MedTech Expert Explains Biocompatibility (in-vitro) Testing | Pressure Tested

Hi, I’m Riwia. I’m a senior lab scientist at Test Labs, and I’m the biocompatibility expert, and I’m going to be pressure tested.

What is in vitro testing?

So, in vitro testing is performed outside a living organism, unlike in vivo testing, where it’s performed within, eg. animal studies. So in vitro studies can help in biocompatibility for medical devices because it’s usually the first screening step for the validation of a medical device.

What are in vitro methods?

So in vitro methods use cell lines. These are established, scientifically sound models which indicate any biological responses. So we use them in cytotoxicity testing as well as skin irritation. In cytotoxicity, we use connective tissue. They’re unanimous around the body, so they give a sound kind of reaction to what is being put on there. So we’ll give a good cytotoxic response, which will be valuable for the whole body.

When is biocompatibility testing required?

So biocompatibility testing is required for any medical device that comes into direct contact or indirect contact with a human. It depends on its duration, intended use, and it’s needed for regulatory bodies and clinical studies as well.

What’s the biggest misconception about ISO 10993-5?

Something that I’ve come across quite a lot is cytotoxicity testing or any type of biological endpoint that’s referred to in the standard being something that’s at the end of a validation, whereas I think it’s more important to have it as a screening, as a first step in your validation to see, okay, are the materials compatible? Is there any risk of any manufacturing processes which can risk the biocompatibility of the device? And the way that you screen for it earlier, you can catch out these risks earlier on than kind of have the costly downstream testing happen at the end. So yeah, have it as your very first step in your validation.

What causes failed cytotoxicity tests?

Something that happens quite frequently is not really realizing what your device is made up of, especially things like dye or any sort of processing aids from the manufacturing process. So all of these small things can add up and then have a big effect on biocompatibility. Some of the studies that I do here at Test Lab, we try and validate the reprocessing steps and see if washing off disinfectants have an effect on biocompatibility. Any residual kind of buildup of disinfectants can definitely cause a negative effect on cells. So those are one of the couple of main reasons why cytotoxicity tests kind of fail. Avoiding failing the test requires quite a good knowledge on the whole history of the manufacturing of the device. That can start from making the device to all the additives that are added in, and then the final product, and then as well as the usability and intended use of the device. So all of it in accumulation needs to be thoroughly looked through, which is something that the BEP, which is the first step of a biocompatibility validation, it looks through all of those steps and then identifies what tests are required for which part.

How many samples do you need?

So typically in science, the golden rule is three. We use three for reproducibility, repeatability as well. So usually we ask clients for three samples for any type of cytotoxicity testing or skin irritation, and this should be in its finalized form of the product. There’s no point in doing a cytotox test with unfinished parts of the product. It doesn’t help with your validation or your regulatory file either. So yeah, three, and in its finalized form. So yeah, we’ve had really big devices before, and as the scientist who’s in charge of the testing can tell you, it’s a lot of brains together to try and figure out how to extract them. But because of our state-of-the-art equipment that we have, we can accommodate any really size of device, as long as they can fit in our shaking incubator. However, if they are too large, we can break them into parts. We have different methods on how to extract efficiently.

What is the minimum surface area required to do testing?

So this is a great question. It’s a question that comes up a lot with our client calls. So we use the standard ISO 10993-12, which elaborates on what type of extraction ratio is required for your device. Typically, for devices that we test at Test Lab, we use the surface area, so that’s three centimeters squared per mil. But depending on the device, we can weigh it as well, and then that would be 0.2 grams per mil. It’s all outlined in that standard to help us decide on what’s the best type of extraction ratio for your device.

What triggers biocompatibility risks?

So usually, any changes in the manufacturing of a device, whether that be a change of supplier or an additive that’s added in, which wasn’t there before, all of these small details can have an effect on biocompatibility. As well as this, changes in your reprocessing steps, whether that’s adding an additional step of disinfection or one less rinse step, all of this can also kind of accumulate and have an effect on biocompatibility as well. So all of these are risks to biocompatibility.

What is skin irritation testing?

So skin irritation testing is a type of biocompatibility test that evaluates the potential of irritants in an extract of a medical device. This is for intact skin, so any device which comes into contact with intact skin. How we perform this test is we use a 3D structure, which is lab-grown, so it’s three layers of cells to mimic the layers of the skin. And then, similar to cytotox, we have a MTT reaction, which allows us to identify cells that are alive and cells that are dead.

What are 3D skin models, and how do they work?

So a 3D skin model that we use for skin irritation is layers of cells which mimic the epidermal layers of skin. We have this brought into the lab, and this reduces the need for animal testing because we can have a more accurate representation of what the effect of the extracts are on the cells. It’s like an elevated sand line. Instead of it just being kind of 2D flat, we’ve got three layers. So based on that, we get more accurate results on what type of irritants we can find based on your device.

What testing mistakes lead to repeat studies?

So one of the things that we get quite a lot is a medical device that’s in its unfinished form. When we test these devices, although that we get results, these can change depending on what other additives are added in, and therefore kind of make the results unreliable. So we do advise clients to give us the final marketed product. That way, the results that we get from biocompatibility testing will be the most accurate for regulatory bodies as well.

How do you reduce the risk of test failure?

So reducing the risk, I think, starts primarily with strong communication between the client and our team, understanding manufacturing steps, processing aids, and things like this do come out through a biological evaluation plan, which we can help you with as well. Once we finalize that, on the lab side, we strictly adhere to aseptic techniques, making sure that everything is of the highest standard to make sure there’s no contamination risks. That way, we have the utmost trust in our results to make sure that they’re the most accurate cytotoxic results or skin irritation results for your device.

How do combination products complicate testing?

So combination products can complicate testing because we have to come up with an extraction plan on how we extract individual components as well as the device as a whole. As we do this, a common way we do it is by quartering off a part of the device that we want to extract individually. And then as well as that, we do the entire device to see if there’s any residual effects of any parts of the manufacturing process or reprocessing process which has an effect on the cells. So we do the whole thing as well as individually to try and have a more robust kind of testing method for the entire device.

What data do regulators expect to see clearly explained?

The main thing is clear scientific explanations on testing strategies, extraction methods, as well as conclusions. This is all wrapped up nicely in a biological evaluation plan, which test labs do provide. And with this, it justifies the need to even do some biocompatibility testing as well. So it’s very important that you have this plan laid out before you start your biocompatibility validations. As well as this, the biological evaluation plan helps with aligning with the principles of the ISO standard, which is to replace, reduce and refine. So having testing, that doesn’t necessarily mean you need to do the whole suite of biocompatibility testing. You may just need to do a cytotox test and then have it scientifically justified to be enough for your device.

What’s the most expensive biocompatibility mistake?

I think that’s a really good question. One of the most costly mistakes is to not prioritize in vitro testing as a screening tool as your first step in your biocompatibility device evaluation. The risk of this is that you go into animal studies, you find out that your device does have a cytotoxic effect, and then have potentially a lot of money go down the drain because you didn’t do that initial kind of screening test before going ahead with the costly animal testing. So I think that’s quite a costly mistake. You should definitely start with doing your in vitro testing first and then going down to do your animal testing. Okay, so that was fun being pressure tested. It’s definitely quite hard to come up with answers on the spot like this. I’m definitely feeling very warm and pressure tested. But yes, I’ll definitely be one of your principal scientists for any biocompatibility testing. So if I’ve not mentioned anything and you still have some questions, please do reach out on our website at testlabsuk.com.