Surbhi Hablani, Bruce Mckee, and Caroline Patel
Group Z consists of a multidisciplinary, international team of students currently studying for a Masters in Biomedical Engineering at Trinity College Dublin. Our combined areas of research include stem cell differentiation for bone tissue engineering, novel scaffold design for cardiovascular grafting and neural signal analysis following auditory stimulation. Over the course of this academic year, we considered medical problems we seek to address and designed solutions to solve these problems or improve on existing solutions primarily utilising 3D printing. In addition, we have also identified, demonstrated and documented a treatment which can alter any printed form of PLA to enhance its surface finish and elastic properties.
An otoscope is a medical device used to examine the inner ear and ear drum. They are often used to detect ear infections and ear aches making them a very important diagnostic tool as the inner ear cannot be visualised without it. In addition, they are often used to inspect the nasal cavity using a similar specula and inside the mouth with the specula removed. In essence, an otoscope can act as three tools in one which makes them a versatile and highly sought after piece of equipment. Current otoscopes on the market can cost up to 2,000 Euros, this simple and easy design can print in a little over 7 hours and will cost less than 8 euros.
The physics behind it all....
In order to determine where the lens should be placed within the otoscope, the lens maker equation was applied. Where f = focal length, R1 = radius of curvature of the lens surface closer to light source, R2 = radius of curvature of the lens further from the light source, d = thickness of the lens and n = refractive index. With the known parameters inputted, the calculated focal length was 39 mm. This represents the distance the lens should be placed from the ear canal. Taking this into account along with the length of the ear canal of an adult and infant, two specula were designed. An infant has a shorter ear canal, so the speculum was designed with a length of 16.8 mm. For an adult it is slightly larger, so the speculum was increased to a length of 25 mm.
The otoscope is designed with 5 total parts and 4 detachable points. The removable cap can be removed to allow a torch or set of batteries to be placed within the hollow body for a light source. It attached to the lens holder that houses the lens. It has an inclined grove to allow the lens to slide into place with ease. The eyepiece has three protruding prongs that when assembled will hold the lens in place and prevent further shifting. The ear piece is an interchangeable speculum for an infant and adult. The adult speculum has a slightly longer body and wider aperture, while the infant speculum has a slightly shorter body and more narrow aperture.
Pocket Mask and Valve
The purpose of a pocket mask is to provide oxygen to an individual in the event they suffer from a respiratory or cardiac arrest. A previous year of students produced a mask which was functional, particularly the valve, but it lacked the shape to properly conform to a human face. The new design ensures a tight fit between the device and the patient's face and incorporates a rubber seal for comfort. Medical assessment of the device indicated that the inlet bore should be increased to reduce the amount of ‘dead space’ when rescue breathes are being delivered. This was a simply modification and doesn’t require valve modification, however, it does need to be scaled up by an additional 46% to accommodate the new geometry.
Pocket Mask Alternative Manufacturing Method
The team considered a method for more rapid manufacture, ideally with a flexible material. The proposed solution was to use silicone and pour it into a mold which has the same profile as the solid print. After curing the valve attachment can be glued to the silicone mouth shield using a common adhesive like Loctite®. The benefit of using a method such as this is that the mold is reuseable, freeing up the 3D printer for other needs whilst still producing pocket masks as required.
Protocol for Flexible PLA
A significant obstacle when designing solutions which utilise 3D printing are the mechanical properties of the final print. PLA is relatively brittle following printing due to the bonds between the layers being relatively weak which contrasts starkly with a stock material which is both strong and elastic. As the printers rely on melting the polymer and depositing it in layers upon which it cools and fuses, the layers are similar to that of the fibres in a composite material. They are strong in the fibre orientation and fail quickly when loaded in the ‘matrix’ direction.
Our version of pocket mask allows the user to create a complete seal, preventing any leaks. This will make inhalation of any medication or provision of oxygen more successful. This will also prevent any surrounding party to be affected from any kind of airborne contagious infections that the user might have. Our efforts were geared towards optimising the fitting of the valve for its effective use.
This forces designers to make compromises in their design which can ultimately lead to a less effective product, or even abandon a design entirely. The protocol we have documented allows any PLA print, or portion of a print, to be treated and regain it’s flexibility and strength. When exposed to Tetrahydrofuran (THF) or a solvent with similar chemical properties, it penetrates the pores of the print, melts the material upon removal and rinsing, allows the layers to form a more uniform and isotropic bond.
We experimented using some of the earlier prototypes of the pocket mask and demonstrated that it was simple, cheap, effective and further optimised the final product.
pla lENGTH (M) print time (hours) Total Cost(Euros)
3.76 7.25 7.71 (Including cost of lens)
2.95 4.75 1.19
30.5 31.75 11.66