High genetic diversity and low differentiation of Michelia coriacea (Magnoliaceae), a critically endangered endemic in Southeast Yunnan, China.

Michelia coriacea, a critically endangered tree, has a restricted and fragmented distribution in Southeast Yunnan Province, China. The genetic diversity, genetic structure and gene flow in the three extant populations of this species were detected by 10 inter-simple sequence repeat (ISSR) markers and 11 simple sequence repeat (SSR) markers. Examination of genetic diversity revealed that the species maintained a relatively high level of genetic diversity at the species level (percentage of polymorphic bands) PPB = 96.36% from ISSRs; PPL (percentage of polymorphic loci) = 95.56% from SSRs, despite several fragmental populations. Low levels of genetic differentiation among the populations of M. coriacea were detected by Nei's G(st) = 0.187 for ISSR and Wright's F(st) = 0.090 for SSR markers, which is further confirmed by Bayesian model-based STRUCTURE and PCoA analysis that could not reveal a clear separation between populations, although YKP was differentiated to other two populations by ISSR markers. Meanwhile, AMOVA analysis also indicated that 22.84% and 13.90% of genetic variation existed among populations for ISSRs and SSRs, respectively. The high level of genetic diversity, low genetic differentiation, and the population, structure imply that the fragmented habitat and the isolated population of M. coriacea may be due to recent over-exploitation. Conservation and management of M. coriacea should concentrate on maintaining the high level of genetic variability through both in and ex-situ conservation actions.

Optimization of Cr content of metastable ß-type Ti-Cr alloys with changeable Young's modulus for spinal fixation applications.

Metallic implant rods used in spinal fixtures should have a Young's modulus that is sufficiently low to prevent stress shielding for the patient and sufficiently high to suppress springback for the surgeon. Therefore, we propose a new concept: novel biomedical titanium alloys with a changeable Young's modulus via deformation-induced ω phase transformation. In this study, the Cr content in the range of 10-14 mass% was optimized to produce deformation-induced ω phase transformation, resulting in a large increase in the Young's modulus of binary Ti-Cr alloys. The springback and cytotoxicity of the optimized alloys were also examined. Ti-(10-12)Cr alloys exhibit an increase in Young's modulus owing to deformation-induced ω phase transformation. In this case, such deformation-induced ω phase transformation occurs along with {332}(ß) mechanical twinning, resulting in the maintenance of acceptable ductility with relatively high strength. Among the examined alloys, the lowest Young's modulus and largest increase in Young's modulus are obtained from the Ti-12Cr alloy. This alloy exhibits smaller springback than and comparable cytocompatibility to the biomedical Ti alloy Ti-29Nb-13Ta-4.6Zr.

Beta type Ti-Mo alloys with changeable Young's modulus for spinal fixation applications.

To develop a novel biomedical titanium alloy with a changeable Young's modulus via deformation-induced ω phase transformation for the spinal rods in spinal fixation devices, a series of metastable ß type binary Ti-(15-18)Mo alloys were prepared. In this study, the microstructures, Young's moduli and tensile properties of the alloys were systemically examined to investigate the effects of deformation-induced ω phase transformation on their mechanical properties. The springback of the optimal alloy was also examined. Ti-(15-18)Mo alloys subjected to solution treatment comprise a ß phase and a small amount of athermal ω phase, and they have low Young's moduli. All the alloys investigated in this study show an increase in the Young's modulus owing to deformation-induced ω phase transformation during cold rolling. The deformation-induced ω phase transformation is accompanied with {332}(ß) mechanical twinning. This resulted in the maintenance of acceptable ductility with relatively high strength. Among the examined alloys, the Ti-17Mo alloy shows the lowest Young's modulus and the largest increase in the Young's modulus. This alloy exhibits small springback and could be easily bent to the required shape during operation. Thus, Ti-17Mo alloy is considered to be a potential candidate for the spinal rods in spinal fixation devices.