Demonstration of human myocardial tissue survival in a novel Miniaturised Myocardial Analysis System (MMAS)

Purpose: "Lab on a chip" or miniaturised analysis systems are becoming a recognised technique in translational medicine. The technology is governed by the physical science of fluid behaviour at the micro and nanoscale, known as microfluidics. A miniaturised micro total analysis system, the MMAS, has been developed to maintain human heart tissue in a biomimetic environment closely correlating with the in vivo conditions, harnessing the inherent advantages of this technology in terms of a high degree of temporal and spatial control. Methods: A device was fabricated in glass for maintaining human heart tissue. Right atrial appendage tissue was obtained during routine cardiac surgery. The tissue was simply dissected to a 2x2x2 millimetre sized-cube, and positioned into the MMAS, which is maintained in an incubator. The tissue is perfused with oxygenated Krebs Henseleit glucose buffer at 37°C, at a flow rate of 20-120 μl/minute. Electrical stimulation to tissue was provided at 1.5Hz/2 volts. The tissue was allowed to equilibrate, kept alive for 5 hours, and finally destroyed by addition of a detergent, Triton X-100. The experiment was divided into three time periods: 0-100 minutes, the equilibration period; 100-300 minutes, the maintenance period; 300-360 minutes, the insult period. Time zero is when tissue is placed in the MMAS. Lactate dehydrogenase (LDH) activity was measured as a marker of tissue death, as was the more specific cardiac biomarker creatine kinase (CK). Oxygen metabolism by the tissue was also determined. Results: Tissue produced LDH activity of 50-100 U/ml/g at the start of the equilibration period, that dropped to 0-10 U/ml/g, indicative that the tissue is viable, for the next 5 hours. When exposed to Triton X-100, the LDH activity increased to approximately 100 U/ml/g (n=8). Similarly, CK activity varied from 0-300 U/L initially, to between 0 and 50 U/L in the maintenance phase, and 50-700 U/L after insult (n=6). The oxygen metabolism showed a drop in partial pressues of oxygen in the buffer, of between 1.5 and 5 kPa, as it flowed across the tissue, of weight between 0.008g and 0.0150g (n=4); as compared with a drop of 0 to 1.5 kPa when no tissue was present in the MMAS. Conclusions: This is the first known demonstration of a novel MMAS to maintain human heart tissue. Preliminary evidence suggests that the system provides a useful experimental technology, complementary to those currently available. The MMAS may be easily used to study other experimental conditions such as ischaemia/reperfusion injury and pharmacological drug testing.