robots couldn’t access.

Dandelion-shaped Mars rovers
Dandelion-shaped rovers ,modified from Michelle Sherman & et al. 2020