DESIGN & TECHNOLOGY

Smart Materials

Developments in modern and smart materials

Smart materials are those with physical or mechanical properties that react to a change in their environment. This reaction, which can include a change in colour, shape or resistance, can be in response to a change in temperature, light, moisture, pressure or an electrical input.

The change is temporary and reversible. The material should return to its previous state when the environmental factor that initialised the change is removed.

S h a p e m e m o r y a l l o y s (NITINOL)

Most metals can be shaped into different forms, but few have a ‘memory’ that allows them to return to their original shape if heated. Nitinol is an alloy of titanium and nickel and is one of the more commonly known shape memory alloys (SMAs). A product manufactured from nitinol can be shaped and deformed, but when heated the metal will return to its original state. An example of a product

manufactured from nitinol are the frames for glasses, particularly those for children.

Nitinol is found in many medical applications, such as the medical fastenings that are used in bone fractures, stents for heart surgery and dental implants such as braces. In both of these applications, the SMA reacts to the natural heat of the body, keeping the wire of the braces under tension and preventing the medical fixings becoming loose.

Polymorph

Polymorph is a thermoforming polymer that is usually supplied ina g r a n u l a r f o r m . I t i s o f t e n categorised as a smart material due to it becoming soft and pliable when heated to a low temperature. When heated in water to 62°C polymorph becomes soft, and the granules merge together and create a volume of polymer that can be easily moulded by hand, solidifying when cool.

It is a versatile modelling material that can be machined and shaped with hand tools when solid, and that becomes soft and pliable if reheated in water. It is often used in schools when modelling ergonomic features on a product.

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Smart fibres, fabrics and polymers

Photochromic pigment

Photochromic pigment changes colour in response to light intensity. It can be found in applications such as sunglasses, where the lens becomes darker or lighter in response to the UV radiation.

Thermochromic pigment

Thermochromic pigments change colour in response to a change in heat. They can be engineered to respond to a specific t e m p e r a t u r e o r t o temperature range and are often used in applications where a visual indicator is needed when a specific temperature has been reached, such as the temperature of a baby’s bath or when baby food is cool enough to eat.

T h e r m o c h r o m i c p i g m e n t s a r e m o s t c o m m o n l y f o u n d i n products that change due to an increase in temperature, but several drinks companies have used thermochromic ink in their labels, to show when the ideal chilled temperature has been reached.

Other possible Smart Technologies

Micro-encapsulation

Micro-encapsulation is a process of applying microscopic capsules to fibres or fabrics. The capsules can contain vitamins, therapeutic oils, moisturisers, antiseptics and anti-bacterial chemicals, to name a few. These substances are released through friction, usually when in contact with the skin. Micro-encapsulated fabrics have many potential uses, all with specific advantages. For example:

• Medical textiles: Antiseptics embedded on dressings delivered directly to the wound, aiding the healing process and with a

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potential reduction in infection. Dressings may need to be changed less often.

• Sportswear: Micro-encapsulated with chemicals to repel odour and prevent fungal infections.

• Childrenswear or for people with sensitive skin: Encapsulated with moisturisers and oils to soothe and heal.

• Household textiles: Lavender and camomile are known for their soothing properties. They can now be encapsulated into bedlinen to aid relaxation.

Biomimetics

Biomimicry is when the inspiration for new fabrics comes from the natural world. These smart technical fabrics mimic different situations found in nature. Fastskin®, developed by Speedo for performance-enhancing s w i m w e a r, i s a n e x a m p l e o f b i o m i m i c r y . I t m i m i c sa shark’s natural sandpaper-like skin so reducing drag in the water. Such was its success that it was banned from competitive swimming in 2009 for giving swimmers an unfair advantage!

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