3D printed 'soft and hard' smart fabrics bring more wearable possibilities

In the field of smart wearable materials, there has been very little research on changing the mechanical properties of wearable materials in the past.
The main difficulty is that while manufacturing wearable materials, it is also necessary to ensure that the mechanical properties of the materials can be changed rapidly
.
Smart textiles can impart electrical, optical, and magnetic properties to fibers or fabrics, enabling them to sense, drive, and process information, and are widely used in energy harvesting, wearable computing, biosensing, health monitoring, and other fields
.

By engineering the constituent materials and their geometry, desired properties such as high impact resistance, thermal regulation or electrical conductivity can be achieved
.
However, traditionally, the vast majority of smart textiles have only focused on sensing and information gathering functions
.
Fabrics with adjustable mechanical properties can provide mechanical feedback to the human body and perform functions such as joint assistance, support, and haptics.
Therefore, they have greater market prospects and application promotion value
.

The team of Prof.
Yifan Wang from Nanyang Technological University in Singapore and Prof.
Chiara Daraio from Caltech has developed a thin, safe and low-cost "chain mail" smart fabric, which is composed of layers of chains arranged in layers.
A structured fabric composed of three-dimensional particles with adjustable flexural modulus
.
This material is a hollow eight-body connection, made of 3D printing, and can be freely switched between soft and hard states within 0.
1 seconds through air pressure adjustment, thus proposing a safe, fast transition rate and light weight for smart wearable materials.
, low-cost feasible solutions
.
Their research results were recently published in Nature, entitled "Structured fabrics with tunable mechanical properties"
.

This work systematically explores the mechanical properties of structured fabrics composed of non-convex interlocking particles with precisely controlled geometry during interference transitions
.
Because the blocking transition is a scale-invariant physical phenomenon, reconfigurable fabrics composed of discrete particles can be realized at different scales
.
In principle, recent advances in additive manufacturing have made it possible to scale fabric thicknesses from micrometers to meters, and to use different constitutive materials for different applications
.
By integrating different confinement methods (e.
g.
, electrical or magnetic control), it is conceivable to program stiffness at different locations of the fabric for applications such as tactile interfaces and medical stimulation
.

Chain mail is complex in shape, but when pressure is applied on their boundaries, the particles interlock and the chain mail blocks
.
At a small external pressure (about 93 kPa), this sheet becomes more than 25 times stiffer than in the relaxed state
.
This significant increase in flexural strength is due to the high tensile strength of interlocking particles, unlike loose particle media
.
Use discrete element simulations to relate the microstructure of chainmail to macroscopic properties and interpret experimental measurements
.

The research is also innovative in its combination of novel design and cutting-edge 3D printing technology
.
The material is difficult to achieve with traditional manufacturing techniques, and without 3D printing technology, such topologically interconnected structures would be difficult to manufacture
.

Compared with traditional fabrics, the smart fabric has the advantages of safety, fast transition rate and low cost
.
First of all, the soft and hard adjustment of the material is adjusted by a micro air pump to adjust the air pressure, which is relatively safe for human wearing; the transition of the soft and hard state can be realized within 0.
1 seconds
.
Taking small smart fabrics such as wrist or elbow pads as an example, the manufacturing cost is about 100 US dollars, and the cost is expected to be several times lower if mass production in the future
.

This smart material can replace the application of traditional robotics in some scenarios
.
Moreover, the size that it can achieve is "any size", that is to say, as long as the 3D printer's precision is high enough, it can also be made into a very thin, small structure
.

Take vascular stent or heart stent surgery as an example, if this kind of material that can become soft or hard at any time is used, then perhaps this very soft stent structure can be put into the human body through minimally invasive surgery.
position, and then adjust it to make it hard
.

In addition, the material can be used for medical support on human outer skin
.
Currently, a plaster cast is commonly used to immobilize the fracture site of a patient with a broken or broken hand
.
However, the cast is very hard and may not be removed for a month or two, making it difficult for the patient to move
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If this new type of material is used, it can be "soft or hard" at any time.
When the fracture site needs support, it can be hardened with air pressure adjustment; when the patient needs to rest, it can be softened again
.
Furthermore, if the 3D printer or fabrication equipment is large enough, such structures can be realized at larger scales
.

According to DeepTech, the research team's development of the material was inspired by granular materials, soft materials that are common in everyday life, such as sand, rice, beans, and more
.
The scientific principle is inspired by the "blocking phase transition" in the field of physics.
Many particles are used to form a smart fabric, and then the soft and hard state of the material can be transformed by applying external pressure
.

Aggregation of granular particles or layered structures whose mechanical properties change during the process of jamming
.
Blocking phase transitions, which are not dependent on temperature changes as in ordinary materials, are governed by local geometric constraints in particulate matter
.
The blocking transition enables the disordered particle system to reversibly switch between deformation with fluid-like plasticity and deformation with solid-like rigidity, accompanied by changes in the packing fraction
.
Blocking has been used to create smart materials with adaptive mechanical properties
.

For example, adding water to the sand and then applying pressure from the outside can make the sand into a stronger castle, which is actually a transition from a soft state to a hard state
.
For another example, vacuum-packed rice feels like a very hard brick, but as long as the vacuum-packed bag is opened, the particles inside can flow freely, which is a change from hard to soft
.

The research team triggered the blockage between the interlocking particles by applying an adjustable pressure at the boundary
.
Encapsulating the two layers in an airtight flexible envelope can still bend easily due to the weak coupling between the two layers
.
To induce clogging, the researchers then applied a confinement pressure (pulling air out of the envelope), resulting in confinement stress at the fabric boundaries
.
This increases the total packing fraction of particles, triggering a blocking transition, increasing the flexural modulus, and transforming the fabric into a load-bearing structure
.

The fabric has good structural reconfigurability and can be shaped into a variety of different shapes, such as flat and arched, and the structure has good mechanical stiffness, capable of bearing loads over 30 times its own weight
.
The fabric also acts as an adjustable protective layer against impacts from external forces
.

Professor Wang Yifan also put forward his ideas for the industrialization of this material
.
He believes that small medical support applications can be implemented in about 5 years, while exoskeleton systems or large-scale construction applications are expected to be in 5 to 10 years
.

As for the room for improvement of this technology, Wang Yifan said that they used a polymer material of nylon polymer in this study.
If they want to further improve the height of this smart fabric, they need to use materials with greater stiffness.
, such as metal materials or carbon fiber materials
.
This requires further research in 3D printing metallic materials or stronger materials
.

According to reports, the team has preliminary results that can be printed in metal
.
Another big room for improvement is that the team's main research focuses on materials and structures, but if it is really applied to wearable materials, such as exoskeleton systems, the entire mechanical system needs to be studied
.
Therefore, the next step for Wang Yifan's team needs to study how to combine this advanced material with other system modules, such as control, sensing, actuation, energy,
etc.