Investigation of the structure and modulus of poly(N-isopropylacrylamide) brushes of various chain lengths and densities by atomic force microscopy

Different types of poly( N -isopropylacrylamide) (PNIPAAm)-modified interfaces have been developed for potential biomedical applications. We investigated the morphology of four types of PNIPAAm brushes with various chain lengths and densities using frequency modulation atomic force microscopy (FM-AFM) for their effective design. PNIPAAm brushes remained hydrated and extended at 25 °C, resulting in uniform surface morphologies irrespective of the brush length. Dehydration at 37 °C induced chain shrinkage, with longer brushes exhibiting more pronounced roughness. Additionally, this structural transition markedly increased the elasticity. Notably, low-density brushes demonstrated rough surfaces even at 25 °C owing to the rounded conformation of sparsely grafted chains. The elasticity change of the dilute PNIPAAm brush with increasing temperature was smaller than that of the dense PNIPAAm brush because the grafted PNIPAAm collapsed owing to the adequate space near the chains. These findings can be applied in the design of PNIPAAm interfaces for biomedical applications. • Four poly( N -isopropylacrylamide) (PNIPAAm)-modified interfaces are developed. • FM-AFM was used for investigating structure and morphology of PNIPAAm brushes. • Surface morphology and elasticity changed with temperature. • Morphology and elasticity changes depended on chain length and density.