Rapid and Low-cost Prototyping of Medical Devices Using 3D Printed Molds for Liquid Injection Molding

The overall goal of this procedure is to create a liquid elastomer device with a custom geometry using 3D printed mold pieces. This is accomplished by first designing the desired mold geometry in CAD software and 3D printing the mold pieces. The second step is to assemble the mold pieces into a full mold next liquid elastomer prepared and injected into the mold cavity.

The final step is curing the liquid elastomer and removing the resultant device from the mold. Ultimately, this technique enables rapid creation of small scale and low cost medical devices in a resource limited environment that would typically only be possible in an industry or larger scale manufacturing setting. The main advantage of this technique over traditional liquid injection molding is that it enables creation of elastomer devices in a resource limited or academic setting.

One may use this technique to create prototype medical devices for use in clinical studies to assess the feasibility of new medical technologies. The ability to rapidly validate new medical devices at cost and with a quick iteration cycle drastically reduces the barriers to device development and proof of ization. The method we specifically is to embed electrical and optical sensors in an intravaginal probe device designed to scan human cervical tissue.

Generally, individuals new to this technique may initially struggle because of the design constraints involved in the use of 3D printed materials and multiple mold pieces to create a mold. We hope that our demonstration of this technique will help guide any future attempts to design a mold and carry out the necessary steps to yield any desired elastomeric device. The first step is to use computer aided design software to design a to scale mold master.

Here in solid works is the Intravaginal probe master. It has a cup like structure at one end and a handle and a separate CAD file. Extrude a rectangle into a rectangular prism, large enough to enclose the mold master.

Import the mold master file into the file with the rectangular prism. Align the mold master such that it is centered and completely encased within the prism. Combine the files and use a subtraction operation to create the mold cavity.

Next, define the pieces of the mold to create a bilateral parting line. Start in the right plain view. Define a rectangular 2D sketch that extends from the base of the cup like structure to the top of the probe handle.

Apply cuts in the positive and negative X directions. This will yield bilateral symmetric mold parts to create a radial parting line. Start in the right plain view.

Use a 2D sketch to create a radially symmetric parting line that includes the Y axis and passes through internal regions of the cup like geometry. Use a revolved cut on the sketch to isolate a radially symmetric mold part to hold the mold together. Define through holes by defining a circular 2D sketch with a standard clearance hole size corresponding the rod or screw to be used.

Then apply the extruded cut feature to the sketch. Both vertical and horizontal through holes are created to fully constrain the mold pieces. After defining all parting lines in through holes, use the same procedure to define an entry point for the elastomer A gate toward the bottom of the mold cavity.

Also, incorporate vents for excess elastomer to drain from the mold. Isolate each mold piece by suppressing or unsuppressed features. Now save each mold piece as a file compatible with the 3D printer to be used.

When done, load the files into the 3D printer and wait until they are done about one day for this mold and setup. After the printing is done and the pieces have been cleaned, assembly is the next step. Bring the mold pieces together along with any components that will be overmolded.Here.

The overmolded components are stainless steel tubing and electronics. For this mold, place threaded rods in some through holes and hold them in place with two jammed nuts on one end to help provide scaffolding when adding a piece, always be certain to align the through holes. When the mold is completed, put the remaining screws and rods in place and secure all rod ends with nuts.

Next, prepare to create a channel into the mold gate. Use a barbed to male lure lock adapter. Insert it into the gate of the mold cavity.

Make sure there is a tight fit. Obtain about four inches of silicone tubing with barb to female lure lock adapters. Attach to each end, connect this tubing to the adapter and the mold cavity gate.

After this step is completed, the injection chamber should be prepared. Proceed with elastomer mixing. After preparing the injection chamber, use the mold volume to determine the needed quantities of elastomer components, part A and B.Then ready a disposable plastic cup, a plastic bag, and several rubber bands.

Placed a plastic on a way scale and tear it. Pour the required quantities of part A and part B into the cup. Color master batches are also added here.

Seal the cup opening by pulling a plastic bag over it. Secure the bag with three to four rubber bands. Next, place the cup in a centrifugal mixer mix for two minutes to ensure homogenous mixing and an additional one to two minutes on the DGAs setting.

Meanwhile, to create the elastomer injection syringe, start with a 50 milliliter syringe with a male lure lock. Use a female lure lock cap to seal the bottom. Then secure the seal with para film and one rubber band.

Retrieve the elastomer and transfer it from the plastic cup into the 50 milliliter syringe. Before adding the plunger position a syringe needle to help avoid trapping air in the syringe. Place the needle sharp side down along the syringe wall without touching the elastomer.

Then put the syringe plunger into the syringe until there is no visible air column between the plunger and elastomer. The next step is to inject the elastomer into the mold. Remove the female cap on the syringe containing the prepared elastomer and connect the exposed male lure lock syringe tip to the female adapter leading to the gate of the assembled mold.

The assembly is now ready for the injection chamber. Secure the air operated syringe adapter of the injection chamber to the back of the syringe, plays both the mold and the syringe in their respective positions. Cover the injection chamber and ensure an airtight seal is formed.

This is the schematic representation of the system. After covering the injection chamber, the next step is to isolate the chamber and make certain the vacuum source is continuous with the chamber and the syringe plunger. Then slowly draw a vacuum until about negative 14.5 PSI is achieved.

Maintain this pressure and break continuity between the vacuum source and the syringe plunger while establishing a connection with the positive air supply. Gradually ramp up positive pressure from the air supply until at least 25 to 35 PSI is achieved. In a few seconds, wait until the syringe plunger has reached the bottom of the syringe before returning the system to atmospheric pressure.

When the mold is recovered, detach the tubes from the mold gate. Place a female lure lock cap on the male adapter to prevent the flow of elastomer. For curing.

Place the mold in a temperature controlled oven. The device in this video is cured at 70 degrees Celsius for five hours. At the end of the curing time, remove the mold from the oven and allow the device to cool to room temperature.

Then demold the device vice. This medical grade instrument was completed in about two days, including printing the mold pieces. A view into the cup like region shows six electrodes and the end of the receptacle for a fiber optic probe.

All overmolded features the entrance for the fiber optic probe and A USB cable for the electrodes are at the rear. With this technique, we have manufactured over 40 intra vaginal probe devices for data collection. In a clinical study, this particular device has allowed us to study the use of cervical fluorescence and impedance to monitor pregnancy.

For signs of preterm birth, It's important to remember to design the mold carefully choose parting lines, and through holes such. The fully assembled mold is constrained both linearly and rotationally, while also allowing easy removal of the fully cured device. Once master, this technique can take a couple of hours or a day, depending on the specific geometry or complexity of the desire to elastomeric device.

We've shown that this is a feasible method of developing prototypes of therapeutic and diagnostic medical devices, but the procedure can be applied to the development of elastomeric devices and many other applications.