Preparation and Structure of Polypeptide Hollow Disks with Spiral Nanopattern Surface

Hollow particles have attracted considerable attentions in recent years for their potential in diverse application fields. In this work, polypeptide-based hollow disk-like and conchoidal particles with surface nanostrips were prepared. For the poly(γ-benzyl-L-glutamate)-b-poly(ethylene glycol) (PBLG-b-PEG) block copolymer, through partial deprotection of the benzyl group of the PBLG block and esterification reaction between the carboxyl group and cinnamic alcohol, poly(γ-benzyl-L-glutamate-co-γ-cinnamyl-L-glutamate)-b-poly(ethylene glycol) (P(BLG/CLG)-b-PEG) block copolymers were obtained. The self-assemblies were prepared by a selective precipitation method. P(BLG/CLG)-b-PEG block copolymers and polystyrene (PS) homopolymers were first dissolved in THF-DMF mixture solvent; by adding water to the solution, core-shell particles with nanostrips on the surface were obtained, in which the hydrophobic PS homopolymer formed the spherical core and the P(BLG/CLG)-b-PEG block copolymers formed surface nanostrips. By changing the composition of THF-DMF mixture solvent, the surface patterns can be regulated. Spiral spheres were formed with V(THF)∶V(DMF) of 5∶5 as initial solvent, and meridian spheres were formed with V(THF)∶V(DMF) of 3∶7 as initial solvent. Under UV-irradiation at λ = 254 nm, a cycloaddition reaction can occur on the C=C double bond of the cinnamyl group. Therefore, the P(BLG/CLG) blocks in the shell of both the spiral spheres and the meridian spheres were cross-linked. To the solution of the shell-crosslinked spiral spheres and meridian spheres, 10-fold of THF was added to remove the PS homopolymers in the core. As a result, hollow nanodisks and hollow conchoidal particles were prepared, and the strip nanopatterns on the surface were retained. The morphology of the particles was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). It was found that the PS homopolymers were efficiently removed from the particles by THF solvent soaking, and the nanostrips prop up the hollow structure of the disk-like particles and conchoidal particles. The morphology and structure of these nanopatterned hollow particles are stable, and they maintain the three-dimensional features under microscopy observations. The inner space of the hollow disk can be refilled with hydrophobic polymers.