|Articles about Biomaterials|
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| Analysis of osteoblast activity at biomaterial-bone interfaces by in situ hybridization
Neo, M., C. F. Voigt, et al. (1996), J Biomed Mater Res 30(4): 485-92.
Abstract: To investigate the effects of bioactive materials on bone formation in vivo, a new experimental model using in situ hybridization has been developed. A hole was drilled bilaterally in the distal epiphysis of rabbit femurs with subsequent implantations of beta-tricalcium phosphate (beta-TCP) cylinders in a press-fit manner. Specimens were collected at 3, 7, 14, and 28 days after operation. Femurs with empty drilling holes, and normal distal femurs without operation were used as controls. All specimens were decalcified and hybridized with a procollagen alpha 1(I) complementary RNA probe labeled with digoxygenin. In normal-bone sections, procollagen alpha 1(I) RNA was clearly demonstrated in periosteal osteoblasts, in osteoblasts in the mineralizing zone adjacent to growth plates, and in osteoblasts lining remodeling canals. As for beta-TCP, labeled osteoblasts around the material were not found at day 3, whereas they were most intensively observed at day 7 and a little less at day 14, in accordance with new-bone formation around the material. Weaker signals were also detected in fibroblasts at day 7. At day 28, osteoblasts lining the surface of newly formed bone were mainly negative, whereas those adjacent to the resorption sites of the beta-TCP showed positive signals, demonstrating an active remodeling at the material surface. The temporal expression of procollagen alpha 1(I) RNA in the beta-TCP specimens was fundamentally the same as that in the empty-hole specimens, suggesting no remarkable acceleration or suppression of bone-forming activity of osteoblasts by beta-TCP, which is consistent with osteoconductive bone formation. This in situ hybridization method was suggested to be a powerful tool in analyzing the biological effects of bioactive materials.
| Analysis of photoinitiated polymerization in a membrane mimetic film using infrared spectroscopy and near-IR Raman microscopy
Murphy, M. R., K. M. Faucher, et al. (2005), Colloids Surf B Biointerfaces
Abstract: A method has been developed to investigate the extent of polymer cross-linking that results following in situ photopolymerization of an acrylate-functionalized phospholipid assembly adsorbed onto a stabilized, membrane-mimetic film produced from a polyelectrolyte multilayer (PEM) on polytetrafluoroethylene (PTFE) grafts. The acrylate phospholipid monomer was synthesized, prepared as a unilamellar vesicle, and fused onto closed-packed acyl chains that make up the PEM membrane-mimetic barrier on the PTFE graft. Both broad band white light and 514.5nm laser radiation were used as excitation sources for photoinitiation; eosin Y was used as the photoinitiator. The use of 514.5nm excitation reduced the time for maximum polymerization of the acrylate lipid from 60min to 240s. Infrared spectroscopy was successfully used to analyze the extent of photopolymerization in simplified model acrylate lipid systems; however, this method could not be used to analyze acrylate polymerization in heterogeneous, multicomponent PEM membrane-mimetic barriers on PTFE grafts. A near-infrared Raman microscopy method based on the ratio of the integrated areas of the CC and CN vibrations was shown to provide equivalent information to the IR method for analysis of the extent of polymerization efficiency in acrylate lipids. In addition, it proved feasible to extend this near-IR Raman method to the in situ analysis of the extent of polymerization in a stabilized acrylate lipid membrane on a PEM film in a PTFE vascular graft. This work describes a new approach for generating and analyzing the robustness of a membrane-mimetic coating on biomaterial surfaces, and may improve our ability to predict the long-term stability of polymeric membrane-mimetic films on implantable medical devices.
| Analysis of posterior capsule opacification
Aslam, T. M., N. Patton, et al. (2005), Acta Ophthalmol Scand 83(5): 635-6; author reply 636.
| Analysis of rat calvaria defects implanted with a platelet-rich plasma preparation: histologic and histometric observations
Pryor, M. E., G. Polimeni, et al. (2005), J Clin Periodontol 32(9): 966-72.
Abstract: OBJECTIVES: It has been suggested that degranulating platelet alpha-granules release growth factors having a potential to modulate bone formation. The objective of this study was to evaluate the osteoconductive potential of a platelet-rich plasma (PRP) preparation. METHODS: Thirty adult male Sprague-Dawley rats were used. The PRP preparation was obtained from 10 ml of whole blood drawn from one age-matched donor rat. The preparation was processed by gradient density centrifugation and stored at -80 degrees C until use. Using aseptic techniques, the PRP preparation soak loaded onto an absorbable collagen sponge (ACS) or ACS alone was surgically implanted into contralateral critical size 6-mm calvaria osteotomies in 18 animals. Twelve animals received ACS versus sham surgery in contralateral defects. Animals were sacrificed at 4 and 8 weeks when biopsies were collected for histologic and histometric analysis. RESULTS: The animals were maintained without adverse events. Bone formation was highly variable in sites receiving PRP and control treatments. Defect bone fill at 4 weeks averaged (+/-SD) 28.8+/-27.4% (PRP/ACS) versus 39.1+/-24.4% (ACS; p=0.2626) and 62.0+/-20.0% (ACS) versus 71.6+/-32.2% (sham surgery; p=0.1088), and at 8 weeks 81.0+/-12.9% (PRP/ACS) versus 64.5+/-28.1% (ACS; p=0.2626) and 75.6+/-34.1% (ACS) versus 74.1+/-24.2% (sham surgery; p=0.7353). Remnants of the ACS biomaterial were observed at both 4 and 8 weeks in sites implanted with PRP/ACS or ACS. CONCLUSIONS: The results suggest that the PRP preparation has a limited potential to promote local bone formation.
| Analysis of shearing stress in the limited durability of bovine pericardium used as a biomaterial
Carrera San Martin, A., J. M. Garcia Paez, et al. (1998), J Mater Sci Mater Med 9(2): 77-81.
Abstract: The objective of the study was to determine the shearing stress exerted by the suture thread under conditions of normal working stress. Thirty-six samples of calf pericardium, similar to that employed in the manufacture of bioprosthetic cardiac valve leaflets, were subjected to tensile testing. Prior to the trial, a continuous suture was sewn in the central zone of each sample, at a 45 degrees angle to the longest axis of the sample, using commercially-available threads (silk, Gore-Tex, Surgilene and nylon). Application of the Mohr circle for combined wear revealed that the shearing stress ranged between 2.68-fold greater (for samples sewn with silk) and 5.48-fold greater (for samples sewn with nylon) than the working tensile stress in the region of the suture. It is concluded that the shearing stress is responsible for the limited durability of sutured samples of calf pericardium prepared to simulate bioprosthetic cardiac valve leaflets.
| Analysis of sterilization protocols for peptide-modified hydrogels
Huebsch, N., M. Gilbert, et al. (2005), J Biomed Mater Res B Appl Biomater 74(1): 440-7.
Abstract: Concerns about the efficacy of ethanol disinfection for implanted biomaterials prompted investigation of an alternative sterilization process, ultraviolet irradiation, for terminal sterilization of N-isopropylacrylamide-based hydrogels containing biomimetic peptides. Ultraviolet irradiation is more easily applied on a laboratory scale than gamma irradiation or electron beam, two commercially utilized methods; thus, UVC irradiation was investigated as a low-cost sterilization procedure that might be performed in laboratories prior to in vivo studies. UVC irradiation at 400 muW/cm(2) for up to 15 h did not prevent growth of Escherichia coli within the hydrogels, while ethanol disinfection did prevent growth for the duration of the experiment (120 h). Furthermore, UVC irradiation caused progressive degradation of peptides containing the Arg-Gly-Arg (RGD) domain. UVC irradiation cannot be used as a terminal sterilization process for peptide-modified materials. The system used in this study is not intended to be adequate for evaluating the sterility of medical devices in accordance with current Good Manufacturing Practice (cGMP); however, it remains a useful, low-cost system for the preliminary evaluation of sterilization procedures in terms of their ability to eliminate pathogenic organisms while preserving the structure of biologically active molecules within in a laboratory setting. Ethanol treatment is still the preferred method for disinfection of bioactive materials containing peptides or UV-degradable groups.
| Analysis of the conserved N-terminal domains in major ampullate spider silk proteins
Motriuk-Smith, D., A. Smith, et al. (2005), Biomacromolecules 6(6): 3152-9.
Abstract: Major ampullate silk, also known as dragline silk, is one of the strongest biomaterials known. This silk is composed of two proteins, major ampullate spidroin 1 (MaSp1) and major ampullate spidroin 2 (MaSp2). Only partial cDNA sequences have been obtained for these proteins, and these sequences are toward the C-terminus. Thus, the N-terminal domains have never been characterized for either protein. Here we report the sequence of the N-terminal region of major ampullate silk proteins from three spider species: Argiope trifasciata, Latrodectus geometricus, and Nephila inaurata madagascariensis. The amino acid sequences are inferred from genomic DNA clones. Northern blotting experiments suggest that the predicted 5' end of the transcripts are present in fibroin mRNA. The presence of more than one Met codon in the N-terminal region indicates the possibility of translation of both a long and a short isoform. The size of the short isoform is consistent with the published, cDNA based, N-terminal sequence found in flagelliform silk. Analyses comparing the level of identity of all known spider silk N-termini show that the N-terminus is the most conserved part of silk proteins. Two DNA sequence motifs identified upstream of the putative transcription start site are potential silk fibroin promoter elements.
| Analytical ultracentrifugation for characterizing nanocrystals and their bioconjugates
Calabretta, M., J. A. Jamison, et al. (2005), Nano Lett 5(5): 963-7.
Abstract: Analytical ultracentrifugation (AU) provides a general way to probe the polydispersity of nanoparticles and the formation of bioconjugates in solution. Unconjugated gold nanocrystals show sedimentation coefficient distributions that are in agreement with size distributions as measured by TEM. AU is sensitive to the size/shape changes elicited by conjugation, in this case to lactose repressor (LacI). AU data reveal saturating protein concentrations for conjugates that correspond to the measured stoichiometry of the complex under these conditions.
| Analytically derived material properties of multilaminated extracellular matrix devices using the ball-burst test
Freytes, D. O., A. E. Rundell, et al. (2005), Biomaterials 26(27): 5518-31.
Abstract: Xenogeneic extracellular matrices (ECMs) have been shown to be effective as naturally occurring scaffolds for soft-tissue repair. As acellular tissue substitutes at the time of surgical implantation, ECMs are subjected to the mechanical forces and micro-environmental conditions representative of the anatomical location in which they are placed. Ideally such natural scaffolds would possess mechanical properties that allow for normal tissue function in and around the implant site. The ball-burst test was used to simulate biaxial forces and to determine the strength of the ECM scaffold under a relevant physiological loading condition. The ball-burst test, in itself, does not quantify intrinsic mechanical properties and therefore a methodology was developed to determine the maximum stress resultant tangent modulus (MSRTM) or the maximum stress tangent modulus (MSTM), stress to failure (sigma(f)), failure stress resultant (N(f)), ball-burst pressure (P), and maximum elongation (lambda(max)) from the raw ball-burst data obtained at a constant-rate of transverse. The analytical methodology was compared to finite element simulations and showed good correlation with the analytical solution presented. The proposed approximations were used to compute biaxial failure properties for a variety of multilaminate ECM devices with varying number of layers, disinfection and sterilization, and organ origin.
| Analyzing biomaterials: a source of controversy
Norman, J. C. (1979), Int J Artif Organs 2(3): 172.
| Analyzing bone, blood vessels, and biomaterials with microcomputed tomography
Guldberg, R. E., R. T. Ballock, et al. (2003), IEEE Eng Med Biol Mag 22(5): 77-83.
| Anatomical outcome and quality of life following posterior vaginal wall prolapse repair using collagen xenograft
Altman, D., A. Lopez, et al. (2005), Int Urogynecol J Pelvic Floor Dysfunct 16(4): 298-303.
Abstract: The aim of this study was to evaluate quality of life, sexual function, and anatomical outcome after posterior vaginal wall prolapse repair using a collagen xenograft. Thirty-three patients were evaluated preoperatively and at 6 and 12 months follow-up (FU). Quality of life and sexual function were assessed using a self-reported questionnaire. Prolapse staging was performed using the pelvic organ prolapse quantification system (POPQ). Preoperatively 3 patients had stage I, 26 patients stage II, and 4 patients stage III prolapse of the posterior vaginal wall. Prolapse of the posterior vaginal wall > or = stage II was observed in 7 patients (21%) at the 6-month FU and in 13 patients (39%) at the 12-month FU. Mean point Bp was reduced from -1.1 preoperatively to -2.5 at 6 months FU (p < 0.01) and -1.8 at 12 months FU (p < 0.01). Previous abdominal surgery was associated with a less favorable anatomical outcome (odds ratio: 2.0, 95% confidence interval: 1.5-3.8). There were no significant changes in sexual function or dyspareunia during the 1-year FU. Preoperatively 76% of the patients reported a negative impact on quality of life as a result of genital prolapse. There was a significant improvement in several variables associated with quality of life at 6 and 12 months FU. Posterior vaginal wall prolapse repair using a collagen xenograft was associated with an unsatisfying anatomical outcome at 1-year FU although several quality of life-associated variables affecting psychosocial function were improved. Improvement was not restricted to postoperative restoration of vaginal topography, and previous surgery had a negative effect on anatomical outcome.
| Anchoring dental implant in tissue-engineered bone using composite scaffold: a preliminary study in nude mouse model
Chen, F., H. Ouyang, et al. (2005), J Oral Maxillofac Surg 63(5): 586-91.
Abstract: PURPOSE: The purpose of this study was to fabricate a tissue-engineered bone graft anchoring dental implant with bone marrow stromal cell (bMSC) seeded coral-implant composite scaffold. MATERIALS AND METHODS: Titanium dental implants (3 mm in diameter) were inserted into the cylinder coral scaffolds (5 mm in diameter and 1 mm in wall thickness). bMSCs were isolated from iliac bone marrow of adult New Zealand White rabbits, induced by dexamethasone and seeded into the composite scaffold at the density of 2 x 10 8 /mL in 200 muL medium. Nine cell coral-implant complexes were incubated in vitro for 5 days. One complex was processed for scanning electronic microscopy. The other 8 complexes, together with 4 coral scaffold without cell acting as control, were implanted subcutaneously into nude mice back. At 1 and 2 months after implantation, 4 specimens from the experiment group and 2 specimens from the control group were harvested respectively. New bone restoration and new bone integration with dental implant were evaluated by gross inspection, manual handling test, radiographic examination, and histologic observation. RESULTS: Specimens harvested at 2 months after implantation were red and similar to native bone. Manual handling test showed that dental implants were fixed in the newly formed bone. Radiographic examination showed that most of the coral scaffold had been absorbed. Bone density x-ray shadow could be observed around the dental implant. Histologic examination showed that large amount of new bone formed around the dental implants and integrated well with the implants in some area. In the control group no bone formation was observed both macroscopically and microscopically. CONCLUSION: The results of the study suggested that the tissue-engineered bone of bMSCs seeded natural coral-implant composite scaffold is promising for dental implant anchoring, which has positive implication for clinical jaw reconstruction.
| Angiogenesis and radiation response modulation after vascular endothelial growth factor receptor-2 (VEGFR2) blockade
Li, J., S. Huang, et al. (2005), Int J Radiat Oncol Biol Phys 62(5): 1477-85.
Abstract: The formation of new blood vessels (angiogenesis) represents a critical factor in the malignant growth of solid tumors and metastases. Vascular endothelial cell growth factor (VEGF) and its receptor VEGFR2 represent central molecular targets for antiangiogenic intervention, because of their integral involvement in endothelial cell proliferation and migration. In the current study, we investigated in vitro and in vivo effects of receptor blockade on various aspects of the angiogenic process using monoclonal antibodies against VEGFR2 (cp1C11, which is human specific, and DC101, which is mouse specific). Molecular blockade of VEGFR2 inhibited several critical steps involved in angiogenesis. VEGFR2 blockade in endothelial cells attenuated cellular proliferation, reduced cellular migration, and disrupted cellular differentiation and resultant formation of capillary-like networks. Further, VEGFR2 blockade significantly reduced the growth response of human squamous cell carcinoma xenografts in athymic mice. The growth-inhibitory effect of VEGFR2 blockade in tumor xenografts seems to reflect antiangiogenic influence as demonstrated by vascular growth inhibition in an in vivo angiogenesis assay incorporating tumor-bearing Matrigel plugs. Further, administration of VEGFR2-blocking antibodies in endothelial cell cultures, and in mouse xenograft models, increased their response to ionizing radiation, indicating an interactive cytotoxic effect of VEGFR2 blockade with radiation. These data suggest that molecular inhibition of VEGFR2 alone, and in combination with radiation, can enhance tumor response through molecular targeting of tumor vasculature.
| Angiogenesis with biomaterial-based drug- and cell-delivery systems
Patel, Z. S. and A. G. Mikos (2004), J Biomater Sci Polym Ed 15(6): 701-26.
Abstract: Angiogenesis, the formation of new blood vessels from existing ones, is an important event in several biological processes, including wound healing. It plays a key role in determining the final functionality and integration of any implanted medical device. In addition, angiogenesis is a required event for organ development and has been accepted as a rate-limiting step in engineering tissue replacements. Besides these regenerative processes, uncontrolled angiogenesis is also involved in a number of pathologies, including tumor growth and metastases. Like angiogenesis, biomaterials also play a role in wound healing after medical device implantation and in tissue engineering. Interactions between the device biomaterials and host tissue will factor into the final device integration. Additionally, tissue-engineering strategies utilize biomaterials to a great extent because the paradigm of tissue engineering involves the use of cells, growth factors and scaffolding matrices in order to regenerate or replace tissue. Since almost all tissues are three-dimensional, the biomaterial scaffold plays an integral role in the paradigm. This review will emphasize the influence of biomaterials on angiogenesis as it applies to medical device implantation, tissue engineering and therapies for pathological angiogenesis.
| Angiogenic effects of suture biomaterials. An experimental study in rats
Foschi, D., F. Corsi, et al. (2001), Eur Surg Res 33(1): 16-20.
Abstract: Angiogenesis is a limiting step of inflammation and wound healing. Although laboratory tests for the evaluation of the angiogenetic effects of biomaterials are available, no investigations have been performed. In this study we examine the angiogenetic effect of suture biomaterials in the rat mesenteric window model. Absolute controls had laparotomy only, controls had mesenteric window wounding, test groups had the insertion of either a thread of collagen, polyglactin 910, polyglycolic acid salt, silk or of a titanium clip. We considered the percentage area of the mesenteric window covered by neovessels. After 7 days, negligible angiogenesis was found in absolute controls, significant angiogenesis in controls, collagen, polyglactin 910 and polyglycolic acid salt treated rats, without differences between treatments. A significant increase of angiogenesis in comparison to the control group was found in rats treated with silk and titanium. Ultramicroscopy of the neovessels showed specific changes of their architecture in titanium-treated rats. In conclusion, angiogenesis during wound healing is differently influenced by the suture material used. Silk and titanium stimulated angiogenesis in a different way.
| Angular-ratiometric plasmon-resonance based light scattering for bioaffinity sensing
Aslan, K., P. Holley, et al. (2005), J Am Chem Soc 127(34): 12115-21.
Abstract: We describe an exciting opportunity for affinity biosensing using a ratiometric approach to the angular-dependent light scattering from bioactivated and subsequently aggregated noble metal colloids. This new model sensing platform utilizes the changes in particle scattering from very small colloids, which scatter light according to traditional Rayleigh theory, as compared to the changes in scattering observed by much larger colloidal aggregates, formed due to a bioaffinity reaction. These larger aggregates no longer scatter incident light in a Cos(2) theta dependence, as is the case for Rayleigh scattering, but instead scatter light in an increased forward direction as compared to the incident geometry. By subsequently taking the ratio of the scattered intensity at two angles, namely 90 degrees and 140 degrees, relative to the incident light, we can follow the association of biotinylated bovine serum albumin-coated 20 nm gold colloids, cross-linked by additions of streptavidin. This new model system can be potentially applied to many other nanoparticle assays and has many advantages over traditional fluorescence sensing and indeed light-scattering approaches. For example, a single nanoparticle can have the equivalent scattered intensity as 10(5) fluorescing fluorescein molecules substantially increasing detection; the angular distribution of scattered light from noble metal colloids is substantially easier to predict as compared to fluorescence; the scattered light is not quenched by biospecies; the ratiometric measurements described here are not dependent on colloid concentration as are other scattering techniques; and finally, the noble metal colloids are not prone to photodestruction, as is the case with organic fluorophores.
| Animal experimentation with tooth derived calcium hydroxyapatite based composites as bone-graft substitute biomaterials
Pal, A. K., T. K. Pal, et al. (1997), Biomed Sci Instrum 33: 561-6.
Abstract: Calcium Hydroxyapatite (HA) has now been clinically accepted as one of the most important alloplastic bonegraft substitute in the management of oral surgical procedures including periodontal bony defects. HA can be synthetically prepared or derived from natural sources. Among the natural sources bovine bone is common but human source is also used. Of late Calcium Hydroxyapatite has been derived from extracted human tooth source. The present study involves the experiments using different varieties of HA in conjunction with chitosan, a binder, to know it's unique biological behaviour of bone bonding. The experiment was designed using 12(Twelve) New Zealand white rabbits on transcortical drilled hole tibial model and the observation was made under optical and scanning electron microscope. Result showed the osteoconductive and bioactive nature of tooth derived HA and biocompatibility of chitosan. The clinical problem of handling the particulate form of HA can be overcome by using chitosan which when mix with HA can stabilize the particle in surgical sites. This has tremendous clinical applications in dental regenerative surgery.
| Animal tissue-polypyrrole hybrid biomaterials: shrinkage temperature evaluation
Khor, E., H. C. Li, et al. (1996), Biomaterials 17(19): 1877-9.
Abstract: The shrinkage temperature of animal tissue-polypyrrole hybrids have been evaluated. The results indicate that the tissue's shrinkage temperature behaviour is retained. The tissues do not appear to have been affected by surface layering with polypyrrole or poly(sodium 3-pyrrolyl-butanesulphonate) (PSPBS). The main influence on the shrinkage temperature appears to be the reaction conditions in producing the hybrids i.e. the solvent and the presence of FeCl3. Hybrids obtained from reactions where the solvent was acetic acid demonstrated irreversible denaturation giving a final lower shrinkage temperature than the original value. All tissues exposed to FeCl3 were found to have higher shrinkage temperatures. This has been attributed to transient coordination bonding between the metal ion and side groups on the amino acid. The single peak of PSPBS-tissue hybrids in acetic acid is probably associated with the effective penetration of the PSPBS into the tissue, permitting some interaction between the functionalities of the conducting polymer and collagen.
| Anode glow discharge plasma treatment of titanium plates facilitates adsorption of extracellular matrix proteins to the plates
Yamamoto, H., Y. Shibata, et al. (2005), J Dent Res 84(7): 668-71.
Abstract: Glow discharge plasma (GDP) supplied to an anode (GDP+) promotes calcium phosphate adsorption onto titanium better than that supplied to a cathode (GDP-). However, the adsorption of extracellular matrix (ECM) proteins is crucial for cell adhesion to titanium. Since GDP+ induced both inorganic adsorption and cell adhesion, we hypothesized that the inorganic adsorption in a culture medium might affect the adsorption of the ECM proteins. In this study, ECM proteins adsorbed on titanium with and without GDP were examined by x-ray photoelectron spectroscopy. After 1 hr of incubation, increasing sodium adsorption on GDP+ specimens induced adsorption of ECM proteins as shown by NH(+) and COO(-) signals without calcium adsorption. In contrast, since no specific adsorption of sodium on GDP-specimens was detected, GDP-did not contribute to the adsorption of ECM proteins. Thus, promotion of sodium adsorption of GDP+ was effective, at least in the initial ECM protein adsorption on a titanium surface.
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