This article is based around a talk given by Professor Alexander Seifalian from NanoRegMed Ltd, UK, at the NANOMED conference hosted by the NANOSMAT Society in Manchester on the 26-28th June 2018. In his talk, Alexander talks about how his company is developing a series of medical implants that are made from a biocompatible graphene-polymer composite.
Regenerative medicine and tissue engineering have been around for a while now, but these fields continue to advance and are now utilizing many different types of nanomaterials. Alexander has created a wide range of prostheses, including a trachea, grafts for heart bypasses, tear ducts, ears, and noses using various materials; including graphene. There has been a need for many years to create grafts which have smaller diameters, are less prone to blockages and can be used in a human patient without it being rejected by the body.
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Most of the biomaterials used in various prostheses have been around for many decades and still encounter problems. So, Alexander and his company have come up with a new range of materials involving graphene for these prosthesis applications.
There are not many areas of medical research where graphene is used, because graphene by itself can be toxic to humans if internalized. But this can be avoided by compositing graphene with other materials. Aside from its strength, graphene’s lightweight nature, antimicrobial properties, flexibility and corrosion resistance make it an ideal material for medical implants when it is formulated into biocompatible materials.
The materials developed by Alexander are a composite of polycaprolactone (PCL), and graphene and the materials can be tuned to be either biodegradable or non-biodegradable depending on the intended application. To make the material, they graft the graphene and then conjugate it to the polymers so that it sits within the polymer matrix, thus preventing it from being harmful to a patient. A critical aspect of why the materials work is because they integrate with the surrounding tissue and cells.
The fabricated materials are very strong, and it requires 80 kilos of force to break the composite. This high strength property can also be further improved, but it is at the expense of the viscoelasticity of the material, which is required for many implant applications. It is also possible to create polycarbonate-graphene composites using this method, but a higher concentration of graphene is required, and this again affects the viscoelastic properties of the composite. It is also possible to 3D print these composite materials into variously shaped scaffolds loaded with stem cells.
Alexander has created many grafts with these materials, and they have been tested on mouse models. These grafts have been shown to grow cells, and the proliferated cells directly integrate with the tissue of interest to help with the growth of new tissue. This type of graft can also be loaded with nitrous oxide (sometimes alongside other kinds of particles or biological matter) and has excellent potential for wound healing applications.
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Alexander has also created artificial arteries using these polymer-graphene composites. It was also possible to conjugated antibodies (made from peptides) inside the artery, which also becomes endothelialized under shear flow. The tunable nature of the composites has enabled Alexander to fabricate these pseudo-arteries with the same viscoelastic properties as natural arteries.
Because medical devices can take a while to become commercialized, all the products created from these composites are not at the commercial level just yet. However, they show a lot of promise and many have gone to clinical trials, with success. One of the key aspects that make this composite an exciting material is its tunability. The ratios can be altered such that it is flexible enough to be used as an artery, or it can be made more rigid for external prostheses, such as the nose. This, coupled with the fact that the materials are biocompatible, make it an interesting area to keep an eye on in the near future.
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