Using microcantilever sensors to measure poly(lactic-co-glycolic acid) plasticization by moisture uptake

Polymeric materials absorb water when exposed to humidity or in contact with aqueous solutions. The polymer and water molecules interact, changing the physicochemical parameters of the material; the most noticeable effect is a decreased glass transition temperature (Tg), known as plasticization. We used microcantilever sensors to measure the Tg versus moisture content in poly(lactic-co-glycolic acid) (PLGA), a biodegradable polymer used in implants and as a drug carrier. We demonstrate a concomitant measurement of the mass absorption and Tg using nanograms of material and an inexpensive setup. The standard deviation of Tg for this system was 0.025 °C, and the variation in Tg with respect to a 1% RH change was clearly resolved. The decrease in the Tg of PLGA was linear (R2 = 0.99) at a rate of 6.03 ± 0.57 °C per mass% of water absorbed. The initial dry Tg of PLGA was extrapolated to 41.24 ± 0.07 °C.