Plastics have been caring for a long time

Polymers give researchers fever

In the late 1940s, as almost all industries began taking an interest in plastics, many medical research laboratories began investigating whether their properties could contribute to bettering the health of humanity. Although the term did not exist at the time, biocompatibility as a concept was being studied. In the medical field, biocompatibility must be perfect in order to prevent any unfortunate interaction between materials and "living matter": inflammatory reaction, potential toxicity, degraded performance over time, etc. All these issues must be resolved before a polymer-based medical device is placed on the market in order to guarantee its health safety. It is easy to understand why it sometimes takes more than a decade between the first research and a device’s launch on the market.

Plastics take matters into their own hands

It is difficult to identify the first polymer-based medical devices. The invention of polymethyl methacrylate (PMMA) contact lenses dates back to the 1930s. They became widespread in the following decade because they were more flexible and therefore less complicated to put on. PMMA was in turn replaced at the beginning of our millennium by silicone hydrogels, particularly oxygen-tight materials that guarantee better user comfort.

Contact lenses were among the first medical devices to make use of polymers. As early as the 1930s, PMMA successfully replaced glass. Contact lenses then became more comfortable and practical.

Another emblematic example is that of prostheses! The best known and certainly the most sensational remain those created for disabled athletes. Carbon and epoxy resin blades enable them to reach speeds close to those achieved by able-bodied athletes. 3D printing has also enabled spectacular advances in the world of health and more particularly in the world of hand prostheses. All these prostheses have in common that they use only polymers because they are easily printable and have all the intrinsic qualities required. This is the case of the polyamide models developed by the British company OpenBionics. These custom-made prostheses are affordable, have reached an excellent degree of sophistication and can be personalised.

PEEK (polyetheretherketone) is another polymer which, since the 1980s, has revolutionised the field of healthcare and more particularly that of implants. It now replaces titanium, which until then was considered to be the most biocompatible material.

Printable and perfectly biocompatible, PEEK is the ideal polymer for bone implants. The relative ease with which it can be printed now makes it possible to manufacture truly custom-made prostheses.

It is found in cervical intermediary elements in the spine, in hip joint prostheses and above all in dental implants. Its excellent biocompatibility allows a perfect fusion with bone tissue and its mechanical properties are very similar to those of the skeleton. Another advantage for those who regularly fly, unlike titanium, it does not set off any alarms when passing through security gates.This polymer is also fairly easy to print. It has thus paved the way for more personalised medicine thanks to the possibility of manufacturing implants perfectly adapted to the morphology of those who wear them.

Polymers under the skin

Their biocompatibility is not the only advantage of polymers for medical use. Some are also biodegradable and therefore naturally assimilated by the human body. The best-known application remains sutures based on PLA (polylactic acid) or PGA (polyglycolic acid) which break down on contact with certain enzymes produced by the body. In some universities, particularly in the United Kingdom, there is a great deal of interest in a new polycarbonate that could be biodegradable. This particularly rigid and resistant polymer could be applied to a fracture and would actively contribute to its healing. Thus, once applied, it would degrade as the bone grows, allowing for shorter consolidation times or the treatment of osteoarthritis or osteoporosis.

In most cases, surgical sutures are made of PLA or PGA which are not only biocompatible, but above all biodegradable polymers. The enzymes produced by the body are sufficient to break them down.

Polymers can also be used in medicines, for several purposes. Many capsules are in fact coated with a thin layer of polymer that can be perfectly absorbed to mask the bad taste of a molecule. However, this is not their main use. Cyclodextrin, a starch-based oligomer, is also widely used to produce what scientists call molecular cages. Their role is to delay the delivery of the active ingredient in order to increase its efficiency. Certain capsules must release their molecules in the intestine and not in the oesophagus in order to be effective. The best solution is to encapsulate the active ingredient in a polymer that will break down more slowly.