3D Tissue Constructs for Dermal Irritation Step-by-Step
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Receipt of Tissues
Each tissue is comprised of human cells in a 3-dimensional tissue structure.
Tissues are inspected for irregularities and then transferred to pre-labeled plates containing pre-warmed medium. The plates are then placed in a humidified incubator to equilibrate the tissues.
After an incubation period, the test material, positive control or negative control is applied directly onto the tissue surface.
Both solid and liquid materials can be tested. Dosing preparation may be adjusted to accommodate specific physical test article characteristics or client needs.
After a specified exposure time, the test material is rinsed from the tissue with a buffered saline solution.
Specific protocols or tissue types may include additional rinsing procedures.
Transfer to MTT
The tissues are transferred to MTT solution and incubated.
MTT is actively taken up by the tissues and subsequently reduced in the mitochondria of living cells. This chemical reaction produces a purple-colored formazan within the cells, causing the live tissues to turn deep purple in color.
Test materials that result in cell death will not produce this color change. The more toxic the test material, the less purple the tissue will be.
Extraction in Isopropanol and Plate Reading
After the MTT incubation, the tissues are transferred from the MTT solution to isopropanol. The isopropanol extracts the purple-colored formazan from the tissues.
Aliquots of each extracted tissue are transferred to a 96-well plate to be read by the spectrophotometer. Absorbance readings from test material treated tissues are compared to negative control tissues. Changes in % cell viability relative to the negative controls are interpreted to evaluate the irritation potential of the test material.
Direct MTT Reduction and Killed Controls
Prior to beginning an assay, each test material is pre-screened for direct MTT reduction.
The test material is added to MTT solution. A color change indicates its ability to directly reduce MTT. Freeze-killed control tissues may be utilized concurrently in the assay to determine the extent of direct MTT reduction (if any) by the test article.