INTRODUCING CONTINUOUS MATERIAL GRADIENTS IN OSTEOCHONDRAL CONSTRUCTS VIA A NOVEL EXTRUSION-BASED 3D PRINT HEAD

Jun 28, 2022, 11:40 AM
10m
Room: S2

Room: S2

Speaker

Beeren, Ivo (Maastricht University)

Description

"Osteoarthritis, a degenerative disease of the cartilage and subchondral bone, is becoming more prevalent due to an aging world population. Although some clinical interventions are available, the solutions are often temporary due to fibrocartilage formation in the long term, which has mismatching mechanical properties. Tissue engineers have been designing osteochondral (OC) scaffolds to induce functional, sustainable regeneration of the articular cartilage. An important characteristic of the OC unit is the presence of continuous gradients such as biochemical or mechanical ones1. Additive manufacturing is preferably used to create porous fibrous architectures to host cells for tissue engineering. To introduce continuous property gradients in these scaffolds, it seems straightforward to continuously extrude an incremental ratio of two biomaterials during the printing process. Although successfully extruded continuous gradients have been achieved with hydrogels2, it remains challenging for solid polymers. Therefore, solid constructs often contain discontinuous gradients with ‘hard’ interfaces, prone to delamination, and moreover a lower degree of biomimicry3. Thus, we aim to design a construct with a continuous material gradient containing specifically addressable groups on the surface to anchor differentiation-inducing peptides. We finally want to create a peptide gradient to gradually direct human mesenchymal stromal cell (hMSC) differentiation, from a chondrogenic towards an osteogenic phenotype, across a construct.
To this end, we synthesized poly(caprolactone) with terminal azide and maleimide groups, which we mixed in a continuous fashion via an in-house developed printhead4. We visualized the continuous material gradient in our constructs with a dye and show control over the gradient distribution. Additionally, mechanical analysis showed that, when comparing a discrete and a continuous gradient, the brittleness of our PCLA is lost in the continuously extruded scaffolds. Furthermore, we successfully modified the surface by reacting complementary dyes on the surface with a density in the 102 pmol/cm2 regime. After a three week cell differentiation study, we observed a strong effect of the differentiation media on hMSC fate. Interestingly, in basic media with our chondrogenic peptide, we observed enhanced (hypertrophic) chondrogenic differentiation in absence of the differentiation factors. Finally, our materials showed good biocompatibility, without severe toxic effects, and abundant tissue regeneration in a subcutaneous rat model.
Overall, we have successfully manufactured a construct with a continuous material gradient via an extrusion-based approach using an in-house developed printhead. Moreover, the continuous gradient construct has more resilient mechanical properties and a modifiable surface, making this fabrication method also interesting for applications beyond OC ones. Our hMSC differentiation study shows promise to influence cell fate in the basic media, but further investigation on the active parameters to achieve larger cell fate differences is required, before moving towards gradual differentiation.

  1. Ansari, S. et al., Acta Biomater. 87, 41–54 (2019)
  2. Idaszek, J. et al., Biofabrication 11, 1–8 (2019)
  3. Lorenzo-Moldero, I. et al., Biofabrication 8, 1–12 (2016)
  4. Sinha, R. et al., Nat. Commun. 12, 1–14 (2021)"

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