In September, Vitro3D was named as one of five Formnext Start-Up Award winners, with the company recognised for the potential of its Volumetric Additive Manufacturing (VAM) technology.
This technology was initially developed at the University of Colorado Boulder in a bid to solve a number of challenges involved in photopolymer 3D printing. With the company raising 1.3 million USD in seed funding last year, it is targeting commercialisation by 2025.
Recently, TCT Group Content Manager Sam Davies sat down with Vitro3D CEO Camila Uzcategui, PhD, as part of an as yet unreleased Additive Insight podcast episode to learn more.
Vitro3D often talks about addressing the limitations of photopolymer 3D printing. What are those limitations and what has been the key to addressing them?
CU: So, by the time that I graduated [from University of Colorado Boulder], and I joined the [Bob] McCleod Lab as a postdoc, we were starting to pivot from digital light production and stereolithography, to really seeing what volumetric additive manufacturing could do in these complex parts and new application spaces. And when we started to do that, we realised that volumetric additive manufacturing could solve some of the biggest challenges when we start to think about photopolymer additive manufacturing, such as the lack of ability to go into really high viscous materials, the fact that you need support structures, in many cases, in order to print these complex parts, and also just the speed of the process. When I was early in my PhD, 3D printing scaffolds for surgeries that we were implanting in some animal models, I was spending 20 to 30 minutes to print one 5 x 5 x 2 mm part. And then [when] I started working on this technology when I was doing volumetric work, we could print something of a similar size in just a few seconds.
So, can you tell us as much as you can about the Volumetric Additive Manufacturing technology?
CU: The best way that I can describe our volumetric additive manufacturing technology is through the idea of a CAT scan. So, [with a CAT scan] you go into a machine, that machine has a circular structure around you and it's taking pictures from a bunch of different angles through some sort of light source. What that does is it takes pictures at these different angles, and then it uses a computational algorithm to then take those pictures and add them all up to create a three dimensional virtual image. So, that is how we get the CAT scan results and have a 3D virtual image of what's going on inside of the body. The principles of the particular volumetric additive manufacturing technology that we work on is an inverse CAT scan. So, rather than taking a picture from a bunch of different angles of a 3D volume, what we do is we take a 3D virtual object, and we deconstruct it into all the different angles that make up that part.
We say that the magic is in the software, because we don't use just a standard slicer to slice a three dimensional virtual object into its two dimensional constituents slices, we have to go through a very robust algorithm that takes this three dimensional virtual object, deconstruct it into these different angles, and then allows us to use this algorithm to then incorporate the properties of the material itself, and then project a two dimensional image for each angle into the volume of a photopolymerisable resin. And then, as those intensities overlap where they're highest, those are the only regions that are going to go from liquid to solid and go through that photo polymerisation.
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I understand that one of the key elements to Vitro3D’s VAM technology is the speed. So, how has Vitro3D been able to facilitate rapid printing while preserving accuracy and resolution?
CU: One of the aspects that makes volumetric 3D printing or volumetric additive manufacturing so magical is our ability to materialise something all at the same time. So, because the process works by getting to a certain energy dose, that critical energy dose is what actually allows us to go from liquid to solid; in photopolymerisation, we're able to materialise the entire part all at once, rather than in this layer by layer process. So, that makes it not only much, much faster, but it gives us new capabilities, such as printing around existing objects, as well as printing a first part and then printing around that first part in a secondary process through this volumetric additive manufacturing over moulding and over printing capability.
Can you tell me about the light or the heat source you're using in this process? What is different about that heat source than, say, a conventional photopolymer printing technology, if anything?
CU: Yeah, so the main difference in our case is that rather than wanting to photopolymerise a small layer of material, which is usually how layer by layer 3D printing methods work in the photopolymer space, we're instead wanting to get as much light through the volume of our resin as we possibly can. So, what that means is that we want our light that is on the sample plane to be as collimated as possible, meaning that it's not changing very significantly through the volume of light. So, what that means is that we have to use very ingenious optical designs to ensure that we understand where the focus is of our two dimensional projection and ensuring that our depth of focus is as large as it can possibly be.
What kind of processes are required in the post-processing stage to then get the part to its final stage?
CU: So, very similar to every other photopolymer based 3D printing method, we use a solvent wash, and then we do a light based post cure. In our case, what we find as particularly interesting is that because we don't require the use of support structures, and we're printing directly into a volume, what we can do is we can automate the post processing steps. So, rather than having to take your part out of a printer, put it into solvent wash, and then take it from there and put it into a post curing oven, we can actually do the entire process inside of our proprietary cartridges, where we can 3D print the structure inside of the cartridge, and then without ever touching it, we should be able to get rid of that unreacted resin swab in a solvent wash and then right in there able to also do a light based post cure.
The reason why light based post cure in our system works so well is because of the nature of the volumetric method. We don't need to use photoabsorbers. So, our lack of photoabsorbers make our post-cure photopolymerisation step really efficient because we don't worry about something that we call in the industry the candy shell effect. So, if you're 3D printing a layer by layer part, and you're only putting it through a photo based post curing step, then because of all the photoabsorber that's in that part, you're really only going to get cure at the edges of that part, which kind of turns into this candy shell, in essence, where the outside of the part is very stiff, but the inside of the parts still may be very green or very soft. So, that's when a lot of heat post processing steps come into play for different chemistries, or even for standard chemistries. But in our case, we can actually get that post cure with light to be very efficient because of our lack of photoabsorbers.
And then, in terms of materials, what kind of materials are you able to process currently?
CU: Yeah, so we're able to process a lot of different materials very similar to every other photopolymerisation additive technology. The main limitation for us is transparency. So because we are working in a volumetric method, we want to ensure that that light is able to get through the volume as much as possible. So we just always need to ensure that our material is transparent to the wavelengths that we're using. Otherwise, we've used a very broad host of materials going from very soft materials, like hydrogels, all the way to really stiff materials like urethane matrices with a secondary material for optical applications. So, what's really awesome about the technology is that not only can you sweep this range of viscosities, but it allows us to access new applications that you just can't access with other photopolymer additive manufacturing technologies due to the viscosity constraints.
