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Sizes of silver nanoparticles (AgNPs) have been shown to affect the biological activity of AgNPs. Hydrogel beads loaded with AgNPs have been extensively employed for biomedical applications. However, the influence of AgNPs sizes on biological activity of AgNP-loaded hydrogel beads has not much studied. Our objectives were to investigate the effect of AgNP sizes on the antibacterial activity, the cyto- and genotoxicity of AgNPs/alginate hydrogel beads. AgNPs of different sizes (⁓10 nm for S-AgNPs, and ⁓50 nm for L-AgNPs) were incorporated into alginate hydrogel beads during the preparation. The results showed that, S-AgNPs/alginate hydrogel beads (⁓89% inhibition) at AgNP concentration of 10 µg/ml tended to inhibit the growth of E. coli greater than L-AgNPs/alginate hydrogel beads (⁓49% inhibition) at the same dose. Moreover, at this effective antibacterial concentration (10 µg/ml), S-AgNPs/alginate hydrogel beads exhibited weak cytotoxic effect to HaCaT cells whereas L-AgNPs/alginate hydrogel beads showed non-cytotoxicity to this cell line. Furthermore, treatment of HaCaT cells with 10 µg/ml of S-AgNPs/ or L-AgNPs/alginate hydrogel beads did not result in a significant change in %DNA in tail when compared to untreated cells. Therefore, these AgNPs/alginate hydrogel beads, especially with smaller sized AgNPs, can be used as an antibacterial biomaterial with low cytotoxicity and genotoxicity to human cells.

Silver nanoparticles have been used in combination with biological polymer for antibacterial application. This study prepared chitosan/alginate/AgNP beads with varying chitosan and alginate concentration to use as an antibacterial material. The sizes of neat beads were larger (1286 ± 172, 1344 ± 142 and 1529 ± 73 μm for C1, C2 and C3, respectively) with increasing concentration of chitosan and alginate. Moreover, smaller beads were observed for the chitosan/alginate/AgNP beads, in which their sizes were 1151 ± 201, 1261 ± 204 and 1324 ± 198 µm for S1, S2 and S3, respectively, when compared to the chitosan/alginate beads. Furthermore, the minimum bactericidal concentration (MBC) of chitosan/alginate/AgNP beads against E. coli was 10, 10 and 3 µg/ml for S1, S2 and S3, respectively. This study suggested that the beads with the higher concentration of chitosan and alginate resulted in the greater bactericidal activity. Therefore, the chitosan/alginate/AgNP beads prepared in this study showed the bactericidal activity which can be used for antibacterial application.

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