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Animate materials PERSPECTIVE
Emerging technologies As science expands our understanding of the world it can lead to the emergence of new technologies. These can bring huge benefits, but also challenges, as they change society’s relationship with the world. Scientists, developers and relevant decision-makers must ensure that society maximises the benefits from new technologies while minimising these challenges. The Royal Society has established an Emerging Technologies Working Party to examine such developments. This is the second in a series of perspectives initiated by the working party, the first having focused on the emerging field of neural interfaces. Animate materials Issued: February 2021 DES6757 ISBN: 978-1-78252-515-8 © The Royal Society The text of this work is licensed under the terms of the Creative Commons Attribution Licence, which permits unrestricted use, provided the original author and source are credited. The licence is available at: creativecommons.org/licenses/by/4.0 Images are not covered by this licence. This report can be viewed online at royalsociety.org/animate-materials
Animate materials
This report identifies a new and potentially transformative class
of materials: materials that are created through human agency but
emulate the properties of living systems. We call these ‘animate
materials’ and they can be defined as those that are sensitive to
their environment and able to adapt to it in a number of ways to
better fulfil their function. These materials may be understood in
relation to three principles of animacy. They are ‘active’, in that they
can change their properties or perform actions, often by taking
energy, material or nutrients from the environment; ‘adaptive’
in sensing changes in their environment and responding; and
‘autonomous’ in being able to initiate such a response without
being controlled.
Artificial materials that are fully animate in all these dimensions
do not exist at present, but there are many examples of materials
with some features that correspond with our definition of animacy,
as well as research that indicates potential ways to improve and
extend their capabilities. The development of such materials has
been identified by the Royal Society as an area of research with
potential to deliver major change, most noticeably in the built
environment, from roads and buildings to transport and industry,
as well as in sectors such as medicine and clothing. Development
and implementation of proto-animate materials are currently being
pursued in many disciplines, but without any formal co-ordination.
The Royal Society is seeking to support interdisciplinary efforts in
the field of animate materials, as well as to improve understanding
of their potential, while identifying steps needed to accelerate their
development in a socially responsible manner.
PERSPECTIVE – Animate materials 3
4 PERSPECTIVE – Animate materials
Contents
An introduction to animate materials.................................................................................................6
What are animate materials?...............................................................................................................10
The science behind animate materials........................................................................................... 13
Active materials.....................................................................................................................................14
Adaptive materials.............................................................................................................................. 20
Autonomous materials...................................................................................................................... 26
Direction of travel: the animacy continuum................................................................................. 32
Animate materials and the perception of risk............................................................................. 34
Animate materials across the scales.............................................................................................. 36
Machine learning and animate materials...................................................................................... 38
Sustainability and circularity: what is needed to ensure
animate materials are beneficial to the environment?............................................................40
The future of animate materials....................................................................................................... 42
The present and future of animate materials.............................................................................. 44
Adapting to animate materials.......................................................................................................... 46
Calls to action.......................................................................................................................................... 48
Interdisciplinary science and long-term sustainability........................................................... 49
Risks, safety and regulation.............................................................................................................51
Communicating with the public..................................................................................................... 54
Acknowledgements...............................................................................................................................55
Image:
Self-healing concrete
© Dr Tanvir Qureshi.
PERSPECTIVE – Animate materials 5
An introduction to
animate materials
MESSAGE FROM THE CO - CHAIRS
Look out of your window or around Different cells, tissues and structures have
your room. You will see a wide range of different functions. Some are structural:
Across the materials – metals, wood, plastics, glass. they are a part of the growing fabric.
scientific world, You might also see living organisms – Others transport water, minerals and
researchers are people, plants, animals. These might sugars from leaves to roots or vice versa.
seem to be very different entities: one
developing tools
lifeless, the other alive. Imagine buildings, roads, bridges, walls
and ideas to and perhaps entire cities that have
create materials But across the scientific world, qualities like these, composed of building
that have life- researchers are developing tools blocks that can mimic some of the
and ideas, many of them inspired by characteristics of cells and that operate
like properties. the mechanisms of nature, to create autonomously together to promote
materials that have life-like properties; growth, adaptation and healing. These
in other words, materials that can sense, are ‘animate materials’.
move, change shape and adapt to their
environment to fulfil particular goals Self-healing materials are at the forefront
such as growing or obtaining nutrients. of the field, with self-repairing paints
already commercially available and
An example of animate properties in the multiple projects exploring possibilities
natural world is displayed by a tree. It for self-healing asphalt, concrete and
is an organism that obtains energy and fibre-reinforced polymers, such as
nutrients from the environment to sustain, those used in aircraft. However, as this
grow and repair itself. It adapts its shape Perspective shows, these only represent
and internal structure to the constraints early branches of animate materials,
and opportunities supplied by the along with current applications in
environment. And it exists within and as medicine, robotics and elsewhere. Other
a component of a wider ecosystem. very different branches may develop
out of a diverse range of research now
The tree achieves these goals through taking place into life-replicating qualities
processes that operate on many scales, of materials at the molecular level. As
from individual molecules to cells to understanding of animate materials
different types of tissues that form its evolves, multiple applications may
organs, such as leaves and roots. emerge across many sectors.
6 PERSPECTIVE – Animate materials
To develop such animate materials Material goods that reach the end of
from scratch, researchers need to draw their useful life could be programmed to
on knowledge from a wide range of separate into their basic components for
Animate
separate disciplines. Techniques for reuse and recycling. materials could
making, analysing and testing them will eventually have
be grounded in the fields of materials Clothing may become responsive,
science and engineering. However, being more like assistive technology
a transformative
animate materials will also draw from the which adapts to changes in people’s effect on all
expertise of other fields, such as organic requirements. New materials are being spheres of life.
and inorganic chemistry, synthetic biology, created that could make clothing or
cell biology and physics. bandages1 respond to changes in a
person’s body temperature and detect
Animate materials could eventually have possible illness2.
a transformative effect on all spheres of
life. Buildings could become an active Robotic-like devices may be developed
part of local ecosystems, harvesting that are not controlled entirely by some
carbon dioxide from the environment to centralised information-processing unit, but
heal themselves. The walls of buildings instead have a degree of intelligence built
could act as bioreactors, using inputs into their fabric, resembling the swarming
such as light, water, heat, algae, bacteria, behaviour of some insects and birds. This
nutrients and gases to generate a range could involve the use of soft, responsive
of products such as purified water, power, materials rather than the hard substances
oxygen, recoverable biomass and heat. of traditional robotic engineering. These
devices might harvest their power from
Medical implants may be able to interact ambient sources rather than needing
with our bodies to enhance healing or periodic charging. They could be sent to
deliver medicines in appropriate doses places to perform tasks that are highly
in targeted parts of the body. hazardous for humans, such as dealing
with radioactive contamination.
PERSPECTIVE – Animate materials 7
8 PERSPECTIVE – Animate materials
Boyle’s list and future thinking In the future, if and when such complex
in science materials and devices have been developed,
The idea of being surrounded by they would be inherently less predictable,
active, animate materials may seem at least to some degree. They could require
like science fiction, but part of the careful regulation and ethical consideration
scientist’s job is to pursue far-off to avoid any unintended consequences of
visions with ambition. Over 300 their behaviour. This might include rigorous
years ago, the natural philosopher, processes for approval and monitoring, new
chemist and founding Fellow of the design codes and standards, measures to
Royal Society, Robert Boyle, set out manage the risk of failure and, ultimately,
a list of things he hoped could be mechanisms by which autonomous
achieved through science. Many, properties could be deactivated. It will also
such as the prolongation of life or be important to communicate the risks clearly,
the art of flying, would have seemed given the potential for misunderstanding in
outlandish to his contemporaries. Yet relation to materials with life-like properties
since Boyle’s time, life expectancy in created in the laboratory. The overarching
the UK has more than doubled, and aim must be to develop materials with life-like
over 7,000 aircraft now take off or properties for the benefit of society.
touch down in the UK on a typical day3.
Perhaps a modern-day Boyle would In order to create a future of animate
include in such a list the ambition of materials, two general priorities are clear.
creating materials that sustain and One is to find ways of bringing together
repair themselves as well as their diverse areas of research: to develop
environment, just as a tree does. shared language and goals and to reveal
connections that already exist. The other
is to consider how animate materials might
change the ways humans interact with
their environment, as well as approaches
to manufacturing goods and resource
management, so that such innovations
can be most efficiently and safely directed
towards social good and the urgent need
to create sustainable societies. ■
Image:
17th century predictions for the future of science
written in the 1660s by Robert Boyle FRS.
PERSPECTIVE – Animate materials 9
What are
animate
materials?
Like life itself, animacy is hard to define Wood is animate when it constitutes the
precisely but generally clear enough when fabric of a tree – there it dictates both the
Animate
it is seen. In the natural world, humans structure and the function of the object
materials can and animals are clearly animate. In a it produces. It grows, mutates and heals,
be defined as different sense, so are plants and oceans. using energy from its surroundings. But
Although lacking animal sentience, they wood has far less animacy once the tree
those that are
move and change, often in response to is felled, separated from its sources of
sensitive to their the environment. Rocks can be seen at the energy and used as timber.
environment other end of a scale of animacy, but even
and able to they can take animate form, such as when Animate materials – those created by
molten rock or magma reaches the surface human agency – can be defined as those
adapt to it in a
in an erupting volcano. that are sensitive to their environment
number of ways and able to adapt to it in a number of
to better fulfil Some natural substances and structures ways to better fulfil their function. This
display some degree of animacy because behaviour can be broken down into three
their function.
of the action of physical forces such as heat. characteristics, or principles, of animacy,
Others exhibit greater intrinsic and self- each of which can be demonstrated at
actuating animate qualities because of the different levels, namely being active,
way they interact with their environment. adaptive and autonomous.
10 PERSPECTIVE – Animate materialsACTIVE ADAPTIVE AUTONOMOUS
‘Active’ means that the ‘Adaptive’ means that they ‘Autonomous’ means that
materials can change their can sense changes in their they can automatically ‘decide’,
properties or perform environment and respond perhaps through some internal
actions, often by taking in a way that maintains or computation, or computation-
energy, material or nutrients promotes their function, like process, on an appropriate
from the environment. typically with a single response to signals or
predetermined outcome. changes in the environment
from a repertoire of possible
outcomes, without being
monitored or controlled.
PERSPECTIVE – Animate materials 11True animate materials, like living ‘Smart materials’, a relatively well-
systems, would rate highly in terms of established concept in materials
A goal for this
all three principles. However, the field engineering, can be classified as active
emerging field is at a very early stage of evolution. and often adaptive, but are not yet
of animate Some materials that are being tested or autonomous. Smart materials change
deployed in practical contexts, such as their properties in response to stimuli
materials could
self-repairing paints, concrete and roads, such as moisture, temperature change or
be defined as are clearly active and adaptive. Other electricity. One example is shape-memory
making these examples display all three features clearly polymers that alter their shape in response
three qualities but remain the focus of curiosity-driven to changes in temperature or stress.
laboratory research at a molecular level.
intrinsic aspects
A goal for this emerging field of animate
of the materials In the following section we review many materials could be defined as making
system. materials that are now the subject of these three qualities intrinsic aspects
research or development. All are active, of the materials system, rather than
to a degree, in that they move or mutate, capabilities supplied by some external
and many are adaptive, in reacting computational network. Thus, an animate
to environmental stimuli, often with a material is itself the mechanism.
predetermined response. The third
principle, autonomy, is not synonymous The three qualities also serve to delineate
with total spontaneity, acting without the limits of animate materials, showing not
external stimulus, but rather means only what they are but what they are not.
adapting or reacting in a way that is They comprise a set of life-like properties
not predetermined but selected by but do not include all the properties of
the material itself from a number of living beings; for example, they are not
potential responses. Inasmuch as a sentient, nor do they have the ability to
hierarchy exists among such materials, reproduce as animals or plants do.
being active is the most fundamental
quality, with adaptation representing The ‘3A’ framework, which outlines active,
a further step in sophistication and adaptive and autonomous principles of
autonomy characterising the most animacy, is not intended to be definitive
advanced materials. but simply to act as a working model to
guide what is still an emerging field and
provide a standardised language that can
aid development across disciplines. ■
12 PERSPECTIVE – Animate materialsThe science
behind animate
materials
Research groups from around the world have been driving
progress towards the development of animate materials.
Some of this research takes direct inspiration and guidance
from nature; some seeks to develop animate properties from
scratch, by rational design. Some is directed very much at
specific applications and problems; some is purely exploratory
and curiosity driven. The research is happening in, and
drawing on, diverse disciplines, from civil engineering and
materials science to molecular biology.
The following sections discuss some of this research that
falls within the three dimensions of the tripartite working
definition of animacy.
PERSPECTIVE – Animate materials 13ACTIVE MATERIALS
Active materials can change their properties or perform actions, taking
energy, material or nutrients from the environment. This section provides an
overview of the emerging science and technology that could underpin active
materials of the future. Few active materials are close to being ready for
use in everyday consumer products, but work is underway to create novel
applications that could transform fields such as engineering and medicine.
Materials with active properties have Another attribute of active materials is
been known and used for a long the ability to ‘remember’ a shape, so that
time. One of the first examples of the material can return to that shape after
such properties to be discovered was being deformed, when given the right
piezoelectricity – the electric charge that stimulus. Shape-memory alloys such as
accumulates in materials such as quartz. nitinol (a mixture of nickel and titanium)
When squeezed, it produces an electrical can be ‘programmed’ with a shape while
voltage – and conversely its shape can warm. The alloy can then be cooled and
be changed by electric fields. Materials bent, but, when it is reheated, it returns to
with these properties have been used its original shape (Figure 1). Such materials
widely in everyday devices such as have been used as strong ‘artificial
headphones and electric toothbrushes, muscles’ in robotics and as components
as well as specialist equipment such as of thermostats.
vibration sensors, sonar systems and
electrically controlled positioning devices.
FIGURE 1
The phase transformation process for shape-memory alloys.
Original shape at low temperature
Cooled Bent
Reverts to original Deformed shape
shape over time at at low temperature
high temperature
Heated
14 PERSPECTIVE – Animate materialsMolecular machines Several types of synthetic molecular Much of the current research on active machines have been created by materials is happening at a micro- or researchers, some of them leading to nanoscale, in part because a lot of this Nobel Prizes in Chemistry. These include: work has been inspired by living matter, molecular motors that rotate in response which is driven by processes taking to an energy input such as light; molecular place at these scales. Living cells rely on switches that can flip between two a variety of protein molecules that can stable forms in response to stimuli such change their shape in response to external as pH or temperature; and molecular stimuli, producing movement. These tweezers – molecules that can hold onto proteins have also been called ‘molecular and transport an object4. By seeking to machines’ because of their ability to emulate some of the basic actions that perform machine-like actions, such as cells and their components perform, transporting objects from one part of a cell these synthetic molecular machines could to another or changing the shape of cells eventually be building blocks for more and tissues; for example, the proteins that complex active materials. drive muscle contractions (Figure 2). FIGURE 2 Illustration of a molecular machine created by Jean-Pierre Sauvage. In this example two molecular loops have been threaded together, creating a structure that can stretch and contract. © Johan Jarnestad/The Royal Swedish Academy of Sciences. PERSPECTIVE – Animate materials 15
Image:
A murmuration of
starlings at Gretna.
© Walter Baxter.
CC BY-SA 2.0.
Experimental and theoretical tools emergent motion might arise in these
Molecular machines represent one of systems. Examples of natural systems that
many types of what scientists know as exhibit emergent motion include flocks of
‘active matter’. Active matter consists of birds and bacteria cultures in a Petri dish.
systems that are made up of units that Only with this sort of understanding is it
can extract energy from their environment likely to be possible to engineer specific
and transform it into movement or types of activity in active matter and in
mechanical work. animate materials. There is therefore a
need to develop new experimental and
The theory of active matter draws on theoretical tools to understand what
ideas from the field of statistical physics active matter can achieve and how it
and considers what kinds of collective, behaves under different circumstances.
16 PERSPECTIVE – Animate materialsActive materials in medicine Another active material with potential for
One area set to benefit from the creation use in drug delivery and elsewhere is the
of materials capable of movement and self-propelled chemical micromotor, which
action is medicine. To carry out surgery can take a variety of forms. One example
or take biopsies, invasive procedures is the so-called ‘Janus-faced’ micromotor,
are often required in order to reach the a tiny sphere whose two halves are made
target tissues. However, molecular or of different substances, such as platinum
microscopic machines small enough to and silica. The microsphere is placed in
be injected into the bloodstream might a liquid, such as a solution of hydrogen
be able to make small incisions, repair peroxide, a chemical that decomposes on
damage, or sense and collect data5. the platinum side only and acts to propel
the object. Bubbles can also be generated
One challenging issue for medicine is that that accelerate the propulsion 8 – 10.
treatments often act in areas beyond the
target area. Chemotherapy, for example, Developments in active materials could
not only attacks cancer cells but also also lead to more sensitive biosensors
kills many others. One way that some that could allow earlier diagnosis or new
researchers have sought to address treatments. These sensors could be
this issue in cervical cancer treatment is supplied by nanoplasmonics, a field that
to modify sperm cells so that they can explores the interactions between light
transport chemotherapy drugs directly and metallic nanoparticles such as tiny
to the tumour. Sperm cells loaded with spheres of gold or silver. Nanoparticles
the chemotherapy agent doxorubicin and can be coated with surface molecules
released in a dish containing miniature that bind to a target to be detected – a
cervical cancer tumours swam to the certain cell type or a virus or pollutant.
tumours, killing 87% of the cells in three Such binding may change the wavelength
days6. Bacteria too are being adapted for of the light that the nanoparticle emits or
use as ‘micro-swimmers’ or ‘bacteria-bots’ absorbs, thereby signalling that the target
to deliver drugs7. molecule has been detected. In terms of
treatments, these nanoparticles can be
designed to target and destroy cancer
cells using electromagnetic radiation
such as infrared laser light 11 – 13.
PERSPECTIVE – Animate materials 17Image:
A scanning electron
microscopy image of
a ‘bacteria-bot’, which
are being studied for
targeted drug delivery.
© 2017 Mostaghaci
et al / CC-BY 4.0.
The rapid changes in colour that Ambient electromagnetic fields
nanoplasmonic materials can exhibit in The possibilities for active materials are
response to environmental changes could broadening with the development of
also be used to produce chameleon- materials systems that can harvest power
like transformations in response to from ambient electromagnetic fields, in
temperature or voltage signals14,15. Recent particular from Wi-Fi signals. Scientists have
work has combined such colour changes created a rectifying antenna, or ‘rectenna’,
with the selective release of antibiotics a few atoms thick which captures such
to produce an active bandage that could electromagnetic waves and converts them
help combat antimicrobial resistance16. to electrical current. Devices like these
This bandage changes from green could be used to provide battery-less
to yellow when it detects a bacterial power for smartphones, laptops, medical
infection and releases antibiotics. When devices and wearable technology 17. Using
drug-resistant bacteria are present, the the same principle, animate materials
bandage turns red. Doctors can then of the future could harvest their energy
shine a light on the bandage, causing it from ambient sources such as Wi-Fi
to produce oxidants that weaken or kill signals, temperature gradients and
the bacteria (Figure 3). mechanical vibrations. ■
18 PERSPECTIVE – Animate materialsFIGURE 3
Illustration showing how an active, colour-changing bandage could help combat
antimicrobial resistance.
KEY
Drug-sensitive Drug-resistant Antibiotics Oxidants
bacteria bacteria
Smart bandage is able to
detect bacterial infection
Bacterial infection detected
The green smart bandage
turns yellow when it detects
a bacterial infection and
releases antibiotics.
Drug-resistant bacteria
still present
When drug-resistant bacteria
are present, the bandage turns
red. Doctors can then shine a
light on the bandage, causing
it to produce oxidants that
weaken or kill the bacteria.
Light shone onto bandage
PERSPECTIVE – Animate materials 19ADAPTIVE MATERIALS
Adaptive materials are those that sense changes in their environment
and respond through action to maintain or promote their function –
for example, by self-healing, including those that overcome typical
problems of degradation such as cracks in roads or walls, or scratches
on the paint of a car.
Such adaptive self-healing has existed to As and when self-healing materials
a degree for millennia. For example, lime become commonplace and used in
mortar, which has been used in buildings multiple structures, the risks of failure will
since the Egyptian pyramids, heals itself need to be managed by building in layers
by growing new crystals in cracks when of resilience so that any failure to activate
water enters, enabling it to react with does not create hazards for human safety
carbon dioxide in the air 18,19. or structural integrity.
Image:
Lime mortar has long-
established self-healing The asphalt mixture used in roads also Extrinsic self-healing
properties and has been displays some self-healing properties Road repair is a major area of research
used widely in buildings as it contains both gravel or rock and focus as the annual highway maintenance
for thousands of years,
bitumen, a viscous black liquid that can budget for England and Wales is around
including in the Egyptian
pyramids. © L-BBE. flow into small cracks in the material. £3.5 billion22 and British drivers are
CC BY 3.0. However, the process is very slow reported to spend nearly £1 billion a year
because of the high viscosity of bitumen on repairs to vehicle damage caused
and is frequently insufficient to prevent by potholes23. Technologies to prevent
such cracks growing to become potholes. the formation of potholes currently
being explored include the 3D printing
Researchers are now seeking to build on of asphalt patches24 to cover cracks
these long-established processes with identified by autonomous driverless cars
the ultimate goal of creating materials that and drones, and heating roads using
do not require maintenance because they infrared25, microwave26 or magnetic energy
are able to self-diagnose continuously sources27. While these are essentially
and repair any damage they suffer. means of complementing or accelerating
the natural healing process of asphalt,
There are already several commercial other researchers are working on new
examples of self-healing paints and technologies to promote self-repair.
coatings being marketed for use in
buildings and vehicles20,21.
20 PERSPECTIVE – Animate materialsFIGURE 4
Images showing cracks in cement-based materials taken on the day of cracking (left)
and after 28 days of healing (right) for: (a) a control sample without microcapsules;
(b) a sample with a medium concentration of microcapsules and (c) a sample with a high
concentration of microcapsules. For both samples with microcapsules, the cracks are
almost completely healed after 28 days.
(a)
(b)
(c)
Note: solid bars correspond to 500 μm. © 2016 Kanellopoulos et al / CC-BY 4.0.
PERSPECTIVE – Animate materials 21One approach that has been used for Intrinsic self-healing
asphalt, concrete and polymers is the Extrinsic self-healing is limited either by the
addition of capsules that crack when they number of times the healing can occur, in
are damaged and release healing agents the case of capsule-based systems, or by
(Figure 4). In asphalt, these capsules are the need for monitoring and intervention,
typically filled with oil-based bitumen in the case of vascular systems.
solvents that fill the cracks faster than
bitumen solvents that aid crack repair28. It would be preferable to make self-
In concrete, the capsules are often made healing an intrinsic property of the
of soft polymers such as gelatin or gum material itself, a possibility that has
arabic filled with epoxy adhesive or been explored in polymers, particularly
sodium silicate, which mineralises on plastics and paints. Polymers are large,
exposure to air and water29. chain-like molecules made of repeating
sequences of smaller molecules joined
Another approach to self-healing together by chemical bonds. When
concrete, known as microbially induced polymers are damaged, these chemical
calcite precipitation30, uses lightweight bonds may be able to achieve some
capsules containing spores of bacteria. degree of recovery, usually by exploiting
When the concrete cracks and the a particular chemical bond or reversible
conditions become favourable, the spores mechanism in the molecular arrangement.
germinate and the bacteria break down This is typically thermally activated,
the nutrients and precipitate calcite into although other stimuli such as light can
the concrete cracks31 – 34. be utilised. Such ‘remendable’ polymers
do not usually exhibit impressive inherent
Self-repair capsules are embedded in mechanical characteristics, often being
the material from the beginning. Once elastomeric in nature36. Broken chain
they have been used they cannot be fragments are particularly able to heal if
replaced, making healing a single-shot the molecular components are linked by
process. In order to achieve repeated relatively weak and reversible physical
healing, researchers have introduced bonds, which act rather like molecular
vascular-like networks into materials, hook-and-loop patches that can be
through which healing agents can be pulled apart and reunited37.
pumped whenever necessary, with
potential for different agents to be Another option for self-healing makes
used under different circumstances35. use of the way polymer chains become
entangled: if the chains can be made
loose and floppy by heating, they can
re-tangle to seal a scratch or crack.
22 PERSPECTIVE – Animate materialsImages:
Soft robotic hands are able to
manipulate fragile objects with
dexterity and repair themselves
when damaged. © Brubotics (VUB).
PERSPECTIVE – Animate materials 23Image:
An arch made from
living building materials,
or ‘living bricks’.
© Dr Srubar / University
of Colorado Boulder
College of Engineering
and Applied Science.
A ground-breaking example is a highly From repair to growth
extensible rubber that can be stretched Adaptivity in materials has the potential to
to many times its original length and that, move beyond self-repair and to replicate
when cut, can be repaired simply by the way living systems grow and adapt to
bringing together the surfaces to self-heal their surroundings.
at room temperature38.
One example is that of living building
Self-healing polymers are also receiving materials40, or ‘living bricks’. These are
increased attention in the development of made by mixing Synechococcus bacteria
soft robotics, which are robots made from with off-the-shelf additives such as
flexible materials such as those found in gelatin, calcite and sand. These materials
organisms. Among the challenges with can be regenerated in response to
soft robots are that rubbery polymers temperature and humidity changes in
can be prone to damage and repairs are ways that potentially go beyond self-
often costly. The Horizon 2020 Future repair to growth.
and Emerging Technologies Programme
project on Self-Healing Soft Robotics
(SHERO) aims to create robots that can
use sensors to identify damage and
autonomously self-heal39.
24 PERSPECTIVE – Animate materialsHydrogels are materials that swell Traditionally, implants were deliberately
or shrink in response to changes in designed to be inert to avoid provoking
temperature, light or acidity41. They have inflammation and immune rejection.
been used for controlled drug delivery42,43 Bioactive glasses are, by contrast,
in fields such as cardiology, oncology, designed to bond with bone without
immunology, wound healing and pain triggering the formation of scar tissue.
management. Some are used in the form
Image:
of injectable particles that self-assemble Bioactive glasses can also deliver other
Hydrogels swell and
in the body. Typically, they release drugs, active ions that have a therapeutic effect, shrink in response to
either as they are biodegraded or as such as strontium to treat osteoporosis47 environmental signals.
they swell, so that the drug molecules or medication for chronic wounds in CC BY-SA 4.0.
previously trapped among the polymer patients with diabetes who have not
chains can escape44. responded to other treatments48. A new
form of 3D-printed and self-healing
Other adaptive materials interact with ‘bouncy’ bioactive glass is now being
living systems to grow and develop – explored as a way of stimulating cartilage
for example, to meld with tissues in the growth following sports injuries49.
body. One well-established example is Structural regenerative materials may
bioactive glass such as BioglassTM, which respond to changes in mechanical load or
has been implanted in over 1.5 million biochemical stimuli to trigger therapeutic
people for orthopaedic and dental surgery or healing mechanisms. ■
over more than two decades45,46.
PERSPECTIVE – Animate materials 25AUTONOMOUS MATERIALS
Autonomous materials are those that select an appropriate response to
stimuli without any kind of external control or guidance. Unlike adaptive
smart materials that have a single response to a specific prompt, such as
glasses that darken in response to ultraviolet light, autonomous materials
show versatility in combining various inputs to generate a suitable
behaviour from a diverse repertoire.
Early research has built on advances generated signals provide the inputs for
in materials science, manufacturing, networks that operate like algorithms
distributed computing and miniaturisation among cells, organs or even whole
to create multifunctional materials that ecosystems to create outputs that
sense, compute, communicate and enable the organism to survive or adapt.
move. Examples include robotic-like Like an organic network, this sort of
materials, such as an amorphous facade ‘computation’ does not need a brain or a
that recognises and changes colour in central command system, although it does
response to a user’s gestures and an involve a complex distributed network of
intelligent skin that senses touch and interacting molecular elements52.
texture using sensor nodes to detect
vibrations50. With further advances across These are the kinds of capabilities that
scales, specialists believe autonomy could would qualify an animate material as
enable responsive infrastructure and being truly autonomous. But creating
prosthetics, as well as everyday items such materials that are capable of even the
as table tops that warm or cool food51. most basic computations is challenging,
and there is no single path to get there.
The key in creating such bio-inspired Three possible approaches are: materials
applications is to replicate the logical made up of smaller components that can
deductions that living beings make be programmed and exhibit complex
as they fulfil basic needs, such as collective behaviour; materials that
recognising that food and warmth are can store and process information;
required for self-preservation. These and material systems that can help us
behaviours can be viewed as a type of understand living systems themselves
computation. Environmental and self- and their origins.
26 PERSPECTIVE – Animate materialsFIGURE 5 Researchers are working to create tiny robotic modules, sometimes called claytronic atoms or ‘catoms’, that in the future may be able to assemble and disassemble into arbitrarily shaped objects such as a chair. Programmable matter Such molecular assembly processes can At the molecular level, the signalling be used to translate information stored processes of living systems use at the molecular level into some sort chemical principles. Unlike rocks and of animate function as a consequence minerals, which have rigid structures of the assembly process. This opens held together by strong covalent up the prospect of materials that or ionic bonds, molecules in living could be constructed to assemble and systems – proteins and nucleic acids disassemble in various ways – so-called for example – generally have weak or ‘programmable matter’. loose interactions such as hydrogen bonding, which enable molecular entities to associate, assemble and disassemble. PERSPECTIVE – Animate materials 27
Image: A self-folding ‘boat’ made from programmable matter (time shown in lower right—mm:ss.s). Images show: (a) flat sheet prior to folding; (b) all actuators receiving current; (c) immediately before magnetic closures engage and (d) finished boat on side (D). © The Harvard Microrobotics Lab. 28 PERSPECTIVE – Animate materials
Large-scale robots and other devices can The long-term ambition is to shrink these
already swarm and interact, from drones components to micrometre or nanometre
to autonomous vehicles. Very small units scales to create what some have called
have self-assembled in two-dimensional ‘smart dust’56. Such tiny elements could
systems and some researchers are now be used to make nanodevices capable
focused on possibilities for self-assembly of sensing, actuating and analytical tasks.
in three dimensions at smaller and smaller However, miniaturisation is challenging.
scales, typically building prototypes at the As well as inherent difficulties in
macroscopic scale as an initial step. In one making components smaller, as the size
approach53, researchers are seeking to scales are reduced, the physical forces
create tiny robotic modules, sometimes that govern the interactions change
called claytronic atoms or ‘catoms’, that can drastically. For example, the different
assemble and disassemble into arbitrarily physics of the nanoscale world requires
shaped three-dimensional objects54 – a the use of entirely new design principles,
coffee cup, say, or an injectable medical consistent with those of cell biology, that
instrument (Figure 5). Although a long make use of the different features of
way off, the goal would be to program this environment, such as self-assembly
the catoms with assembly instructions and responsiveness by molecular
so that a featureless mass of them turns shape change57.
spontaneously into the desired object.
Other researchers have produced Paradoxically, if self-assembly is achieved
sugar-cube-sized ‘smart pebbles’, which at the nanoscale one of the opportunities
are essentially mini-robots that move created would be to build structures that
and form into well-defined shapes. The morph at a large scale by assembling,
pebbles use simple processors, flywheels disassembling and reassembling at the
and magnets for movement and assembly, molecular level. Some researchers have
and are able to self-organise with no envisaged applications such as matter
central commands55. that could be shaped into tools such as
hammers or wrenches, or clothing that
could change its insulating properties
according to the weather58,59. Among
the scientific challenges involved in
developing such materials are creating
the algorithms needed to program the
units to assemble in one out of a huge
number of possible patterns60.
PERSPECTIVE – Animate materials 29Computational materials Chemical information processing can
Autonomous materials of the future could also be done with molecular systems that
share some characteristics with today’s are much simpler than DNA63 and that
digital computing systems if organic, have light photons as an output signal.
microscopic, non-digital equivalents can These systems can perform computer-like
be found. Just as self-driving cars have operations involving two input signals such
been programmed to be able to make as ‘AND’ – where two signals are required
decisions about speed and direction, to trigger a reaction – or ‘XOR’ – where
responding to information from their the presence of one but not another signal
environment, autonomous materials is required. Conversely, the photons might
could be programmed to respond to be inputs that the molecules absorb. Or
internal or external stimuli. they could be chemical: the presence or
absence of some molecule or ion that
One approach to encoding information in binds to the molecular logic gate.
materials is based on using DNA, which
is a highly compact, natural medium for Chemical equivalents of computations
storing and transferring vast volumes of can also be carried out in an analogue
information in living cells. Researchers fashion by exploiting chemical reactions
are now investigating ways to store data that occur continuously over time. This
using technologies that synthesise long approach typically makes use of reactions
strands of artificial DNA to write data such such as the Belousov–Zhabotinsky
as video into individual molecules61. As reaction, a process in which the reaction
well as its storage potential, DNA can also of two ingredients creates constant pulses
be designed to assemble and could be that spread outwards from their source
used to connect units of nanomaterials like ripples, through changes in the
into complex structures62. composition of the mixture via chemical
waves. The interactions between the
waves in these chemical systems have
been shown to be capable of carrying
out tasks such as image processing,
if the reaction is tweaked to make it
light sensitive64; programmable pattern
recognition65; or logic computations66.
30 PERSPECTIVE – Animate materialsA different kind of life
While some research on autonomous
systems is directed towards specific
applications, other curiosity-driven studies
are targeted towards the overlapping
goals of creating new life-like materials and
probing the origins and nature of life as it
exists. Some of these seek to replicate the
natural building blocks of life as closely as
possible, while others are trying to create
new cell-like entities that could lead to
different evolutionary pathways.
Experiments on ‘proto-cells’ made from
non-biological components might point to
a bottom-up route to animate capabilities. For example, they have enabled cell-like Image:
Representative
For example, researchers have explored compartments to self-assemble from
fluorescence microscopy
the synthesis of liquid–droplet protocells inorganic molecules69. The possibility image of micro-arrays
called coacervates, by bringing together that structures might divide and pass of giant unilamellar lipid
two kinds of particles with opposite on properties to successors raises the vesicles (GUVs). GUVs
are being explored as
electrical charges (such as DNA strands possibility that their behaviour could be
platforms to implement
and clay particles). These droplets, unlike tuned and honed by evolving over time chemical signaling in
biological cells, have no membrane – but in response to the environment. The protocells. © 2019 Mann
this can be an advantage as it enables researchers might also impose conditions et al / CC-BY-NC.
them to engulf one another, dividing and that favour the selective emergence
reforming67. Researchers have also made of structures with particular desired
polymeric thermo-responsive ‘protocell’ properties. Such work raises possibilities
particles capable of self-assembling into for new types of evolutionary systems
artificial tissues that swell and shrink in that might cause public concerns. These
response to changes in heat68. would need to be subject to controls
and regulation to avoid unintended
Researchers are also working to develop consequences as outlined later in
chemical systems with properties that this Perspective. ■
have historically been seen as uniquely
biological. These life-like characteristics
might include the potential to evolve by
‘inheritable’ transmission of information.
PERSPECTIVE – Animate materials 31Direction of travel: The animacy continuum
The diagram below organises materials by their overall animacy. It shows a rough direction
of travel from familiar materials to materials that are in their infancy but may underpin the
creation of future animate materials.
Lime mortar has long-
Flint has no animate established self-healing
properties. It is inert and properties and has been
its properties are fixed. Quartz changes shape in used widely in buildings
response to electricity and for thousands of years.
produces an electric charge
when deformed. It was one of
Textiles Woods Composites
the first materials with active
properties to be discovered.
PAST Inanimate materials
Glues Ceramics Metals Polymers
Concrete has no Asphalt or bitumen
intrinsic animate used in asphalt mixture
properties. However, road surfaces is a
work is underway to viscous substance that
make concrete more naturally drains slowly
adaptive by enabling into cracks and thereby
it to self-heal. exhibits some self-
healing properties.
New research is trying
to increase its ability to
self-heal and be more
resilient to damage.
32 PERSPECTIVE – Animate materialsMolecular machines can carry out a variety
of tasks such as transporting other molecules
and moving in specific ways and may be
the building blocks of new materials in the
future. The 2016 Nobel Prize in Chemistry
was awarded for ‘the design and synthesis’
of molecular machines70.
Biomaterials Sensors Nanotechnology Energy- Proto-living Living
harvesting technologies technologies
materials
Animate materials FUTURE
Smart Self-healing Synthetic
materials materials biology
Hydrogels swell and Programmable matter can
shrink in response to be implanted with instructions
environmental signals. like a computer-driven device,
such as cell-like units which are
programmed to replicate and
grow which are programmed
to replicate and grow.
4D printing is a type of
Shape-memory alloys programmable matter. It creates
return to their original 3D objects that transform over
shape when heated, time in reaction to changes in
having been deformed their environment. Image ©
when cold. The Harvard Microrobotics Lab.
PERSPECTIVE – Animate materials 33BOX 1
Animate materials and the perception of risk
As animate materials develop, risks will need to be carefully assessed and managed,
both to prevent harm resulting from the actual properties of such materials and also
Many of the to avoid distorted or unfounded perceptions of risk becoming commonplace and
benefits and hampering progress.
risks of animate
What kinds of risk might animate to furniture or mechanical components,
materials are
materials create? but fears may include the prospect of such
only likely to Animate materials are likely to present materials falling into the hands of those
emerge with their a variety of well-founded risks as they who use them to create weapons.
evolve. For example, use in buildings will
democratisation
raise questions about the consequences How worried should society be about
through multiple of failure. Medical applications will be these risks?
applications examined for risks comparable to those of We believe that short-term risks are
used by millions current therapies – such as sensors that relatively low as animate materials
might misdiagnose conditions, treatments remain at the exploratory stage. In the
of people.
that attack the wrong target or implants medium term we anticipate risks to grow
that have unforeseen side-effects. as materials are programmed but not
yet fully autonomous. In the longer term,
As is often the case with new more autonomy can be expected and
technologies, many of the benefits and while the resulting materials promise
risks of animate materials are only likely to many potential benefits they will be
emerge with their democratisation through less predictable. Careful regulation and
multiple applications used by millions of clear communication will be required to
people. At this early stage those benefits address such concerns. Society should
and risks are largely unknown. prepare for this, but there is plenty of time
to do so, and this should not hold back
However, one potential issue is the development in the short term. However,
possible consequences of widespread there is no room for complacency and
access to programmable matter, described the calls to action that conclude this
in more detail earlier in the report. There Perspective include provisions for
may be many positive uses of nanoscale regulation, including a multidisciplinary
particles that can assemble, disassemble committee to consider options for
and reform into multiple shapes, from tools monitoring and regulation.
34 PERSPECTIVE – Animate materialsRisks of distortion and misrepresentation. suggest that mechanical self-replicating
What was the ‘grey goo hypothesis’? nanomachines will be developed in
The risks of new and emerging technology the foreseeable future”73. Drexler later
can be distorted as a result of public commented that he wished he had
misunderstanding or media coverage. In his “never mentioned the term ‘grey goo’”
1986 book Engines of Creation Eric Drexler, as it had long hampered public rational
one of the pioneers of nanotechnology, debate about nanotechnology 74.
included a couple of paragraphs outlining
an imaginary scenario in which tiny, out-of What can animate materials learn from
control, self-replicating molecular machines the ‘grey goo’ experience? Image:
Omni magazine cover
consume all the biomass on Earth, as they In hindsight, the main problem with from November 1986.
seek to build more of themselves. This the ‘grey goo hypothesis’ is that it The edition contained
speculative scenario was called the ‘grey dominated public and media discussion a story that helped
popularise the term
goo hypothesis’, as the machines would around the risks of nanotechnology
‘nanotechnology’.
turn the world into ‘grey goo’. without being grounded in scientific © Dale O’Dell 1986.
plausibility. The unrealistic doomsday
Over time, the idea gained influence and scenario overshadowed any open
exposure in relation to nanotechnology, and constructive discussion around
appearing in a popular science fiction the emerging area of science.
magazine Omni (1986), in a controversial
article in Wired entitled Why the For animate materials, open and
future doesn’t need us (2000)71 and in constructive debate around the possible
a novel, Prey (2002)72, among many opportunities, risks and long-term impacts
other publications. should be actively encouraged from the
outset. This debate will be vital to ensure
In response to concerns over safety, that the field has a positive impact on
regulatory and ethical challenges society. The learning point from the ‘grey
associated with nanotechnology, the Royal goo’ experience is that information about
Society, in collaboration with the Royal the real benefits and the plausible risks
Academy of Engineering, produced the of the technologies needs to reach the
report Nanoscience and nanotechnologies: public early and thus create resistance to
opportunities and uncertainties. The report any distorted or exaggerated accounts
concluded that “…there is no evidence to of potential impacts. ■
PERSPECTIVE – Animate materials 35Animate materials
across the scales
ANIMATE WORLD SCALE Examining how structures are built up over scales helps to
highlight similarities and differences between animate and
inanimate materials.
HUMAN
Hand In some senses, living matter is no The key distinction between living
different from non-living matter. and non-living matter is that in
At the most basic level, all materials living materials there is an extra
are made up of atoms, and all degree of connectivity between
materials consist of structures at the different scales. They actively
MINIATURE different levels, from the atomic to organise their internal architecture
Hair the nano to the macro. But while by setting up communication
people experience materials as between these scales. It is this
if they were uniform – a block of communication that allows living
concrete looks monolithic; a spoon materials to respond proactively to
feels like a lump of indivisible external stressors: to detect that
MACRO steel – this uniform appearance a stress is occurring and adopt a
Tissue
is an illusion as materials have course of action in response.
different kinds of organisation
at different size scales.
Living materials in particular The key distinction between
MICRO
Cell have a hierarchical architecture. living and non-living matter
This is what often gives them
their distinctive and complex
is that in living materials
properties. It is also the hierarchical there is an extra degree of
nature of materials that scientists, connectivity between the
NANO engineers and designers can
different scales.
DNA learn from as they seek to build
animate materials of the future.
ATOMIC
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