A new hydroxyapatite-based biocomposite for bone replacement

Since the 1970s, various types of ceramic, glass and glass–ceramic materials have been proposed and used to replace damaged bone in many clinical applications. Among them, hydroxyapatite (HA) has been successfully employed thanks to its excellent biocompatibility. On the other hand, the bioactivity of HA and its reactivity with bone can be improved through the addition of proper amounts of bioactive glasses, thus obtaining HA-based composites. Unfortunately, high temperature treatments (1200 °C ÷ 1300 °C) are usually required in order to sinter these systems, causing the bioactive glass to crystallize into a glass–ceramic and hence inhibiting the bioactivity of the resulting composite. In the present study novel HA-based composites are realized and discussed. The samples can be sintered at a relatively low temperature (800 °C), thanks to the employment of a new glass (BG_Ca) with a reduced tendency to crystallize compared to the widely used 45S5 Bioglass®. The rich glassy phase, which can be preserved during the thermal treatment, has excellent effects in terms of in vitro bioactivity; moreover, compared to composites based on 45S5 Bioglass® having the same HA/glass proportions, the samples based on BG_Ca displayed an earlier response in terms of cell proliferation.     

Investigation of polymerizability of ω-alkenyldioxolanes with α-olefins and alkyl vinyl ethers by modified ziegler-natta catalysts

Results are presented of an investigation on the polymerizability of functional olefins, such as allylisopropylidene glycerol (AIPG) and undecenylisopropylidene glycerol (UIPG), in the presence of conventional and modified Ziegler-Natta catalysts based on TiCl₄ or MgCl₂-supported titanium and triisobutylaluminum, hexaisobutyltetraalumoxane, or bisdiethyl-aluminum sulfate. Homopolymerization experiments were performed on AIGP at temperatures of -78, 25, and 50°C; only these at 50°C provided appreciable amounts of polymeric materials insoluble in methanol, whose structures comprise monomeric units derived from opening both dioxolane rings and vinyl double bonds. In spite of all attempts and precautions, polymerization experiments carried out on mixtures of the functional olefins AIPG and UIPG with either 4-methyl-1-pentene or isopropyl vinyl ether gave rise to the homopolymers of the nonfunctional α-olefin and of the vinyl ether, without any appreciable amount of either copolymers or homopolymers of the dioxolane containing monomers. © 1996 John Wiley & Sons, Inc.     

Rapid and direct lodine value and saponification number determination of fats and oils by attenuated total reflectance/fourier transform infrared spectroscopy

A simple, rapid and reproducible method of determining the iodine value (IV) and saponification number (SN) for fats and oils was developed with an attenuated total reflectance/Fourier transform infrared spectrometer and commercially available triglycerides as calibration standards. Partial least squares was used to determine the spectral regions correlating with the known chemical IV and SN values, and the calibration set was augmented with additional standards generated by spectral co-adding techniques. The calibration model obtained was used to analyze commercially available fats and oils with a wide range of IV and SN values, and the results were compared to the values obtained by American Oil Chemists’ Society methods. With the spectrometer calibrated and programmed, IV and SN results could be obtained within 2–3 min per sample, a major improvement over conventional wet chemical methods.     

Amphiphilic Pentablock Copolymers Prepared from Pluronic and ε-Caprolactone by Enzymatic Ring Opening Polymerization

Amphiphilic copolymers are appealing materials because of their interesting architecture and tunable properties. In view of their application in the biomedical field, the preparation of these materials should avoid the use of toxic compounds as catalysts. Therefore, enzymatic catalysis is a suitable alternative to common synthetic routes. Pentablock copolymers (CUC) were synthesized with high yields by ring-opening polymerization of ε-caprolactone (ε-CL) initiated by Pluronic (EPE) and catalyzed by Candida antarctica lipase B enzyme. The variables to study the structure–property relationship were EPEs’ molecular weight and molar ratios between ε-CL monomer and EPE macro-initiator (M/In). The obtained copolymers were chemically characterized, the molecular weight determined, and morphologies evaluated. The results suggest an interaction between the reaction time and M/In variables. There was a correlation between the differential scanning calorimetry data with those of X-ray diffraction (WAXD). The length of the central block of CUC copolymers may have an important role in the crystal formation. WAXD analyses indicated that a micro-phase separation takes place in all the prepared copolymers. Preliminary cytotoxicity experiments on the extracts of the polymer confirmed that these materials are nontoxic.     

Understanding the Selectivity Mechanism of the Human Asialoglycoprotein Receptor (ASGP-R) toward Gal- and Man-type Ligands for Predicting Interactions with Exogenous Sugars

A practical approach for addressing the computer simulation of protein-carbohydrate interactions is described here. An articulated computational protocol was set up and validated by checking its ability to predict experimental data, available in the literature, and concerning the selectivity shown by the Carbohydrate Recognition Domain (CRD) of the human asialoglycoprotein receptor (ASGP-R) toward Gal-type ligands. Some required features responsible for the interactions were identified. Subsequently the same protocol was applied to monomer sugar molecules that constitute the building blocks for alginates and ulvans. Such sugar polymers may supply a low-cost source of rare sugars with a potential impact on several industrial applications, from pharmaceutical to fine chemical industry. An example of their applicative exploitation could be given by their use in developing biomaterial with adhesion properties toward hepatocytes, through interaction with the ASGP-R. Such a receptor has been already proposed as a target for exogenous molecules, specifically in the case of hepatocytes, for diagnostic and therapeutic purposes. The DOCK5.2 program was used to search optimal locations of the above ligands of interest into CRD binding site and to roughly estimate interaction energies. Finally, the binding ΔG of theoretical protein-ligand complexes was estimated by using the DelPhi program in which the solvation free energy is accounted for with a continuum solvent model, by solving the Poisson-Boltzmann equation. The structure analysis of the obtained complexes and their ΔG values suggest that one of the sugar monomers of interest shows the desired characteristics.     

Coal combustion: Correlation between surface area and thermogravimetric analysis data

A series of coals of different rank has been characterized by surface area measurements performed by sorption of both nitrogen and carbon dioxide. While the data obtained with nitrogen do not discriminate among the different coal samples, those based on carbon dioxide sorption do give a significant distinction between the samples. This technique has also been applied to the determination of the surface area of coal samples quenched after stepwise combustion in air atmosphere. It has been possible to establish a useful correlation between the latter data and the burning profile measured by derivative thermogravimetry. The aim of the present study was to gain a better understanding of the coal combustion process on a laboratory scale which could reasonably be extended to combustion plants. The results presented are relevant to some of the multivalent aspects inherent in the coal combustion process and some valuable information has been gained in respect of characterization of solid fuels.     

Localized corrosion of (lean) duplex stainless steels in immersion units of urban wastewater treatment plants

With lower alloying cost and higher mechanical properties, lean duplex stainless steels can be an alternative to the more commonly used austenitic stainless steels. However, these alloys are still not the preferred choice, probably due to a lack of field experience. A study was thus initiated in view of defining the limits of use of selected (lean) duplexes for urban wastewater treatment units. The present paper shows the localized corrosion performance of selected lean duplexes in chloride contaminated solutions. The results are compared with austenitic S30403 and S31603 and with the more standard duplexes S82441 and S32205. The effect of welding was also investigated. Exposures in field municipal wastewater plants were conducted for 1 year in low and high chloride content units. The results show that lean duplexes S32101 and S32202 can be used as alternatives to S30403 and S31603 in low chloride electrolytes. At 500 ppm of chloride content, duplex stainless steel S32304 showed better corrosion resistance than S30403 and S31603. For higher chloride contents (1000 ppm and above) the standard duplexes S82441 and S32205 shall be preferred.     

Diphenyl-Methane Based Thyromimetic Inhibitors for Transthyretin Amyloidosis

Thyromimetics, whose physicochemical characteristics are analog to thyroid hormones (THs) and their derivatives, are promising candidates as novel therapeutics for neurodegenerative and metabolic pathologies. In particular, sobetirome (GC-1), one of the initial halogen-free thyromimetics, and newly synthesized IS25 and TG68, with optimized ADME-Tox profile, have recently attracted attention owing to their superior therapeutic benefits, selectivity, and enhanced permeability. Here, we further explored the functional capabilities of these thyromimetics to inhibit transthyretin (TTR) amyloidosis. TTR is a homotetrameric transporter protein for THs, yet it is also responsible for severe amyloid fibril formation, which is facilitated by tetramer dissociation into non-native monomers. By combining nuclear magnetic resonance (NMR) spectroscopy, computational simulation, and biochemical assays, we found that GC-1 and newly designed diphenyl-methane-based thyromimetics, namely IS25 and TG68, are TTR stabilizers and efficient suppressors of TTR aggregation. Based on these observations, we propose the novel potential of thyromimetics as a multi-functional therapeutic molecule for TTR-related pathologies, including neurodegenerative diseases.     

Weaving patterns of lines and line segments in space

Aweaving W is a simple arrangement of lines (or line segments) in the plane together with a binary relation specifying which line is above the other. A system of lines (or line segments) in 3-space is called arealization ofW, if its projection into the plane isW and the above-below relations between the lines respect the specifications. Two weavings are equivalent if the underlying arrangements of lines are combinatorially equivalent and the above-below relations are the same. An equivalence class of weavings is said to be aweaving pattern. A weaving pattern isrealizable if at least one element of the equivalence class has a three-dimensional realization. A weaving (pattern)W is calledperfect if, along each line (line segment) ofW, the lines intersecting it are alternately above and below. We prove that (i) a perfect weaving pattern ofn lines is realizable if and only ifn 3, (ii) a perfect m byn weaving pattern of line segments (in a grid-like fashion) is realizable if and only if min(m, n) 3, (iii) ifn is sufficiently large, then almost all weaving patterns ofn lines are nonrealizable.Jànos Pach has been supported in part by Hungarian NFSR Grant 1812, NSF Grant CCR-8901484, and the Center for Discrete Mathematics and Theoretical Computer Science (DIMACS), a National Science Foundation Science and Technology Center, under NSF Grant STC88-09648. Richard Pollack has been supported in part by NSA Grant MDA904-89-H-2030, NSF Grants DMS-85-01947 and CCR-8901484, and DIMACS. Emo Welzl has been supported in part by the ESPRIT II Basic Research Actions Program of the EC under Contract No. 3075 (project ALCOM) and DIMACS.     

Hybrid copolymerization of alkyl vinyl ethers with glycidyl ethers

Homopolymerization and copolymerization experiments of isobutyl and dodecyl vinyl ether with propylene oxide, and some glycidyl ethers have been carried out by using both conventional cationic initiators (BF₃, BF₃·OEt₂) and 4-chlorophenyldiazonium tetrafluoborate as cationic photoinitiator. Conventional polymerization experiments performed under vacuum at low and room temperature gave rise to a mixture of the two homopolymers, indicating that the epoxide and vinyl ethers are incompatible with respect to chemical reactivity and that apparently no hybrid copolymerization occurs. Analogous results were obtained in parallel photoinitiated polymerization experiments.