gms | German Medical Science

Objectives: In recent years, cell encapsulation has gained growing attention in cartilage tissue engineering (TE) as it offers the possibility of developing vital 3D tissue analogues. Therefore, the search for suitable hydrogels mimicking the natural extracellular matrix (ECM) as a treatment option for cartilage defects is a key issue in TE. ADA-GEL, a novel hydrogel based on oxidized alginate covalently cross-linked with porcine gelatin, was examined regarding its biocompatibility, bioactive properties as well as suitability as cartilage replacement.

Methods: ADA-GEL hydrogel was prepared by thouroughly mixing of various concentrations 5-7.5 % (w/v) ADA solution with 5-7.5 % (w/v) aqueous solution of gelatine under constant stirring at 37°C. 2 mm diameter beads were generated by extrusion through a pipette under constant pressure. Cross-linking was performed in 100 mM CaCl2 (pH of 7.4) for 10 min. Within this study, prior to mixing with gelatine, ADA solution was laden with human nasal (hNC) or articular (hAC) chondrocytes. The initial cell density was 2x10⁶ and 4x10⁶ cells mL-1. Cell laden beads were cultured for up to 14 days. Cytotoxicity, cell viability, chondrogenic phenotype and neo-synthesis of cartilage-specific components was examined on protein level.

Results and conclusion: The biologically active ADA-Gel beads facilitated the production of cell-laden implants with a high cell density and a homogenous cell distribution. The composition and porosity of the hydrogel constructs provided an optimal nutrition and oxygen supply of the embedded cells. No difference in cell viability and shape was detected between the initial loading densities 2x10⁶ and 4x10⁶ cells mL-1. The round shaped chondrogenic phenotype of the encapsulated cells was maintained in long-term 3D culture. ADA-GEL hydrogels exhibited no cytotoxic effects on used indicator L929 cells. All beads exhibited shape and size stability during 3D long-term culture. Immunohistochemical and biochemical analyses revealed that ADA-GEL hydrogels supports redifferentiation and chondrogenesis of embedded chondrogenic cells. Cells were able to synthesize collagen type II as well as cartilage-specific proteoglycans.

In this study we demonstrated that the non-cytotoxic ADA-GEL hydrogels provide a biologically relevant micro-environment promoting chondrogenic redifferentiation while offering excellent bioactive properties at the same time. These characteristics make ADA-GEL hydrogels a promising tool for 3D printing of patient-individual cartilage defect reconstruction.