Osteoblastic cell response on fluoridated hydroxyapatite coatings: the effect of magnesium incorporation.

Magnesium (Mg) ions were incorporated into fluoridated hydroxyapatite (HA) coating by the sol-gel dip-coating method. Mg in the coating was measured by x-ray photoelectron spectroscopy (XPS). The changes of calcium and magnesium concentrations were recorded to monitor the dissolution behavior of the coatings. In vitro cell responses were evaluated using MG63 cells in terms of cell morphology, proliferation and differentiation. The substitution of Mg and F ions into the HA crystal structure was confirmed by XPS. Only a limited amount of Mg can be incorporated into HA lattice. The dissolution test revealed that Mg incorporation increased the solubility of the coating in the tris-buffered saline solution. The highest solubility was achieved at x = 1.5 (Ca((10-x))Mg(x)(PO(4))(6) F(OH). In the cell culture test, well-spread cells were observed on all the coatings. Also, a significantly positive effect of Mg ions on cell proliferation and late differentiation was found at x = 1.5. Mg incorporation stimulates osteoblastic cell responses on fluoridated hydroxyapatite coatings.

Porous polycaprolactone scaffold for cardiac tissue engineering fabricated by selective laser sintering.

An advanced manufacturing technique, selective laser sintering (SLS), was utilized to fabricate a porous polycaprolactone (PCL) scaffold designed with an automated algorithm in a parametric library system named the "computer-aided system for tissue scaffolds" (CASTS). Tensile stiffness of the sintered PCL strut was in the range of 0.43+/-0.15MPa when a laser power of 3W and scanning speed of 150 in s(-1) was used. A series of compressive mechanical characterizations was performed on the parametric scaffold design and an empirical formula was presented to predict the compressive stiffness of the scaffold as a function of total porosity. In this work, the porosity of the scaffold was selected to be 85%, with micropores (40-100mum) throughout the scaffold. The compressive stiffness of the scaffold was 345kPa. The feasibility of using the scaffold for cardiac tissue engineering was investigated by culturing C2C12 myoblast cells in vitro for 21days. Fluorescence images showed cells were located throughout the scaffold. High density of cells at 1.2x10(6)cellsml(-1) was recorded after 4days of culture. Fusion and differentiation of C2C12 were observed as early as 6days in vitro and was confirmed with myosin heavy chain immunostaining after 11days of cell culture. A steady population of cells was then maintained throughout 21days of culturing. This work demonstrated the feasibility of tailoring the mechanical property of the scaffold for soft tissue engineering using CASTS and SLS. The macroarchitecture of the scaffold can be modified efficiently to fabricate scaffolds with different macropore sizes or changing the elemental cell design in CASTS. Further process and design optimization could be carried out in the future to fabricate scaffolds that match the tensile strength of native myocardium, which is of the order of tens of kPa.

Controlled release of complexed DNA from polycaprolactone film: comparison of lipoplex and polyplex release.

This report investigates the comparative in vitro controlled release and transfection efficiencies of pDNA-lipofectamine complex (lipoplex) and pDNA-poly(ethylene imine) complex (polyplex), from a biodegradable polycaprolactone (PCL) film. The effect of molecular weight of gelatin used as a porogen on in vitro release and transfection efficiency was also studied. A sustained release profile was obtained for naked pDNA and lipoplex from polymeric films for a month, while the release of polyplexes (PEI/DNA) is simply a burst at day 5, with little or no release thereafter. The release of polyplexes from PCL films is retarded due to interaction between the polyplexes and the polymer. A high burst release was seen for naked pDNA which was suppressed in the presence of gelatin. The extent of suppression of the burst effect by gelatin increased with its molecular weight. For complexed pDNA (lipoplex), the release was slow, but could be accelerated using gelatin; again the acceleration in release is dependant on the molecular weight of the gelatin used. The addition of gelatin as a porogen has no effect on the release of polyplexes from PCL films. The bioactivity of released plasmid DNA and complexes was studied by in vitro transfection using COS-7 cells. Transfection was observed from released lipoplexes samples till day 9 from PCL film with lower MW gelatin and till day 18 in the case of PCL films with higher MW gelatin. The results also showed that the bioactivity of released lipoplexes was superior to that of the naked pDNA.

Shape memory in un-cross-linked biodegradable polymers.

Shape memory is extremely useful in minimally-invasive deployment of medical devices, particularly stents used in the cardiovascular system. Current stents employ Nitinol, which exhibits shape memory on the basis of a phase transformation. Cross-linked polymers may also be made to exhibit shape-memory effects, but are sometimes precluded for use in stents for other reasons. Un-cross-linked poly(lactide-co-glycolide) (PLGA) and poly(L-lactic acid) (PLLA) have been used in biodegradable stent prototypes. Their shape memory polymers (SMPs) were investigated in this paper. The three important parameters in SMPs are strain fixity, strain recovery and permanent strain. The effects of deformation temperature, deformation strain level and creeping time on those parameters were evaluated in depth. High deformation temperatures will give high fixity, high recovery, but also high permanent deformation for both PLGA and PLLA. Generally, a lower stress applied for a longer duration (the 'creeping' method) is preferred to a higher stress applied 'instantly' for achieving shape memory. These effects are explained on the basis of molecular orientation and slippage effects.

Effect of pore size and interpore distance on endothelial cell growth on polymers.

The endothelization of polymers using surface modification has received great attention. In particular, creation of physical surface features such as craters or pores has been an active area of research. However, there have been no reported studies of the effects of pore sizes (wide range) and interpore distance on endothelial cell growth. This report details the study done on endothelial cell attachment on the surfaces of polymers modified by porogen leaching. The polymeric system studied includes PLLA and PLGA (80/20). Factors such as porogen type, pore size, and interpore distance were varied, and the surface was evaluated for its influence on endothelial cell growth. Three groups of pore sizes were evaluated: small (5-20 mum), medium (20-45 mum), and large pores (45-90 mum). Two porogens were evaluated: sugar and gelatin. In addition to counting the attached endothelial cells, their proliferation was also quantified. Pore size and interpore distances were evaluated using scanning electron microscopy (SEM), and cell morphology was studied by staining with crystal violet. Analysis of variance demonstrated that the main parameters, pore size and interpore distance were significant in endothelial cell growth. In PLGA (80/20), it was found that endothelial cell growth was enhanced by smaller pore size and lower interpore distance, whereas the growth was poor on PLLA regardless of pore features.

Sustained release of complexed and naked DNA from polymer films.

Controlled release studies of DNA from polymers have been limited, with most studies concentrating on microsphere formulations. This report details a study done on the release and transfection efficiencies of pDNA-lipofectamine complex (lipoplex), from selected polymeric films in which it was dispersed; the release and transfection efficiency was compared with that of naked pDNA. A biodegradable and a biostable polymer were compared. A sustained release profile was obtained from both the polymeric films. For the release of pDNA (naked DNA), a burst effect was always seen, and was suppressed using additives; for complexed pDNA (lipoplex), the release was slow, but could be accelerated using additives. The compositions of the released lipoplexes were also quantified in terms of the fraction that was complexed. In addition, the transfection efficiency of the released complexes and of the naked pDNA was determined in vitro using COS 7 cells. The results also demonstrated that bioactivity of the released complexed pDNA was superior to that of the released naked DNA. Such formulations may be useful for local sustained delivery of lipoplexes from implanted films.

Controlled degradation of multilayered poly(lactide-co-glycolide) films using electron beam irradiation.

The ability to undergo predictable and controlled degradation allows biopolymers to release prescribed dosages of drugs locally over a sustained period. However, the bulk or homogeneous degradation of some of these polymers like poly(L-lactide) (PLLA) and poly(lactide-co-glycolide) (PLGA) work against a better controlled release of the drugs. Inducing the polymers to undergo surface erosion or layer-by-layer degradation could provide a better process of controlled drug release from the polymers. This study has demonstrated that surface erosion degradation of PLGA is possible with the use of a multilayer film system, with PPdlLGA [plasticized poly(D,L-lactide-co-glycolide) (PdlLGA)] as the surface layers and poly(L-lactide-co-glycolide) as the center layer. The use of the more hydrophilic PPdlLGA as the surface layer resulted in a faster degradation of the surface layers compared to the center layer, thus giving a surface erosion degradation effect. The rate of surface degradation could also be controlled with electron beam (e-beam) radiation, where e-beam irradiation was shown to alter the degradation time and onset of polymer mass loss. It was also shown that the more highly irradiated PPdlLGA surface layers had an earlier onset of mass loss, which resulted in a faster reduction in overall film thickness. The ability to control the rate of film thickness reduction with different radiation dose promises a better controlled release of drugs from this multilayer PLGA film system.

Effect of plasticization on heparin release from biodegradable matrices.

Heparin-loaded polymer films of poly-L-lactide (PLLA) and poly-L-lactide-co-glycolide (PLLGA) as well as poly-DL-lactide-co-glycolide (PLGA) were produced. A plasticizer, PEG, was added to the polymers. It was found that the release profile in general consisted of a burst effect, a diffusion-controlled phase and a degradation-controlled phase. The plasticizer accelerated the onset of degradation in all cases, but its effect on the release profile differed significantly depending on the polymer. The plasticizer depressed the burst effect for PLLA, and accelerated the kinetics of the diffusion-controlled phase. For the PLLGA 80/20, however, the plasticizer had no significant effect on the release profile or kinetics. We explain these observations in terms of hydrophilicity and crystallinity effects.