Steve Caplin is puzzled by Jack Dorsey's new messaging app – with a range of just 300 metres. A clip on your ear can improve your fitness. Tiny, edible micro lasers can help with food safety. With bricklayers in short supply, robots could be pressed into service. A 3D-printed house made from soil, lime and fibres could be returned to the earth when no longer needed. Cigarette butts can be used to strength road surfaces. And AI can help interpret incomplete Roman inscriptions.

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