|Articles about Biomaterials|
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| Mathematical analysis of affinity membrane chromatography
Shi, W., F. Zhang, et al. (2005), J Chromatogr A 1081(2): 156-62.
Abstract: A mathematical model including convection, diffusion and Freundlich adsorption is developed. To examine the validity of the model, the affinity membranes were prepared by coating chitosan on the nylon membranes, a ligand of poly-L-lysine was bound to the chitoan-coating membranes, and the adsorption behavior of bilirubin through the stacked affinity membranes was investigated. The agreements between the theoretical and experimental results are exceptional. Using our new model, we show that: (1) As Pe increases, the breakthrough curves become sharper. For Pe greater than 30, the effect of axial diffusion is insignificant; (2) As m increases, the time of total saturation is delayed and the loading capacity at the point of breakthrough is increased; (3) As n decreases, the time of total saturation is delayed and the loading capacity at the point of breakthrough is increased; (4) As r increases, both the time of total saturation and the loading capacity at the point of breakthrough are increased; (5) adsorption rate influences the time of total saturation strongly but contributes little to the loading capacity.
| Mathematical modelling of the distribution of newly formed bone in bone tissue engineering
Pothuaud, L., J. C. Fricain, et al. (2005), Biomaterials 26(33): 6788-97.
Abstract: New bone formation in bone substitutes is usually investigated by histomorphometric global analysis. This study provides a novel mathematical modelling approach of new bone formation in the use of osteoinductive and functionalized biomaterials for bone tissue engineering. We discuss here the repartition and the probability to get new bone formation inside Biphasic Calcium Phosphate (BCP) loaded with autologous osteogenic cells, functionalized with a cyclo RGD peptide, after implantation in rabbits for 2 and 4 weeks. This local analysis allowed us to complement classical global findings and to demonstrate that after 2 weeks of implantation, the probability of new bone formation was significantly higher in RGD-grafted BCP and that new formed bone was largely distributed from the edge to the centre of the implant. While no significant differences were obtained after 4 weeks of implantation between RGD-grafted and non-grafted materials, distribution of new bone formation inside RGD-grafted materials was significantly more homogeneous as demonstrated by our mathematical modelling approach. In conclusion, local analysis of new bone formation inside macroporous substitutes coupled with mathematical modelling constitutes a potential quantitative approach for the evaluation of the osteoconductive and osteoinductive characteristics of such biomaterials.
| Matrigel: basement membrane matrix with biological activity
Kleinman, H. K. and G. R. Martin (2005), Semin Cancer Biol 15(5): 378-86.
Abstract: The basement membrane extracellular matrix contacts epithelial, endothelial, fat and smooth muscle cells. Because this extracellular matrix is so thin, it had been hard to study its composition, structure, and function. An extract of a tumor was found to contain all of the components present in basement and to be very biologically active. This extract, termed Matrigel, Cultrex, or EHS matrix, promotes cell differentiation, and is used to measure the invasive activity of tumor cells. In vivo, it is used for measuring angiogenic inhibitors and stimulators, to improve graft survival, repair damaged tissues, and increase tumor growth.
| Matrix testing for urothelial tissue engineering
Wunsch, L., E. M. Ehlers, et al. (2005), Eur J Pediatr Surg 15(3): 164-9.
Abstract: INTRODUCTION: Surgical reconstruction of the bladder is associated with many well-known complications. Tissue engineering is under discussion as a potential therapeutic strategy and many of the proposed benefits are of special interest for children. Biomaterials play a key role in tissue engineering. Many materials have been proposed for the experimental reconstruction of the bladder and urethra. They determine the biological and mechanical characteristics of the reconstructed tissues. Most publications focus on a single material. In order to identify the most suitable biomaterial it was the aim of this study to compare biological and mechanical features of different biomaterials seeded with urothelial cells in vitro. MATERIALS AND METHODS: Commercially available biomaterials (Biogide, Ethisorb, Lyoplant, SIS, Vicryl, Xenoderm) of biologic or synthetic origin were seeded with urothelial cells. Cell-matrix constructs were cultured and investigated by scanning electron microscopy for surface structure and cell morphology. They were also subjected to extension until failure and the force required was reported as f (max). Values obtained and curve shape were compared to specimens of bladder mucosa and submucosa. RESULTS: Cell adhesion and morphology showed marked differences between materials. Cell shape varied from single spherical cells to confluent layers of flat urothelium. f (max) ranged from 0.02 N to 48.86 N for tested materials and 1.19 N for native bladder mucosa/submucosa. DISCUSSION: The materials showed marked differences in biological and mechanical features in vitro. Cells cultured on biogenic matrices were more similar to native urothelium. Most of the tested materials showed different curve shapes and higher f (max) values than native bladder mucosa.
| Matrix-mediated retention of adipogenic differentiation potential by human adult bone marrow-derived mesenchymal stem cells during ex vivo expansion
Mauney, J. R., V. Volloch, et al. (2005), Biomaterials 26(31): 6167-75.
Abstract: Recently, cell-based approaches utilizing adipogenic progenitor cells for fat tissue engineering have been developed and reported to have success in promoting in vivo adipogenesis and the repair of defect sites. For autologous applications, human bone marrow-derived mesenchymal stem cells (MSCs) have been suggested as a potential cell source for adipose tissue engineering applications due to their ability to be isolated and ex vivo expanded from adult bone marrow aspirates and their versatility for pluripotent differentiation into various mesenchymal lineages including adipogenic. Due to the relatively low frequency of MSCs present within bone marrow, extensive ex vivo expansion of these cells is necessary to obtain therapeutic cell populations for tissue engineering strategies. Currently, utilization of MSCs for adipose tissue engineering is limited due to the attenuation of their adipogenic differentiation potential following extensive ex vivo expansion on conventional tissue culture plastic (TCP) substrates. In the present study, the ability of a denatured collagen type I (DC) matrix to preserve MSC adipogenic potential during ex vivo expansion was examined. Adipocyte-related markers and functions were examined in vitro in response to adipogenic culture conditions for 21 days in comparison to early passage MSCs and late passage MSCs ex vivo expanded on TCP. The results demonstrated significant preservation of the ability of late passage MSCs ex vivo expanded on the DC matrix to express adipogenic markers (fatty acid-binding protein-4, lipoprotein lipase, acyl-CoA synthetase, adipsin, facilitative glucose transporter-4, and accumulation of lipids) similar to the early passage cells and in contrast to late passage MSCs expanded on TCP. The ability of the DC matrix to preserve adipocyte-related markers and functions of MSCs following extensive ex vivo expansion represents a novel culture technique to expand functional adipogenic progenitors for tissue engineering applications.
| Maxillary sinus augmentation using a peptide-modified graft material in three mixtures: a prospective human case series of histologic and histomorphometric results
Gelbart, M., R. Friedman, et al. (2005), Implant Dent 14(2): 185-93.
Abstract: This prospective study assessed vital bone quality and quantity after grafting maxillary sinuses with anorganic bone mineral containing a cell binding peptide (ABM/P-15) in combination with DFDBA (Mix I), hydrogel/ABM/P-15 (Mix II), or PRP (Mix III). Fifteen maxillary sinuses in 12 patients were grafted with the ABM/P-15 mixtures and after 4 to 5 months, cores were taken and analyzed histologically and histomorphometrically. Fifty-nine screw-type implants were placed. Mixes containing a spacer material (Mix I and II) produced greater average vital bone, more mature bone, and more interconnected bone bridges from the cortical (oral) end to the most apical portion, compared to a mix that lacked a spacer material (Mix III). None of the 59 implants failed with any graft material up to 5 months following implant placement. The study demonstrates that new trabecular bone is formed after grafting ABM/P-15 in the sinus floor; that more vital bone is formed when ABM/P-15 is mixed with a spacer material than without; and that implants can be successfully placed.
| Maxillary Sinus Augmentation Using a Synthetic Cell-Binding Peptide: A Histologic and Transmission Electron Microscopy Case Study in Man
Degidi, M., A. Scarano, et al. (2005), Implant Dent 14(4): 371-377.
Abstract: PepGen P-15 is a combination natural anorganic bovine-derived hydroxyapatite matrix coupled with a synthetic cell-binding peptide (P-15). This material has improved bone formation in periodontal osseous defects and bone regenerative procedures. There were 3 specimens retrieved 18 months after a sinus lifting procedure using PepGen P-15. These specimens were treated to be observed under light microscopy and transmission electron microscopy. Light microscopy showed that most of the particles were surrounded by newly formed bone. In some areas, osteoid matrix was present. No acute inflammatory infiltrate was present. In transmission electron microscopy, all phases of bone formation (i.e., osteoid matrix, woven bone, and lamellar bone) were observed in the newly formed bone around the biomaterial particles. In some regions, this newly formed bone seemed to present interdigitations connecting to or entering into the particle surface. To our knowledge, this is the first report presenting data on transmission electron microscopy of PepGen P-15 used in a sinus augmentation procedure in man. Our results confirm previous reports on the clinical effectiveness of this material.
| Maxillary sinus augmentation with Bio-Oss particles: a light, scanning, and transmission electron microscopy study in man
Orsini, G., T. Traini, et al. (2005), J Biomed Mater Res B Appl Biomater 74(1): 448-57.
Abstract: Biological interactions occurring at the bone-biomaterial interface are critical for long-term clinical success. Bio-Oss is a deproteinized, sterilized bovine bone that has been extensively used in bone regeneration procedures. The aim of the present study was a comparative light, scanning, and electron microscopy evaluation of the interface between Bio-Oss and bone in specimens retrieved after sinus augmentation procedures. Under light microscopy, most of the particles were surrounded by newly formed bone, while in a few cases, at the interface of some particles it was possible to observe marrow spaces and biological fluids. Under scanning electron microscopy, in most cases, the particle perimeter appeared lined by bone that was tightly adherent to the biomaterial surface. Transmission electron microscopy showed that the bone tissue around the biomaterial showed all the phases of the bone healing process. In some areas, randomly organized collagen fibers were present, while in other areas, newly formed compact bone was present. In the first bone lamella collagen fibers contacting the Bio-Oss surface were oriented at 243.73 +/- 7.12 degrees (mean +/- SD), while in the rest of the lamella they were oriented at 288.05 +/- 4.86 degrees (mean +/- SD) with a statistically significant difference of 44.32 degrees (p < 0.001). In the same areas the intensity of gray value was 172.56 +/- 18.15 (mean +/- SD) near the biomaterial surface and 158.71 +/- 21.95 (mean +/- SD) in the other part of the lamella with an unstatistically significant difference of 13.79 (p = 0.071). At the bone-biomaterial interface there was also an electron-dense layer similar to cement lines. This layer had a variable morphology being, in some areas, a thin line, and in other areas, a thick irregular band. The analyses showed that Bio-Oss particles do not interfere with the normal osseous healing process after sinus lift procedures and promote new bone formation. In conclusion, this study serves as a better understanding of the morphologic characteristics of Bio-Oss and its interaction with the surrounding tissues.
| Maxillary sinus floor augmentation using a beta-tricalcium phosphate (Cerasorb) alone compared to autogenous bone grafts
Zijderveld, S. A., I. R. Zerbo, et al. (2005), Int J Oral Maxillofac Implants 20(3): 432-40.
Abstract: PURPOSE: A prospective human clinical study was conducted to determine the clinical and histologic bone formation ability of 2 graft materials, a beta-tricalcium phosphate (Cerasorb; Curasan, Kleinostheim, Germany) and autogenous chin bone, in maxillary sinus floor elevation surgery. MATERIALS AND METHODS: Ten healthy patients underwent a bilateral (n = 6) or unilateral (n = 4) maxillary sinus floor elevation procedure under local anesthesia. In each case, residual posterior maxillary bone height was between 4 and 8 mm. In cases of bilateral sinus floor elevation, the original bone was augmented with a split-mouth design with 100% beta-tricalcium phosphate on the test side and 100% chin bone on the contralateral control side. The unilateral cases were augmented with 100% beta-tricalcium phosphate. After a healing period of 6 months, ITI full body screw-type implants (Straumann, Waldenburg, Switzerland) were placed. At the time of implant surgery, biopsy samples were removed with a 3.5-mm trephine drill. RESULTS: Sixteen sinus floor elevations were performed. Forty-one implants were placed, 26 on the test side and 15 on the control side. The clinical characteristics at the time of implantation differed, especially regarding clinical appearance and drilling resistance. The increase in height was examined radiographically prior to implantation and was found to be sufficient in all cases. After a mean of nearly 1 year of follow-up, no implant losses or failures had occurred. DISCUSSION: The promising clinical results of the present study and the lack of implant failures are probably mainly the result of requiring an original bone height of at least 4 mm at the implant location. CONCLUSION: Although autogenous bone grafting is still the gold standard, according to the clinical results, the preimplantation sinus floor elevation procedure used, which involved a limited volume of beta-tricalcium phosphate, appeared to be a clinically reliable procedure in this patient population.
| Mean-field model of immobilized enzymes embedded in a grafted polymer layer
Moskovitz, Y. and S. Srebnik (2005), Biophys J 89(1): 22-31.
Abstract: Two-dimensional mean-field lattice theory is used to model immobilization and stabilization of an enzyme on a hydrophobic surface using grafted polymers. Although the enzyme affords biofunctionality, the grafted polymers stabilize the enzyme and impart biocompatibility. The protein is modeled as a compact hydrophobic-polar polymer, designed to have a specific bulk conformation reproducing the catalytic cleft of natural enzymes. Three scenarios are modeled that have medical or industrial importance: 1), It is shown that short hydrophilic grafted polymers, such as polyethylene glycol, which are often used to provide biocompatibility, can also serve to protect a surface-immobilized enzyme from adsorption and denaturation on a hydrophobic surface. 2), Screening of the enzyme from the surface and nonspecific interactions with biomaterial in bulk solution requires a grafted layer composed of short hydrophilic polymers and long triblock copolymers. 3), Hydrophilic polymers grafted on a hydrophobic surface in contact with an organic solvent form a dense hydrophilic nanoenvironment near the surface that effectively shields and stabilizes the enzyme against both surface and solvent.
| Measurement of directional thermal properties of biomaterials
Bhavaraju, N. C., H. Cao, et al. (2001), IEEE Trans Biomed Eng 48(2): 261-7.
Abstract: This paper presents an experimental technique to measure the directional thermal conductivity and thermal diffusivity of materials. A heated thermistor heats the sample and a sensing thermistor placed about 2.5 mm away measures the temperature rise due the heating pulse at the heated thermistor. An empirical relation between the power delivered by the first thermistor and the temperature rise recorded by the sensing thermistor is used to measure the thermal conductivity of the material along the line joining the thermistors. Diffusivity of the material is determined from the delay between the power pulse in the heated thermistor and the temperature pulse at the sensing thermistor. Signal processing was done to eliminate errors in the measurement due to change of base line temperature. Uncertainty of the measurement technique was found to be 5% when tested in media of known thermal properties. The thermal conductivity and thermal diffusivity of swine left ventricle in normal and ablated conditions were measured using this technique. The thermal conductivity of the tissue dropped significantly from 0.61 to 0.50 W.m(-1).K(-1) after ablation while the diffusivity dropped from 2.1 x 10(-7) to 1.7 x 10(-7)m2.s(-1).
| Measurement of drug release from microcarriers by microdialysis
Hitzman, C. J., T. S. Wiedmann, et al. (2005), J Pharm Sci 94(7): 1456-66.
Abstract: The purpose of this study was to examine the feasibility of the microdialysis sampling technique as a method to precisely and conveniently measure drug release from microcarrier systems such as liposomes and microspheres. Release of 5-fluorouracil (5-FU) from liposomes and microspheres was evaluated in vitro using microdialysis. Retrodialysis calibration using 5-chlorouracil (5-CU) was performed in conjunction with on-line HPLC analysis. At a microdialysis perfusate flow rate of 0.5 muL/min, concurrent 5-FU gain and 5-CU loss ranged from 72% to 75%, while concurrent 5-FU loss and 5-CU ranged from 69% to 71%. After calibration, simultaneous 5-FU release profiles were obtained by continuous microdialysis and discrete equilibrium dialysis sampling using a side-by-side diffusion apparatus. Release rates were characterized by a first-order release model. The release rate constants for a representative liposomal formulation were 0.30 and 1.85/h by microdialysis in the acceptor and donor compartments, respectively, and 0.39/h by equilibrium dialysis in the acceptor compartment. The calculated release rate constant determined by equilibrium dialysis in the donor compartment (1.98/h) agrees with that determined by microdialysis (1.85/h) when the resistance of the equilibrium dialysis membrane with associated first-order rate constant of transfer of 0.42/h is taken into account. Release profiles of 5-FU from a number of different liposome and microsphere formulations were determined. The results indicate that a convenient and reproducible characterization of drug release from various liposome and microsphere formulations is readily obtainable by microdialysis.
| Measurement of fibroblast and bacterial detachment from biomaterials using jet impingement
Bundy, K. J., L. G. Harris, et al. (2001), Cell Biol Int 25(4): 289-307.
Abstract: Fibroblast and Staphylococcus aureus detachment strength from orthopaedic alloys and a tissue culture plastic (Thermanox) have been investigated with jet impingement. For S. aureus, unlike fibroblasts, detachment is caused more by pressure than shear. For these biomaterials, detachment strength is much higher for S. aureus than fibroblasts. Comparing materials under equivalent flow conditions, S. aureus attach to stainless steel and titanium with equal strength and more strongly than to Thermanox. For fibroblasts, detachment strength from all materials was similar. Fibroblast detachment strength from these biomaterials substantially decreases with time at equal flow rates and increases with flow rate at equal exposure times. Detachment strength is very similar for 3T3 and L929 fibroblasts on Thermanox for equivalent flow rate/time combinations, though enhanced adhesion of 3T3 cells was often noted for metals. Time effects are less evident for S. aureus. S. aureus adhesion to metals is more affected by flow rate than fibroblast adhesion.
| Measurement of intracellular hydrogen peroxide induced by biomaterials implanted in a rodent air pouch
Krause, T. J., F. M. Robertson, et al. (1993), J Biomed Mater Res 27(1): 65-9.
Abstract: Biomaterials elicit an inflammatory response that is undoubtedly a factor in their healing and in the complications associated with their use. Herein, we report the modification of a rat air pouch in which we measured the production of intracellular hydrogen peroxide by inflammatory cells adherent to the surfaces of silicone elastomer (SE) and expanded polytetrafluoroethylene (ePTFE). We used the fluorescent probe dichlorofluorescein diacetate (DCFH-DA) to measure the intracellular production of hydrogen peroxide 2 and 7 days after implantation. After 2 days, host cells adherent to ePTFE produced almost 3.5 times more hydrogen peroxide than did cells adherent to SE (P <.001). By 7 days, the H2O2 production of cells adherent to ePTFE had decreased while that on cells adherent to SE was unchanged. These data indicate that the air pouch is a good alternative to other in vivo models for studies of the biological reactions induced by biomaterials.
| Measurement of platelet loss in the blood compatibility assessment of biomaterials
Courtney, J. M., M. Travers, et al. (1987), Biomaterials 8(3): 231-3.
Abstract: In the assessment of the in vitro blood compatibility of biomaterials, platelet loss is often attributed solely to platelet adhesion and consideration is not given to platelets lost in platelet aggregate formation. In order to distinguish between those platelets lost to adhesion and those lost to aggregate formation, the Wu and Hoak method for the quantification of circulating platelet aggregates in patients has been modified to establish a new test procedure. This procedure, which measures both platelet adhesion (PA) in the absence of platelets lost to aggregate formation and also the tendency of a material to induce aggregate formation, has been used to evaluate the influence of a range of polyamides and a hydrogel. The evaluation demonstrated the ability of polymers to induce readily platelet aggregates during in vitro blood-material contact. The sensitivity of the aggregate measurement was exemplified by the polyamides, where PA was similar for materials of different porosity but platelet aggregate formation increased significantly with porosity. The importance of considering platelets lost to aggregate formation was emphasized with the hydrogel, where PA was low.
| Measurement of protein diffusion through poly(D,L-lactide-Co-glycolide)
Fredenberg, S., M. Reslow, et al. (2005), Pharm Dev Technol 10(2): 299-307.
Abstract: A novel method was developed for studying the diffusion of proteins through poly(D,L-lactide-co-glycolide) (PLG), using a diffusion cell. To develop improved formulations for the controlled release of encapsulated drugs it is important to understand the underlying release mechanisms. When using low-molecular-weight PLG as the release-controlling polymer, diffusion through the pores is often proposed as the main release mechanism. The experimental set-up and method of determining the diffusion coefficient were thoroughly evaluated with regard to the reliability and the influence of the stirring rate. A procedure for spraying thin films of PLG onto a filter, which could be placed in the diffusion cell, was optimized. The method was then applied to the determination of the diffusion coefficient of human growth hormone (hGH) through a PLG film. The results show that the method enables measurements of the diffusion coefficient through the polymer film. Neither the stirring rate nor the concentration of hGH influenced the diffusion coefficient. The diffusion coefficient of hGH through degraded PLG films was 5.0 x 10(-13) m2/s, which is in the range that could be expected, i.e., several orders of magnitude smaller than its the diffusivity in pure water. The reproducibility was good, considering the dynamic properties of PLG, i.e., the difference in diffusion coefficients, at, for example, different stages of degradation and for different compositions of PLG, is expected to be much higher. The variation is probably also present in PLG films used for controlled-release formulations. Although the PLG film contains a large amount of water, a considerable time elapsed before pores of sufficient size formed and diffusion through the film started. In two-component diffusion experiments, the difference in diffusion rate did not correspond to the difference in molecular weight of the solutes, indicating a size exclusion effect. This method can be used to study the effect of changes in the formulation specification. By studying the change in the diffusion coefficient through the degradation process of PLG, or similar polymers, a better understanding of diffusion and, thus, also release mechanisms can be obtained.
| Measurement of thermal diffusivity of biomaterials by focused ultrasonic beams (thermal pulse decay method by focused ultrasonic beams)
Nakayama, M. and K. Tanishita (1994), Biomed Mater Eng 4(2): 105-14.
Abstract: This study propose a new simple method of measuring the thermal diffusivity of living tissue by thermal pulse decay technique with focused ultrasonic beam, which does not require the accurate knowledge of Gaussian variance within the focal region. The measurement of temperatures at two different locations outside the focal region replaces the elaborate measurement of the size of the focal region and gives a thermal diffusivity with reasonable accuracy and automatically avoids the artifact due to beam-thermocouple interaction. The focused ultrasound was generated by the bowl-shaped ceramic piezoelectric transducer with the diameter of 30 mm. The focal lengths of transducer were 40 mm and 60 mm and the frequencies 1.7 and 3.6 MHz. The values of thermal diffusivity of biological tissues obtained in this method are fairly close to the previously published values and are also compared to the values obtained by heated thermistor method.
| Measurements of zeta potentials of particulate biomaterials in protein-rich hyaluronan solution with changes in pH and protein constituents
Kitano, T., H. Ohashi, et al. (1998), J Biomed Mater Res 42(3): 453-7.
Abstract: This study was undertaken to determine the zeta potentials of particulate biomaterials in three types of protein-rich hyaluronan solution with changes in pH; a microelectrophoretic method was used. For the purpose of determining the pH value of synovial fluid in various inflammatory conditions, we collected synovial fluid samples from joints with osteoarthritis (OA), rheumatoid arthritis (RA), and those undergoing revisions arthroplasties. The mean values of the pH in the synovial fluid from joints with OA, RA, and revision arthroplasty were shown to be 7.9, 7.5, and 8.1, respectively. The pH-zeta potential curves obtained differed, depending on the biomaterial and the medium. Addition of gamma-globulin to the medium reduced the absolute value of the zeta potentials of some of the biomaterials. The findings of this study suggest that the electrophoretic behaviors of the particulate biomaterials tested in this study are affected by the protein constituents of and pH changes in protein-rich synovial fluid. The values we obtained will be useful as reference standards and will also aid in the study of the surface phenomena of biomaterials.
| Measuring coronary calcium on CT images adjusted for attenuation differences
Nelson, J. C., R. A. Kronmal, et al. (2005), Radiology 235(2): 403-14.
Abstract: PURPOSE: To quantify scanner and participant variability in attenuation values for computed tomographic (CT) images assessed for coronary calcium and define a method for standardizing attenuation values and calibrating calcium measurements. MATERIALS AND METHODS: Institutional review board approval and participant informed consent were obtained at all study sites. An image attenuation adjustment method involving the use of available calibration phantom data to define standard attenuation values was developed. The method was applied to images from two population-based multicenter studies: the Coronary Artery Risk Development in Young Adults study (3041 participants) and the Multi-Ethnic Study of Atherosclerosis (6814 participants). To quantify the variability in attenuation, analysis of variance techniques were used to compare the CT numbers of standardized torso phantom regions across study sites, and multivariate linear regression models of participant-specific calibration phantom attenuation values that included participant age, race, sex, body mass index (BMI), smoking status, and site as covariates were developed. To assess the effect of the calibration method on calcium measurements, Pearson correlation coefficients between unadjusted and attenuation-adjusted calcium measurements were computed. Multivariate models were used to examine the effect of sex, race, BMI, smoking status, unadjusted score, and site on Agatston score adjustments. RESULTS: Mean attenuation values (CT numbers) of a standard calibration phantom scanned beneath participants varied significantly according to scanner and participant BMI (P <.001 for both). Values were lowest for Siemens multi-detector row CT scanners (110.0 HU), followed by GE-Imatron electron-beam (116.0 HU) and GE LightSpeed multi-detector row scanners (121.5 HU). Values were also lower for morbidly obese (BMI, > or =40.0 kg/m(2)) participants (108.9 HU), followed by obese (BMI, 30.0-39.9 kg/m(2)) (114.8 HU), overweight (BMI, 25.0-29.9 kg/m(2)) (118.5 HU), and normal-weight or underweight (BMI, <25.0 kg/m(2)) (120.1 HU) participants. Agatston score calibration adjustments ranged from -650 to 1071 (mean, -8 +/- 50 [standard deviation]) and increased with Agatston score (P <.001). The direction and magnitude of adjustment varied significantly according to scanner and BMI (P <.001 for both) and were consistent with phantom attenuation results in that calibration resulted in score decreases for images with higher phantom attenuation values. CONCLUSION: Image attenuation values vary by scanner and participant body size, producing calcium score differences that are not due to true calcium burden disparities. Use of calibration phantoms to adjust attenuation values and calibrate calcium measurements in research studies and clinical practice may improve the comparability of such measurements between persons scanned with different scanners and within persons over time.
| Mechanical characterization of an unusual elastic biomaterial from the egg capsules of marine snails (Busycon spp.)
Rapoport, H. S. and R. E. Shadwick (2002), Biomacromolecules 3(1): 42-50.
Abstract: Egg capsule material serves as a putative protection mechanism for developing snail embryos facing the perils of the marine environment. We conducted the first quantitative study of this acellular structural protein with the goals of characterizing its chemical and mechanical properties and the relationship of these properties to its biological protective function. We have found that this protein polymer exhibits long-range elasticity with an interesting recoverable yield evidenced by an order of magnitude decrease in elastic modulus (apparent failure) that begins at 3%-5% strain. This material differs significantly from other common structural proteins such as collagen and elastin in mechanical response to strain. Qualitative similarities in stress/strain behavior to keratin, another common structural protein, are more than coincidental when composition and detailed mechanical quantification are considered. This suggests the possibility of alpha-helical structure and matrix organization that might be similar in these two proteins. Indeed, the egg capsule protein may be closely related to vertebrate keratins such as intermediate filaments. We conclude that while this material's bimodal tensile properties may serve as useful protection against the impact loading egg capsules encounter in the intertidal zone, the full biological importance of these capsules is not known.
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