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Materials used for additive technology/printing of foot orthotics

Discussion in 'General Issues and Discussion Forum' started by Craig Payne, Jun 4, 2015.

  1. Craig Payne

    Craig Payne Moderator

    Articles:
    6

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    Can anyone offer any insight into the quality of the materials being used. What about durability etc?

    This comment piqued my interest:
    http://www.oandp.com/articles/NEWS_2015-06-03_02.asp
     
  2. Admin2

    Admin2 Administrator Staff Member

  3. Craig,
    When I first started looking at 3D printing, about 7 years ago I had a number of foot orthoses manufactured using the then high-end printers. One of the issues was fracture along "cleavage" planes. If you look at the image I've attached you can see how the orthotic snapped off in an almost perfect straight line. I'd had the first ray section manufactured at about 1.5mm thickness if memory serves, you can still see part of this, yet it fractured diagonally along the print line.

    I think there may be a difference between fused deposition models (FDM) and selective laser sintered models, the orthoses I had manufactured were FDM

    Materials have come on since then, this one looks interesting:

    http://3dprint.com/22255/3d-printed-insoles-gyrobot/
     

    Attached Files:

  4. Lawrence Bevan

    Lawrence Bevan Active Member

    Hi

    I think this is a really key issue. Ive been looking again at this technology - I know that commercially/large scale its too slow currently but purely from a personal/small scale production stand point it could work.

    However there's little point if the materials dont work or dont last.

    I know of one commercial outlet - http://www.podfo.com/products-1/3d-printed-custom-insole

    They presumably feel confident in their materials. They refer to testing etc.

    I wonder if anyone has spoken to them or whether they themselves have anything to say??

    L
     
  5. Lawrence, I was invited to take a look around their production facility a few years ago. They use selective laser sintering and a proprietary material. The devices I saw had similar characteristics to an " everflex" type shell, if you are familiar with that. Dave Eadley is a member here so perhaps he will comment.
     
  6. blinda

    blinda MVP

    My step-son has just finished his degree in Mechanical Engineering at Plymouth uni - his dissertation was in comparing material characteristics of direct milled parts against printed...(predicted a 2:1, not that I`m proud of him or anything). He`s home tomorrow (and looking for work), I`ll ask him for his tuppenceworth on the article.

    Bel
     
  7. Lawrence Bevan

    Lawrence Bevan Active Member

    Hi Simon and Bel

    Si - thats interesting, so you mean the material was there own product ? I know what you mean with Everflex, flex with quick recoil type feel?

    Bel- thath would be awesome thanks!

    Wonder what Delcam recommend in terms of printer and material??


    L
     
  8. Lawrence Bevan

    Lawrence Bevan Active Member

  9. I mean, they weren't going to tell me nor anyone else what it is!. Since they use SLS it starts as a powder rather than a filament as you would use in FDM. Of the materials I've seen, theirs is by far the best for foot orthosis manufacture in my opinion.

    Biggest problem with 3D printed foot orthoses is that they are all still making the same old foot orthoses but with a different machine- time to think outside the box and re-imagine.
     
  10. As for now, I think the major limitation with 3D printing of foot orthoses is that it really does not offer any advantage in regards to lab production speed of orthoses and seems to be limited in the materials that may be used to produce a durable foot orthosis. So far, I don't see any practical use of this type of orthosis for my practice.

    As far as "thinking outside the box", I think Simon is correct. However, many things that couldn't previously have been done with thermoformed orthoses, such as adding plantar orthosis shell "reinforcing strips" or "grooves" to change the stiffness of the device is already being done by labs that mill orthoses. Possibly this will change over time.

    I believe that the biggest gain in the therapeutic efficacy of foot orthoses will not be additive printing of orthoses, but will be in better determining how to integrate various materials of different stiffnesses, thicknesses and durometers into the exact locations within the foot orthosis that will best relieve tissue stress and improve foot orthosis function for the patient.

    In other words, we don't really need a new way to make orthoses. Rather, we need a better way to determine the optimum geometry, stiffness and frictional characteristics of all parts of foot orthoses to best heal foot and lower extremity injuries, improve gait function and improve the comfort, shoe fit and durability of the orthosis, without making the orthosis cost-prohibitive.

    That's my two cents.:drinks
     
  11. Generally I agree, since this is pretty much all we can do with foot orthoses. However, a shell with a "block" under the rearfoot is really just a reflection of the technology available to John Weed and Tom Sgarlato when they developed the "rearfoot post"; I think there is more that could be done here, maybe along the lines of Tom McMahon's thinking.:drinks
     
  12. eanna

    eanna Member

    Hi guys , take a look at Joseph DeSimone :What if 3D printing were 100x faster ? (Carbon 3D) on TED talks . An awesome talk and live CLIP (continuous liquid interface production) demo on stage . As he says "some mushrooms grow faster than producing some 3D print parts " . What if we could speed things up a 100x and use multiple new materials with no weak points ? Could this tech allow us to produce an orthotic with multiple interfaced materials ? How cool would that be ?
    Cheers Eanna
     
  13. Phil Wells

    Phil Wells Active Member

    Hi all

    I must agree with Simon that it is probably time to start thinking out side the box.
    Maybe printing 'posting' that fits onto the sole of the shoe including flares - heel and forefoot, SACH mods, heel stiffeners etc as well as the contours of a good insole.
    The 3D printing will allow for all facets of a shape to be designed and we can really get creative.

    Phil
     
  14. Boots n all

    Boots n all Well-Known Member

    Phil a heel stiffener is made in about 20 seconds using current methods and the materials are very cheap.
    A flare, again it is cheap to make with existing methods and materials.

    It is the art of attachment and blending these items to the shoe that is the real time consuming job.

    3D printing is of real value when we print otherwise time consuming or technically complex items, not the basic.
     
  15. Lawrence Bevan

    Lawrence Bevan Active Member

    Aren't we putting the cart before the horse? To say the biggest problem is that 3D printing is technology is making the same old foot orthoses isn't quite true - its not the printing technology its the designer of the orthotic you can blame for that!

    The lack of radical design does not negate 3D printing - I think this is a straw man argument Dr S :)

    As far as I can see if I wanted to have a cool scanner linked to a cool desktop printer and do in-house manufacture and gain market share as a result, I can. The key question is not how radical will my design be (initially) but will the material function like good old fashion polyprop?

    It seem like the answers is "maybe, dunno".
     
  16. jlonghurst

    jlonghurst Welcome New Poster

    Hello all. I'm the step-son who has just finished at Plymouth University. This is my first time posting here so I apologise for any formatting errors or breaches of forum etiquette. I also sincerely apologise for the wall of text - it isn't a cut and dry subject unfortunately.

    Starting at this article:

    and

    The DARPA article is a little skewed in my opinion (famous last words). It focuses on processes that utilise a powder based material - most likely SLS and DMLS. The US navy is in the process of trialling RP technologies (rapid prototyping - 3D printing is a bit of a misnomer although applicable to one type of technology) on some of their ships as a method of producing replacement parts. The quote that was pointed out:

    Is only representative of a portion of RP processes. As people have outlined, there are others - FDM, SLA, SLS DMLS, SGC, 3DP (Fused Deposition Modelling, Selective Laser Sintering, Stereo-lithography, Direct Metal Laser Sintering, Solid Ground Curing, 3 Dimensional Printing). DMLS and certain SLS processes can be excluded (I'm assuming you don't want to include metals - please correct me if I'm wrong, I don't know there are orthoses where metal is included. Prosthetic limbs are an interesting application, but perhaps not currently viable). If anyone is interested, I found a huge variability in the metal SLS parts with a bronze infusion (very small sample size unfortunately).

    Where Craig and Lawrence address FDM insoles produced 7 years ago and in 2013, the technology has moved on considerably however the process flaws are still there. Key patents expired in/around 2014, therefore products are cheaper and there are far more material options. Delamination between the layers is still the most likely failure method given the environment and orientations of the applied stress against the printed planes in the part. Stress will be applied in all axes so you can't eliminate the delamination through reorientation of the part on the printer bed - although there will most likely be an optimum orientation for part life but it may require supporting materials which would involve some post processing. I can’t see FDM being a particularly effective method of producing orthoses due to this. Another constraining factor is the requirement for thermoset materials. It seems orthoses are sometimes made from EVA - and there is actually a filament that uses EVA; however the process itself is the weakness - not the material. Unfortunately, without testing, this is difficult to verify and is mostly speculation with regards to the process characteristics.

    More recently where Simon posted

    This looks like a fairly promising material. With that being said, my worry would be uneven stretching between the print layers and different parts or the orthosis resulting in tearing/failure and the likely life of the material. This also assumes you want an orthosis the same density. Varying density in a print is possible, but may induce additional stresses and reduce fatigue life. Gradual increases in density may be possible, but I'm not certain. I can't find any studies through google scholar - they seem to only reference an orthodontic archwire from 1987 or a membrane used in the construction industry. If anyone has any experience with them I would be very interested in how they perform.

    SGC is one of the most accurate RP technologies producing plastic parts, however the processing time is excessive and it’s no longer being used (as far as I can tell) so it can be eliminated.

    SLS is a fairly variably technology. The materials are mostly nylon (polyamide) based with additives that can change the material properties of the part. There are several other materials: glass filled polyamide, carbon fibre, polyurethane and other polyamides. I assume with the carbon fibre and the glass filled polyamide there is a material bead that is coated in a thermoplastic. The thermoplastic melts and binds the part into a solid. Using the correct material, I think that SLS is one of the more likely options to producing an orthotic and is what podfo use. Their 'proprietary polymer' is possibly ‘EOS PrimePart® ST PEBA 2301 | TPA’ or a very similar material created out of a blend of polymers (material properties must be similar). It actually specifies footwear components in the material applications (http://eos.materialdatacenter.com/eo/standard/main/ds).
    While SLS machines are only suited for small to medium batch production - this is exactly what is required. A small to medium batch on an SLS machine could possibly produce up to 50 pairs of orthotics - depending on build chamber size and size of the orthoses. However, cost usually scales with build chamber size - as do operating costs. Where podfo have said they used BS 3518_1993 (this is bend testing) and reached 10 million cycles, I would be interested to see what kind of part they tested (standard test specimen or an actual orthotic?), the testing conditions - loads, temperatures, impact shape, cycle times (shorter cycle times would lead to a worse life as there is less time for elastic recovery). How the orthotics performance degrades over its life would also need to be evaluated and is linked into elastic recovery - even if failure occurs at 10 million cycles, what's the point if it no longer performs as intended at 500,000?

    While SLS is a lovely technology, it has several drawbacks. These include cost - the machines can easily run into the $100,000s and the running costs are high - the build chamber has to be heated to high temperatures and they use a fairly powerful laser. They require proprietary materials and often the use of a 3rd party material might void your warranty (this doesn't just apply to SLS), maintenance costs can be high - the laser will only last so long. Some SLS printers require an inert atmosphere (usually nitrogen) but this is more commonly for metals to eliminate oxidation. The cycle times can be long; the build chamber has to be cooled, usually about 24hrs; this can be decreased by having more than one build chamber so other parts can be printed while some are cooling, however this is an additional cost and you aren't shortening the cycle time for a single part - merely increasing machines output over time.

    A method I haven't seen mentioned here is 3DP. An example printer would be the Objet Eden260VS. It has fairly long print times (comparatively) but it is one of the more versatile methods and the accuracy is more than enough. They also offer a version of the printer with a 1000x1000x500mm print bed which is huge (~$600,000 though). With the addition of a topping material, print times could be increased if accuracy was decreased. In theory, it can print multiple material parts and composite materials in a single print (I've never actually seen evidence of this in person, but plenty of pictures). The problems associated with this would be price, maintenance, and proprietary materials. Costs run from about $100,000 if you can find them at all and a resin cartridge which is around $1300 for 3.6kg. As there are multiple materials in one part and flexible materials available, it may be possible to print a complete insole with little to no post processing required. Keep in mind, while buying an actual printer may not be a viable option (they are expensive); there are bureaus out there that can print these parts. If nothing else, it might give an interesting insight as to how they perform versus a standard insole and how they differentiate price wise.

    The thing I’m curious about is how are the CAD files for the milling generated? Is there a piece of software that does it out of a 3D scanner? And how much can you alter the CAD files, if at all? If you were to get something like this available to you in your practices, the custom tailoring of the materials, the CAD files and modifying the design for inserts or different properties (easily possible I would think) it would be down to the person who is running the machine.
    The link that eanna posted regarded CLIP looks fairly interesting. Fastest I’ve ever seen a part built and possibly even faster than some milling techniques. Downsides are material limitations and it is an incredibly new technology utilising the same principle as SLA with modifications to the process. I can’t imagine it being commercially viable for at least another year yet and as with any new technology there will be kinks to work out.

    I think for 3D printing to be viable as an orthotic production method, it needs to have the ability to either change the properties of the part through design alterations (stiffer part, more support, higher one side, inserts etc.) or the capability to produce a part of a quality that is superior to milling. Without some basic testing and differentiation between processes, it’s hard to recommend any particular method. If I were to go out on a limb, I think the processes that could print insoles would be SLS using the correct material and 3DP; both have their advantages and disadvantages. Some basic fatigue testing would likely prove one superior and give an idea on expected life and performance along with tests to monitor degradation over the parts life.

    If people are interested in microstructures and how they can differ between the processes, I can go into what I know and a little about my experience with SLS parts. I didn’t want to add more to what is already a very long post.
    I hope this helps a little, once again, apologies for the length.
     
  17. Craig Payne

    Craig Payne Moderator

    Articles:
    6
    That was my motivation in starting this thread ... we just do not know how the materials function under the foot when load is applied over longer periods of time. We know about polypro etc
     
  18. Phil Wells

    Phil Wells Active Member

    David

    For Uk pods the application of flares etc is not that easy and they are usually sent away to be added - at a significant cost and time.
    As you know shoe mods are patient friendly and highly effective but under utilised here.
    3D printing may not be the solution but we need something better then our existing set up.

    Phil
     
  19. Lawrence, Kevin wrote:
    I replied:

    This is not a straw-man argument, Lawrence. Nor did I ever make an argument to negate 3D printing. However, if you a going to "gain a market share" in providing the same old orthoses, then the question becomes can you do it faster and cheaper using milling with "known" material response- the answer is yes. So we could close the conversation there. However, if we ask the question: is it possible to design foot orthoses which could not be manufactured via milling, then the answer is yes. Up to you what you want the technology to do, but if you "want to gain a market share" while employing 3D printing, you need to do something that the "millers" can't already do faster and cheaper. As I see it, at the moment if you want a traditional foot orthosis, then 3D printing isn't the way to go; but if you want something different, then you might need to think about this technology.
     
  20. Boots n all

    Boots n all Well-Known Member

  21. Lawrence Bevan

    Lawrence Bevan Active Member

    Im going to the Podiatric Sports Medicine Conference on June 19th.

    Martin McGeough of Firefly Orthotic Laboratory is doing a presentation on 3D printing (I think they have been partner's in the http://www.afootprint.eu/ project.

    Anything new to know I can feed back after

    L
     
  22. daveeardley

    daveeardley Member

    We have been using additive manufacturing for foot orthoses for a number of years now. We have found selective laser sintering (SLS) with Nylon to give the best balance of durability and material properties. i.e. it is light for a given stiffness, being much stiffer equivalent polypropylene and typically over 30% lighter than equivalent milled polyprop. Therefore a semi-flexible device will typically be 2.5 mm thick for a person less than 80kg. The material has been independently tested over 10 million cycles at Newcastle University using the British Standard method for fatigue testing (BS 3518_1993) and the final product has been tested in an in-house test for over 3 million cycles with no breakages.

    Most people are familiar with desktop printers using Fused Deposition Modelling (FDM). We have built many devices using this method and are continuing to develop the process for foot orthoses under the ADDfactor project. The ABS and pla materials typically used for prototyping are far too brittle for extended Foot Orthoses use. There are however new materials emerging in this marketplace all the time and we are investigating some more promising materials and how to use them. The problem with FDM of course is the unreliability and quality of the low cost machines and the high material cost for materials for the higher end machines. With SLS the device is supported in the powder, allowing for much greater design subtlety and possibilities for functional integration. Just the ticket for foot orthoses with variable deformation properties.

    Regardless of the process there will some need for post processing and managing this is also important.

    David Eardley
    Peacocks Medical Group/ Podfo
     
    Last edited: Jun 19, 2015
  23. daveeardley

    daveeardley Member

    As regards, the design, IP prevents me from saying too much. But some of the options we offer now able you to select 1st ray, met dome or full arch flexible panels. The future is being able select relevant segments of the device and make them less stiff according to tissue stress modification or to change the line of centre of pressure.

    Two Northern Universities are both doing work at the moment in partnership with us to Optimise this process from pressure mapping and to see changes in Kinematics . Much work to do!
     
  24. blinda

    blinda MVP

    Awarded a 1st Class BSc (Hons) in Mechanical Design & Manufacture...:drinks:drinks:drinks

    Proud.
     
  25. Is it alright to use POP and polyprop for now?
     
  26. I can't afford a pressure plate therefore I'm asking
     
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