Biomaterials.info - Resources for Engineers

Record 4341 to 4360

UHMWPE wear debris upregulates mononuclear cell proinflammatory gene expression in a novel murine model of intramedullary particle disease
Epstein, N. J., W. E. Bragg, et al. (2005), Acta Orthop 76(3): 412-20.
Abstract: BACKGROUND: We examined the effects of ultra-high molecular weight polyethylene (UHMWPE) particles on mononuclear cell proinflammatory gene expression in a novel murine model. We hypothesized that mononuclear cell gene transcription of tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1beta), interleukin-6 (IL-6) and macrophage chemoattractant protein-1 (MCP-1) would be upregulated by the addition of polyethylene particles in this murine intramedullary rod model. MATERIAL AND METHODS: The model involved a stainless steel Kirschner wire inserted retrograde with a line-to-line fit in bilateral femora of C57bl/6 mice. Additionally, the right femora were injected with 3 x 10(9) UHMWPE particles. Mononuclear marrow cells were isolated by bone marrow aspiration and Ficoll-Paque centrifugation at 2, 4 and 10 weeks post-surgery. Total RNA was isolated and real-time RT-PCR was performed to quantify gene expression. Histological specimens of explanted femora were also analyzed to track the changes in periprosthetic tissue. RESULTS: UHMWPE particles stimulated gene transcription in mononuclear cells when examined at 2, 4 and 10 weeks post-surgery, compared to the rod-only group. Relative levels of IL-1beta and MCP-1 mRNA increased in a linear fashion over the 10-week time-course. IL-6 mRNA showed increased expression which peaked at 4 weeks. TNF-alpha mRNA expression was variable and reached a minimum at 4 weeks. The addition of UHMWPE particles stimulated ingress of macrophages and multinuclear cells of macrophage origin to the bone-implant interface. INTERPRETATION: In this model, a single bolus of UHMWPE particles had a long-term effect on gene transcription in mononuclear cells which perpetuated a chronic inflammatory state. This murine model of intramedullary particle-induced inflammation simulates periprosthetic events associated with implant wear in humans, and may contribute to a more mechanistic understanding of wear-debris associated prosthesis failure.

Ultra Low Temperature Isotropically (U.L.T.I.) Deposited Carbon (Biolyte): A Promising New Flexible Blood Interfacing Biomaterial
Haubold, A. D. and J. C. Norman (1977), Cardiovasc Dis 4(4): 369-370.

Ultrafine titanium dioxide particles in the absence of photoactivation can induce oxidative damage to human bronchial epithelial cells
Gurr, J. R., A. S. Wang, et al. (2005), Toxicology 213(1-2): 66-73.
Abstract: Ultrafine titanium dioxide (TiO(2)) particles have been shown to exhibit strong cytotoxicity when exposed to UVA radiation, but are regarded as a biocompatible material in the absence of photoactivation. In contrast to this concept, the present results indicate that anatase-sized (10 and 20 nm) TiO(2) particles in the absence of photoactivation induced oxidative DNA damage, lipid peroxidation, and micronuclei formation, and increased hydrogen peroxide and nitric oxide production in BEAS-2B cells, a human bronchial epithelial cell line. However, the treatment with anatase-sized (200 and >200 nm) particles did not induce oxidative stress in the absence of light irradiation; it seems that the smaller the particle, the easier it is for the particle to induce oxidative damage. The photocatalytic activity of the anatase form of TiO(2) was reported to be higher than that of the rutile form. In contrast to this notion, the present results indicate that rutile-sized 200 nm particles induced hydrogen peroxide and oxidative DNA damage in the absence of light but the anatase-sized 200nm particles did not. In total darkness, a slightly higher level of oxidative DNA damage was also detected with treatment using an anatase-rutile mixture than with treatment using either the anatase or rutile forms alone. These results suggest that intratracheal instillation of ultrafine TiO(2) particles may cause an inflammatory response.

Ultraporous beta-tricalcium phosphate is well incorporated in small cavitary defects
Anker, C. J., S. P. Holdridge, et al. (2005), Clin Orthop Relat Res(434): 251-7.
Abstract: Numerous bone graft substitutes are available as alternatives to autologous and allograft bone grafts. The use of ultraporous beta-tricalcium phosphate for cavitary bone defects in our institution was based on the hypothesis that it would have gradual but complete incorporation over several months, similar to the smooth transition seen in animal models. This retrospective, uncontrolled study reviews 24 patients who had bone grafting of a cavitary defect with ultraporous beta-tricalcium phosphate mixed with local blood. Radiographically, resorption and trabeculation increased steadily with time, with trabeculation lagging slightly behind resorption. Resorption and trabeculation were more advanced at times beyond 6 weeks in small defects (< 43 cm) compared with large defects (>/= 43 cm). The presence of peripheral radiolucency seen early around nearly all grafts disappeared in small lesions by 1 year, but still was visible in larger lesions at the latest followup. Bone renewal seems to correspond temporally with gradual replacement of graft material, but incorporation is not complete even at 1 year in large defects. Clinically, there is a low rate of complications associated with the use of ultraporous beta-tricalcium phosphate, and patients progressed to unrestricted activities of daily living and recreational activities within 3 months.

Ultrasonic measurement of depth-dependent transient behaviors of articular cartilage under compression
Zheng, Y. P., H. J. Niu, et al. (2005), J Biomech 38(9): 1830-7.
Abstract: We previously reported an ultrasound method for measuring the depth-dependent equilibrium mechanical properties of articular cartilage using quasi-static compression. The objective of this paper was to introduce our recent development for nondestructively measuring the transient depth-dependent strains of full-thickness articular cartilage specimens prepared from bovine patellae. A 50 MHz focused ultrasound transducer was used to collect ultrasound echoes from articular cartilage specimens (n=8) and sponge phantoms with open pores (n=10) during tests of compression and subsequent stress-relaxation. The transient displacements of the tissues at different depths along the compression direction were calculated from the ultrasound echoes using a cross-correlation tracking technique. An LVDT sensor and a load cell were used to measure the overall deformation of the tissue and the applied force, respectively. Results showed that the tissues inside the cartilage layer continued to move during the stress-relaxation phase after the compression was completed. In the equilibrium state, the displacements of the cartilage tissues at the depths of 1/4, 1/2, and 3/4 of the full-thickness reduced by 51%+/-22%, 54%+/-17%, and 50+/-17%, respectively, in comparison with its peak value. However, no similar phenomenon was observed in the sponge phantoms. Our preliminary results demonstrated that this ultrasound method may provide a potential tool for the nondestructive measurement of the transient depth-dependent processes involved in biological and bioengineered soft tissues as well as soft biomaterials under dynamic loading.

Ultrasonically assisted hydrothermal synthesis of nanocrystalline ZrO2, TiO2, NiFe2O4 and Ni0.5Zn0.5Fe2O4 powders
Meskin, P. E., V. K. Ivanov, et al. (2006), Ultrason Sonochem 13(1): 47-53.
Abstract: Ultrasonic-hydrothermal and hydrothermal treatment was used for synthesis of nanocrystalline zirconia, titania, nickel and nickel-zinc ferrites powders from precipitated amorphous zirconyl, titanyl, binary nickel-iron and ternary nickel-zinc-iron hydroxides, respectively. Resulted nanopowders were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption (BET), and magnetic susceptibility measurements. It was established that ultrasonically assisted hydrothermal treatment of amorphous zirconyl and titanyl gels results in significant rise of the rate of ZrO2 and TiO2 crystallization and promotes formation of thermodynamically stable monoclinic zirconia, but does not affect the microstructure and mean particles size of resulting nanopowders. Ultrasonic-hydrothermal processing of co-precipitated amorphous nickel, zinc and iron hydroxides favours formation of nanocrystalline ferrite powders with narrower particle size distribution.

Ultrasonically controlled release of ciprofloxacin from self-assembled coatings on poly(2-hydroxyethyl methacrylate) hydrogels for Pseudomonas aeruginosa biofilm prevention
Norris, P., M. Noble, et al. (2005), Antimicrob Agents Chemother 49(10): 4272-9.
Abstract: Indwelling prostheses and subcutaneous delivery devices are now routinely and indispensably employed in medical practice. However, these same devices often provide a highly suitable surface for bacterial adhesion and colonization, resulting in the formation of complex, differentiated, and structured communities known as biofilms. The University of Washington Engineered Biomaterials group has developed a novel drug delivery polymer matrix consisting of a poly(2-hydroxyethyl methacrylate) hydrogel coated with ordered methylene chains that form an ultrasound-responsive coating. This system was able to retain the drug ciprofloxacin inside the polymer in the absence of ultrasound but showed significant drug release when low-intensity ultrasound was applied. To assess the potential of this controlled drug delivery system for the targeting of infectious biofilms, we monitored the accumulation of Pseudomonas aeruginosa biofilms grown on hydrogels with and without ciprofloxacin and with and without exposure to ultrasound (a 43-kHz ultrasonic bath for 20 min daily) in an in vitro flow cell study. Biofilm accumulation from confocal images was quantified and statistically compared by using COMSTAT biofilm analysis software. Biofilm accumulation on ciprofloxacin-loaded hydrogels with ultrasound-induced drug delivery was significantly reduced compared to the accumulation of biofilms grown in control experiments. The results of these studies may ultimately facilitate the future development of medical devices sensitive to external ultrasonic impulses and capable of treating or preventing biofilm growth via "on-demand" drug release.

Ultrasound preexposure improves endothelial cell binding and retention on biomaterial surfaces
Hsu, S. H., T. B. Huang, et al. (2006), J Biomed Mater Res B Appl Biomater 76(1): 85-92.
Abstract: In spite of the extensive studies regarding the effects of ultrasound on biological systems, the influence of low-intensity ultrasound on endothelial cells has rarely been investigated. In this work, the effect of ultrasound in improving the binding between endothelial cells and biomaterial substrates was evaluated. Based on the results, low-intensity ultrasound could change the morphology and matrix secretion of endothelial cells, and such effects persisted when preexposed cells were seeded to another substrate. The cells preexposed to ultrasound were spread further on the substrate. The actin stress fibers of ultrasound-preexposed cells on RGD-modified surfaces were especially intense and well oriented. Ultrasound could probably activate cellular integrins and subsequently allow RGD to bind them. A much firmer adhesion of ultrasound-preexposed endothelial cells to the biomaterial surface coated with the RGD-containing protein was demonstrated. Finally, polyurethane small-diameter vascular grafts seeded with ultrasound-preexposed endothelial cells showed enhanced cell retention on graft surfaces upon flushing. (c) 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006.

Ultrasound-induced capping of polystyrene on TiO2 nanoparticles by precipitation with compressed CO2 as antisolvent
Zhang, J., Z. Liu, et al. (2005), J Nanosci Nanotechnol 5(6): 945-50.
Abstract: In this work, a route for the synthesis of inorganic/polymer core/shell composite nanoparticles was proposed, which can be called the antisolvent-ultrasound method. Compressed CO2 was used as antisolvent to precipitate the polymer from its solution dispersed with inorganic nanoparticles, during which ultrasonic irradiation was used to induce the coating of precipitated polymers on the surfaces of the inorganic nanoparticles. TiO2/polystyrene (PS) core/shell nanocomposites have been successfully prepared using this method. The transmission electronic micrographs (TEM) of the obtained nanocomposites show that the TiO2 nanoparticles are coated by the PS shells, of which the thickness can be tuned by the pressure of CO2. The phase structure, absorption properties, and thermal stability of the composite were characterized by X-ray diffraction (XRD), UV-vis spectra, and thermogravimetry, respectively. The results of X-ray photoelectron spectra (XPS) indicate the formation of a strong interaction between PS and TiO2 nanoparticles in the resultant products. This method has some potential advantages for applications and may be easily applied to the preparation of a range of inorganic/polymer core/shell composite nanoparticles.

Ultrastructural analyses of the attachment (bonding) zone between bone and implanted biomaterials
Steflik, D. E., R. S. Corpe, et al. (1998), J Biomed Mater Res 39(4): 611-20.
Abstract: This report presents transmission electron and high voltage transmission electron microscopic observations of bone and associated remodeling tissues directly interfacing with endosteal dental implants. Undecalcified interfacial tissues were serially sectioned from mandibular samples encasing 60 implants placed into 30 dogs. Two-dimensional ultrastructural analyses and three-dimensional stereology showed that osteogenesis adjacent to dental implants is a dynamic interaction of osseous cells and a collagenous fiber matrix. This study showed that the interfacial bone consists of a mineralized collagen fiber matrix associated with an inorganic (hydroxylapatite) matrix. This study suggested that an unmineralized collagen fiber matrix initially is laid down directly at the implant surface, and that this matrix then is mineralized. Osteoblasts interacted with this matrix, eventually becoming encased within developing lacunae during the remodeling process. This process formed the cellular (osteocyte) aspects of the developed bone. Osteocyte processes extended through canaliculi directly to the implant surface. Apparently, these processes also were entrapped within canaliculi during the mineralization events. At times, these processes paralleled the implant surface. The bone-implant interfacial zone was primarily fibrillar (both mineralized and unmineralized) in morphology, with an electron-dense, ruthenium positive deposition. This electron-dense material was approximately 20 to 50 nanometers in thickness, and only this thin layer separated the remodeled mineralized bone from the implant.

Ultrastructural analysis of guided nerve regeneration using progesterone- and pregnenolone-loaded chitosan prostheses
Chavez-Delgado, M. E., U. Gomez-Pinedo, et al. (2005), J Biomed Mater Res B Appl Biomater 74(1): 589-600.
Abstract: Recently, numerous guide chambers for the treatment of injured nerves made up of different biomaterials have been designed, capable of hosting living cells or carrying neurotrophic or neuroactive substances to be directly released to the injured tissue. In this study, chitosan prostheses containing neurosteroids (progesterone and pregnenolone) were used for bridging a 10-mm gap in the rabbit facial nerve. Gas chromatography was used to quantify neurosteroid content in the prostheses prior to and after subcutaneous implantation at different periods of up to 60 days. The regeneration of the nerve fibers were evaluated at 15 and 45 days after axotomy by means of ultrastructural morphometric analysis. Different nerve fibers regenerative patterns were seen depending the groups studied and the analyzed stages. At 15 days after axotomy, the newly regenerating tissue revealed Schwann cells holding nonmyelinated nerve fiber bundles in an incipient and organized regenerative pattern. At 45 days, the regenerating tissue showed myelinated nerve fibers of different sizes, shapes, and myelin sheath thickness. Although the regeneration of the nerve fibers under neurosteroid treatment showed statistically significant differences in comparison with vehicle regenerated tissue, progesterone-loaded chitosan prostheses produced the best guided nerve regeneration response. These findings indicate that chitosan prostheses allowed regeneration of nerve fibers in their lumen, and when containing neurosteroids produced a faster guided nerve regeneration acting as a long-lasting release delivery vehicle.

Ultrastructural localization of laminin-5 (gamma2 chain) in the rat peri-implant oral mucosa around a titanium-dental implant by immuno-electron microscopy
Atsuta, I., T. Yamaza, et al. (2005), Biomaterials 26(32): 6280-7.
Abstract: Laminin-5 (Ln-5) is an important molecule associated with epithelial cell adhesion and migration. In the gingiva around the tooth, Ln-5 localizes within basement membranes between the junctional epithelium (JE) and the tooth or connective tissue. Recently, we reported that in the oral mucosa around a dental implant, Ln-5 is expressed within the basement membranes at the implant-peri-implant epithelium (PIE) interface, and at the PIE-connective tissue interface. However, the ultrastructural localization of Ln-5 within or along the PIE has not yet been reported. Therefore, peri-implant oral mucosa was treated with anti-Ln-5 (gamma2 chain) antibody and examined using immuno-electron microscopy. Ln-5 was localized in the cells of the innermost-third layer and basal layer of the PIE. A 100-nm-wide Ln-5-positive internal basal lamina (basement membrane) and hemidesmosomes as adhesion structures were formed at the apical portion of the implant-PIE interface. However, at the upper-middle portion of the interface, these adhesion structures were not observed. Furthermore, at the PIE-connective tissue interface, the Ln-5-positive external basal lamina (basement membrane) and hemidesmosomes were partially deficient. Judging from these findings, we concluded that Ln-5 contributes to the attachment of the PIE to the titanium surface, and that PIE attached to titanium at the apical portion of the dental implant-PIE interface.

Ultrastructural organization and regulation of a biomaterial adhesin of Staphylococcus epidermidis
Veenstra, G. J., F. F. Cremers, et al. (1996), J Bacteriol 178(2): 537-41.
Abstract: Coagulase-negative staphylococci have emerged as important pathogens in infections associated with intravascular devices. Microbial adherence to biomaterial surfaces is a crucial step in the pathogenesis of these infections. Staphylococcal surface proteins (herein referred to as SSP-1 and SSP-2) are involved in the attachment of Staphylococcus epidermidis 354 to polystyrene. In the present study we show that the adhesin protrudes from the cell surface as a fimbria-like polymer. Furthermore, in vitro proteolytic cleavage of SSP-1 produces an SSP-2-like protein which coincides with a loss of adhesive function. SSP-1 expression is down-regulated in a phenotypical variant of S. epidermidis 354 whereas SSP-2 expression is not. These results could suggest that proteolytic cleavage is a key to the regulation of the adhesive state of S. epidermidis in vivo.

Ultrastructure of bone healing in defects grafted with a copolymer of polylactic/polyglycolic acids
Imbronito, A. V., A. Scarano, et al. (2005), J Biomed Mater Res A 74(2): 215-21.
Abstract: Bone substitutes have been used for the treatment of bone defects. The objective of this study was to ultrastructurally evaluate the healing pattern of bone defects filled with a copolymer of polylactic/polyglycolic acid (FisiograftR) at a time point in which it is expected to be only partially degraded, with the purpose to ultrastructurally analyze how the bone is forming around the grafting material. Three 5-mm-diameter bone defects were created in each tibia from 5 rabbits (average weight 2.5 kg) in which the material was randomly implanted. Animals were sacrificed 30 days after surgery and the 30 bone defects were fixed in 2% glutaraldehyde-2.5% formaldehyde, under microwave irradiation, decalcified in EDTA, embedded in Spurr resin, and examined in a Jeol 1010 TEM. All the bone defects were filled with connective tissue, interspersed with different amounts of the filling material and newly formed bone trabeculae. In areas where the degrading copolymer was present in small amounts, newly formed bone matrix was detected; it was deposited by osteoblast-like cells in close relation to the copolymer. In areas where the degrading copolymer formed accumulates, an amorphous multilayered material was identified between the connective tissue and the copolymer. In summary, the copolymer of PLA/PGA studied appears to be an osteoconductive material when it is used to fill bone defects.

Underlying mechanisms at the bone-biomaterial interface
Schwartz, Z. and B. D. Boyan (1994), J Cell Biochem 56(3): 340-7.
Abstract: In order to understand how biomaterials influence bone formation in vivo, it is necessary to examine cellular response to materials in the context of wound healing. Four interrelated properties of biomaterials (chemical composition, surface energy, surface roughness, and surface topography) affect mesenchymal cells in vitro. Attachment, proliferation, metabolism, matrix synthesis, and differentiation of osteoblast-like cell lines and primary chondrocytes are sensitive to one or more of these properties. The nature of the response depends on cell maturation state. Rarely do differentiated osteoblasts or chondrocytes see a material prior to its modification by biological fluids, immune cells and less differentiated mesenchymal cells in vivo. Studies using the rat marrow ablation model of endosteal wound healing indicate that ability of osteoblasts to synthesize and calcify their extracellular matrix is affected by the local presence of the material. Changes in the morphology and biochemistry of matrix vesicles, extracellular organelles associated with matrix maturation and calcification, seen in normal endosteal healing, are altered by implants. Moreover, the material exerts a systemic effect on endosteal healing as well. This may be due to local effects on growth factor production and secretion into the circulation, as well as to the fact that the implant may serve as a bioreactor.

Understanding foods as soft materials
Mezzenga, R., P. Schurtenberger, et al. (2005), Nat Mater 4(10): 729-40.
Abstract: Foods make up some of the most complex examples of soft condensed matter (SCM) with which we interact daily. Their complexity arises from several factors: the intricacy of components, the different aggregation states in which foods are encountered, and the multitude of relevant characteristic time and length scales. Because foodstuffs are governed by the rules of SCM physics but with all the complications related to real systems, the experimental and theoretical approaches of SCM physics have deepened our comprehension of their nature and behaviour, but many questions remain. In this review we discuss the current understanding of food science, by considering established SCM methods as well as emerging techniques and theoretical approaches. With their complexity, heterogeneity and multitude of states, foods provide SCM physics with a challenge of remarkable importance.

Understanding the biodegradation of polyurethanes: from classical implants to tissue engineering materials
Santerre, J. P., K. Woodhouse, et al. (2005), Biomaterials 26(35): 7457-70.
Abstract: After almost half a century of use in the health field, polyurethanes (PUs) remain one of the most popular group of biomaterials applied for medical devices. Their popularity has been sustained as a direct result of their segmented block copolymeric character, which endows them with a wide range of versatility in terms of tailoring their physical properties, blood and tissue compatibility, and more recently their biodegradation character. While they became recognized in the 1970s and 1980s as the blood contacting material of choice in a wide range of cardiovascular devices their application in long-term implants fell under scrutiny with the failure of pacemaker leads and breast implant coatings containing PUs in the late 1980s. During the next decade PUs became extensively researched for their relative sensitivity to biodegradation and the desire to further understand the biological mechanisms for in vivo biodegradation. The advent of molecular biology into mainstream biomedical engineering permitted the probing of molecular pathways leading to the biodegradation of these materials. Knowledge gained throughout the 1990s has not only yielded novel PUs that contribute to the enhancement of biostability for in vivo long-term applications, but has also been translated to form a new class of bioresorbable materials with all the versatility of PUs in terms of physical properties but now with a more integrative nature in terms of biocompatibility. The current review will briefly survey the literature, which initially identified the problem of PU degradation in vivo and the subsequent studies that have led to the field's further understanding of the biological processes mediating the breakdown. An overview of research emerging on PUs sought for use in combination (drug + polymer) products and tissue regeneration applications will then be presented.

Uniaxial and biaxial tensile strength of calf pericardium used in the construction of bioprostheses: biomaterial selection criteria
Garcia Paez, J. M., A. Carrera, et al. (2000), J Biomater Appl 15(1): 47-64.
Abstract: Using morphological and mechanical criteria and applying a method involving paired samples that is widely employed in epidemiology, we obtained an excellent prediction of the mechanical behavior of the calf pericardium used in the construction of cardiac bioprostheses. The method of selection employed in this study may be a highly useful tool for guaranteeing the mechanical resistance of calf pericardium, with a very low level of error.

Uniform encapsulation of stable protein nanoparticles produced by spray freezing for the reduction of burst release
Leach, W. T., D. T. Simpson, et al. (2005), J Pharm Sci 94(1): 56-69.
Abstract: Stable protein nanostructured particles, produced by spray freezing into liquid (SFL) nitrogen, were encapsulated uniformly into microspheres to reduce the burst release over the first 24 h. The denaturation and aggregation of these bovine serum albumin (BSA) high-surface area particles were minimal due to ultra-rapid freezing and the absence of a liquid-air interface. Upon sonication, these friable highly porous, solid protein particle aggregates broke up into submicron particles. These particles were encapsulated into DL-lactide/glycolide copolymer (PLGA) and poly(lactic acid) (PLA) microspheres by anhydrous solid-in-oil-in-oil (s/o/o) techniques. For 5% loading of protein, the burst release after 24 h was only 2.5-4.1%, that is, values fivefold to tenfold lower than those observed for larger more conventional BSA particles. At a loading of 10%, the burst was only 6 and 13% for PLGA and PLA, respectively, and at 15% loading it was only 12% for PLGA. As shown with confocal and scanning electron microscopy (SEM), the low burst is consistent with a uniform distribution of protein nanoparticles, which were about 100 times smaller than the microspheres. Changes in aggregation and secondary structure, which were monitored by size exclusion chromatography and FTIR, respectively, indicated only slight monomer loss (3.9%) and high structural integrity (38% alpha-helix) in the encapsulated protein.

Uniform microporous biomaterials prepared by the Relamineform technique
White, R. A., E. W. White, et al. (1979), Biomater Med Devices Artif Organs 7(1): 127-32.
Abstract: The Replamineform process provides a technique for fabricating microporous ceramic, metal and polymer biomedical implant materials. A range of pore sizes can be made in the same material, thus allowing independent study of the effect of pore size and biomaterial on incorporation of implants. This new family of biomaterials shows promise for helping to determine the optimum characteristics to enhance tissue regeneration.

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