PhD Studentship: Bioinspired fluidic metamaterials for passive directional water transport

Metamaterials use engineered structures to achieve functionality that the constituent materials alone cannot provide. This project explores novel bioinspired fluidic metamaterials which use hierarchical surface patterns inspired by carnivorous plants to control the speed and direction of water transport. Precision control of wetting and liquid flow on surfaces has the potential to transform medical care, save resources, mitigate the effects of climate change and optimise production processes. Engineered surfaces with defined fluid transport properties can revolutionise healthcare applications such as microfluidic point-of-care diagnostics, automated drug delivery, or more efficient wound drainage. Capturing and directing water is essential for fog water harvesting in arid regions.

Passive micro-irrigation systems save water and energy while increasing crop yields. Passive fluid transport surfaces can also improve the sustainability of manufacturing processes by optimising the supply of lubricants and extending the lifetime of moving parts. Insect-eating pitcher plants have hydrophilic trapping surfaces with extraordinary capacity to transport and direct water. The collar-shaped rim of their pitfall traps features ridges and grooves on two distinct length scales, with the microscale grooves further intersected by acute angled, overhanging arches. This is a natural metasurface: the anisotropic hierarchical microtopography makes water spread against gravity within milliseconds and form a thin film on which insects aquaplane to their death.

However, no study to-date has systematically investigated how the microtopographical features interact with each other and with the intrinsic hydrophilicity of the surface to determine wetting and fluid flow. Without this understanding, we are currently unable to unlock the full potential of bioinspired surface design for the microscale control of liquid flow.

This PhD takes a three-step approach:

1. Characterize the diversity of natural plant surfaces and quantify their capacity to guide and transport water. Engineering and Physical Sciences Research Council Doctoral Landscape Award
2. Fabricate synthetic surface replicas (PDMS casts) and systematically vary their hydrophilicity using oxygen plasma treatment to disentangle the contributions of surface chemistry and topography on wetting and water spreading.
3. Utilise two-photon polymerisation, a nanoscale 3D-printing technology, to investigate the effects of individual topographical features (macro- and microscale grooves, overhanging arches) on wetting and water spreading in isolation. These experiments will provide a mechanistic understanding of the functional significance of each topographical feature. By varying feature shape, size and spacing within and beyond the natural parameter space, the student will identify the functional limits of water transport on pitcher plant-inspired metasurfaces.

The data generated from this PhD will provide the foundation for the development of computational models that can accurately predict fluid behaviour on hierarchically ridged surfaces, ultimately the first step towards evidence-based precision design of bioinspired metasurfaces with application-optimised fluid transport properties.

The student will join a culturally diverse, interdisciplinary lab with two decades of experience studying specialised plant surfaces and carnivorous plant traps, supported by two co supervisors with backgrounds in Physics (Calum Williams, Exeter Centre for Metamaterial Research and Innovation) and Engineering (Halim Kusumaatmaja, Institute for Multiscale Thermofluids, University of Edinburgh). They will develop a diverse skillset including surface design, microfabrication and characterisation, experimental design and execution, data analysis, modelling, communication and teamwork.

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