Morphological regulation of rabbit chondrocytes on glucose-displayed surface

Bioconjugation of Carbohydrates to Gelatin Sponges Promoting 3D Cell Cultures

Gelatin sponges are widely employed as hemostatic agents, and are gaining increasing interest as 3D scaffolds for tissue engineering. To broaden their possible application in the field of tissue engineering, a straightforward synthetic protocol able to anchor the disaccharides, maltose and lactose, for specific cell interactions was developed. A high conjugation yield was confirmed by ¹H-NMR and FT-IR spectroscopy, and the morphology of the resulting decorated sponges was characterized by SEM. After the crosslinking reaction, the sponges preserve their porous structure as ascertained by SEM. Finally, HepG2 cells cultured on the decorated gelatin sponges show high viability and significant differences in the cellular morphology as a function of the conjugated disaccharide. More spherical morphologies are observed when cultured on maltose-conjugated gelatin sponges, while a more flattened aspect is discerned when cultured onto lactose-conjugated gelatin sponges. Considering the increasing interest in small-sized carbohydrates as signaling cues on biomaterial surfaces, systematic studies on how small carbohydrates might influence cell adhesion and differentiation processes could take advantage of the described protocol.

Centrifugation assay for measuring adhesion of serially passaged bovine chondrocytes to polystyrene surfaces

A major obstacle in chondrocyte-based therapy for cartilage repair is the limited availability of cells that maintain their original phenotype. Propagation of chondrocytes as monolayer cultures on polystyrene surfaces is used extensively for amplifying cell numbers. However, chondrocytes undergo a phenotypic shift when propagated in this manner and display characteristics of more adherent fibroblastic cells. Little information is available about the effect of this phenotypic shift on cellular adhesion properties. We evaluated changes in adhesion property as bovine chondrocytes were serially propagated up to five passages in monolayer culture using a centrifugation cell adhesion assay, which was based on counting of cells before and after being exposed to centrifugal dislodgement forces of 120 and 350 g. Chondrocytes proliferated well in a monolayer culture with doubling times of 2-3 days, but they appeared more fibroblastic and exhibited elongated cell morphology with continued passage. The centrifugation cell adhesion assay showed that chondrocytes became more adhesive with passage as the percentage of adherent cells after centrifugation increased and was not statistically different from the adhesion of the fibroblast cell line, L929, starting at passage 3. This increased adhesiveness correlated with a shift to a fibroblastic morphology and increased collagen I mRNA expression starting at passage 2. Our findings indicate that the centrifugation cell adhesion assay may serve as a reproducible tool to track alterations in chondrocyte phenotype during their extended propagation in culture.

Bioactive surface modification on amide-photografted poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

Collagen was chemically immobilized on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) films via hydrophilic polyacrylamide spacers, aiming to establish the bioactive surface and the inner surface models. The inner surface modified films presented higher wettability than the surface modified films. Wide-angle x-ray diffraction results showed that the d-spacing values of the inner surface model increased compared with those of the surface model, but there was no significant difference between the amide- and collagen-modified PHBV films. The peak melting temperatures of PHBV and the special endotherm around 70 °C were following the order: PHBV > amide-modified PHBV > collagen-modified PHBV. The weight loss of the collagen-modified PHBV (inner surface model) might involve hydrolyzation and mineralization during 360 days of incubation, with a maximum value of 18.24%, while PHBV films did not show significant weight loss. The pH value of the degradation fluids fluctuated in the range of 6.86-7.22, as the initial pH was recorded at 7.20. Based on the surface model, collagen-modified PHBV scaffolds were prepared, which enhanced chondrocyte adhesion and spread on the biomimetic surface. Two surface modification models might develop a protocol with a view to generating a biocompatible and biomechanical scaffold for use in meniscus regeneration.

Engineering the extracellular environment: Strategies for building 2D and 3D cellular structures

Cell fate is regulated by extracellular environmental signals. Receptor specific interaction of the cell with proteins, glycans, soluble factors as well as neighboring cells can steer cells towards proliferation, differentiation, apoptosis or migration. In this review, approaches to build cellular structures by engineering aspects of the extracellular environment are described. These methods include non-specific modifications to control the wettability and stiffness of surfaces using self-assembled monolayers (SAMs) and polyelectrolyte multilayers (PEMs) as well as methods where the temporal activation and spatial distribution of adhesion ligands is controlled. Building on these techniques, construction of two-dimensional cell sheets using temperature sensitive polymers or electrochemical dissolution is described together with current applications of these grafts in the clinical arena. Finally, methods to pattern cells in three-dimensions as well as to functionalize the 3D environment with biologic motifs take us one step closer to being able to engineer multicellular tissues and organs.

[Development of novel culture system for regulation of hepatocyte function]

Cultured hepatocytes are expected to be used for drug screening and bioartificial liver. Since hepatocytes lose their functions very rapidly in vitro, many attempts have been made to maintain their viability and functions. First, we want to introduce the surface modification of culture substrate using a starburst dendrimer. Addition of fructose to the terminal of the dendrimer was shown to be effective in maintaining hepatocyte function. As the second topic, we will show results of the use of a three-dimensional carrier for hepatocyte cultivation. Hepatocytes and bone marrow stromal cells were cocultured in silane beads, and packed into a radial flow-type bioreactor. The perfusion culture showed the effectiveness of bone marrow stromal cells for the maintenance of hepatocyte function. The next topic will be the trial of adenoviral gene transfer into hepatocytes. Thioredoxin gene was chosen because the products play important roles in redox control and antiapoptosis. The introduction of the gene could inhibit apoptosis and maintain the hepatocyte viability. Finally, we want to introduce the results on differentiation of stem cells into hepatocytes, because it is very difficult to obtain sufficient number of human hepatocytes. Human mesenchymal stem cells were cultured in the presence of several protein factors and the hepatocyte-specific marker was expressed after 2 weeks of induction culture. The use of human stem cells could be an important strategy for the support of a drug development system.