Plastics explore new territories

The media likes to create a buzz about the digital revolution and the developments in connected medicine that it fosters. While the resulting applications contribute greatly to patient comfort, they are not always as revolutionary as one might think. Although less flashy than others, another revolution is brewing in university and pharmaceutical industry laboratories. The aim is to achieve greater individualisation of care by adapting treatments to the specific needs of each patient.

Nerves of plastic

In rich countries, modern medicine has made it possible to significantly extend life expectancy. Today, although we are more or less successfully able to prolong our bodies’ vital functions, tissue engineering, and in particular the engineering of ligaments and tendons, is the area of research where the challenges are among the greatest.  
The first polymer tendon prostheses appeared in the 1980s. They were very effective, but over time they proved to be lacking resistance to wear and tear, meaning that patients would eventually require another operation. Today, medical research is closely following that conducted by polymer manufacturers. For example, there is interest in poloxamers, copolymers of the poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) type which, braided with PLA, could make it possible to design perfectly elastic and theoretically wear-proof artificial tendons.

Some see this as a further step towards transhumanism, the controversial discipline that hopes to make humans immortal. It is still a long way away, but science, including materials science, is advancing. A team from Stanford in the United States claims to have developed an incredibly elastic new polymer that can be stretched up to three times its original length before breaking. This self-healing elastomer expands or contracts under electrical stimulation.

Although artificial ligaments based on elastomers have been around for a long time, research laboratories are now trying to create artificial muscles based on the properties of polymers.

Muscular medicine is closely following the advances made by the laboratory, because such a material could one day replace muscles. The researchers have revealed that this new polymer derives its properties from cross-linking, a chemical process that consists of linking molecular chains together to form a three-dimensional network. We also know that the base polymer has been enriched with metal ions to make it sensitive to electric fields. Potential applications obviously include the partial replacement of muscles and even the possibility of designing artificial skin. The latter would allow prosthesis wearers to regain tactile sensations by connecting this skin to the nervous system in the wearer’s stump.

Nanotechnologies: almost infinite potential applications

A nanomaterial is a natural material, whether accidentally formed or manufactured, containing free particles, either in aggregate or agglomerate form, of which at least 50% have an external dimension between 1 nm and 100 nm. Nanotechnologies applied to polymers in the medical world are paving the way for much less invasive, better targeted and increasingly personalised treatments.  

For some twenty years now, the medical world has been seeking to individualise treatments to make them more effective. The aim is to provide the active ingredient in the right quantity and only where necessary. The treatment of cancer is a good illustration of this. Laboratories are now seeking to develop treatments that will only attack diseased cells without destroying healthy cells. This is a major challenge because chemotherapy treatments are most often injected intravenously and spread throughout the body, weakening healthy cells.
There is still a long way to go, but the way forward is getting clearer. In France, scientists have recently developed a new biodegradable polymer based on vinyl polymers whose manufacturing process remains confidential. However, we know that they have succeeded in creating a covalent bond (a bond between two atoms via the pooling of electrons) between gemcitabine, a molecule that acts against various cancers, and a polymer. While polymers are remarkable vehicles for transporting the drug, the challenge is to find a way to release the drug at the right time and make it reach the targeted cells.

It seems that the future of medicine will involve nanotechnology. In Singapore, a laboratory has designed PET-based nanoparticles capable of targeting diseased cells.

At the Institute of Bioengineering and Nanotechnology in Singapore, a biodegradable polymer that can act against fungal infections of the staphylococcus type has been developed. These nanoparticles based on polyethylene terephthalate (PET) have been modified to be attracted like magnets to infected cells. The first publications from this laboratory have not yet revealed much more information…

At the Johns Hopkins University School of Medicine in the United States, researchers are looking for a way to act against incurable brain cancer. Administering a drug into this organ is not easy, as it consists partly of a particularly viscous fluid that prevents the "healing molecules" from properly finding their way to the intended area. To solve this problem, researchers have coated the molecules with nanoparticles of polyethylene glycol, a well-known, non-toxic polymer. This polymer acts as a lubricant and enables the drug molecules to glide better. Progress still needs to be made because the researchers believe that slightly increasing the size of the nanoparticles should improve their gliding properties.

Polymers roll out the red carpet

Blood is an increasingly precious commodity, especially as donors are becoming more and more scarce. The solution to this problem may lie in the development of artificial blood. Is that really just a pipe dream? An American laboratory in North Carolina is working on it, and its first results seem quite conclusive.
In fact, they have not actually created blood, but rather red blood cells whose mission is to transport oxygen to the organs and carbon dioxide to the lungs. In North Carolina, these synthetic red blood cells were created using an elastomeric fluoropolymer mould in which the cells composed of a polymer hydrogel were moulded. Which one? The scientists simply refer to it as a "prepolymer". Injected into mice, these hydrogel cells showed real efficiency and very good resistance. Moreover, their flexibility allows them to pass through all types of vessels. This discovery would certainly make it possible to manufacture artificial blood one day, but also a drug, or at least its envelope, capable of delivering the active ingredient (the molecule used for healing) to areas of the body that are usually difficult to access.

By creating artificial red blood cells based on a polymer hydrogel, an American laboratory is paving the way for the development of synthetic blood.

Medical robots, polymers designed to soothe

Robotisation is another subject of choice for health researchers. Not surgical arms, but rather small, soft robots that, once introduced into the human body, could provide better care for a patient or make treatment less burdensome. This is the case for diabetics, for example, who have to regularly inject themselves with insulin.

At MIT, researchers have developed a nanorobot carrying a needle made of freeze-dried insulin. For the millions of diabetics worldwide, this could mean an end to the ordeal of daily injections.

At MIT a capsule the size of a blueberry was created from a biodegradable polymer. The capsule encloses a micro needle of freeze-dried insulin. The trick was to find a way to inject the treatment at the right time. To do this, the researchers fitted the capsule with a cap made up of a small sugar cube that melts by the time it reaches the stomach. Once it reaches its destination, the capsule releases the insulin needle, which punctures the stomach lining.

Simple and effective... The capsule is then naturally digested. The only problem is that the cost of this capsule is much higher than that of traditional insulin pens.

Soft robots, most often based on elastomers or silicone, are also at the heart of much medical research around the world. (See our article Robots-and-polymers:-a-deal-set-in-steel). Researchers at the Max Plank Institute in Germany have recently developed a small soft robot measuring just 4 millimetres in size which can be remotely controlled using magnetic sensors. This small caterpillar, once swallowed or inserted into the skin, could travel through the digestive or urinary system, the abdominal cavity or even to the surface of the heart to deposit the medicine in the right place. The originality of this robot lies above all in its extreme mobility and its ability to stretch to overcome all obstacles. It has already been tested in a synthetic stomach and completed that obstacle course with flying colours!

Could they be the beginnings of tomorrow's medicine? It is quite likely because other technologies such as 3D printing are also evolving. Thus, prostheses and robots could soon be manufactured within hospitals according to the needs of their patients. Some laboratories are also looking into the hybridization of materials and are attempting to combine synthetic materials such as polymers with stem cells in order to manufacture new organs, for example. One more step towards the dream of the bionic man? Perhaps, but for the moment the aim is to provide better care by personalising treatments. Achieving that will already be a great step forward.