
Microgels are defined as swollen colloidal particles with diameters ranging from tens of nanometers to several micrometers in size.
We have developed a novel alkaline hydrolysis process that gives rise to pollen grains that were very much softer than its naïve counterparts. This process effectively converts the pollen grains into discrete, pliable microgels. The resultant pollen suspension transitions from a wet sand consistency to an increasingly translucent gel-like slurry with increased hydrolytic processing time.
1) Fan, Park, Shi, Zhang, Liu, Song, Chin, Ibrahim, Mokrzecka & Yang. Transformation of hard pollen into soft matter. Nature communications 11, 1449 (2020).
Microgel Synthesis
Similar to soapmaking, we have designed a sustainable and translatable approach to transform inert pollen into incredible building blocks

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Defatting: Treatment with organic solvent to remove excess lipid coating
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Shell extraction : Pollen incubation in alkaline conditions for 2 h at 80 °C under stirring condition
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Microgel formation : Extended incubation in alkaline conditions at 80 °C for up to 12 h
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Gelation : Swelling of pollen microgels induced by water rinsing

Properties
Stimuli-responsive swelling
By modulating the environmental pH or cation concentrations, the pollen microgels can instantaneously respond by spontaneously swelling or shrinking,
pH Responsive Swelling

Divalent Cation Responsive Swelling

Trivalent Cation Responsive Swelling




Properties
Soft Particles
Although renowned for its robustness, our modular synthesis methodology successfully softens the tough pollen shell, transforming hard pollen particles into pliable building blocks.
Increasing duration of incubation stage leads to corresponding decrease in modulus of the pollen shell

Young’s modulus values of exine and intine layers of various pollen microgels as a function of KOH incubation time.
Ratio of the Young’s modulus values of the exine and intine layers ( decreased from 2.7 to 1.2 after a 24h synthesis.
Fan & Park et al., 2020

Applications of pollen microgels
Pollen has unique geometrical structure with uniform size depending on plant species. Sporopollenin, that is a main component of outer layer of pollen, provides high chemical and mechanical strength. Based on literature, sporopollenin could have aliphatic-polyketide-derived polyvinyl alcohol units and 7-O-p-coumaroylated C16 aliphatic units, although the exact chemical and molecular structures are not fully understood yet. Pollen grains are known to be practically indestructible along with demonstrating excellent biocompatibility, and functionalized pollen particles have been used for environmental and biomedical applications(1-3).
Controlled alkali-treatment transforms pollen into soft microgel particles that can be applied to various conventional material processes. Individual pollen microgel particles can be used as smart drug delivery systems, which are responsive to pH or ion strength changes. Due to the specific microtopography and abundant active functional groups (hydroxy or carboxy) of the alkali-treated pollen materials, sophisticated functions could be achieved by chemical modifications or incorporating other functional micro/nano-materials.
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Wang, H.; Potroz, M. G.; Jackman, J. A.; Khezri, B.; Marić, T.; Cho, N.; Pumera, M. Bioinspired Spiky Micromotors Based on Sporopollenin Exine Capsules. Adv. Funct. Mater. 2017, 27 (32), 1702338.
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Maric, T.; Nasir, M. Z. M.; Rosli, N. F.; Budanović, M.; Webster, R. D.; Cho, N.; Pumera, M. Microrobots Derived from Variety Plant Pollen Grains for Efficient Environmental Clean up and as an Anti‐cancer Drug Carrier. Adv. Funct. Mater. 2020, 30 (19), 2000112.
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Tan, E.; Potroz, M. G.; Ferracci, G.; Jackman, J. A.; Jung, H.; Wang, L.; Cho, N. Light‐induced Surface Modification of Natural Plant Microparticles: Toward Colloidal Science and Cellular Adhesion Applications. Adv. Funct. Mater. 2018, 28 (18), 1707568.