There are many developments under way in connected healthcare, but among the most exciting and cutting edge are smart body implants. Broadly speaking, these fall into two categories.
Firstly, human bio-sensors placed outside the body, which, while effective enough, have the disadvantage of being quite bulky, as well as not always accurate about what is happening inside the body. Wireless sensors implanted within the body, meanwhile, are able to deliver more accurate data on a regular basis, meaning treatments can be more specifically tailored to the patient’s needs.
For those who may not know, these implants are used to sense a physiological response, actuate physiological organs, or to deliver medical treatments. For example, smart surgical ‘nails’ consisting of a strain sensor, electronics and coils for radio signal generation can be sealed in biocompatible titanium and embedded in bone implants.
This enables doctors to track how well the bone is healing and be more precise in terms of how far to push therapy treatments. The challenge with implanted sensors is that they have to be very small. At the same time, they still need to be capable of sending bidirectional communications from within the body, as well as supporting a reliable power source.
Novel sensing
Cambridge-based The Technology Partnership (TTP) is one of the pioneers in this space. Discussing the technology, Paul Winter, technology and product development consultant at TTP, says: “One major part of our business is developing novel sensing ideas, which may be smaller and more accurate.
“The other side is having the ability to understand the various wireless standards and how you marry those two things together to give a system the accuracy that is needed. We work with clients to combine those different pieces of technology.”
Turning to implants, Winter explains: “A lot of the work we have done on implants has been about trying to optimise the pillars of reliable communications. For instance, looking at effective power transfer and minimising the energy requirements of the implants. We’re also looking in some cases to develop novel sensing techniques that are inherently low power themselves, or more sensitive like some of the neuro-stimulation work that we’ve been involved in.”
Neuro-stimulation implants are a new form of pain management. “These are implantable devices inserted a few or tens of millimetres or tenths of millimetres under your skin. Their purpose is to provide electro-stimulation to nerve endings,” explains Winter.
“The problem is that the body gets used to these particular neuro-modulation patterns, so what we need is smarter implants that sense if the body is building up a resistance to it,” he says. “Then effectively you have some kind of closed-loop stimulation programme, which allows the tailoring of that stimulation to be more appropriate as the person’s pain progresses or changes.”
According to Winter, TTP is undertaking a lot of work on sensor design, signal analysis and algorithm development to monitor various disease states and the efficacy of the treatments.
Elaborating further, he says: “We have been working with a university on sensing electrical activity from the nervous system. They are developing velocity selective recording techniques from the vagus nerve.”
The vagus nerve is responsible for the regulation of internal organ functions, vasomotor activity, as well as certain reflex actions such as coughing, sneezing, swallowing and vomiting.
He continues: “In terms of the wireless side of things, you have an implant with some level of actuation and also some level of sensing. You need to be able to control that actuation and record the sensor’s data and do something with it.”
If the implant is relatively shallow, wireless technologies such as Bluetooth can propagate through the body and transmit data to a mobile phone, which can also control the device.
Bespoke communications protocol
Once the information is collected, cloud connectivity then allows algorithms to be deployed on those data sets from which the consultant can infer clinically relevant information. The consultant can then modulate and prescribe different sorts of treatment for the patient. The implant may be programmed with a new wave form or a different type of stimulation, which is more tailored to the patient’s condition.
According to Winter, the deeper the implant, the more challenging things become. “The difficulty [with deep body implants] is how do you power them and how do you extract the data?” he says.
Conventional wireless technologies like Bluetooth, NB-IoT or Wi-Fi can work as a communications technology, but they cannot also power the device as the energies are not sufficient.” With that in mind, TTP has been developing a coil-based system, which is a lower-frequency, inductive power transfer type of technology, able to power multiple implants simultaneously.
“That is combined with effective bidirectional communications, so you can communicate with the implants and extract data back from them,” says Winter.
The challenge here is significant. Getting the required level of power into the implant is hard enough, but the task is made particularly challenging because of their small size. TTP has conducted a lot of electro-magnetic modelling on the power side. But more than that, as standard communications technologies are unusable, it has also had to develop its own bespoke communications protocol.
Discussing this, Winter says: “We looked at what different types of modulation scheme we could use to see which offers the best signal-to-noise ratio for the communications link and looked at the link budget we needed to achieve.”
Supplying power to the implant deep inside the body to keep it charged is also extremely challenging. “You could insert a battery along with your implant,” observes Winter, “but the problem is batteries run out, so you then have to recover that and change your implant, which is not nice for the patient.”
TTP did look at incorporating a rechargeable battery in the implant and then inductively powering it via an external recharging mechanism. The patient might sleep with a charger to recharge their implant, for example.
“But then you are asking the patient to do something, which tends to complicate things, and power transfer into the body is always relatively inefficient,” explains Winter. “And the problem with wearing an external powered belt or patch that powers the internal implant is that it’s effectively blocking your internal communications, so you have to think about that as well.”
To get around these power constraint issues, TTP is using energy harvesting technology to fill up a reservoir of energy inside the implant. The implant then makes use of that energy to carry out its functions and to communicate the data.
To enable this, TTP once again had to develop its own protocol which would work within those constraints. “Like many energy harvesting techniques, you wait until you have sufficient energy. If the device doesn’t have sufficient energy to communicate the data back out, it will have to wait a bit longer to harvest more,” says Winter.
Multiple use cases
It is quite difficult to deliver real-time data under these constraints, meaning that the protocol has to be designed incredibly carefully.
For instance, often these implantables cannot be achieved through the use of conventional discrete circuitry, because the implants are so small. This means developers have to construct an application-specific integrated circuit (ASIC), building up a circuit board using a microcontroller, resistors, capacitors, conductors and so on, wrapped in titanium.
“The key aspects are that we are sensing parameters buried deep inside the body,” says Winter. “We are having to power the implant because it is super-small, and we must have full bidirectional communications with that implant.”
According to TTP, the implants discussed within this article can be put to multiple uses in healthcare. “It could be as simple as detecting infection,” says Winter.
“When a patient goes into surgery, you drop in an implant, so you can know if the wound is infected before it really hurts. “You can monitor the infected wound and prescribe simple medications to alleviate that. The sooner you know about it, the simpler the solution, the lower the cost, and the more comfortable the patient is.”
"The simpler the solution, the lower the cost, and the more comfortable the patient is”
The latest developments in the smart implant field, meanwhile, are focusing on multiple devices in the body. Take the neuro-stimulation implant as an example. These sorts of implants essentially have a plug at the end of them with lots of wires. The surgeon entangles those wires with the patient’s nerve endings. The more wires connected to the nerve endings, potentially the better or more precise the therapy can be. But, with an increased number of connections, it becomes more challenging to find a solution.
Winter says the alternative in the scenario described above is to have several smaller implants with fewer connections, rather than one larger implant with many. This in turn creates its own potential issues. “The problem then is you have to synchronise the implants when you do the neuro-stimulation therapy,” he says.
“So, the next step going beyond what we are doing today is to synchronise multiple implants within a body to provide a co-ordinated therapy. That is a challenge we are starting to look at.” Deep body implants are a good example of how wireless connectivity is changing the way healthcare works. Technology is profoundly changing how care is delivered and the degree to which it can be tailored to an individual patient’s condition.
