In vivo testing of a biomaterial refers to the methodology of testing a biomaterial in the living body of a plant or an animal. This is done in order to determine the biocompatibility of the biomaterial. US Food and Drug Administration (FDA), ASTM International, International Organisation for Standardisation (ISO) and the US Pharmacopeia (USP) have developed certain protocols according to which the in vivo testing of the biomaterials has to be done.
While selecting a biomaterial in a device design, the considerations that should be made is given by,
- Chemical properties
- Physical properties
- Toxicological properties
- Electrical properties
- Morphological properties
- Mechanical properties
MECHANICAL TESTING
Mechanical properties play an important role in the in vivo testing as their properties have to match with the native tissue to be replaced. The nature of tissue contact of the medical device and the duration of contact should be used for consideration while selecting a proper in vivo test. The tests that has to be done for assessing the tissue compatibility is given by,
- Elastic modulus
- Hardness
- Fracture strength
- Fracture toughness
- Compressive strength
- Tensile strength
While the factors that influence biocompatibility is given by,
- Carcinogenic reactions
- Mutagenic reactions
- Inflammatory process
- Quality of biodegradation
- Contact with human blood
Compressive strength
The capacity of a material to withstand the loads that leads to deformation is known as compressive strength. This strength can be determined by means of a compressive test. Non invasive axial loading tests has a lot of advantages when compared with the other loading techniques. In this test, the loads are applied to the bone under aesthetic through the skin and the bone’s articular surfaces other than the periosteum. The scaffolds with a high square pore morphology tends to show a higher compressive strength and a higher modulus than other pore morphologies.
Tensile strength
Tensile strength is defined as the capacity of a material to withstand the loads tending to elongate. The average strength of cortical bone is given by 100 to 230 MPa. Thus, the materials chosen for the implants should match this range. Due to its high tensile strength, collagen can be woven or twisted into a desired form even though it cannot purely be used only for bone regeneration. The approaches used to test the tensile strength is characterised by the orientation and magnitude of the imposed stress and strain over time.
Process of in vivo testing
Some kind of knowledge of tissue compatibility is required for the in vivo testing of the biomaterials. The in vivo testing method focuses on the biocompatibility of the final product The overall process of determining the biocompatibility of tissue involves an in vitro screening of cytotoxicity and finally conduct a confirmatory in vivo testing on the finished device. As animal testing is required for the testing of biocompatibility in a large scale, the number of unnecessary tests and the test animals have to be minimised.
Once the in vitro testing for the biomaterial is done, the in vivo testing can be done based on the devices use. This testing process can range from testing the skin irritation to testing the hemocompatibility of the implant. The turn around time for each test can be from three weeks to greater than several months. Longer turn around periods are seen in sub chronic or chronic implantation. After the completion of testes, the data collected is interpreted by an expert and the results are published.
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