Identification of effective elastic modulus using modal analysis : application to canine cancellous bone

Mechanical properties of cancellous bone play a role in osteoporosis and fracture induction, bone tumor microenvironment, fracture healing and implant fixation. Most characterization methods used to identify cancellous bone Young modulus are compressive tests, which are known to comprise significant limitations especially when they are performed on small size specimens. We hypothesized that modal analysis of straight beams could be proposed as an alternative methodology to obtain effective elastic properties. Theoretical key-points were provided to determine the elastic modulus from natural frequencies and mode shapes. In a first step, the methodology was validated using a synthetic bone model as control. Then, water-jet cutting allowed collecting fourteen regular beam-like specimens in specific zones of canine distal femurs. X-ray microtomography confirmed the preservation of tissue microarchitecture and homogeneity. The first natural frequency in clamped-free boundary conditions was used to obtain mean values of Young modulus, which ranged from 210 MPa to 280 MPa depending on the specimen’s collection site. This was in good agreement with literature data obtained with uniaxial compressive tests. Experimental tests were rapid and reproducible, non-destructive and did not depend on scale factor. Therefore, beam modal analysis can be a compelling methodology for exploring mechanical properties of fragile and scarce biological tissues

Diversity of cacao trees in Waslala, Nicaragua: Associations between genotype spectra, product quality and yield potential

The sensory quality and the contents of quality-determining chemical compounds in unfermented and fermented cocoa from 100 cacao trees (individual genotypes) representing groups of nine genotype spectra (GG), grown at smallholder plantings in the municipality of Waslala, Nicaragua, were evaluated for two successive harvest periods. Cocoa samples were fermented using a technique mimicking recommended on-farm practices. The sensory cocoa quality was assessed by experienced tasters, and seven major chemical taste compounds were quantified by near infrared spectrometry (NIRS). The association of the nine, partially admixed, genotype spectra with the analytical and sensory quality parameters was tested. The individual parameters were analyzed as a function of the factors GG and harvest (including the date of fermentation), individual trees within a single GG were used as replications. In fermented cocoa, significant GG-specific differences were observed for methylxanthines, theobromine-to-caffeine (T/C) ratio, total fat, procyanidin B5 and epicatechin, as well as the sensory attributes global score, astringency, and dry fruit aroma, but differences related to harvest were also apparent. The potential cocoa yield was also highly determined by the individual GG, although there was significant tree-to-tree variation within every single GG. Non-fermented samples showed large harvest-to-harvest variation of their chemical composition, while differences between GG were insignificant. These results suggest that selection by the genetic background, represented here by groups of partially admixed genotype spectra, would be a useful strategy toward enhancing quality and yield of cocoa in Nicaragua. Selection by the GG within the local, genetically segregating populations of seedpropagated cacao, followed by clonal propagation of best-performing individuals of the selected GG could be a viable alternative to traditional propagation of cacao by seed from open pollination. Fast and gentle air-drying of the fermented beans and their permanent dry storage were an efficient and comparatively easy precondition for high cocoa quality. (Résumé d'auteur