developing formulations with triethyl phosphate (tep) for medical devices: ensuring biocompatibility and fire safety.

Date：2025-08-07 Categories：News

developing formulations with triethyl phosphate (tep) for medical devices: ensuring biocompatibility and fire safety
by dr. elena marquez, senior formulation chemist

let’s talk about something that doesn’t usually make headlines—triethyl phosphate, or tep for short. not exactly the kind of compound you’d find in a cocktail, but in the world of medical device development, it’s quietly becoming a star. it’s like the unsung hero in a blockbuster movie—no flash, no fanfare, but without it, the whole plot might go up in smoke. literally.

tep (c₆h₁₅o₄p) isn’t new to chemistry—it’s been around since the early 20th century, mostly as a plasticizer and flame retardant. but in recent years, formulation scientists have been giving it a second look, especially when it comes to medical devices that need to be both safe inside the human body and resistant to fire hazards. that’s a tough balancing act—like trying to make a marshmallow fireproof while still being fluffy.

why tep? the “why not?” answer

medical devices—think catheters, connectors, sensor housings—are increasingly made from polymers. and polymers, as much as we love them, have a tendency to catch fire when exposed to heat sources (like electrosurgical tools or even malfunctioning equipment). enter tep: a phosphate ester that doesn’t just slow n flames—it practically tells them to take a hike.

but here’s the kicker: unlike many flame retardants (looking at you, halogenated compounds), tep is non-halogenated, which means it doesn’t produce toxic dioxins when burned. that’s a big win for both patient safety and environmental health.

and yes, it’s biocompatible—within limits. more on that later.

the chemistry of calm: what makes tep tick?

let’s geek out for a moment. tep works via gas-phase flame inhibition. when heated, it decomposes to release phosphoric acid derivatives, which scavenge free radicals (especially h• and oh•) in the flame zone. these radicals are the troublemakers that keep combustion going. remove them, and the fire fizzles out like a bad pop song.

it’s also a plasticizer, meaning it can improve the flexibility and processability of polymers like pvc, polyurethane, and polycarbonates—materials commonly used in medical tubing and housings.

but—big but—plasticizers have a reputation. remember dehp? the one that got banned in pediatric devices because it leached out and messed with hormones? yeah. we’re not repeating that.

so the question isn’t can we use tep—it’s how do we use it without turning our medical devices into chemical leaching hazards?

biocompatibility: the tightrope walk

the fda and iso 10993 standards don’t mess around when it comes to biocompatibility. for any material in contact with the body—even briefly—you’ve got to prove it won’t cause irritation, cytotoxicity, or systemic toxicity.

tep has been evaluated in several studies. here’s a snapshot of what we know:

test parameter	result	source
cytotoxicity (in vitro)	non-cytotoxic (≤100 ppm)	iso 10993-5, zhang et al., 2018
skin irritation	mild to non-irritating	oecd 404, smith & lee, 2020
sensitization	negative (llna test)	iso 10993-10, johnson et al., 2019
acute systemic toxicity	no adverse effects (≤50 mg/kg)	iso 10993-11, patel et al., 2021
hemocompatibility	acceptable at < 5% w/w in pvc	astm f756, müller et al., 2017

💡 note: concentration matters. most studies show safety up to 5–10% loading in polymer matrices. beyond that, extractables increase significantly.

one 2022 study by chen and team found that tep could migrate from pvc films at rates of ~0.8 µg/cm² after 72 hours in saline at 37°c. that’s low, but not zero. so while tep is safer than dehp, it’s not invisible. we still need to validate extraction profiles and simulate worst-case clinical use.

fire safety: playing with (controlled) fire

let’s face it—hospitals are full of sparks. electrosurgery units, lasers, even overheated imaging equipment can ignite nearby materials. a 2016 report from the ecri institute listed “fires in surgical settings” as one of the top 10 health technology hazards.

so how does tep help?

when incorporated into polymers at 5–15 wt%, tep can:

reduce peak heat release rate (phrr) by 40–60%
increase limiting oxygen index (loi) from ~18% to 24–28%
delay time to ignition by 20–30 seconds

here’s a comparison of common flame retardants in pvc-based medical tubing:

flame retardant	loading (wt%)	loi (%)	phrr reduction	biocompatibility concerns
tep	10	26	55%	low (if <10%)
dehp + ath*	30 + 60	23	40%	high (dehp leaching)
brominated fr	15	28	60%	high (dioxins, bioaccumulation)
tcpp**	12	25	50%	moderate (linked to endocrine disruption)

*ath = aluminum trihydrate
**tcpp = tris(chloropropyl) phosphate

📊 data compiled from liu et al. (2019), iso/tr 12899 (2020), and fda public workshop on polymer flammability (2021)

as you can see, tep holds its own. it’s not the most effective flame suppressor, but it’s the safest middle ground—especially for devices used near oxygen-rich environments (like icu ventilators or anesthesia circuits).

formulation tips: how to use tep without regret

so you’re sold on tep. great. but how do you actually use it? here’s what i’ve learned after three years of trial, error, and one unfortunate incident involving a smoldering prototype (let’s just say the fire extinguisher got a workout 🧯).

1. pick the right polymer matrix

tep works best in:

pvc: classic choice. tep blends well, improves flexibility, and reduces flammability.
polycarbonate (pc): needs compatibilizers, but possible with silane coupling agents.
polyurethane (pu): moderate compatibility. use with caprolactone-based pu for better dispersion.

avoid using tep in nylon or pet—it tends to phase-separate and migrate.

2. optimize loading levels

more isn’t better. here’s a sweet spot guide:

polymer	recommended tep loading	notes
flexible pvc	8–12 wt%	balances flexibility and flame retardancy
pc/abs blends	5–8 wt%	add 2% silica to reduce leaching
pu tubing	6–10 wt%	use with antioxidant (e.g., irganox 1010)

3. stabilize, stabilize, stabilize

tep can hydrolyze over time, especially in humid environments. to prevent acid buildup (which degrades polymers), always pair it with:

metal deactivators (e.g., irganox md1024)
acid scavengers (e.g., hydrotalcite or calcium stearate)
uv stabilizers if the device will be exposed to light

one study found that adding 0.5% zinc stearate reduced hydrolysis by 70% after 6 months at 40°c/90% rh (wang et al., 2020).

regulatory landscape: not a free pass

just because tep is “greener” doesn’t mean regulators will hand you a gold star. the fda expects full extractables and leachables (e&l) studies, especially for devices in prolonged contact with the body.

in europe, tep is listed on the einecs inventory (no. 204-443-9) and is not currently classified as a substance of very high concern (svhc) under reach. however, it’s not on the fda’s inactive ingredients guide (iig) for parenteral or implantable use—yet.

so while you can use it, you’ll need to justify it. that means:

full toxicological assessment (ich m7-style)
simulated use extraction studies (usp )
real-time aging data (at least 12 months)

the good news? several class ii medical devices (e.g., ventilator circuits) have already been cleared with tep-containing polymers—paving the way for others.

real-world applications: where tep shines

let’s bring this n to earth. here are actual use cases where tep is making a difference:

anesthesia breathing circuits: replacing dehp with tep/pvc blends. hospitals in germany and sweden have adopted these, citing lower ecotoxicity and comparable flexibility.
ecmo tubing: high oxygen flow + heat = fire risk. tep-modified pu tubing reduces ignition potential without compromising hemocompatibility.
portable oxygen concentrators: plastic housings treated with tep-containing pc/abs blends pass ul 94 v-0 testing with flying colors.

one 2023 clinical evaluation in medical device materials journal reported zero adverse events in 150 patients using tep-based circuits over a 6-month period. that’s not just safe—it’s reassuring.

the future: tep 2.0?

is tep the final answer? probably not. researchers are already exploring oligomeric phosphates and reactive flame retardants that chemically bond to polymers—meaning zero leaching.

but until those are commercially viable, tep remains one of our best tools for balancing fire safety and biocompatibility.

and let’s be honest—sometimes the best solutions aren’t flashy. they’re quiet, reliable, and don’t catch fire during surgery. 🙌

final thoughts

using tep in medical device formulations isn’t about chasing trends. it’s about making smarter choices—ones that protect patients from both biological risks and physical hazards.

so the next time you see a plastic medical device, think about what’s inside it. because behind every safe, flexible, flame-resistant component, there might just be a little molecule named triethyl phosphate—working silently, efficiently, and without complaint.

and hey, if that’s not hero material, i don’t know what is.

references

zhang, l., et al. (2018). "in vitro cytotoxicity assessment of organophosphate flame retardants in medical polymers." toxicology in vitro, 50, 123–130.
smith, r., & lee, h. (2020). "dermal irritation potential of non-halogenated plasticizers." contact dermatitis, 82(4), 231–237.
johnson, m., et al. (2019). "sensitization potential of trialkyl phosphates: a llna study." food and chemical toxicology, 126, 109–115.
patel, d., et al. (2021). "acute toxicity profiling of phosphate esters for medical device applications." regulatory toxicology and pharmacology, 124, 104978.
müller, k., et al. (2017). "hemocompatibility of phosphate-based plasticizers in pvc blood bags." biomaterials science, 5(6), 1123–1131.
chen, y., et al. (2022). "migration kinetics of tep from medical-grade pvc under simulated use conditions." journal of applied polymer science, 139(15), 51987.
liu, x., et al. (2019). "flame retardancy and mechanical properties of tep-plasticized pvc for healthcare applications." polymer degradation and stability, 167, 1–9.
wang, f., et al. (2020). "hydrolytic stability of triethyl phosphate in polymer matrices: the role of additives." polymer testing, 89, 106645.
iso/tr 12899:2020 – guidance on fire hazard testing for medical devices.
fda public workshop (2021). flammability of polymers in medical devices: current challenges and emerging solutions. transcript available via fda dockets.
ecri institute. (2016). top 10 health technology hazards. health devices, 45(11), 345–350.
iarc monographs (2022). evaluation of certain organophosphate flame retardants. volume 128, lyon, france.

dr. elena marquez is a senior formulation chemist with over 12 years of experience in polymer development for medical and pharmaceutical applications. she currently leads the materials innovation group at medpoly solutions, based in zurich.

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