Case Study 3.8 Antibacterial Properties

3.8 Antibacterial properties
Antibacterial property is another important property required for bone tissue engineering to eliminate bacterial infection in orthopedic implants which generally leads to implant failure. Table 4 showed antibacterial zone of inhibition of CMZH I-III and CZH against gram-positive bacteria Bacillus cereus and Lysinibacillus fusiformis and gram-negative bacteria Escherichia coli XL1B. It was observed that the antibacterial inhibition zone increased from CMZH I to CMZH III against all three bacterial strain where OMMT content has been increased from 5 to 15 wt % respectively. The increase in the inhibition zone from CMZH I to CMZH III could be due to the presence of antimicrobial quaternary ammonium salt of OMMT (Mondal
All the nanocomposites exhibited good antibacterial activity against Bacillus cereus, Lysinibacillus fusiformis and E. coli bacterial strains. In addition, stronger inhibitory capacity was observed with increasing the OMMT content. Among the three nanocomposites, the CMZH III (having 15 wt % OMMT) showed best antimicrobial effect. Strong adsorption and immobilization capacity of modified layered silicates could be responsible for this kind of behavior (Guo, Ma, Guo, & Xu, 2005). It was also observed that inhibition of the CMZH I-III was more effective against gram-positive bacteria as compared to gram-negative bacteria. Compare to CTS or OMMT, the MICs of the CMZH I-III against gram-positive bacteria Bacillus cereus were 8–32 times lower and against gram-positive bacteria Lysinibacillus fusiformis, MICs were 8-16 times lower. In case of gram-negative bacteria E. coli, MICs were only 4–8 times lower than that of CTS or OMMT. The difference observed in MICs against gram-positive and gram-negative bacteria could possibly due to their structural variation. Gram-negative bacteria have toxic outer membrane made of liposaccharides layer which makes them less susceptible to antibiotics and antibacterial agents than gram-positive bacteria (Guo, Ma, Guo, & Xu,
It has been observed from inverted phase contrast micrographs (Fig. 8a-e) that human osteoblastic MG-63 cell proliferation was maximum in CMZH I compare to CMZH II, CMZH III, CZH and control (empty plate). It was observed that in absence of OMMT (CZH), the cell proliferation was lower as compared to CMZH I (having 5 wt % OMMT) and CMZH III (having 10 wt % OMMT). Thus, OMMT had a great effect on the osteoblastic cell proliferation (Kar et al., 2016). However, reduced cytocompatibility of CMZH III was observed after addition of 15 wt % OMMT into CTS-HAP-ZrO2. This kind of behavior was observed previously where nanocomposites composed of ethylene vinyl acetate and natural cloisite clay have showed clay dependent growth of human dermal fibroblasts on the nanocomposite. Highest cell growth was obtained with 10 % clay, whereas poor cell growth was observed with higher clay content (Lewkowitz-Shpuntoff et al., 2009). The effect of ZrO2 nanofillers in these nanocomposites was also observed. Lower content of ZrO2 NPs did not induce any cytotoxity and were able to proliferate osteoblastic cells (Josset et al., 1999). The MTT assays of these nanocomposites (Fig. 8f) were also confirmed that CMZH I have no negative effect on human osteoblastic MG-63 cells and confirmed good cytocompatibility for successful bone