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Micropatterning proteins on polyhydroxyalkanoate substrates by using the substrate binding domain as a fusion partner
Park, J. P., K. B. Lee, et al. (2005), Biotechnol Bioeng 92(2): 160-5.
Abstract: A novel strategy for micropatterning proteins on the surface of polyhydroxyalkanoate (PHA) biopolymer by microcontact printing (microCP) is described. The substrate binding domain (SBD) of the Pseudomonas stutzeri PHA depolymerase was used as a fusion partner for specifically immobilizing proteins on PHA substrate. Enhanced green fluorescent protein (EGFP) and red fluorescent protein (RFP) fused to the SBD could be specifically immobilized on the micropatterns of poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). Laser scanning confocal microscopic studies suggested that two fusion proteins were micropatterned in their functionally active forms. Also, antibody binding assay by surface plasmon resonance suggested that protein-protein interaction studies could be carried out using this system.

Microporosity enhances bioactivity of synthetic bone graft substitutes
Hing, K. A., B. Annaz, et al. (2005), J Mater Sci Mater Med 16(5): 467-75.
Abstract: This paper describes an investigation into the influence of microporosity on early osseointegration and final bone volume within porous hydroxyapatite (HA) bone graft substitutes (BGS). Four paired grades of BGS were studied, two (HA70-1 and HA70-2) with a nominal total porosity of 70% and two (HA80-1 and HA80-2) with a total-porosity of 80%. Within each of the total-porosity paired grades the nominal volume fraction of microporosity within the HA struts was varied such that the strut porosity of HA70-1 and HA80-1 was 10% while the strut-porosity of HA70-2 and HA80-2 was 20%. Cylindrical specimens, 4.5 mm diameter x 6.5 mm length, were implanted in the femoral condyle of 6 month New Zealand White rabbits and retrieved for histological, histomorphometric, and mechanical analysis at 1, 3, 12 and 24 weeks. Histological observations demonstrated variation in the degree of capillary penetration at 1 week and bone morphology within scaffolds 3-24 weeks. Moreover, histomorphometry demonstrated a significant increase in bone volume within 20% strut-porosity scaffolds at 3 weeks and that the mineral apposition rate within these scaffolds over the 1-2 week period was significantly higher. However, an elevated level of bone volume was only maintained at 24 weeks in HA80-2 and there was no significant difference in bone volume at either 12 or 24 weeks for 70% total-porosity scaffolds. The results of mechanical testing suggested that this disparity in behaviour between 70 and 80% total-porosity scaffolds may have reflected variations in scaffold mechanics and the degree of reinforcement conferred to the bone-BGS composite once fully integrated. Together these results indicate that manipulation of the levels of microporosity within a BGS can be used to accelerate osseointegration and elevate the equilibrium volume of bone.

Micro-rotary fatigue of tooth-biomaterial interfaces
De Munck, J., M. Braem, et al. (2005), Biomaterials 26(10): 1145-53.
Abstract: The bonding effectiveness of restorative materials to tooth tissue is typically measured statically. Clinically tooth/composite bonds are however subjected to cyclic sub-critical loads. Therefore, in vitro fatigue testing of dental adhesives should predict better the in vivo performance of adhesives. The objective of this study was to determine the fatigue resistance of two representative adhesives, a self-etch and an etch&rinse adhesive, bonded to enamel and dentin. Therefore, tooth/composite interfaces were cyclically loaded using a miniaturized version of a rotating beam fatigue testing device. Subsequently, the load at which 50% of the specimens fail after 10(5) cycles, was determined as the median micro-rotary fatigue resistance (microRFR). For both adhesives, the microRFR was about 30-40% lower than the corresponding micro-tensile bond strength (microTBS) to both enamel and dentin. Analysis of the fracture surfaces by Feg-SEM revealed typical fatigue fracture patterns. It is concluded that resin/tooth interfaces are vulnerable to progressive damage by sub-critical loads, with the 3-step etch&rinse adhesive being more resistant to fatigue than the 2-step self-etch adhesive.

Microrough surface of metallic biomaterials: a literature review
Wen, X., X. Wang, et al. (1996), Biomed Mater Eng 6(3): 173-89.
Abstract: In this paper, four aspects of microrough surface of metallic biomaterials are reviewed: i.e., the preparation of microrough surface, the technology of surface roughness measurement, the parameters of roughness and the bio-effect of microrough surface. Microrough surfaces (roughness below 50 microns) are easily prepared and conveniently detected in practice. Microrough surfaces allow early better adhesion of mineral ions or atoms, biomolecules, and cells, form firmer fixation of bone or connective tissue, result in thinner tissue-reaction-layer with inflammatory cells decreased or absent, and prevent microorganism adhesion and plaque accumulation, when compared with the smooth surfaces.

Microscopic examination of chitosan-polyphosphate beads with entrapped spores of the biocontrol agent, Streptomyces melanosporofaciens EF-76
Jobin, G., G. Grondin, et al. (2005), Microsc Microanal 11(2): 154-65.
Abstract: Spores of the biocontrol agent, Streptomyces melanosporofaciens EF-76, were entrapped by complex coacervation in beads composed of a macromolecular complex (MC) of chitosan and polyphosphate. A proportion of spores entrapped in beads survived the entrapment procedure as shown by treating spores from chitosan beads with a dye allowing the differentiation of live and dead cells. The spore-loaded chitosan beads could be digested by a chitosanase, suggesting that, once introduced in soil, the beads would be degraded to release the biocontrol agent. Spore-loaded beads were examined by optical and scanning electron microscopy because the release of the biological agent depends on the spore distribution in the chitosan beads. The microscopic examination revealed that the beads had a porous surface and contained a network of inner microfibrils. Spores were entrapped in both the chitosan microfibrils and the bead lacuna.

Microscopic mechanism of water diffusion in glucose glasses
Molinero, V. and W. A. Goddard, 3rd (2005), Phys Rev Lett 95(4): 045701.
Abstract: The preservation of biomaterials depends critically on the mobility of water in the glassy state, manifested as a secondary beta relaxation and diffusion. We use coarse grain simulations to elucidate the molecular mechanism underlying the relaxations for water-glucose glass, finding two pathways for water diffusion: (i) water jumps into neighbor water positions (linking to water structure), and (ii) water jumps into glucose positions (coupling to glucose rotation). This work suggests strategies for enhancing preservation by stiffening the segmental motions of the carbohydrates.

Microscopic observation of bacteria: review highlighting the use of environmental SEM
Bergmans, L., P. Moisiadis, et al. (2005), Int Endod J 38(11): 775-88.
Abstract: Throughout the years, various methods have been adopted to investigate bacteria involved in root canal infection and apical periodontitis. This paper reviews the most commonly used microscopic techniques and discusses their possibilities, limitations and sample preparation. In particular, a recently developed variant of scanning electron microscope (SEM), referred to as environmental SEM (ESEM), is highlighted due to its potential impact across the diverse field of biomaterials research. The performance of this ESEM technique for bacterial observation of endodontic pathogens was illustrated by a practical approach. The paper concludes with a discussion on the possible use of ESEM for testing endodontic treatment modalities under environmental conditions in situ.

Microspheres made of poly(epsilon-caprolactone)-based amphiphilic copolymers: potential in sustained delivery of proteins
Quaglia, F., L. Ostacolo, et al. (2005), Macromol Biosci 5(10): 945-54.
Abstract: Microspheres of amphiphilic multi-block poly(ester-ether)s (PEE)s and poly(ester-ether-amide)s (PEEA)s based on poly(epsilon-caprolactone) (PCL) were investigated as delivery systems for proteins. The interest was mainly focused on the effect of their molecular structure and composition on the overall properties of the microspheres, encapsulating bovine serum albumin (BSA) as a model protein. PEEs and PEEAs were prepared using a alpha,omega-dihydroxy-terminated PCL macromer (Mn= 2.0 kDa) as a hydrophobic component. Hydrophilic oxyethylene sequences were generated using poly(ethylene oxide)s (PEO)s of different molecular mass (Mn= 300-600 Da) in the case of PEEs, or 4,7,10-trioxa-1,13-tridecanediamine (Trioxy) and PEO150 (Mn= 150 Da) in the case of PEEAs. The copolymers showed a decrease of Tm and crystallinity values as compared with PCL. Within each class of copolymers, the bulk hydrophilicity increased with increasing the number of oxyethylene groups in the chain repeat unit. PEEAs were more hydrophilic than PEEs with a similar number of oxyethylene groups. Discrete spherical particles were prepared by both PEEs and PEEAs and their BSA encapsulation efficiency related to copolymer properties. Interestingly, the insertion of short hydrophilic segments is enough to significantly affect protein distribution inside microspheres and its release profiles, as compared to PCL microspheres. Different degradation rates and mechanisms were observed for copolymer microspheres, mainly depending on the distribution of oxyethylene units along the chain. The results highlight that a fine control over the structural parameters of amphiphilic PCL-based multi-block copolymers is a key factor for their application in the field of protein delivery.

Microstructural analysis of implant-bone interface of hydroxyapatite-coated and uncoated Schanz screws
Cimerman, M., A. Cor, et al. (2005), J Mater Sci Mater Med 16(7): 627-34.
Abstract: The aim of the study was to compare the pin-bone interface microstructural characteristics of hydroxyapatite-coated (HAC) and stainless steel Schanz screws after 2, 4 and 6 months of implantation in a sheep model. The microstructure and composition of the hydroxyapatite coating were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. Twelve coated and 12 uncoated screws were implanted into both femora of three sheep, each sheep receiving eight screws. Specimens of polished bone with screws were examined with SEM and light microscope for morphometric analyses. The HAC was approx. 40 microm thick, the grain size ranged from 5 to 40 microm, with pores less than 20 microm. The atomic ratio of Ca/P was 1.62. SEM showed that the bone-implant contact was better with HAC than with uncoated implants. The ingrowth of the bone in the HAC was clearly seen. Morphometric analysis showed good bone-implant contact in 65.1 (+/-24.6)% in the HAC and 32.0 (+/-23.3)% in the uncoated group (p<0.001). Although the percentage of good contact increased with time for both groups, it was significantly higher for HAC screws. Our investigation demonstrated a time dependent improvement of implant-bone contact of the HAC compared to standard stainless steel implants in the chosen experimental conditions.

Microstructural and in vitro characterization of SiO2-Na2O-CaO-MgO glass-ceramic bioactive scaffolds for bone substitutes
Vitale-Brovarone, C., E. Verne, et al. (2005), J Mater Sci Mater Med 16(10): 909-17.
Abstract: In the present research work, the preparation and characterization of bioactive glass-ceramic scaffolds for bone substitutes are described. The scaffolds were prepared by starch consolidation of bioactive glass powders belonging to the SiO2-Na2O-CaO-MgO system using three different organic starches (corn, potatoes and rice) as reported in a previous screening process. The scaffolds, characterized by scanning electron microscopy, showed a porous structure with highly interconnected pores. The pores sizes assessed by mercury intrusion porosimetry put in evidence the presence of pores of 50-100 microm. The structure of the scaffolds was investigated by X-ray diffraction and revealed the glass-ceramic nature of the obtained material. The mechanical properties of the scaffolds were evaluated by means of compressive tests on cubic samples and the obtained results demonstrated their good mechanical strength. The in vitro bioactivity of the scaffolds was tested by soaking them in a simulated body fluid (SBF) and by subsequently characterizing the soaked surfaces by SEM, EDS and X-ray diffraction. Good in vitro bioactivity was found for the starting glass and for the obtained scaffolds. Moreover, the scaffold bioresorption, tested by measuring the samples weight loss in SBF at different periods of time, showed a partial resorption of the scaffolds. Cell culture testing of the three different scaffolds indicated no differences in cell number and in alkaline phosphatase activity; the morphology of the osteoblasts showed good spreading, comparable to bulk material which was used as the control.

Microstructural prototyping of ceramics by kinetic engineering: applications of spark plasma sintering
Shen, Z. and M. Nygren (2005), Chem Rec 5(3): 173-84.
Abstract: The significance of kinetics on the development of microstructures in connection with sintering of ceramics is well recognized. In practice, however, it still remains a challenge to prepare designed microstructures via engineering the sintering kinetics because of an insufficient understanding of the different operative mechanisms that are in many cases overlapping. In this article the kinetic issues involved in sintering are described and discussed with respect to their potential for prototyping microstructures that yield desired properties. By exploiting and mastering the differences present in the kinetics of grain sliding, densification, chemical reactions, and grain growth, respectively, we have established processing principles for producing bulk ceramics with microstructures consisting of nano-sized grains, aligned grains, and/or non-equilibrium-phase constitutions, and for achieving radically improved superplasticity in brittle ceramics. Although the studies quoted in this article were mainly carried out by spark plasma sintering, more general implications of them are expected, including efficient particle sliding, deformation-induced dynamic ripening, superplastic deformation-induced dynamic ripening, and non-equilibrium integration.

Microstructural, mechanical and citotoxicity evaluation of different NiTi and NiTiCu shape memory alloys
Gil, F. J., E. Solano, et al. (2004), J Mater Sci Mater Med 15(11): 1181-5.
Abstract: Transformation temperatures and mechanical properties such as transformation stresses at different temperatures and the superelasticity have been investigated in NiTiCu alloys with various Copper concentrations. The results have been compared with the conventional NiTi alloys. The addition of copper was effective to narrow the stress hysteresis and to stabilize the superelasticity characteristics. Moreover, it produced greater stability on both the transformation temperatures and the forces applied to the different tissues. However, the studies of cell cultured with human fibroblasts showed certain toxicity.

Microstructure and corrosion behaviour in biological environments of the new forged low-Ni Co-Cr-Mo alloys
Hiromoto, S., E. Onodera, et al. (2005), Biomaterials 26(24): 4912-23.
Abstract: Corrosion behaviour and microstructure of developed low-Ni Co-29Cr-(6, 8)Mo (mass%) alloys and a conventional Co-29Cr-6Mo-1Ni alloy (ASTM F75-92) were investigated in saline solution (saline), Hanks' solution (Hanks), and cell culture medium (E-MEM + FBS). The forging ratios of the Co-29Cr-6Mo alloy were 50% and 88% and that of the Co-29Cr-8Mo alloy was 88%. Ni content in the air-formed surface oxide film of the low-Ni alloys was under the detection limit of XPS. The passive current densities of the low-Ni alloys were of the same order of magnitude as that of the ASTM alloy in all the solutions. The passive current densities of all the alloys did not significantly change with the inorganic ions and the biomolecules. The anodic current densities in the secondary passive region of the low-Ni alloys were lower than that of the ASTM alloy in the E-MEM + FBS. Consequently, the low-Ni alloys are expected to show as high corrosion resistance as the ASTM alloy. On the other hand, the passive current density of the Co-29Cr-6Mo alloy with a forging ratio of 50% was slightly lower than that with a forging ratio of 88% in the saline. The refining of grains by further forging causes the increase in the passive current density of the low-Ni alloy.

Microstructure formation and property of chitosan-poly(acrylic acid) nanoparticles prepared by macromolecular complex
Chen, Q., Y. Hu, et al. (2005), Macromol Biosci 5(10): 993-1000.
Abstract: We report here a study on the microstructure formation process of polymeric nanoparticles based on polyelectrolyte complexes. When polyanion poly(acrylic acid) (PAA) was dropped into polycation chitosan (CS) solution, CS-PAA nanoparticles with diverse microstructure would be formed under different experimental conditions. The microstructure of CS-PAA nanoparticles changed from solid spherical nanoparticles to core-shell separative ones and turned back to solid spherical ones with the variation of preparation conditions. The influence of molecular weight of CS and PAA, shell cross-linking, dropping temperature on the size, stability and morphology of CS-PAA nanoparticles were also studied. The nanoparticle size was affected by the molecular weight of CS and PAA, the ratio of amino group to carboxyl group (na/nc) and the incubation temperature as well. The shell-cross-linking provides a means to stabilize these nanoparticles. These nanoparticles can encapsulate plasmid DNA very well, which makes them have great potential in gene delivery.

Microstructures and bond strengths of plasma-sprayed hydroxyapatite coatings on porous titanium substrates
Oh, I. H., N. Nomura, et al. (2005), J Mater Sci Mater Med 16(7): 635-40.
Abstract: Hydroxyapatite (HA) coating was carried out by plasma spraying on bulk Ti substrates and porous Ti substrates having a Young's modulus similar to that of human bone. The microstructures and bond strengths of HA coatings were investigated in this study. The HA coatings with thickness of 200-250 microm were free from cracks at interfaces between the coating and Ti substrates. XRD analysis revealed that the HA powder used for plasma spraying had a highly crystallized apatite structure, while the HA coating contained several phases other than HA. The bond strength between the HA coating and the Ti substrates evaluated by standard bonding test (ASTM C633-01) were strongly affected by the failure behavior of the HA coating. A mechanism to explain the failure is discussed in terms of surface roughness of the plasma-sprayed HA coatings on the bulk and porous Ti substrates.

Microtensile bond strength of different components of core veneered all-ceramic restorations
Aboushelib, M. N., N. de Jager, et al. (2005), Dent Mater 21(10): 984-91.
Abstract: OBJECTIVES: The present study aims to evaluate the core-veneer bond strength and the cohesive strength of the components of three commercial layered all-ceramic systems. Two surface treatments for the core surface finish and different veneering ceramics with different thermal expansion coefficients (TEC) were applied. The selected systems were two CAD-CAM ceramics; Cercon and Vita Mark II and one pressable system; (IPS)Empress 2 for layering technique. METHODS: Standardized core specimens were fabricated according to the manufacturer's instructions, or polished with 1200 siliconcarbide polishing paper. The core specimens were veneered with either its manufacturer's veneer or an experimental veneer with higher TEC. The obtained micro-bars were subjected to the microtensile bond strength test. The obtained data were analyzed using one and two-way ANOVA. A finite element analysis (FEA) model of the test setup was analyzed. Scanning Electron Microscopy (SEM) was carried out at the fracture surface. RESULTS: The core materials were significantly stronger than the veneering materials and the layered core-veneer specimens of which the results were statistically comparable. Polishing the core surfaces did not have an effect on the core-veneer bond strength. Experimental veneer with higher TEC resulted in massive fractures in both the core and veneering material. SEM and FEA demonstrated fracture pattern and mechanism of failure. SIGNIFICANCE: The core-veneer bond strength is one of the weakest links of layered all-ceramic restorations and has a significant role in their success. To exploit fully the high strength of zirconium oxide cores, further research work is needed to improve its bond with its corresponding veneering material.

Microtomography assessment of failure in acrylic bone cement
Sinnett-Jones, P. E., M. Browne, et al. (2005), Biomaterials 26(33): 6460-6.
Abstract: Micromechanical studies of fatigue and fracture processes in acrylic bone cement have been limited to surface examination techniques and indirect signal analysis. Observations may then be mechanically unrepresentative and/or affected by the presence of the free surface. To overcome such limiting factors the present study has utilised synchrotron X-ray microtomography for the observation of internal defects and failure processes that occurred within a commercial bone cement during loading. The high resolution and the edge detection capability (via phase contrast imaging) have enabled clear microstructural imaging of both strongly and weakly absorbing features, with an effective isotropic voxel size of 0.7 microm. Detailed assessment of fatigue damage processes in in vitro fatigue test specimens is also achieved. Present observations confirm a link with macroscopic failure and the presence of larger voids, at which crack initiation may be linked to the mechanical stress concentration set up by adjacent beads at pore surfaces. This study does not particularly support the suggested propensity for failure to occur via the inter-bead matrix; however crack deflections at matrix/bead interfaces and the incidence of crack arrest within beads do imply locally increased resistance to failure and potential improvements in global crack growth resistance via crack tip shielding.

Microvascular response of striated muscle to common arthroplasty-alloys: A comparative in vivo study with CoCrMo, Ti-6Al-4V, and Ti-6Al-7Nb
Kraft, C. N., B. Burian, et al. (2005), J Biomed Mater Res A 75(1): 31-40.
Abstract: The impairment of skeletal muscle microcirculation by a biomaterial may have profound consequences. Due to excellent physical and corrosion characteristics, CoCrMo-, Ti-6Al-4V-, and Ti-6Al-7Nb-alloys are commonly used in orthopedic surgery. Yet concern has been raised with regard to the implications of inevitable corrosion product of these metals on the surrounding biologic environment, particularly in the case of CoCrMo. We, therefore, studied in vivo nutritive perfusion and leukocytic response of striated muscle to these alloys, thereby drawing conclusions on their inflammatory potential. In 28 hamsters, utilizing the dorsal skinfold chamber preparation and intravital microscopy, we could demonstrate that the implant material CoCrMo has a marked impact on local microvascular parameters. While the Ti-alloys Ti-6Al-4V and Ti-6Al-7Nb induced only a transient and moderate inflammatory response, the implantation of a CoCrMo sample led to a distinct and persistent activation of leukocytes combined with disruption of the microvascular endothelial integrity and marked leukocyte extravasation. Animals with Ti-alloys showed a clear tendency of recuperation, while in all but one CoCrMo-treated animals, a breakdown of microcirculation prior to the scheduled end of the experiment was observed. Overall, the alloy Ti-6Al-7Nb was tolerated slightly better than Ti-6Al-4V under the chosen test conditions, though this discrepancy was not statistically significant. Conclusively, the commonly used biomaterials Ti-6Al-7Nb and Ti-6Al-4V induce a considerably lower inflammatory response in the skeletal muscle microvascular system, compared to a CoCrMo-alloy. With a minimum of adverse host reaction, our results indicate that for this particular model Ti-alloys are better tolerated than CoCrMo implant materials.

Microwave irradiated collagen tubes as a better matrix for peripheral nerve regeneration
Ahmed, M. R., S. Vairamuthu, et al. (2005), Brain Res 1046(1-2): 55-67.
Abstract: Collagen is one of the best materials used for nerve guide preparation due to its biocompatibility and desirable tensile strength. In this work, we have compared regeneration and functional reinnervation after sciatic nerve resection with bioresorbable crosslinked collagen guides in 10 mm gap. The crosslinking was carried out either with glutaraldehyde (GTA) or microwave irradiation (MWI). The multilayered collagen membrane used for nerve guides are prepared by lamellar evaporation technique. Functional evaluations of the regenerated nerves were performed by measuring the sciatic functional index (SFI), nerve conduction velocity (NCV), and electromyography (EMG). Transmission electron microscopic studies showed growth of axonal cable with fewer myelinated axons, Schwann cells and more unmyelinated axons present in the case of group treated with uncrosslinked collagen tubes after 1 month of implantation. However, we have observed more myelinated axons in the case of autograft, GTA, and MWI crosslinked collagen tube implants across the gap of 1 cm after the same period of implantation. Smaller myelinated fiber diameter was observed in the case of GTA crosslinked collagen tube group when compared with the autograft and MWI collagen tube groups. There were more myelinated axons during the 3rd and 6th months postoperatively using these conduits as substantiated by light microscopic studies of the regenerated nerve. The conduction velocity and recovery index improved significantly after 5 months reaching the normal values in the autograft and MWI crosslinked collagen groups compared to GTA and uncrosslinked collagen tubes.

Middle molecule removal in low-flux polysulfone dialyzers: impact of flows and surface area on whole-body and dialyzer clearances
Eloot, S., J. Y. de Vos, et al. (2005), Hemodial Int 9(4): 399-408.
Abstract: Some studies found that the removal of middle molecules has a long-term effect on mortality and, even more, is enhanced by high-flux dialysis. In order to enhance middle molecule removal in a low-flux dialyzer, the present study aimed at investigating the combined impact of dialyzer flows and membrane surface area. Blood and dialysate flows were varied within the clinical range 300-500 and 500-800 mL/min, respectively, while the ultrafiltration rate was kept constant at 0.1 L/hr. Single-pass tests were performed in vitro in a single Fresenius F6HPS dialyzer (3 tests) and serially (5 tests) and parallel (3 tests) connected dialyzers. The blood substitution fluid consisted of dialysis fluid in which radioactive-labeled vitamin B12 (molecular weight 1355 Da) was dissolved. Dialyzer clearance as well as whole-body clearance was calculated from radioactivity concentrations of samples taken from the inlet and outlet bloodline. Adding a second dialyzer in series or parallel ameliorated the overall dialyzer and whole-body clearance significantly, except for the highest applied blood flows of 500 mL/min. Better solute removal was also obtained with higher dialysate flows, while the use of higher blood flows seemed advantageous only when using a single dialyzer. Analysis of the ultrafiltration profiles in the different configurations illustrated that enhancing the internal filtration rate ameliorates convective transport of middle molecules. Adequate solute removal results from a number of interactions, as there are blood and dialysate flows, membrane surface area, filtration profile and concentration profiles in the blood and dialysate compartment.

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Last Modified: 8 February 2006