The Keio Twin Research Center (KoTReC) was established in 2009 at Keio University to combine two longitudinal cohort projects — the Keio Twin Study (KTS) for adolescence and adulthood and the Tokyo Twin Cohort Project (ToTCoP) for infancy and childhood. KoTReC also conducted a two-time panel study of self-control and psychopathology in twin adolescence in 2012 and 2013 and three independent anonymous cross-sectional twin surveys (ToTcross) before 2012 — the ToTCross, the Junior and Senior High School Survey and the High School Survey. This article introduces the recent research designs of KoTReC and its publications.

We examined developmental trends and sources of stability and change in adolescent personality by using twin data collected from 1981 to 2010 (273 monozygotic (MZ) and 48 dizygotic (DZ) twin pairs) from a secondary school affiliated with the University of Tokyo. Phenotypic analyses showed high rank-order stability and substantial mean-level increases in neuroticism and declines in extraversion over the adolescent years. Longitudinal bivariate genetic analyses revealed that the best-fitting model for adolescent personality includes additive genetic and non-shared environmental influences. Heritability estimates ranged approximately from 0.30 to 0.60. Additionally, three-year stability in adolescent personality was influenced mainly by genetic factors, and there were both genetic and environmental innovations in mid-adolescence. Our findings suggest that both genetic and environmental effects have significant roles in the etiology of personality development across adolescence.

Calcium phosphate growth on cellulose fibers phosphorylated in 1.5 × SBF (simulated body fluid) solution at various temperatures from 36.5–60 °C was studied. Cellulose fibers phosphorylated by using urea and H3PO4 and then soaked in saturated Ca(OH)2 solution at ambient temperature were found to stimulate the growth of a calcium phosphate coating on their surfaces after soaking in 1.5 × SBF solution for as little as one day. Soaking in 1.5 × SBF solution at higher temperature produced a thicker layer of calcium phosphate on the fibers, which may be due to the decrease of solubility of calcium phosphate. The specific surface area of the coatings decreased with an increase of soaking temperature and soaking time in 1.5 × SBF solution.