Tu30 - Label-free impedance signal-Based Sorting of Pancreatic Islets on size and viability metrics using a pneumatically actuated sidewall diaphragm

In fifteen words or less, explain the significance of this contribution (Novel Aspect).: Novel microfluidic platform combining impedance phenotyping with active diaphragm-based islet sorting.

Abstract Text: The ability to rapidly and selectively isolate viable pancreatic islets within specific size ranges is a critical requirement in islet transplantation therapies to address type 1 diabetes. Current approaches for islet sorting often rely on fluorescent viability staining or destructive insulin assays, which prevent the direct utilization of selected islets for transplantation. In this work, we present a novel label-free microfluidic platform that integrates impedance-based phenotypic detection with pneumatic actuation for real-time sorting of pancreatic islets on size and viability metrics. Our platform leverages low-melting-point Field’s metal 3D sidewall electrodes fabricated using soft lithography and direct injection into SU-8 molds to enable high-fidelity impedance measurements across multiple frequencies, thereby advancing recent work on single-cell and microcarrier aggregate sorting [1]. Pancreatic islets, hydrodynamically focused through a two-electrode pair sensing region, are first characterized by low-frequency impedance magnitude (|ZLF|) to estimate size, followed by high-frequency (HF) electrical opacity (|ZHF|/|ZLF|) to infer membrane integrity and viability. Calibration experiments using polystyrene beads (33-150 µm) revealed a strong linear correlation between particle size and |ZLF|, validating the size-detection metrics. Ethanol-treated and untreated murine islets exhibited distinct opacity values, enabling label-free discrimination between viable and non-viable islets [2]. The sorting module employs a pneumatically actuated sidewall diaphragm integrated adjacent to the main flow channel. Upon detection of a viable islet, a pressure pulse (10-50 psi) is applied to the diaphragm, transiently deforming the channel wall to redirect the islet into the collection outlet. Diaphragm geometry (500 µm Length, 200 µm width, 40 µm thickness) was optimized to enable actuation within a very short time, with minimal shear stress on the islets. This integrated approach combining label-free impedance cytometry with active microfluidic sorting offers a robust, scalable, and physiologically gentle solution for isolating functional pancreatic islets. Its modular construction and compatibility with standard microfluidic workflows make it a promising tool for both research and clinical applications in islet biology and regenerative medicine.