We describe the use of organic catalysis for the ring‐opening polymerization of functionalized lactones and conversion of the resulting aliphatic polyesters into crosslinked nanoparticles that carry additional functional groups amenable to further modification. Specifically, highly functional aliphatic polyester homopolymers, as well as random and block copolymers, were prepared by 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene catalysis, giving polyesters with pendent alkene and alkyne groups. Azide‐alkyne click and thiol‐ene chemistries were used for postpolymerization modification of diblock copolymers possessing alkene groups on one block and alkyne groups on the other block. The polyesters were crosslinked using azide/alkyne cycloaddition, by reaction of α,ω‐diazides with the pendent alkynes on the polyester backbone. This gave polyester nanoparticles possessing alkene functionality, which were subjected to further modification using thiol‐ene reactions to introduce additional functionality. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Despite improvements relative to unmodified counterparts, poly(ethylene glycol) (PEG) conjugation may not be the ideal solution for improving circulatory stability of current nanoparticle carriers or free drugs. Polysialic acid (PSA), a natural polymer for which the body possesses no receptors, has been conjugated directly to biologically active molecules to prevent premature clearance; however, this concept has not yet been applied to nanoparticle drug carrier systems. In the current study, PSA was modified with a long-chain hydrocarbon through reaction of the carboxylic acid side groups with N-decylamine (DA). The resultant PSA-DA conjugates self-assembled into micelles for encapsulation of hydrophobic drug molecules, as demonstrated with Cyclosporine A. Cytotoxicty was dependent on the degree of substitution with DA. On the basis of size and zeta potential, the micelles are capable of passively targeting diseased regions, such as cancer and inflammatory tissue. Further investigations are necessary to explore whether the PSA-based micelles possess stealth properties similar to those of PEG and to establish in vitro and in vivo efficacy.

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Highly efficient photo-cross-linking reactions enable numerous applications in biomaterials. Here, a photopatternable biodegradable aliphatic polyester with benzophenone pendent groups was synthesized by copper-catalyzed alkyne-azide cycloaddition, affording polyesters that undergo UV-induced cross-linking to yield photopatterned films. Using this material, a self-folding multilayer structure containing polyester/hydrogel bilayer hinges was fabricated. Upon swelling of the hydrogel layer, the construct folds into a triangular tube, which subsequently unfolds due to lipase-catalyzed degradation of the polyester layer. The ability to precisely design such degradation-induced structural changes offers potential for biomaterials and medical applications, such as evolving and responsive 2D and 3D tissue engineering scaffolds.

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