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.

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.

Biomimetic potential of some methacrylate-based copolymers: a comparative study.

Preparation of new biocompatible materials for bone recovery has consistently gained interest in the last few decades. Special attention was given to polymers that contain negatively charged groups, such as phosphate, carboxyl, and sulfonic groups toward calcification. This present paper work demonstrates that other functional groups present also potential application in bone pathology. New copolymers of 2-hydroxyethyl methacrylate with diallyldimethylammonium chloride (DADMAC), glycidyl methacrylate (GlyMA), methacrylic acid (MAA), 2-methacryloyloxymethyl acetoacetate (MOEAA), 2-methacryloyloxyethyltriethylammonium chloride (MOETAC), and tetrahydrofurfuryl methacrylate (THFMA) were obtained. The copolymers were characterized by FTIR, swelling potential, and they were submitted to in vitro tests for calcification and cytotoxicity evaluation. GlyMA and MOETAC-containing copolymers show promising results for further in vivo mineralization tests, as a potential alternative to the classical bone grafts, in bone tissue engineering.

Synthesis and use of pHEMA microbeads with human EA.hy 926 endothelial cells.

Cancer has become a major problem in public health and the resulting bone metastases a worsening factor. Facing it, different strategies have been proposed and mechanisms involved in tumor angiogenesis are being studied. Enhanced permeability retention (EPR) effect is a key step in designing new anticancer drugs. We have prepared poly 2-hydroxyethyl methacrylate (pHEMA) microbeads to target human endothelial EA.hy 926 cells, a cell line derived from human umbilical vein endothelial cells. Microbeads were synthesized by emulsion precipitation method and carried positive or negative charges. EA.hy 926 cells were cultured in 24-well plates and microbeads were deposited on cells at various times. Scanning and transmission electron microscopy, flow cytometry, confocal microscopy, and three-dimensional (3D) reconstruction were used to characterize microbeads and their location outside and inside cells. Microbeads were uptaken by endothelial cells with a better internalization for negatively charged microbeads. 3D reconstruction of confocal optical sections clearly evidenced the uptake and internalization of microbeads by endothelial cells. pHEMA microbeads could represent potential drug carrier in tumor model of metastases.

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 r(1)=0.00029 and r(2)=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.

Synthesis and characterisation of core-shell structures for orthopaedic surgery.

This paperwork deals with the obtaining and characterisation of new acrylic cements for bone surgery. The final mixture of cement contains derivatives of methacryloyloxyethyl phosphate, methacrylic acid or 2-acrylamido-2-methyl-1-propane sulphonic acid. The idea of using these monomers is sustained by their ability to form ionic bonds with barium, which is responsible for X-ray reflection and by the biocompatibility of these structures. The strategy consists in the obtaining of core-shell structures through heterogeneous polymerisation, which are used for final cement's manufacture. The orthopaedic cements were characterised by SEM, EDX, compression resistance and cytotoxicity assays.