Biocatalytic synthesis of new polyesteramides from ε-caprolactam and hydroxy acids: Structural characterization, biodegradability, and suitability as drug nanocarriers

The synthesis of polyesters and polyamides by enzyme-catalyzed processes in vitro was developed in the last decades as a green alternative to obtain biodegradable synthetic polymers with various applications, such as nanoparticle-sized carriers for drug delivery. Polyesteramides were much less studied in this respect, although having the presumable advantage of increased mechanical and thermic resistance brought by the amide moieties. In this work, polyesteramides were synthesized for the first time employing as raw materials ε-caprolactam and a hydroxy acid. L-malic, 3-hydroxybutyric, 12-hydroxystearic and 16-hydroxyhexadecanoic acid, respectively, were investigated as co-monomers in solventless or organic medium, using the immobilized lipase Novozyme 435 as catalyst. The short chain hydroxy acids holding secondary hydroxyl groups yielded oligomers with average degree of polymerization no higher than 4, while in the case of the long-chain 12-hydroxystearic acid this value increased to 7. The best results were achieved by using 16-hydroxyhexadecanoic acid in 2:1 M excess at 80 °C, yielding a product with 75% copolymer content and average molecular weight higher than 3000 Da. The emulsion-solvent evaporation method allowed the efficient production of nanoparticles based on this copolymer, with sizes around 230 nm, used for the encapsulation of a model bioactive compound, the anticancer drug sorafenib. Production yields of >70% and encapsulation efficiencies of around 60% are very promising for further development of this approach.