|Articles about Biomaterials|
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| Prediction of elasticity constants in small biomaterial samples such as bone. A comparison between classical optimization techniques and identification with artificial neural networks
Lucchinetti, E. and E. Stussi (2004), Proc Inst Mech Eng [H] 218(6): 389-405.
Abstract: Measuring the elasticity constants of biological materials often sets important constraints, such as the limited size or the irregular geometry of the samples. In this paper, the identification approach as applied to the specific problem of accurately retrieving the material properties of small bone samples from a measured displacement field is discussed. The identification procedure can be formulated as an optimization problem with the goal of minimizing the difference between computed and measured displacements by searching for an appropriate set of material parameters using dedicated algorithms. Alternatively, the backcalculation of the material properties from displacement maps can be implemented using artificial neural networks. In a practical situation, however, measurement errors strongly affect the identification results, calling for robust optimization approaches in order accurately to retrieve the material properties from error-polluted sample deformation maps. Using a simple model problem, the performances of both classical and neural network driven optimization are compared. When performed before the collection of experimental data, this evaluation can be very helpful in pinpointing potential problems with the envisaged experiments such as the need for a sufficient signal-to-noise ratio, particularly important when working with small tissue samples such as specimens cut from rodent bones or single bone trabeculae.
| Prediction of TiO2 nanoparticle phase and shape transitions controlled by surface chemistry
Barnard, A. S. and L. A. Curtiss (2005), Nano Lett 5(7): 1261-6.
Abstract: The effects of surface chemistry on the morphology and phase stability of titanium dioxide nanoparticles have been investigated using a thermodynamic model based on surface free energies and surface tensions obtained from first principles calculations. It has been found that surfaces representing acidic and alkaline conditions have a significant influence on both the shape of the nanocrystals and the anatase-to-rutile transition size. The latter introduces the possibility of inducing phase transitions by changing the surface chemistry.
| Predictors of edge stenosis following sirolimus-eluting stent deployment (a quantitative intravascular ultrasound analysis from the SIRIUS trial)
Sakurai, R., J. Ako, et al. (2005), Am J Cardiol 96(9): 1251-3.
Abstract: To study the interaction of the sirolimus-eluting stent and vessel margins, we analyzed the intravascular ultrasound parameters in 317 edges of 167 stents having 18 edge stenoses at 8 months of follow-up from the SIRIUS trial. Of the baseline parameters, a larger reference percentage of plaque area and a larger edge stent area/reference minimum lumen area were associated with edge stenosis in the sirolimus-eluting stent cohort compared with the incidence of edge stenosis in the bare metal stent cohort. Thus, full lesion coverage and matching the stented segment properly to the adjacent segment using intravascular ultrasound guidance may improve sirolimus-eluting stent implantation efficacy further.
| Prefabrication of vascularized bone graft using a combination of fibroblast growth factor-2 and vascular bundle implantation into a novel interconnected porous calcium hydroxyapatite ceramic
Nakasa, T., O. Ishida, et al. (2005), J Biomed Mater Res A 75(2): 350-5.
Abstract: The aim of this study was to create a prefabricated vascularized bone graft using a novel interconnected porous calcium hydroxyapatite ceramic (IP-CHA) by combining vascular bundle implantation and basic fibroblast growth factor (FGF)-2 administration in a rabbit model. Twenty-four Japanese white rabbits were used. The saphenous artery and vein were passed through the hole of the IP-CHA. In an experimental group, 100 microg of FGF-2 was administered into the IP-CHA before implanting the vascular bundle. In the control group, the saline was administered into the IP-CHA before implanting the vascular bundle. Finally, the IP-CHA was placed subcutaneously in the medial thigh. Neovascularization from the vascular bundle was evaluated at 2 weeks after surgery, and osteogenesis was evaluated at 4 weeks. At 2 weeks, the length and density of newly formed vessels were significantly greater in the experimental group than in the control group. Histological evaluation showed osteoid deposition in the pores of the IP-CHA at 4 weeks in the experimental group, whereas no evidence of osteoid deposition was noted in the control group. This study showed the potential of creating a vascularized bone graft of a predetermined size and shape using a combination of FGF-2 and vascular bundle implantation in the IP-CHA.
| Preferential adsorption of high density lipoprotein from blood plasma onto biomaterial surfaces
Breemhaar, W., E. Brinkman, et al. (1984), Biomaterials 5(5): 269-74.
Abstract: In the present study a two step enzyme immuno assay (EIA) was used for the investigation of the adsorption of proteins and lipoproteins from solutions and from blood plasma onto polymer surfaces. It was found that only a small adsorption of the major blood proteins occurred from plasma. Evidence is presented that the reason for this adsorption behaviour is a preferential adsorption of high density lipoprotein (HDL).
| Preliminary experimental results of a new resorbable biomaterial as pericardial substitute
Fradin, D., T. Causs, et al. (1993), J Thorac Cardiovasc Surg 105(2): 364-5.
| Preliminary investigation of mitoxantrone coating on stent-grafts to inhibit neointimal proliferation
Dirsch, O., U. Dahmen, et al. (2005), J Endovasc Ther 12(4): 479-85.
Abstract: PURPOSE: To investigate the inhibition of neointimal proliferation induced by a stent-graft loaded with mitoxantrone. METHODS: Stent-grafts with and without mitoxantrone loading (150 microg per device) were inserted into the carotid artery of 7 and 6 rabbits, respectively. After an observation period of 28 days, the animals were sacrificed, and a detailed morphological and morphometric workup of the stented vessels was performed. RESULTS: Uncoated stent-grafts induced a thick neointima (median diameter 97+/-99 microm), whereas no neointima formed in mitoxantrone-loaded stent-grafts. However, the loaded devices were not fully covered by an endothelial layer. The underlying media was significantly thinner (31.8+/-5.6 versus 48.6+/-3.3 microm, p=0.002) and showed a widespread loss of smooth muscle cells. CONCLUSIONS: Mitoxantrone loading of a stent-graft inhibited the formation of a neointima. However, important regenerative processes were prevented as well, indicating a local overdose. More experiments using lower doses are warranted.
| Preliminary studies on the clinical application of antigenically altered collagen as a biomaterial in oral surgery
Kramer, H. S. (1973), Trans Int Conf Oral Surg 4: 223-8.
| Preliminary study on human protein adsorption and leukocyte adhesion to starch-based biomaterials
Alves, C. M., R. L. Reis, et al. (2003), J Mater Sci Mater Med 14(2): 157-65.
Abstract: In this study, the adsorption of human serum albumin (HSA), fibronectin (FN) and vitronectin (VN) onto the surface of novel biodegradable materials was evaluated by immunostaining. Specifically, polymeric blends of corn starch with cellulose acetate (SCA), ethylene vinyl alcohol copolymer (SEVA-C), and polycaprolactone (SPCL) were immersed in unitary and competitive systems; that is, binary and more complex protein solutions. For binary solutions, different HSA and FN protein distribution patterns were observed depending on the starch-based surface. Furthermore, the relative amount of proteins adsorbed onto starch-based surfaces was clearly affected by protein type: a preferential adsorption of VN and FN as compared to HSA was observed. On tests carried out with unitary, binary and more complex solutions, it was found that vitronectin adsorption ability was enhanced in competitive systems, which was associated with a lower amount of adsorbed albumin. In order to assess the effect of these human proteins on cell behavior, a mixed population of human lymphocytes and monocytes/macrophages was cultured over pre-coated SEVA-C surfaces. Through anti-CD3 and CD-14 monoclonal antibody labeling and cell counting, leukocyte adhesion onto pre-coated SEVA-C surfaces was analyzed. Based on the results, it was possible to detect albumin long-term effects and fibronectin short-term effects on cell adhesion proving that previously adsorbed proteins modulate leukocyte behavior.
| Premixed rapid-setting calcium phosphate composites for bone repair
Carey, L. E., H. H. Xu, et al. (2005), Biomaterials 26(24): 5002-14.
Abstract: Although calcium phosphate cement (CPC) is promising for bone repair, its clinical use requires on site powder-liquid mixing. To shorten surgical time and improve graft properties, it is desirable to develop premixed CPC in which the paste remains stable during storage and hardens only after placement into the defect. The objective of this study was to develop premixed CPC with rapid setting when immersed in a physiological solution. Premixed CPCs were formulated using the following approach: Premixed CPC = CPC powder + nonaqueous liquid + gelling agent + hardening accelerator. Three premixed CPCs were developed: CPC-monocalcium phosphate monohydrate (MCPM), CPC-chitosan, and CPC-tartaric. Setting time for these new premixed CPCs ranged from 5.3 to 7.9 min, significantly faster than 61.7 min for a premixed control CPC reported previously (p < 0.05). SEM revealed the formation of nano-sized needle-like hydroxyapatite crystals after 1 d immersion and crystal growth after 7 d. Diametral tensile strength for premixed CPCs at 7 d ranged from 2.8 to 6.4 MPa, comparable to reported strengths for cancellous bone and sintered porous hydroxyapatite implants. Osteoblast cells attained a normal polygonal morphology on CPC-MCPM and CPC-chitosan with cytoplasmic extensions adhering to the nano-hydroxyapatite crystals. In summary, fast-setting premixed CPCs were developed to avoid the powder-liquid mixing in surgery. The pastes hardened rapidly once immersed in physiological solution and formed hydroxyapatite. The cements had strengths matching those of cancellous bone and sintered porous hydroxyapatite and non-cytotoxicity similar to conventional non-premixed CPC.
| Preparation and antimicrobial activity of hydroxypropyl chitosan
Peng, Y., B. Han, et al. (2005), Carbohydr Res 340(11): 1846-51.
Abstract: Water-soluble hydroxypropyl chitosan (HPCS) derivatives with different degrees of substitution (DS) and weight-average molecular weight (Mw) were synthesized from chitosan and propylene epoxide under basic conditions. Their structure was characterized by IR spectroscopy, NMR spectroscopy, and elemental analysis, which showed that both the OH groups at C-6 and C-3 and the NH2 group of chitosan were alkylated. The DS value of HPCS ranged from 1.5 to 3.1 and the Mw was between 2.1x10(4) and 9.2x10(4). In vitro antimicrobial activities of the HPCS derivatives were evaluated by the Kirby-Bauer disc diffusion method and the macrotube dilution broth method. The HPCS derivatives exhibited no inhibitory effect on two bacterial strains (Escherichia coli and Staphylococcus aureus); however, some inhibitory effect was found against four of the six pathogenic fruit fungi investigated. Some derivatives (HPCS1, HPCS2, HPCS3, HPCS3-1, and HPCS4) were effective against C. diplodiella and F. oxysporum. HPCS3-1 is the most effective one with MIC values of 5.0, 0.31, 0.31, and 0.16mg/mL against A. mali, C. diplodiella, F. oxysporum, and P. piricola, respectively. Antifungal effects were also observed for HPCS2 and HPCS3-1 against A. mali, as well as HPCS3 and HPCS3-1 against P. piricola. The results suggest that relatively lower DS and higher Mw value enhances the antifungal activity of HPCS derivatives.
| Preparation and application of TiO2 photocatalytic sensor for chemical oxygen demand determination in water research
Chen, J., J. Zhang, et al. (2005), Water Res 39(7): 1340-6.
Abstract: In this work, a TiO(2) photocatalytic sensor was prepared and utilized into flow injection analysis (FIA) for chemical oxygen demand (COD) determination. With a positive bias potential of 0.4V (vs. Ag/AgCl) applied to the sensor and a 12-W quartz UV lamp illuminating it, photocurrent, due to the charge transfer at the interface of TiO(2) sensor and the passing solution, was recorded and its change (deltaI(Photo)) caused by the detected sample was calculated to characterize the COD value of the sample. Under the optimizing conditions, the sensor responded linearly to the COD of D-glucose solution in the range of 0.5-235 mg/L, with a linear correlation coefficient of 0.9998. Its application in artificial wastewater analysis has achieved results in good agreement with those from the conventional dichromate method; meanwhile, the process requires no hypertoxic reagents and less analysis time, suggesting that it would be another appropriate method for COD determination in water assessment.
| Preparation and biocompatibility of novel UV-curable chitosan derivatives
Renbutsu, E., M. Hirose, et al. (2005), Biomacromolecules 6(5): 2385-8.
Abstract: UV-curable chitosans (UVCC-7-10) were synthesized using less-toxic agents. The UVCC-7 was completely cured by UV spot irradiation for 4 s. The UVCC-7 was implanted into murine subcutaneous tissues, and the response to the implantation was observed by histological examination at 7 days after implantation. In the histological findings, the implant was surrounded by thin fibrous granulating tissue with no inflammatory cellular infiltration. Fibroblasts infiltrate between the cured implant. The novel synthesized UVCC-7 showed good biocompatibility.
| Preparation and blood compatibility of new silica-chitosan hybrid biomaterials
Chen, H., X. Tian, et al. (1998), Artif Cells Blood Substit Immobil Biotechnol 26(4): 431-6.
Abstract: The development of new materials containing both organic and inorganic structures is of great interest with respect to achievement of obtaining the special properties, and the solgel process has provided new opportunities for making such materials. In this paper, new silica-chitosan hybrid biomaterials were produced by this technique, using biopolymer chitosan and its heparin-like derivative as the organic species to be incorporated into the silicon alkoxide (TEOS) based network. All the samples made were in form of thin, flexible films with optical clarity. Microphase separated structure was observed in the hybrid surface, with hydrophobic SiO2 and hydrophilic chitosan interleaved. These hybrid materials displayed good blood compatibility in comparison with their single component systems.
| Preparation and characterization of a collagen/chitosan/heparin matrix for an implantable bioartificial liver
Wang, X., Y. Yan, et al. (2005), J Biomater Sci Polym Ed 16(9): 1063-80.
Abstract: A new type of collagen/chitosan/heparin matrix, fabricated by gelation of collagen/ chitosan with heparin sodium containing ammonia, was produced to construct livers by tissue engineering and regenerative engineering. The obtained collagen/chitosan/heparin matrix was found to be highly porous, swelled rapidly in PBS solution and was stable in vitro for at least 60 days in collagenase/lysozyme containing buffered aqueous solution (PBS, pH 7.4) at 37 degrees C. The collagen/chitosan/heparin matrix resulted in a superior blood compatibility compared to the ammonia-treated collagen and collagen/chitosan matrices. The morphology and behavior of the cells on the collagen/chitosan/heparin membrane were found to be similar to those on the collagen membrane but different from those on the collagen/chitosan membrane. Hepatocytes cultured on the collagen/chitosan/heparin matrices exhibited highest urea and triglyceride secretion functions 25 days post seeding. These results suggest that this collagen/chitosan/heparin matrix is a potential candidate for liver tissue engineering.
| Preparation and characterization of bioactive collagen/wollastonite composite scaffolds
Li, X. and J. Chang (2005), J Mater Sci Mater Med 16(4): 361-5.
Abstract: A novel biodegradable collagen/wollastonite composite was prepared as three-dimensional scaffolds by freeze-drying method. Scanning electron microscope (SEM) micrographs of scaffolds showed a continuous structure of interconnected pores, and pore size was about 100 microm. The tensile strength of the scaffolds was improved by incorporation of wollastonite and the in vitro bioactivity of the scaffolds was evaluated by examining the hydroxyapatite (HA) deposition on their surface in simulated body fluid (SBF). After soaking in SBF for 7 days, collagen reconstituted to fibers and HA nodules formed on collagen fibers. The result suggests that the incorporation of wollastonite could improve the mechanical strength and the in vitro bioactivity of the composite. The scaffolds could be a potential biomaterial for bone tissue engineering.
| Preparation and characterization of chitosan-based nanoparticles
Bodnar, M., J. F. Hartmann, et al. (2005), Biomacromolecules 6(5): 2521-7.
Abstract: The present investigation describes the synthesis and characterization of novel biodegradable nanoparticles based on chitosan for biomedical applications. Natural di- and tricarboxylic acids were used for intramolecular cross-linking of the chitosan linear chains. The condensation reaction of carboxylic groups and pendant amino groups of chitosan was performed by using water-soluble carbodiimide. This method allows the formation of polycations, polyanions, and polyampholyte nanoparticles. The prepared nanosystems were stable in aqueous media at low pH, neutral, and mild alkaline conditions. The structure of products was determined by NMR spectroscopy, and the particle size was identified by laser light scattering (DLS) and transmission electron microscopy (TEM) measurements. It was found that particle size depends on the pH, but at a given pH, it was independent of the ratio of cross-linking and the cross-linking agent. Particle size measured by TEM varied in the range 60-280 nm. In the swollen state, the average size of the particles measured by DLS was in the range 270-370 nm depending on the pH. The biodegradable cross-linked chitosan nanoparticles, as solutions or dispersions in aqueous media, might be useful for various biomedical applications.
| Preparation and characterization of kappa-carrageenan immobilized urease
Baysal, S. H. and R. Karagoz (2005), Prep Biochem Biotechnol 35(2): 135-43.
Abstract: Urease was encapsulated within kappa-carrageenan beads. Various parameters, such as amount of kappa-carrageenan and enzyme activity, were optimized for the immobilization of urease. Immobilized urease was thoroughly characterized for pH, temperature, and storage stabilities and these properties were compared with the free enzyme. The free urease activity quickly decreased and the half time of the activity decay was about 3 days at 4 degrees C. The immobilized urease remained very active over a long period of time and this enzyme lost about 70.43% of its orginal activity over the period of 26 days for storage at 4 degrees C. The Michaelis constant (Km) and maximum reaction velocity (Vmax) were calculated from Lineweaver-Burk plots for both free and immobilized enzyme systems. Vmax = 227.3 U/mg protein, Km = 65.6 mM for free urease and Vmax = 153.9 U/mg protein, Km = 96.42 mM for immobilized urease showed a moderate decrease of enzyme specific activity and change of substrate affinity.
| Preparation and characterization of melittin-loaded poly (DL-lactic acid) or poly (DL-lactic-co-glycolic acid) microspheres made by the double emulsion method
Cui, F., D. Cun, et al. (2005), J Control Release 107(2): 310-9.
Abstract: The water soluble peptide, melittin, isolated from bee venom and composed of twenty-six amino acids, was encapsulated in poly (DL-lactic acid, PLA) and poly (DL-lactic-co-glycolic acid, PLGA) microspheres prepared by a multiple emulsion [(W1/O)W2] solvent evaporation method. The aim of this work was to develop a controlled release injection that would deliver the melittin over a period of about one month. The influence of various preparation parameters, such as the type of polymer, its concentration, stabilizer PVA concentration, volume of internal water phase and level of drug loading on the characteristics of the microspheres and drug release was investigated. It was found that the microspheres of about 5 microm in size can be produced in high encapsulation (up to 90%), and the melittin content in the microspheres was up to 10% (w/w). The drug release profiles in vitro exhibited a significant burst release, followed by a lag phase of little or no release and then a phase of constant melittin release. The type of polymer used was a critical factor in controlling the release of melittin from the microspheres. In this study, the rate of peptide release from the microspheres correlated well with the rate of polymer degradation. Moreover, melittin was released completely during the study period of 30 days, which agreed well with the polymer degradation rate.
| Preparation and characterization of microwave-treated carboxymethyl chitin and carboxymethyl chitosan films for potential use in wound care application
Wongpanit, P., N. Sanchavanakit, et al. (2005), Macromol Biosci 5(10): 1001-12.
Abstract: CM-chitin and CM-chitosan films were successfully crosslinked by microwave treatment. Crosslinking of the microwave-treated CM-chitin films involved mainly the carboxylate and the secondary alcohol groups, while crosslinking of microwave-treated CM-chitosan films involved the carboxylate and the amino groups. In addition, the crystallinity of CM-chitin increased with increasing microwave treatment time, whereas an increase in the crystallinity of the microwave-treated CM-chitosan films was not observed. At a similar percentage of weight loss, the crosslinking of either CM-chitin or CM-chitosan films by microwave treatment required much less stringent condition when compared with the crosslinking by autoclave treatment. Based on both direct and indirect cytotoxicity assays, the cytotoxicity of the microwave-treated CM-chitin films was negative, while that of the microwave-treated CM-chitosan films was positive. Human fibroblasts adhered on the surface of microwave-treated CM-chitosan films much better than on the surface of microwave-treated CM-chitin films.
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