The activity of our team has focused primarily on reproducing on a computer the failing of polymeric fibers under moderate tensile loading, brought about by the geometric strain of individual chains and by thermal fluctuations. This seemingly simple process is indeed exceedingly complex at the microscopic scale of atoms and molecules, taking place through the random nucleation of an initial defect (a crack), slowly propagating with time, and eventually triggering a final fiery stage of collective collapse.
Besides basic science reasons, our study is motivated by the interest in the mechanical properties of fibers made of biopolymers, such as proteins, poly-saccharides (i.e.,complex sugars), bundles of DNA and RNA fibers. The mechanical properties of these systems have biological implications. For instance, cancerous tissue differs from the healthy one also in terms of rigidity or elasticity, fragility and toughness. Moreover, most of the bio-systems of interest for our study are of nanometric size. Hence, the insight gained from our research can be transferred to a variety of other research subjects, including bio-medicine, pharmacology and especially drug-delivery, nanotechnology.
As we reduce the system dimensions from micro to nano scale, surface properties become increasingly important. We have studied the thermodynamics of stretching and fracture in single polymer chains in detail where we have focused on the effects due to the systems being small. Thermodynamics is usually limited to working for large systems, but we demonstrate that thermodynamic description still works for stretching individual molecules. This is important for how to describe energy conversion at the single-molecule level.
Polymers are central in many industrial contexts. Polymer cellulose is becoming more and more important as a building block for the development of new materials, cosmetics, as an additive, biomedical applications and in textiles. A bottleneck in the utilization of the good properties of cellulose is to break it down into its constituents. To get through this bottleneck, we study the dissolution mechanism of cellulose bundles under oscillating tensile load. We are now beginning to gain a better understanding of the special conditions that are required to bring about dissolution.
The project ended up focusing on the mechanical and thermodynamic properties of PEO (Polyethylene Oxide) polymer bundles as a model for bio and bio-inspired materials like tendons. The approach was mainly theoretical/computational and involved a close collaboration between physical chemists and computational physicists/material scientists.
Polymeric fibres made of proteins and of polysaccharides represent one of the important structural motifs of bio-systems. In living organisms, fibres are usually assembled in bundles, inter-linked to form gels, or incorporated into bio-minerals, giving origin to a variety of extended tissues such as muscles, cartilage and bones. Present days technology strives to match the properties of these remarkable materials, in many cases attempting to imitate their hierarchical structures, starting from the molecular building blocks to the texture of macroscopic tissues.
The focal interest of our experimental and computational/theoretical collaboration are bio- and bio-inspired fibrous materials for bio-medical applications, exemplified by bio-compatible polymeric adhesives for surgical sutures, gel scaffolds for skin regeneration, artificial tissues to replace tendons and cartilage structures.
Our plan has an applied and a basic science content.
The applied side consists in the development of computer codes able to predict mechanical properties of macroscopic samples and tissues from the structure and elastic behaviour of the individual fibres, based on their self-assembly into bundles and gels.
To achieve this goal, a great deal of new basic understanding is required, concerning the role of the hierarchical supra-molecular organisation of proteins and saccharide polymers into extended 3D structures.To this aim, computations and experiments will be carried out to infer mechanical properties of macroscopic samples and tissues from the structure and elastic behaviour of the individual fibres, accounting for defects, for density fluctuations, for translational and orientation ordering.
A graduate student and a Researcher (Dr. Rajesh Kumar, 1 year) are required to carry out the project.
The organisation of our plan and the composition of our team are meant to pave the way for a larger and more ambitious undertaking on the European scale under the Horizon-2020 framework