Locking Liner Distal End Umbrella Project

Grace Smith

Clarkson University Undergraduate: 

Bachelor of Mechanical Engineering

Minor in Biomedical Engineering

Operation Namaste 

Supervisor:: Jeffery Erenstone CPO

August, 2024

Acknowledgement

My name is Grace Smith and I am an incoming senior at Clarkson University studying Mechanical Engineering with a focus in Biomedical Engineering, in Potsdam, NY. This summer of 2024 I got the opportunity to intern under Jeffery Erenestone and work for NonforProfit Orthotic and Prosthetic organization Operation Namaste. The goal of this project was to develop a low cost prosthetic liner and suspension system for prosthetic devices, specifically to patients in low to middle income countries. Operation Namaste was successful in determining a procedure which addressed “the critical need addressed by the United Nations Development Program in Syria.”(Claudia Ghidini).  The results of our findings will be discussed and compared with the findings of London, Imperial College Biomedical Engineering MsC student Claudia Ghindini. I am extremely grateful to have gotten this opportunity to work and participate in providing service under Founder and CPO Jeffery Erenstone for the Operation Namaste organization.

Operation Namaste has the ability to share findings with low/middle income areas, as well as send successful parts to those areas, increasing material access availability. Much of this write up will be in response from the final report MSc project of Claudia Ghidini “Low-cost linear solution and suspension system for lower limb amputees in low to middle income countries” as we performed the same experimental testing with the same objectives.  From Ghidini, we know that about 40 million people are in need of prosthetic and orthotic services in LMIC (Low to Middle Income Countries). By method of 3D printing we were able to conclude a design and material for a prosthetic liner umbrellas that was most ideal for low income prosthetic patients. An umbrella in a prosthetic device is a piece at the distal end of a liner that allows a suspension connection with the patient and the prosthetic device. Testing factors that were taken into consideration by me (Grace Smith) as well as CPO Jeffery Erenestone, include tensile failure point, as well as linear heat exposure.

Background

Our project initially consisted of 6 different types of umbrellas for static load testing, including three different materials and two differentiating umbrella designs. Each of our 3D prints were performed by the same printer to reduce variability. The printer that was used throughout this project was the Creality Ender-5 S1, known for its 250mm/s printing speed and CR-touch auto leveling. The three filaments used in the Creality Ender 5 S-1 for our umbrellas were from 3D printing filament company Overture, consisting of 1.75mm Polypropylene, 1.75mm Poly Lactic acid, as well as 1.75mm Polyethylene Terephthalate Glycol. Each of these materials were printed using their recommended nozzle and bed temperatures. (Also commonly labeled as PP, PLA and PETG) with two designs each (with insert, without insert). In our tensile static testing, a pin was attached from a loading scale and threaded into a printed umbrella. This force represents the vertical tension that occurs in a patient's suspension; furthermore when a prosthetic is in floating position and tension takes place between the socket and the prosthetic liner. For example, when a patient lifts their prosthetic off of the ground to take another step, the weight of the prosthetic creates a tensile force on the attachment method of the prosthesis, the pin lock suspension. 

Attached below will be front and top views of our two initial umbrella designs that were used in this project. Design 1 includes an umbrella where the pin of a liner is directly threaded into the piece while Design 2 requires a metal insert between the pin and umbrella.

Designs

Design-1: Threaded Umbrella (Without Insert)

                      Frontal View               Top View

         (Image 1.0)                                          (Image 1.2)

Image 1.0 and 1.2 shows our first umbrella design where the pin from (Image 3.2) is directly threaded into the 3D printed material. This shape represents more of a typical umbrella shape where the entirety of the piece is made of one material, typically metal. 

 Design-2: Umbrella (With Insert)

                   Frontal View                Top View

      (Image 2.0)             (Image 2.1)

 Image 2.0 and 2.1 represent our second umbrella design is our insert design, where a metal insert would be threaded into the umbrella where our pin would then be directly threaded into the insert. This design was meant to implement a small piece of metal with hopes to maintain stronger threading attachment, while still reducing the amount and cost of overall material.

Testing

Without access to tensile loading machinery, such as Instrons, Erenstone created a manual lever system that would be used to test tensile stress on our designs. This lever system contained one end where the force would be applied manually using a bucket filled with sand to generate a torque on the opposing end of the lever. The other side of the testing rig is composed of a tensile force scale attached to the lever and a clamp attached to the bottom piece that would hold the tested umbrellas into place. Therefore as the bucket is released from its rest point and weight was generated, the opposing side of the lever would have an upward force generated tension on the grounded clamped umbrella. To properly record our force results we set up a desktop camera and recorded the findings for each successful trail.

Testing Rig: 

                                  Image 3.1       Image 3.2

               (Force Input end)            (Force Output end)

Image 3.1 Shows our red and black bucket that was attached to the end of the lever, while Image 3.1 shows our orange tensile scale with a pin attached to it. This pin represents the typical prosthetic pin that is threaded into a prosthetic umbrella suspension system. This pin attached to the scale is then threaded into each of our umbrellas located in the white and wooden clamp below for tensile testing.

                           Image 3.3    Image 3.4

         (Parallel View)           (Umbrella Clamp)

Our testing rig is composed of a wooden lever loaded by a bucket of sand, created by Jeffery Erenstone in Lake Placid, NY at Operation Namaste Laboratory.

Our bucket was attached to the rig using a line of rope (as seen in Image 3.3), where our load force could be significant because of our lever length. The large lever increases our moment arm for our torque while our increase in bucket weight increases our applied force. This idea supports the formula of torque given below in (Equation 1.0). By alteration of the system, we were able to determine an ideal lever arm length for our force to be our dependent variable within necessary parameters from Ghidini.

Ƭ=r x F

( Equation 1.0 )

Ƭ- Torque

r- magnitude of the lever arm from Force point

F- force applied

Static Tensile Fracture Point Results

Throughout static testing I was able to come up with a consistent routine for accurate and consistent results. With our mechanical testing rig, the load is applied manually using sand poured into a bucket at the end of the lever. Each process had slight variation because of weight bearing strength, but has the same exact process, stress change, and time variables, ultimately attempting to reduce variability of creep results. Although the testing rig had loading force limitations, it was performed to the best of its ability, in an attempt to reduce error and variability.

Each umbrella type was loaded three times until a fracture point was reached, where the process would be repeated for three trails each. Our findings were then averaged and compared to one another below. 

Testing Results

 Threaded Umbrella-(Without Insert): Experiment 1

Graph 1.0

This graph analyzes our data averages for the average load over time for each of the three threaded umbrella materials. Three trials of each of our three materials were performed and averaged.

Each of our three polypropylene results were fairly consistent up until around 50kg. Our maximum forces before failure ranged from 47.6kg- 54.1kg. Although it is a high range, I still considered the results and fracture points to be consistent with polypropylene, but not as strong as PLA.

Although the PLA results were similar throughout the testing, the fracture points show a strong inconsistency. PLA was found to be much stronger than PP, but more inconsistent than PP; therefore we decided to test a third material, PET-G. 

Our PET-G without insert trails were found to be very inconsistent with load forces applied, much like the PLA. For example, during our PET-G  our trial one only made it to around 33 kg, while testing our trail 2 made it to a static load force of around 48kg, and our trail 3 failed instantly during setup. During trail 3, as soon as the load force was applied and connected to the threaded pin, the pin let out and failed.

To better analyze the strength of these materials compared to one another, I took an average of each material's trails and created a trendline in one graph. From the graph, we can conclude that our results were statistically significant with strong treadlines with the following R-values below. Each trendline represents the average load applied over time until a fracture point was reached. From this data, we can easily conclude that our PLA threaded umbrellas remain intact at significantly higher load forces than our Polypropylene and PET-G umbrellas.

Trendline Values for Threaded Materials

Table 1.0

Using our manual testing rig to achieve as consistent results as possible, we can see that during each of our trials a load force was added at an average of around 0.199kg/sec. Although each of our three equations are slightly different, they still represent similar static loading patterns. Lastly, each of our treadlines strongly represent our average material results ranging from a 0.9981 R value to a 1 R value;therefore the treadlines on Graph 1.0 accurately represent our averages from 99.81%-100%.

Umbrella-(With Insert): Experiment 2 

The umbrellas with inserts consisted of a cylindrical metal piece that gets directly threaded into the umbrella. This way the pin of a prosthetic liner gets attached to the metal insert, rather than directly into the umbrella like our without insert design. The goal of this piece is to provide more strength and durability to the umbrella, ultimately providing the same to a liner or socket. With the insert in each material of umbrellas, our results were found to be much more consistent than with our threaded umbrellas. 

Graph 2.0

Although each of our three PP trails were relatively similar, they each had relatively different failure points. With the minimum load failure point being 54kg and the maximum failure point reaching 70kg.

Similar to our PLA without insert Trails, PLA with an insert maxed out our testing rig; therefore we felt it was applicable to run only 2 Trails and minimize maxing out the rig. During our testing we discovered that one PLA with an inserts umbrella’s fracture point was 90.2kg while our Trail 2 umbrella never fractured with a load force of 100.3kg for 624 seconds. Although these findings were somewhat inconsistent our findings were well above our strength parameters.

PET-G with an insert was discovered to be our most reliable umbrella resulting in two successful trails maxing out our testing rig. Once again, we felt that two trials were enough to determine our data, and that it was unnecessary to max out our testing rig as each trial proved to be consistent.  Although one of our umbrellas broke within 135 seconds of our 100kg load, and another remained intact after a 100.3kg load at 624 seconds, these results led us to our conclusion that PET-G with an insert provided the most similar durability to a typical metal umbrella. As a result of these findings, this umbrella's material and design consistently surpassed our load force parameters and was determined to be our future umbrella approach.

I repeated my analysis by repeating calculations with an average of each material's trails and creating a trendline in one graph. Once again concluding that our results were statistically significant with strong tread-lines with the following R-values below. 

Trendline Values for Insert Materials

Table 2.0

Using our manual testing rig to achieve as consistent results as possible, we can see that during each of our trials a load force was added at an average of around 0.204kg/sec. Similar to our equations and R values calculated from Experiment one, our tread-lines showed a significantly strong representation of our averages with a minimum of 99.81% and a maximum of 99.98%. Each of our three material equations strongly represent the static load patterns until fracture point was reached for each of the tested materials. 

Comparing our Average Material Results With Insert Graph to our Average Material Results Without Insert Graph, we see an increased load force strength with our insert achieved for each of our three materials. These findings support our hypothesis that adding a metal insert to our umbrellas will positively affect load force strength of the umbrella. As expected, Polylactic Acid and PET-G were the strongest of the materials, while Polypropylenes fracture point was much lower, therefore we deemed it an unnecessary material to continue our project with. Of the averages we can conclude that Polylactic Acid reached a maximum load force average of 90.3kg while PET-G reached a maximum load force average of 100.15kg

In this experiment we use 3D printing to create our umbrellas, eventually ensuring necessary strength and safety measures. After initial static testing, we decided to narrow our testing categories to two materials (PETG and PLA) and just the one design (with insert). We made this decision because we found that both PETG and PLA were significantly stronger than PP, by at least 30 kg, repeatedly maxing out our testing rig. Similar findings occurred when testing static load with the metal insert of these materials, the testing rig was maxed. Narrowing down these categories of six umbrella types to four allowed us to experiment further on our more reliable designs.

Alternative Consideration-Heat

Although our PLA was found to be strong and reliable, we took into account another realistic factor with PLA.

 CPO and founder of Non for profit Operation Namaste Jeff Erenstone is knowledgeable on different 3D printing filament materials, as well as environmental factors that can affect the function of prosthetic materials. Therefore, we began to analyze the effect of heat on umbrellas with our two strongest materials. Since prosthetic devices are used throughout various environments, we felt it was necessary to take a significant environment into confederation heat. Similar to our initial experiments, we tested static fracture points after heating our umbrella within a pot of water over a hot plate. Our results concluded that heat had a significant effect on the durability of the PLA umbrella when a load force was applied, while our PET-G continued to function our testing rig to maximum capacity. This consideration was referred to as our Experiment 3. 

Erenstone concluded that the most common time a prosthetic liner reaches a high temperature is when it is left in the car during the summer time or in high temperature conditions. In weather.gov Joe Sullivan addresses the effect higher temperatures can have on the inside temperature of a car; therefore our umbrellas embedded in our project takes into consideration the scenario of a liner being left in the car during a hot summer day.

Heat Effects-Experiment 3 

As we continued our research on two materials PET-G and PLA with our insert design, we analyzed our findings below.

Table 3.0

With our determined umbrellas we decided to perform multiple heat tests to see if heating our umbrellas to a possible eternal summer car temperature had an effect on the fracture points.

Using 150°ꜰ water, we performed our same Experiment two but with our umbrella submerged in water over a hot plate to reach a desired temperature. Each test was performed once the umbrella insert reached our desired temperature around 140°ꜰ . 

Heat for our PET-G Trail 1 and Trial 2, no effect on the umbrellas as they continued to max out the testing rig just like in experiment 2. Although our trail 3 umbrella eventually fractured, it remained significantly strong and maxed out the machine with a load force of 100.6 applied. 

As expected, the heat was found to have significant deformation effects on our PLA material as we found the insert to be easily pulled out of our umbrella. After one trial with instant fracture during set up and two successful trials with extremely low fracture points, we concluded it unnecessary to run a third trial with PLA. 

In Image 4.0 we can see the heat effects on our PET-G where it was found to have insignificant deformity on our umbrella and remained intact with our insert; therefore remaining attached to the suspension system

Final Design

After design and material was determined Erenstone explored the next most common breaking point of an umbrella in tension,which was found to be the threading of the liner to the umbrella. Erenstone then developed a final design that helps to improve the tensile strength of umbrella suspension as well as the strength of the threaded umbrella point. This design was experimented by repeating our experiment 2 but with a larger attachment hole of the umbrella; this allowed tensile force to continue to be applied by the pin insert but focus on the breaking point of the flat part of the umbrella. You can see this fracture point to be in the outermost ring of the umbrella that the threading area is being referred to. We can also see this type of attachment shown in Figure 7: Umbrella Sewn into Nylon Sock of Ghinidis paper.

Image 5.0 

From Image 5.0 we can see that from static loading testing focus on our flat umbrella the outermost ring became detached completely from the umbrella. This analysis led to our final design creation and test below. 

                          Frontal View   Top View

               (Image 6.0)  (Image 6.1)

Our final design (Image 6.0 and 6.1) above was successfully static tested concluding our hypothesis based on our previous static loading experiments without and within a prosthetic liner on a mock limb. This testing succeeded with a tensile load force above 60kg.

Conclusion

Through multiple repeated trials and considerations, we concluded that our PET-G with insert umbrella design best met proper safety requirements providing the most ideal suspension design compared to commercially available liners, reducing overall pricing of a prosthetic umbrella liner. Using Ghindini’s personally determined requirements of tensile strength of 61.2kg, and stated load force of commercially available liners (56.07kg), our findings with PET-G were well above desired strength, ensuring safety and increased durability to the piece. 

After completion and final conclusion were finalized, we 3D printed fifteen PET-G umbrellas to be sent to a prosthetic facility located in Nepal, South Asia for prosthetic liner implementation. Operation Namaste’s goal in this project was to provide LMIC with a successful development procedure to suspend a piece of a prosthetic device that lowers the cost of a liner as well as increase accessibility to amputees in need. This project hopes to expand the idea of 3D printed prosthetic umbrellas to multiple areas for increased accessibility to LMIC as well as overall design expansion for prosthetic and orthotic facilities.

As an undergraduate student I was honored to develop a project with Jeffery Erenstone in response to Claudia Ghinidi’s project as well as partake in the Operation Namaste organization. This project provided me with an astonishing research opportunity as well as several skills that I plan to take into my future endeavors in the Prosthetics and Orthotics field. 

Citations:

1) Ghidini, Claudia. Low-Cost Liner Solution and Suspension System for Lower Limb Amputees in Low to Middle Income Countries. 1 Sept. 2021.

2) US. “Look before You Lock!” Weather.gov, 2016, www.weather.gov/lmk/beat_the_heat_and_check_the_back_seat. Accessed 3 Nov. 2024.