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Implantable SoC improves drug therapy

Posted: 13 Feb 2009 ?? ?Print Version ?Bookmark and Share

Keywords:SoC implantable? therapy drug SoC? control precision?

Engineers at National Taiwan University have developed an implantable SoC capable of drug delivery within a living person that has shown potential for improving the effectiveness of drug therapy through precision control, according to a paper presented on Feb. 10 at the IEEE's International Solid State Circuits Conference (ISSCC).

The implantable CMOS SoC features monolithic integration of a wireless controller/actuation circuitry and a drug delivery array, according to the paper. The authors describe the device as the first of its kind.

By releasing drugs such as nonapeptide leuprolide acetate or nitroglycerin, the SoC could be used for applications such as the localized diagnosis and therapy of cancers or providing immediate treatment for heart attack victims, researchers said. The system can be implanted through minimally invasive surgery, and the wireless capability and doctors to make non-invasive therapy modification, they said.

The paper further noted that the proposed SoC would offer lower system cost, smaller device size and lower power consumption than existing technologies.

Integrated OOK circuit
The device is realized in standard 0.35?m CMOS technology with a die size of 1.77 x 1.4mm?. Drug reservoirs within the device are fabricated by CMOS-compatible post-IC processing and addressable by an on-chip microcontroller. An on-off-keying (OOK) wireless circuit is also integrated in the same die for receiving external commands. Drugs are released into the body by the rupturing of membranes covering the drug reservoir following receipt of the wireless commands.

National Taiwan University's Yu-Jie Huang, who presented the paper on the drug-delivery SoC, said the rupture of the membranes for drug delivery occurs by heating those membranes to the point of failure. The temperature required for this rupture to occur, about 1,500K, is "very high," raising concerns about the exposure of human tissue that comes in contact with the device or the drug contained within.

However, the device is "not the first to use this electroactivation technique," and there is precedent for devices heated to this temperature without damage to the tissue or drug, Huang said.

So far, the device has been studied in laboratory conditions outside a living organism but has not yet been implanted within a living organism, Huang said.

According to the paper, the metal membranes capping each reservoir are patterned on the array for directing electrical current to the top of the membranes. The membranesmultiple layers of titanium and platinumare realized by post-IC photolithography and lift-off processes while the cavities for reservoirs are formed by CMOS compatible post-IC deep dry etching from the backside of the die.

The paper noted that titanium and platinum are CMOS-compatible, having been used in standard CMOS process for metal silicides or diffusion barrier. The materials are also biocompatible, according to the paper, which cited research published in a biomedical materials journal.

The paper proposed a rechargeable Li-ion nanowire battery with a capacity of 223mA-hr as the power source for drug-delivery assembly and a miniature (3mm x 3mm) square spiral inductor to pick up energy from external sources as well as a loop antenna to receive wireless command signals. The whole drug delivery assembly can be encased in a biocompatible PDMS package, the paper stated.

During operation, an external OOK command signal in RS232 format is wirelessly transmitted to the SoC, and then received and demodulated by the OOK receiver, the paper stated. According to the demodulated command, the integrated MCU activates the selected drug cell by applying current to its membrane through a switch, leading to the rupture of membrane and the release of drug, it stated.

Research has shown that the membrane failure, which releases the drug, occurs about 50ms after the activation current is applied.

- Dylan McGrath
EE Times

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