Published 6 July 2022 by Vijay Shankar Balakrishnan
Innovative Materials: From Arnold Schwarzenegger’s Terminator to Smart Membranes
Thirty years ago, the Arnold Schwarzenegger-starring sci-fi fantasy film series, Terminator, featured a futuristic robotic villain. Named T-1000, the shape-shifting android villain was the brain-child of Skynet, a human brain-like artificial intelligence machine; and was sent from 2029 back to 1991 to take on the human civilization. The film portrayed the T-1000 as a ‘nanomorph’ built of liquid crystals and gels that allow the android to take multitudes of shapes per its need. Thus, the filmmaker portrayed the idea of nanotechnology as an acrimonious and ambitious imagination.
“It’s really one of the best and coolest Schwazzenegger films,” said Sir Konstantin S. Novoselov. He is a Professor at the Centre for Advanced 2D Materials, National University of Singapore, during his lecture at the 71st Lindau Nobel Meeting. Sir Konstantin shared the 2010 Nobel Prize in Physics with Sir Andre Geim, a physicist at the School of Physics and Astronomy at the University of Manchester, UK. Together, they discovered the innovative carbon-based material called graphene, the one-atom-thin film of carbon atoms snuck together in a honeycomb-like structure. The world’s thinnest and strongest material can conduct electricity and heat.
In his spell-binding lecture, Sir Konstantin showcased how Chemistry progresses in the field of materials science. He showed examples of researchers worldwide working with materials like graphene and regularly identifying exciting phenomena. In his inspiring presentation, the laureate also walked us through how modern materials chemistry opened doors to create 2D materials to engineer versatile materials. He also tantalized the viewers that the next generation of materials may have the ability to shift shapes from 2D to 3D and switch between solids and liquids and vice versa. However, according to him, this paradigm shift in engineering is still in its infancy, and we have a long way to go.
The Bad News
“I have a bit of bad news for you guys: we have got only seven years left as per the Terminator film, so unless we do something crucial and think out of the box, we will never get to this kind of a flexible, self-repair, shape-shifter in real-life,” said Sir Konstantin. He believes the fictional idea of a shape-shifter is still a work in progress because of how humankind approaches technology and how humans design functional systems.
Humans have always approached designing a material or a socioeconomic system in a top-down fashion. A watchmaker starts building a clock by fabricating the cogs and wheels first, which she then has to put together for the watch to be functional as a system. Still, a clock by itself is neither intelligent nor its cogs and wheels. It requires control or a stimulus – a key or a battery in the case of an analogue or a digital timepiece, respectively – to make it work. For this kind of top-down approach to work, a craftsperson must create a complex cocktail of specific and individual pieces they will eventually put together. The designed item will work only when the unique pieces are designed fault-free. Think of other technologies like electronics, like computers or manmade systems like health care. These function only at the system level and always require external control. Moreover, they are not adaptive, prone to faults, require constant monitoring or maintenance, and are energy inefficient in their own respects.
But biological systems are different: they have the functionality from the cell to an organism (system) level. Functionality is spread across all the possible scales. A cell membrane is functional in its own respect, policing the passage of chemicals across a cell. Cell proteins are a different story: they are very selective and sensitive to their cellular environment. Some proteins span the cell membrane, but others penetrate it, arrange themselves into a channel, and smuggle chemicals across the membrane. For the protein to home in on the membrane, the cell produces it within itself. At the same time, molecular chaperones bring it from the ‘protein kitchen’ to the cell membrane. Depending on the cell’s requirement, the membrane-dwelling protein either lodges on the membrane or folds itself into a channel, penetrating the membrane for chemical messengers to pass through it.
Now think about cells communicating between each other or massing together to form a tissue. The tissues then turn into an organ. Organs eventually compile us as a system: the human body. The same in a bacterium, a plant, or an animal. Researchers define this as the bottom-up approach: building up from single individual functional and intelligent blocks, like the liquid crystals and gels that made up the T-1000 in the Terminator films, where the individual building blocks can function alone or in groups. The biological systems are adaptive, versatile, self-healing, and energy-efficient at each material level (membranes made of fat molecules, proteins made of amino acids, etc.).
“Now my question is, can we actually be inspired by these biological systems and develop synthetic materials so that we can delegate some of those functionalities from the system level to actually at the individual material level? ” asked Sir Konstantin. “Can we create functional, smart, flexible, and transformable materials in their own right?”
The Good News
Such smart, flexible materials are called functional intelligent materials. Functional, meaning they are programmable to perform a complex response to external stimuli. They are intelligent, meaning they can be trained to have memory and learn to perform a particular function in response to external stimuli.
Since discovering graphene, several researchers and tech companies have used graphene-based materials differently. For instance, a smartphone company reported a few years ago that it has adopted a graphene-based technology to prevent its latest gaming phone model from overheating. Similarly, a sports equipment company has said it is launching a series of skis and tennis rackets laced with graphene for lighter weight and sturdier performance. There are several such examples.
For example, the Nobel Laureate Dan Shechtman discovered the existence of non-periodic phases of atomic structures in nature. These novel materials are known as quasicrystals in shapes such as icosahedron and are still in infancy to be found in plausible and significant applications in domains such as non-corrosive surgical blades or Teflon-free non-stick coating to stainless steel kitchen utensils.
However, the desired intelligent shape-shifting nanomaterials will have more outstanding functional applications, Sir Konstantin explained. If a company develops a water desalting filtration system using a graphene-based filter, then the filter would prevent only the salt from passing through. But he and his colleagues have been developing smart membranes that, when programmed, can even prevent contaminants from passing through. The smart membrane can sense the molecular shape of the pollutant and then closes itself to avoid toxic substances passing on to the supply system.
“Conventionally, at a desalination plant, you would put a sensor on the filtration unit to screen toxic substances, send the signal from the sensor to a computer to analyze, and then the analyst would stop the filtration to examine further,” he explained. “Here, the smart membrane – the material – is the computer.”
Some of Sir Konstantin’s colleagues are developing more such materials and playing with the materials’ physics, such as their shear or flexibility. Sometimes, they go beyond the biological inspiration and integrate symbiotic biosystems to develop hybrid bio-nano-materials such as living electroactive composites. These LECs contain thin graphene-like polymers coated with symbiotic bacteria, which use the polymer as a surface to grow on. In return, their metabolic production of electrons renders the membranes with electrical properties. Creating such novel biological fuel cells is not just for fun. Instead, they will have biomedical applications such as delivering medical drugs to the human body or having antimicrobial properties. But what is crucial for them to ensure is that there is a feedback loop and that the internal structure of the material changes from memory as it did during the training for the designed and desired function.
“But for training, we need more dynamic artificial intelligence systems, which are not yet available in this case,” Laureate Novoselov said. “Also, with the available traditional materials, it would take much longer to produce smart, functional materials like the ones I described on-demand.”