A shape-memory alloy (SMA) like Nitinol is able to 'remember' its original shape because:

It stores mechanical energy like a spring and releases it when heated A temperature-driven phase transformation in its crystal structure allows it to recover its pre-programmed shape when heated It absorbs water on cooling, which swells the metal back to its original shape An internal computer chip monitors deformation and activates micro-actuators

Which medical application uses Nitinol shape-memory alloy?

X-ray machine housings that change shape to accommodate different body sizes Coronary stents that self-expand to their full diameter once deployed inside a blood vessel Biodegradable sutures that dissolve after the wound heals Thermometers that change colour when body temperature rises above 38°C

A piezoelectric material generates an electric voltage when mechanically squeezed. This effect is used in:

Permanent magnets, electrical motors, and transformers Gas-lighter igniters, sonar transducers, and vibration sensors Solar panels that convert sunlight into electrical current Thermal insulation in spacecraft where heat must not conduct to structure

The converse piezoelectric effect means that applying a voltage to a piezoelectric material causes it to:

Heat up and emit infrared radiation Become magnetic and attract ferrous particles Deform mechanically — it changes shape or vibrates Change colour proportionally to the applied voltage

Why is biocompatibility the most critical property for a material used in a hip implant?

The implant must be visible on MRI scans so surgeons can monitor it The implant must not trigger an immune response, cause toxicity, or degrade harmfully inside the body The implant must conduct electricity to stimulate bone regrowth The implant must be transparent so internal tissues remain visible

Hydroxyapatite is used as a coating on bone implants because:

It is extremely hard and prevents the implant from wearing at the joint surface It is radioactive and sterilises the surrounding tissue to prevent infection It has the same mineral composition as natural bone, encouraging bone cells to grow onto the implant surface It melts at body temperature, sealing gaps between implant and bone

Polylactic acid (PLA) is described as a biodegradable polymer. What makes PLA sustainable compared with conventional plastics like polyethylene?

PLA is stronger than polyethylene so products last longer before disposal PLA is made from renewable plant starch and breaks down into harmless lactic acid under composting conditions PLA requires less energy to process because it is already in liquid form PLA is transparent, reducing the need for dyes and colourants

Embodied energy of a material refers to:

The kinetic energy stored in the material when it is moving at high speed The total energy consumed in extracting, processing, and manufacturing the material into a finished product The thermal energy released when the material is burned The electrical energy the material can store before breakdown

A lifecycle assessment (LCA) of a product evaluates environmental impact:

Only during the manufacturing phase when pollution is highest Only at end of life when the product is disposed of From raw material extraction through manufacturing, use, and end-of-life disposal or recycling Only during product use, since that is when most energy is consumed

The circular economy model differs from the traditional 'take-make-dispose' model because it aims to:

Produce goods faster and cheaper than existing methods Keep materials in use as long as possible through reuse, remanufacturing, and recycling, eliminating waste Eliminate all use of non-renewable materials within ten years Transfer manufacturing from high-income to low-income countries to reduce costs

When selecting a material for a product intended to be recycled, which property is most important from a circular economy perspective?

High strength so the product never needs replacing Low cost so it is economical to throw away after one use Ease of separation from other materials and the ability to be reprocessed with minimal quality loss Bright colour so it is easy to find in landfill

Smart materials are defined as materials that:

Contain embedded microprocessors that control their mechanical behaviour Are produced using artificial intelligence to optimise their crystal structure Respond to changes in their environment (temperature, stress, electrical field) with a useful, predictable change in their properties Are biological materials harvested from living organisms