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• For sports and physiotherapy alike

Researchers at ETH Zurich, Empa and EPFL are developing a 3D-printed insole with integrated sensors that allows the pressure of the sole to be measured in the shoe and thus during any activity. This helps athletes or patients to determine performance and therapy progress.

In elite sports, fractions of a second sometimes make the difference between victory and defeat. To optimize their performance, athletes use custom-made insoles. But people with musculoskeletal pain also turn to insoles to combat their discomfort.

Before specialists can accurately fit such insoles, they must first create a pressure profile of the feet. To this end, athletes or patients have to walk barefoot over pressure-sensitive mats, where they leave their individual footprints. Based on this pressure profile, orthopaedists then create customised insoles by hand. The problem with this approach is that optimisations and adjustments take time. Another disadvantage is that the pressure-sensitive mats allow measurements only in a confined space, but not during workouts or outdoor activities.

Now an invention by a research team from ETH Zurich, Empa and EPFL could greatly improve things. The researchers used 3D printing to produce a customised insole with integrated pressure sensors that can measure the pressure on the sole of the foot directly in the shoe during various activities.

“You can tell from the pressure patterns detected whether someone is walking, running, climbing stairs, or even carrying a heavy load on their back – in which case the pressure shifts more to the heel,” explains co-project leader Gilberto Siqueira, Senior Assistant at Empa and at ETH Complex Materials Laboratory. This makes tedious mat tests a thing of the past. The invention was recently featured in the journal Scientific Reports.

One device, multiple inks
These insoles aren’t just easy to use, they’re also easy to make. They are produced in just one step – including the integrated sensors and conductors – using a single 3D printer, called an extruder.

For printing, the researchers use various inks developed specifically for this application. As the basis for the insole, the materials scientists use a mixture of silicone and cellulose nanoparticles.
Next, they print the conductors on this first layer using a conductive ink containing silver. They then print the sensors on the conductors in individual places using ink that contains carbon black. The sensors aren’t distributed at random: they are placed exactly where the foot sole pressure is greatest. To protect the sensors and conductors, the researchers coat them with another layer of silicone.

An initial difficulty was to achieve good adhesion between the different material layers. The researchers resolved this by treating the surface of the silicone layers with hot plasma.
As sensors for measuring normal and shear forces, they use piezo components, which convert mechanical pressure into electrical signals. In addition, the researchers have built an interface into the sole for reading out the generated data.

Running data soon to be read out wirelessly
Tests showed the researchers that the additively manufactured insole works well. “So with data analysis, we can actually identify different activities based on which sensors responded and how strong that response was,” Siqueira says.

At the moment, Siqueira and his colleagues still need a cable connection to read out the data; to this end, they have installed a contact on the side of the insole. One of the next development steps, he says, will be to create a wireless connection. “However, reading out the data hasn’t been the main focus of our work so far.”

In the future, 3D-printed insoles with integrated sensors could be used by athletes or in physiotherapy, for example to measure training or therapy progress. Based on such measurement data, training plans can then be adjusted and permanent shoe insoles with different hard and soft zones can be produced using 3D printing.

Although Siqueira believes there is strong market potential for their product, especially in elite sports, his team hasn’t yet taken any steps towards commercialisation.

Researchers from Empa, ETH Zurich and EPFL were involved in the development of the insole. EPFL researcher Danick Briand coordinated the project, and his group supplied the sensors, while the ETH and Empa researchers developed the inks and the printing platform. Also involved in the project were the Lausanne University Hospital (CHUV) and orthopaedics company Numo. The project was funded by the ETH Domain’s Advanced Manufacturing Strategic Focus Areas programme.

• General economic developments are dampening mood in composites industry
• Future expectations are optimistic
• Investment climate has remained stable
• Varying expectations for application industries
• Growth drivers have remained unchanged
• Composites Index is pointing in different directions

This is the 20th time that Composites Germany has identified the latest performance indicators for the fibre-reinforced plastics market. The survey covered all the member companies of the umbrella organisations of Composites Germany: AVK and Composites United, as well as the associated partner VDMA.  

General economic developments are dampening mood in composite industry
Like all industries, the composite industry has been affected by strong negative forces in recent years. The main challenges over the last few years have been the Covid pandemic, a shortage of semiconductors, supply chain problems and a sharp rise in the price of raw materials. Furthermore, there have been numerous isolated effects that added to the pressure on the industry.

The main challenges during the past year were primarily a steep increase in energy and fuel prices and the cost of logistics. In addition, the war in Ukraine put a further strain on supply chains that had already been weakened.

Overall, the stock market prices for both electricity and petroleum products are currently showing a clear downward trend. However, the significantly lower prices have not yet percolated from manufacturers and buyers to the end customer.

The aforementioned effects have further dampened the mood in the composites industry. The index assessing the current general business situation in Germany and Europe has dropped even further than before. However, the assessment of the global situation is somewhat more positive.

Despite this generally negative assessment of the current situation, companies are moving in a somewhat more positive direction in the assessment of their own business situations. The companies that were surveyed rated their own positions more positively than in the last survey.

Future expectations are optimistic
The expectations on future market developments are showing a very positive picture. After a significant drop in the last survey, the indicators for the general business situation are now displaying a clear upward trend again. Moreover, respondents were far more optimistic about their own companies’ future prospects.

Investment climate remaining stable
The investment climate has remained at a stable level. Nearly half of the companies surveyed are planning to employ new staff over the next six months. As before, about 70% of respondents are either considering or planning machine investments. Unlike in the previous survey, this value has remained almost unchanged.

Varying expectations for application industries
The composites market is highly heterogeneous in terms of both materials and applications. In the survey, respondents were asked to assess the market developments of different core areas. Expectations turned out to be extremely diverse.

The most important application segment for composites is the transport sector. The number of new registrations of passenger cars has been declining in recent years. This is where we can see OEMs moving away from volume models and opting for more profitable mid-range and premium segments. In this year’s survey, this shows itself in relatively cautious expectations for this segment.

The currently rather pessimistic outlook for the construction industry is leading companies to expect major slumps in this sector, in particular. The building sector, in particular, often reacts rather slowly to short-term economic fluctuations and has long been relatively robust towards the aforementioned crises. Now, however, it seems that this area, too, is being affected by negative influences.

The pessimistic outlook on the sports and leisure sector can be explained by a rather pessimistic view of consumer behaviour.

Expectations about future market developments, on the other hand, are significantly more positive than the figures presented here might suggest.

Growth drivers still stable
As before, the current survey shows Germany, Europe and Asia as the global regions expected to deliver the most important growth stimuli for the composites segment, with Europe playing a key role for many of the respondents.

Where materials are concerned, we are seeing a continuation of the ongoing paradigm shift. Whereas, in the first 13 surveys, respondents always believed that the composites segment would receive its prevailing growth stimuli from CRP, there is now an almost universal expectation that the most important stimuli will be coming from GRP or from all the materials.

Composites Index points in different directions
Despite the many negative influences that have occurred recently, composites appear to be in good shape for the future. Thanks to excellent market developments in 2021, they have almost reached their pre-pandemic level. The outlook for market developments in 2022 have not been finalised but are showing a less positive trend for last year.

Nevertheless, there are many indications to suggest that the generally positive development of the composite industry over the last few years is set to continue. In the medium term, structural changes in the transport sector will open up opportunities for composites to gain a new foothold in new applications. Major opportunities can be seen in areas of construction and infrastructure. Despite the rather weak market situation, these areas offer enormous opportunities for composites, due to their unique properties which predestine them for long-term use. The main assets of these materials are their durability, their almost maintenance-free use, their potential for use in lightweight construction and their positive impact on sustainability. Furthermore, one major growth driver is likely to be the wind industry, provided that it meets the politically self-imposed targets for the share of renewable energies in power consumption.

Overall, the Composites Index shows a restrained assessment of the current situation, whereas the assessment of the future situation is clearly positive. Respondents are apparently optimistic about the future, reflecting the assessment mentioned above: Composites have been used in industry and in serial production for several decades and, despite numerous challenges, they are set to provide immense potential for exploring new areas of application.

The next Composites Market Survey will be published in July 2023.