Strontium folate loaded biohybrid scaffolds seeded with dental pulp stem cells induce in vivo bone regeneration in critical sized defects.

Strontium folate (SrFO) is a recently developed bone promoting agent with interest in medical and pharmaceutical fields due to its improved features in comparison to current strontium based therapies for osteoporosis and other bone diseases. In this work SrFO derivative was synthesized and loaded into biohybrid scaffolds obtained through lyophilisation of semi-interpenetrating networks of chitosan polyethylene glycol dimethacrylate and beta tri-calcium phosphate (ßTCP) fabricated using free radical polymerization. The scaffolds were seeded with pluripotent stem cells obtained from human dental pulp and their potential to regenerate bone tissues were assessed using a critical sized defect model of calvaria in rats and compared with those obtained without SrFO. The results obtained both in vitro and in vivo demonstrated excellent cyto-compatibility with resorption of scaffolds in 4-6 weeks and a total regeneration of the defect, with a more rapid and dense bone formation in the group with SrFO. Thus, the use of stem cells sourced from human dental pulp in combination with SrFO are very promising systems for their application in compromised osseous tissue regeneration.

Evolution of biofilms during the colonization process of pyrite by Acidithiobacillus thiooxidans.

We have applied epifluorescence principles, atomic force microscopy, and Raman studies to the analysis of the colonization process of pyrite (FeS(2)) by sulfuroxidizing bacteria Acidithiobacillus thiooxidans after 1, 15, 24, and 72 h. For the stages examined, we present results comprising the evolution of biofilms, speciation of S (n) (2-) /S(0) species, adhesion forces of attached cells, production and secretion of extracellular polymeric substances (EPS), and its biochemical composition. After 1 h, highly dispersed attached cells in the surface of the mineral were observed. The results suggest initial non-covalent, weak interactions (e.g., van der Waal's, hydrophobic interactions), mediating an irreversible binding mechanism to electrooxidized massive pyrite electrode (eMPE), wherein the initial production of EPS by individual cells is determinant. The mineral surface reached its maximum cell cover between 15 to 24 h. Longer biooxidation times resulted in the progressive biofilm reduction on the mineral surface. Quantification of attached cell adhesion forces indicated a strong initial mechanism (8.4 nN), whereas subsequent stages of mineral colonization indicated stability of biofilms and of the adhesion force to an average of 4.2 nN. A variable EPS (polysaccharides, lipids, and proteins) secretion at all stages was found; thus, different architectural conformation of the biofilms was observed during 120 h. The main EPS produced were lipopolysaccharides which may increase the hydrophobicity of A. thiooxidans biofilms. The highest amount of lipopolysaccharides occurred between 15-72 h. In contrast with abiotic surfaces, the progressive depletion of S (n) (2-) /S(0) was observed on biotic eMPE surfaces, indicating consumption of surface sulfur species. All observations indicated a dynamic biooxidation mechanism of pyrite by A. thiooxidans, where the biofilms stability and composition seems to occur independently from surface sulfur species depletion.