Stereo-complex hydrogels

Li et al. reported on stereo-complex hydrogels from totally aqueous PLLA/ PEG and PDLA/PEG solutions. The copolymers are synthesized by ring-opening polymerization of L-lactide or o-lactide in the presence of mono- or dihydro)q l PEG, using zinc lactate as catalyst. Hydrogels are obtained from aqueous solutions containing equimolar amounts of PLLA/ PEG and PDLA/PEG block copolymers due to the stereo-complexation between PLLA and PDLA blocks. 

Kondo et al. reported a novel fabrication method of polymer nanotubes by combination of an alternate layer-by-layer (LbL) assembly of PLLA and PDLA and the siliea template method. Silica nanoparticles with a diameter of 300 nm were alternately immersed in aeetonitrile solutions of PLLA and PDLA at 50 °C. The immersion process was performed for 10 cycles to deposit 10 double layers of PLLA and PDLA. The resulting partieles were then treated with 2.3% aqueous hydrofluoric acid to remove the siliea core. The hollow eapsules have a spherical shape with a diameter of 320 nm and a shell thiekness of approximately 60 nm. Tubular assemblies with an average diameter of 300 nm and lengths of 2-5 pm are obtained by evaporating water at ambient temperature from a water dispersion of the hollow eapsules on a polyethylene terephthalate (PET) substrate. 

Albertsson and I. Varma, in Degradable Aliphatic Polyesters, Springer Berlin Heidelberg, 2002, vol. 157, p. 1. 

Spassky, M. Wisniewski, C. Pluta and A. Le Borgne, Macromol Chem. Phys., 1996, 197, 2627. 

Pensec, M. Leroy, H. Akkouche and N. Spassky, Polymer Bull, 2000, 45, 373. 

---

Fujiwara T, Mukose T, Yamaoka T, Yamane H, Sakurai S, Kimura Y. Novel thermo-responsive formation of a hydrogel by stereo-complexation between PLLA-PEG-PLLA and PDLA-PEG-PDLA block copolymers. Macromol Biosci 2001 1 204-208. 

In this contribution we intend to provide a eomprehensive review on PLA stereo-complex, including preparation, strueture-properties and biomedical applications. The effect of stereo-complex on the thermal dynamics, hydrolytic degradation, micellization and hydrogelation will be discussed. 

---