• Corpus ID: 72946394

Redesigning and Incorporating the EpiPen into a Smartphone Case.

@inproceedings{Ghoreshi2013RedesigningAI,
  title={Redesigning and Incorporating the EpiPen into a Smartphone Case.},
  author={Kayvon Ghoreshi},
  year={2013}
}

• K. Ghoreshi
• Published 2013
• Education

In the event of anaphylaxis, people need an immediate injection of epinephrine. The EpiPen has provided such injections, but its size can make it somewhat unwieldy for people to carry around. This leads to many people simply not having it with them. The aim of this project is to design an epinephrine auto-injector that is more portable by integrating it into a smartphone case. While the EpiPen uses a spring mechanism, other options such as gas were explored. After testing, it was clear that a gas cartridge could supply sufficient power for injection. In the proposed design, using a gas cartridge helped minimize the size of the device and enabled the needle to be retracted after injection. The design is not only smaller than the current EpiPen, but is also able to be carried with an iPhone case. 1. Background People with allergies face the potentially deadly threat of anaphylaxis, a severe allergic reaction that can occur within seconds of being exposed to an allergen, which commonly includes things like peanuts or the venom of a bee sting. The flood of chemicals from the immune system in response to the allergen can lead to shock as well as a drop in blood pressure and a narrowing of airways which hinders breathing (Mayo Clinic, 2013). Victims require immediate attention at an emergency room as well as an injection of epinephrine. This need for a shot of epinephrine led to the creation of epinephrine auto-injectors, the most prominent of which is the EpiPen. The device delivers two different dosages: 0.15mg of epinephrine for children and 0.30mg for adults. While the EpiPen has enjoyed over 95% market share among epinephrine auto-injectors (Goldenberg, 2013), it still has shortcomings that can be improved upon. One common complaint about the EpiPen is its size. When encased, the device measures out to about 6 inches in length, which can make it uncomfortable to carry. In turn, some people simply choose to not have an EpiPen on their person even though it is recommended that the EpiPen should be available at all times. According to a survey from Sanofi (PR Newswire, 2013), nearly two-thirds of patients and caregivers do not carry their EpiPens as recommended. In addition to the EpiPen being left behind, due to ergonomic factors, general forgetfulness, or other reasons, there is also an issue of usability. In another survey done by Sanofi, nearly half worry that others will not know how to use their, or their child's, epinephrine auto-injector correctly during an emergency. While most medical professionals and EpiPen carriers know how to use the device, there are plenty of people who are unfamiliar with the device and even use it incorrectly. A study by Nguyen (2012) showed ineptitude of school staff in using EpiPens. Among personnel in elementary schools, the majority of which were teachers and lunch aids, only 23.7% were able to use the EpiPen properly, which is incredibly poor given that 89.2% of participants reported prior training in using an EpiPen. These results are particularly worrying because in the case with elementary school children, many may not be able to use an EpiPen themselves and thus rely on teachers and staff to be able to perform the injection. While this does show the need for a more intuitive epinephrine auto-injector, it also points to other necessary factors for an effective device, such as proper training. 1.1 Understanding Injection Mechanisms In order to design a new epinephrine auto-injector, it was necessary to understand how the devices currently on the market worked and what areas could be improved upon. The two chosen devices were the EpiPen and the most recent device, the Auvi-Q. Multiple EpiPens were taken apart in order to understand the mechanics of the device in addition to information provided by the patent. An Auvi-Q could not be acquired, so only the patent was available for understanding the mechanism. The EpiPen works with a spring loaded mechanism. A compressed spring is coiled around the plunger and held in place by the slightly wider top of the plunger. The top of the plunger has a hollowed opening that houses the blue safety cap. When activating the device, the blue safety cap is removed. The needle end of the EpiPen is then pushed against the person’s outer thigh, which pushes the contents of the device upward. This pushes the plunger upward into a narrower hole, causing the top to squeeze in. By squeezing the top of the plunger, the spring is released and allowed to expand. This pushes the plunger downwards, forcing the needle through its cover and into the person’s leg and pushing the fluid out of the vial. As the vial is pushed down, it releases two locking teeth represented as number 340 in Figure 2. This releases a spring in the needle end of the device, expanding the orange sheath, seen in Figure 1, to cover the needle. Figure 1: EpiPen Taken Apart Figure 2: EpiPen Patent Drawing (Young, 2008) The Auvi-Q is the latest epinephrine auto-injector and competitor to the EpiPen. Unlike the cylindrical design of the current EpiPen, it is shaped more like a smartphone. The Auvi-Q is also smaller than the current EpiPen, coming in at 3.5 inches tall, 2 inches wide and a half inch thick. In addition to shape, another major difference from the EpiPen is that the injection from an Auvi-Q is powered by gas rather than a spring. The device is still activated by the release of a spring, but this spring (part 3560 in Figure 3) pushes an azide gas container (part 3412) into a puncturing mechanism (part 3612). The gas is released and this force pushes down the plunger and the needle, injecting the epinephrine fluid. After the injection, the gas is released from the device and the springs on either side of the needle expand, retracting the needle. Figure 3: Auvi-Q Patent Drawing (Edwards, 2011) 1.2 Parts of the EpiPen The EpiPen has two springs: the spring around the plunger and the spring that pushes out the needle sheath. The springs measure 4.625 and 3 inches in length, respectively. Both springs were hung from a ladder and then had different weights attached to them. The spring extensions were recorded to calculate each spring’s spring constant using Hooke’s law. The larger spring (part number 530 in Figure 2) was measured with standard 2.5, 5, 7.5, and 10 pound weights, respectively. The smaller spring (part number 153 in Figure 2), on the other hand, was too weak to handle the larger weights and thus required other objects around the lab that were first weighed in grams and then converted to pounds. These weights came out to .19287, .33069, .64375, and 1.12877 pounds, respectively. A linear regression was used for both sets of data in order to find the spring constants. The larger spring that provided the power for the injection had a calculated spring constant of 8.6466 lbs/in, which falls into the ballpark of a similar Duke study (Addison, 2006) that concluded that the spring constant for the bigger spring was between 8 and 10 lbs/in. The spring constant for the smaller sheath spring came out to 0.6266 lbs/in, although no other study was found to confirm it. Figure 4: Spring Constants and Linear Regressions of EpiPen Springs Some of the other major parts of the EpiPen that will likely need to be included in a new device include the vial, the needle, and the plunger. The vial, made of borosilicate glass, is approximately 4.5cm in length with an inside diameter of 9mm and a wall thickness of about 1mm. It has a cross sectional area of about .636cm2 and a volume of around 3mL. The needle y = 8.6466x + 0.2444 y = 0.6266x 0.0577 0 2 4 6 8 10 12 0.0000 0.5000 1.0000 1.5000 2.0000 W e ig h t (l b s) Spring Extension (in) Large Spring