ASSESSMENT OF POROUS HYDROXYAPATITE FOR BONE REPLACEMENT

PhDHydroxyapatite (HA) is a highly biocompatible calcium phosphate which closely resembles the mineral component of bone. Porous structures composed of biocompatible materials are believed to enhance fixation (and integration) as they encourage the ingrowth of bone into the implant. Consequently there is great interest in the potential of porous HA as an alternative to bone homo grafts and auto grafts. However, despite the interest in the field, there has been no thorough investigation into the physical and structural properties of porous HA and their effects on bone ingrowth. The material used in this study was a carbonated apatite (containing < 0.9 % levels of trace element impurities) with a trabecular macrostructure, that had been converted from bovine cancellous bone. The apparent density of the material ranged from 0.35 -1.45 g.cm-3 and the macrostructural morphology varied from an open equiaxed foam to a columnar honeycomb-like structure. The ultimate compressive stress was strongly related (r = 0.9) to the square of the apparent density, while compressive modulus was influenced by both apparent density and macrostructural morphology. Transmission electron microscopy of human osteoblast-like cells cultured on the material demonstrated that cells were closely associated with the surface. Specimens with densities of 0.6.0.9 and 1.2 g.cm-3 were then implanted in a lapine cancellous site for periods of 10 days, 3, 5, 13 and 26 weeks. After implantation all specimens elicited a highly biocompatible response, with active areas of bone deposition, remodelling and revascularization and no fibrous encapsulation. The amount of bone ingrowth within the implant (25-10%) after.5 weeks was found to vary with apparent density (0.6-1.2 g.cm-3) indicating that osseointegration was a function of macrostructural morphology. Pushout testing of retrieved spedmens indicated that all implants were securely fixed by 5 weeks (2-3 MPa). Compression testing demonstrated that after 5 weeks low density implants were sufficiently reinforced by bone ingrowth to equal the compressive strength of the host tissue (6 MPa) which increased to approximately 20 MPa at 3 and 6 months

The effect of the incorporation of fluoride into strontium containing bioactive glasses

Recently, the porous bioactive glasses have attracted a lot of attention for use as scaffolds for tissue engineering bone; such glasses include the high phosphate, strontium containing glass (Stronbone P). However, the previous studies suggest that strontium can have a detrimental effect on the ability of apatite-like phase formation of the glass. The previously studied high phosphate all Sr glass showed an unidentified phase rather than an apatite-like phase upon immersion. Octa-calcium phosphate (OCP) is believed to be a precursor phase to apatite, however octa-strontium phosphate does not exist. Fluoride is known to knock out the OCP formation and promotes fluorapatite formation. This work presents the incorporation of a small amount of fluoride into calcium/strontium bioactive glasses. Differential scanning calorimetry was used to estimate the glass thermal properties. All of the studied glass compositions were subjected to bioactivity studies in Tris buffer (pH = 7.4) for up to 21 days. The initial glasses and the resultant precipitates were analysed using Fourier transform infrared spectroscopy, X-ray diffraction and magic angle spinning-nuclear magnetic resonance. The findings showed that all the fluoride containing glasses were amorphous and there was a marked increase in the rate of apatite formation in vitro compared to the equivalent fluoride free glasses, particularly for the all strontium containing glass. This indicates that the presence of fluoride affects the pathway of apatite formation, forming fluorapatite directly instead of via the transformation from OCP to hydroxyapatite. Therefore, fluoride may have potential future clinical applications as an additive to increase apatite formation

Strontium substituted bioactive glasses for tissue engineered scaffolds: the importance of octacalcium phosphate

Porous bioactive glasses are attractive for use as bone scaffolds. There is increasing interest in strontium containing bone grafts, since strontium ions are known to up-regulate osteoblasts and down regulate osteoclasts. This paper investigates the influence of partial to full substitution of strontium for calcium on the dissolution and phase formation of a multicomponent high phosphate content bioactive glass. The glasses were synthesised by a high temperature melt quench route and ground to a powder of <38 microns. The dissolution of this powder and its ability to form apatite like phases after immersion in Tris buffer (pH 7.4) and simulated body fluid (SBF) was followed by inductively coupled plasma optical emission spectroscopy (ICP), Fourier transform infra red spectroscopy (FTIR), X-ray powder diffraction (XRD) and (31)P solid state nuclear magnetic resonance spectroscopy up to 42 days of immersion. ICP indicated that all three glasses dissolved at approximately the same rate. The all calcium (SP-0Sr-35Ca) glass showed evidence of apatite like phase formation in both Tris buffer and SBF, as demonstrated after 3 days by FTIR and XRD analysis of the precipitate that formed during the acellular dissolution bioactivity studies. The strontium substituted SP-17Sr-17Ca glass showed no clear evidence of apatite like phase formation in Tris, but evidence of an apatite like phase was observed after 7 days incubation in SBF. The SP-35Sr-0Ca glass formed a new crystalline phase termed “X Phase” in Tris buffer which FTIR indicated was a form of crystalline orthophosphate. The SP-35Sr-0Ca glass appeared to support apatite like phase formation in SBF by 28 days incubation. The results indicate that strontium substitution for calcium in high phosphate content bioactive glasses can retard apatite like phase formation. It is proposed that apatite formation with high phosphate bioactive glasses occurs via an octacalcium phosphate (OCP) precursor phase that subsequently transforms to apatite. The equivalent octa-strontium phosphate does not exist and consequently in the absence of calcium, apatite formation does not occur. The amount of strontium that can be substituted for calcium in OCP probably determines the amount of strontium in the final apatite phase and the speed with which it forms

Rising rural body-mass index is the main driver of the global obesity epidemic in adults

Body-mass index (BMI) has increased steadily in most countries in parallel with a rise in the proportion of the population who live in cities(.)(1,2) This has led to a widely reported view that urbanization is one of the most important drivers of the global rise in obesity(3-6). Here we use 2,009 population-based studies, with measurements of height and weight in more than 112 million adults, to report national, regional and global trends in mean BMI segregated by place of residence (a rural or urban area) from 1985 to 2017. We show that, contrary to the dominant paradigm, more than 55% of the global rise in mean BMI from 1985 to 2017-and more than 80% in some low- and middle-income regions-was due to increases in BMI in rural areas. This large contribution stems from the fact that, with the exception of women in sub-Saharan Africa, BMI is increasing at the same rate or faster in rural areas than in cities in low- and middle-income regions. These trends have in turn resulted in a closing-and in some countries reversal-of the gap in BMI between urban and rural areas in low- and middle-income countries, especially for women. In high-income and industrialized countries, we noted a persistently higher rural BMI, especially for women. There is an urgent need for an integrated approach to rural nutrition that enhances financial and physical access to healthy foods, to avoid replacing the rural undernutrition disadvantage in poor countries with a more general malnutrition disadvantage that entails excessive consumption of low-quality calories.Peer reviewe

Height and body-mass index trajectories of school-aged children and adolescents from 1985 to 2019 in 200 countries and territories: a pooled analysis of 2181 population-based studies with 65 million participants

Summary Background Comparable global data on health and nutrition of school-aged children and adolescents are scarce. We aimed to estimate age trajectories and time trends in mean height and mean body-mass index (BMI), which measures weight gain beyond what is expected from height gain, for school-aged children and adolescents. Methods For this pooled analysis, we used a database of cardiometabolic risk factors collated by the Non-Communicable Disease Risk Factor Collaboration. We applied a Bayesian hierarchical model to estimate trends from 1985 to 2019 in mean height and mean BMI in 1-year age groups for ages 5–19 years. The model allowed for non-linear changes over time in mean height and mean BMI and for non-linear changes with age of children and adolescents, including periods of rapid growth during adolescence. Findings We pooled data from 2181 population-based studies, with measurements of height and weight in 65 million participants in 200 countries and territories. In 2019, we estimated a difference of 20 cm or higher in mean height of 19-year-old adolescents between countries with the tallest populations (the Netherlands, Montenegro, Estonia, and Bosnia and Herzegovina for boys; and the Netherlands, Montenegro, Denmark, and Iceland for girls) and those with the shortest populations (Timor-Leste, Laos, Solomon Islands, and Papua New Guinea for boys; and Guatemala, Bangladesh, Nepal, and Timor-Leste for girls). In the same year, the difference between the highest mean BMI (in Pacific island countries, Kuwait, Bahrain, The Bahamas, Chile, the USA, and New Zealand for both boys and girls and in South Africa for girls) and lowest mean BMI (in India, Bangladesh, Timor-Leste, Ethiopia, and Chad for boys and girls; and in Japan and Romania for girls) was approximately 9–10 kg/m2. In some countries, children aged 5 years started with healthier height or BMI than the global median and, in some cases, as healthy as the best performing countries, but they became progressively less healthy compared with their comparators as they grew older by not growing as tall (eg, boys in Austria and Barbados, and girls in Belgium and Puerto Rico) or gaining too much weight for their height (eg, girls and boys in Kuwait, Bahrain, Fiji, Jamaica, and Mexico; and girls in South Africa and New Zealand). In other countries, growing children overtook the height of their comparators (eg, Latvia, Czech Republic, Morocco, and Iran) or curbed their weight gain (eg, Italy, France, and Croatia) in late childhood and adolescence. When changes in both height and BMI were considered, girls in South Korea, Vietnam, Saudi Arabia, Turkey, and some central Asian countries (eg, Armenia and Azerbaijan), and boys in central and western Europe (eg, Portugal, Denmark, Poland, and Montenegro) had the healthiest changes in anthropometric status over the past 3·5 decades because, compared with children and adolescents in other countries, they had a much larger gain in height than they did in BMI. The unhealthiest changes—gaining too little height, too much weight for their height compared with children in other countries, or both—occurred in many countries in sub-Saharan Africa, New Zealand, and the USA for boys and girls; in Malaysia and some Pacific island nations for boys; and in Mexico for girls. Interpretation The height and BMI trajectories over age and time of school-aged children and adolescents are highly variable across countries, which indicates heterogeneous nutritional quality and lifelong health advantages and risks

Heterogeneous contributions of change in population distribution of body mass index to change in obesity and underweight NCD Risk Factor Collaboration (NCD-RisC)

From 1985 to 2016, the prevalence of underweight decreased, and that of obesity and severe obesity increased, in most regions, with significant variation in the magnitude of these changes across regions. We investigated how much change in mean body mass index (BMI) explains changes in the prevalence of underweight, obesity, and severe obesity in different regions using data from 2896 population-based studies with 187 million participants. Changes in the prevalence of underweight and total obesity, and to a lesser extent severe obesity, are largely driven by shifts in the distribution of BMI, with smaller contributions from changes in the shape of the distribution. In East and Southeast Asia and sub-Saharan Africa, the underweight tail of the BMI distribution was left behind as the distribution shifted. There is a need for policies that address all forms of malnutrition by making healthy foods accessible and affordable, while restricting unhealthy foods through fiscal and regulatory restrictions

Bioactivity And Bone Formation In Silicon-Substituted Hydroxyapatite

Bioactivity and successful bone formation in silicon-substituted hydroxyapatite bone grafts were investigated by using scanning electron microscopy and electron dispersive x-ray spectroscopy. Areas of bone formation have been detected in scanning electron microscopy; and, arranged lamellar collagen has been observed. 20.8% average carbon content rise has been detected between bone graft and the produced bone; and, this has been confirmed to be a gradual increase throughout the interphase. Obvious bone formation and maturation were observed in the samples. Carbon content gradually increased from bone graft to the bone formed, confirming formation of new bone and dissociation of silicon-substituted bone graft

Development of a hydroxyapatite coating containing silver for the prevention of peri-prosthetic infection

We hypothesized that the electrochemical deposition of hydroxyapatite (EHA) can be used to incorporate silver (Ag), providing a controlled and sustained release of Ag ions at a bactericidal concentration. Six groups were investigated: electrochemical co-precipitation of HA and Ag (EHA/Ag); EHA pre-coated discs treated in AgN0(3) (EHA/AgN0(3)); plasma sprayed HA (PHA) pre-coated discs treated in AgN0(3) (PHA/AgN0(3)); EHA with 2 "layers" of Ag (EHA/Ag/2 layers); EHA coating only; and PHA coating only. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) and X-ray diffraction (XRD) analyses quantified coating thickness, calcium/phosphorous ratio, and % atomic silver content, respectively. Inductively coupled plasma-mass spectrometry quantified the amount of Ag released in phosphate-buffered saline, and zone of inhibition tests on agar plates using a lawn of Staph aureus were quantified in each group. XRD and EDX analysis confirmed the presence of Ag in all coatings. EHA coated discs with two layers of Ag and the EHA discs soaked in AgN0(3) showed significantly higher zones of inhibition at all time points when compared with all other groups (except PHA/AgN0(3) on day 0). This study demonstrated that Ag ions can be incorporated into a HA coating using an electrochemical technique. Copyright © 2011 Orthopaedic Research Society

The osteoinductivity of silicate-substituted calcium phosphate

BACKGROUND: The osteoinductivity of silicate-substituted calcium phosphate and stoichiometric calcium phosphate was investigated with use of ectopic implantation. Implants with a macroporosity of 80% and a strut porosity of 30% were inserted into sites located in the left and right paraspinal muscles of six female sheep. METHODS: After twelve weeks in vivo, a longitudinal thin section was prepared through the center of each implant. Bone formation within the implant, bone formation in contact with the implant surface, and implant resorption were quantified with use of a line intersection method. The specimens were also analyzed with use of backscattered scanning electron microscopy and energy-dispersive x-ray analysis. RESULTS: Silicate substitution had a significant effect on the formation of bone both within the implant and on the implant surface during the twelve-week period. Bone area within the implant was greater in the silicate-substituted calcium phosphate group (mean, 7.65% ± 3.2%) than in the stoichiometric calcium phosphate group (0.99% ± 0.9%, p = 0.01). The amount of bone formed at the surface of the implant was also significantly greater in the silicate-substituted calcium phosphate group (mean, 26.00% ± 7.8%) than in the stoichiometric calcium phosphate group (2.2% ± 2.0%, p = 0.01). Scanning electron microscopy demonstrated bone formation within pores that were <5 μm in size, and energy-dispersive x-ray analysis confirmed the presence of silicon within the new bone in the silicate-substituted calcium phosphate group. CONCLUSIONS: The formation of bone within muscle during the twelve-week period showed both silicate-substituted calcium phosphate and stoichiometric calcium phosphate to be osteoinductive in an ovine model. Silicate substitution significantly increased the amount of bone that formed and the amount of bone attached to the implant surface. New bone formation occurred through an intramembranous process within the implant structure