The atypically high modulus of pollen exine

Area of Science:

• Biomaterials Science
• Polymer Science
• Nanotechnology

Background:

• Sporopollenin forms the chemically and mechanically stable exine of pollen grains.
• Its elastic modulus is vital for understanding pollen's functions and for biomaterial applications.
• Existing data on sporopollenin's elastic modulus is scarce.

Purpose of the Study:

• To report the elastic modulus of sporopollenin from three plant species.
• To investigate the impact of chemical treatment and humidity on sporopollenin's mechanical properties.
• To compare sporopollenin's modulus with other non-crystalline biomaterials.

Main Methods:

• Atomic force microscopy (AFM) was used for direct nanomechanical mapping.
• Indentation tests were performed on pollen particles of ragweed, pecan, and Kentucky bluegrass.
• The effect of base-acid treatment and high humidity (90% RH) on modulus was evaluated.

Main Results:

• Sporopollenin exhibited atypically high elastic moduli: 16 ± 2.5 GPa (ragweed), 9.5 ± 2.3 GPa (pecan), and 16 ± 4.0 GPa (Kentucky bluegrass).
• These values exceed those of known non-crystalline biomaterials like lignin and actin.
• Base-acid treatment decreased the modulus by up to 58%, while 90% RH reduced it by 54-72%.

Conclusions:

• Sporopollenin possesses a remarkably high elastic modulus for an amorphous biomaterial.
• Its mechanical properties are sensitive to chemical treatments and environmental humidity.
• Findings support sporopollenin's potential as a robust biomaterial and inform its use in applications like drug delivery.