Mineralization behaviour of some new phema-based copolymers with potential uses in tissue engineering

This paper reports the mineralization ability of 2-hydroxyethyl methacrylate (HEMA) and 2-methacryloylamido glutamic acid (MAGA) based copolymers incubated in synthetic fluids. MAGA monomer was obtained by organic synthesis and next p(HEMA-co-MAGA) copolymers with different compositions were prepared by bulk radical polymerization using benzoyle peroxide as initiator and ethyleneglycol dimethacrylate as cross-linking agent. The monomer and polymers were further characterized by FTIR-ATR spectroscopy to confirm their structure. Finally, polymers ability to initiate the formation and growth of HA crystals onto their surface in synthetic fluids was proven. SEM analysis showed the formation of apatite-like crystals (calcospherites), fact confirmed also by EDX analysis

Polymerization of 2-(hydroxyethyl)methacrylate by two different initiator/accelerator systems: a Raman spectroscopic monitoring

The control of monomer polymerization is important when preparing biocompatible devices. The compound 2-(hydroxyethyl)methacrylate can be polymerized by redox systems using benzoyl peroxide (BPO) (as accelerator) and a substituted amine (as initiator). However, this system is associated with a highly exothermic polymerization, and end-products with inflammatory properties are produced. We have used ascorbic acid (AA) to induce BPO fragmentation and have compared the kinetics of the reaction, by Raman microscopy, with that obtained with a substituted amine. The breaking of the C= bond (Raman stretching vibration at 1641 cm−1) could be monitored in both cases and reflected the incorporation of new monomer molecules into the chain. The AA-induced polymerization was slower than with the substituted amine and was accompanied by the appearance of a new band at 1603 cm−1, assigned to the stretching vibrations of -COOH species incorporated into the chains. Raman microscopy appears to be a powerful tool in the study of polymeric biomaterial preparation

Fluorescence Properties of Photonic Crystals Doped with Perylenediimide

This study aims to present the fabrication of colloidal photonic crystals (PC) with increased fluorescence properties. The use of a highly fluorescent perylenediimide derivate (PDI) during the soap-free emulsion polymerization of styrene–acrylic acid resulted in monodisperse core–shell particles which allowed the fabrication of PC films. The properties of the hybrid material were studied in comparison with hybrid materials obtained by impregnation of films with chromophore solutions. In both cases an increase of the fluorescence response was observed in addition to a blue shift for the PDI core particles, proving the incorporation of the dye inside the copolymer particles

Aluminum inhibits the growth of hydroxyapatite crystals developed on a biomimetic methacrylic polymer.

PROJECT: Aluminum (Al) is an increasing problem in biomedicine since it can interact with phosphates. Bone is one of the preferential target tissues of Al deposition: Al interacts with mineralization and/or bone cell activities. We searched the influence of Al deposition in hydroxyapatite developed on a biomimetic polymer (carboxymethylated poly(2-hydroxyethyl-methacrylate)) which mimics bone mineralization in the absence of cells. PROCEDURES: Pellets of polymer were incubated for 5 days in a synthetic body fluid (SBF) to induce mineralization, then 21 days in SBF containing 20, 40 and 60 μg/L Al(3+). Other pellets were incubated in SBF containing commercial Al foil (33 mg/vial) either in 1, 2 or 6 pieces. The mineral deposits were dissolved in HCl and Ca(2+), PO(4)(3-) and Al(3+) content was measured. Hydroxyapatite was characterized by SEM and X energy-dispersive X-ray analysis (EDX). RESULTS: The amount of Al(3+) was dose-dependently increased in Ca/P deposits on the polymer pellets. At high concentration (or with the 6 Al foils) growth of hydroxyapatite calcospherite was inhibited; only calcified plates emerging from the polymer were observed. Pellets incubated with 1 and 2 Al foils exhibited a reduction in calcospherite diameter and an increase in the Al(3+)/Ca(2+) ratio. EDX identified Al in the mineral deposits. CONCLUSIONS: In this acellular model, Al(3+) altered the growth of calcospherites at low concentration and inhibited their development at high concentration. In SBF, a release of Al(3+) from aluminum foils also inhibited mineralization. This study emphasizes the importance of Al in bone pathology and stresses the question of its release from biomaterials

Chemical structure of methylmethacrylate-2-[2′,3′,5′-triiodobenzoyl]oxoethyl methacrylate copolymer, radio-opacity, in vitro and in vivo biocompatibility

The properties of copolymers (physical, chemical, biocompatibility, etc.) depend on their chemical structure and microstructural characteristics. We have prepared radio-opaque polymers based on the copolymers of methyl methacrylate (MMA) and 2-[2′,3′,5′-triiodobenzoyl]oxoethyl methacrylate (TIBOM). The copolymerization reaction between TIBOM and MMA showed that the reactivity ratios were r1 = 0.00029 and r2 = 1.2146. The composition diagram is typical for a practically non-homopolymerizable monomer (TIBOM) and a very reactive monomer (MMA). The copolymers were analyzed on an X-ray microcomputed tomograph and they proved to be radio-opaque even at low concentrations of TIBOM. The biocompatibility was tested both in vitro (with J774.2 macrophage and SaOS-2 osteoblast like cells) and in vivo in the rat. These materials were found to be non-toxic and were well tolerated by the organism. These combined results led to the suggestion that this type of polymer could be used as dental or bone cements in place of barium or zirconium particles, which are usually added to provide X-ray opacity

Effects of FGF-2 release from a hydrogel polymer on bone mass and microarchitecture

Bone substitutes are widely used for filling and restoring bone defects. Among them, methacrylic polymers are employed in load-bearing bones to seal hip prostheses. Incorporation of growth factors into a polymer device could be a way to enhance bone growth. In the present study, we evaluated the capacity of poly(2-hydroxyethyl methacrylate) – pHEMA – copolymerized with 2-vinyl pyrrolidone – VP – to release proteins. Fibroblast growth factor-2 (FGF-2) was incorporated into cylinders of p(HEMA-co-VP). FGF-2 release was studied by ELISA in vitro and cylinders were implanted in the femoral condyle of white New Zealand rabbits. After 2 months post-surgery, FGF-2 was able to enhance bone formation by increasing bone volume; this effect was evidenced by an increase in trabecular number and bone gain was mainly in the form of woven bone. At 3 months post-surgery, no difference could be evidenced between animals receiving vehicle or FGF-2. Animals receiving vehicle exhibited bone mass higher than at 2 months and woven bone was replaced by mature bone with a lamellar matrix. The hydrogel polymer allowed the release of FGF-2, which in return enhanced bone regeneration soon after surgery but the effect vanished rapidly

Fibres de polyhydroxyalkanoate (PHBV) obtenues par une méthode de filage humide : bonne cytocompatibilité in vitro mais absence de biocompatibilité in vivo en site osseux

Polyhydroxyalkanoates (PHAs) are biomaterials widely investigated for tissue-engineering applications. In this regard, we describe a method to prepare fibers of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) by a wet-spinning technique. Polymer fibers were used to test the cytocompatibility of the material in vitro. We have investigated their behavior in vitro in presence of the osteoblast-like (SaOs2) and macrophage (J774.2) cell lines. The PHBV fibers used were 100-200μm in diameter and offered a large surface for cell adhesion, similar to that they encounter when apposed onto a bone trabeculae. The fiber surface possessed a suitable roughness, a factor known to favor the adherence of cells, particularly osteoblasts. PHBV fibers were degraded in vitro by J774.2 cells as erosion pits were observable by transmission electron microscopy. The fibers were also colonisable by SaOs2 cells, which can spread and develop onto their surface. However, despite this good cytocompatibility observed in vitro, implantation in a bone defect drilled in rabbit femoral condyles showed that the material was only biotolerated without any sign of osteoconduction or degradation in vivo. We can conclude that PHBV is cytocompatible but is not suitable to be used as a bone graft as it does not favor osteoconduction and is not resorbed by bone marrow macrophages

Effect of ursodeoxycholic acid on methionine adenosyltransferase activity and hepatic glutathione metabolism in rats

Background and aims: Both bile salts and glutathione participate in the generation of canalicular bile flow. In this work, we have investigated the effect of different bile salts on hepatic glutathione metabolism. Methods: Using the isolated and perfused rat liver, we studied hepatic glutathione content, and metabolism and catabolism of this compound in livers perfused with taurocholate, ursodeoxycholate, or deoxycholate. Results: We found that in livers perfused with ursodeoxycholate, levels of glutathione and the activity of methionine adenosyltransferase (an enzyme involved in glutathione biosynthesis) were significantly higher than in livers perfused with other bile salts. In ursodeoxycholate perfused livers, methionine adenosyltransferase showed a predominant tetrameric conformation which is the isoform with highest activity at physiological concentrations of substrate. In contrast, the dimeric form prevailed in livers perfused with taurocholate or deoxycholate. The hepatic activities of γ-glutamylcysteine synthetase and γ-glutamyltranspeptidase, enzymes involved, respectively, in biosynthetic and catabolic pathways of glutathione, were not modified by bile salts. Conclusions: Ursodeoxycholate specifically enhanced methionine adenosyltransferase activity and hepatic glutathione levels. As glutathione is a defensive substance against oxidative cell damage, our observations provide an additional explanation for the known hepatoprotective effects of ursodeoxycholate