A UV nanoimprint lithography (UVNIL) process and hybrid polymer nanocomposites are used to produce self-cleaning surfaces, which replicate the sub-micron textures of natural superhydrophobic surfaces such as rose petals and lotus leaves. Food packaging with such surfaces is useful to avoid wasting foods, and to reuse food ware with no need of cleaning.
Gonzalez Lazo et al, 2016. A Facile in Situ and UV Printing Process for Bioinspired Self-Cleaning Surfaces, Materials vol. 9, p. 738
The SHeMat project is a training and research network funded within the scope of the “Seventh Framework Programme” by the European Commission’s “Marie Curie” programme. SHeMat involves 9 partners from 6 different countries as well as 4 associated partners from the private sector. The research activities of SHeMat are situated in the field of self-healing materials. The partners address both fundamental research in material development as well as the complementary aspects of conceptual process chain analysis from a more industrial perspective. Concepts found in nature, for example regarding wound healing in plants are analyzed, and their application into ceramics, polymers and composites are considered. EPFL researchers focused on self-healing coatings and composites based on supramolecular hybrid networks.
Functional composites with active sensing and repair
This project, funded by the Swiss National Foundation, focuses on the analysis and development of functional composite materials with damage control and repair abilities. These composite materials are manufactured by Liquid Composite Molding and integrate healing agents to control and repair damage, under the form of capsules, or of a polymeric second phase. In this project, emphasis is placed on the combination of healing and toughness improvement in fiber reinforced composites, through the combined use of thermoplastic polymers (in the form of discrete powders or fibers or thermoplastic/thermoset blends that phase separate upon polymerization, principally based on PCL polymers). Heating and crack closure, required to activate healing in composites, will be achieved with the help of SMA wires introduced in the reinforcement. The desired outcome of this research is, through analysis of the mechanisms underlying toughness, healing and processing, to propose structural materials with improved properties, with the added capability of repair, assisted by heat and local crack closure, and to propose guidelines and tools to optimize the materials composition and processing route according to the final requirements.
Biocompatible scaffolds for tissue engineering
Composites that mimic bone and cartilage structures for faster tissue regeneration
Aim of the projects are to develop degradable and biocompatible scaffolds for tissue engineering. Bioresorbable scaffolds, i.e. porous constructs, seeded with the appropriate type of cells will provide a template for tissue regeneration, while slowly resorbing, to finally leaving no foreign substances in the body, thus reducing the risk of inflammation and offering more cost effective solutions. Polymers are combined with ceramic prior to be physically foamed or fibres are placed by 3D printing to elaborate various porous and anisotropic biocomposites.
This projects is funded by SNF, more detials can be found here: http://p3.snf.ch/project-150190#
Research Lab: prof. Pierre-Etienne Bourban, Laboratoire de technologie des composites et polymères, in collaboration with the Laboratory of Biomechanical Orthopedics (LBO) at EPFL and the Centre Hospitalier Universitaire Vaudois (CHUV).
Organic nanowires are model systems for the investigation of charge transport in organic semiconductors under nanoscopic confinement, and may serve as potential building blocks for integrated circuits in the future. However, reliable structure-property relationships between the molecular parameters, the intermolecular π–π interactions, the nature of the charge carriers, and macroscopic transport properties are scarce. We have developed a reliable model system for the self-assembly of various chromophores into well-defined nanowires with excellent π–π overlap of the chromophores. These nanowires exhibit an unprecedented light-induced “self-doping”, resulting in exceptionally high charge densities and band-like transport properties.
Our research activities focus on conjugates of synthetic polymers and biologically-inspired peptide sequences. The peptide sequences are adapted from protein structures and direct the structure formation of the synthetic polymer. The use of such peptide sequences offers several unique advantages. First of all, due to the very specific folding and organization properties of the peptide sequences, they allow the organization of synthetic polymers in complex, hierarchically-organized structures that are very difficult to generate otherwise. Secondly, the structure and properties of peptide – synthetic hybrid block copolymers can be manipulated by single amino acid “mutations” in the peptide segments (see Strucutre page). The peptide sequence of the hybrid block copolymers cannot only be used to drive structure formation, but can also be used to encode specific functionalities. This is a subject of ongoing research efforts.
Functionally graded antimicrobial surfaces
In nature a vast diversity of functions rely on graded architectures, with continuous spatial changes of composition and morphologies. Synthetic functionally graded materials represent one of the many novel integrative and bio-inspired strategies as alternatives to conventional polymer processing and soft chemistry routes to produce hybrid organic/inorganic composites hierarchically organized in terms of structure and functions. Based on the principles of functionally graded properties and self-assembly, we created antibacterial surfaces with outstanding activity. These surfaces are made of graded polymer composites with controlled concentration profiles of photocatalytic Fe3O4@TiO2 core–shell nanoparticles. A photo-magnetophoretic process was invented to generate these surfaces. We also produced super-hard polymer-based surfaces, graded permittivity insulators and low stress coatings using this technique.
Cicade’s wings inspired antimicrobial surfaces
Cicada wings antibacterial nanosurfaces. Anti-microbial contamination of surfaces is a central challenge in medical and industrial applications. Conventional bio-chemical approaches rely on the coatings of biocidal sub-stances such as silver and antibiotics. Despite their wide use in various fields, chemical toxicity, antimicrobial durability and antimicrobial resistance remain critical problems. Alternatively, biophysical approaches prevent bacterial contamination by either anti-adhesive repelling or direct contact killing via micro/nanoscale surface topographies. Recently, nanopillar structures of natural cicada’s wings were found to be deadly to Gram negative bacteria by mechanically tearing the attached cells apart. Inspired by the well-defined nanostructures of cicada’s wings, several synthetic types of nanostructures were fabricated: nanopillars, nanorings and nanonuggets. It was found that all the Au nanostructures, regardless their shapes, exhibited similar excellent antibacterial properties. Our micro/nano-fabrication process is a scalable approach based on cost-efficient self-organization and provides potential for further developing functional surfaces to study the behavior of microbes on nanoscale topographies.
Reference: Wu et al, 2016. Antibacterial Au nanostrcutured surfaces, Nanoscale, 8, 2620, DOI: 10.1039/c5nr06157a
Antireflective surfaces for solar cells
Synthetic moth eye textures eliminate light reflection in the front encapsulation of solar cells, leading to a 5% photocurrent increase in thin film tandem a-Si:H and µc-Si devices. The sub-micron antireflective textures are optimized using optical simulations and replicated in a low-shrinkage and superhard hyperbranched polymer nanocomposite by means of a roll-to-roll UV nanoimprint lithography process.
Biomimicking micro/nanopatterned surfaces - 3D Nanolithography
LMIS1 has recently installed a brand new, ultra-high resolution 3D thermal scanning probe nanolithography (th-SPL) tool NanoFrazor. In th-SPL, the heated probe of few nm in radius in contact with the sample induces local mechanical and chemical surface modifications. Such technique allows fabrication a variety of 3D topographies to high accuracy. These structures are in need in printed optics, nanophotonics, medicine and can be used for generation of the templates for nanoimprint lithography.
Nervous system of composite structures
Several projects deal with the introduction of fiber optic sensors in composite structures, quite similarly to a nervous system in the human body. These thin embedded Fiber Bragg Grating sensors send information on local strains and temperature in the structure, which can be used for design validation, performance development and real-time monitoring. A good example was the integration of these sensors in the Alinghi America’s cup challenges in 2007 and 2010 (http://discovery.epfl.ch/page-105680-fr.html)
ENCOMB project (2011-2015)
The EU-FP7-ENCOMB project deals with the Extended Non-Destructive Testing of Composite Bonds. The central problem addressed within ENCOMB is the development of advanced non-destructive testing (NDT) methods for a reliable quality assurance concept for adhesive bonding of carbon fiber reinforced polymers (CFRP) structural aircraft components. The primary objective of ENCOMB is the identification, development, and adaptation of methods suitable for the assessment of adhesive bond quality. The EPFL team contributes by fabricating Bragg grating optical fiber sensors in 125-micron and 50-micron-diameter optical fibres, their integration into different CRFP samples and bond layers, and their characterisation during curing, and during service at different temperatures and exposure to water and contaminated water. Mechanical models are being developed simulating the behavior of CRFP, adhesive, and sandwich structures under thermal load and water diffusion.
Project Leaders: Dr Hans Limberger (Optical Fiber Device group), Prof. John Botsis (Laboratory of Applied Mechanics and Reliability Analysis), Prof. Veronique Michaud (Laboratoire de technologie des composites et polymères)
Silicone embedded distributed piezoelectric sensors for contact detection
The objective of this project is to design a soft, flexible, thin substrate capable of detecting contact. Such system can be used for wearable applications thus enabling the evaluation of external forces and for functionalizing the surface of surgical tools or robotics system allowing fast response contact detection. Layer by layer fabrication technique joined with materials selection allow the achievement low fabrication cost, scalability, fast prototyping and fine tuning of sensor transfer function.
Natural fibre composites
The research goes towards processing and enhanced properties of natural fibers and their biocomposites. We mainly work with flax and cellulose composites. The friction mechanisms in between the layers of each natural fibre explain the good damping performance of some composites used in sport applications for instance. Nano fibrillated cellulose is combined to hydrogels to offer a unique compromise of stiffness and damping in biomedical applications such the replacement of damaged nucleus pulposus in intervertebral disks.
Biologically induced calcite mineralization has been recently brought into focus as an alternative cementation mechanism for soils. The whole process lies on the metabolic activity of unicellular microorganisms that are responsible for generating those conditions that allow for the formulation of calcium carbonate crystals to take place. The technique has its base at two chemical reactions; the hydrolysis of urea catalyzed by the enzyme urease, produced by the bacteria strain Sporosarcina pasteurii, and the calcite precipitation. This knowledge is put to use in an emerging grouting technique called microbial induced calcite precipitation (MICP). By temporarily regulating the concentration of bacteria and chemical constituents in a soil, a new engineering material can be generated through the nucleation of calcite crystals inside the soil matrix. Understanding and controlling this alternative environmentally friendly soil reinforcement technique, exposes innovative applications, such as restoration of weak foundations, seismic retrofitting, erosion protection, seepage flow or pollution mitigation and construction of floating beaches.
Watch Dimitrios Terzis explain his PhD Thesis on this subject in a fun and simple way.
Terzis, D. et al. (2016) Géotechnique Letters 6, 50–57, http://dx.doi.org/10.1680/jgele.15.00134
Materials as chemical sensors
The objective is to explore the possibility of using spider dragline silk as sensing element for fibre-based biosensors by transmitting light through silk fibre and monitoring the change in the silk’s optical properties induced by biochemical compounds. The fast response and high sensitivity of the silk fibre in response to polar compounds paves the way for promising applications for biochemical sensing.
Biomimetic Pieris rapae’s Nanostructure and Its Use as a Simple Sucrose Sensor
We present the replication of the Pieris rapae butterfly optical structure. This butterfly has white wings with black spots. The white coloration is produced by light scattering on pterin beads ranging from 100 to 500 nm whereas black spots correspond to areas without pterin beads, thus revealing a highly pigmented layer underneath. In order to mimic the butterfly wing structure, we deposited SU-8 beads produced by electrospraying on a black absorbing layer made of black SU-8. We thereby replicated the optical effect observed on Pieris rapae. Additional experiments showed that the white coloration replication is a structural color. Finally, we further demonstrate that these optical engineered surfaces can be used for sucrose sensing in the range of 1 g/L to 250 g/L.
Full article here.
Stifness and Flexibility
Turtle shell inspired alpine skis
These alpine skis change stiffness in response to the skier’s position. EPFL researchers helped develop the new skis thanks to a mechanism that mimics turtle scales.
Nanostructures occurring naturally on plants or animals, such as the lotus or various butterflies, have inspired research into developing diverse materials and effects based on similar features. Surface gratings are one form of naturally occurring structural colors – for instance, on the less famous Troides magellanus. Gratigs are much easier to produce artificially then complex nanostructures such as those found in the Morpoho Butterfly. We have developed a new approach for generating visual effects with metallized gratings. Shadow evaporation of aluminum onto dielectric gratings is shown to produce strongly asymmetric color effects. Zero-order effects are combined with ±first-order transmission in the present structures to generate not only polarization but also orientation-dependent colors. We show that a wide palette of colors can be obtained by simply scaling the parameters of the dielectric base grating. The present approach therefore enables the fabrication of entire asymmetric images in a two-step process. Additionally, a floating screen film is created by placing the grating at an increased distance to the light source. The present structures could find applications as security or decorative elements and are well suited for mass production using high-throughput techniques such as roll-to-roll fabrication.
Reference: Lutofl et al, 2015,, Advanced Optical Materials,
Research Lab: prof. Olivier Martin, Nanophotonics and Metrology laboratory