Chengpeng Li

Considering the great harm to the human body caused by severe and massive bleeding, in this study, chitosan-grafted norfloxacin (CTS-NF) composites were prepared with chitosan (CTS) and norfloxacin (NF) as raw materials by a 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide-mediated coupling method to solve the limitations of slow hemostatic and poor anti-infective effects of current dressings on the market. The effects of the mass ratio of CTS to NF (M_CTS/M_NF), reaction temperature T and reaction time t on the grafting rate (η%) of the products were investigated through single factor tests. The preparation process was optimized with the η% as an evaluation index by means of the Box–Behnken test design and response surface analysis. The antimicrobial activity was evaluated by inhibition zone assay, and the hemostatic activity of the prepared composites was evaluated in vitro and in vivo. The results suggested that the optimum preparation conditions were the mass ratio of CTS to NF (M_CTS/M_NF) 5:3, reaction temperature 65 °C, and reaction time 4 h. Under this condition, the η% of CTS-NF was 45.5%. The CTS-NF composites displayed significant antimicrobial activities. Moreover, in vitro hemostasis results revealed that the CTS-NF composite had a lower blood clotting index and absorbed red blood cells to promote aggregation. In vivo ear and live hemostasis, the CTS-NF groups showed short hemostatic time (49.75 ± 3.32 s and 50.00 ± 7.21 s) and more blood loss (0.07 ± 0.010 g and 0.075 ± 0.013 g). The results showed that CTS-NF reduced the bleeding time and volume, exhibiting a significant coagulation effect. Therefore, the CTS-NF sponge is expected to be a new, effective hemostatic and antibacterial material in the future.

Hydrogels based on nanocomposites (NC) structure have acquired a great deal of interest, but they are still limited by relatively low mechanical strength, inevitably losing elasticity when applied below subzero temperatures, due to the formation of ice crystallization. In this study, an anti-freezing and mechanically strong Laponite NC organohydrogel was prepared by a direct solvent replacement strategy of immersing Laponite NC pre-hydrogel into ethylene glycol (EG)/water mixture solution. In the organohydrogel, a part of water molecules was replaced by EG, which inhibited the formation of ice crystallization even at extremely low temperatures. In addition, the formation of hydrogen bonds between Laponite and the monomers of N-isopropylacrylamide (NIPAM) and hydroxyethyl acrylate (HEA) endowed the organohydrogels with high mechanical strength and toughness. The NC organohydrogel can maintain its mechanical flexibility even at −25 °C. The compressive stress, tensile stress, and elongation at the break of N₅H₅L reached 3871.71 kPa, 137.05 kPa, and 173.39%, respectively, which may be potentially applied as ocean probes in low temperature environment.

To develop a novel asymmetric nanofiber membrane with antioxidant and antibacterial activities, biocompatible polyvinyl pyrrolidone (PVP) and polycaprolactone (PCL) were used as carriers to load water-soluble tea tree extract (TTE) and hydrophobic tea tree oil (TTO) via electrospinning and electrostatic spraying, respectively, which was named as TTE-PVP-3/TTO-PCL. The results show that uniform TTE-PVP nanofibers with an average diameter of 95 ± 27 nm could be obtained when the mass ratio of TTE to PVP was set as 1:3. Homogeneous TTO/PCL microspheres with an average size of 4.38 ± 0.79 µm could be obtained when the propulsion speed was 0.08 mm/min and the voltage was 10 KV. The activity study showed that TTE could only improve the antioxidant activity of TTE-PVP-3/TTO-PCL, while TTO could improve the antibacterial activity effectively. Under experimental conditions, the inhibition zones of TTE-PVP-3/TTO-PCL against Staphylococcus aureus and Escherichia coli were 7.50 ± 0.48 mm and 9.55 ± 0.45 mm, respectively, and its scavenging rates for 2,2-diphenylpicrylhydrazyl (DHPP) and hydroxyl radical were 59.79 ± 4.10% and 61.02 ± 4.95%, respectively. In conclusions, TTE-PVP-3/TTO PCL can be potentially used as a new kind of anti-oxidative and antibacterial wound dressings.

To develop agar derivatives with good antibacterial activity and decreased gelling and melting temperatures, two agar–gentamycin conjugates with 9.20% and 12.68% gentamicin immobilized were fabricated by oxidation, Schiff base and reduction reaction, and characterized by a Fourier Transform Infrared Spectrometer, ¹H nuclear magnetic resonance and an elemental analyzer. It was found that the modifications changed the intermolecular interactions, leading to decreased gelling and melting temperatures for the oxidized agar and slightly increased gelling and melting temperatures for agar–gentamycin conjugates. Further studies of antimicrobial properties showed that the two agar–gentamycin conjugates possessed good antibacterial activity, which was positively correlated with the dosage and the immobilization rate of gentamicin. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of agar–gentamycin conjugates with higher immobilization rates of gentamicin against Escherichia coli were 39.1 μg/mL and 156.2 μg/mL, respectively, and the MICs and MBCs against Staphylococcus aureus were 19.5 μg/mL and 78.1 μg/mL, respectively. A biofilm test indicated that certain concentrations of agar–gentamycin conjugate could effectively inhibit the biofilm formation of Escherichia coli and Staphylococcus aureus. In summary, agar–gentamycin conjugates possess good antibacterial activities and may be applied as a new kind of antibacterial material.

Chitosan (CS) is a biodegradable, biocompatible, and non-toxic natural amino-poly-saccharide with antibacterial ability, owing to its positively charged amino groups. However, the low charge density leads to poor antibacterial efficiency which cannot meet the biomedical application requirements. In this study, Tobramycin (TOB) was grafted onto the backbone of oxidized chitosan (OCS) to synthesize oxidized chitosan-tobramycin (OCS-TOB). FTIR, ¹H NMR and elemental analysis results demonstrated that OCS-TOB was successfully synthesized. OCS-TOB/PEO composite fibrous materials were produced by a self-made centrifugal spinning machine. In vitro experiments showed that cells proliferated on the submicro-fibrous OCS-TOB/PEO of appropriate concentration, and the antibacterial ability of OCS-TOB was much improved, compared with pristine CS. The results demonstrated that OCS-TOB/PEO nanofibrous materials could potentially be used for biomedical applications.