Hakan Ayhan

Modified PMMA monosize microbeads for glucose oxidase immobilization

Glucose oxidase (GOD) was immobilized onto modified polymethylmethacrylate (PMMA) microspheres by covalent bonding. Monosize PMMA microbeads with 1.5 μm diameter were produced by dispersion polymerization of methylmethacrylate by using polyvinyl alcohol as a stabilizer. Hydroxyl groups on the microbeads were first converted to aldehyde groups by periodate oxidation. Three amino compounds, namely ammonium hydroxide, ethylene diamine and hexamethylene diamine were incorporated through the aldehyde groups. Then, GOD molecules were immobilized through the spacer-arms by using glutaraldehyde. The highest amount of immobilization and activity were obtained in which hexamethylene diamine was used as the spacer-arm with 14 atom length, and were 2.1 mg g−1 polymer and 129 IU g−1 polymer, respectively. The optimal conditions for GOD immobilization were obtained as follows: pH, 6.0; temperature, 30 °C; immobilization time, 60 min; and GOD initial concentration, 0.10 mg ml−1. The optimal conditions for the GOD-immobilized PMMA microbeads were at pH 6.0 and at a temperature of 30 °C. The Km and Vmax values of the GOD-immobilized PMMA microbeads were, 13.79 mM and 26.31 mM min−1 calculated by non-linear regression, respectively.

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.

Optimization of urease immobilization onto non-porous HEMA incorporated poly(EGDMA) microbeads and estimation of kinetic parameters

Jack bean urease (urea aminohydrolase, EC 3.5.1.5) was immobilized onto modified non-porous poly(ethylene glycol dimethacrylate/2-hydroxy ethylene methacrylate), (poly(EGDMA/HEMA)), microbeads prepared by suspension copolymerization for the potential use in hemoperfusion columns, not previously reported. The conditions of immobilization; enzyme concentration, medium pH, substrate and ethylene diamine tetra acetic acid (EDTA) presence in the immobilization medium in different concentrations, enzyme loading ratio, processing time and immobilization temperature were investigated for highest apparent activity. Immobilized enzyme retained 73% of its original activity for 75 days of repeated use with a deactivation constant kd = 3.72 x 10(-3) day(-1). A canned non-linear regression program was used to estimate the intrinsic kinetic parameters of immobilized enzyme with a low value of observable Thiele modulus (phi < 0.3) and these parameters were compared with those of free urease. The best-fit kinetic parameters of a Michaelis-Menten model were estimated as Vm = 3.318 x 10(-4) micromol/s mg bound enzyme protein, Km = 15.94 mM for immobilized, and Vm = 1.074 micromol NH3/s mg enzyme protein, Km = 14.49 mM for free urease. The drastic decrease in Vm value was attributed to steric effects, conformational changes in enzyme structure or denaturation of the enzyme during immobilization. Nevertheless, the change in Km value was insignificant for the unchanged affinity of the substrate with immobilization. For higher immobilized urease activity, smaller particle size and concentrated urease with higher specific activity could be used in the immobilization process.

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.

Adhesion of different bacterial strains to low-temperature plasma-treated sutures

In this study, five different bacteria with their different strains were isolated and characterized. Contact angles were measured by a captive-bubble technique. Surface-free energies were calculated from the contact angles. Hydrophobicities also were evaluated by rho-xylene adhesion. The zeta potentials and surface charges of the bacteria were obtained. The contact angles of the gram-positive bacteria and gram-negative bacteria were within the range of 48 degrees-69 degrees and 43.5 degrees-55 degrees, respectively, while corresponding surface-free energies were in the limits of 45.4-51.6 erg/cm-2 and 51.7-61.8 erg/cm-2, respectively. The rho-xylene adhesions were parallel to hydrophobicities defined by contact angles, and 32.2-80.3% and 2.3-36.6% for the gram-positive bacteria and gram-negative bacteria, respectively. The zeta potentials for these bacteria were from -650.2 to +17.5 mV and from -159.6 to -6.0 mV, respectively. Most of the bacteria were negatively charged, except the CNS-2 and CPS-1 strains. In the second part of the study, attachment of these bacteria to Vicryl sutures and their DMAEMA and AAc plasma-treated forms were investigated. Hydrophobic bacteria attached more to hydrophobic Vicryl sutures. Both plasma treatments caused significant drops in bacterial attachment in most cases. Effects of AAc plasma treatment were more pronounced.

Effects of Atmospheric Pressure Plasma Treatments on Some Physical Properties of Wool Fibers

Knitted wool fabrics were treated with argon and air atmospheric plasma. Pilling, bursting strength, thermal resistance, thermal conductivity, air permeability, water vapor permeability and friction properties were investigated. The surfaces of untreated and plasma-treated wool fabrics were analyzed by scanning electron microscopy to compare the morphological changes. The outcomes showed that atmospheric plasma treatments affected the physical properties of wool fabrics such as thermal properties, water vapor permeability, air permeability and friction properties. While there was an increase in thermal resistance, water vapor permeability and friction properties; pilling tendency, bursting strength, thermal conductivity and air permeability values decreased.

Adhesion of different bacterial strains to low-temperature plasma treated biomedical PVC catheter surfaces

In this study, firstly five different bacteria (i.e. Coagulase positive and negative staphylococcus, Streptococcus pyogenes, Escherichia coli, Pseudomonas aeruginosa) with their different strains were isolated and used. The contact angle, surface free energy, p-xylene adhesion, and zeta potential of these bacteria were in the range of 43-69 deg, 45.4-61.8 erg cm(-2), 2.3-80.3%, and from -650.2 to + 17.5 mV, respectively. Most of the bacteria were negatively charged. Attachment of these bacteria to PVC catheter and its DMAEMA- and AAc-plasma treated forms were investigated. Bacterial attachment to the hydrophobic PVC catheter was high. Both plasma treatments caused significant drops in bacterial attachment in most of the cases. The effects of AAc-plasma treatment was more significant.

Investigation of blood compatibility of PMEA coated extracorporeal circuits

In this study, the blood compatibility of the PMEA-coated and uncoated hollow fibers was investigated using poly(2-methoxyethyl acrylate) PMEA-coated (X-coating, Terumo Corp., Japan) and uncoated (Capiox SX 18, Terumo Inc., Japan) oxygenators. Total protein, human serum albumin, fibrinogen, erythrocyte, leukocyte and platelets loss quantities were detected on blood samples taken in five different times during cardiopulmonarybypass (CPB) such as; baseline (T1), during CPB (T2), end of CPB (T3), after protamine injection (T4) and intensive care (T5). The average loss of fibrinogen for uncoated and PMEA-coated fiber surfaces was 1.34 and 0.25 g/L, respectively. After operation protein desorption assayfrom the PMEA-coated and uncoated fiber surfaces were examined, and significant protein desorption differences were found as 1.46 and 5.70 mg/dL, respectively. More platelet aggregation was observed for the uncoated fibers. Also for platelet loss quantities, significant differences were found as 116,000 and 36,000 cell/mm3,respectively,for uncoated and PMEA-coated fibers. Less bleeding was observed in the patients operated with oxygenator containing PMEA-coated fibers; more and longer postoperative haemorrhaging were observed when uncoated circuits have been used; fibrinogen losses caused longer blood clotting times. Differences in adsorbed protein quantities on hollow fiber surface and denaturation were examined by the aid of STM images, which showed that more proteins existed in the sample solution of uncoated fiber surfaces.

Albumin adsorption on to large-size monodisperse polystyrene latices having functional groups on their surfaces

Adsorption of bovine serum albumin (BSA) on to large-size monodisperse latices was investigated. Polystyrene (PS) latices in two different sizes with hydroxyl, amino and carboxyl groups on their surfaces were produced by following a two-step polymerization procedure. The effects of pH and ionic strength of the medium on BSA adsorption capacity of the latices were investigated in the existence of two different anions and three different cations, Cl-and SCN- and Na+, Ca2+ and Mg2+, respectively. Maximum adsorption capacities for all latices were obtained near the isoelectric point of BSA. No BSA adsorption was observed with PS latex, especially in the alkaline pH region. The BSA adsorption capacity decreased with increasing ionic strength. Different adsorption behaviors were noted in the PS latices having functional groups on their surfaces.

Coating of silicone-based impression materials in a glow-discharge system by acrylic acid plasma.

OBJECTIVES The main purpose of this study was to demonstrate an increase in the wettability of silicone-based impression materials after coating them with a hydrophilic film in a glow-discharge system. METHODS Two vinyl polysiloxane impression materials, Extrude (Kerr) and Accuflex (GC America Inc.) were used. Impression specimens were treated in a glow-discharge reactor at a radio frequency of 13.56 MHz at different discharge powers (5-20 W) and exposure times (5-60 min). Surface analysis of the specimens was done by FTIR. Surface contact angles were obtained by a captive-bubble method. These results were analyzed by ANOVA and Duncans Multiple Range test (p < 0.05). The total number of voids on the die stone casts was observed microscopically. Linear dimensional accuracy, detail reproducibility, and surface hardness of the die stone casts were also determined. A Student t-test was performed for statistical analysis of these parameters (p > 0.05). RESULTS FTIR spectra indicated that the number of hydroxyl groups on the surfaces increased (p > 0.05) because of the glow-discharge treatment. Contact angle measurements showed an increase (p < 0.05) in surface hydrophilicity. Total void formation in the stone casts decreased. There were no significant differences in the linear dimensional accuracy, detail reproducibility, and hardness, before and after glow-discharge treatment (p > 0.05). SIGNIFICANCE It was concluded that the surface wettability of the impression materials may be increased by plasma deposition, and therefore, the formation of voids was reduced in the stone casts.