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Let’s Chat: Medical Implantable Electronics Integration

In the fascinating area of medical electronics, one of the most exciting and promising developments has been implantables inside the human body. I guess the early 1950s pacemakers and artificial hearts were the pioneering efforts with which we are all familiar.

Just think of the incredible challenges (along with the seemingly miraculous health benefits) that implantables bring to the designer:

  • Very low power, wireless power, or energy-harvesting capabilities are needed for powering the circuitry.
  • The body's has a tendency to reject foreign materials, so maybe an encapsulation technique is needed.
  • What type of IC construction is best for your design? Perhaps die stacking with thin-film battery is a possibility.
  • How will the device communicate with the outside world? A wireless setup? How about body-coupled communication that uses the body itself as the communication medium?
  • What about implantables in the brain? This is such a delicate area — perhaps the most vulnerable to damage by implantables. How do we deal with that?

These are only a few of the incredible challenges we as electronics designers face. How do we integrate all the functionality that can save lives? Severe diabetes, chronic heart problems, and the disabling burden of Parkinson's disease are just a few of the things that could be cured by electronic implantables in the coming future.

We will have a chat session right here on Integration Nation on Thursday, Sept. 19, at 11:00 a.m. EDT (15:00GMT/UTC). I invite you all to join us and our experts in this area to discuss the possibilities of medical implantables, along with proposed solutions to the challenges faced in this effort. Watch for an announcement with instructions regarding how to join us in this text-only monthly forum.

Power management
Cochlear implants and retinal prostheses have already shown that power and data can be transmitted wirelessly to an implanted medical device. Inductive coupling using Class E amplifiers is one way to bring power and data to an implantable device. An external coil at some carrier frequency can send all the data and power needed to operate things such as a cardiac stimulator or a cochlear implant.

Sometimes small rechargeable batteries are used to provide reliable power to the implanted device. Some sort of power management unit with an RF front end that goes to a battery charging and detection function circuit is needed in this setup. The implant power section may use some sort of charge pump design to boost voltages efficiently to the device. Usually the electronics can be accomplished in a CMOS process such as 0.35μm.

As is the case with every design we do in our careers, we will need to make decisions and compromises depending on the system needs. For example, small, battery-operated implant designs will face battery size/capacity and peak power limits. The implant size will also determine antenna size. This will hold down radiation efficiency and put a dent in the communication link's power budget.

Parameterization of various biomedical hardware approaches in terms of size, power, and functionality.(Source: IEEE Microwave magazine1)

Parameterization of various biomedical hardware approaches in terms of size, power, and functionality.
(Source: IEEE Microwave magazine1 )

The inductive link
Low-frequency inductive links can be used to power the electronics inside the implant. The low frequency makes its easier for magnetic fields to penetrate the body.

Implant IC encapsulation, die-stacking plus thin film battery
Individual die can be encapsulated with a biocompatible process and made hermetic at the same time.2 A stack of encapsulation layers covers the die, making it hermetic. The die edges do not have sharp, straight corners. Instead, the edges are sloped. This enhances the encapsulation process.

There can be various subdevices, but each is separately made hermetic and then assembled. A biocompatible metallization connects the subdevices. The final step is a biocompatible embedding process that makes for a single implant.

(a) Biocompatible chip encapsulation and (b and c) the basic concept for an implantable system consisting of thin dies encapsulated with biocompatible bi-direclional diffusion barriers. In (b), only electronics and metellization is embedded. In (c), a second embedding is used to combine the electronic subpart of the device with other parts, such as a thin film battery.(Source: 'An IC-centric biocompatible chip encapsulation fabrication process'2)

(a) Biocompatible chip encapsulation and (b and c) the basic concept for an implantable system consisting of thin dies encapsulated with biocompatible bi-direclional diffusion barriers. In (b), only electronics and metellization is embedded. In (c), a second embedding is used to combine the electronic subpart of the device with other parts, such as a thin film battery.
(Source: “An IC-centric biocompatible chip encapsulation fabrication process”2 )

Here is a more detailed view of the inner structure.

Another example of a five-layer chip-stacking assembly -- specifications (left)and system block diagram (right).(Source: 'A Modular 1mm3 Die-Stacked Sensing Platform withOptical Communication and Multi-Modal Energy Harvesting'3)

Another example of a five-layer chip-stacking assembly — specifications (left)
and system block diagram (right).
(Source: “A Modular 1mm3 Die-Stacked Sensing Platform with
Optical Communication and Multi-Modal Energy Harvesting”3 )

Communication to the outside world
One possibility, especially in cases where long-term monitoring may be warranted with an implant, is body coupled communication. Since sensor node power budgets are burdened with the need to store data to memory and/or transmit data out to some external device, using body area networks formed using body coupled communication can decrease the power used.

The electrical model of the body that is used is one of a simple spreading resistance. Anderson and Sodini validated this model.4

The body area network diagram where body coupled communications can be implemented.(Source: 'Body Coupled Communication: The Channel and Implantable Sensors'4)

The body area network diagram where body coupled communications can be implemented.
(Source: “Body Coupled Communication: The Channel and Implantable Sensors”4 )

Brain implantables 5
The brain computer interface enables neurological and neuromuscular functions to be restored by decoding brain signals into outputs that actually infer brain intentional states. This type of implantable has the same challenges in power, size, and functionality as those shown and discussed on the previous page.

The brain is so much more delicate than most other organs in the body, and great care must be taken when interfacing with it. Implanting electrodes into the brain itself is a risky piece of business. There are two types of such invasive methods: electrocorticography (ECoG) that records electrical brain activity beneath the cranium and single-unit activity (SUA) microelectrodes that can monitor individual neuron action potential firing.

SUA provides high SNR and fine spatial resolution and can decode specific motor movements. Subdural ECoG electrodes have higher spectral BW, larger spatial resolution, and larger amplitudes than non-invasive techniques but not as good as SUA. ECoG is usually chosen, because the safety of its electrodes has been proven in thousands of patients. Also, these electrodes are subdural and do not penetrate the delicate brain cortex.

Insertion loss in a finite-difference time-domain (FDTD) human head modelbetween a subdural grid antenna and an external ear-worn antenna.(Source: 'Low Power Microsystems for Brain Computer Interfaces'5)

Insertion loss in a finite-difference time-domain (FDTD) human head model
between a subdural grid antenna and an external ear-worn antenna.
(Source: “Low Power Microsystems for Brain Computer Interfaces”5 )

Power management, foreign body rejection, and other challenges are all being overcome with a multitude of solutions depending on what you as the designers are trying to accomplish. This is certainly the best time to be an engineer, with technology advancing at a quicker pace than it did 30 years ago.

We hope you'll give us your experiences and expertise on this issue on Thursday, Sept. 19. We welcome your input.

References:

  1. “Wireless implants,” Rizwan Bashirullah, IEEE Microwave magazine supplement, December 2010.
  2. “An IC-centric biocompatible chip encapsulation fabrication process,” Maaike Op de Beeck., Antonio La Manna, Thibault Buisson, Eric Dy, Dimitrios Velenis, Fabrice Axisa, Philippe Soussan, Chris Van Hoof, IMEC; Electronic System-Integration Technology Conference (ESTC), Sept. 13-16, 2010.
  3. “A Modular 1mm3 Die-Stacked Sensing Platform with Optical Communication and Multi-Modal Energy Harvesting,” Yoonmyung Lee, Gyouho Kim, Suyoung Bang, Yejoong Kim, Inhee Lee, Prabal Dutta, Dennis Sylvester, David Blaauw, University of Michigan, Ann Arbor, MI; from ISSCC 2012, Session 23.
  4. “Body Coupled Communication: The Channel and Implantable Sensors,” Grant S. Anderson and Charles G. Sodini, Microsystems Technology Laboratories, Massachusetts Institute of Technology.
  5. “Low Power Microsystems for Brain Computer Interfaces,” Rizwan Bashirullah, Dept. of Electrical and Computer Engineering, University of Florida, Gainesville, FL.

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25 comments on “Let’s Chat: Medical Implantable Electronics Integration

  1. Vishal Prajapati
    September 10, 2013

    This type of systems are very power critical. They need to have power through out entire operating time and has to be as low as possible.

     

    I want to know is there any technique developed for power harvesting inside body like heat or vibration? If not then what type of batteries are used to power the implant for years? What about pacemaker for an example?

  2. Steve Taranovich
    September 10, 2013

    Hello Vishal—-Energy harvesting is defin itely being investigated and I believe it will be implemented in the near future as a power source. The main source of power in implants today is typically wireless inductive power that sometimes includes data. There is also a battery within the implant which is charged by this method. Examples are the cochlear implant and the spinal stimulator for chronic pain in the spine—-visit Medtronics website for more details on this.

    Of course, we are always looking for battery technology with longer life as well as prolonging batteries with lower power integrated electronics.

  3. Davidled
    September 10, 2013

    The most concern is the side effect related to Skin and Body. What if the device is broken inside body? Also there is EMI issue affecting to body. Typically, many questions are raised if this kind of device is embedded to body of patients.  

  4. Vishal Prajapati
    September 11, 2013

    @Steave, that's great insites. So does it mean that patient has to charge the internal battery by once in a while by putting inductive charger on the surface of the body near the implanted device?

  5. Vishal Prajapati
    September 11, 2013

    @DaeJ, you have raised an important concern here. What if the device fails or breaks in side body? The chemical and material hazards will definitely be there apart from that the function for which the device has been implanted will also hamper e. g. pacemaker.

     

    There must be some very stringent testing procudure for these type of electronics. Can anyone elaborate?

  6. Steve Taranovich
    September 11, 2013

    Hello Vishal—Most implants, like those that Medtronics designs,include features
    that provide protection from electromagnetic interference. Most electrical devices and magnets encountered in a normal day are unlikely to affect the operation of an implant but very high EMI can possibly cause damage to device and hence the body.

    This technology of EMI protection, and the challenge of protecting a device implanted into the human body from contaminating the tissue and organs, are greatly improving as technology advances. There will always be some level of danger in any implant, but the question is whether the benefits outweight the dangers—I believe they do.

    The FDA in the US takes these concerns very seriously, as do companies like Medtronic and Cactus Semiconductor. There is a stringent approval and trial process before a device is accepted for human usage.

  7. Steve Taranovich
    September 11, 2013

    Hi Vishal—my brother-in-law just replaced his spinal stimulator from Medtronic with the next generation device. He is able to attach an inductive charger now in a soft belt around his waist and charge his implanted device in 3 hours while sitting and reading or watching TV. This charge lasts a week. A very significant improvement over the first implant he had.

    He barely has any more back pain, as opposed to the chronic and severe pain without this device. He was not able to function with his previous level of pain after trying every other means of pain management. His life is changed for sure, but he can now function at almost 90% normality in his life.

    Do the dangers outweigh the benefits here? If you ask him he will reply with a resounding YES!

  8. green_is_now
    September 17, 2013

    The solution to minimise this is to incorperate an ionic fluid detector within the encapsulated part, If it cracks and still work then the time for corrosion to create problems will be some finite time.

    long enough t activate the warning signal that the implant is broken and needs to be removed ASAP.

     

    If it quits on its own the external charge system-data recovery system needs to alert all concerned that the implant has failed and needs to be removed ASAP.

  9. green_is_now
    September 17, 2013

    I have a battery system and power topology that is ideal for implanable devices.

     

    1) it can extend 1.5x to 2x lifetimes over primary batteries.

    2) It also improves MTBF 10x over rechargeables alone.

     

    Ron Davison

    San Diego

    Efficient Electronic Solutions

  10. Steve Taranovich
    September 17, 2013

    Hello @ green_is_now, Tell us more. Can it pass FDA approval? How safe is it against leakage? What is the chemical makeup?

  11. Netcrawl
    September 17, 2013

    @Steve it's a strict requirement for all implantable electronics, Biological fluid is very corrosive,packaging needs to provide a hermetic seal to prevent leakage of body fluids into the electronics and it must protect the tissue from electronic materials. Packaging is very important because the device experiences dynamic movement.

  12. Netcrawl
    September 17, 2013

    Steve you're right the power for the implantable device is provided by an implantable or rechargeable battery or wireless transmission from an external battery, obviously, the efficiency of this battery is less in the wireless case. cochlear implants operate with an external battery worn by the user, it  needs to be replaced or recharged.

    Energy harvesting could be a good alternative but it still in devlopment and its takes more time to develop that kind of technology.  

  13. jkvasan
    September 19, 2013

    Steve, 

    Very detailed description on how these implants are made. Thanks.

    Any transplant  placed into a human body can trigger the immune system which could think this as a foreign body. The patient is treated with immuno-suppressive drugs which have their own side effects. The polymer discussed in “Ninja Polymer Hydrogel Eliminates Microbes” could be a great solution to this problem.

  14. Netcrawl
    September 19, 2013

    It's a daunting task, it's not pure electronics, it also about science, implantable electronics face challenges of biocompatibility, hermetic packaging, high voltages, large passive devices, and need to learn the language of biology and life sciences. This is not just about electronics; we also need to look for the human body how the body would react if something happened. Packaging is a very strict requirement in implantable device, and crucial. 

  15. jkvasan
    September 19, 2013

    You are right. “Packaging Completes Design” when it comes to medical devices. Biocompatibility is a key requirement.

  16. SunitaT
    September 22, 2013

    Today's implantable circuits offer therapy to treat several conditions. Exciting new apps in neurological stimulation could be used to give pain management, sleep apnea, epilepsy, gastrointestinal disorders, bladder control numerous auto immune syndromes and psychological disarrays for example obsessive compulsive disorder. Implantable systems could now provide specific dosage and intermission delivery of medications to more efficiently treat patient's situations while reducing side effects.

  17. jkvasan
    September 22, 2013

    Sunita,

    Targetted, programmable and accurate delivery of drugs at the point of care can be made possible with the help of such devices. The day is not far when some device would be there always with necessary drugs and when the person gets sick it automatically would deliver the drug and cure her/him then and there. Something like, one gets a fever, the antibiotic is already there inside the body and only delivered when activated.

  18. Brad_Albing
    September 26, 2013

    @green – Like Steve said – more info please – perhaps a blog?

  19. etnapowers
    October 25, 2013

    The solution of utilizing a wireless setup to communicate with the external world has to be tested accurately on human body because it could cause an heating of human tissues and modify the molecolar structure of some organs.

  20. etnapowers
    October 25, 2013

    Is this system integrable in the package of the system? What about area occupation and the compatibility with medical instrumentation requirements?

  21. etnapowers
    November 11, 2013

    The area is so delicate that some implantables should be added only to repair and interface some damaged parts.

  22. etnapowers
    November 11, 2013

    The Biocompatibility is a really important factor and , in case of transient electronics devices, the sensors have to disappear without leaving traces in the human body.

  23. etnapowers
    November 11, 2013

    Adding some implantables in the brain is very difficult because the wireless communication protocol could interfere with the electric pulses inside the brain.

  24. etnapowers
    November 12, 2013

    The electronics designers have to work closely togheter with medical team, stating what clinical parameters can individuate a disease.
    The designers have also the responsability of the design and the conditioning of the related transducers.

  25. etnapowers
    November 12, 2013

    Some clinical parameters of a patient could be combined by the electronic implanted to send some warning messages to a medical center.

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