Crosslinked ELP-based nanoparticles, using the strain promoted azide–alkyne cycloaddition

Abstract

A well-defined elastin-like polypeptide (ELP) block copolymer was synthesized via protein engineering for the formation of shell-crosslinked micellar particles. The block copolypeptide consisted of two domains with different transition temperatures (Tt), with the more hydrophilic block positioned at the N-terminus. At this protein end additional lysines were introduced to facilitate crosslinking. Upon raising the temperature above the Tt of the more hydrophobic block particles were formed. Two methods of crosslinking were investigated. Using genipin the lysines were directly used for particle stabilization. To be able to crosslink and functionalize the nanoparticles in an orthogonal and efficient fashion, another crosslinking strategy was developed, making use of the strain promoted azide–alkyne cycloaddition (SPAAC) reaction. For this purpose the block polypeptide was azidated making use of a diazotransfer reaction. Subsequent assembly and crosslinking using a bis-cyclooctyne reagent resulted in the formation of stable nanoparticles. Encapsulation of a hydrophobic dye showed these nanoparticles to have potential as nanocarriers.