PubMed Health⌕ Search

Biomedical subjects

Michael J McShane

Publications and source records attributed to Michael J McShane.

At least 19 recordsLinked to original sources
PubMed2006

Study of the near-neutral pH-sensitivity of chitosan/gelatin hydrogels by turbidimetry and microcantilever deflection.

The fundamental properties and pH-sensitivity of chitosan/gelating hydrogels were investigated using spectroscopic and microelectro mechanical (MEMS) measurement approaches. Turbidimetric titration revealed that there were electrostatic attractive interactions between tripolyphosphate (TPP), chitosan, and gelatin in the acidic pH range, depending on their degree of ionization. The pH-sensitive swelling behavior of the hydrogels was investigated by monitoring the deflection of hydrogel-coated microcantilevers, which exhibited a sensitive and repeatable response to solution pH. The deflection of the microcantilever increased as the pH decreased, and the response speed of the system exhibited a nearly linear relationship with pH. The effects of the pH and concentration of TPP solution, as well as the ratio of chitosan to gelatin in gel precursor solutions, on the pH sensitivity of the hydrogels were also investigated. It was found that the swelling of the hydrogel is mainly a result of chain relaxation of chitosan-TPP complexes caused by protonation of free amino groups in chitosan, which depends on the crosslinking density set during the formation of the network. An increase in initial crosslink density induced a decrease in swelling and pH sensitivity. It can be concluded from this study that pH-sensitive chitosan gel properties can be tuned by preparatory conditions and inclusion of gelatin. Furthermore, microcantilevers can be used as a platform for gaining increased understanding of environmentally sensitive polymers.

Biosensing Techniques↗
PubMed2006

Fabrication of interdigitated micropatterns of self-assembled polymer nanofilms containing cell-adhesive materials.

Micropatterns of different biomaterials with micro- and nanoscale features and defined spatial arrangement on a single substrate are useful tools for studying cellular-level interactions, and recent reports have highlighted the strong influence of scaffold compliance in determining cell behavior. In this paper, a simple yet versatile and precise patterning technique for the fabrication of interdigitated micropatterns of nanocomposite multilayer coatings on a single substrate is demonstrated through a combination of lithography and layer-by-layer (LbL) assembly processes, termed polymer surface micromachining (PSM). The first nanofilm pattern is constructed using lithography, followed by LbL multilayer assembly and lift-off, and the process is repeated with optical alignment to obtain interdigitated patterns on the same substrate. Thus, the method is analogous to surface micromachining, except that the deposition materials are polymers and biological materials that are used to produce multilayer nanocomposite structures. A key feature of the multilayers is the capability to tune properties such as stiffness by appropriate selection of materials, deposition conditions, and postdeposition treatments. Two- and four-component systems on glass coverslips are presented to demonstrate the versatility of the approach to construct precisely defined, homogeneous nanofilm patterns. In addition, an example of a complex system used as a testbed for in vitro cell adhesion and growth is provided: micropatterns of poly(sodium 4-styrenesulfonate)/poly-L-lysine hydrobromide (PSS/PLL) and secreted phospholipase A(2)/poly(ethyleneimine) (sPLA(2)/PEI) multilayers. The interdigitated square nanofilm array patterns were obtained on a single coverslip with poly(diallyldimethylammonium chloride) (PDDA) as a cell-repellent background. Cell culture experiments show that cortical neurons respond and bind specifically to the sPLA(2) micropatterns in competition with PLL micropatterns. The fabrication and the initial biological results on the nanofilm micropatterns support the usefulness of this technique for use in studies aimed at elucidating important biological structure-function relationships, but the applicability of the fabrication method is much broader and may impact electronics, photonics, and chemical microsystems.

Animals↗
PubMed2006

Real-time assessment of spatial and temporal coupled catalysis within polyelectrolyte microcapsules containing coimmobilized glucose oxidase and peroxidase.

The encapsulation of biological enzymes within polyelectrolyte microcapsules is an important step toward microscale devices for processing and analytical applications, one which could be applied to the realization of minimally invasive sensing technology. In this work, the encapsulation and functional characterization of a bienzymatic coupled catalytic system within polyelectrolyte microcapsules is described. The two components, glucose oxidase (GOx) and horseradish peroxidase (HRP), were coprecipitated with calcium carbonate microspheres, followed by layer-by-layer assembly to form ultrathin polymer film coatings that act as capsule walls after removal of the sacrificial carbonate cores. Encapsulated concentrations of GOx and HRP were determined to be 19.7 +/- 1.0 and 29.4 +/- 3.6 mg/mL, respectively. An 85% decrease in the rate of glucose consumption relative to GOx and HRP in free solution was observed, which is attributed to substrate diffusion limitations. To further understand the temporal and spatial dynamics of the two-step reaction, a technique for monitoring microscale glucose consumption was developed using confocal imaging techniques. Time-based acquisition of capsule/Amplex Red suspensions was performed, from which it was observed that the high concentration of enzyme immobilized within the capsule walls resulted in a greater rate and quantity of glucose consumption at the capsule periphery when compared to glucose consumption within the capsule interior. These findings demonstrate the function of a bienzymatic catalytic system within the controlled environment of polyelectrolyte microspheres and a novel approach to analysis of the internal reactions using confocal imaging that will allow direct comparison with reaction-diffusion modeling and further explorations to optimize the distribution and activity of the encapsulated species.

Aspergillus niger↗
PubMed2006

Glucose sensors based on microcapsules containing an orange/red competitive binding resonance energy transfer assay.

Fluorescent sensing systems offer the potential for noninvasive monitoring with implantable devices, but they require carrier technologies that provide suitable immobilization, accessibility, and biocompatibility while maintaining adequate response characteristics. A recent development towards this goal is a highly specific and sensitive competitive binding assay for glucose using apo-glucose oxidase (apo-GOx) as the recognition element and dextran as the competing ligand; this has been demonstrated as a glucose sensor system by encapsulating the competitive binding assay in semipermeable microcapsule carriers. This paper describes the extension of this sensor design to longer wavelengths in an attempt to increase the applicability to in vivo monitoring. The glucose sensitivity of the tetramethylrhodamine isothiocyanate-dextran (TD) and cyanine Cy5-apo-GOx (CAG) complexes showed five to 10 times greater specificity for beta-D-glucose over other sugars. Microcapsules loaded with TD/CAG complexes exhibited a linear, totally reversible response in the range of 0-720 mg/dL, with a sensitivity (percent change in intensity ratio) of 0.06%/(mg/dL). The decrease in sensitivity observed with the use of longer-wavelength dyes is most likely to be compensated with the deeper penetration of light and reduced tissue scattering. These findings imply that the encapsulation of sensing assay elements in microcapsules is a simple and translatable method for the fabrication of stable biosensors, and optimization of resonance energy transfer pairs and assay component preparation will further improve the response to approach clinically relevant performance.

Apoenzymes↗
PubMed2006

Enzymatic fluorescent microsphere glucose sensors:evaluation of response under dynamic conditions.

Most previous attempts at the development of a "smart tattoo" for glucose monitoring in diabetes--implantable fluorescent microspheres that can be implanted intradermally and interrogated transdermally using light--have focused on the encapsulation of a competitive binding assay for glucose within hydrogel microspheres or polyelectrolyte microcapsules. We recently reported on the development of a microsphere sensor based on an enzymatic scheme, combined with an oxygen-quenched fluorescent reporter element. A novel feature of this design is the use of polyelectrolyte multilayer nanofilms, which are assembled stepwise on the surface of the microspheres, for modulation of glucose and oxygen mass transport, allowing them to be designed for sensitive and safe operation within the "oxygen deficit" present in the skin. In this work, a flow-through sensor testing apparatus was used to demonstrate the reversible response of the sensors under controlled, dynamic conditions. The sensors were shown to be sensitive over at least 0-140 mg/dL glucose, with a response time of less than 2 min. This report also identifies some current problems with the approach, and gives potential solutions towards the development of a practical implantable sensor for glucose monitoring in diabetes.

Biosensing Techniques↗
PubMed2005

Modeling of spherical fluorescent glucose microsensor systems: design of enzymatic smart tattoos.

A two-substrate mathematical model of microspherical optical enzymatic glucose sensors is presented. The sensors are based on the well-known oxidation of glucose by glucose oxidase, and are constructed by the encapsulation of glucose oxidase within hydrogel microspheres coated with ultrathin polyelectrolyte multilayer films. In order to measure glucose via changes in oxygen concentration, a fluorescent oxygen indicator is co-encapsulated with the enzyme. The model was used to predict the temporal and spatial distributions of glucose and oxygen within the sphere for step increases in bulk glucose concentration. In addition, the model was used to observe the effect of varying sensor parameters, namely sphere size, film thickness, enzyme concentration, and mass transport of substrate and co-substrate within the sphere and film coatings, on the response of the sensors. A major finding was that the application of {PSS/PAH} films as thin as 12 nm can drastically improve the sensor performance over uncoated sensors based on calcium alginate microspheres. The model is proposed as an important tool for a priori design of these complex sensor structures.

Computer Simulation↗
PubMed2005

Loading of hydrophobic materials into polymer particles: implications for fluorescent nanosensors and drug delivery.

A straightforward method for loading hydrophobic materials into commercially available polymer nano- or microparticles is described. PMMA and PS nano/microparticles were swelled by an organic solvent with an ionic surfactant (SDS) to stabilize the particles in aqueous solution. FITC and Ru(dpp)3Cl2 were loaded into those particles based on the principle of "like dissolves like". Further surface modification of the loaded particles was achieved via layer-by-layer (LbL) self-assembly. Culture of fibroblasts with the dye-doped, coated particles showed that the cells internalized the fluorescent particles with no apparent toxic effects. The findings suggest the facile process could be useful in a wide range of applications for fluorescent micro/nanosensors and drug delivery.

Drug Delivery Systems↗
PubMed2005

Influence of channel width on alignment of smooth muscle cells by high-aspect-ratio microfabricated elastomeric cell culture scaffolds.

Engineered smooth muscle tissue requires ordered configurations of cells to reproduce native function, and microtechnology offers possibilities for physically and chemically controlling cell organization with high spatial resolution. In this work, poly(dimethylsiloxane) microchannel scaffolds, modified by layer-by-layer self-assembly of polyelectrolytes to promote cell adhesion, were evaluated for use as substrates for the culture of aligned smooth muscle cells. The hypothesis that narrower channels would result in better alignment was tested using channel width dimensions of 20, 30, 40, 50, and 60 microm, in addition to flat (control) surfaces. Alignment of cells was assessed by two different methods, each sensitive to a different aspect of cell alignment from fluorescence micrographs. Two-dimensional fast Fourier transform analysis was performed to analyze the orientation distribution of actin filaments in cells. This was complemented by connectivity analysis of stained nuclei to obtain nuclear orientation distributions. Both methods produced consistent data that support the hypothesis that narrow microchannels promote a highly aligned culture of smooth muscle cells, and the degree of alignment is dependent on the microchannel width. Precise replication of in vivo cell alignment in engineered tissue, with the ability to tailor specific surface chemistries of the scaffold to the desired application, will potentially allow the production of artificial tissue that more closely duplicates the structure and function of native tissue.

Actins↗
PubMed2005

Microcapsule biosensors using competitive binding resonance energy transfer assays based on apoenzymes.

This paper reports the first demonstration of a fluorescence resonance energy transfer based glucose sensor, wherein a competitive binding (CB) assay is encapsulated into polyelectrolyte microcapsules. The work supports the concept that microcapsules are superior to hydrogel systems or other matrixes for competitive-binding-based system, as they provide free movement of the sensing elements within the capsule interior while constant total sensing assay concentration is maintained. The transduction approach employed in these preliminary experiments is also a novel CB system based on a model apoenzyme, apo-glucose oxidase (AG), which is highly specific to beta-d-glucose, as the model target-binding protein. The glucose sensitivity of the fluorescein isothiocyanate (FITC)-dextran and tetramethylrhodamine isothiocyanate-AG encapsulated in microcapsules showed 5 times greater specificity for beta-D-glucose over other sugars, with sensitivity (change in intensity ratio) in the range of 2-6%/mM. It was observed that the sensitivity and range of the response can be tailored by controlling the assay concentration using different FITC-dextran molecular weight and total capsule concentration. The findings support the concepts of using microcapsules to encapsulate CB assays for reversible and stable sensors and the use of apoenzymes as specific molecular recognition elements in CB assays. Further, characterization results for microcapsule glucose sensors demonstrate their suitability for monitoring physiological glucose levels.

Apoenzymes↗
PubMed2005

Stable encapsulation of active enzyme by application of multilayer nanofilm coatings to alginate microspheres.

In an effort to improve the stability for long-term biosensor use, layer-by-layer self-assembly was explored as a potential technique to provide a diffusion barrier to encapsulated glucose oxidase inside alginate microspheres (<5 microm), fabricated using an emulsification technique. The total loss of encapsulated enzyme was reduced to less than 25 and 15% with the application of single PAH/PSS and crosslinked PAH/PAA coatings, respectively, in comparison to at least a 45% loss observed with uncoated and PDDA/PSS-coated microspheres. Furthermore, it was found that enzyme within PAH/PSS- and crosslinked PAH/PAA-coated spheres retained more than 84 and 60% of initial activity, respectively, after three months, whereas uncoated and PDDA/PSS-coated microspheres retained less than 20%.

Alginates↗
PubMed2005

Encapsulation of glucose oxidase and an oxygen-quenched fluorophore in polyelectrolyte-coated calcium alginate microspheres as optical glucose sensor systems.

Microspheres coated with polyelectrolyte multilayers (PEM's) are being investigated for potential use as implantable biosensors-so-called "smart tattoos." In this work, the feasibility of this approach for glucose sensors was demonstrated by glucose oxidase encapsulated within calcium alginate microspheres, followed by entrapment of an oxygen-quenched ruthenium compound in the same microstructure. A novel feature of these microdevices is the formation of multilayer nanofilms on the surface of the microspheres, used to stabilize enzyme entrapment and control substrate diffusion. Confocal microscopy was used to confirm the stable encapsulation of sensor chemistry. The reversible response of sensors to step changes in glucose was observed, and preliminary experimental data were compared to theoretical predictions produced by a computational model. These findings demonstrate the promise of the described nanoengineering approach for production of functional implantable glucose sensor materials.

Alginates↗
PubMed2005

Stabilization of glucose oxidase in alginate microspheres with photoreactive diazoresin nanofilm coatings.

The nanoassembly and photo-crosslinking of diazo-resin (DAR) coatings on small alginate microspheres for stable enzyme entrapment is described. Multilayer nanofilms of DAR with poly(styrene sulfonate) (PSS) were used in an effort to stabilize the encapsulation of glucose oxidase enzyme for biosensor applications. The activity and physical encapsulation of the trapped enzyme were measured over 24 weeks to compare the effectiveness of nanofilm coatings and crosslinking for stabilization. Uncoated spheres exhibited rapid loss of activity, retaining only 20% of initial activity after one week, and a dramatic reduction in effective activity over 24 weeks, whereas the uncrosslinked and crosslinked {DAR/PSS}-coated spheres retained more than 50% of their initial activity after 4 weeks, which remained stable even after 24 weeks for the two and three bilayer films. Nanofilms comprising more polyelectrolyte layers maintained higher overall activity compared to films of the same composition but fewer layers, and crosslinking the films increased retention of activity over uncrosslinked films after 24 weeks. These findings demonstrate that enzyme immobilization and stabilization can be achieved by using simple modifications to the layer-by-layer self-assembly technique.

Adsorption↗
PubMed2005

Macromolecule encapsulation in diazoresin-based hollow polyelectrolyte microcapsules.

A stable enzyme encapsulation technique based on the conversion of weak interactions between diazo resin/poly(styrene sulfonate) to covalent bonds was explored. Photosensitive diazoresin-based polyelectrolyte microcapsules were prepared via layer-by-layer electrostatic self-assembly of poly(styrene sulfonate) and diazoresin on MnCO(3) templates. UV-vis and zeta-potential measurements confirmed the alternate deposition of {PSS/DAR} multilayers on the micrometer-sized dissolvable templates. The DAR-based microcapsules were demonstrated to be permeable to enzymes prior to UV irradiation, while the permeability of the multilayer wall was changed substantially after photo-cross-linking. Encapsulated molecules were stably entrapped after UV irradiation, as shown by confocal microscopy and atomic force microscopy images. Activity assays revealed that encapsulated glucose oxidase possessed 52.8% of the catalytic activity exhibited by the same amount of free enzyme, proving the preservation of native conformation and accessibility of substrate. This encapsulation technique is promising for many biomedical and biotechnological applications, particularly enzyme biosensors, which require stable immobilization of functional components while allowing sufficient transport rates for substrate molecules.

Azo Compounds↗
PubMed2005

Experimental and theoretical aspects of glucose measurement using a microcantilever modified by enzyme-containing polyacrylamide.

We report a glucose oxidase-containing polyacrylamide hydrogel-coated microcantilever sensor for the measurement of glucose. This enzymatic reaction of glucose results in swelling of the hydrogel due to formation of charged ions (gluconate molecules and protons). The microcantilever undergoes reversible and reproducible bending deflection upon exposure to solutions containing various glucose concentrations due to swelling or shrinking of the hydrogels. The microcantilever deflections increase when the glucose concentrations increase. A theoretical model has been built to correlate volume changes of the gel with microcantilever bending. The calculated data matched with the experimental results very well. Such hydrogel-coated microcantilevers could potentially be used to prepare microcantilever-based chemical and biological sensors when other enzymes are immobilized in the hydrogel.

Acrylic Resins↗
PubMed2004

Glucose-sensitive nanoassemblies comprising affinity-binding complexes trapped in fuzzy microshells.

A new design for glucose monitoring with "smart" materials based on self assembly, competitive binding, and resonance energy transfer (RET) is presented. The basic transduction principle is changing RET efficiency from fluorescein isothiocyanate (FITC) to tetramethylrhodamine isothiocyanate (TRITC), as FITC-dextran is displaced from TRITC-Concanavalin A (Con A) with the addition of glucose. Nanoscale fabrication by self-assembly of Con A/dextran into multilayer films, followed by polymer multilayers. The advantages of this approach include physical localization and separation of sensing molecules from the environment via entrapment of the biosensorelements in a semi-permeable polymeric shell, and only functional molecules are included in the sensors. To realize these nanostructures, dissolvable resin microparticles were coated with FITC-dextran+TRITC-Con A multilayers, followed by polyelectrolyte multilayers, and the core particles were then dissolved to yield hollow capsules. The nanoassembly process was studied using microbalance mass measurements, fluorescence spectroscopy, confocal fluorescence microscopy, and zeta-potential measurements. The key findings are that the specific binding between Con A and dextran can be used to deposit ultrathin multilayer films, and these exhibit changing RET in response to glucose. Fluorescence spectra of a microcapsules exhibited a linear, glucose-specific, 27% increase in the relative fluorescence of FITC over the 0-1800 mg/dL range. These findings demonstrate the feasibility of using self-assembled microcapsules as optical glucose sensors, and serve as a basis for work toward better understanding the properties of these novel materials.

Capsules↗
PubMed2003

Multilayer lactate oxidase shells on colloidal carriers as engines for nanosensors.

Self-assembly methods are being studied for construction of nanoscale chemical sensors employing coimmobilized enzymes and indicator dyes. This paper describes the assembly of the catalytic enzyme lactate oxidase in multilayer films on colloidal templates via layer-by-layer self-assembly, which is a step toward achieving nanoengineered biosensors. The architecture of the resulting films was characterized using quartz crystal microbalance and zeta potential analysis, and catalytic activity was characterized colorimetrically. The tailored activity of the functional nanofilms was proportional to the number of enzyme layers deposited during assembly, which provides a basis for designing sensors with specific interactions.

Biosensing Techniques↗
PubMed2002

Potential for glucose monitoring with nanoengineered fluorescent biosensors.

Possibilities for engineering of fluorescent micro/nanoscale devices for glucose sensing are presented. A description of the potential for clinical use is given in terms of overall concept, current knowledge, advantages of the fabrication approach proposed, and challenges that must be addressed prior to clinical use. Deployment of micro/nanoparticles in the dermis may allow transdermal monitoring of glucose changes in interstitial fluid. Using electrostatic self-assembly, an example of nanotechnology for fabrication, two types of sensors are being studied: (1). solid nanoparticles coated with fluorescent enzyme-containing thin films and (2). hollow micro/nanocapsules containing fluorescent indicators and enzymes or glucose-binding proteins. Nanoengineering of the coated colloids and microcapsules allows precision control over optical, mechanical, and catalytic properties to achieve sensitive response using a combination of polymers, fluorescent indicators, and glucose-specific proteins. Challenges to in vivo use include understanding of material toxicity and failure modes, and determining methods to overcome fouling, protein inactivation, and material degradation.

Biosensing Techniques↗