Thermoresponsive and Self-Healing Hydrogel Based on Chitosan Derivatives and Polyoxometalate as an Antibacterial Coating.

Hospital-acquired infections are a serious threat to the recovery of patients. To prevent such infections, an antibacterial coating is an effective method to eliminate bacterial colonization on healthcare-related surfaces. Herein, we report an antibacterial hydrogel composed of silver-containing polyoxometalate (AgP5W30 POM) and carboxymethyl chitosan (CMC). The silver ion is encapsulated inside the POM cage and demonstrates long-lasting bacteriostasis after repeated exposure to both Gram-positive and Gram-negative bacteria. The chemical structure of chitosan derivatives, as well as the concentration and pH, is studied to tune the mechanical properties of the hydrogel. The hydrogel undergoes a gel-sol transition above the critical temperature and possesses self-healing ability. This hydrogel can be readily coated on the surface of versatile bulk materials, which is especially convenient for porous objects and resists the growth of Staphylococcus aureus, Escherichia coli, and methicillin-resistant S. aureus (MRSA). In summary, we envision that the AgP5W30-CMC hydrogel has great potential to serve as an antibacterial coating to decrease the prevalence of hospital-acquired infections.

Shock synthesis and characterization of titanium dioxide with α-PbO2 structure.

The phase transformation behavior of anatase and rutile titanium dioxide with particle sizes of 60 nm and 150 nm under shock compression have been investigated. To increase the shock pressure and reduce the shock temperature, copper powder and a small amount of paraffin were mixed with the TiO2 powder. The shock recovered samples were characterized by x-ray diffraction, Raman spectroscopy, and transmission electron microscope. The results indicate that both anatase and rutile TiO2 can transform to α-PbO2 phase TiO2 through shock-induced phase transition. The transformation rate of α-PbO2 phase TiO2 for anatase TiO2 under shock compression is 100% and pure α-PbO2 phase TiO2 can be obtained, while the transformation rate for rutile TiO2 is over 90%. The influence of the particle size on the yield of α-PbO2 phase TiO2 is not noticeable. The thermal stability of the recovered pure α-PbO2 phase TiO2 was characterized by high temperature x-ray diffraction, thermogravimetric analysis and differential scanning calorimetry. The results show that α-PbO2 phase TiO2 transforms to rutile TiO2 when heated to temperature higher than 560 °C. The mechanisms of the phase transition of TiO2 under shock compression are discussed.