Perfusion bioreactor studies of chondrocyte growth in alginate-chitosan capsules.

The combination of progenitor cells, cell-friendly scaffold, and a three-dimensional culture system has been investigated for the culture of cartilage tissue. We have assessed chondrogenesis of alginate-chitosan-encapsulated STRO-1-isolated human mesenchymal progenitor cells. In addition, ATDC-5 cells and human articular chondrocytes were also evaluated. We have used a novel 3D bioreactor system that enabled perfusion of the capsules with culture medium up to 28 days. Results from culturing all cell types indicated chondrogenesis, both in static and bioreactor culture. The expression of SOX-9 and type II collagen was examined as a marker of differentiation. ATDC-5s expressed both SOX-9 and type II collagen under perfused and static culture conditions. In monolayer cell culture, human articular chondrocytes did not express either SOX-9 or type II collagen and STRO-1 expressed alkaline phosphatase, indicating osteogenesis. However, when these cells were encapsulated in alginate-chitosan, both expressed SOX-9 under static and perfused cultures, but type II collagen was only expressed under perfused culture conditions. We have also noted that the perfusion rates used were too low to ensure a significant advantage over static culture, but that use of the bioreactor eliminated the need for manual feeding and intervention of the cells over the 28-day period.

Human induced pluripotent stem cells are capable of B-cell lymphopoiesis.

Induced pluripotent stem (iPS) cells offer a unique potential for understanding the molecular basis of disease and development. Here we have generated several human iPS cell lines, and we describe their pluripotent phenotype and ability to differentiate into erythroid cells, monocytes, and endothelial cells. More significantly, however, when these iPS cells were differentiated under conditions that promote lympho-hematopoiesis from human embryonic stem cells, we observed the formation of pre-B cells. These cells were CD45(+)CD19(+)CD10(+) and were positive for transcripts Pax5, IL7αR, λ-like, and VpreB receptor. Although they were negative for surface IgM and CD5 expression, iPS-derived CD45(+)CD19(+) cells also exhibited multiple genomic D-J(H) rearrangements, which supports a pre-B-cell identity. We therefore have been able to demonstrate, for the first time, that human iPS cells are able to undergo hematopoiesis that contributes to the B-cell lymphoid lineage.

Validity of DNA analysis to determine cell numbers in tissue engineering scaffolds.

The potential of a DNA content assay, PicoGreen, for use in 3D bioengineered constructs was examined. The assay was tested on ATDC5 cells in situ during culture in typical tissue engineering 3D constructs. Comparisons of cell standards from cell lines and primary cells to lambdaDNA standards was also conducted. An effective working range of the assay within 3D constructs was shown up to 2.5 x 10(5) cells ml(-1). From significant variation found in DNA content between cell lines and primary cells, it was concluded that the most accurate standard to use for the assay was from the cell type being examined.

The effect of hyaluronic acid and phospholipid based lubricants on friction within a human cartilage damage model.

The lubricating abilities of different formulations of high molecular weight hyaluronic acid (HA), dipalmitoyl phosphatidylcholine (DPCC) and mixtures of both HA and DPCC were assessed in an in vitro model. Levels of start-up friction were determined using an osteoarthritis (OA) damaged human cartilage model set within a specially designed friction rig. To examine the long term benefits of HA, the extent of penetration of HA into cartilage tissue was investigated using fluorescently labelled HA and confocal microscopy. It was found that in this model, all formulations of HA and the majority of DPCC lubricants reduced friction (HA 5 and 10 mg ml(-1), DPPC 200 mg ml(-1) reductions of 51.9%, 46.7% and 46.5% respectively), compared to a Ringers solution control. Lubrication was found not to be concentration dependent for HA formulations, but concentration was key for DPCC lubrication (100 mg ml(-1) reduced friction by only 15.9%). By combining HA and DPCC (HA/DPPC; 5 mg ml(-1)/100 mg ml(-1) and 10 mg ml(-1)/200 mg ml(-1)), a further improvement was noted (69.5% and 61.9%, respectively) as the mean levels of friction were reduced by up to a further 17% than the most effective individual formulation (HA 5 mg ml(-1)). Penetration of HA into bovine cartilage by up to 300 microm from the surface was observed over a 48 h period. It was observed that HA specifically targeted the chondrocytes as it was primarily found within the lacunae surrounding the cells.