Preparation And Characterization Of Antimicrobial Core-Shell Polymeric Nanospheres

The synthesis techniques of various functional nanospheres, such as monodispersed nanospheres, fluorescent nanospheres, magnetic nanospheres, and stimuli-responsive nanospheres (pH-sensitive and thermo-sensitive), etc., have been developed very well over the past decades. Due to the rapid development of many fields, including medicine, biochemistry, electron communication and architecture decoration et al., the preparation of core-shell polymeric nanospheres with special performances, such as biocompatibility, degradability and antimicrobial property, has been one of important research aspects of core-shell nanospheres. Our group has developed an easy method of "in-situ" polymerization, that is, "template polymerization", to fabricate core-shell nanospheres at high concentration in water. In this thesis, water-dispersible antimicrobial core-shell nanospheres were prepared via in situ polymerization of acrylic acid (AA) in an aqueous solution of antibacterial agent. Besides, we used a stabilizer to improve the stability of the nanospheres against storage, acid, base and salt. Two kinds of nanospheres were synthesized and characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), Fourier transform infrared spectrometry (FTIR), and thermogravimetric analysis (TGA), etc. Specifically, the following work was carried out:(1) When polymerizing acrylic acid (AA) on antimicrobial poly(hexamethylenediamine guanidine hydrochloride) (PHGM) template in an aqueous solution, driven by electrostatic interactions and hydrogen bonding interactions, PHGM and poly(acrylic acid)(PAA) produced "in-situ" self-assembled into antimicrobial PHGM/PAA nanospheres with inner core of insoluble complexes of PHGM and PAA and outer shell of PHGM. By introducing crosslinker N',N'-methylene bisacrylamide into the initial reaction solution, core-crosslinked nanospheres with a more stable structure could be obtained. The composition and interactions of the nanospheres were characterized by FTIR. TEM presented that PHGM/PAA nanospheres were global and the core-shell structure was indistinct. TGA results indicated that the nanospheres exhibited a little worse thermal stability compared to pure PHGM and the thermal stability was improved as the content of PHGM increased. PHGM/PAA nanospheres we prepared had small size, narrow distribution and little thermo-response, but low storage stability, weak salt-resistance and alkali- resistance.(2) By introducing stabilizer HEC into the initial reaction solution, more stable nanospheres could be obtained. TEM results showed that PHGM/HEC/PAA nanospheres were global and the core-shell structure could not be seen clearly. FTIR results indicated that nanospheres were co-stabilized by hydrogen bonding interactions between HEC and PAA. DLS results showed that the sizes of PHGM/HEC/PAA nanospheres were larger than those of PHGM/PAA nanospheres and the distribution and thermo-response changed a little, whereas, there were a great improvement in storage stability, alkali-resistance and salt-resistance. TGA results indicated that though the nanospheres exhibited lower thermal stability than pure PHGM, its starting decomposition temperature was fairly high (about 200℃).(3) The antibacterial activity assessment result showed a 99% reduction of bacteria (Escherichia Coli and Staphylococcus aureus) could be reached for a PHGM/PAA nanospheres solution of 5 mg/mL by using plate method; and the minimum inhibitory concentration (MIC) of PHGM/HEC/PAA nanospheres was 300 mg/L by using nutrient broth dilution method. The results suggested that these nanospheres exhibited efficient biocidal activity.