Tag Archives: material science

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. 

sticks and stones may break my bones but dirt will wash right off

There you are, sitting in the park eating your spaghetti picnic on your favorite picnic blanket when your pollen allergy acts up. You let out a sneeze powerful enough to compete with Aeolus’ bag of wind, but now your spaghetti is all over your favorite picnic blanket. You immediately go to rinse it off, but your fine Italian sauce has thoroughly soaked in. If only nature had a solution to keep a surface clean. Enter: the lotus leaf.

The lotus leaf is renowned for its ability to stay clean in murky environments. This characteristic of the plant is regularly attributed to its superhydrophobic surface features and chemistry. A superhydrophobic surface is a surface which can maintain a contact angle with water above 150o and is correlated with a low free surface energy—which really means water pools and rolls off rather than soaking into the surface.

Nearly perfectly spherical water droplet on an artificially prepared surface

Modified from Zorba et al. 2008

A key attribute of the superhydrophobic surface is a hierarchical micro- and nanostructure. The microstructure is composed of plant cells grown in little mounds known as a “papillae” with small channels for air flow in between called “stomata.” The nanostructure is composed of hair-like wax crystal towers (epicuticular wax) built on the peaks of the papillae topography. The elevated wax towers combined with the stomata trap air and reduce the contact area of the water with the surface. The epicuticular wax chemistry reduces the adhesion to the towers themselves by being naturally hydrophobic.

Graphic of water drop resting across uneven wax pillars on a lotus leaf

Modified from Zorba et al. 2008

The tips of the wax towers create the largest repelling forces which form larger contact angles, while shorter towers can actually produce adhesive forces that reduce the contact angle. If the air is displaced and filled with water, the contact angle will decrease due to the water-water adhesion which “pulls” the droplet to the surface. Similarly, if the surface is damaged, the wax can be removed and decrease the surface’s hydrophobicity. The wax is naturally soft material and prone to mechanical damage increasing water adhesion and reducing the self-cleaning abilities of the leaf.

The papillae topography is the key to the robustness of the lotus leaf hydrophobicity. The papillae create natural valleys and creases which—like the tops—are still densely packed with wax hairs. When the surface is impacted, only the top of the papillae are exposed to the mechanical force so the wax tubules in the valleys are left undeformed and maintain their hydrophobic characteristics.

Water beads on rain jacket

Photo by Chase Pellerin via Gear Patrol

Hydrophobic surfaces have many applications in everyday life, for example rain jackets and umbrellas perform their best when they are hydrophobic. Manufacturing processes rely on hydrophobic surfaces to reduce oxidation and stay clean in past-paced environments, and your favorite picnic blanket would be much less prone to spaghetti stains if it were hydrophobic. Nature has solutions to keeping surfaces clean; we just have to recognize them.

Soft Robotics: Humanizing the Mechanical

Cassie the robot, created by Dr. Mikhail Jones at Oregon State University
Cassie the Robot, developed by Mikhail Jones, Faculty Research Assistant in Mechanical Engineering at Oregon State University.

In media and science-fiction, robots have stereotypically, and perhaps somewhat unfairly, been depicted as mechanical, stiff assemblies of moving joints and complicated circuitry. While this still holds true for many robots designed today, whether for industry or research, the past few years have seen a growing interest in soft robotics in academia, industry, and popular culture. As the name implies, many research groups have begun investing in constructing robots from compliant, softer materials.

Stickybot, a gecko-inspired robot.
Stickybot, a biomimetic robot.

Inspired by the way organisms in nature survive and adapt to their surroundings (formally known as biomimicry), the advantages of soft robotic components lie in their flexibility, sensitivity, and malleability – delicate tasks or interactions involving other people would be better accomplished by robots made of compliant materials rather than one that could potentially cause harm to the object or person. To that end, many of the applications of soft robotic research have already seen results in the medical industry, from invasive surgery to assistive exosuits. By taking inspiration from biological creatures or mechanisms, softer materials like rubbers and plastics can be actuated to accomplish tasks conventional, “hard” robots could struggle with.

Animation of pneumatic muscle.
Animation of pneumatic air muscle used as robotic actuators.

The most common method of moving these robotic parts is with changes in internal pressure. By creating a “hard”, skeletal frame, and surrounding it with soft, sealed membranes, changes in pressure allow the designer to control its components precisely. By decreasing the pressure and creating a vacuum, the robotic section would shrink or crumple, and increasing it would do the opposite. Researchers at Harvard developed “artificial muscles” by taking this concept a step further; using origami, they were able to design soft robotic mechanisms that could orient themselves into tunable positions as the pressure was changed inside the membrane (as a side note, origami is used in a surprising number of research fields, one of the most famous being satellite deployment). Compared to the challenge of precisely controlling prismatic (sliding) joints and servos in conventional robotics, the compliance of the materials used allow for finer control and smaller ranges of applied forces that are better suited for precise tasks.

Animation of a person demonstrating the Miura fold on a piece of paper
The Miura fold pictured here is often used to deploy large surfaces while minimizing volume, such as for satellites.

Another significant advantage of soft robots over their stiff counterparts is their adaptability to environmental conditions. Generally speaking, robots do not do well in water (or lava, for that matter), but it would have little effect on robots covered in a sealed, pressurized “skin”. This is what inspired NASA in 2015 to fund research into soft robots that could explore the oceans of one of Jupiter’s moons, Europa.  Similarly, a light-activated underwater robotic manta ray was designed at a centimeter scale to study the effect of environmental cues on controllable robots.

Schematic and pictures of soft robot design.
A soft-legged robot with walking capabilities.

While research in soft robotics is still relatively new, it has the potential to significantly affect the role of robots in our daily lives. As a softer, safer, and more environmentally robust alternative to “hard” robots, wearable robotic devices, exploratory robotic fish, and personal medical attendants could soon become commonplace for the general public.

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