Author(s): Alexander Stuart
Mentor(s): Ali Beheshti, College of Engineering and Computing
AbstractThe materials currently used to construct replacement hip and knee joints for humans are stainless steel and titanium. Whilst these materials are strong and fairly biocompatible, they are expensive and can cause adverse long term side effects such as stress shielding. The aim of this project was to construct and evaluate an alternative to these materials, specifically 3-D printed Polylactic Acid and Hydroxyapatite composite (PLA-HA). PLA-HA is a polymer composite of Polylactic Acid (PLA) and Hydroxyapatite (HA). PLA-HA is relatively cheap, very biocompatible, and can be easily adapted for use in a 3-D printer. This vastly simplifies the process of manufacturing unique parts with complex geometries such as a replacement joint. Raw PLA-HA was created in-lab using three different manufacturing methods. These manufacturing methods were Dry Speed Mixing, Wet Speed Mixing, and Magnetic Stirring. The raw PLA-HA was then converted into filament for use in a 3-D printer using a uniaxial filament press. The PLA-HA filament was then to be used to 3-D print three different samples for mechanical testing for each manufacturing method. These samples will be subjected to a variety of tests to characterize their mechanical and surface properties. These tests include destructive tensile tests, micro-indentation, and wear tests. These mechanical and surface properties will then be evaluated to determine if they are sufficient for a joint replacement application. The four different manufacturing methods will also be compared against one another to determine which method produces samples with the desired mechanical properties and distribution of hydroxyapatite throughout its matrix.
Audio TranscriptHello!
My name is Zan Stuart and today I will be discussing my project which was a study of the mechanical and surface integrity of 3-D printed PLA-HA composites. The main motivation behind this project is the orthopedic and biomedical industries. Currently stainless steel and titanium are used for most replacement joints such as hip and knee joints. Now these materials are both strong and don’t corrode, but they are far from perfect for this application, as they often can cause adverse side effects such as stress shielding which weakens the bone surrounding the replacement joint.
PLA-HA, or polylactic acid combined with hydroxyapatite composites are being explored as a viable alternative, as they’re very inexpensive relative to the current options, they exhibit mechanical properties similar to that of bone, which eliminates the effects of stress shielding which I mentioned earlier. They have enhanced biocompatibility due to the fact that hydroxyapatite constitutes a major part of our bone structure, and they can be easily adapted for use with a 3-D printer which allows for the construction of unique parts with complex geometries such as a replacement joint tailored for any given individual.
The experimental process that I’ll be following is creating a base PLA-HA composite using four different manufacturing methods, which are dry speed mixing, wet speed mixing, magnetic stirring, and dry mixing. This raw material will then be extruded into a useable filament for a 3-D printer, and then three samples for each of the aforementioned manufacturing methods will be 3-D printed. Mechanical and surface property tests will be performed on these samples, and the results between the manufacturing methods will be compared.
Filament extrusion took place using a Noztek Pro high temp. uniaxial filament compressor. Raw material, which usually takes the form of pellets off the shelf, is fed into the hopper which you can see in the bottom right. In the bottom left of the hopper, you can see something that looks like a screw. That is the auger which then pushes the raw material through the heated nozzle which you can see in the bottom left, which melts the raw material and compresses it into something that resembles a string. This is the filament to be used in the 3-D printer.
The first of the manufacturing methods that I will cover are wet and dry speed mixing which are both very similar. For wet speed mixing, PLA is combined with dichloromethane, which is a solvent, and left to dissolve until homogenous in a fume hood. This is then combined with hydroxyapatite and Dodecyltrimethoxysilane or WD-10. These are then mixed in the speed mixer which you can see on the right-hand side, until the mixture is homogenous. That mixture is then poured onto an aluminum tray under a fume hood and left to cure and solidify overnight. Dry speed mixing is essentially the same process, minus the liquid solvents of Dichloromethane and WD-10.
Magnetic stirring involves the combination of PLA and DCM once again, but this time in a large glass beaker with a magnetic stirring bead in the center. This mixture is then sealed with silicone paper, and left to dissolve until it’s homogenous. The stirring bead rotates to ensure that the mixture remains homogenous. After the mixture is observed for homogeneity, HA and WD-10 are added and left to stir once again until the mixture is homogenous. The mixture is poured onto an aluminum tray to cure overnight once again.
Dry mixing is a much simpler process. It involves combining raw PLA pellets with dry HA directly into the hopper of the filament extruder. After that is extruded into filament after a single pass, then that filament is shredded and once again passed through the extruder, hopefully the result being better distribution of HA in the PLA matrix.
Now the results for this experiment. I was able to produce raw material using magnetic stirring and wet speed mixing. I was also able to successfully extrude filament, and 3-D print a magnetic stirred sample. I was unfortunately unable to progress enough to A: print samples for all of the different manufacturing methods and B: I was not able to perform mechanical testing on the samples. We’ll get to exactly why momentarily. You can also see in the bottom right I printed part of a magnetic stirred sample, as you can see that sample is obviously not correct. We’ll get into the reasons why shortly.
Some obstacles that I ran into during this project include I ruined a couple batches of magnetic stirred material due to improper sealing of the beaker with the silicone paper. You can see an example of that in the bottom right. It basically solidified when I was attempting to mix it due to the solvent evaporating because of the bad seal.
The extruder’s temperature reading was also inaccurate, meaning that the heat applied wasn’t necessarily what you set it to, which caused problems with inconsistency.
The extruder frequently clogged which you can see on the right-hand side. That has more to do with how the raw material that I created was then shredded and then fed into the extruder, we’ll get into that later.
It was difficult to get a uniform diameter for the filament because of how it was being removed from the extruder. I was basically pulling it out by hand, as hard as I tried it was impossible to get an exactly constant rate of removal. That caused another inconsistency with the filament.
I was also ill for a one-week period, and the lab was closed for two weeks. That was back-to-back. I lost three weeks of time where I could be making more raw material or potentially extruding more filament.
In the future, if I was to repeat this project, I would revise the casting method for the raw material by pouring the mixture into some form of pellet mold. Like I briefly mentioned earlier, when you get this sort of material off of the shelf it often takes the form of a spherical pellet, which feeds into the extruder better. The raw material that I was using was basically shredded flat sheets of plastic which was far from ideal and caused the extruder to clog frequently.
I would use a more accurate method of measuring the temperature of the extruder so that I could ensure that I was consistent with the temperature.
I would also use an automatic spool which would remove the filament from the extruder at a constant rate removing the variable of me pulling it by hand.
Thank you very much for your time, and I hope that you enjoyed my presentation!
My name is Zan Stuart and today I will be discussing my project which was a study of the mechanical and surface integrity of 3-D printed PLA-HA composites. The main motivation behind this project is the orthopedic and biomedical industries. Currently stainless steel and titanium are used for most replacement joints such as hip and knee joints. Now these materials are both strong and don’t corrode, but they are far from perfect for this application, as they often can cause adverse side effects such as stress shielding which weakens the bone surrounding the replacement joint.
PLA-HA, or polylactic acid combined with hydroxyapatite composites are being explored as a viable alternative, as they’re very inexpensive relative to the current options, they exhibit mechanical properties similar to that of bone, which eliminates the effects of stress shielding which I mentioned earlier. They have enhanced biocompatibility due to the fact that hydroxyapatite constitutes a major part of our bone structure, and they can be easily adapted for use with a 3-D printer which allows for the construction of unique parts with complex geometries such as a replacement joint tailored for any given individual.
The experimental process that I’ll be following is creating a base PLA-HA composite using four different manufacturing methods, which are dry speed mixing, wet speed mixing, magnetic stirring, and dry mixing. This raw material will then be extruded into a useable filament for a 3-D printer, and then three samples for each of the aforementioned manufacturing methods will be 3-D printed. Mechanical and surface property tests will be performed on these samples, and the results between the manufacturing methods will be compared.
Filament extrusion took place using a Noztek Pro high temp. uniaxial filament compressor. Raw material, which usually takes the form of pellets off the shelf, is fed into the hopper which you can see in the bottom right. In the bottom left of the hopper, you can see something that looks like a screw. That is the auger which then pushes the raw material through the heated nozzle which you can see in the bottom left, which melts the raw material and compresses it into something that resembles a string. This is the filament to be used in the 3-D printer.
The first of the manufacturing methods that I will cover are wet and dry speed mixing which are both very similar. For wet speed mixing, PLA is combined with dichloromethane, which is a solvent, and left to dissolve until homogenous in a fume hood. This is then combined with hydroxyapatite and Dodecyltrimethoxysilane or WD-10. These are then mixed in the speed mixer which you can see on the right-hand side, until the mixture is homogenous. That mixture is then poured onto an aluminum tray under a fume hood and left to cure and solidify overnight. Dry speed mixing is essentially the same process, minus the liquid solvents of Dichloromethane and WD-10.
Magnetic stirring involves the combination of PLA and DCM once again, but this time in a large glass beaker with a magnetic stirring bead in the center. This mixture is then sealed with silicone paper, and left to dissolve until it’s homogenous. The stirring bead rotates to ensure that the mixture remains homogenous. After the mixture is observed for homogeneity, HA and WD-10 are added and left to stir once again until the mixture is homogenous. The mixture is poured onto an aluminum tray to cure overnight once again.
Dry mixing is a much simpler process. It involves combining raw PLA pellets with dry HA directly into the hopper of the filament extruder. After that is extruded into filament after a single pass, then that filament is shredded and once again passed through the extruder, hopefully the result being better distribution of HA in the PLA matrix.
Now the results for this experiment. I was able to produce raw material using magnetic stirring and wet speed mixing. I was also able to successfully extrude filament, and 3-D print a magnetic stirred sample. I was unfortunately unable to progress enough to A: print samples for all of the different manufacturing methods and B: I was not able to perform mechanical testing on the samples. We’ll get to exactly why momentarily. You can also see in the bottom right I printed part of a magnetic stirred sample, as you can see that sample is obviously not correct. We’ll get into the reasons why shortly.
Some obstacles that I ran into during this project include I ruined a couple batches of magnetic stirred material due to improper sealing of the beaker with the silicone paper. You can see an example of that in the bottom right. It basically solidified when I was attempting to mix it due to the solvent evaporating because of the bad seal.
The extruder’s temperature reading was also inaccurate, meaning that the heat applied wasn’t necessarily what you set it to, which caused problems with inconsistency.
The extruder frequently clogged which you can see on the right-hand side. That has more to do with how the raw material that I created was then shredded and then fed into the extruder, we’ll get into that later.
It was difficult to get a uniform diameter for the filament because of how it was being removed from the extruder. I was basically pulling it out by hand, as hard as I tried it was impossible to get an exactly constant rate of removal. That caused another inconsistency with the filament.
I was also ill for a one-week period, and the lab was closed for two weeks. That was back-to-back. I lost three weeks of time where I could be making more raw material or potentially extruding more filament.
In the future, if I was to repeat this project, I would revise the casting method for the raw material by pouring the mixture into some form of pellet mold. Like I briefly mentioned earlier, when you get this sort of material off of the shelf it often takes the form of a spherical pellet, which feeds into the extruder better. The raw material that I was using was basically shredded flat sheets of plastic which was far from ideal and caused the extruder to clog frequently.
I would use a more accurate method of measuring the temperature of the extruder so that I could ensure that I was consistent with the temperature.
I would also use an automatic spool which would remove the filament from the extruder at a constant rate removing the variable of me pulling it by hand.
Thank you very much for your time, and I hope that you enjoyed my presentation!
2 replies on “Mechanical and Surface Integrity Study of 3D-Printed PLA/ HA Composite”
This was a great presentation! I liked how many pictures you included. Do you know how long this material would last if used for a joint replacement?
This is a super cool project that will definitely have good impacts for future studies!