Precision Micro-Manufacturing of Soft and Stretchable Electronics and Biomedical System

Micromilling is an essential technique in precision manufacturing, enabling the creation of intricate and high-precision components at a microscale. This process utilizes miniature cutting tools to fabricate complex geometries and fine features important in advanced industries such as aerospace, biomedical engineering, and microelectronics, where even minor deviations can impact the performance and reliability of final products. The advantages of micromilling include exceptional accuracy and precision, flexibility to utilize a wide range of materials, and the ability to create complex three-dimensional geometries. These advantages make it an indispensable technique for producing micro-scale components with high-quality surfaces and intricate details that are challenging to achieve using conventional methods. Freeze micromilling, an advanced variation of traditional micromilling, incorporates cooling to enable the use of uncommon materials. This technique maintains the structural integrity of delicate microstructures by ensuring material properties remain stable throughout the machining process. In some cases, the controlled cooling environment (e.g., -20°C) enables the use of new materials (e.g., Eutectic Gallium Indium) and improves material machinability, allowing for the fabrication of complex geometries without compromising quality. In other cases, cold temperatures are crucial to prevent damage to materials, such as allograft cartilage tissue, which must remain frozen until implanted. The overarching objective of this doctoral research is to develop a fabrication and prototyping method using freeze micromilling on unconventional materials used in biomedical and microelectronics fields. This study aims to examine the micro-machinability and final quality of the fabricated features while demonstrating enhanced mechanical and electrical performances.

In the first part of this research, the freeze micromilling process for liquid metals (Eutectic Gallium Indium, EGaIn) is developed, analyzing the relationships between the freeze micromilling parameters and the geometrical characteristics of the fabricated features. Using freeze micromilling enabled the fabrication of soft and stretchable liquid metal circuits with unique features. These features include three-dimensional and high-aspect-ratio geometries. Liquid-metal circuits with such unique features are difficult or impossible to fabricate using current techniques. However, these geometries offer significant functional advantages for various circuits. Furthermore, electrical performance analyses were conducted, and several electrical circuits were fabricated with geometrical features that are not achievable using other fabrication methods.

This research also introduces and evaluates the freeze micromilling of cadaveric human cartilage tissue. The freeze micromilling setup is adjusted to cool the workpiece down to -40°C, preserving the cartilage tissue from degeneration (patented technology US11540921B2). This proposed part of the research includes two aspects: (1) dimensional analysis and burr formation in the micromilling process of cartilage tissue under various cutting conditions, and (2) fabrication of cartilage implants with precise and accurate three-dimensional geometrical structures.