Preparation And Properties Of Tea Tree Oil Liposomes/Chitosansustained-release Antimicrobial Materials

Tea tree oil is a natural antimicrobial agent with broad-spectrum and high efficient antiseptic effect. Chitosan is an ideal bioactive material with good biocompatibility, film forming, water absorptivity, gas permeability, biodegradable and absorbable properties. In order to obtain the sustained-release antimicrobial material with excellent performances, tea tree oil liposomes with high encapsulation efficiency and chitosan were bound by electrostatic interaction to prepare tea tree oil liposomes/chitosan sustained-release antimicrobial material using liposome technology and vacuum freeze-drying technology in this work so that to improve the biological activity and stability of tea tree oil, make tea tree oil have sustained-release property and alleviate its allergenicity. Meanwhile, sustained-release and antimicrobial mechanisms of the material were investigated through comparison and analysis. The main contents and relevant conclusions are as follows:(1) Preparation and basic properties of tea tree oil liposomesTea tree oil liposomes were fabricated by the thin-membrane hydration and sonication method. The optimal preparation process of tea tree oil liposomes was determined by single factor experiment, partial factorial experiment, central composite design and response surface methodology. The actual encapsulation efficiency of tea tree oil liposomes entrapping terpinen-4-ol reached 97.81±0.33%. Tea tree oil liposome vesicles were uniform in size with regular and spherical structure. The particle size was about 75 nm and Zeta potential was about-7.45 mV. Tea tree oil liposomes had the characteristics of high encapsulation efficiency, stability and sustained-release, showing significant antimicrobial effects against S. aureus, E. coli and C. albicans.(2) Structure and basic performances of tea tree oil liposomes/chitosan freeze-dried materialsTea tree oil liposomes/chitosan porous material was prepared by freeze-drying technology using tea tree oil liposomes as the antimicrobial agent and chitosan as the substrate. Tea tree oil liposomes were completely encapsulated in the chitosan matrix and combined with chitosan by electrostatic attraction. Tea tree oil liposomes destroyed the crystalline region and crystal property of chitosan material to form a part of the amorphous structure and reduce the order in the structure of chitosan crystalline region, resulting in the decline of crystallinity and the increase of flexibility. The material had high porosity, excellent fluid absorptivity, gas permeability and erosion resistance. Dry material owned certain mechanical strength but was hard and brittle. The mechanical strength of wet material was lower, but its flexibility was enhanced. The increase of chitosan concentration could improve mechanical property and erosion resistance of the material, but reduce its fluid absorptivity and gas permeability. The increases of tea tree oil liposome concentration and cooling rate in freeze-drying process adversely affected mechanical property, fluid absorptivity, gas permeability and erosion resistance of the material. The increase of glycerol concentration enhanced the plasticity, fluid absorptivity and gas permeability of material, but weakened its erosion resistance.(3) Sustained-release property and mechanism of tea tree oil liposomes/chitosan freeze-dried materialTerpinen-4-ol release of tea tree oil liposomes/chitosan freeze-dried material was non-Fick diffusion or irregular diffusion. Terpinen-4-ol release of the material fitted spherical storage model after the burst phase and terpinen-4-ol release was primarily controlled by distribution effect. The increase of chitosan concentration could weaken the burst effect and reduce release rate. But the increase of tea tree oil liposome concentration, the increase of glycerol concentration and the acceleration of cooling rate in freeze-drying process could enhance its burst effect. Tween-80 could form the hydrophilic layer in the surface of tea tree oil liposomes and decrease the release rate of terpinen-4-ol from the material.(4) Antimicrobial property and mechanism of tea tree oil liposomes/chitosan freeze-dried materialTea tree oil liposomes/chitosan freeze-dried material exhibited significant antimicrobial effects against S. aureus, E. coli and C. albicans. Chitosan concentration and cooling rate in freeze-drying process did not affect the microbicidel effect of material and the increase in the concentration of tea tree oil liposomes could significantly improve its microbicidel effect. But the effect of glycerol concentration on microbicidel property was contrary to that of tea tree oil liposome concentration. The material possessed high clearance rates against S. aureus, E. coli and C. albicans. The increases of chitosan concentration and glycerol concentration attributed to enhance microbe capture capability of the material, but the improvements of tea tree oil liposome concentration and cooling rate in freeze-drying process decreased microbe capture capability of the material. Tea tree oil liposomes/chitosan freeze-dried material could destroy bacterial intercellular substance, disperse cell colony and damage the integrity of cell membrane, finally leading to the death of microbial cell.