The design schematic in the above image is explained below.
Scaffolds and Osseointegrated Prosthetics
Tissue engineering research has not yielded much development with using scaffolds or hydrogels to construct prosthetics. Rather, there has been a greater focus on the recovery of certain parts of the musculoskeletal system rather than applying tissue engineering to artificial devices like prosthetics themselves. (Smith & Grande, 2015).
Using tissue engineering technology in prosthetics could potentially help reduce the cost and time necessary to maintain prosthetics in growing children.
Using scaffolds meant to fit and grow with the residual limb of an amputee at the attachment site of osseointegrated prosthetics could be done to lessen the need to replace prosthetics.
In current prosthetics, metal screws that support the connection between the residual bone and prosthetic have a low biocompatibility, causing infection in half of the patients in one study (Ontario, 2019). Rather than metal connectors, a scaffold using biological materials such as collagen and hydroxyl carbonate apatite would provide the same function while also increasing biocompatibility.
Customizing the size and shape of the scaffold based on measurement taken from the residual limb of the patient would ensure a proper and safe connection to the osseointegrated prosthetic.
In order to ensure that the osseointegrated upper limb prosthetic maintains the health and safety of the child, maintenance of the prosthetic would be done every 5 years, or around the end of the lifespan of an average prosthetic, to ensure that there are no issues.
Use of the Wrist Joint and Terminal Devices
Based on prior technology, both prosthetic wrist joints and the terminal device can be entirely mechanical, meaning that there are no electric parts, or myoelectric, meaning that they use sensors and motors to interpret and recreate nervous system signals within the prosthetic to control it (Arm Dynamics, 2012).
Keeping in mind that the patient is a growing child, the prosthetic will likely need to be replaced every few years due to bodily growth and equipment degradation. This means that the prosthetic should not be mechanically integrated into exposed flesh and bone of the patient, as this could cause fractures (Erwin & Varacallo, 2021).
The prosthetic should be cheap, as it will inevitably be replaced more often in the child’s early growth stages. The child will likely not want to use a prosthetic unless using it is comparable to using their own hand. Their uses for the terminal device are unspecified—it should therefore either adapt to perform many functions with one attachment, or be able to interchange with other attachments easily.
The child’s wrist mechanism should be two different mechanical rotating and locking aluminum disc mechanisms, connected to each other by 3D-printed aluminum, the one by the terminal end of the arm with a fitted hole in the center. Between the two aluminum discs, heavy-duty metal-wrapped wire should be able to push into and clear of the hole. This way, different terminal devices with the same shafted base can be exchanged within the wrist mechanism.
The ability of the wrist to lock would also give the child the option of precise and steady movement at customizable angles that they would not have either without a wrist joint or with only one rotating and locking portion (TRS Prosthetics, 2021).
The most practical terminal device would be entirely mechanical and five-fingered: simple cables within prosthetics like these can simulate movement similar to a hand when portions of the prosthetic are either pulled, pushed or wound either by the residual limb or the other hand. The terminal device’s five fingers would look and act similarly enough to a real hand when compared to other options like a hook or claw, and terminal devices of this sort can be 3D-printed either from plastic or aluminum at home.
3D-printing with plastic generally costs in the range of $50-100 per part, printing with aluminum or other lightweight metals would cost between $250-400 per part (Proto3000, 2020), and as 3D-printing with silicone is fairly new, silicone-printing companies have various listing prices comparable to that of metal. A comparable myoelectric upper arm prosthetic would begin at $18,000 (Medical Center Orthotics & Prosthetics, 2018).
Being entirely mechanical allows for 3D-printing, which in turn allows for parts customized for each patient. 3D-printed prosthetic parts would be cheap to produce, widely available, and able to fit a growing child’s needs while not compromising comfort or quality.