Biomedical subjects

Mark H Schoenfisch

Publications and source records attributed to Mark H Schoenfisch.

At least 19 recordsLinked to original sources

PubMed2006

Nitric oxide-releasing xerogel-based fiber-optic pH sensors.

A xerogel-based optical pH sensor capable of releasing low levels of nitric oxide (NO) and measuring changes in solution pH is reported. Through simple dip-coating procedures, aminoalkoxysilane-based xerogel films modified with N-diazeniumdiolate NO donor precursors and the fluorescent pH indicator seminaphthorhodamine-1 carboxylate (SNARF-1) were sequentially deposited onto optical fibers. The resulting sensors were characterized by fast and linear response to pH throughout the physiological range (pH 7.0-7.8). Real-time chemiluminescence measurements confirmed that the presence of the overlying SNARF-1-containing TMOS layer did not have an inhibitory effect on N-diazeniumdiolate formation or NO release, and the NO-releasing coatings were capable of maintaining NO fluxes >0.4 pmol/cm(2) s up to 16 h. In vitro blood compatibility studies using porcine platelets confirmed the expected thromboresistivity of the NO-releasing xerogel coatings.

Animals↗

PubMed2006

Dendrimers as a scaffold for nitric oxide release.

The preparation and characterization of nitric oxide (NO)-releasing dendrimer conjugates are reported. Generation 3 and 5 polypropylenimine dendrimers (DAB-Am-16 and DAB-Am-64) were modified at the exterior to impart different amine functionalities. The ability to store NO on a dendritic scaffold using N-diazeniumdiolate NO donors was examined via the reaction of primary amine, secondary amine, and amide functionalities with high pressures of NO (5 atm). The secondary amine dendrimer conjugates exhibited a high storage capacity for NO (up to 5.6 micromol NO/mg), greatly increasing the "payload" of released NO over existing macromolecular NO donors. The mechanism of diazeniumdiolate decomposition was proton initiated, generating NO spontaneously under physiological conditions (pH 7.4, 37 degrees C). The NO release durations (>16 h) observed for the secondary amine dendrimers were significantly longer compared to small molecule alkyl secondary amine diazeniumdiolates, thus illustrating a dendritic effect on NO release kinetics. The multivalent exterior of dendrimers allows for the future combination of NO donors and other functionalities on a single molecular scaffold, enabling diverse utility as NO storage/delivery systems.

Azo Compounds↗

PubMed2006

Changes in adsorbed fibrinogen upon conversion to fibrin.

The conversion of adsorbed fibrinogen to fibrin in the presence of the enzyme thrombin was studied using surface plasmon resonance (SPR), a quartz crystal microbalance (QCM), sum frequency generation (SFG), atomic force microscopy (AFM), and an elutability assay. Exposure of adsorbed fibrinogen to thrombin resulted in a mass loss at the surface consistent with fibrinopeptide release and conversion to fibrin. Changes in hydration upon conversion of adsorbed fibrinogen to fibrin were determined from comparisons of acoustic (QCM) and optical (SPR) mass adsorption data. Conversion to fibrin also resulted in the adsorbed layer becoming more strongly bound to the surface and more compact. The elutability of adsorbed fibrinogen by Triton X-100, studied with SPR, decreased from 90 +/- 5 to 6 +/- 2% after conversion to fibrin. The height of the adsorbed monolayer, as determined by AFM, decreased from 5.5 +/- 2.2 to 1.7 +/- 0.8 nm. We conclude that thrombin-catalyzed fibrinopeptide release triggers significant changes in fibrinogen conformation beyond peptide cleavage.

Adhesiveness↗

PubMed2006

Reducing implant-related infections: active release strategies.

Despite sterilization and aseptic procedures, bacterial infection remains a major impediment to the utility of medical implants including catheters, artificial prosthetics, and subcutaneous sensors. Indwelling devices are responsible for over half of all nosocomial infections, with an estimate of 1 million cases per year (2004) in the United States alone. Device-associated infections are the result of bacterial adhesion and subsequent biofilm formation at the implantation site. Although useful for relieving associated systemic infections, conventional antibiotic therapies remain ineffective against biofilms. Unfortunately, the lack of a suitable treatment often leaves extraction of the contaminated device as the only viable option for eliminating the biofilm. Much research has focused on developing polymers that resist bacterial adhesion for use as medical device coatings. This tutorial review focuses on coatings that release antimicrobial agents (i.e., active release strategies) for reducing the incidence of implant-associated infection. Following a brief introduction to bacteria, biofilms, and infection, the development and study of coatings that slowly release antimicrobial agents such as antibiotics, silver ions, antibodies, and nitric oxide are covered. The success and limitations of these strategies are highlighted.

Animals↗

PubMed2006

Poly(vinylpyrrolidone)-doped nitric oxide-releasing xerogels as glucose biosensor membranes.

Nitric oxide (NO)-releasing xerogel membranes were prepared as coatings for an electrochemical glucose biosensor to allow for enhanced biocompatibility while maintaining adequate response times and sensitivity. Formation of the NO-donor species was found to drastically decrease the permeability of the aminosilane-based xerogels to both hydrogen peroxide and glucose. The addition of poly(vinylpyrrolidone) (PVP) polymer enhanced the membrane permeability even after exposure to high pressures of NO (necessary for NO-donor synthesis). The analytical response and NO release of PVP-doped NO-releasing xerogels as glucose sensor membranes were further investigated and found to be enhanced via polymer doping. Doping of the polymer into the xerogel did not compromise the stability of the xerogel as evaluated by silicon leaching studies. Despite the addition of PVP, the NO-releasing xerogels maintained reduced bacterial adhesion characteristics analogous to previous reports for NO-releasing xerogels.

Biosensing Techniques↗

PubMed2006

Improving the biocompatibility of in vivo sensors via nitric oxide release.

The continuous, real-time monitoring of clinically important analytes (e.g., PO2, PCO2, pH, K+, Na+, glucose, and lactate) is of great importance to human health care. Despite considerable efforts spanning several decades, the use of in vivo sensors clinically remains limited due to inadequate biocompatibility. The discovery of nitric oxide (NO) as an effective inhibitor of platelet and bacterial adhesion has opened a new direction of research related to designing the next generation of in vivo sensors. In this Highlight article, recent progress in designing more biocompatible in vivo sensors is described, with a particular focus on preparing interfaces that resist biofouling via controlled NO release.

Bacterial Adhesion↗

PubMed2005

Planar nitric oxide (NO)-selective ultramicroelectrode sensor for measuring localized NO surface concentrations at xerogel microarrays.

A planar ultramicroelectrode nitric oxide (NO) sensor was fabricated to measure the local NO surface concentrations from NO-releasing microarrays of varying geometries. The sensor consisted of platinized Pt (25 microm) working electrode and a silver paint reference electrode coated with a thin silicone rubber gas permeable membrane. An internal hydrogel layer separated the Pt working electrode and gas permeable membrane. The total diameter of the sensor was <or=50 microm, and demonstrated negligible analyte trapping effects. The sensitivity and response time of the ultramicroelectrode sensor to NO were 0.19+/- 0.07 pA nM(-1) and 1-4 s, respectively, with a 5 nM limit of detection. The sensor was employed to correlate the steady-state NO surface concentration and observed platelet adhesion resistance. Results indicate that the required steady-state NO concentration necessary to inhibit platelet adhesion to the micro-patterned xerogels depends on the xerogel geometry.

Animals↗

PubMed2005

Interactions of thrombin with fibrinogen adsorbed on methyl-, hydroxyl-, amine-, and carboxyl-terminated self-assembled monolayers.

We have examined the initial phase of fibrin formation, thrombin-catalyzed fibrinopeptide cleavage, from adsorbed fibrinogen using surface plasmon resonance and liquid chromatography-mass spectrometry. Fibrinogen adsorption impaired thrombin-fibrinogen interactions compared to the interactions of thrombin with fibrinogen in solution. The properties of the underlying substrate significantly affected the extent and kinetics of fibrinopeptide cleavage, and the conversion of adsorbed fibrinogen to fibrin. Fibrinogen adsorbed on negatively charged surfaces (carboxyl-terminated self-assembled monolayers) released a smaller amount of fibrinopeptides, at a reduced rate relative to those of hydrophobic, hydrophilic, and positively charged surfaces (methyl-, hydroxyl-, and amine-terminated self-assembled monolayers, respectively). Additionally, the conversion of adsorbed fibrinogen to fibrin was comparatively inefficient at the negatively charged surface. These data correlated well with trends previously reported for fibrin proliferation as a function of surface properties. We conclude that thrombin interactions with adsorbed fibrinogen determine the extent of subsequent fibrin proliferation on surfaces.

Adsorption↗

PubMed2005

Miniaturized glucose biosensor modified with a nitric oxide-releasing xerogel microarray.

An enzyme-based glucose biosensor modified to release nitric oxide (NO) via a xerogel microarray is reported. The biosensor design is as follows: (1) glucose oxidase (GOx) is immobilized in a methyltrimethoxysilane (MTMOS) xerogel layer; (2) a blended polyurethane/hydrophilic polyurethane coating prevents enzyme leaching and imparts selectivity for glucose; and (3) micropatterned xerogel lines (5 microm wide) separated by distances of 5 or 20 microm provide NO-release capability. This configuration allows for increased glucose sensitivity relative to sensors modified with NO-releasing xerogel films since significant portions of the sensor surface remain unmodified. Glucose diffusion to the GOx layer is thus less inhibited. The micropatterned NO-releasing biosensors generate sufficient NO levels to reduce both Pseudomonas aeruginosa and platelet adhesion without significantly compromising the enzymatic activity of GOx. The glucose response, linearity and stability of the NO-releasing micropatterned sensors are reported.

Absorption↗

PubMed2005

Synthesis of nitric oxide-releasing gold nanoparticles.

We report the synthesis of nitric oxide-releasing gold nanoparticles formed by place-exchange reaction of hexanethiol monolayer-protected clusters with diamine nitric oxide donor precursor molecules, which are subsequently converted to N-diazeniumdiolate NO donors. The nitric oxide release from the N-diazeniumdiolate-modified gold nanoparticles is tunable by varying the number and/or the chemical structure of the exchanged amine ligands. The size and stability of NO-releasing nanoparticles may prove useful for a range of biomedical and pharmaceutical applications.

Amines↗

PubMed2005

Sol-gel derived amperometric nitric oxide microsensor.

An amperometric sol-gel derived nitric oxide microsensor is described. Several silicon-based xerogel membranes are evaluated to identify the optimum composition for maximizing NO permeability while providing sufficient selectivity for NO in the presence of common interfering species. Xerogel permeability and selectivity are further manipulated as a function of reaction/processing conditions. In addition, the effects of incorporating Nafion into the xerogel matrix on sensor performance and the stability of the ensuing xerogel/Nafion hybrid film are evaluated. The optimal permselective membrane is achieved by catalyzing polycondensation of the xerogel composed of methyltrimethoxysilane and (aminoethylaminomethyl)phenethyltrimethoxysilane and Nafion with NO gas. The resulting NO microsensor exhibits a sensitivity of 0.17 +/-0.02 pA/nM (from 25 to 800 nM, r = 0.9991), detection limit of 25 nM (S/N = 3), response time of 9 s (t(95%), a NO concentration change from 400 to 500 nM), selectivity (log K(NOj) amp) of -5.8, <-6, <-6, and <-6 for j = nitrite, ascorbic acid, uric acid, and acetaminophen, and a lifetime of 8 d (82% of initial sensitivity without serious deterioration in selectivity).

Electrochemistry↗

PubMed2005

Influence of antibody immobilization strategy on molecular recognition force microscopy measurements.

A systematic evaluation of the effects of antibody immobilization strategy on the binding efficiency and selectivity (e.g., ability to distinguish between specific and nonspecific interactions) of immunosurfaces prepared with F(ab') antibody fragments of rabbit Immunoglobulin G (IgG) is described. F(ab') was attached to gold surfaces either (1) directly via the formation of a gold-thiolate bond or (2) indirectly through a series of a bifunctional linkers containing an alkane chain or ethylene glycol spacer. Immobilization of F(ab') via the sulfhydryl reactive group located opposite the antigen binding site ensured optimum orientation of the antigen binding site. X-ray photoelectron spectroscopy (XPS) and surface plasmon resonance (SPR) were used to confirm surface modification with the bifunctional linkers and antibody immobilization, respectively. Binding efficiency assays performed with SPR indicated that increasing the length of the linker increased the antigen binding efficiency. Atomic force microscopy (AFM) adhesion force measurements indicated that AFM probes functionalized with directly immobilized F(ab') more effectively discriminated between specific and nonspecific surface-bound proteins than probes modified indirectly via linker-immobilized F(ab'). In addition, a greater number of antibody-antigen binding events were observed with directly immobilized F(ab')-functionalized probes.

Adhesiveness↗

PubMed2005

Fibrin proliferation at model surfaces: influence of surface properties.

Fibrin proliferation from both human fibrinogen solutions and platelet-poor plasma was studied quantitatively as a function of substrate surface properties. A quartz crystal microbalance was used to monitor both protein adsorption and fibrin proliferation in real time at hydrophobic, hydrophilic, positively charged, and negatively charged surfaces. Scanning electron microscopy was used to characterize the morphology of the polymerized fibrin layers. The observed changes in mass indicate that fibrinogen adsorption occurs rapidly and mediates subsequent fibrin proliferation. Notably, substrate surface properties significantly affect the ability of adsorbed fibrinogen to promote fibrin proliferation.

Adsorption↗

PubMed2005

Sol-gel derived potentiometric pH sensors.

A potentiometric sol-gel derived (xerogel) pH sensor based on covalently attached amine groups is described. The sensor consists of a Ag/AgCl electrode coated with a hybrid aminosilane/alkylsilane xerogel film. Various combinations of aminosilanes and alkylsilanes are evaluated for their potentiometric response to pH. The optimal sensor design is composed of (aminoethylaminomethyl)phenethyltrimethoxysilane and methyltrimethoxysilane. This sensor exhibits near-Nerstian response (-55 mV.decade(-)(1)), responds rapidly (< or =3 s) to changes in pH, and has H(+) selectivity coefficients (log K(pot)(H)()+ (, )(j)()) of -13 and -11 for interfering j cations Na(+) and K(+), respectively. In vitro platelet adhesion tests indicate that the xerogel coatings are more blood compatible than conventional poly(vinyl chloride) and poly(urethane) ion-selective electrode coatings.

Amines↗

PubMed2005

Nitric oxide-releasing sol-gels as antibacterial coatings for orthopedic implants.

To assess the benefits of nitric oxide (NO)-releasing sol-gels as potential antibacterial coatings for orthopedic devices, medical-grade stainless steel is coated with a sol-gel film of 40% N-aminohexyl-N-aminopropyltrimethoxysilane and 60% isobutyltrimethoxysilane. Upon converting the diamine groups in these films to diazeniumdiolate NO donors, the NO release from the sol-gel-coated stainless steel is evaluated at both ambient and physiological temperature. Sol-gel films incubated at 25 degrees C have a lower NO flux over the first 24 h compared to those at 37 degrees C, but release more than five times longer. The bacterial adhesion resistance of NO-releasing coatings is evaluated in vitro by exposing bare steel, sol-gel, and NO-releasing sol-gel-coated steel to cell suspensions of Pseudomonas aeruginosa, Staphylococcus aureus, and Staphylococcus epidermidis at 25 degrees C and 37 degrees C. Cell adhesion to bare and sol-gel-coated steel is similar, while NO-releasing surfaces have significantly less bacterial adhesion for all species and temperatures investigated.

Anti-Bacterial Agents↗

PubMed2005

In vitro cytotoxicity of nitric oxide-releasing sol-gel derived materials.

The cytotoxicity of bare and PU-coated nitric oxide (NO)-releasing sol-gel derived materials (sol-gels) was investigated using L929 mouse fibroblasts in both direct and indirect contact models to differentiate between the biological impact of the sol-gel matrix and NO release. The flux of NO was varied up to 150 pmol cm(-2) s(-1) using N-(6-aminohexyl)-aminopropyltrimethoxysilane (balance iso-butyltrimethoxysilane) diazeniumdiolate (NO donor)-modified sol-gels. The addition of a polyurethane (PU) outer membrane greatly improved the stability of the sol-gel matrix without significantly suppressing the NO flux. Direct contact studies demonstrated a cytotoxic effect that was dependent on the aminosilane content of the sol-gel. The use of the thin PU overcoat eliminated this effect. A direct cytotoxicity dependence of NO release for L929 fibroblasts was discovered from indirect contact studies, where 24 h exposure to NO fluxes in excess of 50 pmol cm(-2) s(-1) was cytotoxic.

Animals↗

PubMed2005

Inhibition of implant-associated infections via nitric oxide release.

The in vivo antibacterial activity of nitric oxide (NO)-releasing xerogel coatings was evaluated against an aggressive subcutaneous Staphylococcus aureus infection in a rat model. The NO-releasing implants were created by coating a medical-grade silicone elastomer with a sol-gel-derived (xerogel) film capable of storing NO. Four of the bare or xerogel-coated silicone materials were subcutaneously implanted into male rats. Ten rats were administered 10 microl of a 10(8) cfuml(-1)S. aureus colony directly into the subcutaneous pocket with the implant prior to wound closure. Infection was quantitatively and qualitatively evaluated after 8d of implantation with microbiological and histological methods, respectively. A 82% reduction in the number of infected implants was achieved with the NO-releasing coating. Histology revealed that the capsule formation around infected bare silicone rubber controls was immunoactive and that a biofilm may have formed. Capsule formation in response to NO-releasing implants had greater vascularity in comparison with uninoculated or untreated controls. These results suggest that NO-releasing coatings may dramatically reduce the incidence of biomaterial-associated infection.

Animals↗

PubMed2004

Sol-gel derived nitric oxide-releasing oxygen sensors.

An amperometric sol-gel derived sensor that both releases nitric oxide (NO) and measures physiologically relevant concentrations of oxygen (PO2) is described. The sensor consists of a platinum electrode coated with an aminosilane/ethyltrimethoxysilane hybrid xerogel film. Hydrophilic polyurethane (HPU) is doped into the hybrid film to reduce sensor hydration time and increase oxygen permeability. Diazeniumdiolate NO donors are formed within the polymer matrix by exposing the cured film to high pressures of NO. These coatings release up to 7.2 pmol s(-1) cm(-2) of NO over the first 12 h and maintain detectable levels of NO release through 48 h. Sensors modified with HPU-doped, NO-releasing xerogels exhibit a linear response to O2 within 30 min of polarization at -0.65 V vs. Ag/AgCl, and have a sensitivity of approximately 6 nA/mmHg O2. The xerogel coating is stable in buffer solution with minimal fragmentation over 48 h. In vitro biocompatibility studies indicate that these materials effectively reduce platelet adhesion.

Animals↗