Polymers in drug delivery & medical device
What are polymers ?
The word polymer comes from the Greek. The prefix poly– means “many“ whereas the suffix –mer means “parts“. It refers to a large molecule composed of many repeated subunits also known as monomers. The process by which the monomers get combined and transformed into polymers is known as polymerization. Polymers can be found in nature (cotton from plant, latex from rubber tree, chitin of crustacean shells, wood, protein from eggs and other foods) but it is also possible to get them through various synthetic technologies such as Ring Opening Polymerisation(figure 1), polycondensation….
Application in drug delivery
Drug delivery is the method or process of delivering a pharmaceutical compound to achieve a therapeutic effect in humans or animals (Figure 2). Drug delivery systems must overcome a series of biological barriers to bring the therapeutical agents to the specific pathological site or for a sustained release. Polymeric systems have seen a great potential in this field.
Polymers are easy to formulate into various delivery systems for carrying a variety of drug classes, such as vaccines, peptides, proteins and micromolecules, which have been approved by the Food and Drug Administration for drug delivery use. Different polymeric based devices are available: microspheres, microcapsules, nanoparticles, pellets, implants and films. The technique used for drug encapsulation (single or double emulsification, nonaprecipitation, dialysis, spray drying…) plays a vital role and depends on the intended effect as well as the nature of the drug. The scheme 2 depicted below highlights the encapsulation of a drug with PLGA polymer through emulsification/ solvent diffusion technique:
The scheme 2 : Schematic representation of PLGA nanoparticle preparation by emulsification/solvent diffusion technique: here the entrapped drug is distributed throughout the polymer matrix and the particles surface is covered with a cationic surfactan
Environment-sensing microencapsulation systems offer a unique opportunity to carry functional ingredients in their core and to release them in response to environmental stimuli (temperature, pH, osmolarity, etc.) for desired effects. Figure 3 shows an example of a pH-responsive encapsulation systems. The concept is simple : if the drug targets the intestine, then the polymer that protects the drug should resists to the stomach pH which is about 1-3 and should be unstable to the one of the intestine (case (a)). Conversely, if the drug targets the stomach, then the drug should be encapsulated with a polymer that is unstable to pH 1-3.
Theses kind of polymers may swell, collapse, or change depending on the pH of their environment due to the presence of certain functional group in the polymer chain. pH-sensitive materials can be either acidic or basic, responding to either basic or acidic pH values and can be designed with many different architectures.
Figure 3: General scheme to detail the principle of pH sensitive medication:
(a) Intestine-targeted drug; (b) Stomach-targeted drug
Application in Medical Device
Polymers have also found widespread applications in medical device including orthopedics, neurological, dental, spinal and cardiovascular implants but also in PEKK-based 3D-printed bones. Such polymers are highly stable in lipids, blood and enzymes media, making these materials ideal for long-term orthopedic and dental implant applications such as bone screws, plates and pins, tissue anchors and suture screws. Some other applications are depicted below:
Other applications
Polymers are not limited to release of drugs or medical device but are also used everywhere in our everyday life :
