Preparation of pH-responsive polyurethane nano micelles and their antibacterial application

Considering the differences in pH between bacterial infection microenvironment and normal tissues, a series of pH-responsive drug-release amphiphilic polyurethane copolymers (DPU-g-PEG) have been prepared in this work. Fourier transform infrared (FT-IR) spectroscopy and ¹H NMR was selected to detect the structure of the condensed polymers. The DPU-g-PEG amphiphilic copolymers could form stable micelles with a hydrophilic shell of polyethylene glycol (PEG) and a hydrophobic core of polylactic acid (PLA). We loaded a model drug called triclosan onto DPU-g-PEG micelles and studied how pH affects their particle size, Zeta potential, and drug release performance. The results revealed that when exposed to acidic conditions, the surface potential of DPU-g-PEG micelles changed, the micelles' particle size increased, and the drug release performance was significantly enhanced. These results suggested that the micelles prepared in this study can release more antibacterial substances at sites of bacterial infection. Meanwhile, we also investigated the impact of different ratios of soft and hard segments on the properties of micelles, and the results showed that the pH responsiveness of micelles was strongest when the ratio of soft segments (PLLA diol + PEG 2000): 1,6-hexamethylene diisocyanate (HDI): 2,6-Bis-(2-hydroxy-ethyl)-pyrrolo[3,4-f]isoindole-1,3,5,7-tetraone (DMA) = 1: 1.2: 0.2. Furthermore, the results of inhibition zone test, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) all confirmed the antibacterial activity of triclosan-load DPU-g-PEG micelles. In conclusion, the DPU-g-PEG micelles produced in this study have the potential to be used as intelligent drug delivery systems in the biomedical field.