3D printed robo-fruit packed with sensors can test for freshness

The freshness of future fruit could soon be fundamentally improved, with the help of a fun and fascinating new development from researchers in Switzerland. They have used 3D printing technology to produce a range of replica fruits, fitted with temperature sensors.  Supermarkets, greengrocers, and other companies that transport and store fruit in large quantities will be able to make use of these robo-fruits, in order to better determine the quality of their produce based on a much more accurate thermal reading than would be possible with other methods.

Currently, the ways used to record the temperature of a large amount of fruit are relatively imprecise, so it is difficult to know for sure how a long journey or a long time in storage might have affected the freshness of a shipment. Sensors fitted on the walls of containers can measure the air temperature, but this isn’t completely reliable as the inside of the fruit could still be too warm. An alternative is to manually poke a thermometer through the skin of a piece of fruit, giving an internal temperature reading. This is hardly ideal either, as it can be incredibly time-consuming and also doesn’t fully account for different pieces of fruit having different temperatures depending on where they are in the container.

A potentially effective solution to this problem has now been found by scientists at the Swiss Federal Laboratories for Materials Science and Technology (Empa). The team in Dubendorf has used 3D printing to simulate the physical characteristics of an average piece of fruit. This allows their ingenious new sensor to behave in exactly the same way that a real piece of fruit would in the same ambient conditions, so it can give precise information about the temperature changes that take place within the fruit.

Their method was to X-ray a quantity of a particular type of fruit, and to then use a computer algorithm to create the average shape and texture of that fruit, based on the X-ray. From this virtual 3D model, a physical replica was printed using a mixture of water, carbohydrates and polystyrene. Using these materials for the 3D print job meant that the flesh of the fruit would be imitated to a high degree of accuracy.

Initial results have been very promising, according to project leader Dr Thijs Defraeye. ''We analysed the sensors in the EMPA refrigeration chamber in detail and all the tests were successful,'' he claims. The aim is to eventually expand the project to create enough 3D printed sensors to cover the full range of different fruits. 'We are developing separate sensors for each type of fruit, and even for different varieties', says Defraeye. So far, separate sensors have been produced for the Braeburn and Jonagold varieties of apple, as well as the classic Cavendish banana, the divisive Kent mango and the humble, timeless orange.

The team at EMPA is currently looking for potential industrial partners to manufacture these sensors on a large scale. Each sensor will be available to purchase for around 50 Swiss Francs ($50).

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