The effect of Zirconia/Yttria/Silver substitutions on mechanostructure and cell viability of the synthesized bioceramic bone grafts

Hydroxyapatite (HA) based biografts were synthesized by substitution of Zirconia (Zr), Yttria (Y₂O₃) and Silver (Ag) using the sol-gel method. Fabricated bone grafts (H40ZrYt and H50Yt10) were compared with a control biograft. The effects of Zr and Y₂O₃ and Ag additions on the morphological, mechanical and cell viability of the synthesized biografts were analyzed. The biografts were characterized by X-ray Diffractometer (XRD) and Scanning Electron Microscope (SEM). All biografts were then embedded into the drilled holes (D=3.2 mm) in rabbit femurs. The rabbits were then sacrificed after twelve weeks. Three-point bending (3-PB) tests were conducted on defected and grafted regions. Flexural strength values were found to be 347, 149 and 180 MPa, for the H40ZrYt, H50Yt10 and the control/commercial graft, respectively. Cell viability results indicated that the percentage viability ratios slightly increased after the substitution of Ag into the H50Yt10 biograft at 0.1 and 0.3 µg/ml concentrations and into the H40ZrYt biograft at a 0.1 µg/ml concentration. Although the cell viability was a bit lower in the H50Yt10 graft, the H40ZrYt graft achieved better results compared to the counterpart grafts. Furthermore, the hardness of both of the novel fabricated grafts were found to be higher than the control/commercial graft, however, as the flexture strength of H40ZrYt was higher but H50Yt10 was lower than the control/commercial graft.     

Blend composition dependence of the compatibilizing efficiency of graft copolymers for immiscible polymer blends

This work is concerned with the dependence of the compatibilizing efficiency of graft copolymers on the composition of immiscible polymer blends. A series of graft copolymers of polystyrene (PS) and polyamide 6 (PA6), denoted as PS‐g‐PA6, with different molecular structures were used as compatibilizers. The PS‐g‐PA6 was more efficient for the PS/PA6 (80/20) blend than for the PS/PA6 (20/80) one, indicating that a graft copolymer whose backbone and grafts match the matrix and the disperse phase polymers, respectively, has higher compatibilizing efficiency. This is in disagreement with the literature. Moreover, whatever the blend composition, for PS‐g‐PA6 graft copolymers with the same backbone and the same number of grafts per backbone, the longer the grafts, the higher their compatibilizing and stabilizing efficiency; for a given backbone/graft mass ratio, the longer the grafts and concomitantly the smaller the number of grafts per backbone, the higher the compatibilizing and stabilizing efficiency of the graft copolymer. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

细胞工厂培养沙鼠肾原代细胞制备肾综合征出血热灭活疫苗

目的用细胞工厂代替转瓶培养沙鼠肾原代细胞,制备肾综合征出血热(HFRS)疫苗,减少原代沙鼠用量,提高产量。方法在细胞工厂内培养沙鼠肾原代细胞,以15L转瓶培养作对照,比较两种容器内细胞生长及收获的病毒滴度和抗原含量;病毒液经超滤浓缩后,采用Sepharose-4FF介质色谱纯化,并进行各项检定。结果细胞工厂只需接种转瓶培养所需1/3量的沙鼠肾细胞,就能在同期与转瓶细胞数量相当。接种病毒后,转瓶中的细胞在收获第5次后已脱落(10～20)%,而细胞工厂中的细胞几乎没有脱落;收获至第9次时,细胞工厂中的细胞脱落率才达20%;每次收获的病毒液病毒滴度和抗原含量均较高,且稳定在一定范围。浓缩纯化后,各项检定指标均合格。结论使用细胞工厂培养沙鼠肾原代细胞制备HFRS疫苗不仅提高了收率,而且减少了培养空间,降低了污染,可替代转瓶大规模生产HFRS疫苗。     

Studies in the graft copolymerization of vinyl monomers on cellulosic materials

Graft copolymerization of acrylonitrile, methyl methacrylate, and vinyl acetate on bleached holocellulose initiated by ceric ions in aqueous medium was studied at 29°C. The extent of graft copolymer formation was poly(methyl methacrylate) > polyacrylonitrile > poly(vinyl acetate), indicating the influence of polarity of monomer on graft copolymerization. It was found that, although the molecular weights of the grafted polyacrylonitrile copolymer were lower than the values obtained for poly(methyl methacrylate), the latter was less frequently incorporated on the cellulosic backbone polymer than the polyacrylonitrile grafts. The marked reductions in graft level associated with thiolation of the cellulosic material suggest that hydrogen abstraction reactions from carbon atom carrying hydroxyl groups may not be important in graft copolymer formation.     

Effect of lignin in graft copolymerization of methyl methacrylate on cellulose by ceric ion

The effect of lignin contained in cellulosic materials in graft copolymerization of methyl methacrylate on such materials using ceric ion as initiator was studied. It was found that the percent grafting and the average molecular weight of grafts became lower in samples having a larger lignin content but the number of grafts formed increased proportionally up to lignin content of about 2.5%. Ceric ion reacted at a faster rate with lignin than with cellulose in wood pulp, and the results indicating that the active sites formed on lignin by oxidation with ceric ion accelerate the formation of grafts and increase the number of grafts were obtained. But on the other hand, the active sites participated in the termination reaction of the growing graft polymer radicals to cause lowering of the average molecular weight of grafts.     

Studies on the ability of cellulosic materials to initiate graft copolymerization

The activity to initiate graft copolymerization was investigated for various cellulose samples. Oxidation of the sample with hydrogen peroxide or sodium hypochlorite indicated a remarkable increase in the per cent grafting as well as the number of grafts. This phenomenon must be attributed to the formation of special reactive groups in cellulosic materials. However, the treatment with hot water caused a definite decrease in the per cent grafting or the number of grafts for the graft copolymerization on the sample, indicating a lower activity to initiate graft copolymerization. Accordingly, the reactive groups, once formed on the sample by oxidation, seemed to be easily decomposed by hot water. The ferric ion adsorbed on cellulose increased the per cent grafting and accelerated the formation of grafts, and the contribution of metallic ions to the initiation was recognized as one of the important factors of graft copolymerization.     

Effect of degradative treatments on cotton graft copolymers. Part V. Behavior of poly(acrylamide)-cotton graft copolymers toward acid treatments

Polyacrylamide (Aam)-cotton graft copolymers having 9, 14.5, and 20% graft were synthesized using ferrous cellulose thiocarbonate-hydrogen peroxide redox system. These copolymers as well as ungrafted and initiator-treated cottons were subjected to acid treatments (0.5 N HCl) at 40°, 60°, and 80°C for 15-90 minutes. Hydrolytic susceptibility of the five substrates was assessed by monitoring carboxylic groups, copper, number, nitrogen content (in case of the copolymers), and tensile strength. Results obtained concluded that the copolymers exhibit higher resistance to acid hydrolysis than the ungrafted and initiator-treated cottons. This was explained in terms of involvement of the ? CONH₂ groups of the graft in an interaction with HCl.     

The isolation and characterisation of grafts from glass surfaces and their immiscibility with homopolymer

A procedure for photochemically detaching, isolating and characterising grafts (produced by a method developed previously by the authors) from glass surfaces is described. Preliminary results indicate that the molecular weights and molecular weight distributions can be varied through control of the kinetics of graft formation; our previous studies are seen to have produced a high surface coverage of grafts of high molecular weight. A thermodynamic argument is developed to explain the immiscibility of grafts with free homopolymer for high surface coverage by grafts from which it is seen that the immiscibility is entropy-driven. Comparisons are drawn between our previous studies and relevant studies by other workers and apparent anomolies are explained.     

Relationship between photo-induced scission of cellulose chains and graft copolymerization

Studies were carried out on the relationship between the scission of cellulose chains and the initiation of photo-induced graft copolymerization of methyl methacrylate. The photo-induced scission of cellulose chains was sharply accelerated by the application of irradiation with light shorter than 300 nm, the use of photosensitizer such as ferric ion, the swelling of cellulose samples, and so on. On the other hand, the scission reaction was markedly suppressed by blocking the carbonyl groups contained in the samples by oximation. A linear increase in the number of grafts was indicated with the number of scissions of cellulose chains in the graft copolymerization. However, a number of scissions not contributing to any formation of grafts was also noticed during the induction period of copolymerization. The factors such as short wavelength light, photosensitizer, and swelling, which contribute to the rises in the rate of graft formation and the scission of cellulose chains, worked also to shorten the induction period. As might be expected, appreciable increases of per cent grafting and shortening of induction period were achieved by preirradiation the cellulose samples with light. From the above, it was concluded that the scission of cellulose chains should be a main factor for the initiation of graft copolymerization in the system.     

New block graft of α-TCP with silicon in critical size defects in rabbits: Chemical characterization, histological, histomorphometric and micro-CT study

The study characterized Si-containing α-TCP blocks designed for graft application and examined their osseintegration in rabbit tibiae using histological, histomorphometric and micro-CT techniques. The block grafts were inserted into the critical size defects of 15 rabbits, using both tibiae, and examined at 15, 30 and 60 days. Results showed that new bone grew in direct contact with the block grafts and that the presence of silicon improved the stability and osseointegration of the material. Silicon doped TCP grafts showed enhanced mesenchymal cell differentiation and increased osteoblast activity compared with α-TCP. Furthermore, blocks with the highest concentration of silicon (3% C₂S, 97% TCP) showed better dimensional stability and increased bone-to-implant contact values after 60 days (67.6 ± 5% lateral bone contact and 57.3 ± 3% base bone contact). None of the implanted materials were seen to produce any adverse inflammation. The study found that α-TCP ceramic blocks containing 3% C₂S, offer good bioactivity, biocompatibility and allow new bone growth around the block and within the graft body, making this an ideal block graft material.     

Temporal Roles of Platelet and Coagulation Pathways in Collagen- and Tissue Factor-Induced Thrombus Formation

In hemostasis and thrombosis, the complex process of thrombus formation involves different molecular pathways of platelet and coagulation activation. These pathways are considered as operating together at the same time, but this has not been investigated. The objective of our study was to elucidate the time-dependency of key pathways of thrombus and clot formation, initiated by collagen and tissue factor surfaces, where coagulation is triggered via the extrinsic route. Therefore, we adapted a microfluidics whole-blood assay with the Maastricht flow chamber to acutely block molecular pathways by pharmacological intervention at desired time points. Application of the technique revealed crucial roles of glycoprotein VI (GPVI)-induced platelet signaling via Syk kinase as well as factor VIIa-induced thrombin generation, which were confined to the first minutes of thrombus buildup. A novel anti-GPVI Fab EMF-1 was used for this purpose. In addition, platelet activation with the protease-activating receptors 1/4 (PAR1/4) and integrin αIIbβ3 appeared to be prolongedly active and extended to later stages of thrombus and clot formation. This work thereby revealed a more persistent contribution of thrombin receptor-induced platelet activation than of collagen receptor-induced platelet activation to the thrombotic process.     

Permeation of gases through modified polymer films. I. Polyethylene–styrene graft copolymers

The permeabilities of nitrogen, oxygen, and carbon dioxide through polyethylene–styrene graft copolymer films were measured by means of a gas permeability apparatus based on a modification of Barrer's high vacuum technique. Polyethylene–styrene grafts were prepared by mutual γ-ray irradiation of low-density polyethylene films in styrene–methanol solution. Densities and thicknesses of the graft copolymer films were determined. It was observed that the gas permeability constants decreased with increasing grafting to minimum values at 20–30% styrene grafting and increased again above 30% grafting. These results are explained in terms of a decrease in the free volume of the amorphous regions of the polyethylene by a “filling in” effect of the grafted polystyrene chains. Above 30% grafting, disruption of the crystallites may occur resulting in increased gas permeation. Activation energies for gas permeation through polyethylene–styrene graft copolymer films were calculated and found to decrease with increasing per cent styrene grafting. For nitrogen permeation, the activation energy decreased from 11.7 kcal/mole for unirradiated polyethylene to 9.5 kcal/mole for a 50.5% graft. Corresponding values for oxygen and carbon dioxide were 10.2–8.2 kcal/mole for a 48.7% graft and 8.4–6.5 kcal/mole for a 50.5% graft.     

Improved Apparatus for Rapid Measurement of Viscosity of Glass at High Temperatures

An apparatus is described for measuring the viscosity of glass in the range 6.5 to 13,000 poises. About 15 minutes per point are required to establish a viscosity-versus-temperature curve. About 75 gm. of glass are required for a determination. Precision is good, repair is simple, and maintenance is low. The apparatus is suitable for either research or control purposes.     

Synthesis and properties of amphiphilic copolymers of butyl acrylate and methyl methacrylate with uniform polyoxyethylene grafts

Amphiphilic copolymers of butyl acrylate (BA) and methyl methacrylate (MMA) with uniform polyoxyethylene (PEO) grafts were synthesized by the copolymerization of BA and MMA with a methacrylate‐terminated PEO macromer in benzene with azobisisobutyronitrile as an initiator. The effects of various copolymerization conditions on the grafting efficiency and molecular weight of the copolymers, as well as the effect of the copolymerization time on the conversions of the macromer and the monomers, were reported. The copolymers, with uniform PEO grafts, were purified by successive extractions with water and ether/acetone (3/7) to remove unreacted macromer and ungrafted copolymers of MMA and BA, respectively. The purified graft copolymers were characterized with IR, ¹H‐NMR, membrane osmometry, gel permeation chromatography, and differential scanning calorimetry. The highest grafting efficiency was about 90%, and molecular weight of the copolymers varied around 10⁵. The average grafting number of the copolymer was about 10. A study of the crystalline properties, emulsifying properties, phase‐transfer catalytic ability, and mechanical properties of the graft copolymers showed that the emulsifying volume decreased with the increasing molecular weight of the PEO grafts but increased with the PEO content. The conversion of potassium phenolate in the Williamson solid–liquid reaction obviously increased with an increasing PEO content of the graft copolymers. The crystallinity of the graft copolymers increased with the PEO content of the graft copolymers or the molecular weight of the macromer used. The copolymers, prepared under certain conditions, behaved as thermoplastic elastomers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2982–2988, 2003     

Latexes of starch-based graft polymers containing polymerized acrylonitrile

The scope of graft reactions to produce starch-based latexes was extended by graft polymerization of acrylonitrile (AN) onto gelatinized cationic starch possessing quaternary amine functionality and by graft terpolymerization of AN and t-butylaminoethyl methacrylate (TBAEM) onto gelatinized starch by cerium (IV) initiation at 25°C. Grafting onto starches containing highly basic quaternary amines gave polyacrylonitrile [poly(AN)] grafts having about one fourth the number-average molecular weight (M?_n) (178,000–232,000) of those produced by grafting AN onto starches containing the less basic tertiary amine groups. Sonification at 20 KHz of graft polymerization reaction mixtures having up to 8% solids reduced viscosities from 400–3000 cP to 10–40 cP. Diameters of dried particles measured about 300–1500 Å. Shaker-type agitation during grafting onto starch having quaternary amine groups produced poly(AN) chains with lower M?_n values than those produced during blade stirrer-type agitation. M?_n values of grafted poly(AN) decreased with increasing reaction time, degree of substitution of amine in the starch, gelation time of cationic starch at 95°C, and cerium (IV) concentration. AN was copolymerized with TBAEM at molar ratios of 14–85:1 in grafting onto gelatinized starch to yield copolymer side-chain grafts analyzing 8–52:1 of polymerized AN to TBAEM moieties.     

Impact of spark plasma sintering (SPS) on mullite formation in porcelains

The effect of the spark plasma sintering (SPS) process on mullite formation in porcelains was studied using X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy. SPS affected the kinetics and morphology of formed mullite. After sintering at 1100°C, unlike conventional sintering, SPS promoted the formation of mullite due to the combination of vacuum and applied pressure. Mullite crystal growth was altered by the atmosphere (vacuum), dwell time (0‐15 minutes), and temperature (1000‐1200°C). The applied pressure caused the mullite needles to orient perpendicular to the direction of the applied load. Depending on SPS dwell time, the mullite formed after sintering at 1100°C also had different crystal structure (tetragonal for short dwell time of 0‐5 minutes and orthorhombic for a long dwell time of 10‐15 minutes). Dissolution of mullite was observed at 1100°C by extending the dwell time by up to 15 minutes and the dissolved mullite reprecipitated on the small needles (~40 nm) and coarsened via Oswald ripening resulting in larger mullite needles (~60 nm).     

Synthesis,characterization, and properties of amphiphilic poly(ethyl acrylate) with uniform polyoxyethylene grafts

Amphiphilic copolymers of ethyl acrylate (EA) with uniform polyoxyethylene (PEO) grafts were synthesized by copolymerization of EA with methacrylate terminated PEO macromer in benzene using azobisisobutyronitrile as the initiator. The effects of the molecular weight of the macromers, the charging weight ratio of the macromer to EA, the total monomer concentration, and the amount of initiator on the grafting efficiency (GE) were reported as was the molecular weight of the copolymers. The highest GE reached to above 90% and the molecular weight of the copolymers varied from (5–15) × 10⁴. The reactivity ratio of EA with the macromer was determined to be 0.83. The graft copolymers were purified with extractions and the purified products were characterized with IR, ¹H‐NMR, gel permeation chromatography, differential scanning calorimetry, and membrane osmometry. The average grafting number of the copolymer varied from 2 to 11. The glass‐transition temperature of the poly(EA) in the copolymer was increased because of the partial compatibility of the two components. The crystalline property, emulsifying property, and dilute solution viscosity of the graft copolymers, as well as ionic conductivity of their complexes with alkali metal salts, were studied. The emulsifying volume decreased with the increasing molecular weight of the PEO grafts. The addition of NaOH to the emulsion affected the emulsifying volume only slightly, whereas the addition of HCl changed the oil in water type emulsion into a water in oil type. The conductivity of the LiClO₄ complex of the copolymer with an oxyethylene/Li ratio of 20 reached 3.7 × 10^?5 S/cm at 27°C. The lower the crystallinity of the complex, the higher was the conductivity. The dilute solution viscosity showed the existence of intramolecular microphase separation. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 903–912, 2001     

Thermal crosslinking of poly(methyl methacrylate-co-N,N-dimethylaminopropylacrylamide)

Summary Copolymers of methyl methacrylate(MMA) with N,N-dimethylaminopropylacrylamide (DMA) were heated at various temperatures, and their thermal crosslinking was investigated. A copolymer with a compsition of [MMA]/[DMA] =3 became completely insoluble in chloroform when heated at 180°C for 5 minutes or at 150°C for 20 minutes. Other copolymers containing less than 5 mol % DNA also crosslinked when heated at 170°C for 30 minutes. A mixture of polyMMA with N,N-dimethylaminopropylbenzamide also crosslinked when heated at 170°C. A copolymer of styrene with DMA also crosslinked when heated at above 140°C although the crosslinking was much slower than that of poly(MMA-co-DMA). The formation of imide linkages is proposed as the crosslinking mechanism.     

Graft copolymerization to cellulose. Effect of sodium thiosulfate on hydrogen peroxide initiator system

The effect of sodium thiosulfate on the graft copolymerization of methyl methacrylate to cellulose in the hydrogen peroxide initiator system was investigated. The addition of sodium thiosulfate in general was effective for decreasing the per cent grafting and the average molecular weight of grafts and increasing the formation of homopolymer, and the effects became pronounced with increasing hydrogen peroxide concentration. Moreover, the addition of sodium thiosulfate slightly suppressed the formation of grafts at a hydrogen peroxide concentration of 3 mmole/l., but greatly promoted it at 20 mmole/l. Traces of metallic ions present in cellulose could not be eliminated sufficiently by treatment with 3N hydrochloric acid. Such ions were found to interact with hydrogen peroxide and thus participate directly in the initiation and termination of the polymerization reaction. EDTA, the chelating agent, was highly effective for suppressing such participation of metallic ions. In the hydrogen peroxide initiator system applied to the EDTA-treated samples, sodium thiosulfate caused an effective initiation of graft formation.     

Changes in Protein Adsorption/Desorption on Albuminated Surfaces Due to Cyclic-AMP Release

The major problem facing the development of a small diameter vascular graft (<5 rnm diameter) to be used for the replacement of a coronary artery is thrombogenicity at the interface. When blood comes in contact with an artificial surface, the initial event occurring is the adsorption of plasma proteins on the surface [1, 2], followed by adhesion of platelets and activation of the clotting mechanism resulting in thrombus formation [3,4]. The concentration of the various proteins adsorbed is largely dependent on the surface properties of the material.