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Most scientists don’t think about this, but if you’re culturing cells with FBS, you’re also including a wildly batch-variable, undefined mix of protease inhibitors with downstream consequences for cell biology. The presence of protease inhibitors in FBS is critical for passaging cells with trypsin; these proteins are responsible for deactivating trypsin (assuming you’re using FBS-containing media to quench the reaction, rather than a separate trypsin inhibitor). Unfortunately protease inhibitors are more problematic during the culture process than most people realize - but odds are you’ve never even thought about the impact they’re having on your cells. Protease inhibitors regulate processes like ECM turnover/remodeling, cell-matrix signaling, or migration, invasion, and differentiation. So adding an undefined mix of protease inhibitors to your cultures, courtesy of FBS, inevitably has an impact. This is particularly relevant for studies linked to fibrosis, cancer invasion, differentiation, or organoid/3D culture systems. Here’s where it gets even more interesting: many scientists assume growth factor variation drives most of FBS batch variation, and this does play a role. However, protease inhibitor variation is very much present, largely unappreciated, and has major implications for our research studies. These variable protease inhibitors control how much cells can cut up and remodel their surrounding matrix. If one serum batch inhibits proteases more than another, cells will migrate differently, invade differently, remodel ECM differently, and respond differently to exactly the same experimental signals. So when it comes to publishing research results using different batches of FBS, ECM-related results can vary substantially. That’s a big reason experiments involving migration, invasion, fibrosis, or 3D cultures can be so hard to reproduce. And this is also why many scientists whose experimental readouts depend on ECM dynamics can and should consider working with chemically defined systems.
As always, literature below if you're keen to dive deeper! For more reading: Page-McCaw et al. - for a review on how protease activity controls ECM remodeling, signaling, and cell behavior. https://www.nature.com/articles/nrm2125 Bonnans et al. - shows how protease regulation impacts cancer and fibrosis. https://www.nature.com/articles/nrm3904 Gjorevski et al. - A deeper dive into how chemically defined, tunable systems are important for reproducibility in the context of ECM composition and remodeling studies. https://www.nature.com/articles/nature20168 Not FBS specific, but one of the older papers on protease inhibitors in serum. Love a good study from the 1950s: https://pubmed.ncbi.nlm.nih.gov/14946322/
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If you scroll through the formulations for most foundational basal media (DMEM, RPMI, MEM, etc), here’s what you won’t find: Lipids.
These basal media were created over 50 years ago, before lipid metabolism and membrane biology were well understood. As such, you won’t find key fatty acids, cholesterol, and the delivery systems required to supply them to cells for efficient uptake. This is just one of the many, many reasons that scientists include fetal bovine serum in their cell culture media; it delivers lipid complexity. However, you'll notice a surprising number of serum-free media recipes don’t include many - sometimes any - lipids. This may appear okay for short-term cell growth, or even growth of particularly robust cell lines. But it does have an underappreciated impact. Without lipids, cells often end up with altered membrane composition, shifted eicosanoid pathways, ER stress, and/or rewired inflammatory signaling. Phenotypes like morphology, proliferation rate, and oxidative stress sensitivity often reflect this underlying lipid deficit. This is something we thought a lot about when developing our chemically defined FBS replacement. And it’s something for you to think about if you’re trying to eliminate serum from your cell culture; are you incorporating the right lipids for your cells, and do you have the right strategy to ensure their bioavailability? As always, journal articles below if you want to dive deeper 😊 https://pmc.ncbi.nlm.nih.gov/articles/PMC5661806/ Following a recent article for Beyond Animal Research in New Zealand about the use and limitations of foetal bovine serum (FBS) and Media City's alternative 'FRS Pioneer', I was asked to put together a similar article for Animal-Free Science Advocacy in Australia. Here is a link to the article: Foetal Bovine Serum finally has a superior replacement alternative  Let me tell you what’s driving your FBS batch-to-batch variation; it’s similar to how bear serum varies between summer and winter months (yep, see the comments for that absolute gem of a study).
At first glance, “batch variation” sounds like a QC problem but most biologists will know FBS variability comes down to its animal-derived nature. FBS is essentially a biological snapshot of fetal physiology at a specific point in gestation. The fetal blood is pooled, essentially in an attempt to somewhat standardize the FBS. What scientists might not know, is pooling can help mitigate shifts due to: 🐮 Fetal age: As fetuses mature, albumin levels increase, immunoglobulins rise, and lipid profiles shift. Pooling smooths this out to an extent. 🐮 Stress at harvest: Cortisol and catecholamine spikes in mama cow alter glucose, lactate, and metabolic profiles. Pooling dilutes these acute stress-related changes. Pooling does not (particularly) help mitigate changes due to 🐮 Maternal diet: Micronutrients, fatty acids, and trace minerals pass directly from mama to fetus. 🐮 Seasonality: Pasture quality, climate, and feed composition change micronutrients, hormones, and fatty acids in serum. FBS collected in winter is measurably different from summer (like bears!). 🐮 Geography: Soil composition, water mineral content, and regional feed practices influence trace elements, metal-binding proteins, and vitamin levels found in serum. And this is why you’ll see differences in cells cultured using FBS from South America versus the US versus Europe versus New Zealand. _______ We spent years developing an animal-free replacement for FBS that doesn’t have batch-to-batch variation. To do that, we had to benchmark against FBS - multiple batches of FBS. It’s tough to establish a baseline of “this is what good looks like” when your standard is intrinsically variable. For balance, we worked with ~6 FBS batches. As an extreme example, one batch straight up did not grow our AD-MSCs. This is why scientists batch-test and stockpile FBS to ensure consistency across a series of experiments. Once a given batch of FBS is gone, it’s impossible to precisely replicate the mix of proteins, lipids, metabolites and trace elements. This is also why — where feasible, because it certainly isn’t always feasible (yet) — growing cells in chemically defined media is a good move for scientific reproducibility. Interesting science below if you want to dive deeper, including that study in which mouse cells were cultured with bear serum from summer versus winter, aka hibernation season. https://pubmed.ncbi.nlm.nih.gov/34336951/ - Winter/Summer bear serum, and how it maybe can be used to identify helpful therapeutic agents https://pubmed.ncbi.nlm.nih.gov/39617443/ - Selenium variation in FBS from different geographies....and the result on cells. https://pubmed.ncbi.nlm.nih.gov/29196597/ - Impact of different batches of FBS on cells https://pubmed.ncbi.nlm.nih.gov/1153408/ - An older paper, in which different FBS batches were quantitatively profiled Scientists, I’ll level with you: when I started sharing publicly about building a biotech company without raising VC, it was easy to imagine what a post describing the wrap up of company operations would look like. It was much harder to imagine commercial launch…and yet here we are. Happy launch day. 🥂
One morning a few months ago, something pretty cool happened: Media City Scientific made our first sale. In the afternoon, something even cooler happened: we made our second sale. Today we publicly launch FRS Pioneer - a chemically defined, animal-free replacement for fetal bovine serum (FBS) that’s drop-in and easy to use. How did we get here? ➡️Obsession: indulge me because the word is bandied about, but the formula was a labor of love. I clocked eight days away from a biosafety cabinet in 2025. Four of them were after I gave birth. ➡️Support from Australian scientists: When not in our lab, I was in external labs. We dedicated an entire year to piloting FRS, swapping it directly for FBS across a range of every-day activities in different lab setups. Varied processes for passaging, dilution in different basal media, mixing freeze media, running standard assays, growing cell lines, other cell types, and more. To break a 50+ year old FBS habit, FRS needed to be genuinely user-friendly, and our earliest pilot testers are the real MVPs for helping us get there. __________ FRS Pioneer is not a perfect replacement for fetal bovine serum for every use case, but I’ve been around the entire block when it comes to serum-replacement. I haven’t found anything that comes close to matching its ease of use or broad functionality. Our earliest users have started re-ordering and have encouraged me to launch, so here we are. Our website has data. We’re open for orders. With every order, you’ll get personalized, hands-on support from Katie. We make going serum-free or serum-reduced easy - whether that involves FRS Pioneer, your own in-house media development efforts, or something else. We are an Australian company that will start small but scale globally. We’re scientists too, so talk to us if you want our honest opinion on how FRS Pioneer will perform in your system. ________________________ There are many people reading this who have pushed us along in small and large ways. Thank you. A few years ago, we were quite literally dry walling an R&D lab. Last week, we were putting the final touches on our ISO documentation, negotiating supply chain agreements, and talking to cGMP facilities. There’s a big lift to go, and there will certainly be challenging days ahead, but I’ve become quietly convinced it’s all possible. Cleaning up packaging and empty boxes isn't the most glamorous task. Here's how we've approached it to make it a little more fun and eco-friendly!  It's been a truly massive 2025; if I’ve learned anything from piloting our chemically defined FBS replacement in 15+ Australian laboratories, it’s that even the most basic of cell culture activities varies between labs. Temperature, passaging reagents, thawing processes, cell culture plates; every single one of these variables impacts how cells transition to serum-free media. Unfortunately, these are exactly the kind of insights that don’t make the most exciting scientific papers. Useful insights are hidden in failed experiments that never get shared. Media City Scientific is now preparing for launch of our first product. We’ve thought a lot about how important it is to ensure the transition from FBS to our serum replacement product is super, super smooth. That’s why I’m committing to things that don’t scale; to support early adopters, I’ll offer 1:1 time with every single customer. But as we scale - even globally - we want to see that kind of tailored support scale too. That’s why we’re exploring a collaboration with Carmen Kivisild, PhD and her team at Elnora AI. Their platform is designed to capture negative data and turn it into shared knowledge, so labs can avoid repeating the same dead ends. Together, we’re asking: could the combination of deep scientific expertise and a trained GPT agent effectively support labs to transition away from serum use? We’re hoping to identify a pilot lab anywhere in the world to test this with us - you’ll get all of Media City’s scientific insights, wrapped up alongside a GPT to test whether this is an efficient way of making the transition. If your lab is considering a move away from FBS, or if you have stories about a transition-gone-poorly, let us know! Taking notes over here to make sure adoption can be super smooth ✏️  Lately I’ve been thinking about how to make cell culture more human-relevant: What if all our drug discovery pipelines used physiological glucose levels instead of the 25 mM you find in standard DMEM?
I suspect it would slow things down in the short-term; slower proliferation and poor adaptation of some lines would mean longer experimental timelines. But I imagine the long-term upside would be pretty massive, because right now, we’re actually doing the opposite. Standard DMEM has 25 mM glucose, while human blood sits around 5 mM. That’s a five-fold difference, and enough to push cells into metabolic states they’d never see in vivo. At these supraphysiological levels, cells often lean heavily on glycolysis even when oxygen is plentiful. That can mimic a “Warburg-like” phenotype, but one that may say more about the media than the cancer. The consequences are easy to imagine: - Drug sensitivity profiles that don’t translate to patients - Biomarkers that are actually cell culture artifacts - Potential therapeutic targets discovered under hyperglycemic stress that turn out to be irrelevant in vivo The result is years of expensive R&D on a series of targets that doesn’t efficiently lead to new therapeutics. And here’s the kicker: cells long adapted to 25 mM glucose often struggle when you dial back to physiological 5 mM. That struggle itself tells us something important. We’ve been optimizing our models for convenience and fast proliferation, at the expense of human relevance. Of course, it’s not as simple as “5 mM glucose = human-relevant biology.” Tumors often experience lower glucose than blood, and glucose is just one piece of the puzzle. Still, I can’t help but wonder if we had standardized around human-like conditions decades ago, how many “failed” drugs might have never made it past the cell culture dish and how many more real opportunities might have been identified sooner? Maybe the future includes testing across a panel of media which includes physiological plasma-like media as well as tumor-mimicking low-nutrient media. It would be slower and messier…but possibly much more efficient for patching up our leaking drug development pipelines, which would ultimately make it more cost-effective. Anyway, I realise it’s a possible future rather than an easily solved problem today, but I’m curious to hear any thoughts, especially from folks involved with these sorts of large scale drug discovery screens. Fun fact: The cell culture media you’re probably using was invented before the moon landing.
BME, 1957 DMEM, 1959 RPMI, 1966 Here we are, still using them as the defaults for human cell culture, despite the fact that we have learned so much more about the human body in the past 60-70 years. Enter Plasmax, 2019. Frankly, I’m shocked that it’s not more widely used because it’s a delightfully simple concept; profile human plasma, then recreate it in basal media form. If you want cells to behave like they do in the body, give them something that actually resembles the body. Plasmax is a great reminder that so many of the standard “best practices” we’ve inherited in science were built with the tools and knowledge of their time. As our knowledge and capabilities improve, so should our tools. Don't get me wrong, the original basal media still very much have their place, but let's select our tools deliberately rather than relying on defaults. My two cents? If you’re a scientist studying metabolism, cancer biology, or drug discovery, this is one of those innovations worth paying attention to. All the details can be found in Vande Voorde J, et al. Sci Adv. 2019 https://pmc.ncbi.nlm.nih.gov/articles/PMC6314821/ How much fetal cow goes into 1 x bottle of FBS? It depends on the age of the fetal cow in question, but 150mL-500mL; that’s how much FBS you can harvest from 1 x fetal cow. Really puts into perspective all those bottles of FBS that arrive neatly frozen by the pallet into some companies. There are lots of reasons I’d like to see cell culture’s reliance on FBS disappear; improved reproducibility for experiments and smooth regulatory approval for cell therapies are often called out by my collaborators who want to go chemically defined. But there’s also an emotional ick factor once you start being unable to stop yourself from calculating the number of fetal cows that went into your FBS order. If you’re a Sydney-based scientist, this cow thinks you should know: the third and final stage of external testing for FBS Replacement Solution by Media City Scientific is kicking off September 1st. I provide the animal-free and chemically defined product, you provide the cells. You’ll get one to one support in going chemically defined - even if your process doesn’t ultimately involve FRS - and we’ll be able to launch a product that has been heavily street-tested, so we can be super transparent with scientists about how it works across a broad range of cells. No use case too basic or too unusual, we’ve seen everything from cell culture courses & CHO cells to organoid-based therapies destined for scaled, cGMP manufacturing. Just send me a message ☺️  |
What's been happening?Sharing the Media City journey has been important to us because we want to encourage the next generation of scientists to establish companies that will advance scientific research. Check back regularly for the "building in public" updates on what it looks like to establish a scientific company. Archives
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