January 27, 2020 by Luke James
University of Lincoln researchers in the UK have developed a prototype for a 3D printed and sensor-operated prosthetic arm that can be produced quickly and cheaply.
SIMPA, the so-called ‘Soft-Grasp Infant Myoelectric Prosthetic Arm, was created by the researchers using 3D scanning, additive manufacturing, and an armband based Surface Electromyography (sEMG) system.
As reported in IEEE Robotics and Automation Letters, the prosthetic arm has been designed for children under two years old because traditional active prosthetics are time-consuming to construct and are typically heavy, rendering them unsuitable for use in young toddlers and infants.
Although myoelectric prostheses, those that are muscle-stimulated, are widely used by adults, and SIMPA is the first device of its kind to bring the same technology into smaller dimensions so that it can be used by young children and toddlers.
Producing prosthetics for children has long been viewed as problematic because a child’s fast growth rate means that devices would need to be routinely replaced. This is not ideal given that prosthetics are typically costly to produce, and they also take time to build. However, by using 3D printing, the Lincoln research team is able to produce SIMPA both more cheaply and quickly than conventional prosthetics, and they can be custom made to each individual child’s required size without the need to use plaster casting techniques.
Furthermore, the early fitting of a functional myoelectric prosthetic device in children has been shown to reduce the risk of rejection. This is something else made possible with the use of the SIMPA device.
Most of the SIMPA prosthetic is 3D printed in ABS using the Ultimaker S5. The dimensions for the prototype arm have been based on data from a volunteer, a 4-year-old male. A 3D scan of the stump used for socket modeling was also taken from this individual. This eliminates the need for traditional plaster casting techniques, a time-consuming and uncomfortable process for prosthetic recipients.
When the body of the prosthetic is printed, soft-grip fingers are integrated and are operated with an armband fitted with sensors. These sensors detect the natural electrical signals produced by muscles.
After initial testing rounds, the Lincoln researchers discovered that their SIMPA prosthetic device can allow a toddler to grip and lift various small objects in an identical fashion to how they would with a natural arm.
Furthermore, in some cases where children with upper-limb amputation use prosthetic devices, the child may develop their own methods of grasping and holding objects which can hinder motor neural skills. The research team plans to integrate algorithm training in the device to help avoid this and better develop these motor skills. This would utilize specially designed games to engage with the toddlers and help the system optimize and attune itself to the ‘grab’ signals from the armband.
Dr. Khaled Goher, Ph.D., lead engineer on the project, said, “Our proposed system would utilize a seven-channel pediatric armband with motion sensors allowing infants to benefit from and become familiar with active prosthetics, with evidence showing that the earlier the exposure, the more likely for the prosthetics to be accepted and used throughout life. "So far, the device has been tested for grasp force and effectiveness using a range of everyday objects including toys, bottles and building blocks but the next stage of the project is to test the prototype design on toddlers."
