Scientific Scribbles

The voice of UniMelb Science Communication students

Biodegradable Plastic: It’s Not as Easy as It Sounds

Every day, everywhere, plastic is used.


From food containers, shopping bags, to crucial gadgets in medicine, plastic is now the irreplaceable material around the world. Why? As we all know, plastic is cheap, versatile, and easy to produce. The economic and social relevance of its chemical properties are second to none.


The problem is, plastic wastes are difficult to get rid of. The advantages of plastics lead to its biggest disadvantage – lack of biodegradability.


Photo credit: Snemann on Visual hunt / CC BY-NC-ND


Biodegradable plastic = Solution?


To solve the plastic waste crisis, scientists have come up with something called biodegradable plastic. The purpose of such invention is to eliminate long-lasting plastic wastes from polluting our environment.


As an environmentalist, I was a big fan. For instance, if all conventional single-use plastic was replaced, it means that we can all be free from guilt of ordering a takeaway coffee.


But that’s not the case.


What is biodegradability?


The definition of biodegradable is “capable of being decomposed by bacteria or other living organisms.” However, most of the marketed “biodegradable” plastic is not biodegradable. In fact, those are as detrimental to the environment as any kind of regular plastic.



Photo credit: chesbayprogram on / CC BY-NC



Bio-based v.s. Biodegradable plastic


Bio-based plastic such as PLA — which is made by converting sugar from corn, wheat, or sugar cane – is generally considered as a biodegradable plastic. However, Bio-based plastic is not the same. It is a compostable plastic, which requires specific conditions (e.g. high temperature, moisture) to break down. These plastics will not naturally degrade in landfill.


Photo credit: The U.S. National Archives on Visualhunt



Some research already exposed the false marketing. Some biodegradable plastic bags were found to be intact, just like the conventional ones.


So, is it just a mystery then? Not entirely. There are plastic types that are actually biodegradable in normal landfill, just like we hope it to.



So is there no hope?


Yes, we’ve been deluded by the sound of the sweet label on theses plastics. Supermarkets often take advantage of these bioplastics to increase their corporate image by newly labelling their plastic shopping bags.


But we can’t simply blame everything on the material itself. Recently, I attended a public lecture called “The Future of Plastic” at The University of Melbourne, and the speakers highlighted an important point:


We can’t live without plastic, but each one of us must use them responsibly.


Problems such as microplastics, damage to natural systems aren’t a joke. It is important to be aware.







Compliant Mechanisms: The Future is in 3D

The age-old adage in the creation of tools and mechanisms is that ridged is best. The less a tool moves and bends under stress, the more reliable and predictable it is.  The recent study into flexible mechanisms has posed a serious threat to the idea that convoluted rigid mechanisms are best in terms of design and reliability.

Veritasiums Derek Muller outlines in his video Why Machines That Bend Are Better the eight ways in which flexible / compliant mechanisms are superior to traditional rigid-body mechanisms. The eight P’s of compliant mechanisms outlined by Derek are; Part count, production processes, price, precise motion, performance, proportions, portability, and predictability. It is the combination of these factors which give compliant mechanisms a considerable advantage over contemporary mechanisms. However, can these factors outweigh the inherently niche use cases for compliant mechanisms?

Compliant mechanisms are simple to design and easier to produce. Whereas traditional mechanisms are meticulously designed to eliminate any flexible areas to avoid elastic deformation and thus energy transfer loss, compliant mechanisms take advantage of elastic deformation (which is inherent in all mechanisms no matter the design) to transfer energy / apply force to the intended object. The incredibly low part count (the amount of individual pieces that go into the assembly of a object) of a compliant mechanism when compared to normal ridged body mechanisms means that not only are they easier to design (compliant mechanisms can be designed in a single piece) but this flexibility in design means that they can be produced using multiple production methods such as extrusion and 3D printing.

In addition, compliant mechanisms are also cost-effective and can be more environmentally friendly. Due to their simplistic design and flexible material requirement, compliant mechanisms can be printed using 3D printers, making them cheap, widely accessible and easily replaceable. Compliant mechanisms can also be printed using biodegradable such as PLA plastics, making them more environmentally sustainable than metal mechanisms which may also require the use of lubricant oils, which can be damaging to the environment.


Compliant mechanisms are better suited to harsh environments due to their lower failure rate and increased portability. The introduction of multiple parts and connective joints causes an exponential increase the number of ways in which a mechanism can fail. The need for turning and or sliding joints causes increased friction, causing the mechanism to wear and fatigue over time without constant lubrication. This poses a problem for mechanisms that are designed to work in harsh environments such as space where Lubrication is known to evaporate. Compliant mechanisms can also be manufactured on a microscopic scale, something which is impossible for rigid body mechanisms due to their complexity. This also results in compliant mechanisms increased portability over traditional mechanisms as their relative size and weight are much less.

With their low part count, lack of lubrication, and their ability to be lightweight and miniaturised,  compliant mechanisms are both more reliable and better suited to harsh environments than their rigid body counterparts.



However, despite the advantages that compliant mechanisms have over contemporary mechanisms, The intrinsic design philosophy of compliant mechanisms introduces some flaws inherent to the mechanism.

Traditional mechanisms have decades worth of study, analysis, and design. This allows for the easy integration of multiple rigid-body mechanisms in a system as both the individual actions of the mechanisms as well as their actions in combination are known. The use of compliant mechanisms in complex systems requires detailed knowledge about the behavior of the individual components as well as their combination. The use of rigid components also allows for simplistic, linear calculations that can be used to model and predict the behavior of the component. Flexible, non-linear components are largely designed using trial and error as a result, increasing design overhead and time. Compliant mechanisms also have reduced motion when compared to rigid mechanisms. Whereas rigid mechanisms can continuously rotate and apply immense force, compliant mechanisms are designed specifically to be flexible and thus not rotate continuously, and due to flexibility requirement, there is a limit to the force that can be applied.


Whilst compliant mechanisms demonstrate clear advantages in terms of their design, portability, and cost, the nature of the material and design principles of compliant mechanisms mean that their use case is limited. Thus the combination of compliant and rigid designs that allows both industries and individuals to capitalise on the advantages of both design philosophies is the future of mechanisms.

China’s Great Wall not so great from space?

We’ve all heard that The Great Wall of China is the only man-made object visible from space. You may have heard it from a friend, a teacher, or even a textbook. But is it true?

Actually this is largely a great myth, as not only are many other man-made object visible from space, but the Great Wall may not be all that visible as well.

Ironically, it was a Chinese astronaut, Yang Liwei, who debunked the myth. Liwei – who was China’s first man in space – said upon his return “the scenery was very beautiful… but I didn’t see the great wall.” Unsurprisingly many people in his home country were less than impressed with his comments.

What can we see from space?

Firstly, on the moon you certainly can’t see any man-made objects. The few astronauts that have been there have said that they could see blue oceans, white clouds, yellow sand and the odd patch of vegetation.

If you travel only a couple hundred kilometres up into space and you can actually make out many man-made structures with the naked eye. These include bridges and high-rise buildings.

The Great Wall is very rarely one of these visible man-made objects. What makes the great wall so hard to see is not actually its size, but its colour. The Wall does not provide much contrast from the surrounding landscape, so it is very hard to make out.

Much less impressive landmarks such as desert roads are usually much easier to spot, as they provide more of a contrast to their surrounds.

So, in truth, the Great Wall has been seen from space. However, this has only been possible under the right weather and light conditions.

Earth by Joseph via Flickr

So where did this myth come from?

This myth dates dates back to 1932, when a Ripley’s Believe It or Not! Cartoon said that the “the [Great Wall is] mightiest work of man, the only one that would be visible to the human eye from the moon.” This belief has been perpetuated for decades so much so that pretty much everyone believes it to be the truth.

A few years later the respected adventurer Richard Halliburton made similar claims in his book, Second Book of Marvels, and the claim soon turned into fact, appearing in school textbooks. Importantly these claims were made when no one had been to space, so it was impossible to know if it was truth or not.

Backlash in China

Controversy surrounded the topic when another Chinese astronaut, Leroy Chiao took photos of China from the Internatioanl Space Station in November 2004. These photos were greeted with relief by the Chinese as many thought they proved that The Great Wall could be seen, and were displayed prominently in Chinese newspapers.

However, even the astronaut himself was unsure whether The Great Wall could actually be seen in any of his pictures.

NASA has even weighed in on the debate with NASA’s chief scientist for Earth observation, Kamlesh P. Lulla saying that The Great Wall is generally very hard to see and photograph. However, Lulla went on the acknowledge that The Great Wall was most likely visible in the photographs taken by Leroy Chiao, and that the weather conditions appeared ideal for sighting The Wall.

So, whilst under the perfect conditions the The Great Wall can be seen from space, it is definitely not the only man-made object “that would be visible to the human eye from the moon.”

Robot Vacuums: the gateway to LAZY cleaning.

Bits of toast, chip crumbs and all that flour that dropped trying to make that pizza.

These can all be part of the mess that the standard house builds up.

Robot vacuum cleaners take away from the draining and slow process of sweeping and vacuuming lengths of tiles, floorboards and carpet by using unique computer algorithms and sensors to make sure your home is spotless. What exactly do all those algorithms and sensors do?

Let’s investigate how the robot vacuum always knows where to clean and not fall down the stairs.


Most robot vacuums generally have at least three types of sensors.

  1. Bumper sensors
    The outside of the robot is made up of shock-absorbing bumpers that contract in when hitting objects. It’s primarily used to traverse the obstacles around your house, like chair legs, dining tables and shoes. It usually forces a slight bump towards objects, enough to check whether it’s going under a curtain into a vast, unexplored area. Not enough to push vases of the table so don’t worry about it starting fights.
  2. Cliff sensors
    Infrared light at the bottom of the vacuum is continuously sending signals in front of itself. The light will bounce back if objects or walls are detected but it nothing reflects back, a cliff must have been found. Don’t want it to be falling down the stairs!
  3. Wall sensors
    This helps detect walls — not for collision — but to map out the walls in confined spaces and rooms. The robot uses infrared light to discover unexplored areas and making sure that the vacuum doesn’t just scrape across the side of all the walls in a home.

How does the robot know which direction is next or where to go when it’s stuck in a corner. There are generally 4 algorithms to help navigate it around the home.

  1. Random walk
    Each time the robot hits a wall or obstacle, it will check it’s right and left, rotating a random amount and moving for a random length of time.
  2. Spiral algorithm
    Starts from the centre and create a spiral going out until an obstacle is hit.
  3. ‘S’ shaped pathway
    The robot will move in a ‘S’ shape by:
    a. Right as far as possible
    b. Forward to cover new space
    c. Left as far as possible
    d. Forward to cover new space
    This process is repeated until the whole room is covered.
  4. Wall follow
    Follows the path of the wall until you come back to the same spot

A combination of these makes up how the robot moves and are used according to make sure that it can cover all the spots it can in your house.

The robot will also remember the map of an area, which will later allow it to find the best route to cleaning the home — faster cleaning time.

So if you ever purchase a robot vacuum cleaner, just watch and see twists and turns to make sure that your house is as spotless as it can be.

276/365: Dirty Little Secret: I sweep crumbs under rugs ( by Matt
iRobot Roomba 870 ( by Kārlis Dambrāns

Further Reading


How to make a superbug

Superbugs may sound like another supermarket collectables series; unfortunately, although similarly, they may be your worst nightmare. Superbugs are bacteria which cannot be killed by antibiotics. This means that if you are infected with a superbug, it can be hard to recover because treatment options are limited.

Streptococcus by josh smith via Flickr.

But where do superbugs come from? Can we stop them, or should we collect them all? Here are some instructions on how to make a superbug:

Step 1. Become infected with a pathogen

Bacteria can be classified as a pathogen, an opportunistic pathogen, or a commensal. A pathogen is a microbe which, upon infection, can make you sick. Symptoms can vary from nothing to diarrhoea to sepsis.

On the other hand, commensals (also known as the microbiota) are the bacteria which live with us without making us sick. Some commensals are capable of causing disease given the right conditions and are termed opportunistic pathogens.

Step 2. Take lots of antibiotics

When you have a bacterial infection, you may be prescribed with antibiotics by your doctor. Antibiotics work by either killing the bacteria or by stopping them from multiplying. Bacteria which do not survive are sensitive. Some bacteria are lucky and can survive in the presence of antibiotics. This is because they have genes to counteract the antibiotics so they are resistant.

Difference between antibiotic sensitive and resistant bacteria (Author’s own).

By taking antibiotics, you kill the sensitive bacteria while allowing the resistant bacteria to continue multiplying. Consequently, over-consumption of antibiotics is dangerous because it allows bacteria to continue to develop resistance.

Step 3. Allow time for mutations and DNA exchange

Some bacteria already contain resistance genes which prevent the antibiotics from working. This means they are naturally resistant. Other times mutations can occur in sensitive bacteria which then allows them to become resistant. Another method for sensitive bacteria to become resistant is by obtaining the resistance genes from the naturally resistant bacteria.

Bacterial conjugation (Author’s own).

To do this, bacteria can give their DNA to one another via a method called conjugation (also known as bacterial sex). This is when two bacteria form a small tube-like structure to connect themselves. Plasmids, a circular piece of DNA which may contain resistance genes, are then moved from one bacterium to the other through the tube-like structure. Essentially, they share information on how to become stop antibiotics from harming them.

Moreover, some of the plasmids contain multiple resistance genes. This means the presence of one plasmid can allow the bacteria to be resistant to more than one antibiotic, making treatment even more difficult.

Step 4. Avoid infection and take antibiotics as prescribed (optional)

To prevent the rise of superbugs, antibiotics should be used carefully. Not all bacterial infections require antibiotics. This means that if your doctor doesn’t prescribe you with antibiotics, it is probably for the best. However, if you do have a prescription, it is important you follow the full course, even if you feel better. You should not self-prescribe antibiotics or use left-over antibiotics without consulting a health professional first.

Another way to stop superbugs is to avoid being infected. This means keeping good personal hygiene habits and keeping up to date with your vaccines.

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