High-Aspect-Ratio Titanium Micromachining: Enabling Technology for In Vivo Therapeutic Microdevice Applications

The continuing need for enhanced efficacy, safety, and/or functionality in in vivo therapeutics provides immense opportunity for microelectromechanical systems (MEMS). However, continuing reliance upon materials adopted from the semiconductor industry may ultimately limit the scope of what can be achieved. Many such materials suffer from poor mechanical reliability due to low fracture toughness, which results in extreme sensitivity to stress concentration and predisposition to catastrophic failure by fracture. Although mitigation via robust design and packaging is sometimes possible, this invariably increases complexity and cost. Moreover, in many emerging applications, these avenues are not available, due to design constraint and/or performance restriction, thus underscoring need for development of viable alternatives. Herein, we present an overview of high-aspect-ratio titanium micromachining techniques we have developed to address this need. We then follow with a brief summary of recent results from several applications currently under development. In each, Ti micromachining provides a means for leveraging a host of advantageous properties that yield potential for enhanced safety, reliability, and/or performance. As such, Ti micromachining shows considerable promise for extending the utility of MEMS for in vivo therapeutics.