Ultrasound for Characterizing Colloids - Particle Sizing, Zeta Potential, Rheology

Ultrasonic devices for the measurement of speed of sound (SOS) and broadband ultrasonic attenuation (BUA) generally use either a contact or water bath method. The aim of this study was to compare these two methods while determining the influence of soft tissue, pathlength (heel width and bone width), and a fixed heel dimension on SOS (m/second) and BUA (dB/MHz). Ultrasonic measurements were made using a CUBA Research system utilizing a pair of 1 MHz unfocused transducers with mean precision CV = 0.7% and 6.0% for all SOS and BUA measurements, respectively. SOS and BUA were determined in 24 human cadaveric heels under three conditions: contact method (heel intact), water bath method (heel intact), water bath method (no soft tissue). Although there were significant differences between measurements using contact and water bath techniques (heel intact), their correlations were high (r = 0.858 for SOS and r = 0. 937 for BUA; P < 0.001). After removal of soft tissue, SOS significantly increased (78 m/second; P < 0.001) whereas there was no change in BUA (P > 0.05). Heel width correlated with SOS measurements (-0.224 < r < -0.347; P < 0.001) and bone width correlated with BUA measurements (0.198 < r < 0.276; P < 0.001). The practice of using a fixed heel dimension (Lunar Achilles) was investigated by comparing SOS calculated with measured heel thickness and a value of 4 cm (Lunar Achilles). SOS increased by 42 m/second (2.7%) using the fixed heel dimension compared with measured heel widths. This study demonstrates the similarity between contact and water bath-based methods, while showing that the presence of soft tissue reduces SOS but has no effect on BUA. The use of a fixed heel dimension for calculation of SOS overestimates values obtained when using measured heel dimensions, though the values correlate highly (r = 0.98, P < 0.001). In addition, an increase in heel width tends to cause an underestimation of SOS whereas an increase in bone width tends to overestimate BUA, although the effects are relatively small.

The menopause has a large effect on bone density, and hormone replacement therapy (HRT) has been shown to be an effective treatment for preventing postmenopausal bone loss. The aim of this study was to compare the effects of HRT use on speed of sound (SOS) measurements at the radius, tibia, phalanx, and metatarsal with bone mineral density (BMD) measurements of the lumbar spine and proximal femur. The study population consisted of 278 healthy premenopausal women, 194 healthy postmenopausal women, and 126 healthy postmenopausal women currently receiving HRT for one or more years. SOS measurements were taken at the radius, tibia, phalanx, and metatarsal using the Sunlight Omnisense, and BMD measurements at the lumbar spine and proximal femur using Hologic QDR-4500 densitometers. Z-scores were calculated using the postmenopausal control group. Z-score differences between the postmenopausal controls and HRT group, for the entire group and with the HRT group subdivided into three groups based on duration of HRT usage, were calculated. Significant postmenopausal bone loss was found for all SOS and BMD measurements. A positive effect of HRT usage was found for all SOS measurement sites and lumbar spine BMD, although only the radius and tibia SOS and lumbar spine BMD reached statistical significance. The Z-score differences between the two groups were 0.44, 0.37, 0.15, and 0.26 for the radius, tibia, phalanx, and metatarsal SOS respectively, and 0.28, 0.00, and -0.03 for the lumbar spine, femoral neck, and total hip BMD respectively. A clear effect of the duration of HRT use was seen for the radius measurements, the differences being less marked elsewhere. In conclusion, these results demonstrate a positive effect of HRT on SOS measurements at the radius and tibia and BMD measurements of the lumbar spine.

Speed of sound (SOS) measurements, typically made using 1 MHz broadbandpulses, are increasingly used in the clinical diagnosis of bone disorders.Previous in vitro studies indicate that broadband ultrasound pulsesare susceptible to distortion in cancellous bone, leading to imprecise arrivaltime and SOS measurements. We investigated the effect of bandwidth andfrequency on SOS by comparing measurements made using 1 MHz broadband with1 MHz and 300 kHz narrowband toneburst signals in 15 human proximal femurcancellous bone specimens.There was no significant difference in the value of SOS measured from theleading edge of 1 MHz broadband, 1 MHz toneburst and 300 kHz toneburstsignals. Values of SOS in later regions of 1 MHz and 300 kHz tonebursts fellsignificantly (p<0.001) when compared to earlier regions. This decrease inSOS levelled off by the third complete cycle of 300 kHz toneburst signals,reaching a plateau value of 1961±239 m s-1. No plateau SOSvalue was obtained in1 MHz tonebursts. The reproducibility of SOS, as measuredby the coefficient of variation, was higher for later regions of 300 kHztonebursts than for the leading edge of 300 kHz toneburst and 1 MHz broadbandsignals (p<0.005). The correlation between ultrasound measured modulus andcompressive Young's modulus improved when 300 kHz tonebursts (r2 = 0.83)rather than 1 MHz broadband (r2 = 0.77) signals were used to calculate SOS.The improved SOS reproducibility of later regions 300 kHz tonebursts suggestthat it may be beneficial to use such signals rather than 1 MHz broadbandpulses in SOS measurement. Since no reliable SOS measurements could beobtained from any region of 1 MHz tonebursts, the use of high frequencytoneburst signals in cancellous bone has little value.

Osteoporosis is a highly prevalent but preventable disease and, as such, it is important that there are appropriate diagnostic criteria to identify those at risk of low trauma fracture. In 1994 the World Health Organization (WHO) introduced definitions of osteoporosis and osteopenia using T-scores, which identified 30% of all Caucasian post-menopausal women as having osteoporosis. However, the use of the WHO T-score thresholds of -2.5 for osteoporosis and -1.0 for osteopenia may be inappropriate at skeletal sites other than the spine, hip and forearm or when other modalities, such as quantitative ultrasound (QUS) are used. The aim of this study was to evaluate the age-dependence of T-scores for speed of sound (SOS) measurements at the radius, tibia, phalanx and metatarsal by use of the Sunlight Omnisense, to evaluate the prevalence of osteoporosis and osteopenia at these sites by use of the WHO criteria, and calculate appropriate equivalent T-score thresholds. The study population consisted of 278 healthy pre-menopausal women, 194 healthy post-menopausal women and 115 women with atraumatic vertebral fractures. All women had SOS measurements at the radius, tibia, phalanx and metatarsal and bone mineral density (BMD) measurements at the lumbar spine and hip. A group of healthy pre-menopausal women aged 20-40 years from the pre-menopausal group were used to estimate the population mean and SD for each of the SOS and BMD measurement sites. Healthy post-menopausal women were classified into normal, osteopenic or osteoporotic, based upon the standard WHO definition of osteoporosis and expressed as a percentage. We investigated the age-related decline in T-scores from 20-79 by stratifying the healthy subjects into 10-year age groups and calculating the mean T-score for each of these groups. Finally, we estimated appropriate T-score thresholds, using five different approaches. The prevalence of osteoporosis in the post-menopausal women aged 50 years and over ranged from 1.4 to 12.7% for SOS and 1.3 to 5.2% for BMD. The age-related decline in T-scores ranged from -0.92 to -1.80 for SOS measurements in the 60 to 69-year age group and -0.60 to -1.19 for BMD measurements in the same age group. The WHO definition was not suitable for use with SOS measurements, and revised T-score thresholds for the diagnosis of osteoporosis of -2.6, -3.0, -3.0 and -2.2 and for osteopenia of -1.4, -1.6, -2.3, and -1.4, for the radius, tibia, phalanx and metatarsal, respectively, were recommended.

Covering a range of fields in colloid science, this volume focuses on: surfactant aggregates, micelles, vesicles and liquid crystals; colloidal particles - interaction, structure and aggregation; emulsions and concentrated systems; microemulsions; mixed colloidal systems; rheology; biocolloids; and membranes, films and interfaces.

Chapter 5 - Electroacoustic Theory

The aims of this study were to: (a) examine differences in speed of sound (SOS) between the right (SOS(R)) and left (SOS(L)) radius; (b) detect bone loss following proximal forearm fracture by SOS measurement at the radius; and (c) compare SOS(L) and bone mineral density (BMD) of one-third, mid-distal, ultra-distal and total region of the left radius. Two hundred eighty-seven Caucasian women (mean age 60.4+/-6.7 years) participated in this study. All subjects were right-handed. Twenty-seven women (mean age 63.6+/-8.0 years) had suffered a high-energy fracture of the right or left forearm. The SOS was assessed using a quantitative ultrasound device, whereas BMD was measured by dual energy X-ray absorptiometry (DXA). The SOS(R) was significantly higher than SOS(L) (4047.5+/-121.0 vs 4026.3+/-113.4 m/s; p<0.001). The contralateral absolute difference was 1.94% (95% confidence intervals: 1.73-2.15%). In women who had suffered a fracture of their right forearm, SOS(R) was not significantly higher than SOS(L )(3989.9+/-141.8 vs 3985.0+/-151.1 m/s), whereas the bilateral difference was reduced to 1.45%. In women with a previous fracture of the left forearm, SOS(R) was significantly higher than SOS(L) (4076.9+/-92.8 vs 3992.6+/-124.0 m/s; p<0.01) and the bilateral difference was increased to 2.61%. Of the 260 subjects without fracture, 155 had greater SOS in the right radius, 102 had greater SOS in the left radius and 3 patients had equal values of SOS in both bones. Calculated correlations between SOS and BMD were weak to moderate ( r=0.27-0.41; p<0.0001 for all comparisons). The SOS measurements should be performed on both radial bones. A high-energy forearm fracture results in a decrease in SOS measured at the radius. Radial-bone SOS measurements cannot predict forearm BMD.

Ronald Harry Ottewill, who died from cancer on 4 June 2008 in Wickham, UK, was a colloid scientist with unusually broad vision and great energy. He played an important role in the development of soft condensed matter as a distinct subdiscipline of physics.Ron was born on 8 February 1927 in Southall, a suburb of London. He attended local schools and developed an interest in science; he also excelled at cricket and middle-distance running. In 1948 he received a BSc in chemistry, with subsidiary physics, from London University’s Queen Mary College, where he also earned a PhD, supervised by D. C. Jones, in 1952. His thesis was on the adsorption of hydrocarbon vapors on surfaces. In 1952 Ron joined the department of colloid science at Cambridge University. There, working on antigen-antibody reactions supervised by Paley Johnson, he completed a second PhD in 1955. That work initiated a lifelong interest in light scattering and electron microscopy. He stayed in Cambridge for 12 years and developed broad interests in colloid science. In 1964 Ron moved to the chemistry department at Bristol University; he became a professor in 1971 and remained at Bristol for the rest of his career. Ron’s initial task at Bristol was to set up a one-year MSc program in colloid science. He ran it successfully for many years; the program had some 250 graduates, many of whom rose to senior positions in academia and industry. Ron was an inspiring teacher who continued to give about 60 lectures a year even when he was heavily distracted by other activities.In 1964 physical chemistry research at Bristol was centered on surface science. Ron established a colloid group that quickly became world renowned. At that time a main focus of colloid science was understanding the principles underlying the stability of colloidal particles, particularly charged particles, in dilute suspension. For that purpose, Ron developed various well-characterized “model” systems, first basing them on silver iodide and later using colloidal polystyrene. In the 1970s he was one of the first colloid scientists to recognize the challenges posed by concentrated suspensions. Light-scattering experiments with one of us (Pusey) demonstrated the strong influence of interparticle interactions on both the structure and the dynamics of the suspension. In the late 1970s, Ron and John White, then director of the Institut Laue-Langevin (ILL) in Grenoble, France, pioneered the use of neutron scattering in the study of colloid structure and interactions. That became one of Ron’s main interests for the rest of his career. He was very “hands on” and frequently traveled to Grenoble, where he could be found in the instrument halls late at night. The fact that soft matter now commands a large fraction of the beam time at the ILL and other neutron facilities owes much to Ron’s early insights.The synthesis of colloidal particles, particularly with a narrow distribution of size, is a skilled activity beyond the scope of many physicists. Ron and his group were generous in providing samples for others to use. His poly(methyl methacrylate) particles, developed with Imperial Chemical Industries’ (ICI) paints division, became the standard “hard sphere” model colloid, now used by many physicists. The particles were used by William Russel, Paul Chaikin, and David Weitz in their study of colloidal crystallization on the space shuttle and the International Space Station.Ron also was heavily involved in administration and the promotion of colloid science. At Bristol he served terms as chairman of the school of chemistry and dean of science. He was instrumental in setting up the UK Polymer Colloids Forum, which recently established a medal in his name, and the colloid and interface science group of the Royal Society of Chemistry. Ron chaired committees of the ILL and the UK Science and Engineering Research Council. He was also an active member of the “colloid mafia,” which for many years ran the Gordon Conference on Polymer Colloids. Throughout his career Ron was in demand as a consultant for industrial companies such as Procter & Gamble, Exxon Corp, ICI, and BP, whose scientists appreciated his remarkable ability to provide quick, practical solutions to almost any problem.Although he liked to be in charge, Ron was not particularly well organized. His office, with every surface piled high with books and papers, was a standing joke among colleagues and students. But once you got inside—frequently after waiting in line—and found a vantage point from which to see him through the piles, Ron appeared to have all the time in the world and could unerringly find obscure papers relating to experiments done years earlier.Ron will be sorely missed, especially for his open mind, his keenness to help, and his encyclopedic knowledge.Ronald Harry OttewillBRISTOL UNIVERSITYPPT|High resolution© 2009 American Institute of Physics.

The subject of this book is the rheology of colloidal and nanoparticle dispersions. The reader will quickly appreciate the breadth of the subject area and, furthermore, that mastering colloidal suspension rheology requires some basic knowledge in colloid science as well as rheology. Thus, this chapter introduces some basic and simplified concepts in colloid science and rheology prior to embarking on the main theme of the book. As the term colloid is very general we necessarily need to focus on fundamental aspects of basic colloidal particles, their interactions, and their dispersion thermodynamic properties. These are, of course, the basis for understanding more complex systems. The rheology section is provided as an introduction to the basic concepts (a more advanced treatment of rheological testing of colloidal dispersions is provided in Chapter 9). Therefore, this chapter provides the minimum level of understanding that the reader will find valuable for understanding colloidal suspension rheology, as well as a means to introduce nomenclature and concepts used throughout the book. As a consequence, a reader familiar with either or both subjects may still find it valuable to skim through the material or refer back to it as needed. Colloidal phenomena Colloid science is a rich field with an equally rich literature. The reader is referred to a number of excellent monographs that cover the basics of colloid science in much greater detail. These will be presented without derivation. In particular, we use nomenclature and presentation of many ideas following Colloidal Dispersions [1] and Principles of Colloid and Surface Chemistry [2], which may be of help for further reading and inquiry, and for derivations of the results presented herein. Indeed, there are many additional excellent textbooks and monographs on colloid science, and references are provided where they are most relevant throughout this chapter as well as in the other chapters.

North American male reference population for speed of sound in bone at multiple skeletal sites.

Numerous studies have shown that ultrasonic velocity measured in bone provides a good assessment of osteoporotic fracture risk. However, a lack of standardization of signal processing techniques used to compute the speed of sound (SOS) complicates the comparison between data obtained with different commercial devices. In this study, 38 intact femurs were tested using a through-transmission technique and SOS determined using different techniques. The resulting difference in measured SOS was determined as functions of the attenuation and the velocity dispersion. A numerical simulation was used to explain how attenuation and dispersion impact two different SOS measurements (group velocity, velocity based on the first zero crossing of the signal). A new method aimed at compensating for attenuation was devised and led to a significant reduction in the difference between SOS obtained with both signal processing techniques. A comparison between SOS and X-ray density measurements indicated that the best correlation was reached for SOS based on the first zero crossing apparently because it used a marker located in the early part of the signal and was less sensitive to multipath interference. The conclusion is that first zero crossing velocity may be preferred to group velocity for ultrasonic assessment at this potential fracture site.

Experimental evaluation of bone quality measuring speed of sound in cadaver mandibles

The elasticity of biological tissues is one of the physical characteristics of tissues and has attracted attention as a clinical diagnostic parameter. The elasticity can be determined on the microscopic scale with speed of sound (SoS) measurements using acoustic microscopy. In SoS measurements, a thin-sliced section is attached to a glass slide in the same manner as a light microscopic specimen. There are two main methods for preparing thin sections: paraffin-embedding and frozen-section. The frozen-section method requires fewer processing steps from sectioning to measurement and is considered to reduce artifacts in the sample compared with the paraffin-embedding method. Both methods need fixatives to keep tissue structures. Many reports of measurements using frozen sections are focused on soft tissues with relatively high protein contents. In this study, we determined the SoS in thin sections of four types of organs (brain, heart, liver, and kidney) prepared using two different methods (paraffin-embedding and frozen-section) and four different chemical fixatives (formalin, Karnovsky fixative (KF) 0.5% and 2.0% glutaraldehyde, and ethanol). The SoS in heart and liver samples prepared using KF showed good agreement with reported values for raw samples. For samples fixed with KF, the SoS increased as the glutaraldehyde concentration increased from 0.5% to 2.0%. A brain tumor sample was processed with KF 0.5%, and the SoS in the tumor was significantly higher than that in the non-tumor area. The results confirmed that it is possible to measure the SoS in brain samples with low protein contents using appropriate fixatives.

Adsorption isotherms of neutral poly(ethyleneoxide) (PEO), cationic poly-L-lysine (PLL) and homo- and copolymers of diallyl-dimethyl-ammoniumchloride (DADMAC) and N-methyl-N-vinyl-acetamide (NMVA) on colloidal silica and latex particles were determined from the concentration in the supernatant solution. Layer thickness and flocculation of the particles are measured by photon correlation spectrometry. Adsorbed amount, layer thickness and stability of the suspensions are influenced by ionic strength and pH, molar mass and charge densities of the polymers and of the surface. Correlations between flocculation and adsorption parameters are accomplished. With neutral PEO the stability is determined by the layer thickness adjusted by molar mass and coverage; thicknesses ≥ 4 nm stabilize up to high electrolyte concentrations. With high positively charged PE layers (pH ≤7) stable latex suspensions are guaranteed and large electrokinetic influences on the diffusion coefficient depending on the PE/electrolyte ratio are observed. With increasing ionic strength, latex covered with PE layers of low molar mass flocculates, while for that covered with PE layers of high molar mass stabilization occurs. Adsorption of PDADMAC and P(DADMAC-co-NMVA) result in spontaneous flocculation if a certain amount of PE depending on the charge density according to a definite coverage is added. Flocculation at increasing ionic strength can be controlled by the adsorption of PDADMAC depending on the molar mass. At full coverage the suspensions are stabilized if the thickness of the layer is large enough, dependent on ionic strength, charge density and molar mass of the PE.

Computer Simulation of Flocculation Processes: The Roles of Chain Conformation and Chain/Colloid Concentration Ratio in the Aggregate Structures