Suspension polymerization of 2-hydroxyethyl methacrylate in the presence of polymeric diluents: a novel route to spherical highly porous beads for biomedical applications

The usage of composite nanomaterials in biomedical engineering applications

Nanotechnology is still developing over the decades and it is commonly used in biomedical applications with the design of nanomaterials due to the several purposes. With the investigation of materials on the molecular level has increased the develop composite nanomaterials with exceptional properties using in different applications and industries. The application of these composite nanomaterials is widely used in the fields of textile, chemical, energy, defense industry, electronics, and biomedical engineering which is growing and developing on human health. Development of biosensors for the diagnosis of diseases, drug targeting and controlled release applications, medical implants and imaging techniques are the research topics of nanobiotechnology. In this review, overview of the development of nanotechnology and applications which is use of composite nanomaterials in biomedical engineering is provided.

Porous microsphere and its applications

Porous microspheres have drawn great attention in the last two decades for their potential applications in many fields, such as carriers for drugs, absorption and desorption of substances, pulmonary drug delivery, and tissue regeneration. The application of porous microspheres has become a feasible way to address existing problems. In this essay, we give a brief introduction of the porous microsphere, its characteristics, preparation methods, applications, and a brief summary of existing problems and research tendencies.

Glutaraldehyde-activated chitosan matrix for immobilization of a novel cysteine protease, procerain B

Proteases have several applications in the food industry. We report the immobilization of procerain B, a novel cysteine protease, on glutaraldehyde-activated chitosan beads through covalent attachment. Glutaraldehyde not only serves as a cross-linking agent but also links the procerain B on the surface of bead through primary amine group (either lysine side chain or N-terminal) by Schiff base linkage. Immobilized procerain B was characterized for optimum functional range and stability with respect to pH and temperature. The chitosan-immobilized procerain B has broad pH and thermal optima. The effects of substrate concentration and reusability of immobilized beads were also studied. It showed nearly 50% activity until the 10th use.

Polymeric Microspheres for Medical Applications

Synthetic polymeric microspheres find application in a wide range of medical applications. Among other applications, microspheres are being used as bulking agents, embolic- or drug-delivery particles. The exact composition of the spheres varies with the application and therefore a large array of materials has been used to produce microspheres. In this review, the relation between microsphere synthesis and application is discussed for a number of microspheres that are used for different treatment strategies.

Capacity and tolerance of a new device for ocular drug delivery

A new method to increase the drug-capacity of the OphthaCoil, a flexible and tubular device for delivery of drugs to the tear film of the eye, was explored. Poly(2-hydroxyethyl methacrylate)- and poly(2-hydroxyethyl methacrylate-co-1-vinyl-2-pyrrolidone)-microspheres were prepared by suspension polymerization. The resultant particles were swollen in a highly concentrated solution of either the dye fluorescein sodium or the antibiotic chloramphenicol. The loaded particles were placed in the central cavity of the ocular device. In vitro release profiles showed a six-fold increase of the capacity for the dye fluorescein sodium, but not for the antibiotic chloramphenicol. Flexibility measurements revealed that by introducing microspheres in the central cavity of the device, flexibility did not decrease. Finally, a preliminary in vivo evaluation of the device (n=5) was done for a 2h-period to assess the tolerance of the device in the human eye. Ophthalmologic examinations and photographs of the eye indicated no signs of irritation. Volunteers reported that the presence of the device in the eye could be noticed, but no irritation was reported.

Synthesis and hydration properties of pH-sensitive p(HEMA)-based hydrogels containing 3-(trimethoxysilyl)propyl methacrylate

An amphiphilic hydrogel network was synthesized from a cross-linked poly(2-hydroxyethyl methacrylate) backbone copolymerized with the monomers 3-(trimethoxysilyl)propyl methacrylate (PMA) and dimethylaminoethyl methacrylate (DMAEMA) using tetraethylene glycol diacrylate (TEGDA) as cross-linker and using the radical initiator system comprising N,N,N',N'-tetramethylethylenediamine and ammonium peroxydisulfate. The degree of hydration of hydrogel slabs was investigated as functions of varying monomer compositions and cross-link density and as a function of pH and ionic strength of the bathing medium. As much as a 45% increase in hydration was observed for hydrogels containing 15 mol % DMAEMA upon reducing the pH of the bathing medium from 8.0 to 2.0. This confirms the pH-modulated swelling of amine-containing hydrogels. Increasing the concentration of TEGDA cross-linker from 3 to 12 mol % in a 10 mol % DMAEMA-containing hydrogel resulted in only a 10% reduction in the degree of hydration of the gel. There was, however, a 40-50% reduction in the degree of hydration of a 15 mol % DMAEMA hydrogel upon increasing the molar composition of PMA from 0 up to 20 mol %. The presence of PMA confers hydrophobic character that reduces hydration and introduces additional cross-links that reduce network mesh size. The water content of the hydrogel was consistently higher in buffers of lower ionic strength. The reversible pH-dependent swelling observed in these studies, along with the control of cross-link density afforded by the PMA component, endows these biocompatible materials with potential for use in pH-controlled drug delivery of more hydrophobic drugs and present new compositions for in vitro and in vivo biocompatibility studies.

Acrylic microspheres for oral controlled release of the biguanide buformin

Spherical microparticles based on methacrylic acid-methyl methacrylate copolymer have been developed. The method chosen for the preparation of such microparticles was suspension radical copolymerization of acrylic comonomers in the presence of the ethyleneglycol dimethacrylate as crosslinking agent. The microparticles obtained were characterised by inverse size exclusion chromatography, scanning electron microscopy, swelling degree and exchange capacity. The porous volume of the microspheres ranged from 0.086 ml/g for the microparticles produced by a methacrylic acid/methyl methacrylate ratio of 1/3 and a 10% degree of crosslinking, to 8.57 ml/g for the microparticles produced by a methacrylic acid/methyl methacrylate ratio of 3/1 and 2% degree of crosslinking (in 0.1 N NaCl in phosphate buffer pH 7.4). Also the pore diameter of the swollen microparticles ranged from a few to 120 A. Buformin tosylate - a classical hypoglycaemic drug - was included in the polymer network of the microparticles during the polymerization process. Due to the water solubility of the drug and its low solubility in the organic phase, the entrapment yield did not exceed 15%. However the amount of encapsulated drug as well as the drug released from the microparticles, was dependent on the methacrylic acid/methyl methacrylate ratio, the degree of crosslinking and solvent/comonomers ratio.

DNA adsorption onto polyethylenimine-attached poly(p-chloromethylstyrene) beads

In this study, DNA adsorption properties of polyethylenimine (PEI)-attached poly(p-chloromethylstyrene) (PCMS) beads were investigated. Spherical beads with an average size of 186 microm were obtained by the suspension polymerization of p-chloromethylstyrene conducted in an aqueous dispersion medium. Owing to the reasonably rough character of the bead surface, PCMS beads had a specific surface area of 14.1 m2/g. PEI chains could be covalently attached onto the PCMS beads with equilibrium binding capacities up to 208 mg PEI/g beads, via a direct chemical reaction between the amine and chloromethyl groups. After PEI adsorption with 10% (w/w) initial PEI concentration, free amino content of PEI-attached PCMS beads was determined as 0.91 mequiv./g. PEI-attached PCMS beads were utilized as sorbents in DNA adsorption experiments conducted at +4 degrees C in a phosphate buffer medium of pH 7.4. DNA immobilization capacities up to 290 mg DNA/g beads could be achieved with the tried sorbents. This value was approximately 50-times higher relative to the adsorption capacities of previously examined sorbents.

Materials and biomaterials for interventional radiology

Devices used in interventional radiology have significantly developed in the past few years. In order to understand the trends of this development, we analyzed how new interventional devices are progressively incorporating materials having original physical properties, and how developers are today progressively turning towards biomaterials, with respect to the new regulatory environment, and the requirements of biocompatibility.

The overwet phenomenon in two-component acetone-based primers containing aryl amine and carboxylic acid monomers

OBJECTIVES

The overwet phenomenon was first reported when a moist bonding technique was used with an earlier commercial version of All-Bond 2 (Bisco) that contained BPDM in primer B. This study investigated whether ultrastructural features of the overwet phenomenon could also be detected in other commercially available two-component acetone-based primers containing BPDM, PMDM and PMGDM, as well as an experimental two-component primer containing DSDM.

METHODS

Thirty 1 mm dentin discs prepared from third molars were each conditioned with 10% H3PO4 for 20 s and rinsed for 20 s. They were randomly divided into 5 groups: Group I (Bond-It, Jeneric/Pentron:PMGDM); Group II (Wet Bond, Chameleon Dental Products:PMGDM); Group III (Tenure S, Den-Mat:PMDM); Group IV (present commercial version of All-Bond 2, Bisco:BPDM) and Group V (Experimental two-component primer system containing DSDM in primer B). Following a moist bonding technique using the respective system, discs from each group were further bonded together to form three disc pairs using a chemical-cured resin. Bonded disc pairs were demineralized in EDTA and processed for TEM examination. For this ultramicroscopical study, results such as the features of the overwet phenomenon were analyzed by visual inspection of the specimens in each group (n = 12).

RESULTS

Isolated blister-like spaces of variable dimensions were observed within the primer layer in all groups and possessed the following characteristics: 1) a layer of resin-impregnated dentin was always present along the base of the primary blister; 2) surface primer globules, sometimes containing secondary blisters, were identified within these primary blisters; 3) dentinal tubules within the blister-like spaces were not completely sealed; 4) primer globules were circumscribed by a halo of fine kinked strands of material.

SIGNIFICANCE

Although the technique of moist bonding is based on valid biological principles, incorporation of resin monomers that are immiscible with water rendered the application of current two-component, acetone-based primers very technique-sensitive in terms of tubular seal, when used on moist, acid-conditioned dentin. Further studies should be directed at elimination of this type of oil-in-water (O/W) "macroemulsion" formation through optimal micellar solubilization of these resin monomers in water.

Covalent immobilization of alpha-amylase onto pHEMA microspheres: preparation and application to fixed bed reactor

Microspheres of poly(2-hydroxyethyl methacrylate) with and without cross-linker were prepared by suspension polymerization. As the amount of cross-linker increased, the equilibrium water content, enzyme loading, immobilization efficiency and recovered activity were all adversely affected. Enzyme alpha-amylase was immobilized onto the microspheres after activation with epichlorohydrin. The Km value for the immobilized enzyme (0.90% w/v) was much greater than that of the free enzyme (0.53% w/v). It was found that the inactivation constant (ki) increased from 2.23 x 10(-8) min-1 at 20 degrees C to 1.45 x 10(-4) min-1 at 60 degrees C. Since the enzyme activity increased as the temperature increased, the temperature profile yielded a peak at 50 degrees C. For free enzyme this is at 45 degrees C. The residence time was proportional to the percentage hydrolysis until a residence time of 12 min was reached. Beyond this the activity increase could not match the increase in residence time. The pH profile yielded a broadening upon immobilization in addition to a small shift to higher pH (from 5.5 to 6.0). The continuous run at 30 degrees C, 1.0% w/v starch concentration and flow rate of 40 cm3 h-1 led to only 20% loss in activity after a 120 h operation.

Preparation and evaluation of radiopaque hydrogel microspheres based on PHEMA/iothalamic acid and PHEMA/iopanoic acid as particulate emboli

Highly porous poly(2-hydroxyethyl methacrylate) (PHEMA) microspheres prepared by suspension polymerization of 2-hydroxyethyl methacrylate (HEMA) in presence of polymeric diluents such as poly(methyl methacrylate) (PMMA) in toluene and poly(tetramethylene glycol) (PTMG) were made radiopaque by esterification of the reactive hydroxyl groups with iothalamic acid and iopanoic acid, two radiopaque substances clinically used. Of the various solvents and catalysts examined, tetrahydrofuran (THF) and N,N'-dimethyl paratoluidine (DMPT) were found to be best for obtaining a high degree of conversion. More than 30 wt% iodine could be bound to the microspheres which made them sufficiently radiopaque to be imaged radiographically. Microspheres retained their porosity, swelling ability, hydrophilicity, and surface morphology to a significant extent after iodination. Preliminary implantation studies of such microspheres subcutaneously in rats have shown no adverse tissue reactions over a 6-month period. It is suggested that these microspheres would prove to be useful as particulate emboli in endovascular embolization.