|Articles about Biomaterials|
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| Cortical bone screw fixation in ionically modified apatite cements
Barralet, J. E., C. O. Duncan, et al. (2005), J Biomed Mater Res B Appl Biomater 73(2): 238-43.
Abstract: Hydroxyapatite cements are used in reconstruction of the face; usually in well-defined cavities where the cement can be stabilized without the need for internal fixation. A hydroxyapatite cement that could enable screw fixation and some loading therefore has considerable potential in maxillofacial reconstruction. It has been demonstrated recently that water demand of calcium phosphate cements can be reduced by ionically modifying the liquid component. This study investigated the capacity of an ionically modified precompacted apatite cement to retain self-tapping cortical bone screws. Screw pullout forces were determined in the direction of the screw long axis and perpendicular to it, using cortical bone and polymethylmethacrylate cement as a control. In bending pullout tests, measured forces to remove screws from ionically modified precompacted cement were insignificantly different from cortical bone. However, pullout forces of bone screws from hydroxyapatite cement decreased with aging time in vitro.
| Cost-effectiveness of drug-eluting stents: if only all things were equal. They reduce rates of restenosis but not mortality or infarction--so are they worth it?
Chew, D. P. (2005), Med J Aust 182(8): 376-7.
| Coulombic amino group-metal bonding: adsorption of adenine on Cu110
Preuss, M., W. G. Schmidt, et al. (2005), Phys Rev Lett 94(23): 236102.
Abstract: The interaction between molecular amino groups and metal surfaces is analyzed from first-principles calculations using the adsorption of adenine on Cu110 as a model case. The amino group nitrogens are found to adsorb on top of the surface copper atoms. However, the bonding clearly cannot be explained in terms of covalent interactions. Instead, we find it to be largely determined by mutual polarization and Coulomb interaction between substrate and adsorbate.
| Covalent attachment of oligonucleotides to cellulose acetate membranes
Okutucu, B. and A. Telefoncu (2004), Artif Cells Blood Substit Immobil Biotechnol 32(4): 599-608.
Abstract: During the last decade, DNA has become an increasingly important biomolecule in several areas. DNA technology has found many applications, e.g., in forensic science, environmental studies, diagnosis and archeometry. DNA microarrays and DNA biosensors applying the principle of immobilization of oligonucleotide on solid supports are used in these areas. DNA immobilization can be performed by adsorption and covalent attachment. In this study cellulose acetate was used as a solid support for oligonucleotide immobilization. Cellulose acetate was activated with 1,1'-Carbonyldiimidazole (CDI) and then coupled with 1,6-hexanediamine (HDA) as a linker. A hexadecadesoxy oligonucleotide was also activated by I-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and immobilized on the membrane by coupling via amino groups. The effects of various parameters on the immobilization oligonucleotide were investigated.
| Covalent conjugation of polyethyleneimine on biodegradable microparticles for delivery of plasmid DNA vaccines
Kasturi, S. P., K. Sachaphibulkij, et al. (2005), Biomaterials 26(32): 6375-85.
Abstract: Microparticle-based delivery of nucleic acids has gained particular attention in recent years in view of improving the potency of DNA vaccination. Such improvement has been reported by encapsulation of pDNA within biodegradable microparticles or through surface adsorption on cationic microparticles. However, the intrinsic intracellular barriers for gene delivery to antigen presenting cells (APCs) have not been adequately addressed in the rational design of delivery systems for DNA vaccines. Here we report synthesis and characterization of biodegradable microparticles that (a) can passively target phagocytic APCs, (b) have intrinsic buffering ability that might allow for enhanced phagosomal escape, (c) are not cytotoxic and (d) have improved APC transfection efficiency. Branched polyethyleneimine (b-PEI) was covalently conjugated using carbodiimide chemistry to the surface of poly(lactide-coglycolide) (PLGA) microparticles to create cationic microparticles capable of simultaneously delivering both DNA vaccines as well as other immunomodulatory agents (cytokines or nucleic acids) within a single injectable delivery vehicle. Our results indicate that covalent conjugation of b-PEI allows efficient surface loading of nucleic acids, introduces intrinsic buffering properties to PLGA particles and enhances transfection of phagocytic cells without affecting the cytocompatibility of PLGA carriers.
| Covalent protein immobilization on glass surfaces: application to alkaline phosphatase
Taylor, R. H., S. M. Fournier, et al. (2005), J Biotechnol 118(3): 265-9.
Abstract: Lyophilized alkaline phosphatase (ALPase) was immobilized on aminated glass surfaces using the in vacuo cross-linking process [Simons, B.L., King, M.C., Cyr, T., Hefford, M.A., Kaplan, H., 2002. Zero-length cross-linking of lyophilized proteins. Protein Sci. 11, 1558-1564]. In this procedure, amide bonds were formed between carboxyl groups on the protein and amino groups on the glass surface. After the non-covalently attached enzyme was removed the immobilized ALPase not only retained its activity but could also be used, washed and reused at least six times without significant loss of activity. An average of 1.4+/-0.6 mg of reusable ALPase per gram of glass fibre was immobilized based on the activity of the soluble equivalent.
| Covalent-bonded immobilization of lipase on poly(phenylene sulfide) dendrimers and their hydrolysis ability
Yemul, O. and T. Imae (2005), Biomacromolecules 6(5): 2809-14.
Abstract: Covalent-bonded immobilization of lipase from burkholderia cepacia onto two poly(phenylene sulfide) (PPS) dendrimers with different generations (two and three) was achieved using carbodiimide as a coupling reagent. The hydrolysis activity of olive oil to fatty acid was studied on enzyme-immobilized PPS dendrimers. Enzyme activity was proportional to the enzyme loading, and highest recovered activity was obtained at the medium enzyme loading for both G2 and G3 dendrimers. The immobilization improved the optimum pH and caused the temperature range to widen. Immobilization of enzyme has enhanced the thermal stability of enzyme activity in comparison with free enzyme. The immobilized enzyme as a biocatalyst for batch hydrolysis of olive oil retained 80 approximately 90% activity even after 20 times of recycling. This retention of activity after recycle is very valuable and powerful in enzyme technology. The present noteworthy and vital availability on enzyme reaction of the covalently bonded immobilized lipase on dendrimer came from the structure of dendrimer with a large number of functional terminal groups, which are easily available for immobilization of many lipases at the situation keeping reactive enzymes on the surface of dendrimer.
| Covalently grafted phospholipid monolayer on silicone catheter surface for reduction in platelet adhesion
Krishna, O. D., K. Kim, et al. (2005), Biomaterials 26(34): 7115-23.
Abstract: We report a novel method of surface grafting a polymeric phospholipid system containing an acryloyl end group (1stearoyl-2-[12-(acryloyloxy)-dodecanoyl]-sn-glycero-3-phosphocholine) onto medical grade silicone catheters. The surface of silicone catheters was functionalized in a sequence of steps: plasma polymerization of allyl alcohol on the catheter surface, grafting acryloyl moieties and in situ polymerization of the pre-assembled acryloyl terminated phospholipids on the acryloyl functionalized catheter surface. The surface morphological changes analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM), a sharp decrease in water contact angle, and appearance of N1s peak in XPS analysis indicated a successful monolayer grafting of the phospholipid. In platelet adhesion tests performed using platelets isolated from rabbit plasma, the phospholipid grafted surface showed fewer adhered platelets, without emerging pseudopodes or aggregation. However, ungrafted catheter surface showed large number of platelets in extensively spread and aggregated states. Thus, this modified phospholipid system and its simple grafting technique was very effective with regard to suppressing in vitro platelet adhesion on the silicon catheter surface.
| Cowpea mosaic virus: from the presentation of antigenic peptides to the display of active biomaterials
Chatterji, A., L. L. Burns, et al. (2002), Intervirology 45(4-6): 362-70.
Abstract: The potential of cowpea mosaic virus (CPMV), a plant icosahedral virus, for the presentation of foreign peptides and proteins is reported. The most prominent feature at the virus surface is a region of the smaller of the two coat proteins (S) which has been extensively used for the insertion of foreign peptides. Given the availability of the three-dimensional structure of the native virus and the amenability of foreign peptide-expressing CPMV chimeras to crystallisation, immunological data can be correlated with the conformational state of the foreign insert. The latter is influenced by proteolysis which occurs within the foreign inserts. In an effort to offer an alternative context for peptide expression, extensive exploration of a second region of the S protein is reported with respect to tolerance to small insertions. Moreover, to make CPMV suitable for a wider spectrum of presentation, a technique was developed to allow surface coupling of a peptide which can serve as the anchoring point for a range of proteins. This new approach is also widely applicable for the direct chemical cross-linking of peptides and full-length protein domains to the viral capsid.
| Creativity, ingenuity, serendipity
Holmes, D. R., Jr. (2005), Can J Cardiol 21(12): 1061-5.
Abstract: Some of the earliest experiences of invasive cardiology centred on studying the physiology of congenital heart disease in a series of ongoing attempts to understand pathophysiology and anatomy, and then devising strategies to treat the lesion. Tremendous growth in the field and rapid advances in patient care have become possible due to the collaboration of early investigators, including pediatric cardiologists, cardiovascular pathologists, embryologists, physiologists and cardiovascular surgeons. This group has expanded to include radiologists, vascular biologists and engineers. Mason Sones' serendipitous encounter with a patient led to the thought that one patient's 'complication' might lead to another therapy and, as a result, studies were conducted. Early equipment was bulky, rigid and inflexible. Andreas Gruentzig was instrumental in the development of several new techniques. Throughout the development of invasive cardiology, great attention has been paid to the evaluation of both successful and failed outcomes. Over the intervening years, multiple advances in technology have improved procedures by making invasive cardiology easier, safer and more predictable and have expanded the patient population that could benefit from it. These advances included new devices, such as atherectomy transluminal extraction catheters, as well as with directional coronary atherectomy, rotational atherectomy and laser-based techniques. Interventional cardiology has soared with single-centre and multicentre randomized trials. Intracoronary stents have completely revolutionized therapy, becoming smaller, more flexible and more easily deliverable. With the introduction of drug-eluting stents, restenosis rates have been dramatically reduced. However, chronic total occlusion continues to be a problem in interventional cardiology due to increased risk of early and late complications and increased restenosis rates. New areas continue to be developed, combining the inventions and designs of collaborators. An increased knowledge of the basic pathophysiology of cardiovascular disease, combined with creative technology and imaginative operators, will continue to advance the field.
| Critical threat to the availability of surgical implant material: lesson to be learned from breast implants
Nose, Y. (2005), Artif Organs 29(8): 595-7.
| Crk-associated substrate tyrosine phosphorylation sites are critical for invasion and metastasis of SRC-transformed cells
Brabek, J., S. S. Constancio, et al. (2005), Mol Cancer Res 3(6): 307-15.
Abstract: Crk-associated substrate (CAS, p130Cas) is a major tyrosine phosphorylated protein in cells transformed by v-crk and v-src oncogenes. We recently reported that reexpression of CAS in CAS-deficient mouse embryo fibroblasts transformed by oncogenic Src promoted an invasive phenotype associated with enhanced cell migration through Matrigel, organization of actin into large podosome ring and belt structures, activation of matrix metalloproteinase-2, and elevated tyrosine phosphorylation of the focal adhesion proteins FAK and paxillin. We have now extended these studies to examine the mechanism by which CAS achieves these changes and to evaluate the potential role for CAS in promoting in vivo tumor growth and metastasis. Whereas the presence or absence of CAS did not alter the primary growth of subcutaneous-injected Src-transformed mouse embryo fibroblasts, CAS expression was required to promote lung metastasis following removal of the primary tumor. The substrate domain YxxP tyrosines, the major sites of CAS phosphorylation by Src that mediate interactions with Crk, were found to be critical for promoting both invasive and metastatic properties of the cells. The ability of CAS to promote Matrigel invasion, formation of large podosome structures, and tyrosine phosphorylation of Src substrates, including FAK, paxillin, and cortactin, was also strictly dependent on the YxxP tyrosines. In contrast, matrix metalloproteinase-2 activation was most dependent on the CAS SH3 domain, whereas the substrate domain YxxP sites also contributed to this property. Thus multiple CAS-mediated signaling events are implicated in promoting invasive and metastatic properties of Src-transformed cells.
| Cross-linked cationic polymer microparticles: effect of N-trimethyl chitosan chloride on the release and permeation of ibuprofen
Lu, Z., J. H. Steenekamp, et al. (2005), Drug Dev Ind Pharm 31(3): 311-7.
Abstract: Microparticles made by cross-linking hydrophilic polymers, such as chitosan, have been used to modify the release rate of a loaded drug. In this study a polymer with fixed positive charges, N-trimethyl chitosan chloride (TMC), was used in combination with chitosan to formulate microparticles to investigate its effects on drug release rate and transport across intestinal epithelial cells. The microparticles were prepared by cross-linking these cationic polymer(s) using sodium citrate as the ionic cross-linker. This process was done under homogenization and ultrasonication to control the size of the particles. The addition of TMC to the chitosan microparticles resulted in an increase in particle size of the microparticles and an increase in ibuprofen release rate as compared to the microparticles containing chitosan alone. Permeation of ibuprofen across Caco-2 cell monolayers, after administration of a suspension of the microparticles to the apical side, was not significantly different for the microparticles containing TMC as compared to those consisting of chitosan alone. It was concluded that release of TMC molecules from the microparticles was probably not sufficient to interact with the intestinal epithelial cells in order to change the permeation of the released drug.
| Cross-linked hyaluronan versus collagen for injection treatment of glottal insufficiency: 2-year follow-up
Hertegard, S., L. Hallen, et al. (2004), Acta Otolaryngol 124(10): 1208-14.
Abstract: OBJECTIVES: To evaluate the long-term (24 months) clinical performance (vocal fold function) and safety of hylan B gel as compared with bovine cross-linked collagen in the treatment of patients with glottal insufficiency. MATERIAL AND METHODS: In a prospective trial, 70 patients with glottal insufficiency due to unilateral vocal fold paresis (n =35) or atrophy (n =35) were randomized to received either hylan B gel (n =47) or collagen (n =23) injections into 1 vocal fold. Forty-two of the patients were examined 24 months after treatment. Evaluations were made based on patients' subjective ratings, digitized videostroboscopic measurements, maximum phonation time and phonation quotient. RESULTS: The patients' self-ratings were significantly improved in both the hylan B gel and collagen groups. Videostroboscopic measurements of glottal closure were significantly improved for both groups. The hylan B gel group showed a trend towards less resorption at the injected vocal fold edge in comparison with the collagen group (p =0.05). No serious adverse events were observed. Twenty-eight patients dropped out of the study after 12 months: 18 had been re-injected or operated on with medialization laryngoplasty due to insufficient voice and 10 had either died of causes unrelated to the study or refused to attend follow-up. CONCLUSIONS: No long-term side-effects were found for either the hylan B gel or collagen groups after injection treatment. Both treatments resulted in significantly improved voice as rated by the patients and significantly improved glottal closure. Some resorption was noted for both substances, and approximately 25%, of the patients chose re-treatment 2 years after the initial treatment.
| Cross-linked hyaluronic acid hydrogel films: new biomaterials for drug delivery
Luo, Y., K. R. Kirker, et al. (2000), J Control Release 69(1): 169-84.
Abstract: A new hyaluronic acid (HA)-based hydrogel film was prepared and evaluated for use in drug delivery. This biocompatible material crosslinks and gels in minutes, and the dried film swells and rehydrates to a flexible hydrogel in seconds. HA was first converted to the adipic dihydrazide derivative and then crosslinked with the macromolecular homobifunctional reagent poly(ethylene glycol)-propiondialdehyde to give a polymer network. After gelation, a solvent casting method was used to obtain a HA hydrogel film. The dried film swelled sevenfold in volume in buffer, reaching equilibrium in less than 100 s. Scanning electron microscopy (SEM) of the hydrogel films showed a condensed and featureless structure before swelling, but a porous microstructure when hydrated. The thermal behavior of the hydrogel films was characterized by differential scanning calorimetry. The enzymatic degradation of the HA hydrogel films by hyaluronidase was studied using both SEM and a spectrophotometric assay. Drug release from the hydrogel film was evaluated in vitro using selected anti-bacterial and anti-inflammatory drugs. This novel biomaterial can be employed for controlled release of therapeutic agents at wound sites.
| Cross-linking of scleral collagen in the rabbit using riboflavin and UVA
Wollensak, G., E. Iomdina, et al. (2005), Acta Ophthalmol Scand 83(4): 477-82.
Abstract: PURPOSE: Scleral biomechanical weakness and thinning is known to be one of the main factors in the pathogenesis of progressive myopia. We tried to strengthen rabbit sclera by cross-linking scleral collagen using ultraviolet A (UVA) and the photosensitizer riboflavin. METHODS: Circumscribed 10 x10 mm sectors of the posterior--equatorial sclera of six chinchilla rabbit eyes were treated in vivo using a UVA double diode with 4.2 mW/cm(2) UVA at 370 nm and applying 0.1% riboflavin-5-phosphate drops as photosensitizer for 30 min. 1 day postoperatively biomechanical stress--strain measurements of three treated scleral strips were performed using a microcomputer-controlled biomaterial testing device and compared to non-treated contralateral control sclera. In addition, three treated eyes were examined histologically by light microscopy, TUNEL staining and electron microscopy to evaluate side-effects. RESULTS: Following the cross-linking treatment, the ultimate stress was 11.87+/-1.8 MPa versus 3.63+/-0.40 in the controls (increase of 227.9%, p=0.014), Young's modulus 27.67+/-4.16 MPa versus 4.9+/-.15 MPa in the controls (increase of 464.7%, p=0.021) and ultimate strain 92.2+/-7.43% versus 165.63+/-19.09% in the controls (decrease of 54.52%, p=0.012). Histologically, serious side-effects were found in the entire posterior globe with almost complete loss of the photoreceptors, the outer nuclear layer and the retinal pigment epithelium (RPE). CONCLUSIONS: Our new method of scleral collagen cross-linking proved very effective in increasing the scleral mechanical strength; the new treatment may represent an option for strengthening scleral tissue in progressive myopia. However, serious side-effects were observed in the outer retina. In future studies these side-effects could be avoided by reducing the irradiation dose below the cytotoxic level of the retina. Before its clinical application, the new method should be tested in a myopia animal model.
| Crystal and microparticle effects on MDCK cell superoxide production: oxalate-specific mitochondrial membrane potential changes
Meimaridou, E., J. Jacobson, et al. (2005), Free Radic Biol Med 38(12): 1553-64.
Abstract: We have previously shown that crystals of calcium oxalate (COM) elicit a superoxide (O2-) response from mitochondria. We have now investigated: (i) if other microparticles can elicit the same response, (ii) if processing of crystals is involved, and (iii) at what level of mitochondrial function oxalate acts. O2- was measured in digitonin-permeabilized MDCK cells by lucigenin (10 microM) chemiluminescence. [(14)C]-COM dissociation was examined with or without EDTA and employing alternative chelators. Whereas mitochondrial O2- in COM-treated cells was three- to fourfold enhanced compared to controls, other particulates (uric acid, zymosan, and latex beads) either did not increase O2- or were much less effective (hydroxyapatite +50%, p < 0.01), with all at 28 microg/cm(2). Free oxalate (750 microM), at the level released from COM with EDTA (1 mM), increased O2- (+50%, p < 0.01). Omitting EDTA abrogated this signal, which was restored completely by EGTA and partially by ascorbate, but not by desferrioxamine or citrate. Omission of phosphate abrogated O2-, implicating phosphate-dependent mitochondrial dicarboxylate transport. COM caused a time-related increase in the mitochondrial membrane potential (deltapsi(m)) measured using TMRM fluorescence and confocal microscopy. Application of COM to Fura 2-loaded cells induced rapid, large-amplitude cytosolic Ca(2+) transients, which were inhibited by thapsigargin, indicating that COM induces release of Ca(2+) from internal stores. Thus, COM-induced mitochondrial O2- requires the release of free oxalate and contributes to a synergistic response. Intracellular dissociation of COM and the mitochondrial dicarboxylate transporter are important in O2- production, which is probably regulated by deltapsi(m).
| Crystal structure and morphology of poly(12-dodecalactone)
Kim, E., H. Uyama, et al. (2005), Biomacromolecules 6(2): 572-9.
Abstract: Poly(12-dodecalactone) (PDDL) crystals in the form of chain-folded lamellae were prepared by isothermal crystallization from a 1-hexanol solution. The lozenge-shaped crystals with and without spiral growth have been studied by transmission electron microscopy and atomic force microscopy. Wide-angle X-ray diffraction data, obtained from PDDL lamellae sedimented to form oriented mats and annealed solvent-cast film, were supplemented with morphological and structural data from electron microscopy. PDDL crystallizes as an orthorhombic form with a P2(1)2(1)2(1) space group and lattice constants of a = 0.746 +/- 0.001 nm, b = 0.500 +/- 0.001 nm, and c (chain axis) = 3.281 +/- 0.003 nm. There are two chains per unit cell, which existed in an antiparallel arrangement. The fiber repeat distance is appropriate for an all-trans backbone conformation for the straight stems. Molecular packing of this structure has been studied in detail, taking into account both diffraction data and energy calculations. The setting angles, with respect to the a axis, were +/-43 degrees for the corner and center chains according to intensity measurements and structure factor calculations. The optimized shift along the crystallographic c axis is 0.1c (0.328 nm). A final model was obtained to yield R = 0.180 with X-ray diffraction data and R = 0.162 with electron diffraction data. A brief comparison is also made with related polymer structures.
| Crystallization behavior of silica-calcium phosphate biocomposites: XRD and FTIR studies
Ning, C. Q., Y. Greish, et al. (2004), J Mater Sci Mater Med 15(11): 1227-35.
Abstract: Silica and calcium phosphates (CaP) are the most important ingredients in bioactive materials that bond to bone and enhance bone tissue formation. In this study, silica-calcium phosphate (SiO2-CaP) composites were developed by powder metallurgy method, using silica (SiO2) and anhydrous dicalcium phosphate (CaHPO4) powders (CaP) in the ratios (wt%): 20/80, 40/60, 60/40 and 80/20. The effects of temperature and chemical composition on crystallization and phase transformation of the SiO2-CaP composites were evaluated by XRD and FTIR. Thermal treatment of the starting material suggested that CaHPO4 transforms into: gamma-Ca2P2O7 at 800 degrees C; beta-Ca2P2O7 at 1000 degrees C and alpha-Ca2P2O7 at 1200 degrees C. On the other hand, beta-quartz was the only detected phase after thermal treatment of silica in the temperature range 800-1200 degrees C. For all SiO2-CaP composites, SiO2 and CaP did not modify the crystallization behavior of each other when sintered in the temperature range 800-1000 degrees C. However, at 1200 degrees C, CaP promoted the transformation of gamma-quartz into alpha-cristobalite. Moreover, SiO2 stabilized beta-Ca2P2O7. The modifications in the crystallization behavior were related to ion substitution and formation of solid solutions.
| Culture of osteoblasts on bio-derived bones
Lan, X., Z. M. Yang, et al. (2005), Chin J Traumatol 8(2): 86-90.
Abstract: OBJECTIVE: To study the effect of bio-derived bones, as substitutes of autogenous bone grafts and demineralized cadaver bones, on the attachment, spreading and proliferation of isolated osteoblasts. METHODS: Osteoblasts were isolated from the calvaria of a fetal rabbit through sequential collagenase digestion. In the attachment study, the osteoblasts labeled with 3H-leucine were incubated with the bio-derived bone materials in sterile microcentrifugable tubes for 15, 90 and 180 minutes, and 24 hours, respectively. The attached cells were collected and the radioactivity was measured with liquid scintillation spectrometry. In the proliferation study, the osteoblasts were cultured with the bio-derived bone materials for 24 hours and 3H-thymidine was added during the last 2 hours of the incubation. The attached cells were collected and the radioactivity was measured with liquid scintillation spectrometry. Osteoblasts were seeded on the bone graft materials for 60 or 120 minutes, 24 or 48 hours, and 3 or 7 days, then the co-culture was processed for scanning electron microscopy to observe the interaction of osteoblasts and the bio-derived bone materials. RESULTS: Osteoblasts attached to the bio-derived bone materials in a time-dependent manner. There were significantly (P<0.05) more attached cells after 180 minutes than after 15 and 90 minutes of incubations (P<0.05). Osteoblasts were proliferated in a large amount on the surface and in the materials. Osteoblasts seeded onto 100 mg bio-derived bones resulted in significantly (P<0.05) more measurable proliferation than those seeded onto 10 mg bones. Osteoblasts appeared round as they attached to the materials, then flattened and spread over with time passing. CONCLUSIONS: Bio-derived bones can provide a good environment for the attachment and proliferation of osteoblasts.
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