The Fabrication and Operation of a Continuous Flow, Micro-Electroporation System with Permeabilization Detection

This protocol describes the microfabrication techniques required to build a lab-on-a-chip, microfluidic electroporation device. The experimental setup performs controlled, single-cell-level transfections in a continuous flow and can be extended to higher throughputs with population-based control. An analysis is provided showcasing the ability to electrically monitor the degree of cell membrane permeabilization in real-time.

Current therapeutic innovations, such as CAR-T cell therapy, are heavily reliant on viral-mediated gene delivery. Although efficient, this technique is accompanied by high manufacturing costs, which has brought about an interest in using alternative methods for gene delivery. Electroporation is an electro-physical, non-viral approach for the intracellular delivery of genes and other exogenous materials. Upon the application of an electric field, the cell membrane temporarily allows molecular delivery into the cell. Typically, electroporation is performed on the macroscale to process large numbers of cells. However, this approach requires extensive empirical protocol development, which is costly when working with primary and difficult-to-transfect cell types. Lengthy protocol development, coupled with the requirement of large voltages to achieve sufficient electric-field strengths to permeabilize the cells, has led to the development of micro-scale electroporation devices. These micro-electroporation devices are manufactured using common microfabrication techniques and allow for greater experimental control with the potential to maintain high throughput capabilities. This work builds off a microfluidic-electroporation technology capable of detecting the level of cell membrane permeabilization at a single-cell level under continuous flow. However, this technology was limited to 4 cells processed per second, and thus a new approach for increasing the system throughput is proposed and presented here. This new technique, denoted as cell-population-based feedback control, considers the cell permeabilization response to a variety of electroporation pulsing conditions and determines the best-suited electroporation pulse conditions for the cell type under test. A higher-throughput mode is then used, where this 'optimal' pulse is applied to the cell suspension in transit. The steps for fabricating the device, setting up and running the microfluidic experiments, and analyzing the results are presented in detail. Finally, this micro-electroporation technology is demonstrated by delivering a DNA plasmid encoding for green fluorescent protein (GFP) into HEK293 cells.

Current therapeutic innovations in biomedical research, such as CAR-T (Chimeric Antigen Receptor Engineered T cell) cell therapy and genetic editing using CRISPR (clustered regularly interspaced short palindromic repeat DNA sequences)/Cas9, heavily rely on the ability to deliver exogenous material both successfully and efficiently into the intracellular space¹. In CAR-T therapy, the gold standard to perform the gene delivery step in cell therapy manufacturing is using viral vectors². Though viral-mediated gene delivery is an efficient delivery modality, it also has several drawbacks. These include manufacturing costs, cy....

NOTE: Users should review all MSDS for the materials and supplies used in this protocol. Appropriate PPE should be worn at each step and sterile technique used during experimentation. Sections 1-7 discuss the device fabrication.

1. Device fabrication- Mask design

NOTE: Refer to Figure 2 for an illustration of the microfabrication process. The microfabrication steps are to be carried out in a cleanroom environment. Additio.......

Figure 4 highlights the operating principles behind the single-cell-level membrane permeabilization detection for a single pulse amplitude. Following the initiation of the electroporation experiment, the cell detection algorithm determines an optimal threshold for cell detection via a point-by-point, slope-based detection method. The system then continuously monitors (1) for a significant negative change in the measured electrical current, which is indicative of the entry of a cell. This is .......

The methodology presented within this protocol primarily focuses on the microfabrication of a microfluidic device that is then integrated into a specialized electroporation experimental setup. The term 'recipe', which is often used when describing the specifics of the microfabrication process, hints at the importance of following/optimizing each step to successfully fabricate a functioning device. However, certain critical steps within the process, when not optimized, such as UV exposure time/energy, PVD sputteri.......

The authors would like to acknowledge financial support by the National Science Foundation (NSF CBET 0967598, DBI IDBR 1353918) and the U.S. Department of Education's Graduate Training in Emerging Areas of Precision and Personalized Medicine (P200A150131) for funding graduate student J.J.S. on fellowship.