Thinking with your feet
Nonwovens are employed in many components going into modern footwear, especially in today’s sports and training shoes.
Perhaps their longest established use has been in conventional, heavily-impregnated cellulose-based insoles, historically for leather and then plastic shoes. These were known as ‘Strobel insoles’ after the technique for stitching them to the uppers and linings of shoes, which provided much higher flexibility and strength than other construction methods.
The UK company Texon is credited with introducing the first needlepunched nonwoven insole material back in the 1970s and such products quickly became the industry standard.
Alternatives to the traditional cellulose insole began to emerge in the 1990s, as footwear to a large degree moved away from leather and rigid plastic to more conformable and casual footwear.
Products such as Freudenberg’s Vildona Strobel, based on spunbonded polyester nonwovens, were extremely easy to process using the Strobel stitching method and at the same time, stronger and lighter.
With the introduction of the REACH chemical regulations in the European Union in 2007, footwear insoles had to become completely free of all chemical binders, which led to the introduction of products such as Freudenberg’s Vildona BFS (binder free solution) series.
In addition to being free of all chemical binders, these insoles require significantly lower consumption of raw materials and energy in their manufacture, are 80% based on recycled polyester and 30% lighter than cellulose-based alternatives.
A most recent development from Freudenberg is the Vildona Airliner 2.0 insole technology, which is based on a spunlaced nonwoven substrate in which a superabsorbent polymer is anchored by a chemical reaction process. As such, it offers new levels of breathability for waterproof applications in both shoes and leather goods.
This is clever technology, but insoles in 2015 can be very clever indeed and do much more than simply allow for comfortable walking and weather protection – such as simultaneously keeping the feet warm and counting your calories.
Digitsole, a company based in Nancy, France, has this year started shipping a new generation of device-connected, heated insoles.
The Digitsole connects to a smart device allowing the temperature of the insoles to be adjusted. At the same time it can provide information on steps taken and calories burned via a dedicated IOS and Android app. As a result of the sensor system in the insole, tracking is said to be much more precise and efficient than with wristbands and other products currently on the market.
The insole fits into most types of shoes and is very lightweight while being simple to set up and use.
The award-winning OpenGo Therapist insole developed by Munich-based Moticon, meanwhile, is equipped with some 13 capacitive pressure sensors as well as additional sensors for measuring 3D acceleration and temperature.
The sensors are able to measure weight distribution and motion, to provide data for gait correction and training and prevent overloading on one leg or the other.
In sports analysis, the data can be used to provide useful guidance on an athlete’s distribution of pressure, tread and acceleration, in order to adapt training programmes to make them most effective.
In healthcare, the product is being used to study impact analysis after leg surgery and to correct the activity of those with walking and posture problems. Measuring a patient’s plantar distribution of pressure is already standard in orthopaedic care, in addition to in musculoskeletal rehabilitation programmes.
Inappropriate biomechanical stress after injuries or surgery can be recorded with the OpenGo sensor insole in a simple, reliable manner, and convalescence can be optimised significantly.
The sensor insole is completely wireless and can be used without any additional devices, while being extremely thin and comfortable for the wearer.
Moticon is currently working with the University of Tübingen in a €265,000 SME project, financed by the German Federal Ministry for Economic Affairs and Energy, to develop and evaluate a full analysis and feedback system. This will analyse movement patterns including sensor insole pressure distribution, rolling behaviour, axial leg strain to provide feedback and assistance to patients in recovery programmes.
Some 10-20% of fracture patients suffer from complications after surgery, either for biological reasons – such as inflammation of fractures or tissues – or biomechanical reasons such as the breaking or misalignment of plates and screws. Based on individual measurements, parameters and reference statistics, it is hoped the system will allow the number of such complications to be reduced in the future.
Taking things even a stage further, Wiivv Wearables, headquartered in Vancouver, Canada, has received venture capital backing from investors, including Evonik, as it attempts to become one of the first companies to apply 3D printing to the individualised mass production of insoles.
In Autumn 2015, Wiivv plans to use 3D printing to produce biomechanically-optimised footwear insoles adapted to the specific needs of individual customers.
The start-up company also plans to integrate electronic sensors into the insoles to allow dynamic data to be continuously recorded. This will enable the optimisation of movement sequences and also produce movement profiles that, for example, can measure and predict the degree of fatigue of industrial workers.
3D printing has so far been used primarily for production of prototypes and in small production runs.
For its production, Wiivv is employing polyamide 12 from Evonik in an SLS (selective laser sintering) 3D printing process. Large production runs are made possible by special software which the company has developed in collaboration with biomechanics researchers. Using photographs, the software translates the individual properties of a foot into the three-dimensional form of biomechanically-optimised insoles and transforms it into printing data that the 3D printer can immediately process. Wiivv currently manufactures these insoles at its production and R&D lab in San Diego, California.
The Wiivv process is said to reduce the design and development time of printable 3D models from several hours to seconds. Only three photos taken by the customer on a mobile phone are needed to calculate the printing data. A further advantage is that for fabrication of individual consumer products, the start-up can use an automated 3D printing process instead of the conventional, extremely labour-intensive, manual method.
The current global market volume for insoles is estimated to be worth around €4 billion, with annual growth of 4-5% which promises interesting growth opportunities for the further expansion of nonwovens in the field.
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