Analysis: these artificial materials can be used in many settings, from de-icing aeroplane screens to smart healthcare devices such as stents
By Sairam Pamulaparthi Venkata and Michel Destrade, University of Galway
Will meta lenses with the ability to bend light make Harry Potter-style invisibility cloaks a reality soon? Can we seamlessly integrate artificial materials into the human body as smart tissues? Metamaterials are a new class of artificial materials with exotic properties, not encountered in nature (the Greek word "meta" means "going beyond"). They are made of uniquely designed patterns or structures which enables them to behave and interact with sound, light, electromagnetic fields and other forms of energy in unexpected ways.
Some of the novel properties of meta-materials include slowing and controlling the speed of light, cloaking objects from sound waves and even from view and de-ice or anti-fog coatings for aeroplane glasses/screens to help during landings. Some metamaterials expand in funny ways when stretched. For example, the "LittleHumans" clothing line for the Petit Pli company proposes textiles that can deploy and grow up to seven sizes as children age!
From Disruptive Innovation Festival, Ryan Mario Yasin talks about his Petit Pli company
Metamaterials can play a revolutionary role in biomedicine. In fact, they are already being used in custom-made shoes for diabetic patients to improve wound healing and prevent foot ulcers. Meta-implants for hip replacement are more feasible for bones compared to the traditional metal implants. Medical meta-bandages show enhanced conformability and better adhesion to the skin surface. Meta-biosensors for cancer detection can identify differences in the water content of tumorous and normal tissues. Magnetic metamaterials can help targeted drug delivery; the list goes on.
An interesting category within metamaterials is that of "auxetic" materials. Unlike regular metals or plastics, which thin out when pulled in one direction, these materials expand in all directions when pulled in one direction. To achieve this counter-intuitive property, the materials must be carefully designed at the microscopic scale with pattern assemblies of holes and matter.
As it turns out, cardiac, stomach, lung and skin tissues share these properties of auxetic materials. Hence, auxetic polymer gels are now being used as "dynamic organ patches" for wound sealing. These auxetic gels are better than traditional bandages because they can deform easily in perfect synchronisation with organs and joints, very much like the cardiac or arterial tissue can expand and contract during the diastolic/systolic cardiac phases.
From Duke University, Steve Cummer, professor of electrical and computer engineering at Duke University, explains the concept of metamaterials using some simple illustrations.
According to the World Health Organisation, 80% of premature heart attacks and strokes are preventable. Nonetheless, coronary heart disease is a major cause of death in Ireland and across the world. The most effective treatment so far is a minimally invasive technique called angioplasty, where stents are installed to expand narrow or blocked coronary arteries and increase blood flow to the heart.
Stents are small tubular structures made of wire mesh which deploy inside the artery to open it up and Ireland is a massive global producer of stents, representing four out of five stents used worldwide. Stenting is considered a relatively safe procedure, and more than one million angioplasties are conducted each year in the US alone.
Active research is still being carried out to enhance the efficacy and deliverability of stents, as well as to minimize issues such as inadequate stent expansion, stent fracture, and stent malapposition (poor contact with the vessel walls). Research on auxetic heart stents has shown promising results because auxetic heart stents can anchor better to the walls of arteries and reduce the risk of stent migration.
From TEDx Talks, Prof John Pendry on metamaterials and the science of invisibility
Another important application of metamaterials includes auxetic skin grafts for skin burns or infections. Millions of burn injuries are reported every year worldwide from kitchen incidents, industrial gas leaks or fire accidents. Split-thickness skin grafts are employed in severe cases where healthy skin, harvested from the patient's body, is transplanted to the burnt or infected areas. The rationale is to stretch the skin as much as possible to cover a large area.
Unlike the existing skin graft materials, which can only stretched to a maximum of three times their original size, auxetic skin grafts can potentially stretch up to 30 times. This property is crucial for grafts located at joints such as the elbow or the knee, where large stretches take place all the time.
Metamaterials can play a revolutionary role in biomedicine
To overcome the disadvantages of traditional biomedical implants, a new class of smart medical prosthetics is gaining significant prominence. These smart metamaterials are multifunctional, with patient-specific and self-aware novel features. For example, smart spinal-fusion cage implants can help in bone healing by responding to their environment and self-monitoring their condition. Similarly, metamaterial-made antennas and sensors which have multi-fold improved resolution and faster capture times can greatly improve wireless endoscopy and Magnetic Resonance Imaging (MRI).
Research in metamaterials is growing at an exponential rate. Despite a myriad of uses, their presence as components in everyday life is only starting to be tapped into. It looks like their potential to improve human life seems limitless.
This project has received funding from the European Union’s Horizon 2020 Research and Innovation programme under the Marie Sklodowska-Curie Grant Agreement No. 956401, XS-META Innovative Training Network.
Sairam Pamulaparthi Venkata is a Marie Sklodowska-Curie Early Stage Researcher in the School of Mathematical and Statistical Sciences at the University of Galway. Prof Michel Destrade is Chair of Applied Mathematics at University of Galway. He is a former Irish Research Council awardee.
The views expressed here are those of the author and do not represent or reflect the views of RTÉ
