In search of more polymers for medical purposes

Her thesis is entitled Polimero biodegradakor berrien lorpena eta ezaugarritzea (Obtaining and characterising of new biodegradable polymers). She has also had articles published on this in the Polymer and Macromolecules journals, among others.

PVA or poly(vinyl alcohol) is a biocompatible, biodegradable, water soluble material, and therefore highly suited to use in biomedicine. For example, it is used in the type of gels that dry the moment they touch the skin, as well as in transdermal patches (the ones that are stuck to the skin and release a specific drug that passes through it in a controlled way). Hydrogels made from PVA are fairly commonplace, precisely because of their solubility in water. Lejardi has listed the most common applications: "For encapsulation systems that deliver drugs, for reconstructive surgery, and to make dressings to treat wounds." There are different ways of producing polymer materials, but in this case, the researcher has opted for the chemical modification of the PVA and its subsequent blending with other polymers. But always with biodegradable polymers, like polylactides and polycaprolactones. So she was setting out to incorporate new properties into the original material.

On a molecular level, PVAs do not readily interact with other polymers; that is why when they are kept in their original state, most of the blends are heterogeneous and therefore display very poor mechanical properties. Lejardi has endeavoured to bring PVA closer to these other polymers¹: "PVA has hydroxyl groups in its main chain. The problem is that these hydroxyls associate only with each other. So we inserted hydroxy acids so as to move the hydroxyls away from the main chain." This phenomenon is called esterification: the whole chemical reaction of an alcohol (the hydroxyl) with an acid (the hydroxy acid). That way, hydrogen bonds are created between the PVA and the biodegradable polymers one is intending to blend with it.

Lejardi conducted tests on various biocompatible polymers; after modifying the PVA by means of esterification, she prepared and analysed a wide range of systems for blending polymers. For example, when blending PVA with PCL or poly(epsilon-caprolactone), she obtained an improvement in biocompatibility. And with the PVP or poly(vinyl-pyrrolidone), the results were also good, as the researcher explains: "We knew PVP could be blended with PVA, but we saw that when the blend was carried out with our esterificates, the hydrogen bonds turned out to be more robust."

Having completed her thesis, Lejardi is now preparing to spend four months at the Institute of Polymer Science and Technology in Madrid (ICTP-CSIC) to continue with her research in collaboration with Carmen Mijangos, Professor and PhD holder, who works at the centre. She is planning to explore one of the esterifications she has carried out, as she has seen that it is possible to obtain hydrogel with this particular polymer: "We will be studying the material's self-organisational properties. To do this, we have created nanospheres by means of nanoprecipitation²."