Bio-inspired and bio-mechanical design

Adaptation of Flow Networks and Exclusion Distances

Bronchi, arteries and veins, tree branches and roots, exhibit a fractal topology, i.e. networks formed by channels that successively split into smaller channels. Is the fractal topology optimal for all transport processes taking place between a porous system and a host medium? A thorough review of the geometry of natural flow networks involved in transport processes is performed in order to identify optimal topologies and the underlying physical principles. Finite Difference computations were performed to illustrate the gain of efficiency of a heat exchanger that has a fractal topology (figure below).

Picture: Arson and Santamarina, 2014

Bio-inspired optimization of interwoven flow networks subject to topological and environmental constraints

The fundamental science questions that drive our research are: Why are flow networks fractal in nature? How does nature form flow networks? Can flow networks accommodate to topological constraints, adapt to environmental fluctuations and sustain intra- and inter- species competition? As part of our bio-inspired investigation method, we pose the following questions: Are natural network topologies optimal for engineering design? Is it practical, sustainable and efficient for engineers to deploy networks like living organisms do? Is adaptive design resilient, safe and sustainable? Our goal is to understand accommodation, adaptation and competition of biological networks to optimize the efficiency, resiliency and versatility of utilities networks (e.g. sewage systems, buried cables). We model the formation of networks made by roots and slime mold (Physarum Polycephalum) under variable constraints on environment topology, moisture, temperature, light and chemical composition. We tested the constructal theory for slime mold network deployment and highlighted the information and technology missing to use bio-mimicry based on slime mold growth. We are now designing 2D experiments on plant roots in the absence of obstacles, and with obstacles of various sizes and shapes. We will record videos of plant growth and monitor water and nutrient consumption during the experiments. We will formulate theoretical and numerical models of root growth, and benchmark numerical codes based on continuum approaches vs. on probability architecture. Simultaneously, we will conduct fluid injection tests, observe the formation of fluid flow paths and calibrate numerical models of fluid flow networks. The root system analog is expected to provide a fundamental understanding of the optimal accommodation of fluid flow networks that do not present a fractal topology.

Pictures: Shishkov, 2016

Self Consistent model of dentin stiffness based on microscope image analysis

As one of the main component of teeth with pulp and enamel, dentin plays a major role in tooth strength and mechanical behavior. Dentin is composed mainly of collagen fibrils embedded in a matrix of hydroxyapatite and presents a complex microstructure composed of long tubules embedded in a matrix of inter-tubular dentin; based on these observations, at the micro-scale, dentin can be treated as a fiber-reinforced composite. We used Hashin's self-consistent model to predict dentin orthotropic stiffness. The volume fractions of collagen, peri-tubular dentin and inter-tubular dentin and the orientation of tubules were determined by a statistical analysis of dentin micrographs. Ecole Centrale's MEB and SEM were used to observe dentin at different distances from the pulp within a central section of tooth. Compression tests are currently being conducted at Ecole Centrale in order to calibrate and verify the proposed homogenization scheme. If successful, the model will be extended to three dimensions and applied to demineralized and resin-injected dentin, in order to assess the performance of caried tooth reparation techniques

Pictures: Le Bivic, 2015