Initial Studies Directed toward the Rational Design of Aqueous Graphene Dispersants.

This study presents preliminary experimental data suggesting that sodium 4-(pyrene-1-yl)butane-1-sulfonate (PBSA), 5, an analogue of sodium pyrene-1-sulfonate (PSA), 1, enhances the stability of aqueous reduced graphene oxide (RGO) graphene dispersions. We find that RGO and exfoliated graphene dispersions prepared in the presence of 5 are approximately double the concentration of those made with commercially available PSA, 1. Quantum mechanical and molecular dynamics simulations provide key insights into the behavior of these molecules on the graphene surface. The seemingly obvious introduction of a polar sulfonate head group linked via an appropriate alkyl spacer to the aromatic core results in both more efficient binding of 5 to the graphene surface and more efficient solvation of the polar head group by bulk solvent (water). Overall, this improves the stabilization of the graphene flakes by disfavoring dissociation of the stabilizer from the graphene surface and inhibiting reaggregation by electrostatic and steric repulsion. These insights are currently the subject of further investigations in an attempt to develop a rational approach to the design of more effective dispersing agents for rGO and graphene in aqueous solution.

Structural parameters of normal and osteoporotic human trabecular bone are affected differently by microCT image resolution.

UNLABELLED: This study employed microCT to investigate whether image resolution affects bone structural parameters differently in healthy normal and osteoporotic trabecular bone. With increasing image voxel size, the originally detected differences between sample groups diminished. The results suggest that structural differences may not be reliably detected with clinical scanners. INTRODUCTION: Structural parameters of bone reflect its health status, but are highly dependent on the image resolution. We hypothesized that image resolution affects bone structural parameters differently in normal and osteoporotic trabecular bone. METHODS: Human trabecular bone samples from the iliac crest and the knee were analyzed (normal n = 11, osteoporotic n = 15) using a high-resolution microCT (14 or 18 µm voxel sizes). Images were re-sampled to voxel sizes 1-16 times larger than the original image and thresholded with global or local adaptive algorithms. Absolute and normalized values of each structural parameter were calculated, and the effect of decreasing image resolution was compared between the normal and osteoporotic samples. RESULTS: Normal and osteoporotic samples had different (p < 0.05) absolute bone volume fractions. However, the normalized values showed that the osteoporotic samples were more prone to errors (p < 0.05) with increased voxel size. The absolute values of trabecular number, trabecular separation, degree of anisotropy, and structure model index were different between the groups at the original voxel size (p < 0.05), but at voxel sizes between 60 and 110 µm, those differences were no longer significant. CONCLUSIONS: The results suggest that structural differences between osteoporotic and normal trabecular bone may not be reliably detected with clinical CT scanners providing image voxel sizes above 100 µm.

Technical and practical improvements in arthroscopic indentation technique for diagnostics of articular cartilage softening.

Indentation measurements have been proposed to serve as sensitive in vivo diagnostics of cartilage degeneration. However, practical difficulties have hindered the use of quantitative indentation techniques during routine arthroscopies. In this study we modified the previously commercial indentation technique by designing software for quality control of manual indentations. With the modifications, our aim was to introduce more rapid and less erroneous measurements, as well as more automatic and objective analyses. The performance of the technique was tested in situ using six bovine medial tibial plateaus. All measurements were conducted by three operators. The intraoperator reproducibility was reasonable (CV%  = 7.1%) and the interoperator reproducibility was good (intraclass correlation coefficient  = 0.976). Further, the novel technique was tested by a single operator using 10 bovine medial tibial plateaus. The indentation stiffness values determined with the arthroscopic instrument correlated significantly with the dynamic (r = 0.823) and equilibrium (r = 0.752) moduli as well as tissue water (r =  -0.830) and hydroxyproline (r = 0.776) contents. To conclude, the novel measurement technique showed good reproducibility and was found to give valuable information on cartilage properties. Most importantly, the measurements and analyses were more straightforward and automatic than those introduced in the original indentation approach.

Simultaneous ultrasound measurement of articular cartilage and subchondral bone.

OBJECTIVE: In osteoarthritis (OA), subchondral sclerosis takes place during cartilage degeneration. High frequency ultrasound (12-55MHz) has been shown to diagnose degenerated articular cartilage, while 0.1-1MHz ultrasound has been applied for clinical characterization of bone and diagnostics of osteoporosis. The aim of the study is to investigate, for the first time, the feasibility of 5MHz ultrasound for simultaneous analysis of articular cartilage and subchondral bone. METHODS: Osteochondral samples (n=10) were prepared from fresh and visually normal bovine medial tibial plateaus. Acoustic properties of the cartilage and subchondral bone were measured with a scanning ultrasound system using the pulse-echo geometry and compared with biomechanical, histological and compositional reference data. RESULTS: The apparent integrated backscatter (AIB) from internal cartilage showed significant partial correlations with hydroxyproline (Hypro) (r=0.58, P=0.000), water content (r=-0.52, P=0.001) and dynamic modulus (r=0.57, P=0.000) of the tissue. Weak but statistically significant correlation was found between the bone AIB and mineral density of the subchondral plate (r=-0.34, P=0.041). Topographical variations in cartilage thickness could be detected using ultrasound. Composition, thickness and mechanical properties of the cartilage varied significantly across the tibial plateau. For the calculated ultrasound parameters, the variation was significant only between a few locations. CONCLUSIONS: Pulse-echo ultrasound geometry at 5MHz was feasible for simultaneous measurement of the acoustic properties of articular cartilage and subchondral bone. However, the relationships between the ultrasound parameters and properties of cartilage and bone were not as strong as reported earlier in studies focusing only either on bone or cartilage. Simultaneous measurement of both tissues compromises, due to natural curvature of articulating surfaces, the perpendicularity of the incidence of the ultrasound pulse. Obviously, this source of uncertainty should be minimized in order to enable effective clinical use of ultrasound in simultaneous measurement of articular cartilage and subchondral bone.

Simultaneous computed tomography of articular cartilage and subchondral bone.

OBJECTIVE: Contrast agent enhanced computed tomography (CECT) may be used to detect depletion of superficial proteoglycans in articular cartilage. In principle, computed tomography can also be used to diagnose the state of subchondral bone. Because osteoarthritis affects both cartilage and bone, we aimed to evaluate the feasibility of the CECT to simultaneously assess the state of these tissues. Further, we studied the spatial variation of contrast agent content in the CECT, properties of subchondral bone and the mechanical stiffness of articular cartilage across the bovine medial tibial plateau. METHODS: Osteochondral samples (n=10) were prepared from fresh and visually intact bovine medial tibial plateaus. The dynamic mechanical modulus of the samples was measured using an arthroscopic indentation device. Subsequently, the samples were scanned with a peripheral quantitative computed tomography (pQCT) device prior to and after 35.5h of immersion in an anionic iodinated contrast agent, (ioxaglate) solution. The thickness of the cartilage was measured with ultrasound and pQCT. RESULTS: In the medial tibial plateau, the site-dependent variation in the dynamic modulus, thickness of the cartilage, thickness of the subchondral plate and contrast agent content in the superficial cartilage was statistically significant (P<0.01). The linear correlation between the superficial contrast agent content and the dynamic modulus was rho=-0.80 (P<0.01). DISCUSSION: The CECT enabled simultaneous analysis of the contrast agent penetration into cartilage, cartilage thickness and subchondral bone density and thickness. The contrast agent content in cartilage depends on the composition and structure of the tissue. Thereby the CECT also provided indirect information on the mechanical properties of the tissue, analogously to the dGEMRIC. Thus, the CECT may provide means to diagnose simultaneously the integrity of cartilage and subchondral bone in vivo.

Effect of bone marrow on acoustic properties of trabecular bone--3D finite difference modeling study.

The composition of bone marrow is influenced by many factors, such as age and diseases. The present numerical study investigates the contribution of marrow on the acoustic measurements of trabecular bone. Cylindrical bone samples (n = 11), extracted from three anatomical sites of human cadaver knees, were imaged with a high-resolution microtomography (microCT). Three-dimensional finite difference time domain (FDTD) models (Wave 3000 Pro 2.2, Cyberlogic Inc., NY, USA) were created using the segmented microCT images of each sample. First, we evaluated the effect of voxel size on the computer resource requirements, morphological parameters and acoustic simulations. Second, the effect of bone marrow on ultrasonic measurements was assessed. The simulations were repeated with two voxel sizes before and after substitution of bone marrow (i.e., fat) with water. The voxel size of the FDTD mesh controlled the fine structure of the modeled calcified matrix and significantly affected the simulation results. However, present simulations showed that the effect of bone marrow on ultrasound parameters can be reliably simulated with the applied voxel sizes of 72 and 90 microm. Ultrasound attenuation and speed were found (p < 0.01) to decrease and increase, respectively, when bone marrow was substituted with water. Moreover, reflection from the surface of the sample increased (p < 0.01) and backscatter from internal structures decreased (p < 0.01) after removal of marrow. The effect of bone marrow on the acoustic properties was stronger in samples with low bone volume fraction. The present results indicate that the amount and quality of bone marrow significantly influence the acoustic properties of trabecular bone. Possible interindividual differences in the composition of bone marrow may increase uncertainty in clinical ultrasound diagnostics of osteoporosis. Importantly, the effect is most significant in osteoporotic low-density bone.

Contrast agent-enhanced computed tomography of articular cartilage: association with tissue composition and properties.

BACKGROUND: Contrast agent-enhanced computed tomography may enable the noninvasive quantification of glycosaminoglycan (GAG) content of articular cartilage. It has been reported that penetration of the negatively charged contrast agent ioxaglate (Hexabrix) increases significantly after enzymatic degradation of GAGs. However, it is not known whether spontaneous degradation of articular cartilage can be quantitatively detected with this technique. PURPOSE: To investigate the diagnostic potential of contrast agent-enhanced cartilage tomography (CECT) in quantification of GAG concentration in normal and spontaneously degenerated articular cartilage by means of clinical peripheral quantitative computed tomography (pQCT). MATERIAL AND METHODS: In this in vitro study, normal and spontaneously degenerated adult bovine cartilage (n=32) was used. Bovine patellar cartilage samples were immersed in 21 mM contrast agent (Hexabrix) solution for 24 hours at room temperature. After immersion, the samples were scanned with a clinical pQCT instrument. From pQCT images, the contrast agent concentration in superficial as well as in full-thickness cartilage was calculated. Histological and functional integrity of the samples was quantified with histochemical and mechanical reference measurements extracted from our earlier study. RESULTS: Full diffusion of contrast agent into the deep cartilage was found to take over 8 hours. As compared to normal cartilage, a significant increase (11%, P<0.05) in contrast agent concentration was seen in the superficial layer of spontaneously degenerated samples. Significant negative correlations were revealed between the contrast agent concentration and the superficial or full-thickness GAG content of tissue (|R| > 0.5, P<0.01). Further, pQCT could be used to measure the thickness of patellar cartilage. CONCLUSION: The present results suggest that CECT can be used to diagnose proteoglycan depletion in spontaneously degenerated articular cartilage with a clinical pQCT scanner. Possibly, the in vivo use of clinical pQCT for CECT arthrography of human joints is feasible.

Neural network and wavelet recognition of facial electromyographic signals.

The present aim was to explore the possibilities of using neural networks for recognizing significant changes in electrical activity of human facial muscles. We used multilayer perceptron neural networks to recognize bursts of electromyographic signals recorded with bipolar surface electrodes from two subject's facial muscles. Wavelets were applied for the detection of high frequency components of electromyographic signals. Coefficients of wavelets were used as an input to a neural network in order to differentiate bursts from the signals. The results showed that the recognition of bursts was very successful resulting to 84-97 percent total accuracies. The results were very encouraging and suggest further that the measurement of facial muscle activity may be a potentially useful computer input signal, for example, for affective computing which can be seen as a future versatile interaction between the computer and the user.