A bioactive collagen-β tricalcium phosphate scaffold for tissue engineering

Collagen-phosphate composites (COL/β-TCP) are novel materials that have the potential to be used as bone analogues. The aim of our study was to develop a porous bioactive material composed of type I collagen, the main bone protein and tricalcium phosphate, the mineral phase of natural bone, and investigate their in vitro biocompatibility in a human dermal fibroblast culture system. In order to obtain the bioactive materials, type I collagen was isolated from bovine tendon and characterized by physicochemical methods. β-TCP was obtained from calcium carbonate by thermal decomposition at 900 °C temperature. The powder was examined with X-ray diffraction. Two variants of COL/β-TCP scaffolds (P1 and P2) were prepared and examined by scanning electron microscopy. Our results revealed a microporous structure with small white aggregates of β-TCP, non-homogenous scattered in the collagen framework without any preferential orientation. The biocompatibility of the obtained scaffolds was tested by biochemical and histological methods on human fibroblast cultures. Both materials acted as good subtrates for human dermal fibroblast proliferation and migration.     

Magnesium substitution effect on porous scaffolds for bone repair

Of great interest in developing artificial bone is the incorporation of magnesium (Mg) ions into the ceramic lattice in order to improve the physico-chemical and structural properties of the material and to increase its morphological affinity towards newly formed osseous tissue. In the present study, we evaluated the morphological and biological properties of composite scaffolds fabricated by mixing a nanopowder of Mg-substituted beta-tricalcium phosphate with collagen type I in two dry weight ratios (variant I and II). We used biochemical methods, and electron and light microscopy to investigate their porosity, biodegradability and morphology. Osteoblast cell culture behavior in the presence of nanocomposite variants was also examined. Variant I scaffold presented a higher percentage of cross-links and a better resistance to collagenase degradation compared to variant II scaffold. Their porosity did not vary significantly. Osteoblasts cultivated in the presence of nanocomposite scaffolds for 72 h exhibited good cell viability and a normal morphology. When osteoblasts were injected into the scaffolds, a slightly higher proportion of adhered cells were observed for Mg-substituted samples after 7 days of cultivation. All these results showed that Mg-containing porous composite scaffolds had controlled degradation, allowed osteoblast proliferation and adhesion and are good candidates for bone repair.     

Subversion of monocyte functions by coxiella burnetii: impairment of the cross-talk between alphavbeta3 integrin and CR3

Several intracellular pathogens exploit macrophages as a niche for survival and replication. The success of this strategy requires the subversion or the avoidance of microbicidal functions of macrophages. Coxiella burnetii, the agent of Q fever, is a strictly intracellular bacterium that multiplies in myeloid cells. The survival of C. burnetii may depend on the selective use of macrophage receptors. Virulent C. burnetii organisms were poorly internalized but survived successfully in human monocytes, whereas avirulent variants were efficiently phagocytosed but were also rapidly eliminated. The uptake of avirulent organisms was mediated by leukocyte response integrin (alphavbeta3 integrin) and CR3 (alphaMbeta2 integrin), as demonstrated by using specific Abs and RGD sequence-containing peptides. The phagocytic efficiency of CR3 depends on its activation via alphavbeta3 integrin and integrin-associated protein. Indeed, CR3-mediated phagocytosis of avirulent C. burnetii was abrogated in macrophages from integrin-associated protein-/- mice. In contrast, the internalization of virulent C. burnetii organisms involved the engagement of alphavbeta3 integrin but not that of CR3. The pretreatment of monocytes with virulent C. burnetii organisms prevented the CR3-mediated phagocytosis of zymosan particles and CR3 activation assessed by the expression of the 24 neo-epitope. We conclude that the virulence of C. burnetii is associated with the engagement of alphavbeta3 integrin and the impairment of CR3 activity, which probably results from uncoupling alphavbeta3 integrin from integrin-associated protein. This study describes a strategy not previously reported of phagocytosis modulation by intracellular pathogens.