3D Printed Porous Tissue Engineering Scaffolds with the Self-folding Ability and Controlled Release of Growth Factor

Abstract

Scaffold-based tissue engineering is a major approach in tissue engineering and cells and/or biomolecules can be loaded into the matrix or onto the surface of 3D scaffolds for enhancing tissue regeneration. Scaffolds mimicking the natural extracellular matrix of human tissues can serve very well as a substrate for cell attachment, proliferation, and differentiation and thus facilitate new tissue formation in vivo. The architectures (pore size, shape, interconnectivity, porosity, etc.) and properties (biological and mechanical) of scaffolds should be carefully controlled to match the defect shape and size and features of the target tissue. 3D printing technologies enable us to fabricate porous scaffolds with accurate control over their architectures and properties. On the other hand, 3D printing of shape morphing polymers has attracted great attentions in tissue engineering as scaffolds with shape morphing ability can reshape themselves after implantation to match the defect and anatomy of host tissues. Biomolecules such as growth factors have been often used in tissue engineering to accelerate tissue regeneration; and vascular endothelial growth factors (VEGF) is used in the regeneration of gastrointestinal tract and vasculature. In this study, an extrusion-based 3D printing system was used to construct porous scaffolds which have abilities of self-folding upon heating to the body temperature and controlled release of VEGF. For 3D printed scaffolds, the self-folding ability was achieved by using a shape memory polymer poly(D, L-lactide-co-trimethylene carbonate) (PDLLA-TMC) which could change shape at a temperature greater than 37°C, while the controlled release of growth factor was achieved by using gelatin methacrylate (GelMA) as the functional layer to load VEGF. In scaffold fabrication, a planar porous structure was firstly fabricated by accurate deposition of viscous PDLLA-TMC solution. The permanent tubular shape of PDLLA-TMC was made by folding printed planar porous structure into a tube on a glass stick at 80°C. Then PDLLA-TMC tubular porous structure was flattened at 25°C. Finally, GelMA loaded with VEGF was printed onto the PDLLA-TMC planar porous scaffold layer and crosslinked by UV. Shape morphing of PDLLA-TMC/GelMA-VEGF scaffolds was studied by immersing scaffolds in water at 37°C. Planar porous scaffolds could fold automatically into tubes within 60s. SEM examinations showed that interconnected macropores were regularly arranged on the scaffolds. In vitro release tests revealed a sustained and steady release of VEGF in the 21 day tests. For rat mesenchymal stem cells (rMSCs) seeded on scaffolds, LIVE/DEAD assay results indicated very good cell viability. MTT assay results showed good cell proliferation after 1, 4, 7-day culture. This study has demonstrated a good strategy to develop unique scaffolds for tubular tissues or organs such as vasculature and gastrointestinal tract.