A comparative study of the use of colorimetric assays in the assessment of biocompatibility

A panel of colorimetric assays was assessed for sensitivity, reproducibility, and performance in the investigation of the biocompatibility of a representative range of orthopaedic biomaterials, using a commercially available human osteosarcoma-derived cell line. The MTT assay was the most sensitive, with a detection limit of 4 x 10(2) cells per well against background, while the NR assay was the least sensitive, with no colour change until the cell density reached 2 x 10(4) per well. All of the assays investigated showed a highly significant ''edge'' effect when within-plate reproducibility was examined; between-plate reproducibility was good for all assays except the MTT assay. When the assays were tested on cells adherent on biomaterials, there was a wide variation in the results obtained; in particular, the MTS assay showed poor reproducibility in the presence of materials. The MTT and BrdU assays both showed sufficient precision to detect cells on two of the materials studied. The study demonstrates that colorimetric assays are potentially useful in biocompatibility assessment but must be fully validated for the application chosen.