Philippine E-Journals

Investigations on the Leaf Surface Ultrastructures in Hibiscus tiliaceus Linn.: An Inspiration for Future Biomimetic Applications

Nesse Grace U. Resurreccion | Mariquit M. De Los Reyes | Cresencia M. Lawas | Emmanuel Garcia

 

Abstract:

Biomimetics harnesses nature-inspired principles and properties in the design and synthesis of advanced materials that address simple to complex problems, pushing innovation and ingenuity beyond limits. The use of plants as biological models has provided the necessary stimulus for biomimicry. In this study, the abaxial (bottom) and adaxial (top) leaf surfaces of Hibiscus tiliaceus Linn. were investigated with respect to two parameters: ultrastructures that define the surface morphology, and wetting behavior that is influenced by the hydrophobic or hydrophilic property of the plant leaf. Imaging techniques show that the abaxial side of the leaf consists of a dense network of non-glandular, simple, 8-arm stellate trichomes that are overlapping and intertwined. The adaxial side consists of the same type of trichomes, but with shorter stellate arms, sparsely arranged on the surface, and appears more appressed to the leaf lamina. Results of the contact angle measurements showed that the adaxial surface is hydrophilic (71.71° ± 4.14°) while the abaxial surface is nearly superhydrophobic (142.98° ± 2.92°). Images from atomic force microscopy, plots of height density versus nanostructure height, and log (PSD/nm4 ) vs frequency (per μm) show a higher variation in nanostructure height for the adaxial surface. While roughness is higher on the adaxial surface, fewer single stellates are seen, unlike the greater trichome coverage observed on the abaxial side. The effect of a homogenous overlay of dense stellates on the abaxial surface, and the height variations of nanostructures on these stellates, result in a more effective overall roughness which can explain the nearly superhydrophobic property exhibited by the bottom side. This corroborates published studies that the hierarchy or complexity of surface ultrastructures can be associated with the properties and functions exhibited by plants. This is the first report on the surface morphology and wetting behavior of H. tiliaceus. Data provided in this work will be useful in exploring the future biomimetic potential of the plant, say in the areas of bioremediation and self-cleaning technologies.