Melt electrospinning writing: polymer fibers for tissue engineering

Interview with Prof. Paul Dalton, Department for functional materials in medicine and dentistry, University of Würzburg

Sometimes, soft tissue in our body needs to be replaced after surgery or an injury. But surgeons are not always able to take tissue from other body parts as a replacement. Then, they need to use implants. The production of soft implants that can constantly endure load and stress like our own tissue is a big challenge for research. Melt electrospinning writing can be a solution.

02/01/2016

Photo: Prof. Paul Dalton

Prof. Paul Dalton; © private

In the Interview with MEDICA-tradefair.com, Prof. Paul Dalton talks about melt electrospinning writing, how two soft components make a tough composite for cartilage replacement and how implants could be produced directly in the hospitals of the future.

Prof. Dalton, what exactly is melt electrospinning writing?

Prof. Paul Dalton: In this process, we use electric fields to pull out very small fibers from a polymer melt. These fibers cool down and we can literally “write” with them, meaning we are able to draw structures with them onto a target. This can be a flat or tubular surface. We are also looking into “free-form writing”, meaning writing on a non-ideal surface with a complex shape.

Melt electrospinning writing is a 3D printing technology that specializes in very small fibers. The smallest diameters that we work with are 200 nm and we can go up to 200 µm in size. The most common form of 3D printing is fused deposition modeling, FDM. You are only able to reach minimum sizes of about 50 µm with it. This is a size limit for 3D printing that we are able to beat with melt electrospinning writing.

Photo: Printer head over a glass sheet

Using electrical fields, polymer fibers are drawn onto a target object in melt electrospinning writing with this printer; ©Paul Dalton

What is the difference between melt electrospinning writing and solution electrospinning?

Dalton: Both techniques belong to the field of electrospinning. 99 percent of all research done in this field is about solution electrospinning, the other 1 percent is melt electrospinning. For solution electrospinning, you dissolve a polymer into a solvent before you spin it. But you do not have any control about where the fibers go exactly. In melt electrospinning writing we use heat to melt polymers that flow. And we can choose the location of a fiber with a deviation of about 2 µm. In solution electrospinning you only have control in the centimeter range.

The other difference concerns the use in medical products, of course. Solvents are usually volatile and have a certain amount of toxicity. So, it is a real advantage if you do not need to worry about them being in the product and affecting cells.

Photo: REM picture of stacked fibers

These boxes with a width of 250µm have been produced with melt electrospinning writing; ©Almoataz Youssef

You are not only working with polymers, but also with hydrogels. What role do they play?

Dalton: Last year, we have produced a fiber-hydrogel composite. The remarkable thing about this composite is that it is very strong, while both components individually are quite weak. We added 7 percent of polymer fibers to the hydrogel and achieved a 54-fold increase in the mechanical strength of the gel. This is due to the order and the placement that we put the fibers into.

The idea behind this is to produce a replacement for cartilage in the knees and shoulders. The hydrogel itself is a weak component, but a good environment for cells. The gel is able to provide them with nutrients. As a composite with the polymer fibers it is also able to endure high mechanical load, just like normal cartilage. This composite may be a way to condition cells for cartilage repair and replacement.

Photo: Transparent tissue scaffold against the light

Tissue scaffold made from hydrogel and polymer fibers; ©Paul Dalton

How would you outline a possible future application of melt electrospinning writing and the materials you are able to produce with it for the purposes of tissue engineering?

Dalton: When you make very small fibers, they are very soft and flexible. You could compare a glass rod that breaks when you bend it to an optic fiber that you can bend quite easily and put a knot into. So, this technology is really good for anything which is soft and flexible, like skin, heart patches or the regeneration of peripheral nerves. We are also looking into an artificial ligament that would be implanted into the knee. None of these implants would contain cells but rather encourage them to grow into the material until the body has fully incorporated the implant.

A rather futuristic application of this technology would be printing directly in the hospital. We could customize implants for patients who undergo surgery, maybe even during surgery. There are already hospitals with facilities for 3D printing but they are rather used for the purposes of surgical planning. However, I do not think it will be unbelievable to print and customize implants directly in the hospital in ten years.

Speaking of future applications, how far has this process already been developed?

Dalton: The biggest challenge probably is to increase the manufacturing output: Of course, we would like to manufacture our implants faster. We just received an industry grant from the German Federation of Industrial Research Associations (AiF, Arbeitsgemeinschaft industrieller Forschungsvereinigungen "Otto von Guericke" e.V.) to scale up the process.

Regarding regulations, there is a Singaporean company, Osteopore, who make tissue scaffolds using FDM to repair non-load-bearing bone defects. These scaffolds are already FDA-approved and I see melt electrospinning writing following a similar regulatory path to bring our implants into clinical trials. Before we can enter these, we have to prove that our implants provide an added benefit compared to the status quo in tissue engineering. This is initially done in small animal studies that we still need to conduct.

Photo: Timo Roth; Copyright: B. Frommann

© B. Frommann

The interview was conducted by Timo Roth and translated from German by Elena O'Meara.
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