Intracellular Calcium Quantification

Intracellular calcium content was determined as described in our previous report [62 (link),63 (link)]. Briefly, cells were cultured onto fucoidan/PDA composite-coated surfaces. Seven and fourteen days after osteogenic induction, the intracellular calcium level was quantified using a calcium assay kit (BioAssay Systems, Hayward, CA, USA) according to the manufacturer’s instructions. Standard solution (0~6 mg/dl) was prepared and read optical density with a microplate spectrophotometer at 612 nm. The absorbance of blank standard was subtracted from all standard and sample absorbance values. Calcium concentration of the sample was calculated from the linear regression equation obtained from standard curve. Calcium levels were converted as mg/100 mg of protein.