A recent paper delivered at ISSCC back in February really intrigued me, especially since I used to work as a medical diagnostic equipment designer.
The design described is technically pretty slick. It's an improved method of delivering medication transdermally. This design also demonstrates how designers can take full advantage of integrated analog ICs: Read down further — then try doing this design with a bunch of discrete op amps.
The paper, published as part of the 2013 IEEE International Solid-State Circuits Conference (ISSCC), is “An 87mA⋅min Iontophoresis Controller IC with Dual-Mode Impedance Sensor for Patch-Type Transdermal Drug Delivery System.” The authors are Kiseok Song, Unsoo Ha, Jaehyuk Lee, Kyeongryeol Bong, and Hoi-Jun Yoo. The authors describe an improved method of transdermal drug delivery via iontophoresis.
Some definitions will help:
- Transdermal: literally, across the skin; so a method of transporting a drug across (or through) the dermal tissue layers without the need for pointy objects (good for people who don't like needles);
- Iontophoresis: literally a migration caused by ions (positively or negatively charged atoms or molecules); so, a charge is induced onto the drug molecules, which are then propelled into the tissue.
By way of summary, the authors write the following:
In this paper, we present an iontophoresis controller IC with real-time monitoring of total injected charge quantity and skin condition. The proposed IC contains 32-level programmable current stimulator, a temperature sensor, and a dual impedance sensor to monitor skin temperature, contact impedance, and tissue impedance. The measured temperature and impedances, related with the skin condition, are used for adaptive charge injection by modifying the current stimulation levels through the real-time feedback path. An implemented fabric patch type drug delivery system provides up to 87mA⋅min dosage, larger than the dosage range (80mA⋅min) of commercial iontophoresis patches.
The units of measure above are milliampere-minutes. That's the product of the electrode current and time. The currents used are actually quite low (microamperes) and the time to administer the drug is typically around a few hours.
I find this especially exciting design work (not to mention good karma) — the authors have improved upon previous methods that were simplistic open-loop techniques with a voltage source. Now, they've closed the loop and monitor the current. That's just the beginning.
The device they've designed also monitors a number of conditions and adjusts the excitation current as needed. More importantly, they have designed a low-power mixed signal IC to control the excitation current, thereby making this device sophisticated, compact, and battery operated. Here's a look at their prototype. We can see the physical portion responsible for the drug delivery and the details of the circuit board and programming technique.
Here's a block diagram that provides a bit more detail. The IC certainly has some digital content, but let's not hold that against them. There is a microcontroller to support operations. There is 4kB of memory to hold drug delivery parameters and to record the actual details of the delivery. But as can be seen, there is a very large amount of analog circuitry of many flavors. This device is the poster child of integrated analog.
The device is powered from a coin cell. It uses a boost switcher to generate 3.3V. It has a clock oscillator that uses a 3-bit network of switched capacitors for frequency selection. It uses a 5-bit DAC to set the excitation current level. It has what looks to be a simple inductive loop to allow for non-galvanic connection for programming and data retrieval. It has a temperature sensor. It monitors electrode current to detect an open electrode and sound an alarm. There are active filters (low- and high-pass) and threshold detectors as part of the skin impedance measurement circuitry.
Imagine trying to build this with individual op-amps, switched capacitor filters, power supply devices, and a μP.
Devices like this represent the future of medical diagnostic and treatment delivery systems. Have you had an experience with these devices yet — either designing or using?