Biocompatibility testing measures how compatible a device or material is with a biological system, and is needed to begin human trials of a medical device. Biocompatibility testing can provide an initial screening of whether the components of a medical device may cause adverse effects when interacting with the human body.
Initial Screening and In Vitro Testing
Usually, testing begins with the characterization and analysis of the components of a device. The device is submerged in extraction media under specified conditions to evaluate whether anything that leeches out from the device materials can be potentially harmful or toxic. Additional tests for cytotoxicity can be done to check for effects on tissue cultures before in vivo testing is done. This is done by placing the test article or an extract of the material onto cells to see whether there are any adverse effects. The viability of cells can also be measured by spectrophotometric methods or by counting the number of colonies formed after exposure to the test material.
Various types of in vivo testing exist and are often required by federal agencies for approval of a device depending on its intended use. Sensitization studies tell us whether or not the device contains chemicals that can cause an adverse local or systemic effect after prolonged exposure. It screens for substances that would cause an allergic reaction in humans. Types of sensitization assays include the Guinea Pig Maximization Test, the Closed Patch Test, and the Murine Local Lymph Node Assay. Irritation studies evaluate local irritation on skin and mucus membranes. These include Intracutaneous, Primary Skin Irritation, and Mucous Membrane Irritation tests, which are performed depending on the route of exposure and duration of contact of the intended device.
Systemic toxicity tests involve testing extracts of the device to evaluate whether leachables from the device produce toxic effects. Acute toxicity results in an immediate reaction after an exposure (<24 hours) and also evaluates the potential of materials to cause a pyrogenic, or feverish, effect. Subacute toxicity evaluates products with prolonged (24 hours to 30 days) exposure, while subchronic and chronic toxicity measures results for long term to permanent devices over several weeks or months. Implantation tests are often performed in addition to the previously mentioned tests for devices that will come in contact with living tissue other than skin. After the appropriate time has passed, histopathological examination must be done. Tissue from the surrounding area of the implant is examined for adverse reactions.
Genotoxicity, Hemocompatibility, and Carcinogenesis
Genotoxicity testing evaluates whether a certain material has the potential to affect the integrity of DNA by making it mutagenic or cancerogenic. Hemocompatibility tests range from hemolysis to coagulation to prothrombin time assays and is assessed for devices which will come into contact with blood. It is an evaluation of the amount of damage a device or material can cause to red blood cells. Depending on the intended use and placement of the device, carcinogenesis bioassays and pharmacokinetic studies may also be needed.