Effect of anisotropy on elastic moduli measured by nanoindentation in human tibial cortical bone

Many biological materials are known to be anisotropic. In particular, microstructural components of biological materials may grow in a preferred direction, giving rise to anisotropy in the microstructure. Nanoindentation has been shown to be an effective technique for determining the mechanical properties of microstructures as small as a few microns. However, the effects of anisotropy on the properties measured by nanoindentation have not been fully addressed. This study presents a method to account for the effects of anisotropy on elastic properties measured by nanoindentation. This method is used to correlate elastic properties determined from earlier nanoindentation experiments and from earlier ultrasonic velocity measurements in human tibial cortical bone. Also presented is a procedure to determine anisotropic elastic moduli from indentation measurements in multiple directions. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res.

Elastic and plastic properties of Mo3Si measured by nanoindentation

Single crystal Mo3Si specimens were grown and tested at room temperature using established nanoindentation techniques at various crystallographic orientations. The indentation modulus and hardness were obtained for loads that were large enough to determine bulk properties, yet small enough to avoid cracking in the specimens. From the indentation modulus results, anisotropic elastic constants were determined. As load was initially increased to approximately 1.5 mN, the hardness exhibited a sudden drop that corresponded to a jump in displacement. The resolved shear stress that was determined from initial yielding was 10-15% of the shear modulus, but 3 to 4 times the value obtained from the bulk hardness. Non-contact atomic force microscopy images in the vicinity of indents revealed features consistent with {100}(010) slip.

The management of posterior vitreous detachment by an optometrist

Acute posterior vitreous detachment (PVD) is the most common cause of retinal detachment. The management of this condition can be variable and often undue reliance is placed upon associated signs and symptoms which can be a poor indicator of pathology. Optometrists undertake a number of extended roles, however involvement in vitreo-retinal sub-specialities appears to be limited. One objective was to directly compare an optometrist and ophthalmologist in the assessment of patients with PVD, for this a high level of agreement was found (95% sensitivity, 99% specificity, 0.94 kappa). A review of 1107 patients diagnosed with acute PVD that were re-evaluated in a PVD clinic a few weeks later was undertaken to determine whether such reviews are necessary. One-fifth of patients were found to have conditions undiagnosed at the initial assessment, overall 4% of patients had retinal breaks when examined in the PVD clinic and a total of 7% required further intervention. The sensitivity of fundus examination with +90D and 3-mirror lenses was 85-88% for detecting retinal breaks and 7-85% for pigment in the anterior vitreous for the presence of retinal breaks. Therefore patients with acute PVD should be examined by indirect ophthalmoscopy with indentation at the onset of PVD and 4-6 weeks later. The treatment of retinal breaks with laser retinopexy is performed by ophthalmologists with a primary success rate 54-85%. In a pioneering development, an optometrist undertaking this role achieved a comparable primary success rate (79%). Mid-vitreous opacities associated with PVD are described, and noted in 100% of eyes with PVD. The recognition of this sign is important in the diagnosis of PVD and retinal breaks. The importance of diagnostic imaging is also demonstrated, however the timing in relation to onset may be vital.

Microparticle surface layering through dry coating:impact of moisture content and process parameters on the properties of orally disintegrating tablets

OBJECTIVES: The aim of this study was to investigate the influence of process parameters during dry coating on particle and dosage form properties upon varying the surface adsorbed moisture of microcrystalline cellulose (MCC), a model filler/binder for orally disintegrating tablets (ODTs). METHODS: The moisture content of MCC was optimised using the spray water method and analysed using thermogravimetric analysis. Microproperty/macroproperty assessment was investigated using atomic force microscopy, nano-indentation, scanning electron microscopy, tablet hardness and disintegration testing. KEY FINDINGS: The results showed that MCC demonstrated its best flowability at a moisture content of 11.2% w/w when compared to control, comprising of 3.9% w/w moisture. The use of the composite powder coating process (without air) resulted in up to 80% increase in tablet hardness, when compared to the control. The study also demonstrated that surface adsorbed moisture can be displaced upon addition of excipients during dry processing circumventing the need for particle drying before tabletting. CONCLUSIONS: It was concluded that MCC with a moisture content of 11% w/w provides a good balance between powder flowability and favourable ODT characteristics.