Review of designing an information processing ware for a diabetic chip

Miniaturization of clinical chemistry analyzers can empower research conducted to better understand, diagnose, manage, and cure diseases such as diabetes. For the last decade, we have been working on the design and development of miniaturized clinical chemistry devices, including a Diabetic Chip (diabetiChip). These devices measure a small array of analytes, are small, portable, fast, easy-to-operate, and inexpensive. The chosen analytical method for the diabetiChip uses bioluminescence, which is highly sensitive and specific, and is based on photon counting and specific enzymatic reactions. Bioluminescent reactions were intentionally chosen for analyzing metabolic reactions because they use some of the central nodes of metabolism, such as adenosine triphosphate. Operations of the diabetiChip's information processing ware are the focus of this paper; we show the feasibility of using a set of kinase-containing enzymatic reactions of a firefly bioluminescence-coupled glucose assay in designing the diabetiChip. We have developed and tested the feasibility of the glucose assay; the assay's analytical detection limits (before sample dilution) were 5-185 microM. Uncertainty associated with reporting a 100 microM concentration was about +/- 5 microM. The results show that an FFL bioluminescent-coupled glucose assay is promising in terms of reducing sample volume and cost. The concept of GlucoFaces in visualizing measurements of the diabetiChip is also discussed.

An ImmunoChip prototype for simultaneous detection of antiepileptic drugs using an enhanced one-step homogeneous immunoassay

The development and characterization of a one-step homogeneous immunoassay-based multiwell ImmunoChip is reported for the simultaneous detection and quantitation of antiepileptic drugs (AEDs). The assay platform uses a cloned enzyme donor immunoassay (CEDIA) and a Beta-Glo assay system for generation of bioluminescent signal. Results of the one-step CEDIA for three AEDs (carbamazepine, phenytoin, and valproic acid), in the presence of serum, correlate well with the values determined by fluorescence polarization immunoassay. CEDIA intra- and interassay coefficients of variation are less than 10%. A microfabrication process, xurography, was used to produce the multiwell ImmunoChip. Assay reagents were dispensed and lyophilized in a three-layer pattern. The multiwell ImmunoChip prototype was used to detect and quantify AEDs in serum samples containing all three drugs. Luminescent signals generated from each well were recorded with a charge-coupled device (CCD) camera. The assays performed on an ImmunoChip were fast (5 min), requiring only small volumes of both the reagents (<1 microl/well) and the serum sample. The ImmunoChip assay platform described in this article may be well suited for therapeutic monitoring of drugs and metabolites at the point-of-care setting.

Homogeneous enzyme immunoassay modified for application to luminescence-based biosensors

Application of immunoassay to biosensors for use in the point-of-care setting ideally requires immunoassay without separation steps and with small volumes of both sample and reagents. The suitability of cloned enzyme donor immunoassay (CEDIA), one of a few homogeneous immunoassays available, was investigated for application to biosensors. This method is based on the bacterial enzyme beta-galactosidase, which has been genetically engineered by others into two inactive fragments, enzyme donor (ED) and enzyme acceptor (EA). Association of the ED and EA fragments in the assay results in formation of active enzyme, which acts on substrate to generate a detectable signal. Sensitivity of commercially available CEDIA kits were compared, with respect to the sample and reagent volumes, using three different signal generation processes. The CEDIA kit for valproic acid and three substrates, a colorimetric (chlorophenol red-beta-D-galactopyranoside), a chemiluminescent (Lumi-Gal 530), and a bioluminescent (Beta-Glo Assay System), were employed in the study. Our results indicate that the high sensitivity of the bioluminogenic substrate, D-luciferin-O-beta-galactopyranoside, with short assay time and small volumes of sample and reagents required for the assay, simple handling, and relatively low expense, make this substrate, together with CEDIA, suitable for application to biosensors intended for drug and metabolite monitoring in the point-of-care setting.

Modeling of homogeneous cloned enzyme donor immunoassay

One of the most widely used analytical techniques for sensitive detection of biologically and clinically significant analytes is the immunoassay. In recent years direct immunoprobes allowing label-free detection of the interaction between the antibody and the target analyte have proved their capabilities as fast, simple, and nevertheless highly sensitive methods. Cloned enzyme donor immunoassay (CEDIA) homogeneous assay is based on the bacterial enzyme beta-galactosidase, which has been genetically engineered into two inactive fragments, enzyme donor and enzyme acceptor. Reassociation of the fragments in the assay forms active enzyme, which acts on substrate to generate a colored product. A comprehensive kinetic model of CEDIA is developed to aid in understanding this method and to facilitate development of a truly homogeneous version, potentially applicable to a dipstick-type multianalyte point of care analytical device (ChemChip). Although the standard assay involves a two-step process, we also chose to model a single-combined process, which would be simpler to apply in a ChemChip device. From the modeling simulation, we obtain the time courses of the amounts of product and active enzyme, from which the dynamic ranges can be obtained as 10(-6)-10(-7) and 10(-5)-10(-7)M analyte concentration for two-step and single-combined processes under the conditions of the assumed parameters, respectively. A simple one-step immunoassay has the merit of reducing time and cost and has an improved dynamic range.

Public adventures in diabetes: personal interactivity in a modern science center

About 100 million Americans visit science centers each year to participate in experiential science and technology activities. There is great potential for diabetes awareness and education via the several hundreds of science centers in the United States. Most science centers tend to avoid medically related topics in part because of the difficulty in meeting the interactive goals of science center activities. The Utah Science Center (USC) is addressing these difficulties by creating environments for personal interactive activities in a range of medically related topics, including diabetes. The USC will open in early 2005 in Salt Lake City. The design of diabetes activities for the USC is reviewed: (1) activities (aims, description, stages of development, and partnerships); (2) specific stage I activities (body mass index, "feeling" hypoglycemia, and urine chemistry); and (3) conclusion.

Bioluminescence as a classroom tool for scientist volunteers

There is a great need for practicing scientists to volunteer their time and expertise in the K-12th grade science classroom. We have found that bioluminescence is a fun and exciting way to teach basic science concepts and is an excellent tool for the volunteering scientist. We have had very positive reactions from both teachers and students. The excitement of the students when they first see bioluminescence is contagious. Bioluminescent dinoflagellates are one of the easiest ways to introduce students to this fascinating topic. Many activities and experiments can be done using the bioluminescent dinoflagellates and many students and teachers could benefit from your knowledge and expertise. See you in the classroom.

Phytic acid as an efficient low-molecular-mass displacer for anion-exchange displacement chromatography of proteins

Phytic acid, inositol-hexaphosphoric acid, molecular mass 650, a low-molecular-mass compound, has been identified as a nearly ideal displacer in anion-exchange displacement chromatography for the concentration and purification of model protein mixture. The concentration of low-molecular-mass displacer is a very important parameter for successful separation by displacement chromatography. Displacer concentration influences the formation of the isotachic train and the yield and recovery of the displacement chromatographic process. There is an optimum displacer concentration in which the yield and recovery are highest.

Specific immobilization of in vivo biotinylated bacterial luciferase and FMN:NAD(P)H oxidoreductase

Bacterial bioluminescence, catalyzed by FMN:NAD(P)H oxidoreductase and luciferase, has been used as an analytical tool for quantitating the substrates of NAD(P)H-dependent enzymes. The development of inexpensive and sensitive biosensors based on bacterial bioluminescence would benefit from a method to immobilize the oxidoreductase and luciferase with high specific activity. Toward this end, oxidoreductase and luciferase were fused with a segment of biotin carboxy carrier protein and produced in Escherichia coli. The in vivo biotinylated luciferase and oxidoreductase were immobilized on avidin-conjugated agarose beads with little loss of activity. Coimmobilized enzymes had eight times higher bioluminescence activity than the free enzymes at low enzyme concentration and high NADH concentration. In addition, the immobilized enzymes were more stable than the free enzymes. This immobilization method is also useful to control enzyme orientation, which could increase the efficiency of sequentially operating enzymes like the oxidoreductase-luciferase system.

Thin-layer ion-exchange chromatography of proteins

Thin-layer chromatography (TLC) is one of the simplest and most convenient techniques to separate small molecules. Of a variety of TLC separation modes, only size-exclusion was successfully used to separate proteins. In this paper, adsorption-TLC was used to separate proteins. The net charges were calculated for four model proteins, albumin, transferrin, lactoferrin and lysozyme, under different pH values. The suitable pH values for separation were determined according to the results from such calculations. Then, the adsorption isotherms of the four proteins were measured to deduce the ionic strength for appropriate elution conditions. Optimal conditions, 0.01 M bicine and pH 8.50, and a three-step elution process (1st step 0.01 M NaCl, 2nd 0.025 M NaCl, and 3rd 0.10 M NaCl), were obtained. Finally, the four model proteins were successfully separated under these elution condition.

Behavior of Model Proteins, Pretreated in Urea and/or Dithiothreitol, at Air/Solution Interfaces

The behavior of the model proteins, lysozyme, myoglobin, and beta-casein, pretreated in urea and/or dithiothreitol, at air/solution interfaces was studied by surface pressure-area techniques. The data suggested that in the absence of pretreatments the globular proteins are only partially unfolded at the interfaces. The interfacial activity was enhanced by the pretreatment (lysozyme in 8 M urea with 0.2 M dithiothreitol and myoglobin in 8 M urea). The interfacial activity of casein, a random-coil type protein, was not influenced by the pretreatment (8 M urea), as it readily and completely unfolds at the interfaces. The unfolding of globular proteins at the interfaces is apparently restricted by both disulfide and noncovalent bonds. Pretreatment can relax those restrictions, resulting in more complete interfacial unfolding. Copyright 1998 Academic Press. Copyright 1998Academic Press

Minimizing interferences in the quantitative multielement analysis of trace elements in biological fluids by inductively coupled plasma mass spectrometry

The determination of trace and ultratrace elements in biological fluids, including urine and serum, by inductively coupled plasma mass spectrometry (ICP-MS) is discussed. Nonspectral interferences and their corrections by external calibration and calibrator addition are discussed in detail. External calibration with internal calibration and dilution is mostly sufficient to correct for encountered biological matrix effects. For some elements, such as Cs and Zn, the use of calibrator addition provides more accurate results. The importance of spectral interferences and their elimination by isotope selection was also studied. Two examples, Cu and Zn, demonstrate the prime importance of selecting an isotope with minimal polyatomic interferences for analysis. By using 65Cu and 68Zn, accurate results for urine and serum can be obtained without excessive pretreatment of samples. Two reference materials, Bio-Rad Lyphochek urine and Kaulson Contox sera, were analyzed. Accuracy was evaluated by comparison with target values, and precision was estimated by the CV within 95% confidence.

Minimizing interferences in the quantitative multielement analysis of trace elements in biological fluids by inductively coupled plasma mass spectrometry

The determination of trace and ultratrace elements in biological fluids, including urine and serum, by inductively coupled plasma mass spectrometry (ICP-MS) is discussed. Nonspectral interferences and their corrections by external calibration and calibrator addition are discussed in detail. External calibration with internal calibration and dilution is mostly sufficient to correct for encountered biological matrix effects. For some elements, such as Cs and Zn, the use of calibrator addition provides more accurate results. The importance of spectral interferences and their elimination by isotope selection was also studied. Two examples, Cu and Zn, demonstrate the prime importance of selecting an isotope with minimal polyatomic interferences for analysis. By using 65Cu and 68Zn, accurate results for urine and serum can be obtained without excessive pretreatment of samples. Two reference materials, Bio-Rad Lyphochek urine and Kaulson Contox sera, were analyzed. Accuracy was evaluated by comparison with target values, and precision was estimated by the CV within 95% confidence.

Specific immobilization of firefly luciferase through a biotin carboxyl carrier protein domain

Firefly luciferase (Photinus pyralis) was fused with a histidine tag and a biotin carboxyl carrier protein (BCCP) domain at its amino terminus. Highly purified recombinant luciferase was obtained by a one-step purification protocol, utilizing immobilized metal affinity chromatography. The novel BCCP-luciferase had properties, stability, and activity similar to those of native luciferase. The biotin molecule on the BCCP domain allowed specific immobilization of BCCP-luciferase on avidin-coated surfaces via the biotin-avidin interaction.

Protein adsorption on low temperature isotropic carbon: V. How is it related to its blood compatibility?

Based on our research on blood protein interactions with low temperature isotropic carbon (LTIC) and data from the literature, we propose that the carbon surface has strong interactions with adsorbed proteins. In this paper we focus on how a relatively blood-compatible material interacts with plasma proteins. We present our results on the structure and properties of the LTIC surface utilizing SEM, STM, XPS, and contact angle measurements. We briefly review protein adsorption on LTIC using DSC, impedance, radioisotopes, and two-dimensional gel electrophoresis. LTIC is characterized by a microporous, oxidized, hydrophobic, and domain mosaic structure. Surface polishing smoothens the roughness and removes the porosity, while largely destroying the ordered atomic texture, making the surface more random and more amorphous. The LTIC surface denatures all adsorbed proteins studied. The rate of protein adsorption is high and the surface concentration is large. The LTIC surface adsorbs all proteins without preference. The surface also tenaciously retains proteins such that they cannot be displaced by buffer or exchanged by proteins in solution. We conclude that LTIC accomplishes its blood compatibility through a passivating film of strongly adsorbed bland proteins, which do not interact with platelets nor participate in blood coagulation. We also suggest mechanisms for the production of such a film by the LTIC surface.

Photoaffinity labeling of antibodies for applications in homogeneous fluoroimmunoassays

A homogeneous noncompetitive immunoassay based on photoaffinity labeling techniques is described. Using this method, a fluorophore (reporter) can be specifically attached to an antibody in the vicinity of its antigen-combining sites. Upon antigen binding, changes in the fluorescence spectrum of the reporter molecule are often observed. Two fluorophores, pyrene and dansyl, were evaluated for this purpose. Also, this technology is ideal for fluorescence energy-transfer immunoassays that require labeling of the antibody with either a donor or acceptor fluorophore. In such cases, a fluorescent dye can be specifically attached near the antigen-combining site, where it can participate in high-efficiency energy transfer with its complementary fluorophore attached to the antigen.

Association of Graft Copolymers of Alkyl Methacrylates with α-Methyl-ω-hydroxy-poly(oxyethylene) ethacrylates

Solution properties of the statistical copolymers of alkyl methacrylates (AMA) with α-methyl-ω-hydroxy-poly(oxyethylene) methacrylates (MPOEMA) (nonionic polysoaps) were studied using static and dynamic ligh scattering as a function of monomer composition and concentration in aqueous and methyl cellosolve solutions. The solubility of the copolymers in water was found to be dependent on molar contant of AMA. While copolymers with low content of hexyl methacrylate (HMA) (0 and 20 mole %) were directly soluble in water, forming true solutions with a low content of large swollen aggregates, copolymers with a higher content of HMA or lauryl methacrylate (LMA) were not directly dispersable in water. A special procedure, the stepwise dialysis from methyl cellosolve solutions against water, had to be used to prepare them in the pseudomicellar form. The copolymers were directly soluble in methyl cellosolve and its water solution containing up to 60 vol.% of water. Nevertheless, the light scattering experiments were dominated by light scattering of swollen particles of aggregated copolymer molecules. The copolymers were not soluble in the mixtures containing 70-100 vol.% of water. Paramaters of aggregates in the mixture with 60 vol.% of water and in pure water were found to be very similar.

Protein adsorption on low-temperature isotropic carbon: I. Protein conformational change probed by differential scanning calorimetry

This is the first of a set of articles on protein adsorption on low-temperature isotropic carbon (LTIC), a reputed blood compatible material. Surface-induced conformational changes of albumin, fibrinogen, and some small proteins were measured by differential scanning calorimetry (DSC) on LTIC powders and colloidal silica. The LTIC surface significantly alters the DSC response (denaturation?) in proteins studied in different buffer solutions. We use the term "denaturation" to refer to altered protein behavior in the adsorbed state. Hydrophobic interactions between LTIC and the proteins are thought to be the major driving force. The presence of air at the water-carbon interface seems to prevent the surface denaturation of fibrinogen. The silica surface greatly denatures albumin but only slightly denatures fibrinogen. Because LTIC is considered to be a nonthrombogenic material, but silica is considered to be a thrombogenic one, whether a surface denatures adsorbed proteins cannot be the sole criterion for its blood compatibility. The latter largely depends on what protein the surface denatures, and in what sequences.

Protein adsorption on low temperature isotropic carbon. III. Isotherms, competitivity, desorption and exchange of human albumin and fibrinogen

In this paper we consider the adsorption of albumin and fibrinogen on low temperature isotropic carbon (LTIC). A subsequent paper considers the adsorption of other plasma proteins [Feng L, Andrade JD, Colloids and Surfaces (in press)]. Carbon fragments and silica plates were used as adsorbents. Adsorption was carried out by incubating the adsorbents in solutions of 125I-labelled and unlabelled proteins (single component system), or with buffer-diluted human plasma (multicomponent system). Adsorbed proteins then underwent displacement by buffer, by single protein solutions or by dilute plasma. Results show that the LTIC substrate adsorbs a large amount of proteins before saturation, which may be due to multilayer adsorption. LTIC also irreversibly holds adsorbed proteins against the exchange agents used; little adsorbed proteins can be displaced, even after a very short adsorption time. There is no preferential adsorption for either albumin or fibrinogen on LTIC from their binary solutions, suggesting that both proteins have high affinities for the surface. Such strong interactions between LTIC and proteins are not attributed to electrostatic interactions. On the other hand, protein adsorption on the silica surface is selective and reversible, with a much higher affinity for fibrinogen than albumin and an even higher affinity for some other plasma proteins. The paper also discusses the effect of sequential protein addition to a solution on the surface concentration and suppression of adsorption of both proteins in the presence of other plasma proteins. A very important conclusion is that the LTIC surface is very active towards proteins adsorption.

Surface atomic and domain structures of biomedical carbons observed by scanning tunneling microscopy (STM)

STM has been used to study the surface domain and atomic structures of three biomedical carbons: glassy carbon (GC), low-temperature isotropic carbon (LTI), and ultra-low-temperature isotropic carbon (ULTI). The images show atomic lattices on both GC and LTI, but not on ULTI. The lattices contain many defects; lattices in GC are more ordered than those in LTI. The images also show patchlike carbon crystallites with sizes of 3-15 nm for GC, 2-8 nm for LTI, and 1-3 nm for ULTI. The crystallites from surface domains that may differ in surface properties due to different orientations of the crystallites. Mechanical polishing makes the LTI surface more amorphous and more homogeneous. Based on the STM observations, we evaluate several hypotheses on the blood compatibility of biomedical carbons.

Manipulation of Proteins on Mica by Atomic Force Microscopy

The atomic force microscope was used to image adsorption of a monoclonal IgM on mica in real time. Under the smallest possible force we could achieve (<4 nN), the cantilever tip behaved as a molecular broom and was observed to orient protein aggregates in strands oriented perpendicularly to the facet of the cantilever tip. Rotating the scan direction preserved the orientational relationship, as seen by the formation of rotated strands. When the applied force was increased, the distance between the strands increased, indicating the amount of protein that can be swept depends on the applied force. The effect of scanning increased the apparent surface coverage of IgM. Manipulation of a deposited fibrinogen layer with a 4-nN repulsive force was observed only after tens of minutes, but not to the extent that strands formed, indicating a greater adhesion between the fibrinogen and mica than between IgM and mica. With an applied repulsive force of 30 nN, fibrinogen strands formed and the protein was manipulated to produce the block letter U. At a much higher repulsive force, the entire scanning area was swept clean.

Needs, problems, and opportunities in biomaterials and biocompatibility

There are four topics related to biomaterials and biocompatibility which I feel are key problems, are often unrecognized, and are therefore rich opportunities for work in the near future: (i) the covalent instability of proteins, (ii) the concept of statistical specificity and statistical heterogeneity, (iii) the issue of solid surface dynamics and surface relaxation, and (iv) the growing concern with the costs of health care and of medical research. Each is briefly discussed in this paper.

Interaction of plasma proteins with heparinized gel particles studied by high-resolution two-dimensional gel electrophoresis

In order to further the understanding of protein-surface interactions in the coagulation system, we have chosen to study plasma protein adsorption onto heparin-immobilized surfaces. Heparin-binding proteins are abundant in plasma: a search of amino acid sequences revealed that many plasma proteins have possible heparin binding sites. Plasma protein adsorption to the heparinized surfaces is monitored by a novel technique in which the solution depletion of proteins is analytically determined using quantitative two-dimensional polyacrylamide gel electrophoresis (2-D PAGE). This method enables simultaneous, quantitative detection of the majority of plasma proteins before, during, and after their adsorption onto high surface area adsorbents. Using computerized densitometry of silver-stained 2-D PAGE gels, the amount of each protein can be determined from the integrated optical density of each protein "spot." Kinetics of adsorption and adsorption isotherms of four important heparin binding proteins, antithrombin III (ATIII), complement factor C3 (C3), apolipoprotein AI (Apo-AI) and apolipoprotein AIV (Apo-AIV) are reported in this paper. From the adsorption isotherms, the apparent binding constants of each protein-immobilized heparin complex, Ka, were calculated. The surface binding constants were of the same order of magnitude as the respective solution binding constants in the literature. The surface binding constants followed the same order as the respective solution binding constants: Ka (ATIII) greater than Ka (Apo-AIV) greater than Ka (C3) greater than Ka (Apo-AI), indicating that protein binding to the immobilized heparin used is not essentially different from solution binding.

Vroman effects, techniques, and philosophies

Leo Vroman's work on blood-materials interaction over the years has motivated and influenced much of our work in this field. Here we show how most of our studies on proteins at interfaces can be traced to Vroman's ideas presented in Blood over 25 years ago. Specifically, we briefly discuss simple proteins at simple interfaces, complex interfaces, complex proteins at interfaces, multi-parameter phenomena, and scientific communication and education.

Surface properties of copolymers of alkyl methacrylates with methoxy (polyethylene oxide) methacrylates and their application as protein-resistant coatings

New polymeric surfactants, copolymers of alkyl methacrylates with methoxy (polyethylene oxide) methacrylates, were synthesized and characterized by gel permeation chromatography. They were studied as possible means to produce polyethylene oxide-rich surfaces by a simple coating treatment on common hydrophobic medical materials. They were further studied as cleaners for the removal of proteins preadsorbed on hydrophobic surfaces. The surface properties of the copolymers such as the adsorption properties of the copolymer on a hydrophobic surface, low density polyethylene, the protein-resistant character of the prepared polyethylene oxide surfaces and the effectiveness of the copolymers for removal of proteins pre-adsorbed on the surface, were investigated by X-ray photoelectron spectroscopy and by using 125I-labelled copolymers and 125I-labelled proteins. The surface properties of the synthesized copolymers were compared with those of commercially available polyethylene oxide containing block copolymer surfactants.

Spatially resolved detection of antibody-antigen reaction on solid/liquid interface using total internal reflection excited antigen fluorescence and charge-coupled device detection

Spatially-resolved detection of antibody-antigen reactions at the solid/liquid interface was investigated by total internal reflection excited fluorescence from large area flat surfaces. Anti-HSA immunoglobulin G (IgG) antibody was immobilized at four spatially distinct spots. Binding of fluorescein-labeled human serum albumin (HSA) from the solution to immobilized antibody was detected by a cooled charge-coupled device (CCD) as a charge in the fluorescence intensity. A two-dimensional representation of the fluorescence was obtained during the binding reaction time of 25 mins. The contributions from bound and free antigen to the total signal were evaluated. The influence of the scattered excitation light and the normalization of fluorescence signal with respect to the two-dimensional incident light intensity distribution are discussed.

The influence of adsorption of native and modified antibodies on their activity

Immobilization of biomolecules to solid phase materials has been widely used in many areas (e.g., purification, analytical chemistry, and catalysis). The interfacial properties of immobilized antibodies on pretreated silica and hydrogel surfaces were explored by comparing native and modified antibodies with respect to their surface activity. The antibody was modified by exposing it to a low pH solution prior to immobilization. Both physical adsorption and covalent immobilization methods were studied. It was found that the surface activity of the modified antibody is higher than that of the native antibody on two silica surfaces. The results of this study demonstrate that the adsorption properties of the antibodies play an important role in their covalent immobilization on certain types of solid supports.

Protein-resistant surfaces prepared by PEO-containing block copolymer surfactants

Polyethylene oxide(PEO)-containing nonionic polymeric surfactants were studied as a possible means to produce PEO-rich surfaces by a simple coating treatment of a common hydrophobic medical material--polyethylene. Surface tension and adsorption properties of PEO/polypropylene oxide(PPO) and PEO/polybutylene oxide(PBO) block copolymer surfactants on a hydrophobic surface (low density polyethylene, LDPE) were investigated, using the Wilhelmy plate surface tension technique and x-ray photoelectron spectroscopy(XPS). The protein resistance of the surfactant-treated surfaces was evaluated by XPS and 125I-labeled proteins. The data presented indicate that adsorption of the surfactants on LDPE is dependent on the molecular geometry of the surfactants. Adsorption of human albumin was significantly decreased on the surfactant-treated LDPE surfaces, as compared with the untreated surface. Surfactants suitable for the preparation of PEO-rich surfaces and possible mechanisms for their protein resistance are discussed.

Scanning tunnelling microscopic images of amino acids

We present images of amino acids adsorbed on highly orientated pyrolytic graphite (HOPG) obtained with the scanning tunnelling microscope (STM) in air. Individual molecules can be observed although the majority of adsorbates appear to form clusters. In the case of leucine, methionine, and tryptophan, two molecules often associate together to form a dimer. Single or dimer glycine molecules were not seen, but a cluster of a number of them was observed. The various adsorbed states may be related to the different interactions between the amino acids and the graphite surface. The mechanism of image formation of the amino acids is probably related to charge transfer mechanisms.

On-line sensors for coagulation proteins: concept and progress report

The assessment of blood damage and of the activation of the coagulation, complement and/or inflammatory systems by cardiovascular and extracorporeal devices is difficult at best. Immunoassay methods are now available for the measurement of many of the proteins, enzymes and peptides involved in coagulation, thrombosis, complement and inflammation. We present a long-range project and plan to develop an array of remote, on-line, semicontinuous immunosensors for selected coagulation proteins, based on fluoroimmunoassay principles. The free/bound separation step is performed optically. Excitation of fluorescence is performed via an evanescent wave produced by total internal reflection and waveguide optics. Fluorescence emission is collected only in the near field. Means to deliver fluorescently-labelled reagent and to modify the antigen-antibody binding constant are presented and discussed. The results of non-specific binding, plasma-blood fluorescence, and blood compatibility are also discussed.

Plasma protein adsorption: the big twelve

We have discussed the general principles of protein adsorption at solid-liquid interfaces from single component and multicomponent solutions, based on qualitative kinetic models that include mass transport considerations, initial interaction energies, surface-dependent conformational changes, and possible desorption processes. We have surveyed plasma protein components greater than one milligram per milliliter in concentration, which we call "The Big Twelve." We considered their size, concentration, diffusion coefficient, structure and function, and methods of estimating their "surface denaturability" by using bulk solution measures of denaturation and conformational change. We have suggested that the role of the carbohydrate moieties in plasma proteins may have some bearing on their adsorption properties. We further suggest that lipoproteins, because of their lipid phase transition and conformational lability at body temperature, may tend to dominate the adsorption process, particularly on mobile elastomeric polymer surfaces. We suggest that detailed consideration of the structure and characteristics of each of the proteins involved is necessary in order to begin to understand plasma adsorption processes. Detailed characterization and understanding of the solid surface in the aqueous and protein environments are also required.

Adsorption of low density lipoproteins onto selected biomedical polymers

This study examines the interaction of human low density lipoprotein (LDL) with a select group of biomedical polymers. The adsorption characteristics of LDL on cured filler-free poly(dimethyl Siloxane) (C-PDMS), Biomer, Cardiomat 610, Kraton 1650, poly(hydroxyethyl methacrylate) (PHEMA) and glass are presented. Adsorption of LDL to charged hydrophilic glass control surfaces occurred rapidly, reaching plateau concentrations within one minute (0.19 +/- 0.01 ug/cm2). Adsorption of LDL to polymer surfaces appeared to be dependent upon both the polymer hydrophobicity (or apolar nature), and flexibility (or dynamic nature) at the interface. Increased surface concentrations were observed for Biomer (0.32 +/- 0.01 ug/cm2) as well as other polymers which exhibited both hydrophobic and elastomeric properties. Temperature changes between 25 degrees C and 37 degrees C were found to significantly influence the surface concentration of LDL on Biomer (0.16 +/- 0.01 ug/cm2 at 25 degrees C versus 0.32 +/- 0.01 ug/cm2 at 37 degrees C). A lipid core phase transition at 36 degrees C was believed to be responsible for the temperature influence. Preliminary competitive adsorption studies of LDL with albumin (HSA) and serum on silicone surfaces suggests that LDL adsorption occurred rapidly and preferentially (0.25 +/- 0.01 ug/cm2 for LDL alone; 0.33 +/- 0.01 ug/cm2 for LDL + HSA; 0.15 +/- 0.01 ug/cm2 LDL + serum). Preliminary studies on the role of LDL in calcification were not conclusive. It can be concluded that LDL adsorption is dependent upon polymer hydrophobicity, flexibility and temperature. Competitive adsorption experiments suggests that LDL may have a substantial influence on protein adsorption.

Human haptoglobin adsorption by a total internal reflection fluorescence method

Haptoglobin (Hp) is one of the major protein constituents of plasma. Three different forms are found in the population. The 1-1 and 2-2 forms adsorb similarly onto hydrophobic silica [treated with dimethyl dichlorosilane (DDS)] and onto clean silica, although the affinities on the silica surface are lower at 60 minutes contact time. The two forms desorb differently from silica, but desorb similarly from DDS-silica. Adsorption is less reversible on the hydrophobic surface. Due to its adsorbtion tendencies and its high concentration in plasma, the adsorption of Hp may be important in blood interaction at solid-liquid interfaces.

Biomaterials: applications----innovations----principles: the contributions of C. William Hall

Bill Hall has always had practical goals and objectives, be it an artificial heart, a cardiac assist device, a percutaneous lead, an artificial skin, or a direct skeletal attachment endoprosthesis. Always a careful analysis of the problem, with a keen understanding and appreciation of the biologic and physiologic nature and properties of the tissues with which he was working and must interface, led to innovative approaches which permitted him to work with, rather than against, natural biologic forces and processes. Bill Hall's understanding and practical successes have led to a set of principles that will help guide the education and development of future generations of biomaterial scientists and engineers, and through them and their medical coworkers, the development and application of devices and methods for patient treatment.

Immunochemical detection by specific antibody to thrombin of prothrombin conformational changes upon adsorption to artificial surfaces

Polyclonal antihuman alpha-thrombin antibodies produced in rabbits reacted minimally (less than 0.05%) in solution with human prothrombin. However, when prothrombin was adsorbed to artificial surfaces such as polyvinyl chloride (PVC), the cross-reactivity of surface-bound prothrombin with antibody IgG to thrombin (greater than 95% purity) was shown to be significantly enhanced. On PVC, the molar ratios of antibody IgG to thrombin/prothrombin approached the same level as that of antibody IgG to thrombin/thrombin when thrombin was adsorbed to the same material. The analyses of antigen-antibodies interaction, in solution with a direct binding assay by immune precipitation at high-speed centrifugation (160,000 g, 30 min), and on solid-phase PVC, were accomplished by use of double-labeling technique, i.e., 131I-thrombin (or 131I-prothrombin) and 125I-antibody IgG to thrombin. The results appear to suggest that prothrombin adsorption to PVC has resulted in some molecular conformational changes so that immunologically the adsorbed prothrombin resembles that of adsorbed thrombin on the same PVC surface.

Oxy- and deoxyhaemoglobin adsorption onto glass and polymer surfaces

The adsorption of deoxyhaemoglobin (deoxyHb) and oxyhaemoglobin (oxyHb) was determined on clean glass, n-pentyl triethoxysilane (NPS)-treated glass, polystyrene (PS), and a polyetherurethane (PEU). The adsorbed amounts range from 0.1 to 0.6 micrograms/cm2 for oxyHb and from 0.3 to 0.7 micrograms/cm2 for deoxyHb. DeoxyHb adsorbs onto all these surfaces more than oxyHb. The more hydrophobic the surface, the more adsorption of both deoxy and oxyHb forms. These results suggest the oxyHb and deoxyHb interact differently with the surfaces studied. It is likely that the surface hydrophobicity of Hb plays a major role in Hb adsorption onto surfaces; the deoxyHb surface is more hydrophobic than the oxyHb surface. The binding sites for Hb adsorption may include the clefts between alpha 1, beta 1. A surface-induced dimerization mechanism is proposed to explain the adsorption of oxyHb.

Minimizing the aggregation of neutral insulin solutions

Various solution additives affect the solubility and macroaggregation of insulin in buffered aqueous solutions at physiological pH. The solubility of insulin may be improved with the addition of small amounts of aspartic acid, glutamic acid, EDTA (ethylenediaminetetraacetic acid), lysine, Tris buffer, or bicarbonate buffer. In addition, the propensity of dissolved insulin to reaggregate and precipitate may be inhibited by such additives. Buffered physiological (pH 7.4) saline solutions containing 0.001-0.003 M lysine in the presence of 0.005 M EDTA or 0.01 M lysine in the absence of EDTA improve insulin solubility and are effective in minimizing aggregation. Solutions thus prepared may be suitable for application in intravenous insulin infusion devices and may be useful commercial insulin preparations.