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Biomedical subjects

A Denizli

Publications and source records attributed to A Denizli.

29 records · Page 2Linked to original sources
PubMed1995

Heparin-immobilized polyhydroxyethylmethacrylate microbeads for cholesterol removal: a preliminary report.

Heparin-attached polyhydroxyethylmethacrylate (PHEMA) microbeads were investigated for specific removal of cholesterol from human and rabbit plasma. PHEMA microbeads were prepared by a suspension polymerization technique and activated by cyanogen bromide (CNBr) in an alkaline medium (pH 11.5). Heparin was then immobilized by covalent binding onto these microbeads. Cholesterol adsorption onto PHEMA microbeads containing two different amounts of immobilized heparin, i.e., 57.3 and 122.7 mg/g, from both hypercholesterolaemic human and rabbit plasma was investigated. The non-specific cholesterol adsorptions on the plain PHEMA microbeads were 0.47 mg/g and 0.30 mg/g from human and rabbit plasmas, respectively. About 35% and 32% of the cholesterol was removed from human and rabbit plasmas, respectively, when the heparin-immobilized PHEMA microbeads were used.

Adsorption↗
PubMed1995

Protein A immobilized polyhydroxyethylmethacrylate beads for affinity sorption of human immunoglobulin G.

Protein A immobilized polyhydroxyethylmethacrylate (PHEMA) microbeads were investigated for the specific removal of HIgG from aqueous solutions and from human plasma. PHEMA microbeads were prepared by a suspension polymerization technique and activated by CNBr in an alkaline medium (pH 11.5). Protein A was then immobilized by covalent binding onto these microbeads. The amount of immobilized protein A was controlled by changing pH and the initial concentrations of CNBr and protein A. The maximum protein A immobilization was observed at pH 9.5. Up to 3.5 mg protein A/g PHEMA was immobilized on the CNBr activated PHEMA microbeads. The maximum HIgG adsorption on the protein A immobilized PHEMA microbeads was observed at pH 8.0. The non-specific HIgG adsorption onto the plain PHEMA microbeads was low (about 0.167 mg of HIgG/g PHEMA). Higher adsorption values (up to 6.0 mg of HIgG/g PHEMA) were obtained in which the protein A immobilized PHEMA microbeads were used. Much higher amounts of HIgG (up to 24.0 mg of HIgG/g PHEMA) were adsorbed from human plasma.

Chromatography, Affinity↗
PubMed1995

DNA-immobilized polyhydroxyethylmethacrylate microbeads for affinity sorption of human immunoglobulin G and anti-DNA antibodies.

Polyhydroxymethacrylate (PHEMA) microbeads were prepared by a suspension polymerization technique and activated by CNBr in an alkaline medium (pH 11.5). DNA molecules were immobilized onto CNBr-activated PHEMA beads. The amount of immobilized DNA was controlled by changing the medium pH and the initial concentrations of CNBr and DNA. The maximum DNA immobilization was observed at pH 5.0. Non-specific adsorption on the plain PHEMA microbeads was less than 0.1 mg/g. Much higher values, up to 2.75 mg/g, were achieved with the CNBr-activated PHEMA microbeads. Human immunoglobulin G (HIgG) adsorption onto PHEMA microbeads containing different amounts of DNA on their surfaces from aqueous solutions containing different amounts of HIgG at different pH values was investigated. The maximum HIgG adsorption was observed at pH 7.0. Non-specific HIgG adsorption onto the plain PHEMA microbeads was low (about 0.167 mg/g). Higher adsorption values, up to 7.5 mg/g, were obtained with the DNA-PHEMA beads. HIgG and anti-DNA antibody removal from the blood plasma obtained from a healthy donor and a patient with systemic lupus erythematosus (SLE) were also investigated. The maximum amounts of HIgG adsorbed from aqueous solution and human plasma onto the DNA-PHEMA microbeads were 7.35 and 23.46 mg/g, respectively. Anti-DNA antibody adsorption value was 40 mg/g.

Animals↗
PubMed1995

Collagen and fibronectin immobilization on PHEMA microcarriers for hepatocyte attachment.

Polyhydroxyethylmethacrylate (PHEMA) microcarriers in a size range of 150-250 microns were prepared by a suspension polymerization in an aqueous phase containing magnesium oxide. The hydroxyl groups on the PHEMA microcarriers were activated by cyanogen bromide. In order to improve cell attachment, cell-adhesive proteins, namely, collagen and fibronectin were immobilized onto PHEMA microcarriers. The nonspecific adsorption values for collagen and fibronectin were 0.10 mg collagen/g PHEMA and 0.044 mg fibronectin/g PHEMA, respectively. Collagen and fibronectin immobilization on PHEMA microcarriers were studied at different pH by using single protein solutions containing different amounts of proteins, at a constant temperature of 20 degrees C. The maximum immobilizations were 0.85 mg collagen/g PHEMA (at pH: 9.5) and 0.52 mg fibronectin/g PHEMA (at pH: 7.4). Hepatocyte attachment onto these biologically modified PHEMA microcarriers was studied. Hydrophilic PHEMA microcarriers did not support cell attachment. High hepatocyte attachment yields (up to 75% surface coverage) were observed on collagen and fibronectin immobilized PHEMA microcarriers.

Animals↗
PubMed1994

Monosize microbeads based on polystyrene and their modified forms for some selected medical and biological applications.

Polymeric particles are produced by different polymerization techniques. Phase inversion (dispersion) polymerization is one of the recent techniques to obtain monosize polymeric microbeads in the size range of 1-50 microns. The size and monodispersity of these microbeads can be adjusted by using several solvent systems (e.g., alcohol-water mixtures) with different polarities and by changing the type and amount of monomer, initiator and stabilizer. Surfaces of these microbeads can be further modified by different techniques including coating with different copolymers. Monosize polymeric microbeads are widely used in medical and biological applications as carriers, such as in immunoassays and cell separation, in site-specific drug delivery systems, in nuclear medicine for diagnostic imaging, in studying the phagocytic process, in affinity separation of biological entities, etc. Here, some important aspects of the production of monosize microbeads based on polystyrene and their modified forms are briefly discussed, and some selected medical and biological applications are summarized.

Biopolymers↗
PubMed1993

Nonspecific adsorption and covalent coupling of heparin on polyacrylate based microbeads.

Polyacrylate based microbeads were prepared by copolymerization of four different acrylate monomers, namely 2-hydroxyethylmethacrylate (HEMA), ethyleneglycoldimethacrylate (EGDMA), methylmethacrylate (MMA) and dimethylaminoethylmethacrylate (DMEAMA). These beads were further activated with CNBr at alkaline pH. The extend of nonspecific adsorption and covalent coupling of heparin on these beads were investigated in a batch reactors at different temperatures. The effects of initial concentrations of activation agent and heparin were also studied. Nonspecific heparin adsorption on the microbeads containing DMAEMA was significantly higher than the others. Nonspecific adsorption decreased with increasing temperature. Heparin was covalently coupled on CNBr activated microbeads. The amount of coupled heparin increased by increasing concentration of CNBr.

Acrylates↗
PubMed1992

Biologically modified PHEMA beads for hemoperfusion: preliminary studies.

Polyhydroxyethylmethacrylate (PHEMA) beads were prepared by phase separation polymerization. Hydroxyl groups on PHEMA beads were activated with CNBr at alkaline pH. Adsorption of heparin, blood proteins (i.e. albumin, fibrinogen and gamma-globulin), protein A, HIgG and DNA on these beads were studied. Preparation and activation procedures are given here. The preliminary results of these studies are also reported.

Adsorption↗
PubMed1992

Hepatocyte immobilization on PHEMA microcarriers and its biologically modified forms.

Polyhydroxyethylmethacrylate (PHEMA) based microcarriers with different bulk structures were prepared by a phase inversion polymerization technique. PHEMA surfaces were further modified chemically by glow-discharge treatment, and biologically by covalent attachment of fibrinogen and collagen. Hepatocytes were isolated from young male Wistar rats using an in situ portal vein collagenase perfusion technique. Freshly isolated hepatocytes were seeded at 6 x 10(5) cells/mL and microcarrier concentration was 10 g/L. Stationary microcarrier cultures were carried out in standard (nontissue culture) polystyrene petri dishes in a humidified 5% CO2 incubator at 37 +/- 0.5 degrees C. Cell attachment was followed by light microscopy by taking samples from the culture medium every 30 min. Urea and protein syntheses by microcarrier-attached hepatocytes were determined by standard techniques. Nonswellable (highly cross-linked) hydrophilic PHEMA microcarriers did not support cell attachment and viability. However, swellable (low cross-linked) PHEMA microcarriers (pretreated in FBS) allowed high attachment and cell spreading. PHEMA microcarriers treated in dimethylaminoethylmethacrylate (DMAEMA) glow-discharge plasma also improved the cell attachment characteristics of the PHEMA microcarriers. The highest attachment efficiencies (immobilization yields) were observed with the biologically modified PHEMA microcarriers, especially modified with fibronectin. Metabolic activity, as estimated by urea and protein syntheses, was also higher in these microcarriers.

Animals↗
PubMed1988

Subcutaneous polymeric matrix system p(HEMA-BGA) for controlled release of an anticancer drug (5-fluorouracil). II: Release kinetics.

A subcutaneous polymeric drug delivery system, which consists of a polymeric matrix of poly(hydroxyethyl methacrylate-bisglycol acrylate), was developed. 5-fluorouracil was used as the model anticancer drug. Polymer-drug beads with a diameter of 3 mm were prepared by low-temperature radiation polymerization. In order to modify the release rate, polymeric beads with different composition, drug loading and crosslinking density were obtained. The kinetics of drug release were described by the expression Mt/M infinity = ktn. The diffusional release exponent 'n', which was calculated from the release curves, indicated that the mechanism of drug release from the polymeric matrix is due to the anomalous (non-Fickian) type of diffusion.

Acrylates↗
PubMed1988

Subcutaneous polymeric matrix system poly(HEMA-BGA) for controlled release of an anticancer drug (5-fluorouracil). I. Synthesis and structure.

The present study was an attempt to design a new polymer-drug composite system for local chemotherapy. Poly(hydroxyethylmethacrylate-bisglycolacrylate) carriers containing an anticancer drug, 5-fluorouracil, were prepared by low temperature radiation polymerization technique. By changing the relative amounts and the types of ingredients, drug loading and radiation dosage, polymer-drug composites with different structural properties were obtained. This paper presents the preparation procedure and analyses some of the structural properties of these novel composites.

Acrylates↗