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Characterization of chitosan-polycaprolactone blends for tissue engineering applications
Sarasam, A. and S. V. Madihally (2005), Biomaterials 26(27): 5500-8.
Abstract: The objective of this work was to study the effect of blending chitosan with poly(epsilon-caprolactone) (PCL) on their biomechanical properties. After testing the effect of molecular weight (MW), temperature, and humidity on the tensile properties in dry, wet at 25 degrees C and wet at 37 degrees C conditions, chitosan with a MW>310 kD was selected for use in the blend. Homogeneous blends of 25%, 50% and 75% PCL compositions were formed by dissolving chitosan and 80 kD PCL in a common solvent of approximately 77% aqueous acetic acid. Taking advantage of the low melting point of PCL, blend membranes were processed at 25, 37, 55 degrees C water bath or 55 degrees C oven into films. Also, membranes were solvent annealed using chloroform vapors. Tensile properties were analyzed in wet conditions at 25 degrees C. Support for cell viability and distribution of cytoskeletal actin were analyzed by in vitro cell culture of mouse embryonic fibroblasts (MEFs). Differential scanning calorimetry studies indicated the miscibility of the two components when approximated using Nishi-Wang equation. Drying the films at 55 degrees C in an oven formed membranes without separation of two phases. However, the analyzed tensile properties showed no significant alterations relative to chitosan. On the contrary, significant improvements were observed after solvent annealing. Interestingly, increased viability and redistribution of actin fibers was observed on blends formed with 50% PCL and 75% PCL relative to individual polymers. In summary, 50:50 blends when processed at 55 degrees C in an oven showed significant improvement in mechanical properties as well as support for cellular activity relative to chitosan.

Characterization of cortical neuron outgrowth in two- and three-dimensional culture systems
Lin, P. W., C. C. Wu, et al. (2005), J Biomed Mater Res B Appl Biomater 75(1): 146-57.
Abstract: To improve the ability of regeneration by grafting living cells or by adding growth factor to a lesion site, it is important to find good biomaterials for neuron survival and regeneration. This study focused on two- and three-dimensional cultures in a matrix using biomaterials such as agarose, collagen, fibrin, and their mixtures, because these are considered to be suitable biomaterials for neuron outgrowth. Cortical neurons were dissected from E17 rat embryos and cultured in agarose gel, collagen gel, fibrin glue, and mixtures of collagen and fibrin. Results showed that neurons cultured in collagen gel and fibrin glue had longer periods of survival (more than 3 weeks) and better neurite extension than those observed in agarose gels. As to the survival rate according to the MTT and lactate dehydrogenase assays, fibrin glue was the most suitable biomaterial for neuron survival among the biomaterials examined. With two-dimensional fibrin plating, neuron cells exhibited cell aggregation and stress fibers, but the same results were not observed with collagen gel. There were no differences in neurite extension and survival in the mixtures of collagen and fibrin. The results suggest that collagen and fibrin can provide a suitable substrate for a three-dimensional culture matrix for neuronal survival and differentiation.

Characterization of crosslinking effects on the physicochemical and drug diffusional properties of cationic hydrogels designed as bioactive urological biomaterials
Jones, D. S., G. P. Andrews, et al. (2005), J Pharm Pharmacol 57(10): 1251-59.
Abstract: This study examined the effects of concentration and type of crosslinker (tetraethyleneglycol diacrylate, TEGDA; diethyleneglycol dimethacrylate, DEGDMA; and polyethyleneglycol dimethacrylate, PEGDMA) on the mechanical and drug diffusional properties of hydrogels that had been selected as candidate coatings for bioactive medical devices. Hydrogels (dimethylaminoethylmethacrylate-co-vinylpyrrolidone; 1:1) were prepared by free radical polymerization and characterized using tensile analysis, dynamic contact angle analysis and analysis of swelling at pH 6.0. The release of fusidic acid and chlorhexidine was evaluated using buffered medium at pH 6.0 and, in addition, using dissolution medium that had been buffered to pH 9 in the presence and absence of elevated concentrations of calcium, representative of urinary encrustation. Crosslinker concentration, but not type, affected the advancing and receding contact angles. Conversely, both crosslinker type and concentration affected the mechanical and swelling properties of the hydrogels. Maximum swelling and elongation at break were associated with the PEGDMA-crosslinked hydrogels whereas TEGDA-crosslinked hydrogels exhibited the maximum ultimate tensile strength and Young's modulus. Drug release from all systems occurred by diffusion. The mass of chlorhexidine and fusidic acid released was dependent on crosslinker type and concentration, with hydrogels crosslinked with PEGDMA offering the greatest mass of drug released at each sampling period. The mass of fusidic acid but not chlorhexidine released at pH 9.0 in a calcium augmented medium was lower than that released in the same medium devoid of elevated calcium, due to the formation of the poorly soluble calcium salt. In conclusion, this study has uniquely examined the effects of crosslinker type and concentration on physicochemical and drug release properties essential to the clinical and non-clinical performance of bioactive hydrogels for medical device application.

Characterization of degradation behavior for PLGA in various pH condition by simple liquid chromatography method
Yoo, J. Y., J. M. Kim, et al. (2005), Biomed Mater Eng 15(4): 279-88.
Abstract: The aim of this study was to detect the amount of lactic acid (LA) and glycolic acid (GA) in poly(D,L-lactide-co-glycolide) (PLGA) by development a simple HPLC method and to determine the pH of media, which can influence on degradation of PLGA and drug release. Analysis of in vitro degradation behavior of PLGA with two different molecular weights as 8000 and 33,000 g/mol were performed in various media conditions (pH 3.0, 5.0, 7.0, and 9.0 of PBS and distilled water (approx. pH 5.8)). Also, effect of some additives on PLGA degradation was also investigated in pH 7.0 of PBS. GA and LA were easily detected by a simple HPLC method (retention time: 6.5 min and 10.2 min, respectively). The result showed that GA was released larger amount than that of LA considering the initial sample weight of polymers, due to the higher hydrophilic property. In the lower pH of media conditions, the PLGA was faster degraded generally. The presence of various additives, moreover, affected decrease of pH and slight acceleration of LA and GA detection.

Characterization of experimental composite biomaterials
Jones, D. W. and A. S. Rizkalla (1996), J Biomed Mater Res 33(2): 89-100.
Abstract: A comparison was made among the elastic moduli of various combinations of dimethacrylates that may be used as matrix resins in dental restorative composite biomaterials systems. Two ceramic filler materials with contrasting shape and size were synthesized by wet chemistry; these were used to produce a range of experimental composite systems. Dynamic elastic moduli determinations were used to study the influence of filler volume, filler size/shape, use of silane coupling agents, and storage in water. The filler was varied from 0 to 59% by volume for filler A and from 0 to 48% volume for filler B. Silane treatment was found to have a significant effect on modulus. Moduli for composite materials containing silane-treated filler were higher compared to materials containing the same volume loading of non-silane-treated filler. Using a light curing resin as a matrix gave a significantly higher modulus for a filler loading of 38% by volume. Storage in water for 29 days was found to have only a slight effect on moduli for composite systems containing in excess of 20% by volume of filler. The experimental composite systems produced slightly higher values for moduli than were predicted by the theoretical Reuse constant stress model.

Characterization of glycosaminoglycans in tubular epithelial cells: calcium oxalate and oxalate ions effects
Borges, F. T., Y. M. Michelacci, et al. (2005), Kidney Int 68(4): 1630-42.
Abstract: BACKGROUND: The interaction between tubular epithelial cells and calcium oxalate crystals or oxalate ions is a very precarious event in the lithogenesis. Urine contains ions, glycoproteins and glycosaminoglycans that inhibit the crystallization process and may protect the kidney against lithogenesis. We examined the effect of oxalate ions and calcium oxalate crystals upon the synthesis of glycosaminoglycans in distal [Madin-Darby canine kidney (MDCK)] and proximal (LLC-PK1) tubular cell lines. METHODS: Glycosaminoglycan synthesis was analyzed by metabolic labeling with (35)S-sulfate and enzymatic digestion with specific mucopolysaccharidases. Cell death was assessed by fluorescent dyes and crystal endocytosis was analised by flow cytometry. RESULTS: The main glycosaminoglycans synthesized by both cells were chondroitin sulfate and heparan sulfate most of them secreted to the culture medium or present at cellular surface. Exposition of MDCK cells to oxalate ions increased apoptosis rate and the incorporation of (35)S-sulfate in chondroitin sulfate and heparan sulfate, while calcium oxalate crystals were endocyted by LLC-PK1, induced necrotic cell death, and increased (35)S-sulfate incorporation in glycosaminoglycans. These effects seem to be specific and due to increased biosynthesis, since hydroxyapatite and other carboxylic acid did not induced cellular death or glycosaminoglycan synthesis and no changes in sulfation degree or molecular weight of glycosaminoglycans could be detected. Thapsigargin inhibited the glycosaminoglycan synthesis induced by calcium oxalate in LLC-PK1, suggesting that this effect was sensitive to the increase in cytosolic calcium. CONCLUSION: Tubular cells may increase the synthesis of glycosaminoglycans to protect from the toxic insult of calcium oxalate crystals and oxalate ions, what could partially limit the lithogenesis.

Characterization of heparin affin regulatory peptide signaling in human endothelial cells
Polykratis, A., P. Katsoris, et al. (2005), J Biol Chem 280(23): 22454-61.
Abstract: Heparin affin regulatory peptide (HARP) is an 18-kDa secreted growth factor that has a high affinity for heparin and a potent role on tumor growth and angiogenesis. We have previously reported that HARP is mitogenic for different types of endothelial cells and also affects cell migration and differentiation (12). In this study we examined the signaling pathways involved in the migration and tube formation on matrigel of human umbilical vein endothelial cells (HUVEC) induced by HARP. We report for the first time that receptor-type protein-tyrosine phosphatase beta/zeta (RPTPbeta/zeta), which is a receptor for HARP in neuronal cell types, is also expressed in HUVEC. We also document that HARP signaling through RPTPbeta/zeta leads to activation of Src kinase, focal adhesion kinase, phosphatidylinositol 3-kinase, and Erk1/2. Sodium orthovanadate, chondroitin sulfate-C, PP1, wortmannin, LY294002, and U0126 inhibit HARP-mediated signaling and HUVEC migration and tube formation. In addition, RPTPbeta/zeta suppression using small interfering RNA technology interrupts intracellular signals and HUVEC migration and tube formation induced by HARP. These results establish the role of RPTPbeta/zeta as a receptor of HARP in HUVEC and elucidate the HARP signaling pathway in endothelial cells.

Characterization of hydroxyapatite films obtained by pulsed-laser deposition on Ti and Ti-6AL-4v substrates
Blind, O., L. H. Klein, et al. (2005), Dent Mater 21(11): 1017-24.
Abstract: OBJECTIVES: Pulsed-laser deposition (PLD) is a development process to obtain hydroxyapatite (HA) thin film. It is an alternative to hydroxyapatite deposition techniques usually employed to cover orthopaedic or dental titanium implant surfaces. The aim of this study is to find out the characteristic ratio for Ca/P (1.66) deposit on titanium implant with the PLD process. METHODS: In a preliminary study, the coating parameters of pure and highly crystalline HA on Ti or Ti-6Al-4V substrates were verified by analysing the deposit by Rutherford backscattering spectroscopy (RBS). Ablation parameters to reach a stoichiometric hydroxyapatite composition (ideal Ca/P atomic ratio) and to control the growth of crystalline phases were: 575 degrees C for the substrate temperature, 0.4 mbar H2O vapour pressure in the ablation chamber, the target substrate distance was 40 mm and the deposition time was 120 min. In a second part, the film properties were analysed by means of XRD, SEM, AFM. The coating adhesion of the HA to the substrate was determined with a micro scratch tester. RESULTS: The analysed HA thin films showed a perfect crystallized and textured deposit. Sample observation and surface quality analysis demonstrated a surface roughness and adhesion of the films to the substrates compatible with biological applications. SIGNIFICANCE: These results suggest that pulsed-laser deposition is a suitable technique to obtain crystalline and adherent hydroxyapatite films on Ti or Ti-6Al-4V substrates. The quality of the HA deposit with the PLD process could be an interesting option for coating dental implant.

Characterization of irradiated blends of alpha-tocopherol and UHMWPE
Oral, E., E. S. Greenbaum, et al. (2005), Biomaterials 26(33): 6657-63.
Abstract: Adhesive/abrasive wear in ultra-high molecular weight polyethylene (UHMWPE) has been minimized by radiation cross-linking. Irradiation is followed by melting to eliminate residual free radicals and avoid long-term oxidative embrittlement. However, post-irradiation melting reduces the crystallinity of the polymer and hence its strength and fatigue resistance. We proposed an alternative to post-irradiation melting to be the incorporation of the antioxidant alpha-tocopherol into UHMWPE prior to consolidation. alpha-Tocopherol is known to react with oxygen and oxidized lipids, stabilizing them against further oxidative degradation reactions. We blended GUR 1050 UHMWPE resin powder with alpha-tocopherol at 0.1 and 0.3 wt% and consolidated these blends. Then we gamma-irradiated these blends to 100-kGy. We characterized the effect of alpha-tocopherol on the cross-linking efficiency, oxidative stability, wear behavior and mechanical properties of the blends. (I) The cross-link density of virgin, 0.1 and 0.3 wt% alpha-tocopherol blended, 100-kGy irradiated UHMWPEs were 175+/-19, 146+/-4 and 93+/-4 mol/m3, respectively. (II) Maximum oxidation indices for 100-kGy irradiated UHMWPE previously blended with 0, 0.1 and 0.3 wt% alpha-tocopherol that were subjected to accelerated aging at 80 degrees C in air for 5 weeks were 3.32, 0.09, and 0.05, respectively. (III) The pin-on-disc wear rates of 100-kGy irradiated UHMWPE previously blended with 0.1 and 0.3 wt% alpha-tocopherol that were subjected to accelerated aging at 80 degrees C in air for 5 weeks were 2.10+/-0.17 and 5.01+/-0.76 mg/million cycles, respectively. (IV) Both accelerated aged, alpha-tocopherol-blended 100-kGy irradiated UHMWPEs showed higher ultimate tensile strength, higher yield strength, and lower elastic modulus when compared to 100-kGy irradiated, virgin UHMWPE. These results showed that alpha-tocopherol-blended 100-kGy irradiated UHMWPEs were not cross-linked to the same extent as the 100-kGy irradiated, virgin UHMWPE.

Characterization of knitted polymeric scaffolds for potential use in ligament tissue engineering
Ge, Z., J. C. Goh, et al. (2005), J Biomater Sci Polym Ed 16(9): 1179-92.
Abstract: Different scaffolds have been designed for ligament tissue engineering. Knitted scaffolds of poly-L-lactic acid (PLLA) yarns and co-polymeric yarns of PLLA and poly(glycolic acid) (PLGA) were characterized in the current study. The knitted scaffolds were immersed in medium for 20 weeks, before mass loss, molecular weight, pH value change in medium were tested; changes in mechanical properties were evaluated at different time points. Results showed that the knitted scaffolds had 44% porosity. There was no significant pH value change during degradation, while there was obvious mass loss at initial 4 week, as well as smooth molecular weight drop of PLLA. PLGA degraded more quickly, while PLLA kept its integrity for at least 20 weeks. Young's modulus increased while tensile strength and strain at break decreased with degradation time; however, all of them could maintain the basic requirements for ACL reconstruction. It showed that the knitted polymeric structures could serve as potential scaffolds for tissue-engineered ligaments.

Characterization of mode II-wear particles and cytokine response in a human macrophage-like cell culture
Rolf, O., B. Baumann, et al. (2005), Biomed Tech (Berl) 50(1-2): 25-9.
Abstract: Informations about wear particles in metallosis (mode II wear) and their effects in vitro and in vivo are limited. The aim of this study was to characterize wear particles obtained intraoperatively and to analyse their effects on cytokine response in an established human macrophage-like cell culture model. METHOD: Wear particles were obtained intraoperatively from four patients with metallosis resulting from CrCoMo/PE/TiAIV-implants (mode II wear) (3 knee, 1 hip prosthesis). After purification, particles were characterized regarding to their composition and size (particle size analyser, electron microscopy, edx-analysis, histological slices). The effects of particles on the release of cytokines (PDGF, IL-1beta, IL-8, TNF alpha) were determined in an established human macrophage-like cell culture system by ELISA-assays. RESULTS: The metal wear particles consisted of TiAIV with a mean size of 0.1 +/- 0.15 microm, independent of the prosthesis location. CrCoMo particles could not be detected. In the cell culture model 1456 x 10(8) particles per 1 x 10(6) macrophages released maximum amounts of TNFalpha (8-fold) and IL-8 and IL-1beta (5-fold) while the survival rate of the cells was more than 90 percent. A particle-dependent increase of PDGF-levels could not be detected. CONCLUSION: As already shown for mode I wear particles (contact between primary bearing surfaces), also mode II wear particles cause release of bone resorbing cytokines in a macrophage-like cell culture model. Because their local and systemic effects in vivo are still not completely understood, we recommend a complete removal of wear particles in cases of metallosis to avoid possible immunological reactions of the body as well as periprosthetic osteolysis.

Characterization of non-neuronal elements within fibronectin mats implanted into the damaged adult rat spinal cord
King, V. R., J. B. Phillips, et al. (2006), Biomaterials 27(3): 485-96.
Abstract: Previous studies have shown that mats made from fibronectin (FN) integrate well into spinal cord lesion sites and support extensive axonal growth. Using immunohistochemistry, we have investigated the non-neuronal factors that contribute to these properties. Extensive vascularization was observed in FN mats by 1 week along with heavy macrophage infiltration by 3 days post-implantation. By 1 week post-implantation, laminin tubules had formed and were associated with axons and p75 immunoreactive Schwann cells. By 4 weeks post-implantation, most axons were associated with Schwann cell derived myelin. Few oligodendrocytes were present within the mat, even with an increase in the number of oligodendrocyte precursors around the implant site by 7 days post-implantation. Astrocyte proliferation also occurred in the intact tissue, with a prominent glial scar forming around the implant within 4 weeks. However, by 2 months post-implantation astrocytes were present in the FN implant site and were intermingled with the axons. Axonal ingrowth and integration of the FN mats is probably due to the ability of FN mats to support and organize infiltration of Schwann cells and deposition of laminin. At later time points, myelinated axons remain in the implant site, even after other elements (e.g. macrophages and laminin) have disappeared. Both of these properties are likely to be important in the design of biomaterial bridges for CNS regeneration.

Characterization of oak and birch dust-induced expression of cytokines and chemokines in mouse macrophage RAW 264.7 cells
Maatta, J., M. L. Majuri, et al. (2005), Toxicology 215(1-2): 25-36.
Abstract: Occupational exposure to wood dust is related to several respiratory diseases, such as allergic rhinitis, chronic bronchitis, and asthma. However, virtually nothing is known about molecular mechanisms behind wood dust-induced pulmonary inflammation. To elucidate the effects of wood dust exposure on cytokine and chemokine expression in murine macrophage cell line cells, mouse RAW 264.7 cells were exposed to two selected hardwood dusts, oak and birch. TiO2 and LPS were used as controls. Expression patterns of several cytokines, chemokines, and chemokine receptors were assessed by real-time quantitative PCR system and by ELISA. Exposure to birch dust caused a major increase in TNF-alpha and IL-6 protein levels whereas a weaker induction of TNF-alpha protein was found after exposure to oak dust. Inorganic TiO2 dust did not induce significant cytokine expression. With respect to the chemokines, a dose-dependent, about 10-fold induction of CCL2 mRNA and protein was found after exposure to birch dust. Oak dust induced weakly CCL2 protein. Similarly, birch dust induced a strong expression of CCL3, CCL4, and CXCL2/3 mRNA whereas only moderate levels of these chemokine mRNAs were detected after oak dust exposure. In contrast, expression of CCL24 mRNA was inhibited by more than 40-fold by both oak and birch dusts. TiO2 dust induced about five-fold expression of CCL3 and CCL4 mRNA but did not affect significantly other chemokines. These results suggest that exposure to birch or oak dusts may influence the development of the inflammatory process in the airways by modulating the expression of macrophage-derived cytokines and chemokines.

Characterization of plasma polymerized silicone coatings useful as biomaterials
Chawla, A. S. and R. Sipehia (1984), J Biomed Mater Res 18(5): 537-45.
Abstract: Plasma polymerization techniques were used to deposit a layer of filler-free silicone rubber on a variety of substrate materials. The thickness of the deposited film was 0.5-0.8 micron. As it is the surface of the biomaterial that comes in direct contact with the body fluids, the surface of the biomaterial is of paramount importance. In this study, the plasma polymerized biomaterials were characterized. Thus, the scanning electron microscope (SEM) showed the surfaces to be smooth. To study the surface layer of the deposited polymer, Fourier-transform infrared spectrometry in the attenuated total reflection (ATR) mode was used. The deposited material was indeed silicone polymer with adsorption bands at 1262, 1020, and 802 cm-1 for the Si-CH3 bending, Si-0-Si stretching, and Si-CH3 bending, respectively. To find the bonding nature of the polymer, electron spectrometry for chemical analysis (ESCA) was used. The silicone polymer was shown to be highly cross-linked. To find the molecular weight between cross-links, swelling studies were done. Thus the results of the study show that the plasma polymerization could produce a filler-free silicone layer on a variety of substrate materials.

Characterization of plasma proteins adsorbed onto biomaterials. By MALDI-TOFMS
Oleschuk, R. D., M. E. McComb, et al. (2000), Biomaterials 21(16): 1701-10.
Abstract: The analysis of plasma proteins adsorbed onto a polyurethane (PU) biomaterial was performed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). This article marks the first study on MALDI-TOFMS analysis of multiple proteins adsorbed from plasma, in vitro, onto the surface of a biomaterial to easily enable their characterization. Plasma standards from three different hosts were placed in contact with non-porous PU, a model biomaterial. Following the use of washing protocols developed in our laboratory, the biomaterial was analyzed, directly, with MALDI-TOFMS. Proteins with molecular weights (Mr) ranging from ca. 6.5 to 150 kDa were observed in the mass spectra and characterized upon comparison with proteins of known Mr. The proteins observed were tentatively identified as those known to adsorb onto PU, both in vitro and in vivo. In an attempt to model in vivo sorption, the PU biomaterial was exposed to freshly collected canine plasma, in vitro, for different lengths of time. Corresponding MALDI-TOFMS spectra displayed increasing protein signal for a number of different proteins with increasing times of exposure to plasma. This method provided qualitative and semi-quantitative analysis of the proteins adsorbed onto the biomaterial surface.

Characterization of polyelectrolyte complexes between chondroitin sulfate and chitosan in the solid state
Chen, W. B., L. F. Wang, et al. (2005), J Biomed Mater Res A 75(1): 128-37.
Abstract: Chondroitin sulfate (ChS) was used to form polyelectrolyte complexes with chitosan (ChI), and its potential as a colon-targeted drug carrier was investigated. In order to determine the optimal conditions for the formation of a stable polyelectrolyte complex, the formation of ChS/ChI complexes was examined at two different pH values with various weight ratios, or at a fixed molar ratio of ChS/ChI of 1/2 under various pH conditions. The molar compositions of the various ChS/ChI complexes were quantitated with the use of solid-state 13C CP MAS NMR. The equivalent molar ratios of the complexes ranged from 0.47 to 0.54, in agreement with the data determined by elemental analysis. The fact that these values were close to 0.5 suggests that most of the --OSO3- and the --COO- groups on ChS formed strong electrostatic interactions with the --NH3+ groups on ChI, obeying a simple stoichiometric reaction between two oppositely charged moieties. Similar compositions of the complexes were obtained under most conditions tested; however, different strengths of the interactions between the two polysaccharides were noted from measurements of the water-associated transition and thermal degradation temperatures and the degree of ChS dissolution. FTIR and 13C NMR clearly showed H-bond formation at low pH, indicating that in addition to the varying degrees of electrostatic interaction, H bonding may be involved in complex formation. The highest degradation temperature, as determined by thermal gravimetric analysis, and the lowest ChS sol fraction, as measured by gel permeation chromatography, were observed with the complex prepared at pH 5, with a 1:1 mole ratio of the two opposite charges in feed. This complex also exhibited the highest water-associated transition temperature, as determined by differential scanning calorimetry. Furthermore, the swelling behavior of these complexes was pH dependent; this is a property that can potentially be exploited to control drug release from these complexes under specific pH conditions.

Characterization of porous PLGA/PLA microparticles as a scaffold for three dimensional growth of breast cancer cells
Sahoo, S. K., A. K. Panda, et al. (2005), Biomacromolecules 6(2): 1132-9.
Abstract: We have designed and evaluated biodegradable porous polymeric microparticles as a scaffold for cell growth. The hypothesis was that microparticles with optimized composition and properties would have better cell adhesion and hence cell growth into a tissue-like structure. Solvent-evaporation method was modified using sucrose as an additive to form large porous microparticles of poly(D,L-lactic-co-glycolic) (PLGA) and polylactide (PLA) polymers. Microparticles containing hydrophilic polymers (poly(vinyl alcohol) and chitosan) incorporated in their internal matrix structure were also formulated. Different formulations of microparticles were evaluated for physical properties, cell adhesion, and cell growth in culture. PLA microparticles containing poly(vinyl alcohol) (PVA) in the matrix structure (PLA-PVA) and treated with serum prior to cell seeding demonstrated better cell adhesion and cell growth than other formulations of microparticles. Cells were seen to grow into clumps, engulfing microparticles completely with time, and forming a 3-D tissue-like structure. Cell density of 1.5 x 10(6) cells per mg of microparticles was achieved in 9 days of culture, which was a 7-fold increase from the initial seeding cell density. The mechanism of better cell growth on PLA-PVA microparticles appears to be due to the PVA associated with the internal matrix structure of microparticles. These microparticles demonstrated better wetting in culture and also cell adhesion. In addition to tissue engineering applications, microparticles with cancer cells grown into a tissue-like structure in vitro can be potentially used as a model system for preclinical evaluation of the cytotoxic effect of anticancer agents.

Characterization of rhBMP-2 pharmacokinetics implanted with biomaterial carriers in the rat ectopic model
Uludag, H., D. D'Augusta, et al. (1999), J Biomed Mater Res 46(2): 193-202.
Abstract: Recombinant human bone morphogenetic protein-2 (rhBMP-2) is a member of the bone morphogenetic protein family involved in de novo bone induction. Successful use of rhBMP-2 requires implantation with a biomaterial which can act as a scaffold for cell invasion for osteoinduction and retains rhBMP-2 at a site of implantation. This study was carried out to characterize rhBMP-2 pharmacokinetics from a variety of biomaterial carriers in a rat ectopic model. Retention of rhBMP-2 within carriers after 3 h was variable among the carriers (range, 75-10%), with collagenous sponges retaining the highest fraction of implanted dose. A gradual loss of rhBMP-2 was subsequently observed, the kinetics of which was strongly dependent on the implanted carrier. Collagenous carriers were observed to lose rhBMP-2 gradually from the implant site, whereas some of the mineral-based carriers retained a fraction of implanted rhBMP-2 within the implants. These differences in protein pharmacokinetics among carriers, in addition to their physicochemical nature, are expected to affect the biological activity of implanted rhBMP-2.

Characterization of sol-gel bioencapsulates for ester hydrolysis and synthesis
Soares, C. M., H. F. de Castro, et al. (2005), Appl Biochem Biotechnol 121-124: 845-59.
Abstract: Candida rugosa lipase was entrapped in silica sol-gel particles prepared by hydrolysis of methyltrimethoxysilane and assayed by p-nitrophenyl palmitate hydrolysis, as a function of pH and temperature, giving pH optima of 7.8 (free enzyme) and 5.0-8.0 (immobilized enzyme). The optimum temperature for the immobilized enzyme (50-55 degrees C) was 19 degrees C higher than for the free enzyme. Thermal, operational, and storage stability were determined with n-butanol and butyric acid, giving at 45 degrees C a half-life 2.7 times greater for the immobilized enzyme; storage time was 21 d at room temperature. For ester synthesis, the optimum temperature was 47 degrees C, and high esterification conversions were obtained under repeated batch cycles (half-life of 138 h).

Characterization of the importance of polysaccharide intercellular adhesin/hemagglutinin of Staphylococcus epidermidis in the pathogenesis of biomaterial-based infection in a mouse foreign body infection model
Rupp, M. E., J. S. Ulphani, et al. (1999), Infect Immun 67(5): 2627-32.
Abstract: The production of biofilm is thought to be crucial in the pathogenesis of prosthetic-device infections caused by Staphylococcus epidermidis. An experimental animal model was used to assess the importance of biofilm production, which is mediated by polysaccharide intercellular adhesin/hemagglutinin (PIA/HA), in the pathogenesis of a biomaterial-based infection. Mice were inoculated along the length of a subcutaneously implanted intravenous catheter with either wild-type S. epidermidis 1457 or its isogenic PIA/HA-negative mutant. The wild-type strain was significantly more likely to cause a subcutaneous abscess than the mutant strain (P < 0.01) and was significantly less likely to be eradicated from the inoculation site by host defense (P < 0.05). In addition, the wild-type strain was found to adhere to the implanted catheters more abundantly than the PIA/HA-negative mutant (P < 0.05). The reliability of the adherence assay was assessed by scanning electron microscopy. To exclude contamination or spontaneous infection, bacterial strains recovered from the experimental animals were compared to inoculation strains by analysis of restriction fragment length polymorphism patterns by pulsed-field gel electrophoresis. In vitro binding of the wild-type strain and its isogenic mutant to a fibronectin-coated surface was similar. These results confirm the importance of biofilm production, mediated by PIA/HA, in the pathogenesis of S. epidermidis experimental foreign body infection.

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Last Modified: 8 February 2006