Uniform partial dissolution of bone mineral by using fluoride and phosphate ions combination.

Mineral content is one of the main predictors of the mechanical properties of bone tissue. The contribution of the bone mineral phase to the mechanical properties of bone has been investigated by reducing the mineral content of bone with different in vitro treatment techniques such as hydrochloric acid (HCl), ethylenedinitrilo tetraacetic acid (EDTA), and fluoride ion treatment. In this study, we propose a new treatment technique which combines fluoride and phosphate ions. Bovine femur specimens were used to determine the mechanical properties of cortical bone after different fluoride phosphate ion combination treatments. The treatment solutions, which contain different fluoride and phosphate ion concentrations, dissolved part of the bone mineral in a uniform manner throughout the bone samples. Dissolution by products, which precipitated in the bone tissue, contained calcium fluoride with phosphate ions (CaF(2)/P) and fluorapatite/fluorhydroxyapatite-type material (FAp/FHAp) and acted as filler. Depending on the fluoride and phosphate concentration in a treatment solution, the precipitated material's ratio of FAp/FHAp to total fluoride containing phase (FAp/FHAp + CaF(2)/P) in bone tissue also changed. High fluoride ion content in treatment solutions generated more CaF(2)/P type of precipitate, and low fluoride ion concentration generated more FAp/FHAp type precipitates as compared to high fluoride concentration treatments. These experiments show that phosphate ions are another important parameter of a treatment solution, in addition to ionic strength, pH, and the duration of treatment. In vitro, phosphate fluoride combinations partially dissolve bone mineral content in a wider range than fluoride treatment alone in a uniform manner. With this new technique one can control more precisely the partial dissolution of the bone mineral and mineral phase's contribution to mechanical properties of bone tissue.

High frequency ultrasound prediction of mechanical properties of cortical bone with varying amount of mineral content.

In this study, we evaluate if high frequency ultrasound impedance measurements can predict the mechanical properties of bones where the amount of bone mineral is varied. The motivation stems from the potential utility of ultrasound as a noninvasive technique to evaluate and monitor the mechanical properties of bone during treatment of diseased states where the ratio of mineral content to organic matrix content could change (e.g., metabolic bone diseases, osteoarthritis, osteogenesis imperfecta, fracture healing). Eleven cortical bovine femur samples, which were taken along the long axis of femur, were used in each group. Bone samples with reduced mineral content (estimated to be 21% and 35% less than the control) were obtained by immersing samples into fluoride ion solution for 3 and 12 d. Control and fluoride treated samples were first tested mechanically in tension. Acoustic impedances of the mechanically tested samples were obtained by using scanning acoustic microscopy (SAM). Results from mechanical tests indicate that the tensile elastic modulus of the samples was highly correlated to the yield strength (r(2) = 0.94, p < 0.01) and to the ultimate strength (r(2) = 0.75, p < 0.01). SAM results indicate that the acoustic impedances were significantly correlated to the elastic modulus (r(2) = 0.85, p < 0.01), yield strength (r(2) = 0.86, p < 0.01) and ultimate strength (r(2) = 0.70, p < 0.01). These results show that ultrasonic techniques could potentially be used to predict the in vivo ultimate strength of bone tissue caused by changes in mineral content.

Osteopontin deficiency and aging on nanomechanics of mouse bone.

Osteoporosis is a bone disease characterized by low bone mass and deterioration of the tissue leading to increased fragility. Osteopontin (OPN), a noncollageneous bone matrix protein, has been shown to play an important role in osteoporosis, bone resorption, and mineralization. However, OPN's role in bone mechanical properties on the submicron scale has not been studied in any detail. In this study, nanoindentation techniques were utilized to investigate how OPN and aging affect bone mechanical properties. Hardness and elastic modulus were calculated and compared between the OPN-deficient mice (OPN(-/-)) and their age and sex-matched wild-type (OPN(+/+)) controls. The results show that the mechanical properties of the young OPN(-/-) bones (age < 12 weeks) are significantly lower than that of the youngest OPN(+/+) bones. This finding was confirmed by additional microindentation testing. Biochemical analysis using micro-Raman spectroscopy indicated more mineral content in young OPN(+/+) bones. Older (age > 12 weeks) bones did not show any significant differences in mechanical properties with genotype. In addition, OPN(+/+) bones show a decrease in mechanical properties between young and older age groups. By contrast, OPN(-/-) bones showed no significant change in mechanical properties with aging.

Polarized light reflection from strained sinusoidal surfaces.

We propose optical polarization imaging as a minimally invasive technique for measuring the mechanical properties of plastics and soft tissues through their change in reflectance properties with applied strain or force. We suggest that changes in surface roughness are responsible for the linear reflectivity changes with applied stretch or strain. Several aspects of this model are tested, including the dependence on the angle of incidence, the change in scattering and absorption coefficients with strain, and the lateral spatial resolution. The application of the technique to multilayer structures such as skin and competing optical effects such as laser speckle are discussed.

Measurement of skin stretch via light reflection.

A noninvasive technique for measuring the stretch of skin is described. The technique utilizes changes in the reflectivity of polarized light intensity as a monitor of skin stretch. Measurements of in vitro pigskin and in vivo human skin show that the reflectivity of polarized light intensity increases linearly with stretch. The changes in diffusive reflectivity properties of skin result from the alterations that take place in the roughness across the thickness of the skin layers due to stretch. Conceptually, as the roughness of a layer decreases with stretch, a smoother reflecting media is produced, resulting in a proportional increase in the specular reflection. Results can be easily extended to a real-time stretch analysis of large tissue areas that would be applicable for mapping the stretch of skin.