Dose- and time-dependent effect of bioactive gel-glass ionic-dissolution products on human fetal osteoblast-specific gene expression.

Bioactive glasses dissolve upon immersion in culture medium, and release their constitutive ions into solution. There has been some evidence suggesting that these ionic-dissolution products influence osteoblast-specific processes. Here, the effect of 58S sol-gel-derived bioactive glass (60% SiO(2), 36% CaO, 4% P(2)O(5), in molar percentage) on primary osteoblasts derived from human fetal long bone explant cultures is investigated, and it is hypothesized that critical concentrations of sol-gel-dissolution products (consisting of a combination of simple inorganic ions) can enhance osteoblast phenotype in vitro by affecting the expression of a number of genes associated with the differentiation and extracellular matrix deposition processes. Cells were exposed to a range of 58S dosages continuously for a period of 4-14 days in monolayer cultures. Quantitative real-time RT-PCR analysis of a panel of osteoblast-specific markers showed a varied gene expression pattern in response to the material. The highest concentration of Ca and Si tested (96 and 50 ppm, respectively) promoted upregulation of gene expression for most markers (including alkaline phosphatase, osteocalcin, and osteopontin) at the latest time point, compared to non-58S-treated control, although this observation was not statistically significant. The same 58S concentration produced higher ALP activity levels and increased proliferation throughout the culture period, compared to lower dosages tested; however, the results generated were again not statistically significant. The data overall suggest that no significant effect can be ascribed to the ionic products of 58S bioactive gel-glass dissolution tested here and their ability to stimulate osteoblastic marker gene expression.

Investigation of localized delivery of diclofenac sodium from poly(D,L-lactic acid-co-glycolic acid)/poly(ethylene glycol) scaffolds using an in vitro osteoblast inflammation model.

Nonunion fractures and large bone defects are significant targets for osteochondral tissue engineering strategies. A major hurdle in the use of these therapies is the foreign body response of the host. Herein, we report the development of a bone tissue engineering scaffold with the ability to release anti-inflammatory drugs, in the hope of evading this response. Porous, sintered scaffolds composed of poly(D,L-lactic acid-co-glycolic acid) (PLGA) and poly(ethylene glycol) (PEG) were prepared with and without the anti-inflammatory drug diclofenac sodium. Analysis of drug release over time demonstrated a profile suitable for the treatment of acute inflammation with ∼80% of drug released over the first 4 days and a subsequent release of around 0.2% per day. Effect of drug release was monitored using an in vitro osteoblast inflammation model, comprised of mouse primary calvarial osteoblasts stimulated with proinflammatory cytokines interleukin-1ß (IL-1ß), tumor necrosis factor-α (TNF-α), and interferon-γ (IFN-γ). Levels of inflammation were monitored by cell viability and cellular production of nitric oxide (NO) and prostaglandin E2 (PGE2). The osteoblast inflammation model revealed that proinflammatory cytokine addition to the medium reduced cell viability to 33%, but the release of diclofenac sodium from scaffolds inhibited this effect with a final cell viability of ∼70%. However, releasing diclofenac sodium at high concentrations had a toxic effect on the cells. Proinflammatory cytokine addition led to increased NO and PGE2 production; diclofenac-sodium-releasing scaffolds inhibited NO release by ∼64% and PGE2 production by ∼52%, when the scaffold was loaded with the optimal concentration of drug. These observations demonstrate the potential use of PLGA/PEG scaffolds for localized delivery of anti-inflammatory drugs in bone tissue engineering applications.

Delivery of definable number of drug or growth factor loaded poly(DL-lactic acid-co-glycolic acid) microparticles within human embryonic stem cell derived aggregates.

Embryoid bodies (EBs) generated from embryonic stem cells are used to study processes of differentiation within a three dimensional (3D) cell environment. In many instances however, EBs are dispersed to single cell suspensions with a subsequent monolayer culture. Moreover, where the 3D integrity of an EB is maintained, cytokines or drugs of interest to stimulate differentiation are often added directly to the culture medium at fixed concentrations and effects are usually limited to the outer layers of the EB. The aim of this study was to create an EB model with localised drug and or growth factor delivery directly within the EB. Using poly(DL-lactic acid-co-glycolic acid) microparticles (MPs) with an average diameter of 13µm, we have demonstrated controllable incorporation of defined numbers of MPs within human ES cell derived EBs, down to 1 MP per EB. This was achieved by coating MPs with human ES cell lysate and centrifugation of specific ratios of ES cells and MPs to form 3D aggregates. Using MPs loaded with simvastatin (pro or active drug) or BMP-2, we have demonstrated osteogenic differentiation within the 3D aggregates, maintained in culture for up to 21days, and quantified by real time QPCR for osteocalcin. Immunostaining for RUNX2 and osteocalcin, and also histochemical staining with picrosirius red to demonstrate collage type 1 and Alizarin red to demonstrate calcium/mineralisation further demonstrated osteogenic differentiation and revealed regional staining associated with the locations of MPs within the aggregates. We also demonstrated endothelial differentiation within human ES cell-derived aggregates using VEGF loaded MPs. In conclusion, we demonstrate an effective and reliable approach for engineering stem aggregates with definable number of MPs within the 3D cellular structure. We also achieved localised osteogenic and endothelial differentiation associated with MPs releasing encapsulated drug molecules or cytokines directly within the cell aggregate. This provides a powerful tool for controlling and investigating differentiation within 3D cell cultures and has applications to drug delivery, drug discovery, stem cell biology, tissue engineering and regenerative medicine.

Novel surface entrapment process for the incorporation of bioactive molecules within preformed alginate fibers.

A physical entrapment technique has been developed for the surface engineering of preformed alginate fibers. Surface engineering was carried out at room temperature in aqueous solutions without additional solvent, a catalyst/initiator, a chemical cross-linking agent, or a temperature increase. Entrapment of surface-modifying molecules was achieved by exposing the alginate fibers to a Na(+)-rich NaCl/CaCl2 mixture solution, which caused the formation of a moderate dissociation layer into which the modifier could diffuse within a few seconds. The surface dissociation was then reversed by the addition of a large excess of multivalent cations, which resulted in collapse of the interface and immobilization of the modifying species. Rhodamine-tagged poly(ethylene glycol)s of different molecular weights were used as model molecules to investigate the effect of process parameters on the entrapment efficiency. It was found that the entrapment efficiency as well as the distribution of the modifier within the alginate fibers was determined by several factors, including the NaCl/CaCl2 ratio in the preswelling solution, exposure time, and concentration and molecular weight of the modifiers. The morphology of the fibers was not significantly changed in terms of shape and size after the entrapment process. By this technique, poly(L-lysine) (PLL) coupled with cell adhesion peptide sequence GRGDS (PLL-GRGDS) was entrapped within alginate fibers, and it was demonstrated that the modification promoted the attachment of mouse 3T3 fibroblasts.