(14i) Mechanical Stress Sensing with Molecularly Thin Films

Polydiacetylenes (PDAs) are a unique class of polymers that exhibit controllable colorimetric transitions. From an initial non-fluorescent blue phase, application of different stimuli (light, heat, or mechanical stress) can induce a transition to a fluorescent red phase. This blue to red transition makes PDAs ideal for potential use as sensors. Furthermore, PDAs derived from fatty acid diacetylenes can form self-assembled vesicles and Langmuir films.

I will present our recent work in developing high-quality PDA vesicles and Langmuir films for use as mechanical stress sensors of cell exerted forces. Fatty acid diacetylenes compressed on a Langmuir-Blodgett trough form stable trilayer films which were then polymerized via UV light. The mechanical stress sensitivity of the films can be quantitatively controlled by the fatty acid chain length, subphase composition and film depositions conditions. This behavior was quantified using a coupled fluorescent microscope­­â€”Surface Forces Apparatus. It was found that increasing the monomer chain length directly increased the blue to red transition stress threshold. These stresses are comparable to cell-exerted stresses. This was then demonstrated by tracking the locomotion and migration of the slime mold Physarum polycephalum, revealing new phenomenon as the slime mold explores its environment.