All around us, slipped into backpacks, handbags, and pockets, are millions of small but powerful devices ready to dispense life-saving medicine in an instant. Two million Americans use epinephrine autoinjectors, better known by the brand name EpiPen, that let people with serious allergies quickly inject epinephrine into their leg muscles. Twenty million Americans carry prescriptions for albuterol, an asthma medication that’s administered with an inhaler.
Inhalers and epinephrine injectors are marvels of engineering and mass manufacturing. During moments of extreme physical difficulty, as throats close and lungs seize up, they make it straightforward for patients to accurately dispense critical medication in seconds.
Inside these devices are complex mechanical systems that stand ready to activate quickly and intuitively. We put them in our Neptune CT scanner to see how they work. Let’s look inside.
Want to go deeper on these devices? Join Scott Johnston for an interactive walkthrough using high-resolution CT scans on Wednesday, August 3, 2022 at 1pm Eastern Time/10am Pacific Time. Register here.
Inhalers have existed since the 1770s, addressing everything from simple coughs to asthma. Until the late 20th century, they were cumbersome and difficult to use correctly–critical drawbacks that prevent patients from getting the medication they need.
The dry powder inhaler was introduced in the 1980s and represents a significant advance in usability over familiar aerosol inhalers; today it’s the leading asthma drug delivery device. Let’s use our CT scanner to see how it works.
A storage hopper in the inhaler’s handle contains albuterol sulfate along with alpha-lactose monohydrate, a carrier. Shaking the device mixes the two components and enhances delivery. The inhaler’s mouthpiece is protected by a hinged cover connected to a complex cam. Opening the cover kicks off a mechanical sequence that automatically prepares a dose of medication for inhalation.
The act of opening the mouthpiece cover rotates the cam, releasing a preloaded spring that operates a set of bellows near the top of the inhaler. The bellows force a metered dose of medicated powder into a dispensing chamber, which the user inhales through the mouthpiece. As the user inhales, fresh air flows in through the louver above the mouthpiece, picks up medication in the dispensing chamber, and flows into the mouthpiece through a one-way valve.
While older aerosol inhalers require a carefully-timed sequence of dispensing and inhaling, this powder inhaler separates the two steps; after opening the mouthpiece, the user simply needs to inhale the pre-metered dose of medication at their convenience.
After inhaling, the user closes the mouthpiece cover, loading the bellows spring to prepare the device for its next use. Along the way, another cam arm connected to the mouthpiece cover hits a ratchet gear that advances a printed tape from one spool to another, changing the count of remaining doses visible through a small window in the back of the inhaler.
The EpiPen is arguably the most infamous drug-delivery device—but not because of its engineering. EpiPen’s manufacturer, Mylan, raised its price by 500% in the decade leading up to 2016. That year saw generic epinephrine autoinjectors reach the market, lowering prices and introducing innovative new features. Let’s start with the brand-name EpiPen and then see how it compares to a more recently-designed competitor.
The EpiPen is assembled with a plastic snap-fit housing that compresses a large spring down to 35mm. When released, the spring expands four-fold, sending the entire inner mechanism downward and pushing a needle into the user’s body before dispensing epinephrine.
A syringe in the middle of the EpiPen is filled with epinephrine; one end is connected to a 15.2 mm long needle, and the other is closed by a plunger. When the needle assembly is fully extended from the device, it reaches a hard stop. The spring continues to push downward, now driving the plunger through the syringe and pushing the drug through the needle.
What does this extra spring do? It’s connected to an orange plastic cover that’s clipped to the EpiPen’s housing in three different places. During injection the clips are released. After injection, as the device is withdrawn from the user’s muscle, this spring extends the orange cover over the exposed needle to reduce the risk of unintended piercing.
Using an EpiPen requires significant force—the user must maintain a fluid swing-and-push motion—which is intimidating for many people and difficult to manage during an allergic crisis. Kaleo designed Auvi-Q to be easier to use than a traditional EpiPen: rather than jamming it into a leg muscle from several inches away to activate the needle, the user simply presses and holds an Auvi-Q against the leg. The device automatically drives and retracts its needle, with drug delivery happening in less than two seconds—one second faster than the EpiPen. Let’s see how it works.
When the user presses the end of the Auvi-Q against their leg, two snapfits release a preloaded spring that drives a needle through the seal on a gas canister. As the gas escapes, it pressurizes the middle chamber, activating the main delivery needle.
The drug canister is driven onto the needle, and the entire mechanism is driven toward the user’s leg. When the needle assembly is fully extended, a plunger forces the drug through the needle. This action preloads another spring, which overcomes the pressure of the gas to retract the needle back into the enclosure after use. The entire injection and retraction process takes less than two seconds.
Auvi-Q has an additional feature that’s separate from the injection mechanism: an electric voice prompt system guides users through the administration process. The top speaker has a high cone reflex to project the instructions loudly. A memory card connected to the speaker stores the audio cues.