Orthon - Dynamic Insole with Pressure Offloading for Gait Optimization

Summary

ORTHON’s purpose is to create a proof of concept for a dynamic orthotic system capable of treating severe foot conditions that concern painful flat foot and ulcer prone diabetic foot issues. This dynamic orthotic looks like a wearable shoe insert that can detect pressure and/or temperature in order to react with the necessary support for the user’s foot. For such conditions, the current medical orthotic solution is a rigid, static shoe insert originally invented in the 1950s. Meanwhile, the human foot is one of the most dynamic mechanical structures in the body with 33 joints and 26 bones. Although they may be clinically effective, many users find their rigid inserts to be uncomfortable, discontinuing the prescribed use and resulting in surgery.

20% of the world's population have some degree of flat feet, which essentially means that the medial arch in their foot is less than 10mm off the ground during midstance. 7% of those with flat feet experience painful flat feet. Those 7% are what we were concerned about. With painful flat feet, there is overpronation and with overpronation, there are strains in the tendons of the foot. Those strains lead to several sharp pains throughout the foot. While rigid insoles are in the market to prevent the overpronation of the foot, it ends up creating new problems for the wearer, such as a poking sensation that will not go away, and a foot locked in a tense position. That being said, we need an insole that can support the foot in key areas only when needed to prevent both the overpronation of the foot, and the uncomfortable poking sensation.

Diabetic neuropathy affects roughly 50% of diabetic patients, progressively reducing sensation in the lower extremities. Without the ability to perceive localized pressure or pain, patients are prone to developing plantar ulcers, a leading cause of lower-limb amputation. Current insole solutions are static and cannot adapt to dynamic loading conditions during gait. This project investigated the feasibility of a magnetorheological (MR) fluid-based orthotic insole capable of dynamically redistributing plantar pressure in real time, offering a more responsive approach to ulcer prevention for this at-risk population.

Technical Approach/Methodology

For painful flat feet we went with a fully mechanical system that will rely on the body's gait movement and energy. By using the energy applied from the body itself we can have more precise reaction times for the arch plate to be activated. The four stages of the gait we are analyzing are heel strike, midstance, toe-off, and swing. The importance of each of these stages is to define when we want the arch plate to be activated.

With the design, we have a heel plate which initiates a slider-crank mechanism to move forward and push the arch plate up. The arch plate is made of PLA and has slits in its design which allows for it to bend upward when its center is being pushed up. The most important stage of the gait cycle is midstance, since the medial arch would normally be fully collapsed during this time, so that is where our arch support needs to be at its strongest. That being said, the slider crank mechanism will be pushed far enough forward to so that it can be locked in its position which holds the deflection from the arch plate until toe-off. During toe-off, there is another linkage system coming from the forefoot plate to move the slider crank back to where it was which alleviates the arch support, since it is not needed anymore.

In summary, the painful flat feet prevention system, in response to the gait cycle, is designed to have gradual increase in arch plate deflection from heel-strike to midstance, maximum arch plate deflection held from midstance to toe-off, and finally, a deactivated arch support during toe-off, throughout the swing phase, until the heel strikes the ground again. The mechanical system includes the slider-crank linkage system, the toe-off linkage system, arch plate, fore plate, heel plate, and a base plate, all made of PLA. Since we don't want any stakeholders to constantly step on something as hard as PLA, we have a silicone mold which encases the entire mechanical system.

For diabetic neuropathy, the proposed insole integrates two sensing modalities to detect early indicators of ulcer risk: force-sensitive resistors (FSRs) to identify regions of elevated plantar pressure and thermistors to detect localized skin temperature elevation associated with inflammation. These sensors provide the feedback needed to trigger a mechanical response. That response is delivered through magnetorheological fluid, a suspension of iron particles in a carrier oil that reversibly transitions from a liquid to a semi-solid state when exposed to a magnetic field. The fluid is housed in discrete silicone pods embedded throughout the insole. When a high-risk pressure zone is detected, an electromagnet activates, stiffening the fluid in the corresponding pod and redistributing load away from the vulnerable area in real time.

Outcomes

Painful Flat Feet:

The project involves a lot of SolidWorks utilization and reiterations. There were multiple ideas that were built on right away such as an arch plate with slits, and springs between the heel plate and bottom plate. In time, there were multiple actuation forms that were assembled in SolidWorks, 3d printed, and tested. We started with a simple lever between the heel and the arch, and we eventually evolved to a slider-crank mechanism traveling along a U-bar which was held until the forefoot plate collapsed enough to push a linkage against the slider-crank to revert the arch plate back to its initial flat position.

Diabetic Neuropathy:

The project produced research documenting the comparative performance of multiple sealing and manufacturing approaches for MR fluid encapsulation in flexible silicone pods. Bench-level prototypes were fabricated and tested. Sensor calibration and characterization testing was conducted for both the FSR and thermistor arrays to establish reliable detection thresholds. A control system was developed and evaluated to process sensor inputs and trigger the appropriate electromagnet response. Insole thickness was also assessed across manufacturing iterations to ensure the device remained within a clinically viable form.

Overall, both projects involved a lot of research and medical background knowledge from our sponsor Dr. Moamen Elhaddad to create something novel. This is a project that has shown promise for the concept of a dynamic insole as a preventative product from the consequences of painful flat feet and diabetic neuropathy. For example, for both painful flat feet and diabetic neuropathy, we found that silicone would be a great way to contain either MR fluid or a mechanical system. Given the resources, we managed to discover how this concept can be developed further, mainly with a bigger abundance of expensive materials such as MR fluid and dragon skin silicone for a more forgiving test process.

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