Would you use an induction coil to charge the implant?
Schneider-Ickert: We have developed different methods in recent years, induction being one of them. Ultrasound is another way to charge and power an implant, for example. Wireless optical communication is yet another option. Ultrasound is a great solution for deeply placed implants, as it can penetrate deep into the tissue. Induction is still the most effective choice for implants that are not as deep seated. Back to your point of miniaturization: Electronics design should also facilitate fewer components. We are currently working on the EU-funded EXTEND project, in which we are wrapping an ASIC in a silicone tube with electrodes. The outside diameter is less than one millimeter. This only works if the ASIC is just 0.3 millimeters in diameter, which is the case with the EXTEND project.
Earlier you mentioned the lifespan of products. How long do these implants typically last?
Ruff: I cannot give you a blanket statement in this case. A pacemaker works for 5 to 10 years before the battery needs to be replaced. The goal is therefore to supply energy transfer from outside so implants can last 20 years or a lifetime.
As a developer, are you conducting tests for this, or do you rely on user results?
Schneider-Ickert: You can easily track energy consumption in the laboratory since we know the system’s requirements. It allows you to extrapolate and make a prediction, for example. It’s not always as easy to assess when you analyze different parts of an implant.
Circling back to “networked systems”: How difficult is it to implant this type of system into the body?
Ruff: The primary advantage of networked systems is greater biostability, which you mentioned earlier. Typically, if you want to stimulate several points in the body, you use a central implant as the hub of the implant electronics. The connecting cables are the vulnerable spot of these systems. Imagine this type of control unit for a hand prosthesis. I would have to route the cables to points or to a stimulation in the forearm passing over joints and into the chest area: It’s only a matter of time before these cables get damaged. On the other hand, you no longer need these cable connections if you have networked systems comprising multiple highly miniaturized implants with an integrated stimulator, a discharge unit, and a system that receives power. If an implant fails, it is much easier to correct it because it is far simpler to replace miniaturized implantable electronics than exchanging the central implant. These are benefits we expect to see, which is why we continue our research efforts in this area.
The other side of the coin is that you must supply an entire networked system with energy, not just one implant. Yet all implants have different energy needs! While one implant is in active mode, another is in standby or sleep mode, and a third implant is located far deeper inside the muscle. This means every implant has specific energy needs at different times, and you must meet these needs. Unfortunately, delivering an arbitrary amount of energy into the body does not work as this would result in power loss. The implant would heat up, which is in clear violation of regulatory compliance. That's why you must ensure each implant only receives as much energy as it truly needs, while simultaneously ensuring the supplied energy suffices to avoid disruptions of function. We are developing a unique closed-loop control system to address this issue, which is a major technology challenge. The same applies to communication. I no longer communicate with a base unit and an implant, but I communicate with a network of implants that might also exchange information with one another. I may not reach all implants via my extracorporeal base unit, which means the commands send from the outside to the inside may have to be routed through multiple implants. It’s a real network architecture, which also presents a big challenge.