Dissolvable Metals for Transient Electronics

A remarkable feature of modern silicon electronics is its ability to remain physically invariant, almost indefinitely for practical purposes. Although this characteristic is a hallmark of applications of integrated circuits that exist today, there might be opportunities for systems that offer the opposite behavior, such as implantable devices that function for medically useful time frames but then completely disappear via resorption by the body. We report a set of materials, manufacturing schemes, device components, and theoretical design tools for a silicon-based complementary metal oxide semiconductor (CMOS) technology that has this type of transient behavior, together with integrated sensors, actuators, power supply systems, and wireless control strategies. An implantable transient device that acts as a programmable nonantibiotic bacteriocide provides a system-level example.

Nanomaterials that can circulate in the body hold great potential to diagnose and treat disease. For such applications, it is important that the nanomaterials be harmlessly eliminated from the body in a reasonable period of time after they carry out their diagnostic or therapeutic function. Despite efforts to improve their targeting efficiency, significant quantities of systemically administered nanomaterials are cleared by the mononuclear phagocytic system before finding their targets, increasing the likelihood of unintended acute or chronic toxicity. However, there has been little effort to engineer the self-destruction of errant nanoparticles into non-toxic, systemically eliminated products. Here, we present luminescent porous silicon nanoparticles (LPSiNPs) that can carry a drug payload and of which the intrinsic near-infrared photoluminescence enables monitoring of both accumulation and degradation in vivo. Furthermore, in contrast to most optically active nanomaterials (carbon nanotubes, gold nanoparticles and quantum dots), LPSiNPs self-destruct in a mouse model into renally cleared components in a relatively short period of time with no evidence of toxicity. As a preliminary in vivo application, we demonstrate tumour imaging using dextran-coated LPSiNPs (D-LPSiNPs). These results demonstrate a new type of multifunctional nanostructure with a low-toxicity degradation pathway for in vivo applications.

Today, more than 200years after the first production of metallic magnesium by Sir Humphry Davy in 1808, biodegradable magnesium-based metal implants are currently breaking the paradigm in biomaterial science to develop only highly corrosion resistant metals. This groundbreaking approach to temporary metallic implants is one of the latest developments in biomaterials science that is being rediscovered. It is a challenging topic, and several secrets still remain that might revolutionize various biomedical implants currently in clinical use. Magnesium alloys were investigated as implant materials long ago. A very early clinical report was given in 1878 by the physician Edward C. Huse. He used magnesium wires as ligature for bleeding vessels. Magnesium alloys for clinical use were explored during the last two centuries mainly by surgeons with various clinical backgrounds, such as cardiovascular, musculoskeletal and general surgery. Nearly all patients benefited from the treatment with magnesium implants. Although most patients experienced subcutaneous gas cavities caused by rapid implant corrosion, most patients had no pain and almost no infections were observed during the postoperative follow-up. This review critically summarizes the in vitro and in vivo knowledge and experience that has been reported on the use of magnesium and its alloys to advance the field of biodegradable metals. Copyright (c) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.