An Ischemia Model on a Chip

Abstract

Ischemia refers to reduced blood flow to tissues. Coronary ischemia can cause heart attack, and cerebral ischemia can cause stroke. Ischemic heart attack caused more than 7 million deaths in 2008, counting for more than 12% of total global mortality. Short‐term fatality rate following first ischemic stroke could exceed 20%, and long‐term mortality rate following minor ischemic stroke was reported to be more than 30%. Many in vivo models have been established to study ischemia pathology and explore ways to re‐establish proper oxygen supply and blood flow to ischemic tissues. However, complicated in vivo environment often makes it difficult to identify small changes occurring at cellular/molecular level. In vitro models were also widely used to study ischemia. It is common to keep cultured cells under hypoxic conditions without flow. The major limitation of those in vitro models is the lack of physiological relevance, as ischemic tissue is usually surrounded by healthy blood vessels with normal blood supply. To investigate how hypoxia and stagnant flow conditions affect ischemia development, and how vascular cells within the ischemic area interact/communicate with surrounding blood vessels, a simple “ischemia model on a chip” was developed. Microfluidics channels (50 – 100 μm in diameter, and 50–100 μm apart) in various configurations were fabricated using PDMS. Human coronary artery endothelial cells (HCAEC) were grown to confluence within the channels. The “chip” was then isolated from ambient air using paraffin wax. Channels simulating healthy blood vessels were perfused with normal culture medium at physiological flow rate. Channels simulating ischemic blood vessels were filled with culture medium (no flow) with significantly reduced oxygen. The chip was kept at 37°C for 1 hour. A live‐dead assay was used to assess endothelial cell viability within the healthy and ischemic microfluidics channels. Immunofluorescence microscope was used to examine cell morphology. The results indicated that paraffin wax coating effectively maintained the low oxygen level within the ischemic microfluidics channels. HCAEC had high viability and normal morphology under physiological oxygen and flow conditions. Ischemic conditions induced cell death and decreased cell surface area. Overall, this “ischemia on a chip” model provided a simple and physiologically relevant solution to simulate complicated in vivo environment. Both flow conditions and oxygen level within the microfluidics channels can be controlled to mimic various physiological or pathological conditions; vascular endothelial cells can be cultured to cover the inside of the channels to simulate blood vessels. Thus, ischemia‐induced cellular responses (such as inflammation and angiogenesis) and ischemic‐healthy blood vessel communications can be investigated.