Influence of titanium nanoscale surface roughness on fibrinogen and albumin protein adsorption kinetics and platelet responses.

Biomaterials with nanoscale topography have been increasingly investigated for medical device applications to improve tissue-material interactions. This study assessed the impact of nanoengineered titanium surface domain sizes on early biological responses that can significantly affect tissue interactions. Nanostructured titanium coatings with distinct nanoscale surface roughness were deposited on quartz crystal microbalance with dissipation (QCM-D) sensors by physical vapor deposition. Physico-chemical characterization was conducted to assess nanoscale surface roughness, nano-topographical morphology, wettability, and atomic composition. The results demonstrated increased projected surface area and hydrophilicity with increasing nanoscale surface roughness. The adsorption properties of albumin and fibrinogen, two major plasma proteins that readily encounter implanted surfaces, on the nanostructured surfaces were measured using QCM-D. Significant differences in the amounts and viscoelastic properties of adsorbed proteins were observed, dependent on the surface roughness, protein type, protein concentration, and protein binding affinity. The impact of protein adsorption on subsequent biological responses was also examined using qualitative and quantitative in vitro evaluation of human platelet adhesion, aggregation, and activation. Qualitative platelet morphology assessment indicated increased platelet activation/aggregation on titanium surfaces with increased roughness. These data suggest that nanoscale differences in titanium surface roughness influence biological responses that may affect implant integration.

Coil-to-Bridge Transitions of Self-Assembled Water Chains Observed in a Nanoscopic Meniscus.

Ten downward portions in the large oscillatory force-distance curve reported earlier are analyzed to understand a nanoscale water meniscus confined between a sharp probe and a flat substrate in air. The sigmoidal shape of each portion leads to the assumption that the meniscus is made up of n independent transitions of two states: one for a coil state and the other for a bridge state. The analysis reveals that each downward portion occurs due to a coil-to-bridge transition of n self-assembled water chains whose length ranges between 197 and 383 chain units. The transition provides novel insights into water's unique properties like high surface tension and the long-range condensation distances.

Intentional removal of erroneously deployed coronary stents: A case series and review of the literature.

Most reports of stent retrieval involve undeployed, embolized stents. While the retrieval of fully deployed stents has been sporadically reported, most of these were not intentional. The feasibility and safety of intentional retrieval of fully deployed, but erroneously placed stents have not been well described. We report four cases of successful, intentional stent retrieval for stents placed erroneously in an aorto-ostial position. The stents were retrieved at varying times after deployment, ranging from immediately to up to 5 years. In all cases, stents were retrieved successfully with no complication. We conclude that the intentional retrieval of fully deployed, but erroneously placed stents is feasible and safe when stenting involved an aorto-ostial location.

Nanostructured Medical Adhesives.

Suturing has been the gold standard approach to close wounds for many decades. However, suturing causes tissue damage, which is accompanied by foreign body reaction, entry of pathogens, complications, infection, or death. In addition, the procedure is usually time-consuming, requiring manual dexterity and free moving space. Other adhesive approaches have been proposed and demonstrated with great potential, including laser-assisted tissue closure with either photothermal or photochemical reactions, application of nanoparticles, glues, constructs based on extracellular matrix (ECM), microbarbs, bio-inspired structures, and tape. The quality of closure has been evaluated by histological methods, indexing, morphology, tensile testing, patency rate, leakage pressure, and burst pressure. All the novel tissue joining methods aim to provide an adhesive with appropriate strength, non-cytotoxicity, and minimal damage. The capability for rapid attachment and release may further reduce surgical procedure time. More research is needed to prove the feasibility of new tissue joining techniques based on the type of tissue, surface chemistry, and working environment.

Current Advancements in Transdermal Biosensing and Targeted Drug Delivery.

In this manuscript, recent advancements in the area of minimally-invasive transdermal biosensing and drug delivery are reviewed. The administration of therapeutic entities through the skin is complicated by the stratum corneum layer, which serves as a barrier to entry and retards bioavailability. A variety of strategies have been adopted for the enhancement of transdermal permeation for drug delivery and biosensing of various substances. Physical techniques such as iontophoresis, reverse iontophoresis, electroporation, and microneedles offer (a) electrical amplification for transdermal sensing of biomolecules and (b) transport of amphiphilic drug molecules to the targeted site in a minimally invasive manner. Iontophoretic delivery involves the application of low currents to the skin as well as the migration of polarized and neutral molecules across it. Transdermal biosensing via microneedles has emerged as a novel approach to replace hypodermic needles. In addition, microneedles have facilitated minimally invasive detection of analytes in body fluids. This review considers recent innovations in the structure and performance of transdermal systems.

In Vitro Sugar Interference Testing With Amperometric Glucose Oxidase Sensors.

BACKGROUND: Electrochemical enzymatic glucose sensors are intended to measure blood or interstitial fluid glucose concentrations. One class of these glucose sensors are continuous glucose monitors (CGMs), indicated for tracking and trending of glucose concentrations in interstitial fluid and as an adjunct to blood glucose testing. Currently approved CGMs employ a glucose oxidase (GOx) electrochemical detection scheme. Potential interfering agents can impact the accuracy of results obtained by glucose sensors, including CGMs. METHODS: Seven sugars, seven sugar alcohols, and three artificial sweeteners were in vitro screened for interference with amperometric glucose oxidase (GOx) sensors at concentrations greater than physiologic concentrations. Galactose was investigated further at physiologically relevant concentrations using a custom amperometric system. Furthermore, glucose and galactose calibration experiments were conducted to facilitate multiple enzyme kinetic analysis approaches (Michaelis-Menten and Hill equation) to understand the potential source and mechanism of interference from galactose. RESULTS: Under in vitro testing, except for galactose, xylose and mannose, all screened compounds exhibited interference bias, expressed in mean absolute relative difference (MARD), of ⩽ 20% even at concentrations significantly higher than normal physiologic concentrations. Galactose exhibited, CGM-dependent, MARD of 47-72% and was subjected to further testing. The highest recorded mean relative difference (MRD) was 6.9 ± 1.3% when testing physiologically relevant galactose concentrations (0.1-10 mg/dL). Enzyme kinetic analysis provided calculations of maximum reaction rates ( imax ), apparent Michaelis constants ( Kmapp ), and Hill equation h parameters for glucose and galactose substrates for the enzymes in the CGMs. CONCLUSION: Under the conditions of in vitro screening, 14 of the 17 compounds did not exhibit measuarable interference. Galactose exhibited the highest interference during screening, but did not substantially interfere with CGMs under the conditions of in vitro testing at physiologically relevant concentrations. Enzyme kinetic analysis conducted with galactose supported the notion that (1) the reactivity of GOx enzyme toward nonglucose sugars and (2) the presence of enzymatic impurities (such as galactose oxidase) are two potential sources for sugar interference with GOx glucose sensors, and thus, should be considered during device development.

Inkjet deposition of itraconazole onto poly(glycolic acid) microneedle arrays.

Poly(glycolic acid) microneedle arrays were fabricated using a drawing lithography process; these arrays were modified with a drug release agent and an antifungal agent by piezoelectric inkjet printing. Coatings containing poly(methyl vinyl ether-co-maleic anhydride), a water-soluble drug release layer, and itraconazole (an antifungal agent), were applied to the microneedles by piezoelectric inkjet printing. Microscopic evaluation of the microneedles indicated that the modified microneedles contained the piezoelectric inkjet printing-deposited agents and that the surface coatings were released in porcine skin. Energy dispersive x-ray spectrometry aided in confirmation that the piezoelectric inkjet printing-deposited agents were successfully applied to the desired target areas of the microneedle surface. Fourier transform infrared spectroscopy was used to confirm the presence of the component materials in the piezoelectric inkjet printing-deposited material. Itraconazole-modified microneedle arrays incubated with agar plates containing Candida albicans cultures showed zones of growth inhibition.

Use of Drawing Lithography-Fabricated Polyglycolic Acid Microneedles for Transdermal Delivery of Itraconazole to a Human Basal Cell Carcinoma Model Regenerated on Mice.

Itraconazole is a triazole agent that is routinely used for treatment of nail infections and other fungal infections. Recent studies indicate that itraconazole can also inhibit the growth of basal cell carcinoma (BCC) through suppression of the Sonic Hedgehog (SHH) signaling pathway. In this study, polyglycolic acid microneedle arrays and stainless steel microneedle arrays were used for transdermal delivery of itraconazole to a human BCC model which was regenerated on mice. One-by-four arrays of 642-µm-long polyglycolic acid microneedles with sharp tips were prepared using injection molding and drawing lithography. Arrays of 85 stainless steel 800-µm-tall microneedles attached to syringes were obtained for comparison purposes. Skin grafts containing devitalized split-thickness human dermis that had been seeded with human keratinocytes transduced to express human SHH protein were sutured to the skin of immunodeficient mice. Mice with this human BCC model were treated daily for 2 weeks with itraconazole dissolved in 60% dimethylsulfoxane and 40% polyethylene glycol-400 solution; transdermal administration of the itraconazole solution was facilitated by either four 1 × 4 polyglycolic acid microneedle arrays or stainless steel microneedle arrays. The epidermal tissues treated with polyglycolic acid microneedles or stainless steel microneedles were markedly thinner than that of the control (untreated) graft tissue. These preliminary results indicate that microneedles may be used to facilitate transdermal delivery of itraconazole for localized treatment of BCC.

Polyglycolic acid microneedles modified with inkjet-deposited antifungal coatings.

In this study, the authors examined use of piezoelectric inkjet printing to apply an antifungal agent, voriconazole, to the surfaces of biodegradable polyglycolic acid microneedles. Polyglycolic acid microneedles with sharp tips (average tip radius = 25 ± 3 µm) were prepared using a combination of injection molding and drawing lithography. The elastic modulus (9.9 ± 0.3 GPa) and hardness (588.2 ± 33.8 MPa) values of the polyglycolic acid material were determined using nanoindentation and were found to be suitable for use in transdermal drug delivery devices. Voriconazole was deposited onto the polyglycolic acid microneedles by means of piezoelectric inkjet printing. It should be noted that voriconazole has poor solubility in water; however, it is readily soluble in many organic solvents. Optical imaging, scanning electron microscopy, energy dispersive x-ray spectrometry, and Fourier transform infrared spectroscopy were utilized to examine the microneedle geometries and inkjet-deposited surface coatings. Furthermore, an in vitro agar plating study was performed on the unmodified, vehicle-modified, and voriconazole-modified microneedles. Unlike the unmodified and vehicle-modified microneedles, the voriconazole-modified microneedles showed antifungal activity against Candida albicans. The unmodified, vehicle-modified, and voriconazole-modified microneedles did not show activity against Escherichia coli, Pseudomonas aeruginosa, or Staphylococcus aureus. The results indicate that piezoelectric inkjet printing may be useful for loading transdermal drug delivery devices such as polyglycolic acid microneedles with antifungal pharmacologic agents and other pharmacologic agents with poor solubility in aqueous solutions.

Direct observation of self-assembled chain-like water structures in a nanoscopic water meniscus.

Sawtooth-like oscillatory forces generated by water molecules confined between two oxidized silicon surfaces were observed using a cantilever-based optical interfacial force microscope when the two surfaces approached each other in ambient environments. The humidity-dependent oscillatory amplitude and periodicity were 3-12 nN and 3-4 water diameters, respectively. Half of each period was matched with a freely jointed chain model, possibly suggesting that the confined water behaved like a bundle of water chains. The analysis also indicated that water molecules self-assembled to form chain-like structures in a nanoscopic meniscus between two hydrophilic surfaces in air. From the friction force data measured simultaneously, the viscosity of the chain-like water was estimated to be between 10(8) and 10(10) times greater than that of bulk water. The suggested chain-like structure resolves many unexplained properties of confined water at the nanometer scale, thus dramatically improving the understanding of a variety of water systems in nature.

Imaging stability in force-feedback high-speed atomic force microscopy.

We studied the stability of force-feedback high-speed atomic force microscopy (HSAFM) by imaging soft, hard, and biological sample surfaces at various applied forces. The HSAFM images showed sudden topographic variations of streaky fringes with a negative applied force when collected on a soft hydrocarbon film grown on a grating sample, whereas they showed stable topographic features with positive applied forces. The instability of HSAFM images with the negative applied force was explained by the transition between contact and noncontact regimes in the force-distance curve. When the grating surface was cleaned, and thus hydrophilic by removing the hydrocarbon film, enhanced imaging stability was observed at both positive and negative applied forces. The higher adhesive interaction between the tip and the surface explains the improved imaging stability. The effects of imaging rate on the imaging stability were tested on an even softer adhesive Escherichia coli biofilm deposited onto the grating structure. The biofilm and planktonic cell structures in HSAFM images were reproducible within the force deviation less than ∼0.5 nN at the imaging rate up to 0.2s per frame, suggesting that the force-feedback HSAFM was stable for various imaging speeds in imaging softer adhesive biological samples.

Mechanical property investigation of soft materials by cantilever-based optical interfacial force microscopy.

Cantilever-based optical interfacial force microscopy (COIFM) was applied to the investigation of the mechanical properties of soft materials to avoid the double-spring effect and snap-to-contact problem associated with atomic force microscopy (AFM). When a force was measured as a function of distance between an oxidized silicon probe and the surface of a soft hydrocarbon film, it increases nonlinearly in the lower force region below ∼10 nN, following the Herzian model with the elastic modulus of ∼50 MPa. Above ∼10 nN, it increases linearly with a small oscillatory sawtooth pattern with amplitude 1-2 nN. The pattern suggests the possible existence of the layered structure within the film. When its internal part of the film was exposed to the probe, the force depends on the distance linearly with an adhesive force of -20 nN. This linear dependence suggests that the adhesive internal material behaved like a linear spring with a spring constant of ∼1 N/m. Constant-force images taken in the repulsive and attractive contact regimes revealed additional features that were not observed in the images taken in the noncontact regime. At some locations, however, contrast inversions were observed between the two contact regimes while the average roughness remained constant. The result suggests that some embedded materials had spring constants different from those of the surrounding material. This study demonstrated that the COIFM is capable of imaging mechanical properties of local structures such as small impurities and domains at the nanometer scale, which is a formidable challenge with conventional AFM methods.

Force-feedback high-speed atomic force microscope for studying large biological systems.

We designed and developed a high-speed atomic force microscope (HSAFM) utilizing a force-feedback scheme for imaging large biological samples. The system collects three simultaneous images: a deflection image, a topographic image, and a force image. We demonstrated that this force-feedback HSAFM is capable of acquiring large topographic images of Escherichia coli biofilms at approximately one frame per second in air. We discuss how the self-actuating cantilever and the piezo tube follow those larger biological topographic features during the HSAFM imaging process.

Indirect rapid prototyping of antibacterial acid anhydride copolymer microneedles.

Microneedles are needle-like projections with microscale features that may be used for transdermal delivery of a variety of pharmacologic agents, including antibacterial agents. In the study described in this paper, an indirect rapid prototyping approach involving a combination of visible light dynamic mask micro-stereolithography and micromolding was used to prepare microneedle arrays out of a biodegradable acid anhydride copolymer, Gantrez(®) AN 169 BF. Fourier transform infrared spectroscopy, energy dispersive x-ray spectrometry and nanoindentation studies were performed to evaluate the chemical and mechanical properties of the Gantrez(®) AN 169 BF material. Agar plating studies were used to evaluate the in vitro antimicrobial performance of these arrays against Bacillus subtilis, Candida albicans, Enterococcus faecalis, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. Large zones of growth inhibition were noted for Escherichia coli, S. aureus, Enterococcus faecalis and B. subtilis. The performance of Gantrez(®) AN 169 BF against several bacteria suggests that biodegradable acid anhydride copolymer microneedle arrays prepared using visible light dynamic mask micro-stereolithography micromolding may be useful for treating a variety of skin infections.

Multiphoton microscopy of transdermal quantum dot delivery using two photon polymerization-fabricated polymer microneedles.

Due to their ability to serve as fluorophores and drug delivery vehicles, quantum dots are a powerful tool for theranostics-based clinical applications. In this study, microneedle devices for transdermal drug delivery were fabricated by means of two-photon polymerization of an acrylate-based polymer. We examined proliferation of cells on this polymer using neonatal human epidermal keratinocytes and human dermal fibroblasts. The microneedle device was used to inject quantum dots into porcine skin; imaging of the quantum dots was performed using multiphoton microscopy.

Effects of long-term hypoxia on enzymes of carbohydrate metabolism in the Gulf killifish, Fundulus grandis.

The goal of the current study was to generate a comprehensive, multi-tissue perspective of the effects of chronic hypoxic exposure on carbohydrate metabolism in the Gulf killifish Fundulus grandis. Fish were held at approximately 1.3 mg l(-1) dissolved oxygen (approximately 3.6 kPa) for 4 weeks, after which maximal activities were measured for all glycolytic enzymes in four tissues (white skeletal muscle, liver, heart and brain), as well as for enzymes of glycogen metabolism (in muscle and liver) and gluconeogenesis (in liver). The specific activities of enzymes of glycolysis and glycogen metabolism were strongly suppressed by hypoxia in white skeletal muscle, which may reflect decreased energy demand in this tissue during chronic hypoxia. In contrast, several enzyme specific activities were higher in liver tissue after hypoxic exposure, suggesting increased capacity for carbohydrate metabolism. Hypoxic exposure affected fewer enzymes in heart and brain than in skeletal muscle and liver, and the changes were smaller in magnitude, perhaps due to preferential perfusion of heart and brain during hypoxia. The specific activities of some gluconeogenic enzymes increased in liver during long-term hypoxic exposure, which may be coupled to increased protein catabolism in skeletal muscle. These results demonstrate that when intact fish are subjected to prolonged hypoxia, enzyme activities respond in a tissue-specific fashion reflecting the balance of energetic demands, metabolic role and oxygen supply of particular tissues. Furthermore, within glycolysis, the effects of hypoxia varied among enzymes, rather than being uniformly distributed among pathway enzymes.