Objective To find a new material for biomedical scaffold.Methods Composite films from poly-L-lactic acid(PLLA)and opal powder were fabricated.Osteoblasts seeded on the composite films and control ones were examined.Cell densities and morphologies on these films were studied by scanning electron microscopy(SEM).Cell growth and differential function were assessed by 3-(4,5-dimethyltyiazol-2-yl)-2,5-diphenyl tetrazolium bromide(MTT)test.Results SEM study showed that the addition of powder could improve the adhesion between osteoblasts and the composite films.MTT test proved that cell proliferation was improved when opal powder was added.This improvement came from the negative ion given off by the opal powder.The negative ions either accumulate at the cell membrane or enter into the cells.Accumulation of negative ions at the cell membrane leads to a change of electric potential difference across the cell membrane which should be in a proper range for the cells to perform their normal physiological function.If the negative ions enter the cells,they may take part in biochemical reactions whenever possible.In this way,the ions also affect the cell normal metabolism.Conclusion Osteoblasts grow well on opal/PLLA composites and the negative ion from opal powder is responsible for the enhancement of cell growth.This study provides a new material for biomedical scaffold.