Biocompatibility Test

Biocompatibility is defined as the degree of “how well a material lives” in a human body after being implanted. Therefore, biomaterials go through in vivo or in vitro tests in order to be implanted. In vivo tests are on living organisms while in vitro tests are on a test tube or petri dish. This blog mentions an example from each type of the tests. Firstly, there is the MTT assay which measures the biocompatibility on 3 materials, e.g. Perspex, Delrin and Polyvinyl chloride (PVC). MTT assay is an in vitro test because the cells – HaCaT that are used to test the biocompatibility are seeded onto biomaterial disks under a controlled condition.

These cells are an immortalised epithelial cell line which is capable of skin keratinocyte differentiation. It is called the MTT assay because MTT is a reagent (MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide) added to measure cell metabolism by turning into purple on metabolically active cells. The change in absorbance at 570nm is measured on a absorbance plate reader after the purple product is eluted by isopropanol. The higher the absorbance rate, the higher the population of active cells. This is an important assay because the more active cells on the materials, the less degree of cytotoxicity the materials have as there are fewer cells that are damaged or dead. As PVC is tested in MTT assay, the assay ensures that the PVC is safe enough to be used in dialysis tubes for patients (contact with cells in dialysis). Furthermore, the assay takes place in a lab with an ISO standard of 10993-5. Therefore, the materials are proven to be biocompatible with credibility. The next type of test is a vivo test which is the intracutaneous irritation test. The biomaterial of interest is put into a solution of 4 elution vehicles, such as saline, alcohol, PEG and vegetable oil, for 72 hours. Because the elution vehicles help materials to elute before eluting themselves in the body under the influences from polar and non-polar components (blood plasma and lipid cell membrane). The elution is then injected at 15 degrees just beneath the skin of rabbits.

If the rabbit body rejects the materials, there will be swelling from inflammation. This means same will happen when the material is implanted into a human body which makes the test very important.