gms | German Medical Science

Objectives: Regeneration of articular cartilage is challenging, due to its unique anatomical architecture and composition its ideal biomechanics and cellular requirements. A chondro-inductive bioactive glass (BG) as a cell carrier (scaffold) could provide an opportunity to regenerate injured cartilage. The aim of this study was to increase the stability of a novel pure bioactive glass scaffolds tailored for cartilage (CAR12N) by solvent phase infiltration with the degradable polymer poly-L-lactic acid (PLLA) and to characterize the cell adherence to the composit and its effect on the chondrogenic phenotype of chondrocytes or chondrogenesis of human mesenchymal stromal cells (hMSCs).

Methods: Therefore, BG/PLLA composit scaffolds infiltrated one-, two- or threefold with PLLA were characterized with respect to polymer distribution, topology and stability in comparison to pure BG scaffolds. Cell adherence, proliferation, survival and expression of cartilage-specific extracellular matrix components as well as chondrogenic transcription factors were analyzed in composit and pure BG scaffold cultures with primary porcine articular chondrocytes (pACs) and primary hMSCs in a dynamic long-term culture (up to 35 days).

Results and conclusion: Light microscopic evaluations showed that comparing the distribution of PLLA between the scaffold levels (superior, middle, bottom-layer) revealed a certain inhomogenicity. As expected PLLA infiltration significantly reduced the overall porosity, but composits remained still highly porous after triple infiltration (porosity >70%). The topology did not significantly change (strut length/thickness, pore perimeter). PLLA infiltration increased the stiffness of the scaffolds. No scaffold variant was cytotoxic and no decrease in viability was detectable. In particular, PLLA improved the adherence as well as DNA and sulfated glycosaminoglycan (sGAG) contents of scaffolds colonized with hMSCs. The metabolic activity of both cell types on the four scaffold variants was stable over cultivation time of 35 days. Both cell types, in particular hMSCs, colonized not only the bioglass struts but also the PLLA and formed cell layers on the pore walls. Successful chondrogenesis of hMSC colonized scaffolds was demonstrated by immunoreactivity for collagen type II, cartilage proteoglycans and the transcription factor SOX9. BG and PLLA infiltrated scaffolds showed an increasing relative expression of cartilage related genes, including collagen type II, IX and XI, aggrecan, cartilage oligomeric matrix protein and the transcription factors SOX9 and FOXO1 not only on pAC but also on hMSC colonized scaffolds after 21 days compared to the 7 day cultivation time point.

Based on this novel data, BG/PLLA composit scaffolds may be used in the future for cartilage tissue engineering after a single infiltration with PLLA. The maintenance of the chondrogenic phenotype of chondrocytes as well as the initiation of chondrogenesis of hMSCs was demonstrated.