Determination of Second Virial Coefficient of Proteins Using a Dual-Detector Cell for Simultaneous Measurement of Scattered Light Intensity and Concentration in SEC-HPLC

AbstractA method is proposed for the measurement of the B22 value of proteins in aqueous solutions in flow-mode that utilizes a novel fabricated dual-detector cell, which simultaneously measures protein concentration and the corresponding scattered light intensity at 90°, after the protein elutes from a size-exclusion column. Each data point on the chromatograms obtained from the light scattering detector and the concentration (ultraviolet) detector is converted to Rayleigh’s ratio, Rθ, and concentration, c, respectively. The B22 value is calculated from the slope of the Debye plot (Kc/Rθ versus c) generated from a range of concentrations obtained from these chromatograms for a single protein injection. It is shown that this method provides reliable determination of the B22 values for such proteins as lysozyme, chymotrypsinogen, and chymotrypsin in various solution conditions that agree well with those reported in literature

The Resistance of Cortical Bone Tissue to Failure under Cyclic Loading is Reduced with Alendronate

Bisphosphonates are the most prescribed preventative treatment for osteoporosis. However, their long-term use has recently been associated with atypical fractures of cortical bone in patients who present with low-energy induced breaks of unclear pathophysiology. The effects of bisphosphonates on the mechanical properties of cortical bone have been exclusively studied under simple, monotonic, quasi-static loading. This study examined the cyclic fatigue properties of bisphosphonate-treated cortical bone at a level in which tissue damage initiates and is accumulated prior to frank fracture in low-energy situations. Physiologically relevant, dynamic, 4-point bending applied to beams (1.5 mm × 0.5 mm × 10 mm) machined from dog rib (n=12/group) demonstrated mechanical failure and micro-architectural features that were dependent on drug dose (3 groups: 0, 0.2, 1.0 mg/kg/day; Alendronate [ALN] for 3 years) with cortical bone tissue elastic modulus (initial cycles of loading) reduced by 21% (p<0.001) and fatigue life (number of cycles to failure) reduced in a stress-life approach by greater than 3-fold with ALN1.0 (p<0.05). While not affecting the number of osteons, ALN treatment reduced other features associated with bone remodeling, such as the size of osteons (−14%, ALN1.0: 10.5±1.8, VEH: 12.2±1.6, ×103 µm2; p<0.01) and the density of osteocyte lacunae (−20%; ALN1.0: 11.4±3.3, VEH: 14.3±3.6, ×102 #/mm2; p<0.05). Furthermore, the osteocyte lacunar density was directly proportional to initial elastic modulus when the groups were pooled (R=0.54, p<0.01). These findings suggest that the structural components normally contributing to healthy cortical bone tissue are altered by high-dose ALN treatment and contribute to reduced mechanical properties under cyclic loading conditions

Post-traumatic acute bilateral facial nerve palsy: A management dilemma

Acute bilateral facial nerve paralysis is a rare clinical entity, and its management remains very controversial (operative or conservative). Here we are presenting a case of acute onset bilateral facial nerve palsy following head injury with bilateral temporal bone fracture with clinico-radiographic contrary. Patient was managed conservatively with complete recovery. By this article, authors want to stress on combining clinical examination and radiological findings for decision making of this rare entity and tried to evaluate the management

Crack Growth Resistance of Human Tooth Enamel: Mechanisms of Toughening and Energy Dissipation

Enamel, located on the surface of teeth, is the hardest and the most highly calcified tissue of the human body. Cracks and craze lines are often observed in the enamel, but they rarely cause tooth fracture. The primary objective of this dissertation is to characterize the crack growth resistance of human enamel and develop a mechanistic understanding of crack extension and the fracture toughness. Controlled crack growth under Mode I cyclic and monotonic loads was achieved in unique inset Compact Tension (CT) specimens embodying a section of cuspal enamel. Cracks were grown in the forward (from outer enamel inwards) and reverse (from inner enamel outwards) directions and the responses were compared quantitatively and with the responses of sintered hydroxyapatite (HAp). In addition, a hybrid approach was adopted where experimental measures of crack extension and the near tip displacement field were used as solutions for a finite element model that quantify the contributions from toughening mechanisms to the critical stress intensity for fracture. Results from the fatigue crack growth evaluation showed that crack growth was more stable in the forward direction and occurred over twice the spatial distance achieved in the reverse direction. The fatigue crack growth exponent (m) for enamel (m = 7.71.0) was similar to that for the HAp (m = 7.91.4) whereas, the crack growth coefficient (C) for enamel (C=8.7E-04 (mm/cycle).(MPa.m0.5-m0.5-m0.50.50.50.50.5<</. The intrinsic mechanisms contributed to approximately 23% of total toughness, whereas the extrinsic mechanisms contributed to more than 50% of the total toughness. Results from the present investigation showed that enamel is primarily an extrinsically toughened tissue and the microstructure of enamel is designed to be most effective at resisting crack extension initiating from damage at the tooth's surface