Wright State University - Prosthetic Socket Layer Analyzer

INTRODUCTION

Patient safety is a key concern in the process of manufacturing prosthetic sockets. Prosthetic Design, Inc. (PDI) uses 3D printing technology to produce lower limb prosthetic sockets. However, the strength and durability of these prosthetic sockets is still unknown. Defects can arise in the 3D printing process, such as premature cooling of the layers, or uneven layers. These defects can result in gaps within the socket, which are more prone to microfractures. Microfractures can compromise the durability and strength of the socket, which in turn may decrease patient safety during use. Working with a Senior Design group from Wright State University, the goal of this project was to develop a device to analyze each layer of a 3D printed socket.  The device will be used to measure the thickness of the plastic to determine if there are any microfractures within the material.

METHOD

After researching different methodology for measuring the thickness, an Acoustic Emission Method was determined to be the best option to move forward with. The design of the device consisted of a power brick, a pulse generator, a power amplifier, two probes, and an oscilloscope. These components together utilized an Acoustic Emission Method to calculate the thickness of layers within the socket. Through MATLAB, the thickness was calculated using the time from a generated waveform and the speed of sound through the material. The calculated thickness was cross-checked with a user-input expected thickness. Calculated thickness values exceeding 90% of the expected values were considered structurally sound, and “good” sockets. Thickness values below 90% were considered “bad” sockets.

RESULTS

Table 1: Caliper and Acoustic Emission thickness measurements

Table 1 shows average manual thickness measurements using Vernier Calipers compared to the calculated thickness values using the Acoustic Emission Method. The three sockets shown in Table 1 represent three “good” sockets, with thickness values above 90% of the expected value. Figures 1 and 2, below, show representative screenshots from MATLAB for different waveforms obtained for a “good” and “bad” socket through the Acoustic Emission Method.

Figure 1: “Good” socket                                                                                     Figure 2: “Bad” Socket

Above, Figure 2 shows a correctly identified “bad” socket, as the device identified a bad layer within the socket where there was a crack.

DISCUSSION and CONCLUSION

Shown in Table 1, the thickness values from the Acoustic Emission Method were significantly lower than the respective caliper measurements. The differences in these measurements could be due to inaccurate measurements of the layers using the calipers or calculation of the speed of sound, since the group utilized the material properties of polypropylene. The actual material of the sockets was undisclosed to the group. Additionally, limited resources and funding provided restrictions for the group to utilize ideal measurement probes and measure multiple data points during one continuous testing session. Though the project did not reach completion, further research into this method could result in a working prototype for PDI.

CLINICAL APPLICATIONS

Due to increased use of 3D printed technology for lower limb prosthetics, it is important to find a way to confirm the thickness measurements of sockets, as well as test for microfractures within the material. Safety of individuals wearing these 3D printed sockets is of top priority for PDI. Therefore, it is important to develop a device to ensure the strength and durability is maintained for 3D printed lower limb prosthetic sockets.

FUNDING SUPPORT

Wright State University – Senior Design Budget

John Ausec¹, Kent Fagen¹, Spencer Garrett¹, Mark Pleger¹,

Wright State University¹, Fairborn OH, Prosthetic Design, Inc.², Clayton OH