Bioprinting of Zonal Cartilage Scaffolds Using Different Cell Densities

Abstract

The use of allografts for the treatment of critical size cartilage defects holds disadvantages including the limited number of donors and the compromised chondrocyte viability. These limitations have prompted researchers to explore different options, such as cartilage engineering. Bioprinting, a promising tissue engineering technique, could be used to fabricate biomimetic constructs that can potentially replace allografts. The present study explores the generation of a biomimetic chondrocyte density gradient in full-thickness bioprinted Alginate/NFC scaffolds with a PCL framework and investigates the effect of this zonal distribution of cells on the production of cartilage matrix within the scaffolds. To this end, two types of scaffolds were bioprinted; one with a graded three-zone distribution of cells (bottom zone: 5×106 cells/ml, middle zone: 10×106 cells/ml, top zone: 20×106 cells/ml), and another with a homogeneous cell density (10×106 cells/ml) and cultured for 25 days. Furthermore, the mechanical properties of the multi-material scaffolds were evaluated. The results showed that a three-zone cell density gradient could be achieved using extrusion-based bioprinting. The gradient was maintained for 25 days in scaffolds cultured in non-chondrogenic media (absence of ascorbic acid) but was transformed into a two-zone gradient within the first 14 days, in cultures with chondrogenic media (presence of ascorbic acid in the medium), and maintained as such until the end of the experiment. The zonal distribution of cells led to a zonal distribution of sGAGs, after 14 days of culture, with the sGAGs deposition being increased in the areas of high cell density. However, there was no significant Collagen deposition within the scaffolds at any time point during the experiment. This study attempts to shed light into one of the gradients of the native cartilage tissue (cell density gradient), with the hope of contributing to the development of a biomimetic fully functional engineered cartilage scaffold in the future.