Research plans vs reality

This week I have done the final few prints for the radiopacity project. I have been working on this project since June and it is satisfying to see how far the project has come since then. The paper is also coming together nicely, and I am excited for when I can post the results of the project.

In research, things rarely happen as originally planned, often due to completely unforeseen factors. I have decided to focus this blog on how real timelines are often quite different to the plan. This week was my second time ‘hacking the printer’ on my own, and this time I was much more confident. This week, I had three things to print:

  1. Print a hand with radiopaque bone (within TangoBlack, a black rubber material to represent the soft tissue of the hand)
  2. Samples for mechanical testing the material (5 of each)
  3. Samples for a second mechanical test (5 of each)

The hand was the biggest job (4 hours) and I originally planned to get the two mechanical testing samples done in a second print job (1.5 hours). Here is my original plan for the two days:

This plan wasn’t being super optimistic, either. I gave myself extra time to make the material and set up before printing, with an hour between prints to clean and setup for the next print. Friday was block booked for cleaning and getting the printer back to full working condition for Monday morning. ‘Test and clean’ from the timeline means checking how badly the printer had been blocked up while printing the radiopaque material, unblocking the print heads and making sure there are no issues before beginning the next print. This is the part that I had rushed in previous prints, cutting corners and continuing with the print even though heads were blocked, because I thought that ignoring one or two blocked heads (out of ~100) would not affect the end results. This was a huge lesson for me, as I now know that this step is crucial. One or two blocked heads at the start can ruin an entire print and result in repeating the entire job, which in the long run, is more time consuming, and also a waste of material. I made sure to mix my material after any break in printing – as I had not done this last time. This time, after mixing well before every print, there were hardly any blockages.

So, this time I did not cut corners with the cleaning step, but the real timeline was still quite different from the planned timeline:

The ‘reality’ timeline was going perfectly (almost too perfectly!) until 13:30, when I realised the hand part was printing but no bone was showing up. I cancelled the job and checked the printer for blockages, but there were no print heads blocked. We had this problem a few months previously, and to be honest we are still unsure what went wrong. The 3D hand file (consisting of two parts – the bone and the surrounding soft tissue) successfully printed with clear ink as the skeleton and black rubber material as the soft tissue, but would not print the radiopaque material. Eventually, I decided to swap the cartridge tag to trick the printer into thinking that it was printing just clear ink (as I knew it had already successfully printed the skeleton from this cartridge earlier in the week). I tried a tiny hand first – ‘Test print’ in the ‘reality’ plan (shown below, the hand is less than 1cm long). This print was successful so I started the print of the hand at 18:00 and went home while it continued to print.

Print 3, during printing

While trying to resolve the hand issue, I split ‘print 2’ from the plan into two parts. I thought two smaller prints would make more sense because if the print failed again, there would be less material wasted. The first small print (Print 2 in the reality plan) was successful but the second (Print 3) was cancelled as parts did not reach the correct height. By 16:00 I had the idea about swapping ID tags so the hand skeleton could be printed, so I abandoned print 3 and printed the hand.

The following morning I saw that the hand was printed successfully. I removed the hand from the print tray, made up some more material, and attempted print 3 again – the final print. Again, this print did not reach the height that it was supposed to. I tried again, and this time the print was fine.

Overall, I was very happy with these two days of work. Even though the printing took nearly twice as long as I had planned, I still managed to get them all done before the weekend. Most importantly, there was very little blocked heads during the print – I am going to credit this to the fact that I took more time to set up/ clean the printer before plowing ahead and printing as I had done previously. I also think that mixing the ink before every single print helped to reduce blockages, and was worth the extra time as this reduced the clean up time after each print. I look forward to getting the hand x-rayed next week to show exact radiopacity of the print!

Life-size hands:
The hand on the left is the failed attempt, as the radiopaque ink never printed (you can see the print is incomplete as it was cancelled).
The hand on the right is the successful print with visible bone inside

Polyjet Technology

The last few weeks have been primarily focused on producing a paper, summarising the work I have done since I started with the Design Factors research group. This project involves creating a radiopaque 3D printing ink (parts printed with this ink will show up on x-ray whereas they usually would not). I have been collecting my results, and putting all of this data into the paper, as well as the methods I used to obtain these results. I will do an entire blog about this paper when it has been published – there are some really cool images to show off the work (*spoiler alert: it was successful!). Firstly, I would like to explain the workings of the printer and printing technology before getting into the details of the project.

Last time I wrote about the printer itself, so this blog will focus on the technology of 3D printing that I am using during my project: Polyjet Technology (photopolymer jetting). A broader term for this technology is Material Jetting. Polyjetting is Stratasys‘ variation of this 3D printing method.

Polyjet is one 3D printing technology (there are many more and these will be covered in future posts). The Connex 500 is the printer that I have access to for my research. This printer makes use of polyjet technology, which involves drops of ink being placed (similar to the below cartoon, but directly onto the print bed/ previous layer, and drops are not as continuous as they appear in the animation). Polyjetting is a type of ‘Material jetting’.

From: Design World Online

Polyjet uses liquid ink to create solid objects. The liquid ink is photocurable, meaning that it solidifies when it is exposed to light (specifically ultraviolet light). First, the ink is heated to a specific temperature, reducing viscosity for best flow properties for the ink. For the Connex 500, this is 70°C. After each layer has been deposited, the UV lamp travels over the print bed and cures all liquid ink droplets, creating the next solid layer of the object.

From: 3D Hubs

The cartoon above illustrates how an ‘X‘ would be printed. The red colour with white fill is the solid object, the grey lines outside this shape indicate the support material (this was explained in the previous post). It is worth noting that there is no support material above the ‘X‘, as there is nothing to support, and it would be wasteful. The print bed lowers as the component is printed, so the print heads work in an x-y plane.

There are, of course, advantages and disadvantages associated with polyjet technology. One main advantage for polyjet is the dimensional accuracy, great surface finish and precision when printing. Even though a limitation of 3D printing, in general, is a lack of available material, polyjet has a range of colours, flexibility/rigidity and optical transparency/opacity properties. An added advantage of the Connex 500 is the multi-material feature, allowing us to combine two inks to further enhance these properties.

A significant disadvantage of polyjet is poor mechanical properties, but this goes for 3D printing in general. As objects are printed in layers, there is significant weakness between these layers, so print orientation is important. As well as this, polyjet-printed parts’ mechanical properties degrade over time due to their photosensitivity. Polyjet inks and print heads are quite expensive, which may deter some users, but if you are looking for high-quality parts it is worth the extra costs.

Polyjet is ideal for small parts/prototypes. I often use it for fixtures or molds. For example, when I was mixing small glass vials by ultrasonication, the vials were vibrating and crashing into each other, leading to the vials cracking. I printed a divider to keep the vials separated and it worked perfectly (images below). There is ongoing medical device development within the research group and the printer is often used in the early device design/prototype stage.

Hopefully I will have the paper out soon and I can go into greater detail about it here, as well as disscussing my new project! There is a huge amount of overlap between the radiopacity project and my PhD project, so it has been quite a smooth transition for me, so far!

The Connex

This blog is coming a little later than I would have liked, but this week has been super busy. As mentioned in the first blog, I am currently writing up a paper for publication, as well as completing the material property testing for same.

The 3D printer that I have access to for my project is the Connex 500. This printer can print two materials at the same time (in different combinations to vary properties, or printing one material within another). The printer is shown in the first image below. The print tray, where components are actually printed is under the top panel. The two material cartridges are inside the door on the right and the two support material cartridges are inside the door on the left. This is clearer in the image on the right, with all panels and doors fully opened.

The build tray is shown below. The print head location is circled but as they are all downward facing they cannot be seen in full detail.

This printer uses Polyjet technology and uses liquid ink. There are two print heads per material, each has ~100 openings to allow droplets to be deposited to build up each layer. A layer of the liquid is immediately cured by UV lamps and becomes solid. This layer then acts as a foundation for subsequent layers. Printing a solid block is easy, as the first layer is deposited and cured on the print tray, the second layer printed on the first, third layer printed on the second, and so on.. But, in cases where the object is not a completely solid shape (for example, the hand skeleton below), support material is needed to create the same solid foundation for the next layers. This material is waxy in texture and is washed off as part of the post-processing. The hand was printed from the bottom up, in the same orientation as in the photo below. In this particular print, there would have been four or five times more support material used than the material that the hand is made from.

The image on the left below shows the hand being printed. The black material is the bone, white-ish material is the soft tissue and the dark grey is the support material. The second image shows the hand with support material removed.

This 3D printer was one of the more expensive printers on the market when it was released in 2014, selling for $250,000! The Connex’s main selling point is that it can print multi-material parts. It has very thin layers (as thin as 0.16mm, but more commonly we use 0.32mm) which give very good print resolution. One of Stratasys’ materials is a transparent, biocompatible ink (MED610) for medical and dental use; another major factor when the research group were deciding to get this particular printer.

The size and cost of the machine might lead you to believe that it is complicated to operate, but in fact it is quite straightforward. The software is very user friendly and the printer itself is easy to operate. I have been working on the machine for a few months now and I feel like I have learned how to do most tasks in relation to printing and general maintenance.

I am now able to get the printer back to perfect working conditions after taking it apart (to do test prints with the material I am developing as part of my research project). At the start it was quite intimidating to mess with such an expensive piece of equipment, but after a few successful attempts of putting it all back together I am getting more confident. This week was my first time ‘hacking the printer’ on my own. Even though the print quality was not as good as I would have liked (the print heads blocked up significantly), I learned an awful lot working by myself. Second time ‘hacking the printer’ on my own should give better results!

Introduction

First, a little bit of background on how I got to where I am..

I have been studying in UL for the past 6 years. I began my undergrad in Applied Physics in September 2013. I graduated in May 2017 and went straight into a taught masters (Biomedical Device Materials).

My favourite elements of both my undergrad and Masters were the research projects (both materials related – one was on printing a material for orthopaedics that would stimulate bone growth once grafted, the second was developing a material that bacteria could not adhere to). I enjoyed beginning a new project, immersing myself in all of this new information and slowly becoming familiar with this new area of science. I enjoyed the lab element also – running a multitude of tests and again, building up the knowledge of this relatively new field. It was quite satisfying to have built up a project and compile all of the project background, experimental data, results and conclusions in one neat document. This feeling of satisfaction and accomplishment is why I decided to pursue a PhD in material science. I am excited to start a new project, immerse myself in it fully and eventually become an expert in this field.

As I was coming to the end of the Masters I decided I would like to remain in research and I began looking for possible projects. During the material science masters I had done an assignment on an area of my own choice. I chose to write about ‘3D Printing in Medicine’. As part of this assignment, I learned the variety of areas that 3D printing can be used. I was surprised at the range of areas that 3D printing was already being applied to in medicine, such as anatomical models for planning surgeries, explaining procedures to patients, educating medical students, prototypes for medical devices, small medical devices, and of course, prosthesis.

I had decided that this (relatively) new and exciting area that I was now fascinated by was the area I wanted to study. I was shocked to find out that there was a research group in UL that had a multi-material 3D printer (it can place 2 materials at the same time, building components within other components). As a long shot, I emailed the head of the research group and asked if he had any material science related projects that I could get involved with. To my disbelief, he scheduled a meeting with me for the following week. I met up with the head of the research group and a second member of the group. I was given a tour of the lab and shown the printer and a variety of printed components – extremely exciting stuff! They had a project that they thought I would be a good fit for – suspending additives in the liquid 3D printing resin to change the properties of the final components. The property they were trying to enhance was radiopacity (making the component show up on x-rays, wheres the ordinary ink does not). I also felt that I was a good fit for this, given my background in physics and material science (along with my new found love for 3D printing). I was offered a research position working on this project for the summer. Needless to say, I accepted!

At the end of the summer, it was decided that we would apply for PhD funding for me to continue working with 3D printing and with the same research group (https://designfactors.ie/), but in a slightly different area. This time, instead of enhancing the radiopaque properties on the 3D printing ink, I would be making the printed components antimicrobial. Specifically, these antimicrobial components would be small accessories for PEG feeding tubes, specifically for children with Cystic Fibrosis. PEG tubes are supposed to be a short-term feeding solution, but often are left longer than this (if the child is too sick to go for surgery to replace the tube). This long-term use can result in degradation which leads to leaks/cracks in the PEG line. PEG feeding tubes are basically ideal incubators for micro-organisms (37 degrees Celsius, humid conditions) and are outside of the reach of the patient’s immune system, which increases risk of infection (which poses an extreme risk for patients with Cystic Fibrosis). The idea of a repair accessory/ device which is inherently anti-microbial was crafted to combat these two issues with PEG tubes.

I applied for funding from the Irish Research Council (under the Irish Research Council Enterprise Partnership Scheme) and this application was successful! Our enterprise partner is the National Children’s Research Centre – who have a high quality Cystic Fibrosis research team and have ongoing research in infection and immunity. I look forward to working alongside this partner.

So, we have been working on the radiopacity project since June (my summer internship was extended to Christmas, and then until the end of February). My PhD official start date was 1st March 2019, and I am now in between wrapping up the radiopacity project (hopefully publishing a paper on the key findings shortly) and kicking off the PhD project!