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PubMed2005

Surface modification of poly(ether urethane urea) with modified dehydroepiandrosterone for improved in vivo biostability.

In this study, a fatty acid urethane derivative of dehydroepiandrosterone (DHEA) was synthesized and evaluated as a polyurethane additive to increase long-term biostability. The modification was hypothesized to reduce the water solubility of the DHEA and physically anchor the additive in the polyurethane during implantation. Polyurethane film weight loss in water as a function of time was studied to determine the polymer retention of the modified DHEA. The polyurethane film with unmodified DHEA had significant weight loss in the first day (10%) that was previously correlated to rapid leaching of the additive. The polyurethane film with modified DHEA had significantly less weight loss at all time points indicating improved polymer retention. The effect of the modified DHEA additive on the biostability of a poly(ether urethane urea) was examined after 5 weeks of subcutaneous implantation in Sprague-Dawley rats. Optical micrographs and infrared analysis of the specimens indicated that the modified DHEA bloomed to the surface of the film forming a crystalline surface layer approximately 10-15 microns thick. After explantation, this surface layer was intact without measurable differences in surface chemistry as monitored by attenuated total reflectance-Fourier transform infrared spectroscopy. There was no evidence of degradation of the polyurethane underneath the modified DHEA surface layer as compared with the polyurethane control. We have concluded that the modified DHEA self-assembled into a protective surface coating that inhibited degradation of the polyurethane. The roughness of the modified DHEA surface layer prevented adherent cell analysis to determine if the additive retained the ability to down-regulate macrophage activity. Subsequent studies will investigate the ability of surface-modifying additives to modulate cellular respiratory bursts in addition to the formation of an impermeable barrier. This bimodal approach to improving biostability holds great promise in the field of polyurethane biomaterials.

Animals↗

PubMedDate not supplied

Nanoparticle multilayers: surface modification of photosensitive drug microparticles for increased stability and in vitro bioavailability.

The results of this study report the novel use of electrostatic layer-by-layer nanoassembly of biocompatible nanoparticulate TiO2 multilayers to coat irregular nifedipine (NF) microcrystals to increase the photostability of the drug when exposed to simulated sunlight and to increase the dissolution rate and possibly the bioavailability of the drug after oral administration. The photostability of NF microcrystals (35 microm) coated with multiple bilayers of positively charged PDDA and negatively charged nanosized TiO2 particles (20-25 nm) was measured when exposed to an illuminance of 12 W/m2 corresponding to a light dose of 30 k lux or 25 W/m2 corresponding to light dose of 60 k lux. The dissolution rate of nifedipine from the coated microcrystals was measured in simulated gastric fluid containing 0.05% w/v polysorbate 80. Coating with one TiO2 layer increased the shelf life of nifedipine by 30 hours independent of the intensity of the light exposure. With an increase in the number of TiO2 layers; the photostability of the drug was enhanced even more. A TiO2 monolayer decreased the contact angle by 20 degrees for water and 33 degrees for the dissolution medium as compared with uncoated NF surfaces. This increase in wettability due to a decrease in contact angle increased the dissolution rate of nifedipine microcrystals coated with 1 PDDA/TiO2 bilayer 13-fold after 10 minutes, 5-fold after 1 hour, and 2-fold after 12 hours when compared to uncoated microcrystals. It is assumed that TiO2 increased the photostability because the nanoparticulate multilayers acts as a potential filter protecting the drug from damaging light rays reaching the drug crystals. The dissolution rate was increased because the hydrophilic TiO2 nanoparticles increased the aqueous wettability of the drug crystals thereby preventing aggregation in the dissolution medium. This ensured that the maximum drug surface area was exposed to the dissolution medium.

Biological Availability↗

PubMedDate not supplied

Surface modification to reduce nonspecific binding of quantum dots in live cell assays.

Nonspecific binding is a frequently encountered problem with fluorescent labeling of tissue cultures when labeled with quantum dots. In these studies various cell lines were examined for nonspecific binding. Evidence suggests that nonspecific binding is related to cell type and may be significantly reduced by functionalizing quantum dots with poly(ethylene glycol) ligands (PEG). The length of PEG required to give a significant reduction in nonspecific binding may be as short as 12-14 ethylene glycol units.

Acrylic Resins↗

PubMed2006

Polymer-coated magnetic nanoparticles: surface modification and end-functionalization.

ATRP (atom transfer radical polymerization) approach was employed to synthesis polymer-coated magnetite nanoparticles. These particles had an average diameter of 7.1 nm and a narrow size distribution. Characterization was performed using various techniques like Transmission Electron Microscopy (TEM), Ultraviolet-Visible spectroscopy (UV-vis), Fourier Transform Infrared spectroscopy (FTIR), Atomic Force Microscopy (AFM), and Vibrating Sample Magnetometry (VSM). The challenge was to obtain a thin shell and discrete particles in an unagglomerated state. Several factors like presence/choice of solvent, monomer-to-initiator concentration and structure of initiator were found to play a key role in this study. Attempts have been made to tailor the polymer shells by end-functionalization. This work has an enormous biomedical application potential.

Crystallization↗

PubMed1985

Surface modification of proteins. Activation of monomethoxy-polyethylene glycols by phenylchloroformates and modification of ribonuclease and superoxide dismutase.

A single-step method of activation of monomethoxypolyethylene glycols suitable for its binding to polypeptides and proteins is proposed. Based on the reaction with 2,4,5-trichlorophenylchloroformate or p-nitrophenylchloroformate, it gives reactive PEG-phenylcarbonate derivatives. The PEG intermediate is stable on storage, the activating group is easily quantified,and the reaction with amino acid and proteins proceeds rapidly at pH near neutrality. The PEG derivatization of enzymes with this procedure is less inactivating than those previously reported. Ribonuclease and superoxide dismutase were modified and the effect of (a) bound polymer on clearance time in rats, (b) antibody recognition, and (c) on the enzymatic activity toward low and high molecular weight substrates were studied.

Amino Acids↗

PubMedDate not supplied

Gelatin nanoparticles by two step desolvation--a new preparation method, surface modifications and cell uptake.

A new two-step desolvation method for manufacturing gelatin nanoparticles was developed. After the first desolvation step, the low molecular gelatin fractions present in the supernatant were removed by decanting. The high molecular fractions present in the sediment were redesolved and then desolvated again at pH 2.5 in the second step. The resulting particles can then be easily purified by centrifugation and redispersion. The different fractions obtained during the process were analysed by gel permeation chromatography (GPC). Based on these results, it can be concluded that the molecular weight of gelatin has a decisive influence on the stability of the manufactured gelatin nanoparticles. In addition, two fluorescent dyes (Texasred and fluoresceinamine) were coupled to the nanoparticles for cell uptake studies. The fluorescent nanoparticles showed a high uptake into monocytes/macrophages.

Cells, Cultured↗

PubMed2004

Novel surface-modification techniques for polymer-based separation media. Stimulus-responsive phenomena based on double polymeric selectors.

A pair of polymeric selectors potentially responding to stimulation was introduced onto monosized porous polymer particles to be evaluated as a packing material for HPLC. Possible complexes formed between polyacrylamide (PAAm) and poly(methacrylic acid) (PMAA) were utilized as stimulus responsive polymeric selectors. Uniformly sized base polymer particle was prepared by multi-step swelling and polymerization method, while the introduction of PAAm and PMAA was done by newly invented modification technique. In this technique, a solvent in which both acrylamide (AAm) and methacrylic acid (MAA) monomers are soluble, but PAAm and PMAA are insoluble, was utilized as a modification medium. The polymer particle doubly modified with PAAm and PMAA was utilized as packing material for HPLC and the stimulus responses were evaluated by changing temperature or pH to check change of the slope of a Van't Hoff plot. By using water as a mobile phase, the expected inflection point of the Van't Hoff plot was observed at upper critical solution temperature (UCST) of the polymer complexes and the temperature responsive ability was observed. Moreover, pH responsive ability was studied by using buffer of either pH 4 or 10 as mobile phase. Slope of the plot was changed in buffer of pH 4, but no change of slope was observed in the buffer of pH 10.

Chromatography, High Pressure Liquid↗

PubMed2004

Surface modification of poly(ethylene-co-vinyl alcohol): hydroxyapatite immobilization and control of periodontal ligament cells differentiation.

To reveal and control the differentiation and proliferation of the periodontal ligament (PDL) cells and to develop a highly organized hybrid implant possessing periodontium, hydroxyapatite (HAP) was immobilized on the poly(ethylene-co-vinyl alcohol) (EVA) by alternate soaking method following with carboxyl groups' introduction through ozone exposure. Human PDL cells were cultured on the ozone-exposed EVA, collagen-immobilized EVA, HAP-immobilized EVA, HAP plate, tricalcium phosphate plate, and conventional tissue culture dish. Cell proliferation was highest on the collagen-immobilized EVA and lowest on the HAP-immobilized EVA. Alkaline phosphatase activity and osteocalcin secretion were highest on the HAP-immobilized EVA. These results suggest that PDL cells were differentiated toward bone-like cells on the HAP-immobilized EVA.

Adsorption↗

PubMed1975

Surface modifications evoked by estradiol and diethylstilbestrol in isolated endometrial cells: evidence from lectin probes and extracellular release of lysosomal protease.

Endometrial cells were isolated from the uteri of ovariectomized rats. The inhibitory effect of alpha-methyl-D-mannoside on fluorescein-labeled concanavalin A (Con A) binding to these cells indicates that they possess specific binding sites for Con A. The lectin also mediates adsorption of homologous erythrocytes to these cells. Both Con A binding and Con A-mediated hemadsorption to endometrial cells are depressed at 4 C compared with these functions in cells maintained at 22 C. Gross elevations in lectin-mediated hemadsorption to endometrial cells are evident following prior exposure to 1 X 10(-9)M concentrations of diethylstilbestrol (DES) or estradiol-17beta, but not to the physiologically inactive 17 alpha-epimer, at 22 C. The enhancement of hemagglutinability cannot be attributed to a corresponding increase in lectin binding at 22 C. Although estrogen treatment elicited significant increments in Con A binding as early as 5 min after addition of estrogen to cell suspensions, the increment in agglutination attributable to hormone treatment consistently ranged from 1.5-3 times greater than the increase in lectin binding. These estrogenic effects were reduced by incubation of the endometrial cells at 4 C or when cortisol, 3 X 10(-6)M, was present with estradiol-17beta. In parallel experiments, treatment with DES and estradiol-17beta, but not estradiol-17 alpha, also enhanced the release of cathepsin B 1 and acid phosphatase from uterine segments into the particle-free extracellular media in which the tissues had been incubated for 30-60 min. The marked increment in the extracellular activity of the lysosomal hydrolases induced by estrogen treatment was suppressed in cells incubated at 4 C or when cortisol was present concomitantly. These and related data suggest the hypothesis that acute increments in lysosomal hydrolase activity may contribute to cell surface alterations which have been described in both normal and aberrant processes of cell growth.

Acid Phosphatase↗

PubMed2006

Sol-gel based surface modification of electrodes for electro analysis.

In chemical analysis and electrochemical catalysis modified electrodes have been used in a wide range. In addition to the several methods of electrode modification reported in literature, the sol-gel route offers a possibility of preparing ceramic like films under rather mild conditions. This enhances the possibility of incorporation of temperature sensitive particles such as enzymes, microorganisms, proteins and several other biomolecules into such composite layers, resulting in very inert and stable matrices useful for analytical applications. The present paper, in addition to providing an overview of the various analytical applications of sol-gel processes, presents the fabrication and evaluation, of a novel sol-gel based potentiometric sensor for pH measurement. The performance characteristics of the sol-gel based pH sensor is evaluated using buffers in the pH range 2-10 prepared using standard buffer compositions reported in literature. The results show a linear correlation between negative logarithm of hydrogen ion concentration and measured millivolt response.

Biosensing Techniques↗

PubMed2005

Comparison of surfactants for dynamic surface modification of poly(dimethylsiloxane) microchips.

In the present report, the use of negatively charged surfactants as modifiers of the background electrolyte is reported using poly(dimethylsiloxane) (PDMS) microchips. In particular, the use of anionic surfactants, such as sodium dodecyl sulfate, phosphatidic acid, and deoxycholate, was studied. When surfactants were present in the run buffer, an increase in the electroosmotic flow (EOF) was observed. Two additional effects were also observed: (i) stabilization of the run-to-run EOF, (ii) an improvement in the electrochemical response for several biomolecules. In order to characterize the analysis conditions, the effects of different surfactant, electrolyte, and pH were studied. EOF measurements were performed using either the current monitoring method or by detection of a neutral molecule. The first adsorption/desorption kinetics studies are also reported for different surfactants onto PDMS. The separation of biologically important analytes (glucose, penicillin, phenol, and homovanillic acid) was improved decreasing the analysis time from 200 to 125 s. However, no significant changes in the number of theoretical plates were observed.

Adsorption↗

PubMed2006

Surface modification of metallic cardiovascular stents by strongly adhering aliphatic polyester coatings.

This article reports on a novel two-step strategy for the coating of cardiovascular stents by strongly adhering biocompatible and biodegradable aliphatic polyesters. First, a precoating of poly(ethylacrylate) (PEA) was electrografted onto the metallic substrate by cathodic reduction of the parent monomer in dimethylformamide (DMF). The electrodeposition of PEA, in a good solvent of it, was confirmed by both Infra-red and Raman spectroscopies. The pendant ester groups of PEA were then chemically reduced into aluminum alkoxides, able to initiate the ring-opening polymerization (ROP) of either D,L-lactide (LA) or epsilon-caprolactone (CL). Growth of biodegradable PLA or PCL coatings from the adhering precoating was confirmed by both Infra-red and Raman spectroscopies, and directly observed by scanning electron microscopy (SEM). This type of coating can act as an anchoring layer for the subsequent casting of drug-loaded polyester films allowing the controlled release of antiproliferative agents for the treatment of in-stent restenosis.

Biocompatible Materials↗

PubMed1997

Lymphatic uptake and biodistribution of liposomes after subcutaneous injection: III. Influence of surface modification with poly(ethyleneglycol).

PURPOSE: The aim of the present paper was to assess the effect of inclusion of distearoylphosphatidylethanolamine-poly(ethyleneglycol) (DSPE-PEG) into liposomal bilayers on the lymphatic uptake and lymph node localization of liposomes after subcutaneous administration. METHODS: [3H]-Cholesteryloleylether labeled liposomes of various composition and sizes were injected s.c. into the dorsal side of the foot of rats. At several time-points after injection, blood levels of liposomes were determined. Lymphatic uptake from the s.c. site of injection and lymph node localization in regional lymph nodes were determined at the end of the 52 h observation period. RESULTS: The results demonstrate that inclusion of DSPE-PEG into several types of liposomes has only a modest effect on lymphatic uptake. Also lymph node localization is only slightly affected by PEG-mediated steric stabilization. CONCLUSIONS: Factors other than the presence of a steric barrier are more important in determining lymphatic uptake from the s.c. injection site. The observation that lymph node localization was only slightly affected by PEG-coating strongly suggests that macrophage uptake is not the only important mechanism of lymph node localization of s.c. administered liposomes.

Animals↗

PubMed2005

Surface modification of gold and quantum dot nanoparticles with chitosan for bioapplications.

Gold (Au) and quantum dot (QD) nanoparticles, which have been extensively used in many fields, were encapsulated with a natural polymer, chitosan, to improve their biocompatibility. Characterization was performed using ultraviolet-visible, dynamic light scattering, atomic force microscopy, and transmission electron microscope analyses. It was found that a Au/chitosan ratio of 1:1 and smaller produced chitosan-encapsulated Au nanoparticles of a sufficiently small size, and this result was then applied in the chitosan encapsulation of QDs. The biocompatibility of both types of nanoparticles was assessed in cell culture studies using HT29 human colon carcinoma and NIH 3T3 mouse fibroblast cells. MTT and trypan blue exclusion assays revealed that both chitosan-encapsulated Au nanoparticles and QDs exhibited improved biocompatibility over their bare, nonencapsulated counterparts. Therefore, this study showed that chitosan could be used to encapsulate both Au nanoparticles and QDs in order to enhance their biocompatibility. The approaches developed in this study can also be extended to other nanoparticles for bioapplications as well.

Animals↗

PubMed2003

Irradiation effects in MALDI, ablation, ion production, and surface modifications. Part II. 2,5-dihydroxybenzoic acid monocrystals.

Irradiation effects at low and high laser fluence on 2,5-dihydroxybenzoic acid large crystals were investigated. Contrary to what was observed for matrices as cinnamic acid derivatives, no chemical degradation of matrix is evidenced and continuous ablation as well as ion production resulted of extended irradiation in all the fluence range corresponding to classical matrix-assisted laser desorption /ionization. Ripples are formed on the base of the crater for a limited number of laser shots under moderate fluence. For extended irradiation, conical shape craters are formed with the axis of the crater oriented along the incident direction of the laser beam. A study of the craters showed that ablation through the ablated volume slowly varied with the laser fluence when a strong increase of ion production (matrix and analyte) was recorded. Ablation volume was found to vary non-linearly with the number of laser shots. On a same spot, the ablated volume and the ion production were measured as a function of the laser energy. With an increasing laser energy (or fluence), the ablated volume slowly increases when the ion production strongly increases. This gives evidence of a decoupling between ablation and ionization. Interaction of the plume with the incoming beam is thus probable.

Crystallization↗

PubMed2002

Surface modification of extrasynovial tendon by chemically modified hyaluronic acid coating.

We investigated a method for chemically binding hyaluronic acid (HA) to extrasynovial tendon and the effect of chemically modified HA on the gliding resistance of tendon. Canine peroneus longus (PL) tendons were immersed into one of three different solutions (saline, 1% HA, or 1% chemically modified HA) for 2 h. The gliding resistance of treated PL tendons was measured at 1, 5, 10, 20, 50, and 100 cycles in a saline bath. After treatment with unmodified HA and chemically modified HA, the gliding resistance of the PL tendons decreased significantly compared with the saline-treated tendons (p < 0.05), and this effect of the two HA treatments persisted through 10 cycles. For cycles 20-100, the gliding resistance of PL tendons treated with chemically modified HA remained significantly lower than that of tendons treated either with saline or unmodified HA (p < 0.01). The effect of paratenon removal on gliding resistance was neither statistically significant for repetitions beyond 10 cycles, nor was it an independent predictor of gliding resistance, as the effect (higher resistance after paratenon removal) was mainly seen in the saline-treated tendons. Chemically modified HA-treated extrasynovial tendons may improve gliding of tendon graft and reduce adhesion postoperatively, compared with traditional grafts.

Animals↗

PubMed1995

A new porous surface modification technology for peritoneal dialysis catheters as an exit-site cuff to reduce exit-site infections.

Catheter exit-site infection continues to be a more common morbid event in patients undergoing peritoneal dialysis. Previous attempts to place a biointegration material at the next site have failed to reduce infection rates. This study reports the use of an innovative microporous silicone material placed as a cuff around the catheter at the exit site. The porous material has a pore-sized distribution that stimulates and facilitates capillary ingrowth into the pores. This capillary ingrowth prevents scar tissue formation, increases blood supply, and theoretically improves the immunological competence of the tissue at the vulnerable exit site. Twenty-five test catheters (12 using standard exit-site creation and 13 using the Moncrief-Popovich implantation technique) were implanted in a canine model. The exit-site infection rate in a canine model without the microporous material was 100% at 2 months. The corresponding results with the microporous material was 40% at 2 months. The majority of the test catheters showed progressive drying and healing at the exit site. Sixty percent of the catheters healed quickly and remained infection-free. Biointegration of the microporous material at the exit-site was demonstrated. Several exit site infections with the test catheters treated only with local therapy (without systemic or topical antibiotics) demonstrated progressive healing and secondary adequate biointegration. Because of these encouraging results, human studies were initiated, with the first human implant occurring in August, 1994. A 10-patient project is planned for the next year.

Animals↗

PubMed2001

Amphiphilic poly-N-vinylpyrrolidones: synthesis, properties and liposome surface modification.

Certain amphiphilic water-soluble polymers including amphiphilic derivatives of polyvinyl pyrrolidone (PVP) were found to be efficient steric protectors for liposomes in vivo. In this study, we have tried to develop synthetic pathways for preparing amphiphilic PVP and to investigate the influence of the hydrophilic/hydrophobic blocks on some properties of resulting polymers and polymer-coated liposomes. To prepare amphiphilic PVP with the end stearyl (S) or palmityl (P) residues, amino- and carboxy-terminated PVP derivatives were first synthesized by the free-radical polymerization of vinyl pyrrolidone in the presence of amino- or carboxy-mercaptans as chain transfer agents, and then modified by interaction of amino-PVP with stearoyl chloride or palmitoyl chloride, or by dicyclohexyl carbodiimide coupling of stearylamine with carboxy-PVP. ESR-spectra of the hydrophobic spin-probe, nitroxyl radical N-oxyl-2-hexyl-2-(10-methoxycarbonyl)decyl-4,4'-dimethyl oxazoline, in the presence of amphiphilic PVP demonstrated good accessibility of terminal P- and S-groups for the interaction with other hydrophobic ligands. Spontaneous micellization and low CMC values (in a low micromolar range) were found for amphiphilic PVP derivatives using the pyrene method. In general, S-PVP forms more stable micelles than P-PVP (at similar MW, CMC values for S-PVP are lower than for P-PVP). It was found that amphiphilic PVP incorporated into negatively charged liposomes effectively prevents polycation(poly-ethylpyridinium-4-vinylchloride)-induced liposome aggregation, completely abolishing it at ca. 10 mol% polymer content in liposomes. Additionally, the liposome-incorporated PVP prevents the fluorescence quenching of the membrane-incorporated hydrophobic fluorescent label [N-(4-fluoresceinthiocarbamoyl)dipalmitoyl-PE] by the free polycation. PVP-modified liposomes were loaded with a self-quenching concentration of carboxyfluorescein, and their destabilization in the presence of mouse serum was investigated following the release of free dye. Amphiphilic PVP with MW between 1,500 and 8,000 provides good steric protection for liposomes. The degree of this protection depends on both polymer concentration and molecular size of the PVP block.

Animals↗