Adjacent tissues (cartilage, bone) affect the functional integration of engineered calf cartilage in vitro.

OBJECTIVE: An in vitro model was used to test the hypothesis that culture time and adjacent tissue structure and composition affected chondrogenesis and integrative repair in engineered cartilage. METHOD: Engineered constructs made of bovine calf chondrocytes and hyaluronan benzyl ester non-woven mesh were press-fitted into adjacent tissue rings made of articular cartilage (AC), devitalized bone (DB), or vital bone (VB) and cultured in rotating bioreactors for up to 8 weeks. Structure (light and electron microscopy), biomechanical properties (interfacial adhesive strength, construct compressive modulus), biochemical composition (construct glycosaminoglycans (GAG), collagen, and cells), and adjacent tissue diffusivity were assessed. RESULTS: Engineered constructs were comprised predominately of hyaline cartilage, and appeared either closely apposed to adjacent cartilage or functionally interdigitated with adjacent bone due to interfacial deposition of extracellular matrix. An increase in culture time significantly improved construct adhesive strength (P<0.001), modulus (P=0.02), GAG (P=0.04) and cellularity (P<0.001). The type of adjacent tissue significantly affected construct adhesion (P<0.001), modulus (P<0.001), GAG (P<0.001) and collagen (P<0.001). For constructs cultured in rings of cartilage, negative correlations were observed between ring GAG content (log transformed) and construct adhesion (R2=0.66, P<0.005), modulus (R2=0.49, P<0.05) and GAG (R2=0.44, P<0.05). Integrative repair was better for constructs cultured adjacent to bone than cartilage, in association with its solid architectural structure and high GAG content, and best for constructs cultured adjacent to DB, in association with its high diffusivity. CONCLUSIONS: Chondrogenesis and integrative repair in engineered cartilage improved with time and depended on adjacent tissue architecture, composition, and transport properties.

Surface protein characterization of human adipose tissue-derived stromal cells.

Human bone marrow stromal cells are a multipotent population of cells capable of differentiating into a number of mesodermal lineages as well as supporting hematopoeisis. Their distinct protein and gene expression phenotype is well characterized in the literature. Human adipose tissue presents an alternative source of multipotent stromal cells. In this study, we have defined the phenotype of the human adipose tissue-derived stromal cells in both the differentiated and undifferentiated states. Flow cytometry and immunohistochemistry show that human adipose tissue-derived stromal cells have a protein expression phenotype that is similar to that of human bone marrow stromal cells. Expressed proteins include CD9, CD10, CD13, CD29, CD34, CD44, CD 49(d), CD 49(e), CD54, CD55, CD59, CD105, CD106, CD146, and CD166. Expression of some of these proteins was further confirmed by PCR and immunoblot detection. Unlike human bone marrow-derived stromal cells, we did not detect the STRO-1 antigen on human adipose tissue-derived stromal cells. Cells cultured under adipogenic conditions uniquely expressed C/EBPalpha and PPARdelta, two transcriptional regulators of adipogenesis. Cells cultured under osteogenic conditions were more likely to be in the proliferative phases of the cell cycle based on flow cytometric analysis of PCNA and Ki67. The similarities between the phenotypes of human adipose tissue-derived and human bone marrow-derived stromal cells could have broad implications for human tissue engineering.

Walking versus breathing: mechanical differentiation of sea urchin podia corresponds to functional specialization.

The podia of sea urchins function in locomotion, adhesion, feeding, and respiration; but different podia on a single urchin are often specialized to one or more of these tasks. We examined the morphology and material properties of podia of the green sea urchin, Strongylocentrotus droebachiensis, to determine whether, despite apparent similarities, they achieve functional specialization along the oral-aboral axis through the differentiation of distinct mechanical properties. We found that oral podia, which are used primarily for locomotion and adhesion, are stronger and thicker than aboral podia, which are used primarily for capturing drift material and as a respiratory surface. The functional role of ambital podia is more ambiguous; however, they are longer and are extended at a lower strain rate than other podial types. They are also stronger and stiffer than aboral podia. In addition, all podia become stronger and stiffer when extended at faster strain rates, in some cases by nearly an order of magnitude for an order of magnitude change in strain rate. This strain-rate dependence implies that resistance to rapid loading such as that imposed by waves is high compared to resistance to slower, self-imposed loads. Thus, the serially arranged podia of S. droebachiensis are functionally specialized along an oral-aboral axis by differences in their morphology and mechanical properties.