Evaluation of rapid volume changes of substrate-adherent cells by conventional microscopy 3D imaging.

Precise measurement of rapid volume changes of substrate-adherent cells is essential to understand many aspects of cell physiology, yet techniques to evaluate volume changes with sufficient precision and high temporal resolution are limited. Here, we describe a novel imaging method that surveys the rapid morphology modifications of living, substrate-adherent cells based on phase-contrast, digital video microscopy. Cells grown on a glass substrate are mounted in a custom-designed, side-viewing chamber and subjected to hypotonic swelling. Side-view images of the rapidly swelling cell, and at the end of the assay, an image of the same cell viewed from a perpendicular direction through the substrate, are acquired. Based on these images, off-line reconstruction of 3D cell morphology is performed, which precisely measures cell volume, height and surface at different points during cell volume changes. Volume evaluations are comparable to those obtained by confocal laser scanning microscopy (DeltaVolume < or = 14%), but our method has superior temporal resolution limited only by the time of single-image acquisition, typically approximately 100 ms. The advantages of using standard phase-contrast microscopy without the need for cell staining or intense illumination to monitor cell volume make this system a promising new tool to investigate the fundamentals of cell volume physiology.

Photochromic behavior of spiropyran in polymer matrices.

The photoexcitation, relaxation, and optical erasure regimes of spiropyran- (SP-) doped polymer films were studied. Cellulose acetate, poly(vinyl acetate), and poly(methyl methacrylate) (PMMA) were used as host polymer matrices. We studied the character of the photoreaction for both coloring and bleaching processes. Reversible holographic recording in SP-PMMA films and the origin of the photochemical fatigue was studied upon repeated UV-visible irradiation cycles.

[Mechanical evaluation of a ligament fixation system for ACL reconstruction at the tibia in a canine cadaver model]. / Evaluation mécanique d'un système de fixation ligamentaire pour la reconstruction du LCA au niveau du tibia sur un modèle canin cadavérique.

OBJECT: Excellent fixation of an artificial ligament in bone is mandatory for initial stability. ACL reconstruction with the LARS artificial ligament may fail if anchorage to bone is inadequate. The weak metaphyseal bone of the proximal tibia is prone to inadequate fixation. This study evaluates the initial mechanical stability of two techniques with an interference screw on the tibial side of an ACL reconstruction with the LARS ligament. METHODS: Six left tibias were obtained from 1 to 3 year old mongrel dog weighing 20 to 26 kg. ACL straight line reconstruction according to the technique described by J.P. Laboureau was performed with a 4.5 mm drill. Two tunnels were created in the tibia, one oblique and one transverse, the latter 2 cm below the former. Reconstruction was done with a 30-fiber LARS ligament and a 5.2 mm x 15 mm conical titanium cannulated interference screw. Group I had an interference screw in the oblique tunnel and group II had an interference screw in the transverse tunnel. Pull-out tests were performed parallel to the oblique tunnel on an Instron 8521 machine at a speed of 5 mm per minute until failure. The oblique tunnel was tested first then the transverse tunnel. RESULTS: Group I (n = 6): sliding value = 238 +/- 115 N. Group II (n = 6): sliding value = 998 +/- 148 N. This is statistically significant (p < 0.001, student t-test). CONCLUSION: One interference screw in a transverse tibial tunnel for ACL reconstruction with the LARS ligament is 4 times more resistant on loading and impact than an oblique screw.

A mechanical comparison of the immediate stability of three fixation devices used in wrist arthrodesis: a cadaveric study.

This study was designed to determine which of 3 fixation devices used in wrist arthrodesis provides the greatest immediate stability along 2 axes of movement. Twenty cadaver wrists were mechanically tested. Group 1 consisted of 7 wrists stabilized using a 2.3-mm Steinmann pin. Six wrists from the second group were immobilized with a 9-hole, 3.5-mm AO dynamic compression plate. The third group consisted of 7 wrists stabilized with an 8-hole, short-bend, precontoured low-contact dynamic compression plate. Stiffness and fracture force were determined in both forced flexion and forced pronation. The results showed that the Steinmann pin was the least stable of the 3 constructs in both axes of movement. No differences were observed between the 2 compression plates for either of the 2 axes of movement.

[Biomechanical evaluation and clinical correlation of 3 methods of internal fixation of metacarpophalangeal arthrodesis of the thumb]. / Evaluation biomécanique et corrélation clinique de trois méthodes de fixation interne dans l'arthrodèse métacarpo-phalangienne du pouce.

Three methods of internal fixation for MCP arthrodesis of fifteen cadaveric thumbs were used to analyze the biomechanical stability by applying a palmar force, lateral force, and torsion moment. The techniques used included two K-wires 0.045 in parallel (BK), 2 cerclage metallic wires #25 perpendicular to each other (CP), and a 6-holes plate and screws construct from Synthes (PV). The initial rigidity was measured using a Bionix MTS-858. The results after statistical analysis showed: 1) CP was just as rigid as PV for the palmar and lateral tests; 2) CP was, overall, superior to BK in palmar and lateral tests; 3) no difference existed in torsion between the three types of fixation. A comparison was done between the rigidity of the fixation techniques used and the rates of bony nonunion found in the literature. The mean rates of nonunion were reported to be 0-4.0% for the following techniques: CP, tension band wiring (TB), plate and screws, external fixation, compression screw. The rates of nonunion were higher, 7.5-12.5%, for BK, cerclages not perpendicular (CM), bone pegs. According to the results of this biomechanical study and the review of the literature, fixation with BK is the least rigid, and fixation with CP is just as rigid as with PV. The success clinically of CP is yet to be demonstrated. Other studies on the properties of CP for fatigue would be necessary to give a better analysis.