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PubMed1994

Effect of surface treatments on the repair strength of a light-activated denture repair resin using censored data.

OBJECTIVES: The aim of this study was to evaluate the effect of three different chemical surface modifications on the bond strength of light-activated denture repair resin (Triad, Dentsply International) to a heat-cured resin (Lucitone, Dentsply International). METHODS: Transverse flexure test specimens were made, with surface treatment of 1) Triad bonding agent, 2) unreacted Lucitone monomer, and 3) a 1:1 mixture of methylene chloride and monomer, using two different application times (2 and 4 min). For all except one group, 18 specimens were made. The controls were solid single composition bars, 18 for each material. The elastic modulus in transverse flexure was measured for each material. The statistical analysis employed the Weibull distribution. Fracture strength values were obtained in a three-point flexure test. RESULTS: It was noted that many fractures occurred away from the interface and the center member of the test fixture. For those fractures, the observed fracture strength is a censored value of the fracture strength. Algorithms for the statistical treatment of censored data were used to get the maximum likelihood estimates of the fracture strength. A mechanical model showed that under three-point bending of a beam of two joined materials, fractures will occur in the part with the higher elastic modulus. This finding is indeed observed in the data. The 4 min monomer treatment showed the highest estimate of the bond strength (187.8 MPa). SIGNIFICANCE: Censored data can be used to obtain fracture strength estimates, and the censoring indicates that the bond strength may exceed the strength of the bulk material.

Acrylic Resins↗

PubMed1987

Redox behaviour of anti-tumor platinum (II) compounds (carboplatin) at solid electrodes.

The electroactivity of a cytostatic complex of platinum (II) possessing no halide ligand (carboplatin) has been studied in aqueous media using platinum and carbon paste electrodes. Cyclic voltammetry has been conducted in order to elucidate the redox behaviour of carboplatin as a function of chloride concentration. Reduction was not observed although oxidation was detected. The nature of the compounds formed during the electro-oxidation was directly related to free chloride ions. At the carbon paste electrode, the reduction of the oxidized species occurred in two steps with the formation of cis-platinum structures and a subsequent electrodeposition of platinum particles. The surface modification step at the carbon paste electrode has demonstrated electrocatalytic properties of the electrode towards platinum (II) complexes possessing halide ligands in their structures. Electrodeposition of platinum ions at a platinum electrode surface as well as a judicious choice of working parameters allows quantitative determinations in the concentration range 3 x 10(-4) - 1 x 10(-5) M.

Journal Article↗

PubMed2005

Biofilms and antibiotic therapy: is there a role for combating bacterial resistance by the use of novel drug delivery systems?

The conventional view of antibiotic resistance is one where bacteria exhibit significantly reduced susceptibility to antimicrobials in laboratory tests by mechanisms such as altered drug uptake, altered drug target and drug inactivation. Whilst these mechanisms undoubtedly make a major contribution to antibiotic failure in the clinic, the phenomenon of clinical failure in spite of sensitivity in laboratory tests is also well recognised. It is in this context that attention has focussed on bacteria growing as adherent biofilms, not only as the mode of growth of device-related infections associated for example with artificial joints and venous catheters, but also with other chronic infections such as those occurring in the respiratory tract. Growth as a biofilm almost always leads to a significant decrease in susceptibility to antimicrobial agents compared with cultures grown in suspension and, whilst there is no generally agreed mechanism for the resistance of biofilm bacteria, it is largely phenotypic. That is, when biofilm bacteria are grown in conventional laboratory suspension culture they become susceptible to antimicrobials. A number of elements in the process of biofilm formation have been studied as targets for novel drug delivery technologies. These include surface modification of devices to reduce bacterial attachment and biofilm development as well as incorporation of antimicrobials-again to prevent colonisation. Electrical approaches have been used either to release antimicrobials from device surfaces or to drive antimicrobials through the biofilm. Other technologies not specifically focussed on biofilms include aerosolized delivery of antibiotics to the lung and formulation into liposome and polymer-based vehicles. Liposomal systems have been widely studied, either to target antibiotics to the surface of bacterial biofilms, or by virtue of their property of being taken up cells of the reticuloendothelial system, to target antibiotics towards intracellular bacteria. Many polymer-based carrier systems have also been proposed, including those based on biodegradable polymers such as poly(lactide-co-glycolide) as well as thermoreversible hydrogels. Their contribution to the prevention or resolution of infection is reviewed.

Anti-Bacterial Agents↗

PubMed2006

Probing proteins on functionalized silicon surfaces using matrix-assisted laser desorption/ionization mass spectrometry.

Flat H-terminated Si(111) substrates modified with alkyl monolayers terminated with hydrophobic and hydrophilic functional groups were prepared using known surface functionalization methods and characterized by FTIR, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The surfaces were then used for the study of non-specific binding of proteins from complex mixtures (using standard mixture of proteins with average molecular weight approximately 6-66 kDa) by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Protein adsorption on these surfaces (following on-probe fractionation of the mixture) was found to be dependent on the nature of surface functional groups, and nature and pH of rinsing solutions used. The results obtained in this work demonstrate that simple silicon-based surface modifications can be effective for direct analysis of complex mixtures by MALDI-MS. Preliminary results obtained using similarly functionalized porous silicon substrates proved that such substrates are (due to their increased surface areas) better performing than flat silicon.

Adsorption↗

PubMedDate not supplied

Tailoring of bioresorbable polymers for elaboration of sugar-functionalized nanoparticles.

Maleic copolymers with different contents of galactose moieties and dodecyl chains were synthesized and used as both a stabilizer and a surface coating for the preparation of poly(epsilon-caprolactone) nanoparticles by the emulsification-diffusion technique. The size of the nanoparticles was controlled by varying the initial concentration of the modified maleic copolymers. As the concentration of the latter increased, the particle size decreased, indicating that the copolymers serve as a stabilizer. Moreover, surface modification of nanoparticles was confirmed by xi-potential measurements. Nanoparticles were also shown to be recognized by a galactose-specific lectin, demonstrating the presence of galactose units on the particle surface. This approach offers opportunities for the production of novel targeted drug delivery systems.

Biocompatible Materials↗

PubMed2006

Tumor targeting by surface-modified protein microspheres.

Protein microspheres have been used in the fields of biomedical imaging and drug delivery, but surface modification for cell targeting has been problematic. We have for the first time used an electrostatic adhesion approach to adhere arginine-glutamic acid-aspartic acid (RGD) containing peptides to the surface of protein microspheres for the purpose of targeting these vesicles to tumor cells. RGD sequences are recognized by integrin membrane receptors, which are overexpressed in various tumors. We have succeeded in modifying the surface of serum albumin core-shell microspheres, which have a fluorescent nonaqueous core by using several polylysine peptides containing the RGD sequence. Fluorescence microscopy reveals that these modified microspheres are selectively bound and taken up by HT29 human colon cancer cells in vitro.

Antineoplastic Agents↗

PubMed1999

Surface characterization of polymers for medical devices.

A survey is given on analytical techniques currently applied to the surface characterization of biomedical polymers. The techniques include spectroscopies, thermodynamic and electrochemical measurements and microscopies, respectively. To illustrate the motivation for surface analysis, the hypotheses on the correlations between surface parameters and hemocompatibility of polymers are briefly examined. The applications of the examined methods are illustrated by a number of examples. These examples include the characterization of cellulose membranes (low-flux hemodialysis membranes) by streaming potential measurements and by inverse contact angle measurements. The use of surface spectroscopies (ATR-FTIR and XPS) is demonstrated by considering the optimization of surface modification procedures of vascular prostheses made from poly(tetrafluoroethylene). Furthermore, the characterization of water-swollen cellulose membranes by scanning force microscopy is shown. Finally, the extended application of physico-chemical surface analysis to the investigation of protein adsorption is considered. An example deals with in situ spectroscopic ellipsometry used to study the adsorption of fibrinogen onto a plasma-deposited hydrophobic fluoropolymer and onto poly(ethyleneoxide)-grafted fluoropolymer, respectively.

Biocompatible Materials↗

PubMed2006

Structural modifications in chronic microwire electrodes for cortical neuroprosthetics: a case study.

Long-term viability of chronic invasive neural probes is a necessary condition for extracting robust control signals directly from neural tissue. Although immune/tissue response is a leading factor in the degradation of single neuron recording, we investigate a second component of signal degradation connected to the structural changes associated with microwire electrodes chronically exposed to extracelluar environments in vivo. Scanning electron microscopy is used to assess the surface modifications to the electrodes after an implantation duration of four weeks in rats. The electrode developed a smooth fracture surface, a reduction of the metal diameter, and pitting in the insulation of the electrode structure. Over the duration of implantation, recording properties of the electrode were marked by a reduction in the peak-to-peak amplitude in neuronal firing.

Action Potentials↗

PubMed2006

Surface heparinization of polyurethane via bromoalkylation of hard segment nitrogens.

Previous research from our group has demonstrated that bromoalkylation of polyurethane elastomers via base mediated activation of the urethane-hard segment nitrogen groups can be used to either attach bisphosphonate groups to confer calcification resistance or append cholesterol to promote endothelial cell adhesion. In the present studies we further explore the potential of this chemical approach by investigating bulk carboxylation of polyurethanes via bromoalkylation to enable surface heparinization for thromboresistance. Thus, polyurethane (PU) was modified with pendant 7-carboxy-5-thiaheptyl groups using a polymer-analogous reaction of bromobutylated PU with tetrabutylammonium 3-mercaptopropionate in mild conditions. The grafting of polyallylamine (PAA) onto the surface of carboxylated PU via direct coupling of amino and carboxy groups resulted in high levels of PAA (up to 8 mug/cm(2)). The surface-aminated PU was further covalently modified with unfractionated heparin as confirmed by FTIR. Fluorescence labeling of PAA hydrochloride and heparin with BODIPY-FL was used to quantify the extent of surface modifications. Heparin was covalently bound at a high level (1.11 +/- 0.06 mug/cm(2)) and was shown to be active, with demonstrable Factor Xa inhibition and platelet factor IV binding. It is concluded that surface amination of bulk-carboxylated PU represents a novel approach for heparinizing PU; carboxylation followed by surface amination represents another important dimension of bromo-alkyl activation of polyurethane hard segments, thereby enabling heparinization.

Alkylation↗

PubMed1996

Decreased prostaglandin E2 synthesis by lens epithelial cells cultured on heparin-surface-modified poly(methyl methacrylate).

PURPOSE: To evaluate whether heparin surface modification reduces prostaglandin E2 (PGE2) synthesis by lens epithelial cells (LECs) after intraocular lens (IOL) implantation. SETTING: Nishi Eye Hospital, Jinshikai Medical Foundation, Osaka, Japan. METHODS: The prostaglandin E2 (PGE2) concentration was determined in an incubation medium of human cataract LECs cultured on heparin-surface-modified (HSM) poly(methyl methacrylate) (PMMA) plates at 1, 2, 3, and 4 weeks of culture. A medium without heparin served as a control. RESULTS: The PGE2 concentration was significantly lower in the HSM than in the control medium at 3 and 4 weeks of culture. CONCLUSION: The results are consistent with the clinical observation of significantly decreased inflammation in eyes with HSM IOLs, indicating that such modification increases PMMA's biocompatibility with LECs.

Cataract↗

PubMed1995

In vivo platelet deposition on polytetrafluoroethylene coated with fibrin glue containing fibroblast growth factor 1 and heparin in a canine model.

BACKGROUND: We previously reported that the coating of expanded polytetrafluoroethylene (ePTFE) with fibrin glue containing fibroblast growth factor 1 (FGF-1) and heparin accelerates endothelial coverage of grafts implanted into animals. We report here the effect of this surface modification on early platelet deposition. MATERIALS AND METHODS: Nine dogs received 7-cm ePTFE grafts, 60-microns internodal distance, 4-mm internal diameter, as bilateral aortoiliac implants, one coated (luminal cross section and abluminal surface) with fibrin glue (fibrinogen 32.1 mg/mliters, thrombin 0.32 U/mliters) containing FGF-1 (11 ng/mliters and heparin (250 U/mliters), the other uncoated. After 5, 30, or 120 minutes of circulation with blood containing autologous platelets radiolabelled with indium 111, gamma emissions were quantitated on explants and correlated to surface areas measured by computerized planimetry. RESULTS: Both global and segmental comparisons showed significantly (P < 0.05, Student's t-test) less platelet deposition on coated than on uncoated grafts after 120 minutes of circulation, but no difference at 5 and 30 minutes. CONCLUSIONS: In this model, ePTFE coating with fibrin glue containing FGF-1 and heparin shows no adverse effect on early platelet deposition.

Animals↗

PubMed2002

Effect of surface chemistries and characteristics of Ti6Al4V on the Ca and P adsorption and ion dissolution in Hank's ethylene diamine tetra-acetic acid solution.

This study examined the influence of chemistries and surface characteristics of Ti6Al4V on the adsorption of Ca and P species and ion dissolution behavior of the material exposed in Hank's solution with 8.0 mM ethylene diamine tetra-acetic acid at 37 degrees C. The variation of chemistries of the alloy and nano-surface characteristics (chemistries of nano-surface oxides, amphoteric OH group adsorbed on oxides, and oxide thickness) was effected by surface modification and three passivation methods (34% nitric acid passivation. 400 degrees C heated in air, and aged in 100 degrees C water). X-ray photoelectron spectroscopy and Auger electron spectroscopy were used for surface analyses. The chemistries of nano-surface oxides in a range studied should not change the capability of Ca and P adsorption. Nor is the capability affected significantly by amphoteric OH group and oxide thickness. However, passivations influence the surface oxide thickness and the early stage ion dissolution rate of the alloy. The rate-limiting step of the rate can be best explained by metal-ion transport through the oxide film, rather than hydrolysis of the film. Variation of the chemistries of titanium alloy alters the electromotive force potential of the metal, thereby affecting the corrosion and ion dissolution rate.

Adsorption↗

PubMedDate not supplied

"SMART" drug delivery systems: double-targeted pH-responsive pharmaceutical nanocarriers.

To develop targeted pharmaceutical carriers additionally capable of responding to certain local stimuli, such as decreased pH values in tumors or infarcts, targeted long-circulating PEGylated liposomes and PEG-phosphatidylethanolamine (PEG-PE)-based micelles have been prepared with several functions. First, they are capable of targeting a specific cell or organ by attaching the monoclonal antimyosin antibody 2G4 to their surface via pNP-PEG-PE moieties. Second, these liposomes and micelles were additionally modified with biotin or TAT peptide (TATp) moieties attached to the surface of the nanocarrier by using biotin-PE or TATp-PE or TATp-short PEG-PE derivatives. PEG-PE used for liposome surface modification or for micelle preparation was made degradable by inserting the pH-sensitive hydrazone bond between PEG and PE (PEG-Hz-PE). Under normal pH values, biotin and TATp functions on the surface of nanocarriers were "shielded" by long protecting PEG chains (pH-degradable PEG(2000)-PE or PEG(5000)-PE) or by even longer pNP-PEG-PE moieties used to attach antibodies to the nanocarrier (non-pH-degradable PEG(3400)-PE or PEG(5000)-PE). At pH 7.4-8.0, both liposomes and micelles demonstrated high specific binding with 2G4 antibody substrate, myosin, but very limited binding on an avidin column (biotin-containing nanocarriers) or internalization by NIH/3T3 or U-87 cells (TATp-containing nanocarriers). However, upon brief incubation (15-30 min) at lower pH values (pH 5.0-6.0), nanocarriers lost their protective PEG shell because of acidic hydrolysis of PEG-Hz-PE and acquired the ability to become strongly retained on an avidin column (biotin-containing nanocarriers) or effectively internalized by cells via TATp moieties (TATp-containing nanocarriers). We consider this result as the first step in the development of multifunctional stimuli-sensitive pharmaceutical nanocarriers.

Drug Carriers↗

PubMed2003

Biological behavior of sol-gel coated dental implants.

The biocompatibility of dental implants coated with titania/hydroxyapatite (HA) and titania/bioactive glass (BG) composites obtained via sol-gel process was investigated using an in vitro and in vivo model. A device for the in vitro testing of screw-shaped dental implants was developed, in order to well compare the two experimental models studying the behavior of human MG63 osteoblast-like cells seeded onto a particular geometry. The expression of some biochemical parameters of osteoblastic phenotype (alkaline phosphatase specific activity, collagen and osteocalcin production) and some indications on cells morphology obtained by scanning electron microscopy were evaluated. The in vitro and in vivo models were compared after implants insertion in rabbit tibia and femur. The removal torque and histomorphometric parameters (percentage of bone in contact with implant surface and the amount of bone inside the threaded area) were examined. A good agreement was found between the in vitro and in vivo models. These experiments showed better performances of HA and BG sol-gel coated dental implants with respect to uncoated titanium; in particular, it was found that in vitro the HA coating stimulates osteoblastic cells in producing higher level of ALP and collagen, whereas in vivo this surface modification resulted in a higher removal torque and a larger bone-implant contact area. This behavior could be ascribed to the morphology and the chemical composition of the implants with rough and bioactive surfaces.

Journal Article↗

PubMed2000

Vitamin E modified cellulose membrane.

There has been a demand for hemodialysis membranes of better biocompatibility, the use of which would reduce the incidence of complications in patients who have been under long hemodialysis treatment. We developed a surface modification technique consisting of forming efficiently a synthetic polymer layer on the inside of the regenerated cellulose hollow fiber without impairing fiber performance. Our newly developed membrane has excellent biocompatibility by modifying the inner surface and by immobilizing vitamin E (alpha-tocopherol), which serves as an antioxidant, to the modified surface.

Animals↗

PubMed2000

The effect of fluorinated surface modifying macromolecules on the surface morphology of polyethersulfone membranes.

Polyethersulfone (PES) has been recently adopted for membrane materials in applications such as ultrafiltration and haemodialysis. As a biomaterial, the factors which affect the blood compatibility of PES membranes include surface energetics, hydrophobicity, and surface morphology. Surface fluorination of materials has been found to create surfaces with improved blood compatibility and chemical stability. One novel approach to generating fluorinated polymer surfaces has included the use of fluorinated surface modifying macromolecules (SMMs). These macromolecules have been reported to establish fluorinated functional groups at surfaces of polymeric materials without significantly affecting the physical properties of the base polymer. However, to date there has been relatively little information published on the nature of the surface structure for PES materials containing these SMMs. In this study, synthesized SMMs with varying chemical compositions were characterized and blended with PES, and fabricated into flat sheet membranes. The bulk thermal transitions of PES materials were not significantly altered by the addition of 4 wt% SMMs. Contact angle data showed that the addition of SMMs in PES created more hydrophobic surfaces, accompanied by an increase in surface heterogeneity. X-ray photoelectron spectroscopy studies confirmed the presence of elemental fluorine at the surface. Through microscopy studies, it was shown that surface modification was achieved by the migration of SMM concentrated microdomains to the air-membrane interface. The generated microdomains (approximately 1-2 microm in diameter) are dispersed within the top 8 microm of the surface. The concentration of microdomains was gradually depleted from the surface to the bulk of the membrane. A schematic of the morphology for SMMs within the PES membrane surface was proposed.

Fluorine↗

PubMed2003

Reduced platelet adhesion on the surface of polyurethane bearing structure of sulfobetaine.

Poly(etherurethane)s are widely used as blood-contacting biomaterials due to their good biocompatibility and mechanical properties. Nevertheless, their blood compatibility is still not adequate for the more demanding applications. Surface modification is an effective way to improve the blood compatibility and retain the bulk properties of biomaterials. The purpose of present study was to design and synthesize a novel nonthrombogenic biomaterial by modifying the surface of poly(etherurethane) with zwitterionic monomer. Films of polyurethane were grafted with sulfobetaine by a three-step procedure. In the first step, the film surfaces were treated with hexamethylene diisocyanate (HDI) in toluene at 50 degrees C in the presence of di-n-butyl tin dilaurate (DBTDL) as a catalyst. The extent of the reaction was measured by ATR-IR spectra; a maximum number of free NCO group was obtained after a reaction time of 90 min. In the second step, the hydroxyl group of 4-dimethylamino-1-butanol (DMAB) was allowed to react in toluene with isocyanate groups bound on the surface. In the third step, sulfobetaine was formed on the surface through the ring-opening reaction between tertiary amine of DMAB and 1,3- propane-sultone (PS). It was characterized by ATR-IR, XPS. The data showed that the grafted surfaces were composed of sulfobetaine. The results of the contact angle measurements showed that they were strongly hydrophilic. The state of platelet adhesion and shape variation for the attached platelets was described. The modified surface shows excellent blood compatibility feature by the low platelet adhesion.

Betaine↗

PubMed2004

Preparation and a time-resolved fluoroimmunoassay application of new europium fluorescent nanoparticles.

New silica-based europium fluorescent nanoparticles having surface amino groups were prepared by a covalent binding-copolymerization technique. In the nanoparticles, the fluorescent Eu3+ chelate molecules were covalently bound to silicon atoms to protect the nanoparticles from dye leaking in bio-applications. The amino groups on the surface of nanoparticles made the surface modification and bioconjugation of nanoparticles easier. The nanoparticles were characterized and developed as a new type of fluorescence probe for a highly sensitive time-resolved fluoroimmunoassay (TR-FIA) of human hepatitis B surface antigen (HBsAg).

Journal Article↗