Biomaterials.info - Resources for Engineers

Record 2501 to 2520

Influence of octacalcium phosphate coating on osteoinductive properties of biomaterials
Habibovic, P., C. M. van der Valk, et al. (2004), J Mater Sci Mater Med 15(4): 373-80.
Abstract: In this study, we investigated the influence of octacalcium phosphate (OCP) coating on osteoinductive behaviour of the biomaterials. Porous titanium alloy (Ti6Al4V), hydroxyapatite (HA), biphasic calcium phosphate (BCP) and polyethylene glyco terephtalate/polybuthylene terephtalate (PEGT-PBT) copolymer, all uncoated and coated with biomimetically produced OCP, were implanted in back muscles of 10 goats for 6 and 12 weeks. Uncoated Ti6Al4Vand HA did not show any bone formation after intramuscular implantation. All OCP coated implants, except PEGT-PBT, did induce bone in the soft tissue. The reason for the non-inductive behaviour of the copolymer is probably its softness, that makes it impossible to maintain its porous shape after implantation. Both uncoated and OCP coated BCP induced bone. However, the amount of animals in which the bone was induced was higher in the coated BCP implants in comparison to the uncoated ones. Osteoinductive potential of biomaterials is influenced by various material characteristics, such as chemical composition, crystallinity, macro- and microstructure. OCP coating has a positive effect on osteoinductivity of the biomaterials. The combination of the advantages of biomimetic coating method above traditional methods, and a good osteoinductivity of OCP coating that is produced by using this method, opens new possibilities for designing more advanced orthopaedic implants.

Influence of orthopedic particulate biomaterials on inflammation and synovial microcirculation in the murine knee joint
Zysk, S. P., H. Gebhard, et al. (2004), J Biomed Mater Res B Appl Biomater 71(1): 108-15.
Abstract: The purpose of the present study was to examine changes in the synovial microcirculation as well as synovial tissue responses to exposure to titanium, polymethylmethacrylate (PMMA), ceramic (Al(2)O(3)), cobalt-chromium alloy (Co-Cr), and polyethylene (PE) particles in an in vivo model. The particulate biomaterials were injected into the left knee joint of female Balb/c mice and assessment of the synovial microcirculation using intravital fluorescence microscopy as well as histological evaluation of the synovial tissue response were performed on day 7 after particle administration. Intravital microscopic measurements revealed that all tested biomaterials caused significantly (p < 0.05) enhanced leukocyte-endothelial cell interactions and an increase of functional capillary density compared to controls. In the histological examination PMMA, Al(2)O(3), PE, and Co-Cr particles provoked significantly (p < 0.05) enhanced inflammatory tissue responses in comparison to tissue from control animals. Titanium particles showed significantly (p < 0.05) less leukocyte-endothelial cell interactions than the other particulate biomaterials and caused significantly (p < 0.05) minor membrane thickening compared to PE and PMMA particles. In conclusion, all tested particulate biomaterials were capable of inducing inflammatory responses in the present study. Our data suggest that titanium particles may cause less leukocyte activation and inflammatory tissue responses than other particulate biomaterials used in total joint arthroplasty.

Influence of oxygen on the proliferation and metabolism of adipose derived adult stem cells
Wang, D. W., B. Fermor, et al. (2005), J Cell Physiol 204(1): 184-91.
Abstract: Articular cartilage is an avascular connective tissue that exhibits little intrinsic capacity for repair. Articular cartilage exists in a reduced oxygen (approximately 5%) environment in vivo; therefore, oxygen tension may be an important factor that regulates the metabolism of chondrocyte progenitors. A number of recent studies have developed tissue engineering approaches for promoting cartilage repair using undifferentiated progenitor cells seeded on biomaterial scaffolds, but little is known about how oxygen might influence these engineered tissues. Human adipose-derived adult stem (hADAS) cells isolated from the stroma of subcutaneous fat were suspended in alginate beads and cultured in control or chondrogenic media in either low oxygen (5%) or atmospheric oxygen tension (20%) for up to 14 days. Under chondrogenic conditions, low oxygen tension significantly inhibited the proliferation of hADAS cells, but induced a two-fold increase in the rate of protein synthesis and a three-fold increase in total collagen synthesis. Low oxygen tension also increased glycosaminoglycan synthesis at certain timepoints. Immunohistochemical analysis showed significant production of cartilage-associated matrix molecules, including collagen type II and chondroitin-4-sulfate. These findings suggest oxygen tension may play an important role in regulating the proliferation and metabolism of hADAS cells as they undergo chondrogenesis, and the exogenous control of oxygen tension may provide a means of increasing the overall accumulation of matrix macromolecules in tissue-engineered cartilage.

Influence of P/L ratio and peroxide/amine concentrations on shrinkage-strain kinetics during setting of PMMA/MMA biomaterial formulations
Silikas, N., A. Al-Kheraif, et al. (2005), Biomaterials 26(2): 197-204.
Abstract: This study investigated the effects on polymerisation shrinkage-strain for two unmodified powder and liquid formulations of polymethyl methacrylate (PMMA), methyl methacrylate (MMA) dough-type systems, by varying the powder/liquid (P/L) ratio. Furthermore, the shrinkage-strain effects for the 1.0:1.0 P/L ratio of adding additional amounts of amine and benzoyl peroxide (BPO) were studied. The rationale was the continuing importance of bone cements and the renewed interest in acrylic biomaterials, based on MMA and PMMA co-polymers, as used in new fibre-reinforced systems, where low P/L ratios may be important. Shrinkage-strain is directly related to extent of monomer conversion and has intrinsic importance related to interfacial disruption. Shrinkage-strain kinetics were determined using the "bonded disk" method. The first series of experiments studied two unmodified self-curing materials (MEA and PAL), where specimens with different P/L ratios by volume (3.0, 2.5, 2.0, 1.5 and 1.0 to 1.0) were mixed for 60s. In these formulations, final shrinkage-strain values correlated positively with P/L ratios, rather than negatively, as would be expected from fully polymerised material. This highlights a problem of under-polymerisation through deviation from an optimum or recommended P/L ratio. When an additional 1.0% BPO was added in the powder, final shrinkage-strain values correlated negatively rather than positively, with P/L ratio for both products, except at ratio 1.0:1.0. Specimens mixed at 1.0:1.0 P/L ratio, with increasing amounts of BPO and amine resulted in higher final shrinkage-strain values, indicative of more complete polymerisation. Shrinkage-strain and optimum polymerisation are related, but clinically rather antagonist properties with respect to effective biomaterial utilisation and performance. In both design and surgical application of these polymethacrylate formulations, possible adverse effects of changing P/L ratio, producing either excessive shrinkage-strain or under-polymerisation, must be understood and where possible controlled.

Influence of parenteral iron therapy and oral vitamin E supplementation on neutrophil respiratory burst in chronic hemodialysis patients
Hodkova, M., S. Dusilova-Sulkova, et al. (2005), Ren Fail 27(2): 135-41.
Abstract: BACKGROUND: Bioincompatibility of hemodialysis (HD) membranes is responsible for neutrophil activation leading to oxidative stress, which can be further increased by intravenous (IV) iron (Fe) administration. The aim of our study was to monitor neutrophil respiratory burst during HD and to find out whether this process is influenced by IV Fe and oral vitamin E administration. METHODS: Within four HD sessions, blood samples were taken from seven chronic HD patients at time 0 (before HD), 60, 70, and 130 min of HD session. Neutrophil respiratory burst was assessed by luminol-enhanced chemiluminescence (CL). Plasma advanced oxidation protein products (AOPP) concentration was measured spectrophotometrically. During the second and the fourth HD, 62.5 mg of sodium ferric gluconate was applied IV in the 65th minute of HD. Before the last two HD, the patients were given orally 200 mg of vitamin E daily for 7 days. Patient's results were compared with healthy controls. RESULTS: Predialysis CL is higher in patients than in controls (1,926 +/- 436 vs. 1,083 +/- 325 RLU, p<.01). CL decreases in the 60th min of HD (1,926 +/- 436 vs. 1,220 +/- 599 RLU, p<.05); thereafter, it remains stable. After Fe application, CL increases at time 130 compared with CL at time 60 (1,303 +/- 269 vs. 877 +/- 292 RLU, p<.05). AOPP concentration is higher in patients than in controls (137.5 +/- 42.7 vs. 88.9 +/- 24.8 micromol/L, p<.01) and remains unaffected by vitamin E supplementation. After vitamin E intake, predialysis CL remains significantly higher than in controls, and changes in CL during HD are minimal despite Fe administration. CONCLUSION: HD patients' neutrophils generate more oxygen radicals than in healthy individuals. This production decreases during HD and then increases after IV Fe administration. Short-term vitamin E administration attenuates this fluctuation of neutrophil oxidative metabolism, without affecting the total degree of oxidative stress.

Influence of partially cross-linked alginate used in the production of alginate microspheres by emulsification
Lee, H. Y., L. W. Chan, et al. (2005), J Microencapsul 22(3): 275-80.
Abstract: Spherical and discrete calcium alginate microspheres had been produced by the emulsification technique. The microencapsulation process was highly efficient, but drug release from microspheres was rapid. A more orderly chain arrangement of the polymeric chains would give rise to a stronger and less permeable matrix capable of sustaining drug release. Therefore, the potential of using partially cross-linked alginate in the production of microspheres by emulsification was explored. The size and roundness of the microspheres, its drug content and drug release property were determined. The more viscous alginate solutions when reacted with more calcium salt added resulted in larger microspheres produced. Microspheres made from partially cross-linked alginate exhibited lower drug content and higher T75% values in drug release studies. This was due to decreased flexibility of the polymer chains which were partially held together by calcium ions, reducing subsequent interaction with the calcium ions resulting in lower drug entrapment efficiency and a more permeable microsphere matrix.

Influence of selected wound dressings on PMN elastase in chronic wound fluid and their antioxidative potential in vitro
Schonfelder, U., M. Abel, et al. (2005), Biomaterials 26(33): 6664-73.
Abstract: Exudates from non-healing wounds contain elevated levels of proteolytic enzymes, like elastase from polymorphonuclear granulocytes (PMN elastase), reactive oxygen species (ROS) and reactive nitrogen species (RNS). The overproduction of proteolytic enzymes leads to reduced concentrations of growth factors and proteinase inhibitors, resulting in an imbalance between degradation and remodelling processes. Thus, the reduction of protein-degrading enzymes and scavenging of ROS and RNS seem to be suitable ways to support the healing process of chronic stagnating wounds. The aim of this study was to test selected wound dressings from different biomaterials (collagen, oxidized regenerated cellulose (ORC) and ORC/collagen mixture), regarding their antioxidative potential in vitro and their influence on the concentration and activity of PMN elastase in chronic wound fluid. Antioxidant capacity of the investigated wound dressing was determined by a pholasin-based chemiluminescent assay. PMN elastase concentration was determined by means of ELISA. Enzyme activities could be measured by a fluorescence assay. As the presented data demonstrates, all tested materials showed antioxidant capacity. In addition, the investigated materials were able to reduce the concentration and activity of PMN elastase. Beside other aspects, such as biocompatibility, biodegradability, fluid absorption and clinical effects (e.g. angiogenesis and microcirculation), the understanding of these properties may help to support the further refinement of wound dressings for improved wound healing.

Influence of sterilization on injectable bone biomaterials
Zahraoui, C. and P. Sharrock (1999), Bone 25(2 Suppl): 63S-65S.
Abstract: Injectable biomaterials used in bone surgery include acrylic bone cements, calcium phosphate cements, and new composite-type biomaterials with a mineral content and an organic phase dispersed or dissolved in water. Cellulose derivatives, chitosan solutions, alginates, and other polymers are studied as useful modifiers and binding agents in calcium phosphate cements. We have developed proprietary polyester copolymers including lactic acid moieties and present here results concerning the effect of sterilization on the physico-chemical properties of derived bone biomaterials. Chitosan solutions show a dramatic decrease in viscosity after 25-kGy gamma sterilization. Aqueous copolylactic solutions also show, by capillary electrophoresis, that hydrolysis occurs to liberate monomers after 25-kGy gamma sterilization. Heat sterilization also degrades chitosan solutions, and ultrafiltration is difficult because of high viscosity. However, apatite-copolylactic solids can be steam sterilized without deterioration. Gelatin has been used as a natural polymer to bind apatite particles. Gel exclusion chromatography reveals crosslinking of the chains by irradiation. Standard acrylic cements contain monomers sterilized by ultrafiltration because they do not tolerate irradiation. We have used ultrafiltration to prepare aqueous copolylactic solutions without polymer hydrolysis. Implantation of calcium phosphate cement modified by copolylactic acid in a rabbit metaphyseal model defect shows progressive substitution of the biomaterial by new bone tissue. At 3 months, a mild inflammatory reaction still remains associated with the continuing resorption of the biomaterial. These results show that interesting biological properties can be obtained with products not sterilized by irradiation. Undoubtedly, many biopolymers are fragile and, like reactive monomers, need to be sterilized by special methods if they are to be used in injectable, liquid form.

Influence of stirring-induced mixing on cell proliferation and extracellular matrix deposition in meniscal cartilage constructs based on polyethylene terephthalate scaffolds
Neves, A. A., N. Medcalf, et al. (2005), Biomaterials 26(23): 4828-36.
Abstract: The response of engineered meniscal cartilage constructs to stirring-induced mixing in spinner flasks was investigated. Polyethylene terephthalate scaffolds were seeded with meniscal fibrochondrocytes from 6 month-old sheep and cultured under a variety of stirring regimes for 28 days. Stirring-induced mixing increased up to 7-fold the deposition of glucosaminoglycans and up to 3-fold the deposition of collagen, when compared to static cultures. High and medium intensity stirring induced rapid cell proliferation, with maximal cell densities achieved within the first seven days of cultivation. Under these conditions, collagen and glucosaminoglycan deposition occurred predominantly in association with cell proliferation, the specific deposition rate of these biopolymers decreasing markedly after 7 days of cultivation, when the cell number reached a plateau. Constructs exposed to the highest intensity stirring had the highest levels of collagen and glucosaminoglycans and a more homogeneous cell distribution. As the success of the integration at a repair site in the knee of a meniscal construct is likely to be dependent on the cellular activity of the construct, these studies suggest that cultivation of meniscal cartilage constructs, under these conditions, should not extend for more than 7 days.

Influence of strain, biomaterial, proteins, and oncostatic chemotherapy on Staphylococcus epidermidis adhesion to intravascular catheters in vitro
Galliani, S., A. Cremieux, et al. (1996), J Lab Clin Med 127(1): 71-80.
Abstract: Initial adhesion of four phenotypically different strains of Staphylococcus epidermidis to 16 silicone, polyurethane, or hydrophilic polyurethane catheters was assessed in vitro by a bacterial radiolabeling method. The effect of catheter exposure to plasma proteins, to an anticancer polychemotherapy (5-fluorouracil, doxorubicin, cyclophosphamide), or to both of them was determined. Bacterial adhesion on native catheters was dependent on the hydrophobicity of both bacteria and catheters. The four strains tested adhered preferentially to silicone catheters (p < 0.05); adhesion was moderate to polyurethane surfaces, whereas the least adhesion was obtained for hydrophilic polyurethane catheters. Adsorption of plasma proteins on the surface produced a marked decrease in adhesion on silicone (-66.2%; p < 0.001) and polyurethane (-32.8%; p < 0.01) catheters and a marked increase in adhesion on hydrophilic surfaces (+91.7%; p < 0.05). Chemotherapeutic treatment of the catheter produced a slight but not significant decrease in adhesion on silicone (-17.4%) and polyurethane (-19.8%) catheters and a marked increase in adhesion on hydrophilic polyurethanes (+148.2%; p < 0.001). The in vitro simulation of catheter use suggested that oncostatic drugs and plasma proteins play an important role in S. epidermidis adhesion to intravascular catheters. Overall, bacterial adhesion is lowest on hydrophilic polyurethane catheters before and after simulation of catheter use.

Influence of surface energy of modified surfaces on bacterial adhesion
Liu, Y. and Q. Zhao (2005), Biophys Chem 117(1): 39-45.
Abstract: There are a number of contrary reports on the effect of surface energy of substrates on bacterial adhesion. Some reports showed that bacterial adhesion decreased with decreasing surface energy of substrates; while other reports showed that bacterial adhesion decreased with increasing surface energy of substrates. In this study Escherichia coli adhesion on the Ni--P--PTFE coatings with various surface energies was investigated and the extended DLVO theory was used to calculate the interaction energy between bacteria and the substrates in water. The theory explained the effect of surface energy of substrates on bacterial adhesion.

Influence of the radiopacifier in an acrylic bone cement on its mechanical, thermal, and physical properties: barium sulfate-containing cement versus iodine-containing cement
Lewis, G., C. S. van Hooy-Corstjens, et al. (2005), J Biomed Mater Res B Appl Biomater 73(1): 77-87.
Abstract: In all acrylic bone cement formulations in clinical use today, radiopacity is provided by micron-sized particles (typical mean diameter of between about 1 and 2 microm) of either BaSO(4) or ZrO(2). However, a number of research reports have highlighted the fact that these particles have deleterious effects on various properties of the cured cement. Thus, there is interest in alternative radiopacifiers. The present study focuses on one such alternative. Specifically, a cement that contains covalently bound iodine in the powder (herein designated the I-cement) was compared with a commercially available cement of comparable composition (C-ment3), in which radiopacity is provided by BaSO(4) particles (this cement is herein designated the B-cement), on the basis of the strength (sigma(b)), modulus (E(b)), and work-to-fracture (U(b)), under four-point bending, plane-strain fracture toughness (K(IC)), Weibull mean fatigue life, N(WM) (fatigue conditions: +/-15 MPa; 2 Hz), activation energy (Q), and frequency factor (ln Z) for the cement polymerization process (both determined by using differential scanning calorimetry at heating rates of 5, 10, 15, and 20 K min(-1)), and the diffusion coefficient for the absorption of phosphate-buffered saline at 37 degrees C (D). For the B-cement, the values of sigma(b), E(b), U(b), K(IC), N(WM), Q, ln Z, and D were 53 +/- 3 MPa, 3000 +/- 120 MPa, 108 +/- 15 kJ m(-3), 1.67 +/- 0.02 MPa check mark m, 7197 cycles, 243 +/- 17 kJ mol(-1), 87 +/- 6, and (3.15 +/- 0.94) x 10(-12) m(2) s(-1), respectively. For the I-cement, the corresponding values were 58 +/- 5 MPa, 2790 +/- 140 MPa, 118 +/- 45 kJ m(-3), 1.73 +/- 0.11 MPa check mark m, 5520 cycles, 267 +/- 19 kJ mol(-1), 95 +/- 9, and (3.83 +/- 0.25) x 10(-12) m(2) s(-1). For each of the properties of the fully cured cement, except for the rate constant of the polymerization reaction, at 37 degrees C (k'), as estimated from the Q and ln Z results, there is no statistically significant difference between the two cements. k' for the I-cement was about a third that for the B-cement, suggesting that the former cement has a higher thermal stability. The influence of various characteristics of the starting powder (mean particle size, particle size distribution, and morphology) on the properties of the cured cements appears to be complex. When all the present results are considered, there is a clear indication that the I-cement is a viable candidate cement for use in cemented arthroplasties in place of the B-cement.

Influence of the selection of the suture material on the mechanical behavior of a biomaterial to be employed in the construction of implants. Part 1: Calf pericardium
Garcia Paez, J. M., A. Carrera, et al. (2001), J Biomater Appl 16(1): 47-67.
Abstract: A hydraulic stress simulator was employed to study the mechanical behavior of the calf pericardium used in the construction of cardiac valve leaflets. One hundred eighty pairs of tissue samples were subjected to tensile testing to rupture. One of the two samples from each of 144 pairs (four series of 36 pairs each) was sutured with commercially available threads made of nylon, silk, Prolene or Gore-Tex, while the other sample in each of these pairs was left unsewn. The remaining 36 pairs were employed as controls in which neither of the two samples was subjected to suturing. The sutured tissue samples showed a significant decrease in tensile strength at rupture (range: 11.81 to 26.04 MPa) when compared with unsutured samples (range: 39.38 to 87.96 MPa; p < 0.01). The application of morphological and mechanical selection criteria to maximize the homogeneity of the samples provided excellent fit with respect to the stress/strain curves. This method made it possible to carry out a predictive study of the mechanical behavior of a sutured sample, based on that observed in the corresponding unsutured fragment. The interaction of the different suture materials with the pericardial tissue was also assessed by comparing the mechanical behavior of the sutured samples with that of the control samples. At stresses of less than 0.8 MPa, samples sewn with Gore-Tex were found to show the least difference with respect to the controls, indicating that this material presented the lowest degree of interaction with the pericardium. In conclusion, the degree of the loss of resistance to tearing of the sutured samples is of no value in the selection of the optimal suture material. The selection process applied makes it possible to predict the mechanical behavior in response to suturing of a given unsewn tissue specimen by determining that of its sutured mate. The similarity between the findings in samples sewn with Gore-Tex and in the unsutured controls indicates a lesser degree of interaction between the suture material and the pericardium employed in the construction of cardiac valve leaflets.

Influence of the selection of the suture material on the mechanical behavior of a biomaterial to be employed in the construction of implants. Part 2: Porcine pericardium
Garcia Paez, J. M., A. Carrera, et al. (2001), J Biomater Appl 16(1): 68-90.
Abstract: Using a hydraulic stress simulator, the mechanical behavior of the porcine pericardium used in the construction of cardiac valve leaflets was characterized following the same procedure employed with calf pericardium in Part 1 of this study. One hundred fifty pairs of tissue samples were subjected to tensile testing to rupture. One of the two samples from each of 120 pairs (four series of 30 pairs each) was saturated with commercially available threads made of nylon, silk, Prolene or Gore-Tex, while the other sample in each of these pairs was left unsewn. The remaining 30 pairs were employed as controls in which neither of the two samples was subjected to suturing. The sutured tissue samples showed a significant decrease in tensile strength at rupture (range: 11.61 to 21.22 MPa) when compared with unsutured samples (range: 50.80 to 89.45 MPa; p < 0.01). When these results were compared with their equivalent in calf pericardium, no significant differences were observed (the mean values at rupture in calf pericardium ranged between 211.61 MPa and 26.04 MPa). Again, the application of morphological and mechanical selection criteria to ensure the homogeneity of the samples provided excellent fit with respect to the stress/strain curves. The interaction of the different suture materials with the pericardial tissue was also assessed by comparing the mechanical behavior of the sutured samples with that of the control samples. At the working stress of a cardiac valve leaflet, 0.250 MPa, samples sewn with Gore-Tex were found to show the least difference in behavior with respect to the controls, indicating that this material presented the lowest degree of interaction with the pericardium. In conclusion, the suture clearly has deleterious effects on the resistance of both calf and porcine pericardium, which showed no statistically significant differences in terms of resistance to rupture when their respective sutured or unsutured samples were compared, except in the case of porcine pericardium sewn with silk, which presented lower resistance to rupture in all the zones studied. These findings suggest that the hypothesis that porcine pericardium is less resistant is erroneous. The Gore-Tex suture also presented a lower degree of interaction with the porcine pericardium, with values similar to the working stress of a cardiac valve leaflet. This methodology and the results should be evaluated in dynamic studies, such as fatigue testing, that not only confirm the resistance of the material but establish the durability of the samples being assayed.

Influence of the substrate binding characteristics of fibronectin on corneal epithelial cell outgrowth. Student Research Award in the Doctoral Degree Candidate Category, Fourth World Biomaterials Congress (18th annual meeting of the Society for Biomaterials), Berlin, Germany, April 24-28, 1992
Pettit, D. K., T. A. Horbett, et al. (1992), J Biomed Mater Res 26(10): 1259-75.
Abstract: The outgrowth of corneal epithelial cells onto a polymeric substrate is expected to be the primary event in the epithelialization of a synthetic corneal graft. Circular corneal buttons (5 mm) were punched from excised rabbit corneas and placed onto bare substrates or substrates preadsorbed with fibronectin (fn), albumin, or binary mixtures of both fn and albumin. Cell outgrowth areas were measured after culturing the buttons for 4 days in serum-free medium. Fibronectin adsorption to the materials was measured from pure and binary solutions with 125I-radiolabeled fibronectin. A parameter thought to be related to the binding strength of fn to polymeric substrates was measured in parallel experiments by partial elution of the adsorbed fn by 3% sodium dodecyl sulfate (SDS). Following pure solution fibronectin adsorption a range of outgrowth areas was measured (from 0.86 +/- 0.03 cm2 for glass to 1.49 +/- 0.03 cm2 for TCPS). On all of the materials tested cell outgrowth areas increased following fn preadsorption and decreased following albumin preadsorption relative to bare surfaces (p less than 0.05). Following preadsorption with binary protein mixtures cell outgrowth areas increased with fibronectin adsorption, however, the outgrowth areas were not determined solely by the concentration of fn adsorbed onto the surfaces. This result suggested that the biological efficiency of the adsorbed fibronectin was substrate-dependent. When the cell outgrowth data were cross-plotted against fn retention following SDS elution, the outgrowth areas were found to increase along with increases in fn retention. Based on these data we suggest that epithelial cell outgrowth may be partially governed by the tightness of binding between the fn molecules and the underlying substrate.

Influence of the supramolecular structure and physicochemical properties of cellulose on its dissolution in a lithium chloride/N,N-dimethylacetamide solvent system
Ramos, L. A., J. M. Assaf, et al. (2005), Biomacromolecules 6(5): 2638-47.
Abstract: The present work deals with the effects of structural variables of celluloses on their dissolution in the solvent system LiCl/N,N-dimethylacetamide, LiCl/DMAc. Celluloses from fast growing sources (sisal and linters), as well as microcrystalline cellulose (avicel PH-101) were studied. The following structural variables were investigated: index of crystallinity, I(c); crystallite size; polymer porosity; and degree of polymerization determined by viscosity, DPv. Mercerization of fibrous celluloses was found to decrease DPv, I(c), the specific surface area, and the ratio pore volume/radius. The relevance of the structural properties of cellulose to its dissolution is discussed. Rate constants and activation parameters of cellulose decrystallization, prior to its solubilization, have been determined under nonisothermal conditions. The kinetic parameters calculated showed that dissolution is accompanied with small, negative enthalpy and a large, negative entropy of activation.

Influence of the vehicle on the properties and efficacy of microparticles containing amphotericin B
Sanchez-Brunete, J. A., M. A. Dea, et al. (2005), J Drug Target 13(4): 225-33.
Abstract: New microparticles containing amphotericin B (AMB) have been developed and manufactured by spray drying. To this end albumin, polylactic-co-glycolic acids (PLGA) and poly(sebacic anhydride) have been employed as drug carriers. The selection of the solvent used to disperse the drug and the vehicle before spray drying was critical on production yields and physical properties of the microparticles. Once particle size, morphology and dispersability in some aqueous media were shown to be acceptable for an intravenous administration, in vivo efficacy was evaluated and compared with the reference medicine Fungizone. Microparticles prepared with albumin, albumin heated at a high temperature, some kinds of PLGA or polyanhydride, as well as Fungizone, were tested in an experimental hamster model of infection with Leishmania infantum, by evaluating the evolution of parasitic burdens in spleen, liver and antibody responses. After the injection of three doses corresponding to 2 mg of AMB per kilogram each, diverse reactions were reported depending on the vehicle. The best dispersability, reduction of parasites and antibody response were achieved when the treatment was performed with AMB in albumin microspheres.

Influence of three currently used bone replacing materials on the in vitro proliferation of human peripheral blood mononuclear cells
Wanschitz, F., A. Nell, et al. (2005), Clin Oral Implants Res 16(5): 570-4.
Abstract: OBJECTIVES: A cell culture system for biocompatibility testing of bone grafting materials is described. We investigated the in vitro viability and proliferative response of peripheral blood mononuclear cells (PBMC) from 10 healthy donors in the presence of three materials currently used for bone grafting: Algipore, Bio-Oss and Bone Source, for immunologic biocompatibility testing. MATERIAL AND METHODS: PBMC isolated from venous blood from 10 healthy donors were incubated for 4 days with each bone replacing material, in the presence and absence of interleukin-2 (IL-2). After 4 days, H3-thymidine was added for 18 h and the incorporated radioactivity was measured with a beta-plate counter. RESULTS: Basal PBMC counts were 152.9+/-66.2 counts per minute (c.p.m.) (mean+/-SD), in the presence of 0.4 U IL-2/well 206.5+/-83 c.p.m. were measured. With Algipore and Bio-Oss, which are deproteinized bone replacing materials, the proliferation rate of PBMC with IL-2 was not significantly modified: for Algipore 151+/-51 c.p.m./+IL-2 188.8+/-62 c.p.m., for Bio-Oss 144.5+/-64.9 c.p.m./+IL-2 176.3+/-71.23 c.p.m. For Bone Source 164.2+/-80.4/+IL-2 188.3+/-81 c.p.m. were measured. CONCLUSION: This in vitro experiment indicates, that the investigated bone replacing materials are not acting as specific antigens/haptens and are not generating increased proliferative responses of human PBMC from healthy donors. Even with IL-2, that induces proliferation of T lymphocytes, which encountered their specific antigen, the proliferation rate of PBMC from healthy donors was not increased after incubation with this bone grafting materials.

Influence of three-dimensional scaffold on the expression of osteogenic differentiation markers by human dermal fibroblasts
Hee, C. K., M. A. Jonikas, et al. (2006), Biomaterials 27(6): 875-84.
Abstract: Current research in the field of tissue engineering utilizes biomaterial scaffolds, cells, and growth factors for the creation of a functional, biologically active tissue. This study examined the effect of two commercially available, three-dimensional scaffolds, ultraporous beta-tricalcium phosphate ceramics (beta-TCP, Vitoss) and open-celled poly(lactic acid) foams (OPLA, Drilac), on the osteogenic differentiation potential of human dermal fibroblasts. Serum-free, chemically-defined medium containing the metabolic factor 1alpha,25-dihydroxyvitamin D(3) was used to promote an osteogenic phenotype in these cells. Osteoblast differentiation was assessed using PCR and immunohistochemical methods to detect gene and protein expression for the osteoblast markers alkaline phosphatase, osteopontin, and osteocalcin. Dermal fibroblasts cultured on beta-TCP scaffolds in chemically-defined medium with vitamin D(3) exhibited up-regulated gene and protein expression compared to cells cultured on OPLA scaffolds. These results suggest that Vitoss (beta-TCP) scaffolds seeded with dermal fibroblasts and maintained in chemically-defined medium with vitamin D(3) are better suited for bone tissue engineering applications than Drilac (OPLA) foams.

Influences of nano-TiO2 on the chloroplast aging of spinach under light
Hong, F., F. Yang, et al. (2005), Biol Trace Elem Res 104(3): 249-60.
Abstract: The effects of nano-TiO2 (rutile) on the chloroplast aging of spinach under light were studied. The results showed that when the chloroplasts were illuminated for 1, 5, and 10 min with 500 micromol/cm2/min light intensity, respectively, the evolution oxygen rate was rapidly increased; when the chloroplasts were treated for 20, 30, and 40 min with 500 micromol/cm2/min light intensity, respectively, the evolution oxygen rate was gradually decreased. While spinach was treated with 0.25% nano-TiO2, the rate of evolution oxygen of chloroplasts in different illumination times (1, 5, 10, 20, 30, and 40 min) was higher than that of control, and when the illumination time was over 10 min, the reduction of the evolution oxygen rate was lower than that of control. It suggested that nano-TiO2 treatment could protect chloroplasts from aging for long-time illumination. The mechanism researches indicated that nano-TiO2 treatment could significantly increase the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), decrease accumulation of reactive oxygen free radicals and the level of malondialdehyde (MDA), and maintain stability of membrane structure of chloroplast under light.

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