Coatings and surface treatment
breakthrough ideas, designers often underestimate the challenge of foreign body response – and that’s usually where these ideas die,” Veiseh notes. “You come up with your perfectly designed device, you put it in the body, and then the body rejects it. This barrier has curtailed a lot of innovation when it comes to implantables.”
An attuned threat response Foreign body response (FBR) is the term used to describe the body’s immune reaction to a foreign object. As Veiseh explains: “The immune system is really good at identifying things that don’t belong there, and it has a number of different mechanisms for trying to eliminate them. But when the immune cells are physically unable to ‘chew up’ and eliminate an implant, then they start adhering to the surface of it and they initiate a cascade, which is what we call the foreign body response.” When this happens, different types of immune cells “orchestrate”, building up scar tissue around the implant in order to wall it off from the rest of the body. For some medical devices, such as knee and breast implants, this is not a big deal. “The devices are somewhat inert and don’t need to physically interact with the body,” says Veiseh. “But for active devices that have sensing or actuated components, such as a pacemaker or a neural recording device, this is a major barrier, which limits the utility of these [applications] in the body.” Veiseh has recently concluded a study into lipid deposition on the surfaces of implants, as one strategy for targeting FBR. “We identified small molecule coatings,” he explains. “One of the things that we realised is that these molecules tend to attract a suppressive type of macrophage immune cell. As these immune cells crawl on the surfaces of implants, we realised that they leave behind lipid vesicles – these extracellular kind of blobs of cells that are chock full of cytokines.” Veiseh observed that these vesicles could tag material with either an “attack” or “do not attack” signal. “We did quite a lot of work on this in different contexts with different types of coatings, as well as looking at explanted human devices, and we noticed that, indeed, there is a correlation between the composition of these extracellular vesicles that are deposited on to these implants, and whether you get foreign body responses or not,” he adds. Veiseh describes the results of the study as “an overarching mechanistic insight” which is relevant for devices that exist on the market today, as well as a guide to the future development of devices. “We’ve tested these small molecule coatings in large animals and we’re working on advancing them to the clinic in different contexts,” he says.
Medical Device Developments /
www.nsmedicaldevices.com
Fighting the immune system Veiseh’s study is just one amongst a number of innovative approaches that are currently being tested and deployed in the fight against FBR. At the University of Cambridge, for example, Dr Damiano Barone, clinical lecturer in the Department of Clinical Neurosciences and a practising neurosurgeon, has been working on a study that explores the prevention of FBR through something called “inflammasome inhibition”. Barone’s expertise is in bioelectronics, exploring the relationship between neural interfaces – electronic devices that interact with the nervous system – and the body. For this application, the ideal device is “one that goes into the brain”, he says. “You want as much information as you can get, and the only way to get this is to be close [to the brain]. Unfortunately, there are lots of problems with this, and one of the major ones is the fact that every time you implant something into the brain it gets kind of rejected.”
The barrier of FBR has prevented innovations beyond commonly seen cardioverter defi brillators from reaching the clinic.
“The immune system is really good at identifying things that don’t belong there, and it has a number of different mechanisms for trying to eliminate them.”
Omid Veiseh
When it comes to neural interfaces, FBR becomes a serious obstacle because, as Barone explains, once the scar tissue begins “building up between the brain and the electrodes”, the signal doesn’t pass anymore, and eventually it stops altogether. “That’s one of the main reasons why many advanced brain-computer interfaces have not translated into humans,” he adds. Barone’s study takes a pharmaceutical approach to FBR, examining the effects of dexamethasone – the immunosuppressant anti-inflammatory drug often used to treat cancer patients – on inflammation.
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