Biology subjects

Pugno, N. M.

Publications and source records attributed to Pugno, N. M..

4 recordsLinked to original sources

bioRxiv2020

Micromechanical homogenisation of a hydrogel-filled electrospun scaffold for tissue-engineered epicardial patching of the infarcted heart

This study aimed at developing a formulation to link microscopic structure and macroscopic mechanics of a fibrous scaffold filled with a hydrogel for use as a tissue-engineered patch for local epicardial support of the infarcted heart. Mori-Tanaka mean field homogenisation, closed-cell foam mechanics and finite element (FE) methods were used to represent the macroscopic elastic modulus of the filled fibrous scaffold. The homogenised constitutive description of the scaffold was implemented for an epicardial patch in a FE model of a human cardiac left ventricle (LV) to assess effects of patching on myocardial mechanics and ventricular function in presences of an infarct. The macroscopic elastic modulus of the scaffold was predicted to be 0.287 MPa with the FE method and 0.290 MPa with the closed-cell model for the realistic fibre structure of the scaffold, and 0.108 and 0.540 MPa with mean field homogenization for randomly oriented and completely aligned fibres. Epicardial patching was predicted to reduce maximum myocardial stress in the infarcted LV from 19 kPa (no patch) to 9.5 kPa (patch), and to increase the ventricular ejection fraction from 40% (no patch) to 43% (patch). The predictions of the macroscopic elastic modulus of the realistic scaffold with the FE and the closed-cell model agreed well, and were bound by the mean field homogenisation prediction for random and fully aligned fibre orientation of the scaffold. This study demonstrates the feasibility of homogenization techniques to represent complex multiscale structural features in an simplified but meaningful manner.

bioengineering↗

bioRxiv2019

Mechanics of snake biting: Experiments and modelling

Among all the vertebrates, snakes possess the most sophisticated venom delivering system using their fangs. Fangs of many animals are well adapted to the mechanical loads experienced during the functions such as breaking the diet and puncturing the skin of the prey. Thus, investigation and modelling of puncturing mechanics of snakes is of importance to understand the form-function relationship of the fangs and tissue-fang interactions in detail. We have thus chosen fangs of two snake species i.e. viper (Bitis arietans) and burrowing snake (Atractaspis aterrima), with different shape and size and performed insertion experiments using tissue phantoms. Our results showed that both the species have similar mechanical properties but there was a difference in the insertion forces owing to the difference in shape of the fang. Also, our modelling of the fang-tissue interactions predicted some parameters close to the experimental values. Thus, our study can help in the development of bioinspired needles that can potentially have reduced insertion forces and less damage to the tissue.

bioengineering↗

bioRxiv2019

Mechanics of wood boring by beetle mandibles

Wood boring is a feature of several insect species and is a major cause of severe and irreparable damage to trees. Adult females typically deposit their eggs on the stem surface under bark scales. The emerging hatchlings live within hard wood during their larval phase, avoiding possible predation, whilst continually boring and tunneling through wood until pupation. A study of wood boring by insects offers unique insights into the bioengineering principles that drive evolutionary adaptations. We show that larval mandibles of the coffee wood stem borer beetle (Xylotrechus quadripes: Cerambycidae) have a highly sharp cusp edge to initiate fractures in Arabica wood and a suitable shape to generate small wood chips that are suitable for digestion. Cuticle hardness at the tip is significantly enhanced through zinc-enrichment. Finite element model of the mandible, based on the differential material properties at the tip, intermediate and base regions of the mandible, showed highest stresses in the tip region; these decreased to significantly lower values at the start of the hollow section. A hollow architecture significantly reduces bending stresses at mandibular base without compromising the structural integrity. A scaling model based on a fracture mechanics framework shows the importance of the mandible shape in generating optimal chip sizes. These findings contain general principles in tool design and put in focus interactions of insects and their woody hosts.

bioengineering↗

bioRxiv2019

Prey capturing and feeding apparatus of dragonfly nymph

Aquatic predatory insects, like the nymphs of a dragonfly, use rapid movements to catch their prey. Dragonfly nymphs are voracious predators that feed on smaller aquatic organisms. In this study, we examine dragonfly nymph (Libellulidae: Insecta: Odonata) mouthparts that are used in prey capturing and feeding. In particular, we characterise the morphology of the labium and mechanical properties of the mandibles of the nymph. Additionally, we record and analyse the preying mechanism using high-speed photography. The morphological details suggest that the prey capturing mechanism is a complex grasping mechanism with additional sensory organs that might aid in sensing the surroundings. The times taken for the extension and retraction of labial organ during prey capture was 187{+/-}54 ms. The Youngs modulus and hardness of the mandibles samples were 9.1{+/-}1.9 GPa and 0.85{+/-}0.13 GPa. Gradation in the mechanical properties was also observed in the mandible tip regions with increased properties at the tip end. The overall mechanism with its sensory capabilities provides a unique design to develop bioinspired underwater deployable mechanisms.

bioengineering↗