Micro- and nanostructures of polylactide stereocomplexes and their biomedical applications

The discovery of stereocomplexation, secondary interaction between enantiomeric poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) provides a method for the creation of novel biomaterials with distinctive chemical and physical stability. Stereocomplexation opens a new way for the preparation of diverse micro- and nanostructures such as uniform microspheres, hollow particles, micelles, nanocrystals, nanofibres, nanotubes and polymerosomes. Herein, we describe the design of stereocomplex assemblies for specific applications and methods for their preparation. This review focuses primarily on the use of stereocomplex assemblies in biomedical applications due to the improved stability and physicochemical properties in comparison to enantiomeric polylactides. To make the polylactide stereocomplexes soluble in water and, as a consequence, to improve compatibility with the human body, various amphiphilic copolymers with PLLA and PDLA enantiomeric segments can be prepared. Stereocomplexation can facilitate their self-assembly into micro- and nanoparticles, stabilize the particle size and morphology and can also have an influence on the in vivo degradation rate and cytotoxicity of these materials. Stimuli-responsiveness in stereocomplex assemblies can be achieved by copolymerization of lactide with, for example, thermoresponsive N-isopropylacrylamide or amino acids with pH-sensitive pendant groups. Stereocomplex micro- and nanoparticles are used for encapsulation of various bioactive compounds: anticancer drugs, antibiotics and proteins. Finally, examples of materials in which high thermal and mechanical stabilities delivered as a result of stereocomplexation play a crucial role, i.e. hydrogels, nanofibres, microcellular foams and artificial skin, are described. The preparation of biomaterials and biomedical systems based on polylactide stereocomplex assemblies opens new opportunities in this field. (c) 2015 Society of Chemical Industry