Template Synthesis of Stimuli-Responsive Nanoporous Polymer-Based Spheres via Sequential Assembly

Nanoporous polymer-based spheres were synthesized via sequential assembly of macromolecules (e.g., polyelectrolytes (PEs), peptides, and proteins) in mesoporous silica (MS) particles, followed by removal of the MS templates. The sequential infiltration of PEs in the mesopores for the model system poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) was demonstrated by various methods, including nitrogen sorption, thermogravimetric analysis, Fourier transform infrared, and confocal laser scanning microscopy (CLSM). The influence of parameters such as layer cross-linking, solution pH, ionic strength, and MS pore size on the synthesis of the PAA/PAH nanoporous polymer spheres (NPS) was investigated. Cross-linking between PAA and PAH was found to add structural integrity to the NPS, while the solution pH and ionic strength govern the conformation of the PEs in solution and the subsequent ability of the PEs to infiltrate the mesopores and thereby form intact NPS. Transmission and scanning electron microscopy data show that the PAA/PAH NPS have pores ranging from about 5−50 nm, which was further confirmed by CLSM of protein-loaded NPS. The PAA/PAH NPS exhibited a high capacity for enzyme loading (ca. 470 mg mL - 1 for lysozyme), with stimuli-responsive reversible loading and release of the protein triggered by changes in solution pH. The general applicability of the reported approach is demonstrated by the preparation of NPS containing peptides, proteins, and low molecular weight molecules. MS fibers were also used as templates to generate PAA/PAH nanoporous fibers, showing that this process is applicable to templates with different morphologies. These nanoporous materials are envisaged to find application in biosensing, enzyme catalysis, and controlled drug delivery.