Researchers at the US Army Aviation Medical Research Laboratory have used 3D printing to produce and test customizable earplugs for members of the US Armed Forces. New technologies from Army scientists can be used to protect ears to prevent hearing damage to members of the armed forces. Damage to soldiers’ hearing will not only limit their ability to participate in social interactions, but will also make them more vulnerable and lose their readiness on the battlefield.

Additively manufactured earplugs

Currently, soldiers must wear some kind of hearing protection device (HPD), and those who are often exposed to hazardous noise must join the Army Hearing Program (AHP). The plan aims to prevent hearing loss through a series of clinical hearing services, but soldiers are by no means the only vulnerable group. In the United States, an estimated 2 million is spent on workers claiming compensation for hearing loss each year.

Making ear molds to deal with hearing loss is also a risky job. For example, sometimes the impression material will go over the "earplug" and cause injury, which may result in surgical intervention or even hearing loss. Army researchers are trying to mitigate such risks by using a combination of scanning methods and 3D printing. Combining these technologies can produce customized earplugs and allow researchers to evaluate the benefits and performance of each method.

The traditional manufacturing process requires the creation of a physical ear mold impression, which is then shipped to the earplug manufacturer. Then, cast the "ear print" into a negative ear mold, or scan through an ear pressure scanner to generate a digital model. Both methods are currently used, so in order to compare and optimize different technologies, the researchers created six different earplug samples. Three different digital ear scanning methods, including physical ear prints and digital scanning, and internal 3D printing methods are used.

3D modeling and printing earplugs

U.S. Army researchers first used light capture methods to create 3D models of the ears and ear canals of 20 volunteers. These models were then modified using computer-aided design (CAD) software to create custom-fitting earpieces made using each of the three manufacturing methods. Scanning was performed using a series of scanners in order to evaluate the most efficient scanners provided by eFit, 3Shape and Lantos. Therefore, five subjects will use impression-shaped earplugs, five from eFit scans, five from 3Shape, and five from Lantos.

Use Cyfex Secret Ear Designer software to model the digital scan internally, and use Envisiontec Perfactory Micro 3D printer and E-Silicone M material to make the earplug shell. After printing, the case is washed in isopropanol solution and dried under air pressure. It takes about 15 minutes at 60°C to cure the material with the pressure polymerization unit Polymax 1.

Provide the earplugs to the test subjects, let them evaluate the comfort of each design, and the results of each manufacturing method are different. Although physical ear print products provide the best hearing protection, on average, they are also the least comfortable. Importantly, it turns out that earplugs made using digital scanning are far less effective than earplugs made using physical impressions. According to the researchers, this can be attributed to the skills and techniques of the person making the impression, so further research is necessary to perfect the process. ​