Biomedical subjects

E Pişkin

Publications and source records attributed to E Pişkin.

At least 55 records · Page 3Linked 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

Monosize poly(ethylcyanoacrylate) microspheres: preparation and degradation properties.

Monosize, biodegradable poly(ethylcyanoacrylate) (PECA) microspheres in the size range of 0.5-2.5 microns were prepared by a relatively new polymerization technique, the so-called dispersion polymerization. The polymerizations were performed by using a stabilizer system containing a poly(ethyleneoxide)/poly(propyleneoxide) (PEO/PPO) copolymer and dextran in the aqueous HCl solution as a dispersion medium. Phosphoric acid was used as a catalyst, stabilizer, monomer concentrations, and the pH of dispersion medium on the monomer conversion, average size, and size distribution of the PECA microspheres were studied. The resultant microsphere size was mainly controlled by PEO/PPO copolymer and HCl concentrations. To explain the degradation mechanism, the degradation of monosize PECA microspheres was studied in in vitro conditions. The partially degraded beads were observed by electron microscopy. The results indicated that the degradation of monosize PECA microspheres occurred mainly by surface erosion.

Biodegradation, Environmental↗

PubMed1995

A potential soft tissue filling material: chloramphenicol loaded poly(D,L-lactide) sponges.

Poly(D,L-lactide) (PDLLA) homopolymers were produced by the ring opening polymerization of a D,L-lactide dimer by using stannous chloride as the catalyst. Chloramphenicol loaded PDLLA sponges were pre- pared by a solvent evaporation procedure by using the PDLLA homopolymers with three different molecular weights (i.e., 11,000, 20,000 and 35,000 daltons). Chloramphenicol loading was changed by using three different solvents (i.e., acetone, ethyl acetate, and acetonitrile) and by changing the initial polymer concentration and its molecular weight and the initial concentration of the drug. Higher degradation rates of the chloramphenicol loaded PDLLA sponges in alkaline pH 9.0 and at 37 degrees C were observed. Chloramphenicol release rates were also high at these conditions. It was concluded that chloramphenicol release was both degradation and diffusion controlled.

Acetonitriles↗

PubMed1995

Biodegradable polymers as biomaterials.

Biomaterials are used in prostheses and medical devices for different purposes. Polymers are the most diverse class of biomaterials. All biomaterials must meet certain criteria and regulatory requirements before they can be qualified for use in medical applications. Biocompatibility is one of the most important requirements. Both nondegradable polymers are designed to degrade in vivo in a controlled manner over a predetermined time. The main mechanism of in vivo degradation of polymers is 'hydrolytic degradation', in which enzymes may also play a role (i.e. 'enzymatic degradation'). Both natural e.g., collagen, and synthetic e.g., poly(alpha-hydroxy) acids, biodegradable polymers are used in biomedical applications. Many of the current polymers and processing techniques need to be improved in order to produce polymers with better performance in biological media. An important trend in related research and development is the synthesis of novel polymers, which would exhibit improved biocompatibility, and be bioresponsive.

Animals↗

PubMed1995

Rifampicin-carrying poly(D,L-lactide) microspheres: loading and release.

Rifampicin-loaded poly(D,L-lactide) (PDLLA) microspheres in the size range of 0.8-8.0 microns were prepared by a modified solvent evaporation method. Rifampicin loading was changed by using different types of solvents (i.e. methylene chloride, chloroform, and carbon tetrachloride) with different solvent/polymer ratios and different emulsifiers (i.e. methyl cellulose, gelatin, and Tween-20), and by changing the initial drug/polymer ratio. These rifampicin-loaded PDLLA microspheres degraded much faster in the medium at basic pH (9.8) and at high temperatures (55 degrees C). Rifampicin release was also high under these conditions. It was concluded that rifampicin release was both degradation- and diffusion-controlled.

Biocompatible Materials↗

PubMed1995

Degradation and drug release characteristics of monosize polyethylcyanoacrylate microspheres.

Monosize, biodegradable poly(ethylcyanoacrylate) (PECA) microspheres with a diameter of 1.3 microns were prepared by a relatively new polymerization method, the so-called phase inversion polymerization. The effects of pH and temperature on the degradation behavior of PECA particles were investigated. PECA microspheres were degraded mainly by surface erosion. The degradation rate increased with increasing pH temperature. A model drug, i.e. 2,4-dinitrophenylhydrazine (DNPH) was loaded into the monosize PECA microspheres during polymerization. The drug incorporation into the PECA microspheres increased with increasing initial drug concentration in the monomer phase. Drug release from the PECA microspheres was investigated at different pH. Higher drug release rates were observed in the neutral and alkaline media as compared with the acidic medium.

Biodegradation, Environmental↗

PubMed1995

Phagocytosis of monosize polystyrene-based microspheres having different size and surface properties.

In this study, nondegradable monosize polystyrene (PS) based polymeric microspheres with different size and surface chemistries were prepared by different polymerization techniques. Surfaces of the plain microspheres were further modified biologically by albumin (BSA) or fibronectin (Fn) preadsorption. Phagocytosis of these polymeric microspheres by leukocytes and macrophages were investigated. The phagocytic response of both leukocytes and macrophages decreased by increasing size of the particles. More hydrophilic particles phagocytosed less. Positive charges increased the uptake while negative charges oppositely reduced the uptake. BSA on the surface almost prevented the uptake, while Fn caused opsonization.

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↗

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↗

PubMed1991

Evaluation of 99mTc labelled monodisperse polystyrene/polyacrylate latex particles for the study of colon transit and morphology.

A new radiopharmaceutical for the study of colon transit time and morphology is proposed. Polymeric latexes, as monodisperse polymeric spheres (1-10 microns in diameter), were prepared by a coaxial dispersion polymerization of styrene and dimethylaminoethyl-methacrylate (DMAEA). They were labelled with 99mTc by the tin reduction method with high efficiency (greater than 99%). The label was stable up to 48 h at pH values of 1-8 at room temperature. Scintigrams obtained in rabbits after oral administration of 37 MBq of 99mTc-latex particles showed that greater than 90% of the dose remained in the gastrointestinal tract. The cumulative faecal excretion was 8.6 +/- 6.7 in 24 h and 21.3 +/- 13.8% in 48 h. In human studies the colon was well visualized at 4 h. The thyroid and the urinary bladder were not detected on scintigrams, indicating the stability of the label in vivo. Our results demonstrated that the radiopharmaceutical developed in the present study was ideal for the intended purpose.

Adult↗

PubMed1991

Cell-culturing characteristics of newly developed PHEMA microcarriers: their use with BHK21 cells.

Baby hamster kidney (BHK) fibroblasts, as model cells, have been proliferated on acrylic based microcarriers. Microcarriers were prepared by a novel suspension polymerization of acrylic monomers. Hydroxyethyl methacrylate was the basic monomer. Ethylene glycol dimethacrylate was used as the cross-linker. A hydrophobic comonomer, namely, methyl methacrylate, was included in order to adjust the hydrophilicity of the resultant matrix. An acrylic comonomer with positively charged tertiary amine groups, i.e., dimethylaminoethyl methacrylate, was also added in order to optimize the surface charge of the carriers. The adhesion, spreading, and growth characteristics of BHK cells on these novel beads were studied either in stationary or in submerged culture conditions. The results demonstrate that the cell attachment and growth can be controlled by changing the degree of charge and the hydrophilicity of the poly(hydroxyethyl methacrylate) matrix.

Animals↗

PubMed1990

Blood plasma proteins on polyurethane and alkylsiloxane plasma-treated polyurethane surfaces. Dynamic approach by stimulus-response technique. Part 2. Evaluation of adsorption data by moment technique.

In this study, interactions of blood proteins (i.e. albumin and fibrinogen) with polyurethane biomaterial surfaces were investigated in an in vitro bead column test circuit using a stimulus-response technique. The dynamic sorption process of radiolabelled proteins on the surfaces was followed by detecting the radioactivity at the exit stream of the column, which was the response of a pulse stimulus at the inlet. The mathematical model was described and solved using 'parameter estimation by cybernetic moment technique', and the adsorption rate constants of plasma proteins on different biomaterial surfaces were calculated. By evaluation of the response curves with standard and cybernetic moment techniques, the following results were obtained. Albumin and fibrinogen adsorption is competitive, and the competition is strongly dependent upon the surface characteristics of the biomaterial. Preadsorption or preferential adsorption of albumin decreases the fibrinogen adsorption, and therefore increases the biocompatibility of material surface. Adsorption of blood plasma proteins are irreversible. The moment technique can also be used for the evaluation of stimulus-response data of biological systems, to determine the process parameters.

Adsorption↗

PubMed1990

Structural and cellular characterization of solvent-casted polyurethane membranes.

Fibroblastic cell attachment and growth characteristics of different polyurethane (PU) films were tested. These films were prepared by a classical solvent-casting procedure. By changing the composition and the type of casting solution (i.e. tetrahydrofurane, dioxane, dimethyl formamide-tetrahydrofurane, tetrahydrofurane-dioxane, etc.) PU films with different physical and chemical bulk and surface structures were obtained. Structural properties of these films were investigated by scanning electron microscopy, equilibrium swelling experiments and contact-angle studies. In stationary cell culture tests, a model cell-line, i.e. baby hamster kidney (BHK) were used. Thus the effects of structural properties on the cell behaviour were investigated. The results demonstrate that it is possible to achieve different cell responses by changing the preparation conditions of the films. While the cell attachment is excellent on porous PU surfaces, the others showed similar adhesion. Better proliferation of BHK cells was obtained with PU films prepared from dioxane solution.

Animals↗

PubMed1990

Swelling of PHEMA based membranes in ethanol and their nitroglycerin permeabilities.

The aim of this study is to prepare PHEMA based polymeric membranes for a transdermal delivery system, which includes a skin permeation enhancer (i.e. ethanol) for nitroglycerin. Membranes were prepared by bulk polymerization of HEMA monomer. Polymerization was achieved in the presence of EGDMA, as the cross-linker, and AIBN as the initiator. MMA was used as a comonomer to improve the mechanical properties and to adjust the permeabilities of the resulting membranes. Water was also included in the polymerization mixture to control the matrix structure. Membranes with different chemical and physical structures were prepared. Swelling behaviour of these matrices in ethanol were observed. Nitroglycerin diffusion through swollen membranes (in ethanol) were investigated. It was obtained that the relative amounts of ingredients (i.e., HEMA, MMA, EGDMA and water) in the casting solutions affect both the equilibrium swelling values and the permeabilities. By increasing the water content and by decreasing the amounts of MMA and EGDMA both parameters can be increased. AIBN does not affect these parameters significantly.

Ethanol↗

PubMed1990

Cell adhesion to the surfaces of polymeric beads.

The main goal of this study is to determine the relationship between the surface properties of polymeric materials and fibroblastic cell adhesion. Therefore, two series of polymeric beads, PHEMA and PS, were tested in microcarrier-facilitated cell culture systems. The crosslinked PHEMA beads were prepared by suspension polymerization of HEMA monomer in the presence of various acrylic monomers (i.e. MMA, EGDMA, DMAEMA). The hydrophobic PS beads were used after coated with different alkylamine monomers (i.e. EDA, ALAM, TEA) by plasma polymerization process. The cell culturing studies were performed with BHK cells in stationary culture conditions and the cell adhesion characteristics were determined by the common methods. Attachment of the BHK cells on these microcarriers were satisfactorily modeled by surface saturation type of mathematical expression. The results demonstrated that, there were finite number of sites on the microcarrier surfaces available for adhesion. Number of these sites depends on the surface charge density which was supplied by amine groups and surface wettability. It is possible to achieve desired cell adhesion and also growth, by changing the chemical structure of beads with suitable modification methods.

Allylamine↗

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↗