Biological Materials

Este breve ensayo presenta una visión general sobre la patentabilidad del material biológico
y su marco legal. Algunas referencias a legislaciones y resoluciones internacionales
relacionadas a este tema se presentan como parámetro de reflexión, con la finalidad de
vincular algunos tópicos relativos a los derechos humanos.

The equine hoof has been considered as an efficient energy absorption layer that protects the skeletal elements from impact when galloping. In the present study, the hierarchical structure of a fresh equine hoof wall and the energy absorption mechanisms are investigated. Tubules are found embedded in the inter-tubular matrix forming the hoof wall at the microscale. Both tubules and intertubular areas consist of ker-atin cells, in which keratin crystalline intermediate filaments (IFs) and amorphous keratin fill the cytoskeletons. Cell sizes, shapes and IF fractions are different between tubular and intertubular regions. The structural differences between tubular and intertubular areas are correlated to the mechanical behavior of this material tested in dry, fresh and fully hydrated conditions. The stiffness and hardness in the tubule areas are higher than that in the intertubular areas in the dry and fresh samples when loaded along the hoof wall; however, once the samples are fully hydrated, the intertubular areas become stiffer than the tubular areas due to higher water absorption in these regions. The compression behavior of hoof in different loading speed and directions are also examined, with the isotropy and strain-rate dependence of mechanical properties documented. In the hoof walls, mechanistically the tubules serve as a reinforcement, which act to support the entire wall and prevent catastrophic failure under compression and impact loading. Elastic buckling and cracking of the tubules are observed after compression along the hoof wall, and no shear-banding or severe cracks are found in the intertubular areas even after 60% compression, indicating the highly efficient energy absorption properties, without failure, of the hoof wall structure. Statement of Significance The equine hoof wall is found to be an efficient energy absorbent natural polymer composite. Previous studies showed the microstructure and mechanical properties of the hoof wall in some perspective. However, the hierarchical structure of equine hoof wall from nano-to macro-scale as well as the energy absorption mechanisms at different strain rates and loading orientations remains unclear. The current study provides a thorough characterization of the hierarchical structure as well as the correlation between structure and mechanical behaviors. Energy dissipation mechanisms are also identified. The findings in the current research could provide inspirations on the designs of impact resistant and energy absorbent materials.

Cell intrinsic motility and morphology are highly affected by its surrounding environmental conditions. Extracellular proteins have been thoroughly studied along with their effects on Rho GTPases, which been closely linked with cellular movement. Therefore, we investigated the contributing effects two ECM proteins, fibronectin and collagen, have on NIH-3T3 fibroblast motility. In this study, cell motility is characterized through a novel biophysical assay that uses the correlations of the cellular and nuclear centroid minutely displacements to precisely explain the subcellular activity of 3T3 fibroblasts on ECM and also quantify their migration capacity. The results suggest that a fibronectin-rich environment positively affects effective cell displacement and migration potential, compared to a collagen substrate which induced stagnant behavior associated with loss of cell polarity and increased cell sampling, or membrane ruffling. The student t-test was applied to indicate the statistical difference (p < 0.001). This provides us with an insight of the ECM effects on subcellular activity and on the cell-ECM interaction in general. Knowledge gained from these experiments could prove useful in cancer prognosis, diagnosis, or treatment.

The osseous sword of a swordfish (Xiphias gladius) is specialized to incapacitate prey with stunning blows. Considering the sword’s growth
and maturation pattern, aging from the sword’s base to the tip, while missing a mechanosensitive osteocytic network, an in-depth understanding of its mechanical properties and bone quality is lacking. Microstructural, compositional, and nanomechanical characteristics of the bone along
the sword are investigated to reveal structural mechanisms accounting
for its exceptional mechanical competence. The degree of mineralization, homogeneity, and particle size increase from the base toward the tip, reflecting aging along its length. Fracture experiments reveal that crack-growth toughness vastly decreases at the highly and homogeneously mineralized tip, suggesting the importance of aging effects. Initiation toughness, however, is unchanged suggesting that aging effects on this hierarchical level are counteracted by constant mineral/fibril interaction. In conclusion, the sword of the swordfish provides an excellent model reflecting base-to-tip-wise aging of bone, as indicated by increasing mineralization and decreasing crack-growth toughness toward the tip. The hierarchical, structural, and compositional changes along the sword reflect peculiar prerequisites needed for resisting high mechanical loads. Further studies on advanced teleosts bone tissue may help to unravel structure–function relationships of heavily loaded skeletons lacking mechanosensing cells.

The brown pelican (Pelecanus occidentalis) wields one of the largest bills of any bird and is distinguished by the deployable throat pouch of extensible tissue used to capture prey. Here we report on mechanical properties and microstructure of the pouch skin. It exhibits significant anisotropy, with the transverse direction having maximum nominal tensile strains of 200% to 300%, triple the value in the longitudinal direction. This is a higher extensibility than most conventional skin and is the result of the requirement of the sac to net fish; it should expand laterally, with controlled longitudinal stretch. Transmission electron microscopy provides microstructural evidence of the directionality of the collagen fibers and reveals the individual collagen fibrils with a bimodal diameter distribution having peaks at 100 and 170 nm. These dimensions are similar to collagen in mammal skin. In the lateral direction, the fibers form a curvy pattern with a radius of approximately 2 μm wherein the fibrils reorient, straighten, slide, and stretch elastically under tensile load. A second mechanism operates in the transverse direction; the membrane forms a corrugated pattern that, upon straightening of collagen fibrils, confers additional extensibility. This elicits the anisotropic response observed in tensile testing. This work focuses on the mechanical characterization based on the effect of relative bird age, sample location on the pouch, and strain rate. Anterior-posterior location and strain rate are not major influencers on exhibited strengths and extensi-bilities. However, bird age and dorsal-ventral location are found to affect the mechanical response of the pouch significantly. A physically-based constitutive model is developed for the middle layer of the gular sac, based on observations, which predicts maximum stresses, strains, and the shape of the stress-strain curve consistent with the experimental results. Statement of significance The pouch of the pelican, which is used to capture its prey, represents a superlative design by Nature in that it possess remarkable stretchablility and damage tolerance. We find that this results from the marked curvature of the collagen fibrils from which it is composed, which induces numerous energy-absorbing mechanisms where the fibrils reorient, straighten, slide, and stretch elastically under tensile load. The damage-tolerance is further enhanced by the natural gradient in its * Corresponding authors.