Cytotoxicity testing extraction process

In comparison with osteoblasts, tests conducted with the use of human fibroblasts demonstrated higher cytotoxicity of the examined PSU and its composites with nanosilver. After a 24-h incubation of tested materials with fibroblasts, the percentage of the live cells was lower than in the case of the tests performed after 48 h of incubation. Such behavior suggests that, despite the toxic effect, the process of cell multiplication continues. In the case of diluted extracts, a significant decrease of cytotoxicity was observed. The cytotoxic effect of the materials on fibroblasts and the related lower vitality of these cells can be a beneficial phenomenon, if the implant material is intended for the regeneration or replacement of the bone tissue, as one should aim at the activation of the osteoblasts (osteogenic cells) and a simultaneous inhibition of the fibroblasts activity. 

However, antioxidant screening in complex mixtures of plant origin requires simple and rapid in vitro models for a possible combination with chromatographic techniques such as TLC, HPLC, HSCCC, or CPC. The reduction of the stable free-radical DPPH (l,l-diphenyl-2-picryUiydrazyl) by antioxidant substances is currently the most widely used chemical test for the screening of plant extracts. Only a few bioassay-guided fractionation processes have also evaluated the antimicrobial, antibacterial activity, or cytotoxicity of fractions enriched in specific flavonoids by using HSCCC or CPC liquid-liquid systems [30, 35]. 

For biocompatibility testing using cytotoxicity (ISO 10993-5), the samples are either tested directly, as in an agar overlay test, or are extracted, as in minimum essential medium elution. Extraction is a process in which the test material is typically subdivided, placed in an extraction vessel, and covered with the exttaction vehicle. Polar and nonpolar extraction vehicles are used separately. Examples of polar extraction vehicles are water, cell culture media, and physiological saline, that is, 0.9 % aqueous NaCl solution, which is usually the preferred polar vehicle for biological assays. Examples of nonpolar vehicles include cotton seed oil and sesame seed oil. 

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