Effect of strontium substitution on the material properties and osteogenic potential of 3D powder printed magnesium phosphate scaffolds.

3D powder printing is a versatile method for the fabrication of individual bone implants and was used for the processing of in vivo degradable ceramic scaffolds based on ammonium magnesium phosphate hexahydrate (struvite). In this study, synergetic effects could be achieved by the substitution of magnesium phosphate cements with strontium carbonate. This substitution resulted in 8.2 wt%, 16.4 wt%, and 24.6 wt% Sr2+ doped scaffolds, with a 1.9-3.1 times increased radiopacity compared to pure struvite. The maximal compressive strength of (16.1 ±â€¯1.1) MPa found for strontium substituted magnesium phosphate was in the range of cancelleous bone, which makes these 3D printed structures suitable for medical application in low-load-bearing bone areas. In an ion release study over a course of 18 days, the release of strontium, magnesium, calcium, and phosphate ions from scaffolds was analyzed by means of inductively coupled plasma mass spectrometry. Independent of the scaffold composition the Mg2+ concentrations (83-499 mg/l) continuously increased in the cell media. The Sr2+ release varied between 4.3 µg/day and 15.1 µg/day per g scaffold, corresponding to a Sr2+ concentration in media between 1.14 mg/l and 7.24 mg/l. Moreover, decreasing calcium and phosphate concentrations indicated the precipitation of an amorphous calcium phosphate phase. The superior osteogenic properties of strontium substituted magnesium phosphate, e.g. the increase of osteoblast activity and cell number and the simultaneous suppression of osteoclast differentiation could be verified in vitro by means of WST-assay, TRAP-staining, and SEM imaging.

Ionic modification of calcium phosphate cement viscosity. Part I: hypodermic injection and strength improvement of apatite cement.

A broadening of the indications for which calcium phosphate cements (CPC) can be used, for example, in the field of vertebroplasty, would require injectable and higher strength materials. Unmodified CPC are not injectable due to a filter-pressing effect during injection. In this work we demonstrated that an effective method for improving the injection properties of CPC was by the use of sodium citrate solution as a liquid component. Cement consisting of tetracalcium phosphate (TTCP) and monetite (DCPA) mixed with water up to a powder:liquid ratio (P:L) of 3.3 g/ml had an injectability of approximately 60%. The use of 500 mM trisodium citrate solution instead of water decreased the viscosity of the cement paste to a point, where complete injectability (>95%) through an 800 microm diameter hypodermic needle could be achieved at low loads. The reduction in water demand of the cement effected by the use of sodium citrate enabled high P:L mixes to be formed which were 400% stronger than cements made with water. The effect was less pronounced with compacted cements such that at 9 MPa applied pressure, 58% improvement was obtained and at 50 MPa 36% improvement was measured yielding a cement with a compressive strength of 154 MPa. The liquefying effect of sodium citrate was thought to derive from a strong increase in the surface charge of both the reactants and the product as determined by zeta-potential measurement.

Characterization of the Streptomyces violaceoruber SANK95570 plasmids pSV1 and pSV2.

We have analyzed the structure of two extrachromosomal elements of the methylenomycin producing actinomycete Streptomyces violaceoruber SANK95570. The presence of the circular plasmid pSV1 which was supposed to contain the genes for methylenomycin biosynthesis could be verified. Physical mapping of pSV1 revealed a size of 175.35 kb for this plasmid. In addition we generated a restriction map for the 100-kb linear plasmid pSV2. Cloning and sequencing of the terminal ends of pSV2 indicated the presence of 426-bp terminal inverted repeats. Both pSV2 termini show significant homology to the chromosome ends of Streptomyces coelicolor A3(2) which is a closely related strain to S. violaceoruber SANK95570.