3D printed lasts and insoles
Some people are unfortunate enough to be either born with deformed feet or to acquire them through illness or injury and therefore need special footwear.
The orthopaedic shoemaker tasked with making them faces a major problem from the outset as no two customers are ever alike. It is not just a case of different sizes between the right foot and the left, as one may be normal and the other not; alternatively, they may both be of a totally different shape. This clearly leads to all manner of manufacturing problems and it is for this reason that orthopaedic footwear is frequently so complex and always expensive.
Custom-made shoes of this nature are special. They are the therapy of choice for patients whose condition cannot be treated effectively with ready-made shoes, alterations or orthoses. With a severely deformed foot, a custom-made shoe is the only real choice available to assure a proper fit, protection from irritation and the hope of remaining ambulatory. They can also be produced with an almost unlimited list of special accommodations such as built-in rocker bottoms, wedging, heel-pitch and toe shapes. To meet such a wide range of therapeutic requirements and cosmetic needs, special lasts have to be produced for each individual patient.
Time consuming
Orthopaedic shoemakers usually need weeks to make custom-fit shoes for their patients with much of the time spent in producing the necessary lasts. This has traditionally involved a great deal of time and skill which inevitably costs money.
The advent of foot scanners followed by 3D printing using advanced polymers has brought about radical changes that are helping to reduce both the time and increases costs involved in producing orthopaedic footwear. In the forefront of this trend are German materials manufacturer Covestro and orthopaedic services provider GeBioM mbH and its subsidiary go-tec GmbH, also from Germany, who have together made it possible to 3D print this type of last.
Using traditional methods, an orthopaedic last shaped to suit the individual requirements of a particular patient, is produced manually in a time-consuming process. Once it has been finished, the fit of the last is controlled by a so called trial shoe. This is a flexible, transparent foil, which gives the orthopaedic shoemaker the necessary feedback he needs to carry out his work. This is why it has traditionally taken so long and cost so much to produce a pair of orthopaedic lasts.
All this has changed with the introduction of 3D printing. Now the foot can be scanned, the last constructed by digital means within minutes rather than hours and then, as a real game changer, the trial shoe is printed to control the work. If the trial shoe does not fit properly, the last can be adjusted digitally until it does. In this way, the shoemaker gets a digitally created 3D printed last on which he can produce his shoes. All the tedious hand measuring and shaping has been removed so both time and cost are drastically reduced and output is increased.
A successful marriage
The key to this development has been the marriage of go-tec’s specialisation in software solutions and technology with Covestro’s wide experience in developing industrial 3D printing materials within its Addigy range of polymers. The challenge was to find a suitable material for 3D printing of plastic shoe lasts. The main problem encountered here was in creating a material that could meet the demanding requirements needed in order to make it similar to wood, the material usually used. It also had to cope with the heavy wear and tear the shoe last would be subjected to in the shoemaker’s workshop.
The solution was a highly versatile custom-made Addigy TPU filament based on the company’s polymer that provided both transparency and high elongation at break. Furthermore, the material proved tough enough to withstand nails, hot pressing and grinding in a workshop environment. This has enabled go-tec to print a bendable, transparent test shoe that can be put on a patient’s foot in less than two hours after measuring and which can then be used for printing a final customised shoe last thus shortening the lead time for orthopaedic shoes by two to three weeks.
3D printed insoles
Any orthopaedic footwear is expensive to produce and the worse the deformity of the patient’s feet, the more expensive it can become. However, less severe conditions can often be accommodated by well-designed comfort shoes, factory made on a deeper last that offers more toe room, a choice of width fittings and removable insert insole options. There can nevertheless still be extra work involved in producing these inserts to suit individual feet. They have traditionally been made by hand from cork because it is extremely light, offers excellent shock-absorption and cushioning, and is also easy to work. Today, they are increasingly being produced using polyurethane-based polymers and 3D printing where once again Covestro, GeBioM and go-tec are playing an important role.
Using their system, the patient visits an orthopaedic workshop where their feet are scanned with any one of go-tec’s scanning devices in either 2D or 3D to find out where exactly the pain is located. An orthopaedic specialist then constructs the individual insole based on the scan in the go-tec CAD software. He or she then defines the stiffness of the material needed for each point of the insole, so that the patient’s problem is not only solved by the shape of the insole, but also by the choice of a material with the right degree of softness. Based on these specifications, the insole is printed on a special 3D printer, which is able to print flexible Addigy FPU 79A TPU filament to produce a finished pair of Cubix insoles that fit into the patient’s shoes (Cubix is a component of go-tec’s CAD application that enables the individual setting of degrees of hardness).
Further benefits
Lukas Breuers, 3D printing expert at Covestro, says, "Our new TPU plastic and a printer developed specifically for this application make it possible to print very soft structures. The material and printer were harmonised during development to achieve a perfect result. With the help of the automated software solution, soft and hard structures can be combined in a shoe insole, achieving a level of customisation that was previously virtually impossible." The TPU used also meets the requirements for medical devices with regard to cytotoxicity and skin sensitisation in accordance with DIN EN ISO 10993-5 and 10993-10 standards.
In addition to functionality, the development of the material also focused on its ecological footprint as Marcel Domenghino, managing director of GeBioM, points out: "It was important to us that the new solution also allows for improved sustainability. Currently, the production of insoles also generates large amounts of waste. Moreover, the insoles themselves are hazardous waste after use. With 3D printing, we now enable our customers to produce in a waste-free manner by using only the material that is needed for the insoles." Covestro is in fact currently working on a recyclable TPU for this application thus creating an essentially circular process. For instance, the spools on which the filament is wound are already reused.
3D printing and TPU materials offer new possibilities for orthopaedic footwear.
All credits: COVESTRO
