3D printed magnetic soft millirobots for intelligent magnetic digital microfluidics

• Main Author: Zhou, Aiwu
• Other Authors: Lum Guo Zhan
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2024
• Subjects: Engineering; Circulating vat polymerization; Magnetic soft minature robots; Digital microfluidics
• Online Access: https://hdl.handle.net/10356/177116
• Institution: Nanyang Technological University

Magnetic digital microfluidics (MDM) technology is capable of manipulating droplets of nano or microliters, rendering it a superior platform for applications in the filed of medicine, biology, and chemistry, owing to reduced reagent consumption and simplified fluidic operation compared to conventional benchtop platforms. However, all the droplet manipulations of existing MDM systems are constrained to a 2D plane since a hydrophobic surface is required to maintain the shape of the droplet. Transferring droplets across different platforms is necessary for numerous applications that require specific reaction conditions such as temperature and pH. So far, this process usually requires manual operations that are less efficient and accurate. Therefore, magnetic soft millirobots (MSMRs) that can potentially address this problem are proposed in this thesis. The proposed MSMRs are able to handle small objects precisely and dexterously. Once the surface of these MSMRs is coated with a hydrophobic material, they manage to maintain the droplet shape and handle the droplet as a softball. However, the functions of existing MSMRs are restricted due to their relatively simple structures limited by conventional manufacturing techniques which face great challenges in the fabrication of intricate structures. As a result, to create MSMRs with intricate structures and hence versatile functions, I propose to implement a vat photopolymerization-based 3D printing technique to produce magnetic parts free of geometric constraints. However, conventional vat photopolymerization typically suffers from particle sedimentation and strong interference between the laser source and magnetic particles, which results in weak magnetic response because of the nonuniform distribution of magnetic particles and low particle loading (<1%). Here, circulating vat polymerization (CVP), a novel 3D printing technique designed specifically for magnetic composite fabrication, was proposed to address this issue. The particle loading effects were systematically studied to optimize the materials, parameters, and setups for CVP. It was found that SrFe12O19 was the ideal magnetic particle for printing, reaching a loading ratio of up to 30% and high uniformity. Subsequently, several tethered and untethered MSMRs that can manipulate droplets in 3D were printed monolithically, and then magnetically controlled shape morphing and motion of these MSMRs were demonstrated. To show the potential applications and advantages of MSMRs in the MDM field, an MDM platform powered by AI was built to control MSMRs for detecting carbapenem antibiotic resistance in hazardous biosamples with closed-loop control, and the capability of performing failure detection, rectification, and result analysis. CVP provides a novel way of producing MSMRs with sophisticated structures that enable various deformations, it is expected to lead the development of MSMRs with more advanced functions that can assist droplet manipulations in MDM platforms; the integration of AI also allows the fully automated control of MSMRs for bioassays with high efficiency, reliability, and accuracy, which enables the construction of an intelligent MDM platform for a wide range of biomedical applications.