A group of researchers from the Indian Institute of Science Education and Research (IISER) Kolkata and Indian Institute of Technology Kharagpur, developed a new class of materials that they claim can repair themselves when fractured, within milliseconds.
The research has also made it to the coveted Science journal published by the American Association for the Advancement of Science. The scientists claimed that the highly crystalline materials, when broken into pieces, can self-heal and re-join in a matter of a second, and repair themselves so precisely that they become indistinguishable from the undisturbed materials.
The scientists hope that the discovery can spark a revolution in the field of digital technology, such as broken screens of gadgets and other new-age technologies.
The researchers said materials applied in technologies undergo mechanical impacts which often make the devices irreparable. The idea prompted the team to delve deep in search of self-repairing materials to enhance the longevity of the devices without external intervention.
“Wound healing in living tissue and bone has inspired many synthetic self-healing polymers, gels and other soft materials in the last decade or so. However, replicating such repair in crystalline materials has remained a challenge as they are rigid and prevent diffusion of material at the damaged part due to dense and regularly arranged molecules in them,” a statement released by the team read.
Professor C Malla Reddy, a recipient of the prestigious 2015 Swarnajayanti fellowship from the department of science and technology, and his team at Kolkata-based IISER developed a new class of solid materials that with a head-to-tail (positive end-to-negative end) polar arrangement in the crystalline state generates opposite electrical potentials at the fractured surfaces. These charges allow instant recombination and self-repair of the broken crystals without any external help. The scientists said that during the repair, fractured pieces travel with a honeybee wing-like motion with acceleration comparable to diesel cars.
Another team from IISER led by Professor Nirmalya Ghosh used a custom-designed state-of-the-art polarisation microscopic system to probe and quantify the structural order of the piezoelectric self-healing organic crystals with nanometer-scale spatial resolution.
The scientists said that these crystals, which belong to a general class of piezoelectric materials, can generate electricity under pressure, which in turn can heal and retain their crystalline nature which is important for many applications.
Piezoelectric crystals have a broad range of applications in precision engineering, including transducers, mechanical sensors, energy harvesters, biomedical implantables, etc. Piezoelectricity studies conducted by Professor Bhanu Bhusan Khatua and his student, Dr Sumanta Karan from IIT Kharagpur, evaluated the potential of these self-healing crystals for electricity generation and durability in devices.
“Since the previous decade, tremendous research has been done to find self-healing property in the unnatural polymers, gels and composites which are soft and amorphous in nature. Various strategies have been employed to mimic nature but almost all of them need at least one stimulus such as heat, light, solvent or a chemical healing agent. And universally all materials fail when the broken parts fall apart’, Professor Reddy said.
IISER’s Surojit Bhunia further said, “Taking cues from nature we explored the inherent piezoelectricity of crystalline materials for finding self-healing property. It is long known that piezoelectricity plays a key role in initiating self-healing in mechanically wounded natural biomaterials, like bone and collagen. Hence, our discovery in organic materials may provide further insights into the complex natural materials.”
Another corresponding author of this paper, Professor Nirmalya Ghosh, who is also the laureate of the SPIE G G Stokes award in optical polarisation, said, “We have used a custom-designed state-of-the-art polarisation microscopic system at IISER Kolkata to probe and quantify the structural order of the piezoelectric organic crystals with nanometer-scale spatial resolution. This unique experimental system in combination with a suitable polarisation analysis model enabled quantitative assessment and understanding of the self-healing behaviour of the crystals by sensing changes in nanoscale structural anisotropy.”
Professor Ghosh added that the new class of optical material exhibiting strong polarisation and non-linear optical response and having extraordinary self-healing capability may open the door for a new generation of integrated and miniaturised photonic devices for numerous technological applications in optical sensing, in high precision metrology and in optical nano probing among others.
Dr Sumanta Karan from IIT Kharagpur said Piezoelectric materials can withstand prolonged mechanical loading-unloading cycles in many applications such as a transducer, energy harvesters, mechanical sensors, actuators etc, which is why its fracture healing ability is critical to boosting the durability.
The team of scientists comprises Professor Reddy, Professor Ghosh, Professor Khatua and the team, including Surojit Bhunia, Shubham Chandel, Sumanta Kumar Karan, Somnath Dey, Akash Tiwari, Susobhan Das, Nishkarsh Kumar, Rituparno Chowdhury, Saikat Mondal, Ishita Ghosh and Amit Mondal. The materials in the work are patented by IISER Kolkata.
