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PubMed2002

Low-density lipoprotein particle size, central obesity, cardiovascular fitness, and insulin resistance syndrome markers in obese youths.

OBJECTIVE: (1) To determine the prevalence of small dense low-density lipoprotein (SDLDL) particles in obese youths and (2) to compare youths with SDLDL and large buoyant LDL (LBLDL) subclass phenotypes in total body and abdominal fatness, cardiovascular (CV) fitness, and markers of the insulin resistance syndrome (IRS). DESIGN: For group comparisons, subjects were dichotomized into either SDLDL phenotype group or LBDL phenotype group based on LDL particle size. SUBJECTS: Obese 13 to 16-y-olds (n=80) who had a triceps skinfold greater than the 85th percentile for gender, ethnicity, and age. MEASUREMENTS: LDL particle size, plasma lipids and lipoprotein concentrations, plasma glucose and insulin concentrations, and blood pressures; percentage body fat, visceral adipose tissue (VAT); VO(2) at a heart rate of 170 bpm as an index of CV fitness. RESULTS: The prevalence of the SDLDL phenotype was 54% among the 80 obese youths. Although overall body fatness (ie BMI and percentage body fat) and CV fitness were similar between the two LDL phenotype groups, the SDLDL phenotype group had significantly higher weight, waist circumference and VAT than the LBLDL phenotype group. With respect to the IRS markers, youths with the SDLDL phenotype had significantly higher triacylglycerol (TAG), very low-density lipoprotein cholesterol (VLDLC), apolipoprotein B (apo B), and total cholesterol-to-high-density lipoprotein ratio (TC/HDLC) than youths with the LBLDL phenotype. LDL particle size as a continuous variable was significantly correlated with TAG, VLDLC, apo B, HDLC, and TC/HDLC. Plasma TAG and HDLC concentrations were independent predictors of LDL particle size. CONCLUSION: (1) The SDLDL phenotype was common in obese youths and (2) the relationships of LDL particle size with several of the IRS markers suggested that already in adolescence the expression of the SDLDL phenotype might be an important risk factor for future coronary heart disease mortality and morbidity.

Abdomen↗

PubMed2006

Particle-size distribution and packing fraction of geometric random packings.

This paper addresses the geometric random packing and void fraction of polydisperse particles. It is demonstrated that the bimodal packing can be transformed into a continuous particle-size distribution of the power law type. It follows that a maximum packing fraction of particles is obtained when the exponent (distribution modulus) of the power law function is zero, which is to say, the cumulative finer fraction is a logarithmic function of the particle size. For maximum geometric packings composed of sieve fractions or of discretely sized particles, the distribution modulus is positive (typically 0<alpha<0.37). Furthermore, an original and exact expression is derived that predicts the packing fraction of the polydisperse power law packing, and which is governed by the distribution exponent, size width, mode of packing, and particle shape only. For a number of particle shapes and their packing modes (close, loose), these parameters are given. The analytical expression of the packing fraction is thoroughly compared with experiments reported in the literature, and good agreement is found.

Journal Article↗

PubMed1992

Change in LDL particle size is associated with change in plasma triglyceride concentration.

Low density lipoprotein (LDL) particle size is inversely associated with plasma triglyceride concentration in cross-sectional analyses. In the present study, changes in the LDL particle size of 227 participants of the Framingham Offspring Study were analyzed longitudinally by nondenaturing gradient gel electrophoresis at two examinations that were separated by 3-4 years. All subjects had triglyceride concentrations < 400 mg/dl at both exams. Using laser scanning densitometry to assess mean LDL particle size, 56% of samples displayed a change in size: 41% had a one-band size change, 13% had a two-band change, and 2% had a three-band change. These changes in size corresponded to a 15% change in pattern type, based on pattern A and B terminology. There was a significant inverse association between change in LDL size and change in triglyceride (p < 0.0001) and glucose (p < 0.004) concentrations, body weight (p < 0.02), and age (p < 0.03). There was also a significant positive association with change in high density lipoprotein (HDL) cholesterol concentration (p < 0.0001). Change in LDL cholesterol concentration, as calculated by use of the Friedewald formula, however, showed no significant association with change in LDL size (p < 0.9). There was also no significant association with change in smoking or blood pressure, but there was a nonsignificant inverse trend associated with alcohol intake (p < 0.08).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

The cryopreservation of liposomes. 2. Effect of particle size on crystallization behavior and marker retention.

Liposome dispersions (bilayer composition Phospholipon 100H/dicetylphosphate (molar ratio 10:1) dispersed in 10 mM Tris buffer) are frozen in a differential scanning calorimeter. In the cooling curves of the dispersions a heat-flow below -40 degrees C is observed. This heat-flow is due to the crystallization of maximally supercooled water. Evidence is provided that at this temperature, defined as the homogeneous nucleation temperature, part or all encapsulated water in the liposomes crystallizes. At a cooling rate of 10 degrees C/min only for small liposomes with particle sizes below approximately 0.2 micron the internal volume crystallizes at the homogeneous nucleation temperature. After a freezing/thawing cycle of the liposomal dispersions retention of the water-soluble marker carboxyfluorescein (CF) was significantly better if crystallization of the encapsulated volume occurred at the homogeneous nucleation temperature. Up to 55% retention of CF in dispersions with mean vesicle sizes below 0.2 micron was found after storage for 45 min at -50 or -75 degrees C. Only relatively small particle size alterations were found in comparison with the original mean particle sizes after a freezing/thawing cycle with storage for 45 min at -50 or -75 degrees C. Independent of particle size, dispersions stored for 45 min at -25 degrees C showed low CF retention (less than 10%) after thawing. For most of the liposome dispersions stored at -25 degrees C, large particle size alterations compared to the original particle sizes were observed after a freezing/thawing cycle.

Cryopreservation↗

PubMed2004

Effect of ascorbic acid and particle size on iron absorption from ferric pyrophosphate in adult women.

The effects of added ascorbic acid and particle size on iron absorption from ferric pyrophosphate were evaluated in adult women (9-10 women/study) based on erythrocyte incorporation of iron stable isotopes (57Fe or 58Fe) 14 days after administration. Three separate studies were made with test meals of iron-fortified infant cereal (5 mg iron/meal) and the results are presented as geometric means and relative bioavailability values (RBV, FeSO4 = 100%). The results of study 1 showed that iron absorption was significantly lower from ferric pyrophosphate (mean particle size 8.5 microm) than from FeSO4 in meals without ascorbic acid (0.9 vs. 2.6%, p < 0.0001, RBV 36%) and in the same meals with ascorbic acid added at a 4:1 molar ratio relative to fortification iron (2.3 vs. 9.7%, p < 0.0001, RBV 23%). Ascorbic acid increased iron absorption from ferric pyrophosphate slightly less (2.6-fold) than from FeSO4 (3.7-fold) (p < 0.05). In studies 2 and 3, RBV of ferric pyrophosphate with an average particle size of 6.7 microm and 12.5 pm was not significantly different at 52 and 42% (p > 0.05), respectively. In conclusion, the addition of ascorbic acid increased fractional iron absorption from ferric pyrophosphate significantly, but to a lesser extent than from FeSO4. Decreasing the mean particle size to 6.7 microm did not significantly increase iron absorption from ferric pyrophosphate.

Adult↗

PubMed2004

Milk-derived fatty acids are associated with a more favorable LDL particle size distribution in healthy men.

A predominance of small dense LDL (sdLDL) particles is a well-established component of the atherogenic lipoprotein phenotype associated with insulin resistance and increased risk for coronary heart disease. However, the influence of diet on LDL particle size distribution is not clear. We investigated (cross-sectionally) the relations between LDL profile and dietary fatty acids (FAs) in 291 healthy men (62-64 y old) with a range of insulin sensitivities. Individuals completed a 7-d dietary record, and fasting plasma insulin, lipid, and lipoprotein concentrations as well as serum and adipose tissue FA composition were determined. The LDL profile was examined by polyacrylamide gradient gel electrophoresis, protein-staining, and quantitative scanning, giving LDL peak particle size and the percentage distribution of LDL in 4 subfractions. The men were divided into tertiles of percentage distribution of sdLDL. Small dense LDL was positively related to plasma triacylglycerol and fasting insulin concentrations (both P < 0.0001) and inversely related to HDL cholesterol (P < 0.0001). No strong relations were found between sdLDL and the reported intake of SFA, monounsaturated fatty acids, or PUFA. However, individual FAs typically found in milk products were associated with a more favorable LDL profile (i.e., fewer sdLDL particles). This was shown for 4:0-10:0 and 14:0 in the diet (both P < 0.05), 15:0 and 17:0 in serum phospholipids (both P < 0.05), and 15:0 in serum nonesterified FAs (P < 0.01). Furthermore, 20:3(n-6) in adipose tissue and serum phospholipids was positively related to sdLDL. Therefore, LDL particle size distribution appears to be modified by dietary factors with an apparently beneficial effect of milk products.

Adipose Tissue↗

PubMed1982

Effects of particle size and perfusate composition on the uptake of colloidal gold by the rabbit thoracic aorta perfused in situ.

The influence has been investigated of particle size on the uptake of radioactive gold colloid by the rabbit thoracic aorta perfused in situ. Particles ranging in diameter from 14 nm to 40 nm were suspended in 0.9% NaCl and infused either at a pressure of 15 mm Hg for times of between 2 1/2 and 60 min or at pressure of between 15 and 160 mm Hg for 5 min. Uptake by the whole intima-media increased with perfusion time and hydrostatic pressure but did not depend on particle size. Radioactive assay of serial sections across the aortic wall also showed that particle size did not influence the distribution of tracer. An effect of perfusate composition on uptake was demonstrated in further experiments in which particles either 14 or 40 nm in diameter were suspended in pooled rabbit serum and infused at pressures of between 15 and 140 mm Hg for 5 min. Uptake and transmural distribution were again independent of particle size, but uptake was 4-5-fold less than when the particles were perfused in saline. Under all perfusion conditions radioactivity fell steeply across the intima and then rose gradually across the media and adventitia. Radioactivity in the outer media and adventitia increased with perfusion time but little change could be detected in intimal activity. In transmission electron micrographs, particles in the intima were not seen to penetrate the internal elastic lamella and in the outer media particles remained extracellular and did not enter collagen bundles. Autoradiographs showed that particles in the intima were uniformly distributed around the circumference of the vessel but in the outer media and adventitia particles usually clustered close to the vasa vasorum.

Animals↗

PubMed2003

The polymorphism of the beta3-adrenergic receptor gene is associated with reduced low-density lipoprotein particle size.

People with a predominance of small, dense low-density lipoprotein (LDL) particles appear to be at increased risk for coronary disease, independent of LDL cholesterol levels. The Trp64Arg variant of the beta3-adrenergic receptor gene is reported to be associated with abdominal obesity and resistance to insulin, and as a consequence, this variant may be a genetic factor in the development of atherosclerosis. Therefore, we investigated whether the beta3-adrenergic receptor polymorphism contributes to the distribution of LDL particle size in 136 Japanese subjects, aged 33 to 59 years, who visited for a routine annual checkup. None of these subjects were taking any medication. The diameter of LDL particles was determined at their peak size using nondenaturing 2% to 16% polyacrylamide gradient gels using fresh plasma samples. The genotype frequencies were: Trp/Trp, 71.3%; Try/Arg, 22.1%; and Arg/Arg, 6.6%, with allele frequencies of 0.82 for Trp64 and 0.18 for Arg64. The subjects with the Arg/Arg genotype had significantly higher levels of fasting plasma insulin and triglycerides and an insulin resistance index of homeostasis model assessment (HOMA-R), and significantly smaller LDL particle size than did the subjects with the Trp/Trp genotype. After adjusting for fasting insulin, body mass index (BMI), and HOMA-R index, there was no longer an observed difference in LDL particle size. The number of the Arg64 allele in individuals was significantly related with fasting insulin, BMI, triglycerides, glycosylated hemoglobin (HbA1c), and fasting glucose, and it was inversely related with LDL particle size. After adjusting for triglyceride, fasting insulin levels, and HOMA-R index, LDL particle size was no longer inversely correlated with the Arg allele. These findings suggest that the Trp64Arg variant in the beta3-adrenergic receptor gene may be associated with reducing LDL particle size, probably due to insulin resistance.

Adult↗

PubMed2006

Influence of particle size on drug delivery to rat alveolar macrophages following pulmonary administration of ciprofloxacin incorporated into liposomes.

In order to confirm the efficacy of ciprofloxacin (CPFX) incorporated into liposomes (CPFX-liposomes) for treatment of respiratory intracellular parasite infections, the influence of particle size on drug delivery to rat alveolar macrophages (AMs) following pulmonary administration of CPFX-liposomes was investigated. CPFX-liposomes were prepared with hydrogenated soybean phosphatidylcholine (HSPC), cholesterol (CH) and dicetylphosphate (DCP) in a lipid molar ratio of 7/2/1 by the hydration method and then adjusted to five different particle sizes (100, 200, 400, 1000 and 2000 nm). In the pharmacokinetic experiment, the delivery efficiency of CPFX to rat AMs following pulmonary administration of CPFX-liposomes increased with the increase in the particle size over the range 100-1000 nm and became constant at over 1000 nm. The concentrations of CPFX in rat AMs until 24 h after pulmonary administration of CPFX-liposomes with a particle size of 1000 nm were higher than the minimum inhibitory concentration of CPFX against various intracellular parasites. In a cytotoxic test, no release of lactate dehydrogenase (LDH) from rat lung tissues by pulmonary administration of CPFX-liposomes with a particle size of 1000 nm was observed. These findings indicate that efficient delivery of CPFX to AMs by CPFX-liposomes with a particle size of 1000 nm induces an excellent antibacterial effect without any cytotoxic effects on lung tissues. Therefore, CPFX-liposomes may be useful in the development of drug delivery systems for the treatment of respiratory infections caused by intracellular parasites, such as Mycobacterium tuberculosis, Chlamydia pneumoniae and Listeria monocytogenes.

Administration, Intranasal↗

PubMed1987

Deposition and clearance of monodisperse aerosols in the calf lung: effects of particle size and a mucolytic agent (bromhexine)

Mucociliary clearance and retention of monodisperse aerosols of radiolabelled polystyrene particles of both 3.3 microns and 5 microns diameter were investigated in four healthy calves and two sick calves. The effect of the mucolytic agent bromhexine was also assessed at two dosage levels. There were significant differences (P less than 0.05) in clearance rate constant between calves, but similar patterns of clearance for each calf. These characteristics of mechanical lung clearance did not vary over a two month period. Values of clearance rate constant and percentage retention varied significantly (P less than 0.001) between the two different particle sizes, 5 microns particles giving faster clearance and lower retention of particles than 3.3 microns particles. Bromhexine at the recommended dose of 1.6 mg/kg 0.75 caused a significant (P less than 0.05) increase in clearance rate in both healthy and sick calves, but affected percentage retention only in sick calves. This study illustrates the variation in mucociliary clearance rates shown by individuals and also underlines the importance of particle size in aerosols used for studies of pulmonary deposition and clearance. The work also indicates that bromhexine may be of use in the therapy of respiratory disease in calves.

Aerosols↗

PubMed2005

In vitro determination of the optimal particle size for nebulized aerosol delivery to infants.

We investigated the in vitro influence of breathing patterns on lung dose (LD) and particle size distribution in an infant upper airway cast model in order to determine the optimal particle size for nebulized aerosol delivery to infants. Budesol (nebulizer solution of budesonide) delivery from a perforated vibrating membrane nebulizer (eFlow Baby functional prototype) through an upper airway cast of a nine month old infant (SAINT-model) was measured at a fixed respiratory rate (RR) of 30 breaths per minute (bpm) and a tidal volume (Vt) of 50, 100, and 200 mL, respectively, and at a fixed Vt of 100 mL and a RR of 30, 60, and 78 bpm, respectively. LD expressed as a percentage of the nominal dose (ND; range, 5.8-30.3%) decreased with increasing Vt (p < 0.001) and with increasing RR (p < 0.001). Median mass aerodynamic diameter (MMAD) after passage (range, 2.4-3.4 microm) through the upper airway cast showed a negative correlation with increasing Vt (p < 0.001) and with increasing RR (p = 0.015). Particles available as LD for all simulated breathing pattern showed a particle size distribution with a MMAD of 2.4 microm and a geometric standard deviation (GSD) of 1.56. From our in vitro study, we conclude that the optimal particle size for nebulized aerosols for inhalation therapy for infants should have a MMAD of <2.4 microm.

Administration, Inhalation↗

PubMed2001

The effects of particle size distribution on the settleability of CSOs pollutants.

Over the past decades, flocculation and/or sedimentation processes have been adopted to remove pollutants from CSOs. It has been learned that major factors affecting settlement of pollutants are the particle size distribution, their settling velocities and their specific gravity. It is, therefore, a good idea to analyze the particle size distribution and settleability of CSOs pollutants in order to develop details in designing a process. Discussed in this study are pollutant characteristics of CSOs such as particle size distribution and settleability of pollutants. The power law function is applied and is found to be an effective and reliable index for expressing the particle size distribution of pollutants in CSOs. Based on the particle size spectrum analysis, the tendency toward settling and simultaneous flocculation-settling phenomenon of CSOs pollutants is described. Based on the regression analysis it is observed that the derived constants of curves representing settling velocity profile are proportional to the initial concentration of particles and to the beta-values of power law distributions. It is also revealed that the simultaneous flocculation-settling processes are effectively described by the changes of the average particle diameter and of the beta-values of power law distributions.

Geologic Sediments↗

PubMed2005

In vivo tumor targeting of tumor necrosis factor-alpha-loaded stealth nanoparticles: effect of MePEG molecular weight and particle size.

The aim of this study is to reveal the influence of methoxypolyethyleneglycol (MePEG) molecular weight and particle size of stealth nanoparticles on their in vivo tumor targeting properties. Three sizes (80, 170 and 240nm) of poly methoxypolyethyleneglycol cyanoacrylate-co-n-hexadecyl cyanoacrylate (PEG-PHDCA) nanoparticles loading recombinant human tumor necrosis factor-alpha (rHuTNF-alpha) were prepared at different MePEG molecular weights (MW=2000, 5000 and 10,000) using double emulsion method. The opsonization in mouse serum was evaluated by Coomassie brilliant blue staining of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Phagocytosis was evaluated by incubating (125)I-rHuTNF-alpha-loaded nanoparticles with mouse macrophages (RAW264.7). The pharmacokinetics, biodistribution and tumor targeting studies were performed in S-180 tumor-bearing mice. Higher MePEG molecular weight provided thicker fixed aqueous layer thickness (FALT) and smaller particle size offered higher surface MePEG density. The serum protein adsorption and phagocytic uptake were markedly decreased for the nanoparticles with higher MePEG molecular weight or smaller size. The particles (80nm) made of PEG(5000)-PHDCA, possessing a thicker FALT (5.16nm) and a shortest distance (0.87nm) between two neighboring MePEG chains, showed the strongest capacity of decreasing protein adsorption and phagocytic uptake. These particles extended the half-life of rHuTNF-alpha in S-180 tumor-bearing mice by 24-fold (from 28.2 min to 11.33 h), elevated the rHuTNF-alpha peak concentration in S-180 tumors by 2.85-fold and increased the area under the intratumoral rHuTNF-alpha concentration curve by 7.44-fold. The results of the present study showed PEG-PHDCA nanoparticles with higher MePEG molecular weight and smaller particle size could achieve higher in vivo tumor targeting efficiency.

Animals↗

PubMed1988

An investigation of optimal gold particle size for immunohistological immunogold and immunogold-silver staining to be viewed by polarized incident light (EPI polarization) microscopy.

We investigated the optimal gold particle size for use with polarized incident light (epi polarization) microscopy with immunogold immunohistological preparation in both immunogold indirect (IGS) and silver-enhanced immunogold-silver staining (IGSS) techniques. A range of gold particle sizes from 5 nm-40 nm was used along with tissue of known immunoreactivity with a well-characterized primary monoclonal antibody. Checkerboard titrations were carried out for each technique and for each particle size. The preparations were viewed using a standard polarized incident light microscope and assessed in a semi-quantitative manner. Adequate visualization of gold particles was achieved using the indirect staining method only with a particle size of 40 nm. With silver enhancement (IGSS), particles of all sizes were clearly seen. However, 5-nm particles were considered optimal for this method because of reduced background staining, high titration of antisera possible, and crisp localization of the visual signal.

Gold↗

PubMed1981

Oral versus vaginal absorption in oestradiol in postmenopausal women. Effects of different particles sizes.

Crystalline oestradiol-17 beta is poorly absorbed from the gastrointestinal tract. Three different fractions and a standard fraction containing oestradiol- 17 beta of a known particle size and surface area, were administered orally, to postmenopausal women, to test if changes in particle size will influence the absorption. The bioavailability of each fraction was determined by measurements of peripheral plasma oestrogens. Two different dosages of the standard fraction were given vaginally to compare the bioavailability after oral and vaginal administration. The gastrointestinal absorption was dependent of the particle size of oestradiol. The smaller particle the more rapid and effective absorption as reflected by increasing area under the plasma concentration curve of oestrone and oestradiol. The smallest particle, however, resulted in a pronounced initial oestradiol peak. The coarser particles were more slowly absorbed with more even plasma oestrogen elevation for a sustained period of time. The vaginal absorption of oestradiol was more effective than the gastrointestinal. When the same amount of an equal preparation according to particle size, was given vaginally the maximal plasma concentration was almost 40 times higher than when given orally.

Absorption↗

PubMed2006

Effect of weight loss resulting from a combined low-fat diet/exercise regimen on low-density lipoprotein particle size and distribution in obese women.

Weight loss resulting from diet interventions has been shown to favorably affect low-density lipoprotein (LDL) particle size and distribution, and, hence, decrease cardiovascular disease risk. However, the effect of a dietary weight loss strategy when combined with exercise, on LDL electrophoretic characteristics, has yet to be tested. This study examined the effect of a weight loss intervention that combined a low-fat diet with moderate endurance training, on LDL particle size and distribution in obese women. Thirty obese, hypercholesterolemic women participated in a controlled longitudinal weight loss trial, which consisted of (1) a 2-week pre-stabilization phase, (2) a 20-week weight loss phase, and (3) a 2-week post-stabilization phase. Weight reduction resulted from a low-fat diet (<30% fat, 50%-60% carbohydrate, 20% protein) combined with an endurance training program (>40 minutes moderate training, 3 times per week). Mean weight loss was 14.8% (P < .01) of initial body weight. Total, LDL cholesterol, and triacylglycerol concentrations decreased (P < .01) by 8.9%, 7.5%, and 27.1%, respectively, whereas high-density lipoprotein cholesterol concentrations increased (P < .01) by 9.9%. No significant differences were noted for LDL peak or integrated particle size. The relative proportion of small, medium, and large particles was not significantly different posttreatment. Estimated cholesterol concentrations in large- and medium-sized LDL particles decreased (P < .05) by 15.3% and 5.9%, respectively, as a result of weight loss. No effect was noted for estimated cholesterol concentrations in small size LDL particles. In conclusion, these findings suggest that weight loss, resulting from a low-fat diet/exercise program, has only a minimal effect on LDL particle size and distribution.

Adult↗

PubMedDate not supplied

Drug particle size influence on enteric beads produced by a droplet extrusion/precipitation method.

The influence of drug particle size on the production of enteric beads by a polymer precipitation technique was investigated. Drug particle dimensions are known to play an important role in most microencapsulation techniques. Bead morphology was greatly influenced by drug particle size, and spherical shaped beads could only be obtained after size reduction of nimesulide crystals. This is confirmed by the angle of repose measurements, which show a significant decrease in theta values when beads are formulated with smaller drug particles. Furthermore, results show that drug encapsulation efficiency and in vitro drug release rates are also greatly dependent on both drug particle size and drug/polymer ratio in the initial suspension. Preparations containing 10.2 microm drug particles show a two-fold increase in the release rates when compared to those prepared with 40 microm particles.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed2005

Hydrolysis of tetracalcium phosphate under a near-constant-composition condition--effects of pH and particle size.

Tetracalcium phosphate (TTCP) is a component of a number of calcium phosphate cements used clinically for bone defect repairs. The strength, phase composition, and solubility of the set cement are highly dependent on the reactions of the cement components during setting. This study investigated hydrolysis reactions of TTCP under solution compositions chosen to mimic the compositions of the cement liquid during setting. The study utilized a pseudo-constant-composition technique that allowed both the rate and stoichiometry of the reaction to be determined while the reaction proceeded under a specific, constantly held solution pH, thereby keeping a constant calcium-to-phosphate ratio in solution. The hydrolysis experiments were conducted using either a fine (median particle size 3.5 microm) or coarse (median particle size 13.2 microm) TTCP powder at pH 7, 8 and 10. Low crystalline calcium (Ca)-deficient hydroxyapatite (HA) was the product in all experiments. Both the solution pH and TTCP particle size produced significant effects on all aspects of the hydrolysis reaction. At a given pH, the fine TTCP produced a HA product with a greater Ca deficiency than did the coarse TTCP. For a given particle size, the Ca deficiency generally decreased with increasing pH. Hydrolysis reaction rate generally decreased with increasing pH or TTCP particle size. At pH 7 and 8, the solution was undersaturated with respect to TTCP and supersaturated with respect to HA, suggesting that the reaction rate was limited by TTCP dissolution. In contrast, at pH 10, the solution was approximately saturated with respect to TTCP and highly supersaturated with respect to HA, suggesting that HA formation was the rate-determining step of the reaction. The findings provided useful insights into the setting reaction mechanisms of TTCP-containing calcium phosphate cements.

Biocompatible Materials↗