Mechanical adaptability of the Bouligand-type structure in natural dermal armour.

Arapaima gigas, a fresh water fish found in the Amazon Basin, resist predation by piranhas through the strength and toughness of their scales, which act as natural dermal armour. Arapaima scales consist of a hard, mineralized outer shell surrounding a more ductile core. This core region is composed of aligned mineralized collagen fibrils arranged in distinct lamellae. Here we show how the Bouligand-type (twisted plywood) arrangement of collagen fibril lamellae has a key role in developing their unique protective properties, by using in situ synchrotron small-angle X-ray scattering during mechanical tensile tests to observe deformation mechanisms in the fibrils. Specifically, the Bouligand-type structure allows the lamellae to reorient in response to the loading environment; remarkably, most lamellae reorient towards the tensile axis and deform in tension through stretching/sliding mechanisms, whereas other lamellae sympathetically rotate away from the tensile axis and compress, thereby enhancing the scale's ductility and toughness to prevent fracture.

Sequential bone healing of immediately loaded mini-implants.

INTRODUCTION: The relatively small size and the ability to load mini-implants without delay are important changes in the simplification of bone rigid anchorage. The purpose of this study was to analyze interfacial healing 1, 4, and 12 weeks after the placment of titanium mini-implants in New Zealand rabbits by removal torque test (RTT) and scanning electron microscopy (SEM). METHODS: Eighteen animals were used in the experiment, in which 72 titanium grade 5 mini-implants 2.0 mm in diameter and 6.0 mm long, were placed. Each animal received 4 mini-implants; 2 were immediately loaded with 1 N. RESULTS: The RTT means for the unloaded mini-implants at 1, 4, and 12 weeks were 15.2 +/- 4.2 N mm (n = 5), 13.1 +/- 5.7 N mm (n = 5), and 54.4 +/- 12.8 N mm (n = 4), respectively. The loaded groups had means of 12.7 +/- 5.1 N mm (n = 4), 11.1 +/- 5.4 N mm (n = 4), and 32.9 +/- 12.8 N mm (n = 5) for the same healing periods, respectively. The statistical evaluation indicated significance in the comparison between loaded and unloaded 12-week groups (P <0.05). SEM analysis in the loaded group showed the formation of less fibrous interfacial tissue after 4 weeks and more lamellar appearance after 12 weeks. CONCLUSIONS: The immediate 1-N load did not cause significant changes in the fixation of the mini-implants after 1 and 4 weeks of bone healing. Nevertheless, after 12 weeks, the loaded group had significantly lower RTT values than the unloaded group without compromising the stability of the mini-implants (P <0.05).