Tiny inventions with huge implications: micro-bots and nanoparticles

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As our understanding of nanoscopic phenomena improves through research efforts made possible by technological advancements, scientists from multiple disciplines have taken advantage of newfound knowledge to manipulate materials on a near-atomic scale. This precise and deliberate organisation of molecules to create specialised structures shows great potential for applications in wide range of disciplines including both robotics and medicine.

A paper published in the Journal of the American Chemical Society 2 weeks ago describes the work of a team of scientists lead by Karen Wooley and Justin Smolen at Texas A&M University. The team focused on the drug delivery method to treat cancer-related tumours forming in the lungs. While the strong chemotherapy drug paclitaxel(PTX) effectively kills cancer tissues in lab trials, it does this indiscriminately in the human body, consequently resulting in the death of noncancerous cells leading to negative side effects. PTX is usually administered directly into the veins which means the drug is often diluted by the time it reaches tumours within the lungs.

To prevent both the negative toxicity effects associated with PTX and to increase the dosage amounts that reach the lungs, the team created nanoparticles out of glucose derived substances which contained a safer pro-form of PTX known as diPTX. The nanoparticles were inhaled rather than injected in order to ensure direct contact with the lung tumours as part of the respiratory system. With an average size of around 30nm, the diPTX filled nanoparticles could travel through the mucous lining of the airway, lungs and tumour and be distributed throughout a malignant tumour much more efficiently.

Once arrived at the sight of cancer the positively charged glucose derived nanoparticles are attracted to certain negative charges that are in high concentration within tumour tissues. Arriving at these negatively charged tissues causes the nanoparticles to open leading to a dispersal of diPTX. Pro-drug diPTX gains electrons and transforms into the chemotherapy drug PTX. The positively charged nature of the nanoparticles ensures that noncancerous tissues are not actively targeted in the same way the cancer tissues are. Under lab conditions, tumour cells grown in dishes exposed to the nanoparticles saw a 55% release of the drug into the cancer tissue within a 2 day period; the team hypothesises even higher rates of the drug will be released due in humans to the natural degradation of the particles by the human body.

While other nanoparticles have been previously created in an attempt to improve drug delivery to lung tumours, the chemical make up of these particles have not been as biodegradable and often dissociate into toxic byproducts. This newly created glucose based nanoparticle dissociates into CO2, Glucose, and Ethanol; all of which are products naturally produced by metabolism in the human body. Because of the biodegradable nature of the nanoparticle, it is more readily diffused into tumours. Mice with lung tumours treated with these nanoparticles saw a 40% reduction in the size of their tumours with no significant side effects on other cells in their body. Future trials of these nanoparticles will gradually bring us closer towards using them in human cancer treatment.

A photo of one of the multiple conformations Hygrobot can take. Image: (Shin B et al. 2018)

Apart from applications in medicine, nanoscopic material manipulation has allowed scientists based at Seoul National University in South Korea to create a robot which harnesses the power of humidity to allow directional movement. While micro-bots have the potential to be used in military, industrial and environmental applications the major problem is the current lack of a power source to drive these robots without frequent human intervention. Ho-Young Kim and colleagues took inspiration from nature's plants which move almost exclusively through hydraulics, or the movement of fluid from one region of tissue to another. The ability to change size in response to moisture content also known as hygroexpansivity served as the basis of mechanics for the aptly named 'Hygrobot'

Nano-fibres made of hygroexpansive materials were paired with a non-hygroexpansive tape. When near a humid surface, the nano-fibres would take in water causing expansion and bending of the robot upwards towards air with less moisture. Distance from the human surface causes drying of the hygroexpansive layer causing the robot to conform back to its original conformation and bend downwards to repeat the process. The bending process causes the two legs of the organisms to move in one direction. The simplistic yet extremely practical robot resembles a crawling insect; another organism of inspiration for the team.

In their recent publication in Science Robots, the South Korean research group optimised the travel speed of the robot using a mathematical approach. The team demonstrated a potential application of hygrobot by applying antibiotics to the legs of the robot and allowing it to travel across an E.Coli filled petri dish using nothing more than the humidity of the petri dish to power its movement.

While these are a few examples of how recent advancements in nanotechnology have redefined what is possible in some fields, there are many more examples of groundbreaking findings which can simply be found by sifting through any major scientific journal.

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