Evaluation of the repair of diaphyseal fracture of femoral bone using bone marrow mesenchymal stem cells in nicotine-bearing rat.

OBJECTIVE: Following bone fractures during accidents, some patients suffer from poor repair of bone fractures and subsequent aesthetic and psychological problems. One of the treatments is based on transplantation of stem cells (seeded on scaffolds) to the lesion site. Bone marrow stromal cells (BMSCs) are multivalent stem cells which are able to reproduce and differentiate into osteogenic cells. The objective of this study was to evaluate the treatment of bone fractures by means of transplantation of the latter cells in rats. METHODS: In this study, the therapeutic effect of mesenchymal stem cells from bone marrow adipocytes was evaluated in bone fractures. BMSCs were isolated from rat femur. Two sources of differentiated and non-differentiated osteocyte cells were provided and mixed with collagen in order to be transferred to animals divided in three main groups of model: nicotine, non-nicotine and control groups. After four weeks, the repair of the fracture that had been inflicted by a 2­mm drill into the diaphyseal region of the femoral bone was investigated by radiographic tests and histopathologic staining. RESULTS: The radiographic results as well as those of histopathologic staining showed that osteogenesis was more intensive in the non-nicotine group than in the nicotine group with differentiated and non-differentiated osteocyte cells. CONCLUSION: The transplantation of differentiated BMSCs to a bone lesion affected the repair of bone fractures while the nicotine agent played an important role in delaying the bone regeneration (Tab. 1, Fig. 8, Ref. 31).

Demonstration of angle-dependent Casimir force between corrugations.

The normal Casimir force between a sinusoidally corrugated gold coated plate and a sphere was measured at various angles between the corrugations using an atomic force microscope. A strong dependence on the orientation angle of the corrugation is found. The measured forces were found to deviate from the proximity force approximation and are in agreement with the theory based on the gradient expansion including correlation effects of geometry and material properties. We analyze the role of temperature. The obtained results open new opportunities for control of the Casimir effect in micromechanical systems.

Radial distribution function of rod-like polyelectrolytes.

We study the effect of electrostatic interactions on the distribution function of the end-to-end distance of a single polyelectrolyte chain in the rod-like limit. The extent to which the radial distribution function of a polyelectrolyte is reproduced by that of a wormlike chain with an adjusted effective persistence length is investigated. Strong evidence is found for a universal scaling formula connecting the effective persistence length of a polyelectrolyte with the strength of the electrostatic interaction and the Debye screening length.

Constraints, histones, and the 30-nm spiral.

We investigate the mechanical stability of a segment of DNA wrapped around a histone in the nucleosome configuration, under the assumption that the proper model for this packaging arrangement is that of an elastic rod that is free to twist and that writhes subject to mechanical constraints. We find that the number of constraints required to stabilize the nuclesome configuration is determined by the length of the segment, the number of times the DNA wraps around the histone spool, and the specific constraints utilized. While it can be shown that four constraints suffice, in principle, to insure stability of the nucleosome, a proper choice must be made to guarantee the effectiveness of this minimal number. The optimal choice of constraints appears to bear a relation to the existence of a spiral ridge on the surface of the histone octamer. The particular configuration that we investigate is related to the 30-nm spiral, a higher-order organization of DNA in chromatin.