Scaffold-free approach produces neocartilage tissue of similar quality as the use of HyStem™ and Hydromatrix™ scaffolds.

Numerous biomaterials are being considered for cartilage tissue engineering, while scaffold-free systems have also been introduced. Thus, it is important to know do the scaffolds improve the formation of manufactured neocartilages. This study compares scaffold-free cultures to two scaffold-containing ones. Six million bovine primary chondrocytes were embedded in HyStem™ or HydroMatrix™ scaffolds, or suspended in scaffold-free chondrocyte culture medium, and then loaded into agarose gel supported culture well pockets. Neocartilages were grown in the presence of hypertonic high glucose DMEM medium for up to 6 weeks. By the end of culture periods, the formed tissues were analyzed by histological staining for proteoglycans (PGs) and type II collagen, gene expression measurements of aggrecan, Sox9, procollagen α1(II), and procollagen α2(I) were performed using quantitative RT-PCR, and analyses of PG contents and structure were conducted by spectrophotometric and agarose gel electrophoretic methods. Histological stainings showed that the PGs and type II collagen were abundantly present in both the scaffold-free and the scaffold-containing tissues. The PG content gradually increased following the culture period. However, the mRNA expression levels of the cartilage-specific genes of aggrecan, procollagen α1(II) and Sox9 gradually decreased following culture period, while procollagen α2(I) levels increased. After 6-week-cultivations, the PG concentrations in neocartilage tissues manufactured with HyStem™ or HydroMatrix™ scaffolds, and in scaffold-free agarose gel-supported cell cultures, were similar to native cartilage. No obvious benefits could be seen on the extracellular matrix assembly in HyStem™ or HydroMatrix™ scaffolds cultures.

Effects of Articular Cartilage Constituents on Phosphotungstic Acid Enhanced Micro-Computed Tomography.

Contrast-enhanced micro-computed tomography (CEµCT) with phosphotungstic acid (PTA) has shown potential for detecting collagen distribution of articular cartilage. However, the selectivity of the PTA staining to articular cartilage constituents remains to be elucidated. The aim of this study was to investigate the dependence of PTA for the collagen content in bovine articular cartilage. Adjacent bovine articular cartilage samples were treated with chondroitinase ABC and collagenase to degrade the proteoglycan and the collagen constituents in articular cartilage, respectively. Enzymatically degraded samples were compared to the untreated samples using CEµCT and reference methods, such as Fourier-transform infrared imaging. Decrease in the X-ray attenuation of PTA in articular cartilage and collagen content was observed in cartilage depth of 0-13% and deeper in tissue after collagen degradation. Increase in the X-ray attenuation of PTA was observed in the cartilage depth of 13-39% after proteoglycan degradation. The X-ray attenuation of PTA-labelled articular cartilage in CEµCT is associated mainly with collagen content but the proteoglycans have a minor effect on the X-ray attenuation of the PTA-labelled articular cartilage. In conclusion, the PTA labeling provides a feasible CEµCT method for 3D characterization of articular cartilage.

Cationic Contrast Agent Diffusion Differs Between Cartilage and Meniscus.

Contrast enhanced computed tomography (CECT) is a non-destructive imaging technique used for the assessment of composition and structure of articular cartilage and meniscus. Due to structural and compositional differences between these tissues, diffusion and distribution of contrast agents may differ in cartilage and meniscus. The aim of this study is to determine the diffusion kinematics of a novel iodine based cationic contrast agent (CA(2+)) in cartilage and meniscus. Cylindrical cartilage and meniscus samples (d = 6 mm, h ≈ 2 mm) were harvested from healthy bovine knee joints (n = 10), immersed in isotonic cationic contrast agent (20 mgI/mL), and imaged using a micro-CT scanner at 26 time points up to 48 h. Subsequently, normalized X-ray attenuation and contrast agent diffusion flux, as well as water, collagen and proteoglycan (PG) contents in the tissues were determined. The contrast agent distributions within cartilage and meniscus were different. In addition, the normalized attenuation and diffusion flux were higher (p < 0.05) in cartilage. Based on these results, diffusion kinematics vary between cartilage and meniscus. These tissue specific variations can affect the interpretation of CECT images and should be considered when cartilage and meniscus are assessed simultaneously.

Chondrocyte behavior on nanostructured micropillar polypropylene and polystyrene surfaces.

This study was aimed to investigate whether patterned polypropylene (PP) or polystyrene (PS) could enhance the chondrocytes' extracellular matrix (ECM) production and phenotype maintenance. Bovine primary chondrocytes were cultured on smooth PP and PS, as well as on nanostructured micropillar PP (patterned PP) and PS (patterned PS) for 2 weeks. Subsequently, the samples were collected for fluorescein diacetate-based cell viability tests, for immunocytochemical assays of types I and II collagen, actin and vinculin, for scanning electronic microscopic analysis of cell morphology and distribution, and for gene expression assays of Sox9, aggrecan, procollagen α1(II), procollagen α1(X), and procollagen α2(I) using quantitative RT-PCR assays. After two weeks of culture, the bovine primary chondrocytes had attached on both patterned PP and PS, while practically no adhesion was observed on smooth PP. However, the best adhesion of the cells was on smooth PS. The cells, which attached on patterned PP and PS surfaces synthesized types I and II collagen. The chondrocytes' morphology was extended, and an abundant ECM network formed around the attached chondrocytes on both patterned PP and PS. Upon passaging, no significant differences on the chondrocyte-specific gene expression were observed, although the highest expression level of aggrecan was observed on the patterned PS in passage 1 chondrocytes, and the expression level of procollagen α1(II) appeared to decrease in passaged chondrocytes. However, the expressions of procollagen α2(I) were increased in all passaged cell cultures. In conclusion, the bovine primary chondrocytes could be grown on patterned PS and PP surfaces, and they produced extracellular matrix network around the adhered cells. However, neither the patterned PS nor PP could prevent the dedifferentiation of chondrocytes.

Hypertonic conditions enhance cartilage formation in scaffold-free primary chondrocyte cultures.

The potential of hypertonic conditions at in vivo levels to promote cartilage extracellular matrix accumulation in scaffold-free primary chondrocyte cultures was investigated. Six million bovine primary chondrocytes were cultured in transwell inserts in low glucose (LG), high glucose (HG), or hypertonic high glucose (HHG) DMEM supplemented with fetal bovine serum, antibiotics, and ascorbate under 5 % or 20 % O2 tension with and without transforming growth factor (TGF)-ß3 for 6 weeks. Samples were collected for histological staining of proteoglycans (PGs) and type II collagen, analysis by quantitative reverse transcription plus the polymerase chain reaction (RT-PCR) of mRNA expression of aggrecan and procollagen α1 (II) and of Sox9 and procollagen α2 (I), and quantitation of PGs and PG separation in agarose gels. Cartilage tissues produced at 20 % O2 tension were larger than those formed at 5 % O2 tension. Compared with LG, the tissues grew to larger sizes in HG or HHG medium. Histological staining showed the strongest PG and type II collagen staining in cartilage generated in HG or HHG medium at 20 % O2 tension. Quantitative RT-PCR results indicated significantly higher expression of procollagen α1 (II) mRNA in cartilage generated in HHG medium at 20 % O2 tension compared with that in the other samples. TGF-ß3 supplements in the culture medium provided no advantage for cartilage formation. Thus, HHG medium used at 20 % O2 tension is the most beneficial combination of the tested culture conditions for scaffold-free cartilage production in vitro and should improve cell culture for research into cartilage repair or tissue engineering.

Five percent oxygen tension is not beneficial for neocartilage formation in scaffold-free cell cultures.

We have investigated whether 5% oxygen tension (O(2)) is beneficial for neocartilage formation when chondrocytes are cultured in transwell-COL inserts. Six million bovine primary chondrocytes were cultured in an insert with DMEM supplemented with 10% fetal bovine serum and antibiotics, with or without glucosamine sulphate (GS) in a 5% or 20% O(2) environment for 2, 4, or 6 weeks. The samples were collected for the histological staining of proteoglycans (PGs) and type II collagen, quantitative reverse transcription with the polymerase chain reaction (RT-PCR) analyses of the mRNA expression of aggrecan and procollagen α(1)(II), procollagen α(2)(I) and hyaluronan synthase 2, quantitation of PGs, and agarose gel electrophoresis. Neocartilage produced at 20% O(2) appeared larger than that at 5% O(2). Histological staining showed that more PGs and type II collagen and better native cartilage structure were produced at 20% than at 5% O(2). The thickness of neocartilage increased during the culture period. Quantitative RT-PCR showed that the procollagen α(1)(II) mRNA expression level was significantly higher at 20% than at 5% O(2). However, no significant difference in gene expression and PG content was found between control and GS-treated cultures at either 20% or 5% O(2). Thus, in contrast to monolayer cultures, engineered cartilage from scaffold-free cultured chondrocytes at 20% O(2) produced better extracellular matrix (ECM) than that at 5% O(2). PGs were mainly large. Exogenous GS was not beneficial for the ECM in scaffold-free chondrocyte cultures.