Cotton-like glass fibres, bone defect, and 3D-printing – an interview with J.M.F. Ferreira [PART 2/2]

Do you remember the first part of the interview with José Maria da Fonte Ferreira? If you liked it, we have the second and the last part for you today. So… let’s cut to the chase and get back to answering the question we posed 2 weeks ago…

CLICK HERE TO READ THE FIRST PART OF THE INTERVIEW

But what kind of single additive? What was it?

It was exactly sodium carboxymethyl cellulose (CMC) of high molecular weight. It’s, let's say, a long polymeric chain with a few functional groups, which dissociate, releasing a few ions of sodium to the solution. The functional groups become negatively charged and might be slightly adsorbed at the surface of the particles through small segments, extending laces and tails to the solution, while the entanglement of the long chains thickens the liquid media, increasing the viscosity of the system. So, when we load the CMC solution with particles, we have a double thickening effect, one due to the entanglement of the long polymeric chains, and the other due to the increasing charge of solids. We reach a solid volume fraction of 45% vol., which is much higher than we attempt before using other dispersing agents, hardly achieving much above 30% vol. So, using CMC we went up to 45% vol. Thanks to that, the elastic properties of the paste were good enough to allow extruding the filaments and keeping their shape.

(Dear readers, we’re still referring to the poor processing ability of the Bioglassò 45S5, namely by robocasting.)

Using CMC as a single and multifunctional processing additive, we got a paste-like system that could be put into syringes. The syringes were then squeezed by the robocasting machine and the extruded filaments could be deposited to build scaffolds by 3D printing.

Okay. But how did you come up with carboxymethyl? That it can make it solid?

Being an organic additive, the polymeric additive will be burned off during the sintering step. If CMC is burned slowly there will not be leftovers of it. Only bioglass will remain there.

But are there other possible options? Let's say other alternative polymers?

Yes! Other interesting copolymeric systems can be used with similar purposes. They consist of hydrophobic and hydrophilic segments, the interactions of which are strongly dependent on temperature, changing from a liquid-like to a solid-like flow behaviour.

So, can I ask a question about the cotton-like fibres, cotton-like glass, right? That's the thing that you are developing here, right?

Right! This is what we intend to develop here with professor Buczyński. Imagine cotton fibres, flexible and soft. This is the kind of texture we are interested to develop from our bioactive glasses in the frame of this project.

But it’s not the thing you’re working on along with Sygnis company?

No, no. What we intend to do with Sygnis, is to undertake discussions and preliminary experiments towards guiding them to set a 3D printing equipment aiming at extruding, in a near future, our bioactive glasses directly from the glass melts. It’s another more challenging and straightforward way for producing bioactive scaffolds.

As you’re showing me this extrude, I would like to make a remark that it reminds me of my trip to Murano, Italy, where I saw how they made sculptures out of glass. That’s exactly what you do when working with glass?

Well, these guys at Murano also take profit from the flow properties of the glass melts to build their sculptures, using a traditional approach from which we can learn. But for our particular purpose, the glass compositions will be melted in an adapted crucible, a container with a hole at the bottom, through which a glass drop comes out and is then stretched by mechanical and centrifugal forces to acquire the desired fibrous structure.

Yes, and later it becomes solid. But how quickly?

All of this is very complex and needs to be kept under strict control, including the environmental temperature of the melt and around the tip from where the glass flows, the temperature gradient, and the cooling rate, etc.. A set of processing parameters needs to be kept under specific and very well controlled conditions.

And it must be extremely hot, right?

Yeah. We might be talking about 800-900 oC. There is the temperature range we are looking for. It means that the temperature range should be strictly controlled and should be checked quickly, and even some pressure over the glass probably will be necessary to force the flow to come out.

The idea is to deposit the glass filaments and enable them to cool without undergoing crystallization. This is important for the filaments do not stick to each other, because during cooling, there is some shrinkage and sticking to each other will lead to mechanical stresses and loss of flexibility.

And it can break.

Yes, especially if there is a drastic thermal shock, it’ll break. If you deposit something fluid over something that is already hardened, it means that the shrinkage of what you are just depositing will be higher because the other remaining part has already shrunk and strengthened something. It means exactly that temperature of this environment should be kept under control to prevent, let's say, mechanical stresses, to develop above a certain level that put in danger the integrity of the produced fibres.

Okay, so let’s get back to cotton-like glass fibres. There is a step aiming at the development of a device for producing this kind of cotton-like fibres, but you also say: “glass wool”.

Glass wool is used to thermally isolate houses. We want a structure similar to that of this glass wool, but made of our bioactive glasses. Not for isolating but for fulfilling bone defects. Large bone defects can be originated, for example, when cancer tumours are removed from the bones and we want to fulfil that part. Scaffolds and cotton-like fibres could be used for this purpose.

When there is, let's say, an accident and one might lose part of a broken bone, which also needs to be regenerated. There are many situations that justify the use of regenerative materials to help healing bone defects.

Great idea! I have a question about Portugal. What could you recommend to see, where would you go on a holiday in Portugal?

Portugal has many different landscapes when one moves from the North to South, or from the littoral towards the interior parts. We have extensive sandy beaches and beautiful mountains to see, depending on what you most appreciate.

I like the mixture, this combination when there is a lake or sea and mountains, everything. I want everything, I want it all (laugh).

I think in that case, if you visit the North, near Braga, for example, there is a national park where you can find amazing things: waterfalls. It’s wonderful. And when it comes to beach, you have a long coast. From the North to the South, you can just select what you prefer in terms of beach. The South is warmer and might be preferred for sea lovers. Let's say, Algarve contacts with the Mediterranean Sea, so the water is warmer there.

Have you already tried the Baltic Sea? Because it's so cold.

No, never.

So, do you like Poland?

Yes, especially this time. I don't like much winter time. It's too cold for me.

And how do you find Warsaw?

I like it pretty much, especially the ancient part of the city.

I thank you very much for talking with me.

#bagbone #polonezbis NCN National Science Centre

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