• ExpHand Prosthetics

4 Ingredients for the Perfect Prosthetic Arm

Updated: Aug 23, 2021

ExpHand prosthesis holds the hand

With increasingly more prosthetics companies trying to convince customers of their revolutionary devices, parents of children with limb differences may find themselves more lost than ever! After all, how can a piece of plastic or metal replace a human hand?

In this article, we bring you behind-the-scenes of what goes into making a prosthetic arm for children. From how we introduce motor functions in the arm to how we ensure practicality in a bunch of situations, here are 4 elements that make the ExpHand suitable for your child's needs.

1. Elastics and strings take over muscle and tendon activity

In theory, replicating muscle and tendon signals seems like a tough mission. But if we look at them purely from a physics point of view, we realise that they are merely elastic strings that move various body parts.

So elastics and strings allowed us to copy muscle and tendon activity in the hand, as the prosthetic fingers grip around objects and then pull back to their natural open position. By adjusting the elasticity of the strings in our prosthetics, we can control the force needed to move the fingers to the desired level.

2. Pulleys make it easy to move your fingers

There is one issue though! Just adjusting the elasticity of the strings is not enough to make the ExpHand as practical as we would like. This is why we added a pulley system - yes, the same one from your year 7 physics class - to further decrease the force required to move the fingers.

3. Straps ensure that the prosthesis is easy to use

One of our main goals, when we designed the ExpHand, was to create as much leverage as possible to make the prosthetic a breeze to use. By rule of thumb, the less leverage there is, the harder it is to make something move.

Our solution was to use multiple straps below the elbow which ensure that we are pulling from as far away from the elbow as possible. The mechanism gave the ExpHand the optimal leverage for little children to handle with ease.

4. Materials suitable for any environment

Our skin is not only our biggest organ but an engineering miracle only mother nature could create. Just think about it: the skin allows us to connect with and learn about the surrounding environment, it is strong enough to withstand most weather conditions, and continuously repairs and regenerates itself. How could an artificial material begin to replicate all these functions?

When they are young, children want to touch, pick-up and play with as many things as possible. Since prosthetics are used in lots of different situations and conditions, we needed to find a durable, 3D-printable, and nice-to-the-touch material.

PLA is a plastic that meets all of the above criteria and more. Whether it's hot or cold, wet or dry, prosthetics made of PLA stand the test of time. The fact that the material is widely available allows us to keep our production costs to a minimum in order to make the ExpHand accessible to everyone, regardless of income. It is also biodegradable, meaning that old prosthetics can and will be recycled or repurposed.

These 4 ingredients make the biggest difference when it comes to integrating a prosthetic device into children's daily lives. True, there is nothing revolutionary about elastic bands and pulleys but their use in prosthetic arms is life-changing.

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