Experimental demonstration of bindingless signal delivery in human cells via microfluidics

The cellular signal transduction is commonly believed to rely on the direct "contact" or "binding" of the participating molecule reaction that depends positively on the corresponding molecule concentrations. In living systems, however, it is somewhat difficult to precisely match the corresponding rapid "binding," depending on the probability of molecular collision, existing in the cellular receptor-ligand interactions. Thus, a question arises that if there is another mechanism (i.e., bindingless) that could promote this signal communication. According to this hypothesis, we report a cellular model based on the examination of intracellular calcium concentration to explore whether the unidentified signal delivery in cells exists, via a microfluidic device. This device was designed to isolate the cells from directly contacting with the corresponding ligands/molecules by the particular polydimethylsiloxane (PDMS) membranes with different thicknesses. Results show a significant increment of calcium mobilization in human prostate cancer PC-3 cells by the stimulation of endothelin-1, even up to a separated distance of 95 μm. In addition, these stimulated signals exhibited a bump-shaped characteristics depending on the membrane thickness. When the PDMS membrane is capped by SiO₂, a particular trait that resembles the ballistic signal conduction was observed. A theoretical model was developed to describe the signal transport process across the PDMS membrane. Taken together, these results indicate that the unidentified signal (ligand structural information) delivery could occur in cells and be examined by the proposed approach, exhibiting a bindingless communication manner. Moreover, this approach and our finding may offer new opportunities to establish a robust and cost-effective platform for the study of cellular biology and new drug development.