Peek behind the paper: developing ‘cartridges’ for bioprinting tissues

In this exclusive interview for 3DMedNet, David Shreiber and Madison Godesky (both Rutgers University; NJ, USA) discuss the research behind the development of bioink ‘cartridges’ containing proteins, ligands and cells for the customized bioprinting of different tissues on demand.

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I am Dr. David Shreiber. I have been a faculty member in the Department of Biomedical Engineering at Rutgers, the State University of New Jersey (NJ, USA) since 2002 and I am now Chair of the department. 

I am Madison Godesky. I recently graduated from Rutgers with my PhD in biomedical engineering. I now work as a Scientific Liaison for L’Oréal (Clichy, France).

Could you please tell us about the project covered in the recent 3DMedNet news piece, as well as any other related projects you may currently be working on?

Our lab has generally focused on bioengineering applied to the nervous system. We study how the brain and spinal cord are injured during trauma and ways to protect, repair, or regenerate the tissue after injury, often with the help of biomaterials. Our biomaterials research has expanded into the bioink described in the Biointerphases paper and other bioinks, such as photoreactive collagen. 

When we started with this project, we did not intend or expect to delve into bioinks.

Our project emerged from collaborative research to engineer biocompatible, biodegradable grafts to enable regeneration of peripheral nerves. 

The graft comprised a tube made from woven, biodegradable polymer; a hydrogel filler with physical properties to encourage nerve regeneration; and small molecules and peptides that were bound to the filler that stimulated nerve regeneration. 

Our role was to develop the hydrogel filler including grafting the molecules. Originally, we used type-I collagen as the hydrogel filler. Early into the project, we discovered that the collagen was incompatible with the ‘tube’ for our purposes and began investigating the thiolated hyaluronic acid-polyethylene glycol diacrylate (HA-S/PEGDA) system.  

With these materials, two independent reactions drive gel formation and maturation. First, the acrylates on PEGDA rapidly react with the thiols on the HA-S to form an initial gel. Then, over time, the remaining thiols react with each other to strengthen and stiffen the gel.  

We realized that these two reactions could be exploited to independently control the stiffness of the gel and the type and number of binding sites or ligands that the gel presents to cells by essentially mixing these ‘inks’ in different ratios. 

These features are very important characteristics of natural tissue and bioengineered scaffolds that contribute to instruct cell behaviors such as differentiation of stem cells, migration of cells for wound healing, proliferation and matrix remodeling.  

In the Biointerphases paper, we demonstrate independent control of stiffness and ligand density and the resulting distinct behaviors of skin fibroblasts. We have a follow-up paper in the works that demonstrates the ‘printability’ of the materials.

How do you envision your work translating into the medical field?

Many tissues are heterogenous, and the heterogeneity is generally critical to the function of the tissue. 

Our bioinks may contribute to printing tissue with spatial control of different cells and ligands to recreate scaffolds for layered tissues, like skin and cartilage, or more complex ones, such as neural tissues and kidney. It can also have value in creating systems  that mimic natural tissue to study cell behavior and test therapeutics or other consumer products in vitro.

What challenges have you faced with developing your bioink and bioprinting technique?

One problem we had was that the second reaction that drives gel maturation takes a long time to go to completion – more than 2 weeks. This was certainly impractical for our research and was a significant flaw for a bioink. We recognized that the thiol-thiol reactions could be accelerated by introducing low concentrations of oxidizing agents, such as hydrogen peroxide or dimethyl sulfoxide. This allowed us to decrease the gel maturation time from weeks to a day or even hours. 

What challenges with current bioprinting techniques might your bioink and technique help to overcome?

Much like an inkjet printer can produce virtually any color by mixing cyan, yellow, magenta and black inks in different combinations, we envision a system where a bioprinter can produce a hydrogel scaffold with different combinations of gel stiffness, cell types, and active ligands to provide the cells with the right physical and adhesive cues to direct desired cell behaviors.

What’s next for you and your research? 

Our next goal is to identify a target tissue for bioprinting. 

We have our eye on retina – no pun intended – because of its layered structure and the need for a transparent material, which is a property of this bioink. 

Skin is another target tissue. Hyaluronic acid, which is the main component of our ink, is an increasingly popular component of cosmetic consumer products because it drives tissue hydration. 

As we mentioned, bioink development is not our laboratory’s primary focus. 

Sometimes approaching a problem from a different perspective can highlight new opportunities. 

However, to move this approach forward, we expect to work with 3D (bio)printing experts and we have already begun some collaborations at Rutgers. 

The opinions expressed in this feature are those of the interviewee/author and do not necessarily reflect the views of 3DMedNet or Future Science Group.

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