Actual Replacement

For a limb replacement, that means building a system that can actively contribute to movement, remain connected to a changing body, and respond to the person using it with less effort and attention.

We’re starting with the below-knee limb, developing an ecosystem of compatible devices as one integrated technology system. Individual components will change as we learn. What should remain consistent is that each improvement helps the complete limb work more naturally with the person.

Today, much of the work of making a prosthesis function as a system falls to the clinician. Components from different manufacturers are selected and assembled around a socket that depends on skilled manual fabrication. Fit and alignment are established for the individual, then adjusted manually as their needs change. There is an enormous amount of expertise in that process. We believe more of the customization, integration, and ongoing adjustment can be built into the technology itself, giving clinicians better tools and reducing physical strain on the user.

That starts with being clear about the function we want to restore. Energy storage and return devices make use of energy the user puts into the system. Quasi-passive and semi-active ankles can go further by adjusting angle or resistance to suit terrain and gait. Those are valuable capabilities, but they do not by themselves provide the active energy of a biological joint. Synthesizing biological functionality requires the ability to supply energy and control how it is delivered through movement, including dynamic propulsion.

This is why we’re developing around full active actuation. We need the authority to drive the joint and control the torque it applies, so it can actively contribute to movement as well as respond to it. Dynamic actuation is a significantly harder approach and takes more time. We’re choosing it intentionally because it gives us a foundation we believe is necessary for the function we want to build toward. Our below-knee configurations around the Genesis Ankle’s current GEN-5 design and upcoming GEN-6 package are steps in that direction.

Once a joint can supply power, the rest of the limb has to make that power useful. The forces have to pass through a reliable, comfortable connection to the body. The controller needs to understand what is happening at that connection and in the world around it. The person needs to be able to move without consciously managing the machinery. These are closely coupled engineering problems. Developing them together expands what the complete limb can do.

A socket that fits well at the first appointment is a starting point. The body continues to change over the course of the day, and the connection needs to keep working through those changes. We’re developing a scan-to-manufactured socket with active volume management around that requirement. The smart liner is part of the same architecture, with a future role in carrying motion signals from the user into the control system. Physical fit and useful information about the person belong together. Clinical judgment, fitting, and alignment remain essential, while the technology should carry more of the ongoing adjustment burden.

The same thinking applies to control. More capability should let the user spend less attention on the limb. We’re developing a shared-control architecture around the ankle’s onboard sensing and control and, as the interface develops, motion signals from the smart liner.

In the shared-control architecture we’re working toward, routine gait is handled largely autonomously. When the system recognizes a sufficiently clear intentional signal from the user, that input takes priority so they can deliberately direct their synthetic joint within safe operating limits. The system should then return safely to autonomous support when appropriate, without requiring a manual mode change. That is what we mean by a copilot: continuous assistance that reduces cognitive workload, alongside the ability to act intentionally.

Information also needs to move in the other direction. A biological limb gives the person feedback about what it is doing and what it is interacting with. Returning meaningful sensation is a longer-term part of our direction, with its own interface and validation work. The smart liner’s intended motion signals are an input to the controller; giving information back to the user is a further capability to develop. Together, these directions of communication could make the limb more intuitive to use.

We also have to judge every added capability by what it asks of the person living with it. Weight, battery capacity, packaging, and charging are part of the engineering problem from the beginning. A system needs a lightweight profile that fits around human anatomy. Batteries should not be annoying to recharge, and charging should fit into the technology workflow people already have. The same standard applies to intuitive, consumer-tech-grade mobile apps and low-friction onboarding. Users should be able to customize the experience without becoming responsible for managing every detail.

This is also why manufacturing belongs in the same conversation as the joint and its intelligence. If every personalized system requires extensive manual work to make its parts fit and function together, delivering the technology remains difficult. We want personalization to be a repeatable capability of the system, beginning with the individual’s geometry and continuing through how the limb adjusts in use.

Foundry is how we’re putting that approach into a manufacturing workflow. The initial process we’re working toward starts with an ordinary phone scan and produces a complete, assembled adaptive socket, ready for a clinician to fit and align without having to fabricate it manually. From there, the larger goal is for one scan to define the personalized geometry needed to fabricate and assemble a complete below-knee limb from compatible components.

The scan establishes a starting point for a system that has to keep responding after it leaves the factory. The joint, body interface, sensing, and control all have a role in that. Foundry gives us a way to bring those pieces together around an individual and deliver them as a product designed to work together from the beginning.

There is a great deal still to develop and validate. Our direction is to make more of the function inherent to the limb itself. As the technology changes, that gives us a consistent way to decide what belongs in the system and why. We believe actively assistive, integrated limb replacements will become the new standard of care, and we’re working as hard as we can to build them.

— The Genesis Dynamics Team