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Printing fantastic foot orthoses

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Mart, Dec 4, 2012.

  1. Mart

    Mart Well-Known Member


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    This thread is somewhat wacky but has a serious element; I confesss to being guilty of Fantasizing about foot orthoses.

    Simon Spooner speculated within a great article “Foot orthoses” published recently in Foot & Ankle Specialist

    “The use of direct milling and 3D printing makes this process much easier. Combining this with finite element modeling allows the manner in which the orthoses deforms under load and thus the reaction forces at the foot–orthosis interface to be better controlled for during the design process and the orthoses to effectively be “calibrated” for the individual in terms of its load/ deformation characteristics”

    As a holy grail for fabrication I would definitely follow any path leading towards this.

    However there remains a problem. Even if material characteristics can be “designed” (to fit individual need), the individual’s need remains indeterminate initially because the ZOOS (read article if this is unclear) are only likely to be discovered empirically. This is in part because parameters describing the effect of the environment which the body functions within and the physiological response to stress cannot be usefully predicted to allow a model to be created around which calibration is possible. I would speculate also that trying to work within a range of values which might be calculated for a specific population segment would be too wide to model with sufficient precision to predict an individual prescription.

    Simon also mentioned

    “Within the next few decades, we may even see the use of magneto-rheological fluids controlled by a microprocessor that is capable of managing the foot orthoses load/deformation characteristics on a step by- step basis based on input data obtained from force measuring transducers at the base of the foot orthoses”.

    I think that this would add useful information but perhaps even with this level of sophistication, empirical iterative testing may be needed to “tune” a foot orthoses optimally.

    Also implied was that foot orthoses may be best used if its effect is reduced with time to allow incremental beneficially increased stress to the injured structure(s) after sufficiently healed.

    If this is true then rather than attempt a precise prescription from outset, perhaps visionary ideas for foot orthoses design might be best directed towards allowing precise incremental adjustment based on empirical findings.

    As Kevin Kirby mentioned, this is currently done, rather crudely but somewhat effectively simply by substituting materials with different properties and modifying contours and posts to usefully influence amount and position of ground reaction forces as part of foot orthoses design.

    Since this thread is speculative in nature I am curious to learn if anyone has thought about ways to exploit the internal geometric structure of solid cellular materials in a way that allows their stiffness to be “adjustable”?

    As 3D printing technology develops, fabrication resolution may reach a point where it may be possible to start to design cellular materials from ABS or that other layering technology develops allowing different materials to be used.

    If this is true I could envisage being able to tune material stiffness by altering angulations, thickness and density of cell walls in predicable ways. A usefully adjustable material would allow its properties to be influenced and memorized by some external force.

    This would likely need to occur at a molecular level.

    Just for fun (or fantastically the start of a nice little earner) it occurred to me that this may be possible by impregnating the ABS material used for printing with magnetically sensitive metallic particles.

    The foot orthoses is then printed with ABS using a cellular structure which can be modified by applying a pulsed magnetic field. This would heat the material according to frequency of pulse (friction from vibrating particles) allowing bending and altering the position of cellular structure by applying magnetic force vectors strategically.

    Anyone up for testing this idea as an exercise of informed imagination to the point where it might be taking seriously or should we stick to using our grinders for the time being?

    Cheers

    Martin

    Foot and Ankle Clinic
    1365 Grant Ave.
    Winnipeg Manitoba R3M 1Z8
    Phone [204] 837 FOOT (3668)
    Fax [204] 774 9918
    www.winnipegfootclinic.com
     
  2. You got it, Martin. You got it. Note the term "to be better controlled for" as opposed to: "be controlled". Controlled, or graded loading as the ZOOS expands?- this is where I think non-Newtonian polymers come in. However, I'm tired now and ready for bed, I'll come back to this thread if it develops.
     
  3. Admin2

    Admin2 Administrator Staff Member

  4. Mart

    Mart Well-Known Member

    You bet; you guys have not just published a definitive snapshot about what is understood pertaining to thinking about, using and designing foot orthoses but also usefully addressed educational and political issues around the subject. I would encourage anyone who has not read this paper to do so, it is essential reading.

    http://fas.sagepub.com/content/5/5/334.full.pdf html

    Simon please could you post an example of a non-Newtonian polymer which you see as useful in foot orthoses design? I tried using cornstarch and water but it just stuck to my socks.

    I have been trying to find out more about the Glasgow Caledonian University foot orthoses printing project but the URL link seems flaky at the moment

    So before getting to carried away in fantasy land has anyone else actually printed an ABS foot orthoses? If so please comment on what was used and discovered.

    Cheers

    Martin

    Foot and Ankle Clinic
    1365 Grant Ave.
    Winnipeg Manitoba R3M 1Z8
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  5. Martin,

    Thank you for your kind words regarding our paper. In 2007 I had some test foot orthoses printed by various commercial 3D printers. I've attached a couple of pictures of one of these printed in ABS plastic. The area which is thinned beneath the first ray segment was 1mm thick. ABS is brittle and as you can see, a section of the device cracked away (the crack propagated along a print line) so that now it looks like a first ray cut-away. The other areas of the shell were 3-4mm thick which creates a very rigid device. I do not think that ABS is the best material to print foot orthoses though.

    I met recently with a commercial UK orthotics company who are involved in the Glasgow project. They are using a different material in conjunction with selective laser sintering. I am not at liberty to divulge any further information. Suffice to say, their material looks to be an ideal candidate for foot orthoses construction in terms of its material properties.

    In terms of non-Newtonian polymers, it depends whether you want something which is shear thickening (dilatant) or shear-thinning. For a dilatant, I've experimented with space putty and D3o http://en.wikipedia.org/wiki/D3o . I've attached a couple of pictures of a test device which employed space-putty as a dilatant, encapsulated within the rearfoot post. For a shear-thinning I would suggest syrup, since you're in Canada, I guess it would have to be maple syrup, but you will need to find a way to encapsulate it- this is where I think those silicone-gel filled insoles might come in, replace the silicone with a shear-thinning liquid. Then place the liquid bag between the top-cover and and orthotic shell.

    Kevin and I discussed these concepts some years ago, as I recall we couldn't decide on whether a shear-thinnning or a shear-thickening approach was the way forward. I guess it depends what you are trying to achieve.

    I also think the approach described here has great potential: http://christophbehlingdesign.com/case-studies/reebok-1/
     

    Attached Files:

  6. Mart

    Mart Well-Known Member

    I agree that the Reecharge PS idea is fascinating and ahead of anything I had regarded as fantastic in my initial post. I get the impression that this remains a work in progress; do you know if they are in production or even available for scrutiny as prototypes?

    Cheers

    Martin

    Foot and Ankle Clinic
    1365 Grant Ave.
    Winnipeg Manitoba R3M 1Z8
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  7. As far as i am aware, it is an exercise in design.
     
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