Cytotoxicity Assays in Medical Device

Medical devices are used in different healthcare set-ups such as the diagnosis of illness, to monitor treatments, treat both acute and chronic illnesses.

These medical devices need to pass biocompatibility tests to ensure that these medical devices are safe for patients.
Cytotoxicity testing is one of the biocompatibility tests needed for medical devices that come in contact with human tissues.
Cytotoxicity tests are performed in-vitro to determine the toxicity of medical devices and their materials. The devices need to meet safety standards to pass the cytotoxic tests.

To assure the safety and effectiveness of a new or modified medical device, it must undergo a nonclinical safety assessment, which may include biocompatibility testing, before entering a human clinical trial or getting regulatory approval.

The standard set of testing includes cytotoxicity, irritation, and sensitization. Additional testing may be necessary depending on the product's features, intended use, and type and duration of contact with the body (FDA, 2016; ISO 10993-1, 2019).
In vitro cell culture systems are used in cytotoxicity testing, which is a fundamental requirement of all important standards for the biological assessment of medical devices, to assess cellular health endpoints such as growth, replication, and morphology following exposure to a test material or its extract or leachate.

In theory, it provides a quick, standardised, sensitive, and cost-effective way of determining whether a material contains potentially biologically harmful substances or chemicals. One of the advantages of cytotoxicity testing is that it may be utilised as a screening assessment throughout product development to evaluate both the device's raw material components and the end device itself.
 Compared to animal models, in vitro testing models have added advantage to deliver test results that are less expensive, quicker, more accurate, and more reliable.
Quantitative and qualitative methods for determining the cytotoxic effect:
Quantitative method:  This is a colorimetric assay that can be carried out through either direct contact or extracts. The percentage of cells that are inhibited or die after contact with the test material determines the performance of this test material. In MTT assay If viability is reduced to < 70 % of the blank, it has a cytotoxic potential. The 50 % extract of the test sample should have at least the same or higher viability than the 100 % extract; otherwise, the test should be repeated [2].
Qualitative method: The cells are visualised using cytochemical staining under a microscope. Analysing morphological alterations, including those that impact membrane integrity, cell lysis, detachment, and vacuolization. On a scale of 0 to 4, assign a grade to each cell, with 0 denoting discrete intracytoplasmic granules, indicating no cell lysis, and 4 denoting virtually complete or entire cell lysis. 
Sample preparation must adhere to ISO 10993-12. There must be both negative and positive controls for each test.
Any failure of in vitro cytotoxicity should be investigated to determine the risk of in vivo toxicity as it is a cause for concern. This may not indicate that a medical device is necessarily not biocompatible. 
Points to be considered during the cytotoxicity study: 
a)    that the correct extraction conditions and parameters were used during testing, 
b)    that all technical and negative controls were present and showed the expected viability to demonstrate the validity of the assay,
c)    that no expired products were used,
d)    that variability between technical replicates was acceptable,
e)    during the sample preparation, the following points need to be considered
o  flushing of the device or removal of certain components from the extraction 
o    if the testing was performed at an accredited lab, then all conditions should be met, and verify that nothing was overlooked. If the particulates or pH change information is not provided in the test report, then it is important to find out that no particulates or pH changes were observed in the extract of the device. If particulates were observed in the extract of the device, the manufacturer should consider this as a potential source of cytotoxicity.
One of the most essential components of the in vitro biological evaluation system is the cytotoxicity test, which is continually being developed and improved because of advances in modern cell biology.
The ability to quickly screen materials for potential negative effects, as well as the ability to test a smaller amount of material than an in vivo study that is estimated by body weights or surface areas, are just a few of the benefits of using in vitro model systems in medical device toxicity testing. There are three quantitative methods (MTT, XTT, and NRU) and three qualitative methods (elution assay, agar overlay/diffusion, and direct contact method).
Test results for cytotoxicity might be either positive or negative. Each instance of in vitro cytotoxicity failure should be examined to ascertain whether there is a risk, although this does not suggest that a medical device is not biocompatible in all cases.
Decos will help you select the appropriate cytotoxicity testing method for your medical device, analyse any cytotoxicity failures, and evaluate the clinical safety of the patient as well as the toxicological risk. 
1.    ISO 10993-1, Biological evaluation of medical devices-Part 1: Evaluation and testing within a risk management 
2.    ISO 10993-5, Biological evaluation of medical devices-Part 5: Tests for in vitro cytotoxicity
3.    ISO 10993-12, Biological evaluation of medical devices-Part 12: Sample preparation and reference materials