Raw Data for the Elastic Modulus of Sporopollenin
Meredith, J. Carson
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Sporopollenin, the polymer comprising the exine (outer solid shell) of pollens, is recognized as one of the most chemically- and mechanically-stable naturally-occurring organic substances. The elastic modulus of sporopollenin is of great importance to understanding the adhesion, transport, and protective functions of pollen grains. In addition, this fundamental mechanical property is of significant interest in using pollen exine as materials for drug delivery, reinforcing fillers, sensors, and adhesives. Yet, the literature reports of sporopollenin modulus are very limited. We provide the first report of the elastic modulus of sporopollenin of pollen particles from three plant species: ragweed (Ambrosia artemisiifolia), pecan (Carya illinoinensis) and Kentucky bluegrass (Poa pratensis). Modulus was determined with atomic force microscopy by using direct nanomechanical mapping of the pollen shell surface. The moduli were atypically high for noncrystalline organic biomaterials, with average values of 16 ± 2.5 GPa (ragweed), 9.5 ± 2.3 GPa (pecan) and 16 ± 4.0 GPa (Kentucky bluegrass). The amorphous pollen exine has a modulus exceeding all non-crystalline biomaterials, such as lignin (6.7 GPa) and actin (1.8 GPa). In addition to native pollens, we have investigated the effects of exposure to a common preparative acid-base chemical treatment and elevated humidity on modulus. Acid-base treatment reduced the ragweed modulus by up to 58% and water vapor exposure at 90% relative humidity reduced the modulus by 54% (pecan) and 72% (Kentucky bluegrass).