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At least 1,063 records · Page 59Linked to original sources

PubMed2003

Mechanical behaviour and biocompatibility of poly(1-vinyl-2-pyrrolidinone)-gelatin IPN hydrogels.

IPN hydrogels based on poly(1-vinyl-2-pyrrolidinone) and gelatin were obtained by casting of aqueous solution using potassium persulphate and glutaraldehyde as respective crosslinking agents. Studies of swelling and mechanical behaviour showed that the samples of different composition can incorporate high content of water and still exhibit high compression strength. The composition has influence at the global crosslinking density what affects the mechanical performance. In vitro biocompatibility and hemocompatibility were also investigated. The materials do not interfere on the cellular functions and neither induce platelet adhesion. From this preliminary evaluation, it is possible to conclude that these hydrogels have potential for applications in the biomedical field.

Biocompatible Materials↗

PubMed1997

Effect of calcium carbonate on the compliance of an apatitic calcium phosphate bone cement.

Clinical requirements for calcium phosphate bone cements were formulated in terms of the initial setting time, the final setting time, the cohesion time and the ultimate compressive strength. Three cement formulations were tested. The previously developed Biocement H was made of a powder containing alpha-tertiary calcium phosphate and precipitated hydroxyapatite. Biocement B2 powder was made by adding some CaCO3 to Biocement H, whereas Biocement B1 was made by adding some CaCO3 but with simultaneous adjustment of the amount of precipitated hydroxyapatite.The liquid/ powder ratio of the cement paste and the accelerator concentrations (percentage Na2HPO4) in cement liquid were varied. For Biocement H there was no combination of L/P ratio and percentage Na2HPO4 for which all clinical requirements were satisfied. However, there was an area of full compliance for Biocements B1 and B2, of which that for B1 was the largest. Therefore, Biocement B1 may be applied in clinical situations as those in orthopaedics, plastic and reconstructive surgery and oral and maxillofacial surgery, even when early contact with blood is inevitable.

Apatites↗

PubMed1997

Antibiotic delivery system using bioactive bone cement consisting of Bis-GMA/TEGDMA resin and bioactive glass ceramics.

A novel drug delivery system containing cephalexin (CEX) as a model drug using a new bioactive bone cement consisting of 15% bisphenol-alpha-glycidyl methacrylate (Bis-GMA), 15% triethylene-glycol dimethacrylate (TEGDMA) resin and 70% apatite- and wollastonite-containing glass-ceramic (A-W GC) powder was investigated. A-W GC powder containing CEX powder hardened within 5 min after mixing with Bis-GMA/TEGDMA resin, and furthermore its compressive strength was expected to be higher than that of polymethylmethacrylate cement. In vitro CEX release from bioactive bone cement pellets in a simulated body fluid at pH 7.25 and 37 degrees C continued for more than 2 weeks. The drug release rate increased with increasing amount of CEX in the mixture. All of the drug release profiles followed the Higuchi equation at the initial stage, but not at later stages. As hydroxyapatite was precipitated out on the cement surface, the drug release rate decreased. These results suggest that the CEX release rate from bioactive bone cement could be controlled by varying the amount of drug in the cement system.

Biomechanical Phenomena↗

PubMed1999

Synthesis and properties of hydroxyapatite/poly-L-lactide composite biomaterials.

Calcium hydroxyapatite (HAp) and poly-L-lactide (PLLA) were synthesized chemically. The obtained HAp was of high purity and, after special thermal treatment, of high crystallinity as well. Synthesis of PLLA was performed using L-lactide as a monomer and nontoxic initiator. In this way a polymer of large molar weight (about 400,000) was obtained. The HAp and PLLA obtained were used as constituents of the HAp/PLLA composite biomaterial, a potential material for implants. The composite was obtained by mixing completely dissolved PLLA with granules of HAp. The composite was compacted by cold and hot pressing at pressures of 49.0-490.5 MPa and temperatures of 20-184 degrees C. The material obtained at optimum process parameters had a density of 99.6% and compressive strength of 93.2 MPa.

Biocompatible Materials↗

PubMed1999

Influence of glass composition on the properties of glass polyalkenoate cements. Part I: influence of aluminium to silicon ratio.

Hydrolysis of aluminium-oxygen-silicon bonds is thought to be the first step in the setting reaction of polyalkenoate cements and the aluminium to silicon ratio of the glass is widely believed to be a dominant factor determining cement properties. The properties of glass polyalkenoate cements based on the generic glass composition (6 + X)SiO2 x (4 - X)Al2O31.5P2O5 x 4CaOCaF2 with varying aluminium to silicon ratio were studied. Setting and working times of the cement pastes, compressive strength, un-notched fracture strength, Young's modulus, fracture toughness and toughness were evaluated for the cements. In contrast to previous studies the aluminium to silicon ratio was not found to influence the cement properties significantly. The high phosphorus content of the glasses studied is thought to reduce the influence of the aluminium to silicon ratio of the glass, as a result of phosphorus locally charge balancing four coordinate aluminium ions in the glass network, as well as providing an additional mechanism of degradation in the form of hydrolysable phosphorus-oxygen bonds.

Aluminum Compounds↗

PubMed2000

Influence of glass composition on the properties of glass polyalkenoate cements. Part IV: influence of fluorine content.

The influence of fluorine content of the glass in a series of glasses based on: 4.5SiO2-3.0Al2O3-1.5P2O5-(5.0-X)CaO-XCaF2 was investigated on their cement formation with poly(acrylic acid). Increasing the fluorine content of the glass was found to reduce the glass transition temperature, as a result of fluorine replacing bridging oxygens by non-bridging fluorines. Working and setting times of the cement pastes reduced with increasing fluorine content of the glass. Compressive strength and Young's moduli increased with fluorine content initially and then remained approximately constant. Fracture toughness, toughness and un-notched fracture strength were not significantly influenced by fluorine content. The results are consistent with fluorine simultaneously disrupting the glass network and reducing the basicity of the glass.

Fluorine↗

PubMed2000

The effects of mitomycin-C and stenting on airway wound healing after laryngotracheal reconstruction in a pig model.

OBJECTIVE: To assess the effects of mitomycin-C (MTC) and endoscopic stenting on airway wound healing after laryngotracheal reconstruction. DESIGN: A prospective, blinded, randomized controlled animal study. SUBJECTS: Twenty-six domestic pigs (Sus scrofula) divided into four groups. INTERVENTIONS: Each animal underwent single-stage laryngotracheal reconstruction (SSLTR) with auricular cartilage grafts and stenting. Group 1 animals were sacrificed on postoperative day 3, and group 2 animals on postoperative day 7. On postoperative day 7, groups 3 and 4 underwent endoscopy, stent removal, and application of MTC (0.5 mg/ml) or placebo (normal saline). Group 3 animals were sacrificed on postoperative day 14, group 4 animals on day 21. Two additional animals from each experimental group were prepared for election microscopy studies. Segments of reconstructed airway were evaluated grossly and histologically for all animals. Additional tonometric evaluation was performed on two stents to determine their compressive strength. MAIN OUTCOME MEASURES: Healing, reepithelization, graft incorporation, and airway diameter. RESULTS: Two-thirds of the animals demonstrated some degree of stent collapse on endoscopy. Granulation tissue formation was seen in all animals, and resolved with stent removal. No animal experienced airway compromise due to granulation tissue formation. Stenting was seen to induce a submucosal fibroproliferative response and scarring, with loss of normal glandular architecture, in all animals. MTC did not affect the acute inflammatory response, reepithelization of the graft site, or formation of the subepithelial fibroproliferative response. MTC treated animals, however, demonstrated better graft incorporation with fibrocartilage proliferation of the graft. Untreated animals demonstrated liquefactive necrosis of the graft, without evidence of neochondrification of the graft. CONCLUSIONS: The pig airway is an adequate model of wound healing following SSLTR and stenting. Metallic ballon expandable stents can be successfully used following SSLTR, allowing for immediate postoperative extubation. However, the formation of a submucosal fibroproliferative response and mucosal scarring seen in our study raises some concerns with the current stent design. Before stenting is widely clinically applied, the optimum stent design needs to be developed. Finally, MTC seems to prevent the liquefactive necrosis of SSLTR grafts and promote neochondrification, allowing improved graft incorporation. Further studies are needed to asses the long-term effects of MTC on healing and restenosis, and its effects on cartilage growth and formation, following SSLTR.

Animals↗

PubMed2001

The use of chitosan gels as matrices for electrically-modulated drug delivery.

This study evaluated and characterized the use of chitosan gels as matrices for electrically modulated drug delivery. Chitosan gels were prepared by acetylation of chitosan and subsequently hydrated to facilitate further studies. After determining the degree of deacetylation, hydrated and unhydrated gel formulations were characterized for their microviscosity and compression strength. In the electrification studies, gel mass variation, surface pH changes, and later, release-time profiles for neutral (hydrocortisone), anionic (benzoic acid), and cationic (lidocaine hydrochloride) drug molecules from hydrated chitosan gels were monitored in response to different milliamperages of current as a function of time. Hydrated gels had very similar microviscosity while exhibiting differences in the gel strength, results which are not inconsistent as they pertain to different aspects of the gel. The cumulative gel mass loss and rate of gel mass loss increased with an increase in the milliamperage (mA) of the applied current. Gel syneresis - principally involving electroosmosis and gel collapse - was pronounced, particularly at higher mAs and for chitosan gels with lower degrees of acetylation. The surface pH values of the gels were lower at the anode and higher at the cathode, in accordance with reports in the literature. The release of the model drugs from the gel matrix was in the order benzoic acid>hydrocortisone>lidocaine, which is consistent with the electrokinetically competing forces that are involved in these gels. Adequate characterization of electrical effects on formulation matrices, such as chitosan gels, is critical to the development of effective and reliable electrically modulated drug delivery systems.

Benzoic Acid↗

PubMed1999

Application of bis-eugenol to a zinc oxide eugenol cement.

OBJECTIVES: To assess the usefulness of dimerized eugenol (bis-eugenol) in dentistry, the physical properties of zinc oxide eugenol cement (ZOE) with bis-eugenol and the cytotoxicity of bis-eugenol were studied. METHODS: Setting time, compressive strength, solubility and disintegration of ZOE cement with bis-eugenol according to the specifications of JDMAS315 were evaluated. The cytotoxicity of bis-eugenol and eugenol toward two different cell types, HGF (a primary culture of human gingival fibroblast) and HSG (a human epidermoid carcinoma cell line derived from a salivary gland) was evaluated by the MTT test and in terms of cell survival. RESULTS: Addition of bis-eugenol to ZOE did not decrease the physical properties when employed at the ratio of 9:1 or 6:1 (liquid ND:bis-eugenol, w/w). Bis-eugenol was less toxic than eugenol in the cell culture tests. CONCLUSIONS: The results of this assay demonstrated that bis-eugenol is useful in ZOE.

Adenocarcinoma↗

PubMed2000

Solidification and stabilization of asbestos waste from an automobile brake manufacturing facility using cement.

Currently, the generated brake lining waste dust, which contains asbestos as its major component, is disposed of into a secure landfill without any additional treatment. As an alternative to this, solidification/stabilization (S/S) disposal of the dust was investigated using Portland cement alone and Portland cement mixed with activated carbon (AC), as the binders. Toxicity Characteristics Leaching Procedure (TCLP) results on the solidified matrix showed that cement was able to immobilize the heavy metals, Ba, Zn, Cr, Pb, Cu and Fe, to within the limits set by the US EPA for TCLP. Addition of AC to the cement reduced the leaching of heavy metals by an additional 4-24% compared to cement alone. The pH of the TCLP leachate extracted from virgin cement, and from dust treated with cement with or without AC was found to increase to 10.9-12.5 as opposed to an initial value of 4.93 for the TCLP extract for the untreated dust. Results of ANS 16.1 (modified) leach protocol revealed that Ba in cement-treated samples showed the highest leach rate, followed by Zn, Pb, Cr, Cu and Fe. The leach rate of heavy metals decreased with progress in time. Cement mixed with AC exhibited similar leach characteristics, however, the leach rate was lower. The linear relationship between the cumulative fraction leached (CFL) and the square root of leaching time in all cement-based samples indicate that a diffusional process is the controlling transport mechanism for the leaching of the heavy metals. The obtained Leachability Indices (L(i)) of 7.6-9.1 and 8.3-9.5 for cement and cement with AC, respectively, were low but exceeded the guidance value of 6, which clearly indicates that all the heavy metals studied are retained well within solid matrices. Cement-based S/S hardening times increased from 30 to 96 h as the dust content increased from 40 to 70 wt.%. The resulting solid matrices exhibited a compressive strength ranging from 1 to 12 MPa, which was well above the specified limit of 414 kPa for such matrices. An economic analysis indicates that the disposal costs for the dust in the only available secure landfill would increase by 40.3% if one were to go for the cement S/S option. Addition of AC to the cement would escalate this by an additional 43.8%. Although the S/S of brake lining dust using cement effectively immobilized the heavy metals of concern, cost considerations may hinder the commercial adaptation of this technique for waste disposal unless new regulatory demands are implemented.

Asbestos↗

PubMed2001

Properties of Portland cement--stabilised MSWI fly ashes.

In the present paper, the properties of Portland cement mixtures containing fly ashes (FA) collected at four different Italian municipal solid waste incineration (MSWI) plants were investigated. In particular, physical/mechanical characteristics (setting time, unconfined compressive strength (UCS) and shrinkage/expansion), as well as the acid neutralisation behaviour of the solidified products were considered. The FA composition, revealing enrichment in heavy metals, chlorides and sulphates, significantly altered the hydration behaviour of Portland cement. Consequently, for some of the investigated FA the maximum allowable content for the mixtures to achieve appreciable mechanical strength was 20 wt.%. Even at low FA dosages setting of cement was strongly delayed. In order to improve the properties of FA/cement mixtures, the use of additives was tested.Moreover, the acid neutralisation capacity (ANC) of the solidified products was evaluated in order to assess the ability of the matrix to resist acidification, and also to provide information on hydration progression, as well as on heavy metal release under different pH conditions. Comparison of the results from the present work with previous studies carried out on spiked mixtures lead to the conclusion that the mechanical properties of the stabilised FA could not be predicted based on the effect exerted by heavy metals and anions only, even when the dilution effect exerted on cement was taken into account. It was likely that a major role was also played by alkalis, which were present in the FA at much higher concentrations than in cement.

Chlorides↗

PubMed2000

Soil mixing of stratified contaminated sands.

Validation of soil mixing for the treatment of contaminated ground is needed in a wide range of site conditions to widen the application of the technology and to understand the mechanisms involved. Since very limited work has been carried out in heterogeneous ground conditions, this paper investigates the effectiveness of soil mixing in stratified sands using laboratory-scale augers. This enabled a low cost investigation of factors such as grout type and form, auger design, installation procedure, mixing mode, curing period, thickness of soil layers and natural moisture content on the unconfined compressive strength, leachability and leachate pH of the soil-grout mixes. The results showed that the auger design plays a very important part in the mixing process in heterogeneous sands. The variability of the properties measured in the stratified soils and the measurable variations caused by the various factors considered, highlighted the importance of duplicating appropriate in situ conditions, the usefulness of laboratory-scale modelling of in situ conditions and the importance of modelling soil and contaminant heterogeneities at the treatability study stage.

Chemical Phenomena↗

PubMed2003

Tibial plateau stress fracture: a complication of unicompartmental knee arthroplasty using 4 guide pinholes.

Unicompartmental knee arthroplasty has gained popularity recently as a treatment for unicompartmental tibiofemoral non inflammatory arthritis. Tibial plateau stress fracture after unicompartmental knee arthroplasty (UKA) through guide pin holes placed in the proximal tibia has not been previously reported. In each case in this report, the compressive strength of the proximal tibia was reduced by the drilling of multiple holes for the placement of guide pins and holes for the lugs of the tibia component resulting in fracture through these holes between 3 and 18 weeks (median 8 weeks) post-operatively. In at least one case, the medial tibial cortex was violated by one pin. All cases required revision total knee arthroplasty (TKA). It is intuitive to caution against the use of multiple guide holes in the proximal tibia in UKA. If 3 or more hole pins are deemed necessary, surgeons must be aware of the potential for stress fracture and monitor patients accordingly. Peripheral pins that infract the medial tibial cortex should also be avoided.

Aged↗

PubMed1987

Vacuum mixing of acrylic bone cement.

A partial-vacuum (500-550 mmHg), slow-speed (2 Hz) system for optimal blending of the liquid and powder components of Simplex-P acrylic bone cement was developed to eliminate five different sources of porosity observed with x-ray during the course of cement preparation and specimen fabrication. The vacuum mixing system produces set specimens of less than 1% porosity that have significant improvements over specimens prepared with conventional mixing in the mechanical properties of tensile and compressive strength and uniaxial tensile fatigue life. Hence, a much stronger cement can be available in surgery without any change in original chemical composition.

Bone Cements↗

PubMed2001

Leaching characteristics of paraffin waste forms generated from Korean nuclear power plants.

Leaching tests of paraffin waste forms including boric acid, cobalt, strontium and cesium were performed to investigate the leaching characteristics of paraffin waste forms which had been generated in Korean nuclear power plants. The leaching tests were conducted according to ANSI/ANS-16.1 test procedure and the cumulative fractions leached (CFLs) of boric acid, cobalt, strontium and cesium were obtained. The compressive strength before and after the leaching test was measured for various waste forms with different mixing ratios of boric acid to paraffin. It was observed that boric acid and other nuclides immobilized within paraffin waste forms were congruently released and the leaching rates were influenced by reacted layer depth as the dissolution reaction progressed. A shrinking core model based on the diffusion-controlled dissolution kinetics was developed in order to simulate the test results. The CFLs and the leaching rates were well expressed by the shrinking core model and the cross-sectional view of specimen after the test demonstrated the applicability of this model with the shrinking dissolution front to the leaching analysis of paraffin waste forms.

Boric Acids↗

PubMed2001

Synthetic aggregates from combustion ashes using an innovative rotary kiln.

This paper describes the use of a number of different combustion ashes to manufacture synthetic aggregates using an innovative rotary 'Trefoil' kiln. Three types of combustion ash were used, namely: incinerated sewage sludge ash (ISSA); municipal solid waste incinerator bottom ash (MSWIBA-- referred to here as BA); and pulverised fuel ash (Pfa). The fine waste ash fractions listed above were combined with a binder to create a plastic mix that was capable of being formed into 'green pellets'. These pellets were then fired in a Trefoil kiln to sinter the ashes into hard fused aggregates that were then tested for use as a replacement for the natural coarse aggregate in concrete. Results up to 28 days showed that these synthetic aggregates were capable of producing concretes with compressive strengths ranging from 33 to 51 MPa, equivalent to between 73 and 112% of that of the control concrete made with natural aggregates.

Conservation of Natural Resources↗

PubMed2001

Immobilisation of PAH in waste materials.

This paper gives an overview of the results of a research project into the possibilities of immobilising polycyclic aromatic hydrocarbons (PAH), that are present in waste materials. The results show that with hydraulic binders the waste materials can be solidified. The PAH do still leach to a relatively high extent. However, this PAH leaching can be decreased by more than a factor 10 by means of the addition of a specific additive. The immobilisation product fulfils technological requirements for the use as a road base construction material, such as compressive strength.

Construction Materials↗

PubMed2001

Stabilization of chloro-organics using organophilic bentonite in a cement-blast furnace slag matrix.

The application of cement-based stabilisation/solidification treatment to organic-containing wastes is made difficult by the adverse effect of organics on cement hydration. The use of organophilic clays as pre-solidification adsorbents of the organic compounds can reduce this problem because of the high adsorption power of these clays and their compatibility with the cementitious matrix. This work presents an investigation of the effect on hydration kinetics, physico-mechanical properties and leaching behaviour of cement-based solidified waste forms containing 2-chlorophenol and 1-chloronapthalene adsorbed on organophilic bentonites. These were prepared by cation exchange with benzyldimethyloctadecylammonium chloride and trimethyloctadecylammonium chloride. The binder was a 30% pozzolanic cement, 70% granulated blast furnace slag mixture. Several binder-to-bentonite ratios and different concentrations of the organics on the bentonite were used. Kinetics of hydration were studied by measurement of chemically bound water and by means of thermal and calorimetric analyses. Microstructure and other physico-mechanical properties of the solidified forms were studied by means of mercury intrusion porosimetry, scanning electron microscopy and unconfined compressive strength measurement. Leaching was checked by two different leaching tests: one dynamic, on monolithic samples, and the other static, on powdered samples. This study indicates that the incorporation of the organic-loaded bentonite in the binder matrix causes modifications in the hardened samples by altering cement hydration. The effects of the two organic contaminants are differentiated.

Adsorption↗