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Objectives In tissue regeneration research, the term “bioactivity” was initially used to describe the resistance to removal of a biomaterial from host tissues after intraosseous implantation. Hydraulic calcium silicate cements (HCSCs) are putatively accepted as bioactive materials, as exemplified by the increasing number of publications reporting that these cements produce an apatite-rich surface layer after they contact simulated body fluids. Methods In this review, the same definitions employed for establishing in vitro and in vivo bioactivity in glass–ceramics, and the proposed mechanisms involved in these phenomena are used as blueprints for investigating whether HCSCs are bioactive. Results The literature abounds with evidence that HCSCs exhibit in vitro bioactivity; however, there is a general lack of stringent methodologies for characterizing the calcium phosphate phases precipitated on HCSCs. Although in vivo bioactivity has been demonstrated for some HCSCs, a fibrous connective tissue layer is frequently identified along the bone–cement interface that is reminiscent of the responses observed in bioinert materials, without accompanying clarifications to account for such observations. Conclusions As bone-bonding is not predictably achieved, there is insufficient scientific evidence to substantiate that HCSCs are indeed bioactive. Objective appraisal criteria should be developed for more accurately defining the bioactivity profiles of HCSCs designed for clinical use.

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BACKGROUNDWhile many studies have found that migration can benefit home communities and family members left behind by increasing household income, thus easing liquidity constraints on investment; less is known about how "internal" migration and remittances affect the educational performance of the children who are left behind in the source communities. OBJECTIVEMy aim in this paper is to examine the effects of migration on the educational attainment of left-behind rural children in northwest China. To gain a better understanding of whether the educational performance of these children improves or suffers when adult family members migrate, I attempt to disentangle the effects of remittances from the effects of migration. METHODSThe data used in this study come from the 2004 wave of the Gansu Survey of Children and Families. To account for the possible endogeneity of migration-related variables, I use the migration network variables to instrument for different migration strategies. RESULTSThe results show that the absence of adult household members, including parents, has a negative effect on the educational performance of the children left behind, but that remittances can partially compensate for this loss. Boys' educational performance does not seem to be greatly affected by the migration of adult household members. By contrast, the absence of adult household members is shown to have a large negative effect on girls' educational performance, and the positive effect of remittances is also found to be significant for girls. CONCLUSIONSThe findings may be of interest to other developing countries with large internal migration flows and to the relevant policy makers, as the results suggest that

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