Mickael Castro

Evaluation of force generation mechanisms in natural, passive hydraulic actuators.

Pine cones are well known natural actuators that can move their scales upon humidity gradient. The mechanism manifests itself through a displacement easily observable by the naked eye, but coupled with stress generation. In ancient Egypt, wooden wedges were used to break soft blocks of stone by the generated swelling stress. The purpose of the present study is to evaluate the ability of pine cone scales to generate forces while being wetted. In our experiments, a blocking force of around 3N is measured depending on the position on the pine cone where the scales are extracted. A fairly good agreement is obtained when theoretical results based on bimetallic strip systems are compared with experimental data, even if overestimation is observed arising from the input data considered for dry tissues. Inspired by a simplified pine cone microstructure, a biocomposite analogue is manufactured and tested. Although an adequate blocking force can be generated, it has a lower value compared to natural pine cones which benefit from optimized swelling tissue content and interfacial bond strength between them. This study provides new insights to understand the generation of force by pine cones as well as to develop novel biocomposite functionalities.

Sulfonated poly(ether ether ketone) [SPEEK] nanocomposites based on hybrid nanocarbons for the detection and discrimination of some lung cancer VOC biomarkers

The analysis of a volatolome is a promising approach to allow the early diagnosis of diseases such as cancers. However, one important challenge is to take the chemical fingerprint of the complex blend of volatiles, for many of them only present at the sub-ppm level. We have investigated a facile route to differentiate the chemo-resistive behaviour of quantum resistive vapour sensors (vQRS) and provide them with a strong methanol selectivity by simply changing the sulfonation degree of poly(ether ether ketone) up to 85%. The hybridization of carbon nanotubes (CNTs) with fullerene (C60) structured in a 3D architecture by spray layer-by-layer (sLbL) has allowed us to boost significantly the sensitivity of sensors to reach the sub-ppm level (340 ppb). After their integration into an e-nose, PEEK-nanocarbon sensors were found to effectively discriminate both single and binary mixtures of volatile organic compounds (VOCs) and among all biomarkers to detect preferentially methanol with a high signal to noise ratio (200).

Flax fibers – epoxy with embedded nanocomposite sensors to design lightweight smart bio-composites

Abstract Lightweight smart bio-composites with damage sensing ability have been designed. Conductive polymer nanocomposites-based quantum resistive sensors (sQRS) have been embedded in a unidirectional flax fibers – epoxy bio-composite samples using a spray layer by layer process to monitor their structural health and eventually anticipate their failure. The in situ piezo-resistive responses of sQRS under monotonic and incremental cyclic tensile tests were analyzed to learn more about the damage mechanisms and predict behavior changes in the laminated bio-composites. sQRS signals were found to be well correlated with the typical mechanical traces of flax fibers/epoxy composites, thus allowing reliable conclusions about structural changes taking place in the core of the bio-composite under strain. In particular, the analysis of sQRS gauge factor evolution with strain level proved to be helpful to assess the probability of damage. This new contribution to the understanding of flax fiber-based composites’ mechanical behavior is expected to be of special interest as the sliding of fibrils weakly assembled in bundles makes it difficult to approach.

Different strategies to Taylor quantum resistive vapor sensors functionality to detect sub ppb of volatile biomarkers

This research aimed to enhance the mechanical properties of carbon steel (AISI 1040) by an optimized and controlled heat treatment process. It is well-known that some mechanical properties such as hardness and toughness are inversely related to each other. Thus, the target objective of the work was to find the best possible heat treatment for carbon steel to get an optimum combination of tensile strength, hardness, and toughness. Experimental samples (108 specimens) were prepared and divided into four groups which were subjected to different heat treatment conditions and different mechanical tests. The mechanical properties of the groups were evaluated for comparison and analysis after the series of heat treatment processes. The procedure started by heating the specimens to 860°C to harden the carbon steel and then quenching them in oil or water, next tempering processes were carried out at several tempering temperatures. It was found the quenching agent and the tempering temperature had considerable effect on the mechanical properties while the optimum parameters depended on the properties that were preferred.