Optimization of Regeneration Conditions for Hyaline Articular Cartilage during Minced Cartilage Implantation – Characterization of an Innovative Hydrogel Matrix

Objectives: The aim of this study was the development of a novel hydrogel based approach for minced cartilage implantation and the in vitro characterization of the hydrogel as a carrier matrix. This matrix is intended to improve the regeneration conditions for hyaline articular cartilage and to resemble native articular cartilage in its tribological properties. Methods: In this ongoing study, human articular cartilage was obtained from femoral condyles that were resected during knee arthroplasty surgery in 15 patients (8 male, 7 female, age: 73.2 ± 8.6 years). Articular cartilage was harvested and minced with a scalpel under sterile conditions. Enzymatically and ionically cross-linked alginate-dialdehyde-gelatin (ADA-GEL), prepared at 37 °C under constant stirring was used as a hydrogel. Minced cartilage was added to the hydrogel matrix. From this, hydrogel minced cartilage scaffolds (HMC-scaffolds) with 10 mm diameter were produced and incubated in cell culture medium at 37 °C for 5 weeks. The degradation of the HMC-scaffolds was determined through weekly wet weight measurements. Gene expression of the HMC-scaffolds was performed with focus on mRNA expression level of collagen I (Col1), proteoglycan 4 (PRG 4), SOX 9, aggrecan, and cartilage oligomeric matrix protein (COMP). For tribological analysis, HMC-scaffolds with a cartilage content of 20 w/v%, 40 w/v%, and 80 w/v% were produced and their coefficient of friction was determined after seven days of incubation under a load of 10 N. Novocart®inject (Tetec, Reutlingen), which is used for autologous chondrocyte transplantation, served as a reference material. Statistical comparisons were performed using ANOVA and subsequent Bonferroni correction. Results: The degradation of the HMC-scaffolds was 6 % after two weeks (maximum) and 2 % after four weeks (minimum). Col1 expression was constant over the five weeks incubation period and significantly lower compared to Novocart®inject (P = 0.001). PRG4 showed an increase in mRNA expression over the incubation period from ∆ct = 483.3 ± 1027 (after one week) to 1729.0 ± 967.8 (after five weeks; P < 0.001). There was no difference compared to Novocart®inject. SOX9 (∆ct = 1275.5 ± 4747.5 after one week) and COMP (∆ct = 47.9 ± 111.8 after one week) showed no significant changes of mRNA levels over time and no difference compared to Novocart®inject. The mRNA expression of aggrecan (∆ct = 14.7 ± 26.4 after one week) was significantly lower (P < 0.001) compared to Novocart®inject (∆ct = 295 ± 409). The coefficient of friction of HMC-scaffolds was 0.18 ± 0.04 with 20 w/v% cartilage content, showing a significant reduction on 0.09 ± 0.02 (P < 0.001) for HMC-scaffolds with 40 w/v% and 80 w/v% cartilage content. This means that HMC-scaffolds with higher cartilage contents are within the range of native articular cartilage (0.074 ± 0.029; P > 0.05) and below Novocart®inject (0.34 ± 0.01; P < 0.001). Conclusion: Hydrogel minced cartilage scaffolds are stable in cell culture over a long period of time. Their gene expression for cartilage matrix proteins is at a comparable level to those of a clinical established matrix used for autologous chondrocyte transplantation and their tribological properties are comparable to native articular cartilage.