Ultrafast Laser Processing of Nanostructured Patterns for the Control of Cell Adhesion and Migration on Titanium Alloy.

Femtosecond laser texturing is a promising surface functionalization technology to improve the integration and durability of dental and orthopedic implants. Four different surface topographies were obtained on titanium-6aluminum-4vanadium plates by varying laser processing parameters and strategies: surfaces presenting nanostructures such as laser-induced periodic surface structures (LIPSS) and 'spikes', associated or not with more complex multiscale geometries combining micro-pits, nanostructures and stretches of polished areas. After sterilization by heat treatment, LIPSS and spikes were characterized to be highly hydrophobic, whereas the original polished surfaces remained hydrophilic. Human mesenchymal stem cells (hMSCs) grown on simple nanostructured surfaces were found to spread less with an increased motility (velocity, acceleration, tortuosity), while on the complex surfaces, hMSCs decreased their migration when approaching the micro-pits and preferentially positioned their nucleus inside them. Moreover, focal adhesions of hMSCs were notably located on polished zones rather than on neighboring nanostructured areas where the protein adsorption was lower. All these observations indicated that hMSCs were spatially controlled and mechanically strained by the laser-induced topographies. The nanoscale structures influence surface wettability and protein adsorption and thus influence focal adhesions formation and finally induce shape-based mechanical constraints on cells, known to promote osteogenic differentiation.

Tensile rupture of medial arterial tissue studied by X-ray micro-tomography on stained samples.

Detailed characterization of damage and rupture mechanics of arteries is one the current challenges in vascular biomechanics, which requires developing suitable experimental approaches. This paper introduces an approach using in situ tensile tests in an X-ray micro-tomography setup to observe mechanisms of damage initiation and progression in medial layers of porcine aortic samples. The technique requires the use of sodium polytungstate as a contrast agent, of which the conditions for use are detailed in this paper. Immersion of the samples during 24h in a 15g/L concentrated solution provided the best compromise for viewing musculo-elastic units in this tissue. The process of damage initiation, delamination and rupture of medial tissue under tensile loading was observed and can be described as an elementary process repeating several times until complete failure. This elementary process initiates with a sudden mode I fracture of a group of musculo-elastic units, followed by an elastic recoil of these units, causing mode II separation of these, hence a delamination plane. The presented experimental approach constitutes a basis for observation of other constituents, or for investigations on other tissues and damage mechanisms.

Biaxial loading of arterial tissues with 3D in situ observations of adventitia fibrous microstructure: A method coupling multi-photon confocal microscopy and bulge inflation test.

Disorders in the wall microstructure underlie all forms of vascular disease, such as the aortic aneurysm, the rupture of which is necessarily triggered at the microscopic level. In this context, we developed an original experimental approach, coupling a bulge inflation test to multiphoton confocal microscopy, for visualizing the 3D micro-structure of porcine, human non-aneurysmal and aneurysmal aortic adventitial collagen under increasing pressurization. The experiment complexity on such tissues led to deeply address the acquisition major hurdles. The important innovative features of the methodology are presented, especially regarding region-of-interest tracking, definition of a stabilization period prior to imaging and correction of z-motion, z being the objective's axis. Such corrections ensured consistent 3D qualitative and quantitative analyses without z-motion. Qualitative analyses of the stable 3D images showed dense undulated collagen fiber bundles in the unloaded state which tended to progressive straightening and separation into a network of thinner bundles at high pressures. Quantitative analyses were made using a combination of weighted 2D structure tensors and fitting of 4 independent Gaussian functions to measure parameters related to straightening and orientation of the fibers. They denoted 3 principal fibers directions, approximately 45°, 135° and 90° with respect to the circumferential axis in the circumferential-axial plane without any evident reorientation of the fibers under pressurization. Results also showed that fibers at zero-pressure state were straighter and less dispersed in orientation for human samples - especially aneurysms - than for pigs. Progressive straightening and decrease in dispersion were quantified during the inflation. These findings provide further insight into the micro-architectural changes within the arterial wall.

A new method to assess the deformations of internal organs of the abdomen during impact.

OBJECTIVES: Due to limitations of classic imaging approaches, the internal response of abdominal organs is difficult to observe during an impact. Within the context of impact biomechanics for the protection of the occupant of transports, this could be an issue for human model validation and injury prediction. METHODS: In the current study, a previously developed technique (ultrafast ultrasound imaging) was used as the basis to develop a protocol to observe the internal response of abdominal organs in situ at high imaging rates. The protocol was applied to 3 postmortem human surrogates to observe the liver and the colon during impacts delivered to the abdomen. RESULTS: The results show the sensitivity of the liver motion to the impact location. Compression of the colon was also quantified and compared to the abdominal compression. CONCLUSIONS: These results illustrate the feasibility of the approach. Further tests and comparisons with simulations are under preparation.