Development of conical soluble phosphate glass fibers for directional tissue growth.

One of the challenges of tissue engineering is the regulation of vascularization and innervations of the implant by the host. Here, we propose that using soluble phosphate glass (SPG) fibers, incorporated in dense collagen constructs will allow us to control the rate and direction of tissue ingrowth. The idea here was to generate channels with tailored direction using conical phosphate glass fibers. The changing surface area-to-mass ratio of conical fibers will make them to dissolve faster from their narrow ends opening up channels in that direction ahead of any ingrowing cells. In this study, we show that SPG fibers can be manipulated to produce conical shape fibers using graded dissolution. Our result shows that 40 µm fibers of composition ratio 0.5 (P(2)O(5)):0.25 (CaO):0.25 (Na(2)O) and dissolution time of 8-10 h have a mean reduction in fiber diameter of 8.85 ± 2.8 µm over 19.5 mm fiber length, i.e., a mean rate of 0.5 µm/mm (n=20) change. These conically shaped fibers can also be manipulated and potentially used to promote uniaxial cell-tissue ingrowth for improved innervations and vascularization of tissue engineered constructs.

Cell attachment and response to photocured, degradable bone adhesives containing tricalcium phosphate and purmorphamine.

The aim of this study was to quantify and provide evidence as to how addition of tricalcium phosphate (ß-TCP) and the Hedgehog agonist purmorphamine to a degradable bone adhesive affects cell attachment/proliferation and Hedgehog pathway activation. Fourier transform infrared spectroscopy demonstrated that high levels (75 wt.%) of ß-TCP addition reduced the photocure rate of the chosen poly(propylene glycol-co-lactide) dimethacrylate (PPLM) bone adhesive, but this problem was overcome by increased light exposure. In phosphate-buffered saline the total surface mass loss of set 15 mm diameter PPLM films was ∼3.2 mg in 12 weeks, irrespective of thickness (200 or 400 µm) or ß-TCP level (50 or 75 wt.%). With 400 µm samples there was additional bulk material loss. Proliferation of pre-osteoblast cells (MC3T3-E1) on the set adhesive surfaces was enhanced by decreased sample thickness or filler content increase. Degradation evidence suggested that both effects were due to reduced acidic polymeric degradation products. Activation of the Hedgehog pathway was quantified by measuring Gli expression in Light II reporter cells. The 0.01 and 0.1 wt.% purmorphamine in composite discs (400 µm, 75 wt.% ß-TCP) enhanced Gli expression of attached cells 2- and 5-fold, respectively, without influencing their number. Pre-storage of the composite samples in culture medium had no detrimental effect on this response. Furthermore, sample storage medium gave no enhanced Gli expression in cells on tissue culture plastic. This suggests drug release levels were very low. Purmorphamine and ß-TCP incorporation in PPLM adhesives might, therefore, provide prolonged enhancement of in vivo bone repair without systemic drug side-effects.

In vitro studies on the influence of surface modification of Ni-Ti alloy on human bone cells.

The in vitro cell behavior on Nitinol after different surface treatments was investigated. As references samples, commercially pure titanium (cpTi) and bioactive titanium were used. The surface treatments influenced the topography, surface energy, crystallographic structure, ion release, chemistry, and ability to form apatite layer from simulated body fluids. Regardless of the surface treatment, the bioactivity study showed that the kinetics of apatite film formation was similar for all tested samples. No clear indication of the surface characteristics influence on the ability for calcium-phosphate precipitation was evident. Cell activity studies showed that ground nickel titanium, spark oxidized and thermally oxidized (at 400 degrees C and below) had higher cellular activity and caused increased alkaline phosphatase (ALP) and osteocalcin (OC) expression which was comparable to control tissue culture plastic and titanium reference samples. Regardless of surface modifications, preimmersion of the samples in media for 72 h resulted in cell proliferation at the same level for all samples. Therefore, it can be concluded that preconditioning of samples alters surface properties and modulates the cell response regardless of the initial surface treatment and its properties. Moreover, a detrimental effect on cell response was observed after 7 and 14 days in culture for alkali treated samples. This was attributed to a high surface nickel concentration and a high nickel ion release rate from these surfaces.

Development of remineralizing, antibacterial dental materials.

Light curable methacrylate dental monomers containing reactive calcium phosphate filler (monocalcium phosphate monohydrate (MCPM) with particle diameter of 29 or 90microm) and beta-tricalcium phosphate (beta-TCP) at 1:1 weight ratio in a powder:liquid ratio (PLR) of 1:1 or 3:1 and chlorhexidine diacetate (0 or 5 wt.%), were investigated. Upon light exposure, approximately 90% monomer conversion was gained irrespective of the formulation. Increasing the PLR promoted water sorption by the set material, induced expansion and enhanced calcium, phosphate and chlorhexidine release. Concomitantly, a decline in compressive and biaxial flexural strengths occurred. With a reduction in MCPM particle diameter, however, calcium and phosphate release was reduced and less deterioration in strength observed. After 24h, the remaining MCPM had reacted with water and beta-TCP, forming, within the set materials, brushite of lower solubility. This provided a novel means to control water sorption, component release and strength properties. Measurable chlorhexidine release was observed for 6weeks. Both diffusion rate and total percentage of chlorhexidine release decreased with lowering PLR or by adding buffer to the storage solutions. Higher chlorhexidine release was associated with reduced bacterial growth on agar plates and in a biofilm fermenter. In cell growth media, brushite and hydroxyapatite crystals precipitated on the composite material surfaces. Cells spread on both these crystals and the exposed polymer composite surfaces, indicating their cell compatibility. These formulations could be suitable antibacterial, biocompatible and remineralizing dental adhesives/liners.

Controlled microchannelling in dense collagen scaffolds by soluble phosphate glass fibers.

A problem with tissue engineering scaffolds is maintaining seeded cell viability and function due to limitations of oxygen and nutrient transfer. An approach to maintain suitable oxygen concentrations throughout the scaffold would be to controllably incorporate microchannelling within these scaffolds. This study investigated the incorporation of unidirectionally aligned soluble phosphate based glass fibers (PGF) into dense collagen scaffolds. PGF are degradable, and their degradation can be controlled through their chemistry and dimensions. Plastic compression was used to produce composite scaffolds at three different weight percentage while maintaining greater than 80% resident cell viability. PGF-collagen scaffold composition was quantified through thermogravimetric analysis as well as being morphologically and mechanically characterized. PGF degradation was measured through ion chromatography, and channel formation was verified with ultrasound imaging and SEM. The free movement of coated microbubble agents confirmed the channels to be continuous in nature and of 30-40 microm diameter. These microchannels in dense native collagen matrices could play an important role in hypoxia/perfusion limitations and also in the transportation of nutrients and potentially forming blood vessels through dense implants.