The shape of pacifier nipples are chosen to ensure comfort and proper orthodontic development for the users. The most common of these nipples are the cherry baglet and orthodontic nipples. The Cherry baglet consists of a ball shaped tip on a trunk that is symmetrical all the way around. The orthodontic nipple has a smaller flattened ball shaped tip on trunk with a distinct bend in it to better fit the mouth. The orthodontic nipple is better designed to promote development, however has only one right way up and thus can be improperly used or rejected by users.
The location of the saliva channel was chosen to maximize the quantity and rate of saliva collection by placing the channels at the largest saliva pools in the mouth. For the orthodontic nipple design, a single channel was placed at the bottom of the nipple to draw saliva from the pool secreted in the bottom of the user’s mouth. This design was not possible for the cheery baglet nipple as it does not have a distinct top and bottom, thus two channels were placed at the sides of the nipple drawing saliva from the cheeks.
Movement of Saliva
Various means of collection were considered to draw saliva from the users mouth to the pacifier internals. A differential pressure could be utilized to draw saliva from the users mouth into the pacifier. This would be accomplished by means similar to a nasal respirator where by squeezing on a pocket of air, a vacuum would be created to then draw in the salvia. Although conceptually simple in design this method would require physical interaction with the pacifier to collect the saliva and poses the risk of saliva being drawn unintentionally if the air sac is not positioned in a secure location.
More favourably, a passive means of drawing saliva would be using capillary action. This method would work by having stronger adhesion of the saliva to the walls of the channel then to itself causing it to be drawn throughout the channel. To ensure the capillary action of the saliva various surface coating agents would need to be tested to achieve the correct surface tension between the saliva and the nipple.
Regardless of the means to create the saliva flow’s driving force, a one-way valve would be required to ensure that no back mixing of the saliva and protein would reach the users mouth. The most common means of these are ball, diaphragm, or swing check valves that operate by having a ball, plug, or flap that seals a channel. Once the inlet fluid reaches the cracking pressure the object is displaced, and fluid can move along the channel until the pressure drops causing the object to re seat itself in the plugged position thus preventing back flow.
A plug type check valve posed difficulty in implementation in the pacifier channel due to the size constraints of the mechanical equipment. A simpler means of preventing backflow could be achieved using a duckbill valve. This valve is manufactured from an elastic material in the shape of the beak of a duck. Fluid can be forced through the funnel section to open and flow through the slit of the valve, but backpressure cannot open the valve from the pointed side of the valve.
Combining elements from each of the aforementioned valves an elastomer flap type valve can be constructed like that of a Gatorade squeeze water bottle. This valve would operate such that a rubber seal consisting of multiple flaps would be forced open by a cracking pressure, and then resealed once pressure was lost. The effective construction of this design however would require carefully chosen construction material to allow for valve flexibility as well as very tight clearances in manufacturing to minimize back mixing risk.
Computer Aided Design and 3D Printing
The first iteration of the pacifier body (pictured above) consisted of 4 parts: A faceplate, a backplate, a Cherry Baglet shaped nipple, and a fastener for connecting the pacifier to the nipple. All computer aided design was performed by Joel Tod. The nipple was printed out of formlabs Flexible Photoreactive Resin on a FormLabs Form 2 3-D printer. All other components were printed out of Polylactic Acid filament on an Ultimaker 2 3-D printer. The total volume of the assembly was 48155.43mm3, and the dimensions are shown above in mm. The results of the first print attempt provided large insights into our future designs. The first issue that we faced was cracking in the nipple, due to the difficulty of the 3D printer to produce a hollow and spherical object. The thin walls at this size were not possible, and any supporting material was unable to be removed. Any external pressure on the hollow nipple resulted in cracking on the nipples sides. Additionally, the tolerances on the printer were not small enough, leading to interference in the fit of the faceplate and backplate. The two surfaces had to be sanded down to allow for the fit. Upon consultation with Healthcare Professionals, and Autism Ontario, we were provided with invaluable feedback on our first design. One issue raised was that the current design was too large, and that the pacifier would need to be very light weight to not cause any strain on the babyies' necks. Additionally, of greatest concern was that the fastener piece might come apart from the nipple and the body and could serve as a choking hazard. They therefore suggested a direct junction between the nipple and the pacifier body to remove the choking hazard.
In our second iteration at constructing the pacifier. We implemented structural design changes and resolved issues pointed out to us by healthcare experts and Autism Ontario. To resolve cracking of the nipple, the nipple was not thin walled. As well, the shape was changed to an orthodontic style nipple. This design produced no cracking upon printing. To ameliorate concerns surrounding choking hazards, the nipple fastening bit was removed. The nipple now connects directly to the pacifier body through a tight fit without intervening pieces. To reduce the weight of the pacifier, the new design was printed with a smaller face plate with decreased infill density and, lower wall thickness and infill density on the backplate. Final dimensions are shown above and are in mm. The final volume of this design was 42044.02mm3, 12.7% less than the previous design.
For the third iteration the faceplate was kept identical. The backplate was changed slightly. The ridges of the backplate are slightly larger than the faceplate on the top and bottom to allow for easy removal. As well, there is now a rectangular space at the end of the backplate to keep the internal components in place. The nipple changed slightly as well. The hole was changed from being where the nipple narrows to being on the flat portion near the front of the nipple. This allows for easier retrieval of saliva as the hole will no longer be covered by the lips. As well, the shaft of the nipple was extended to increase the clearance between the faceplate and the expansion portion of the nipple. The updated nipple and final assembly can be seen below.