Michael A. Matthews

University of South Carolina, Columbia, South Carolina, United States

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Publications (68)115.85 Total impact

  • Lin Yu · Michael A. Matthews
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    ABSTRACT: This paper reports new data on the production of hydrogen from water vapor plus NaBH4, or NaBH4 + 10% CoCl2. Data were collected with the aid of an isothermal semi-batch reactor with in-situ H2 rate measurement. The reaction of NaBH4 to generate H2 proceeds via three steps: deliquescence, dissolution and reaction. The deliquescence regime of NaBH4 in the presence of 10 weight percent CoCl2 is defined. The H2 yield is quantified at various reaction conditions (reaction temperature 70–120 °C, relative humidity 31–69%). CoCl2 significantly accelerates the rate of H2 production compared to deliquescence + reaction of pure NaBH4. It is also found that a combination of high temperature and high relative humidity contributes to high H2 rate and yield, and either of the two factors dominates the reaction at different conditions. A two-part reactor model accounting for the mechanism of the steam hydrolysis by NaBH4 is developed. The model captures the dissolution + reaction step as well as reaction-only step and was validated by experimental data.
    No preview · Article · Mar 2014 · International Journal of Hydrogen Energy
  • Lin Yu · Perry Pellechia · Michael A. Matthews
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    ABSTRACT: The hydrolysis of NaBH4 in liquid solution has been extensively studied in the past few years; however, data on the kinetics of self-hydrolysis in concentrated solution are few. This work reports the kinetic modeling of self-hydrolysis of 10-20 wt.% NaBH4 at 25-80 degrees C. Also, pH data were obtained independently of the reaction kinetics data. The data obtained from Boron-11 NMR measurements and pH are used to determine kinetic parameters. An empirical power law model is evaluated over a wide pH range. The effects of temperature, pH and initial sodium borohyride concentration are reported. The power law model reproduced the trends of the kinetics of the hydrolysis reaction. In addition, a pseudo first order model derived from a proposed reaction mechanism is evaluated. The behavior of the pseudo first order rate constant k is interpreted in terms of the effect of pH. Copyright
    No preview · Article · Jan 2014 · International Journal of Hydrogen Energy
  • Praneshwar Sethupathy · Inas AlNashef · Michael A. Matthews · John W. Weidner
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    ABSTRACT: Double Potential Step Chronoamperometry (DPSC) was used to determine the rate constants for the homogeneous reactions of alcohols with the superoxide ion (O2•-) at different temperatures in two room temperature ionic liquids (RTILs). The technique was first tested by determining the pseudo first order rate constant for reduction of azobenzene to hydroazobenzene that, in turn, undergoes the benzidine rearrangement. Our results were in good agreement with values reported in the literature using DPSC and conventional kinetic methods. The activation energy for the oxidation of benzyl alcohol is 19.1 kJ/mol in [bmim][HFP]; which is in good agreement with the value reported in the literature. The corresponding values of δS≠ δH≠ and δG≠ for the reaction of superoxide ion with benzhydrol in [bdmim][HFP] calculated at T=45°C are -0.49 kJ/mole, 22.4 kJ/mole, and 177.9 kJ/mole, respectively. The second order rate constant for the oxidation of benzyl alcohol at 10°C in RTIL in [bmim][HFP] was determined to be =1.3 L mol-1 s-1. The pseudo first order rate constant for the homogeneous reaction of O2•- with different primary and secondary alcohols in 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][HFP]) and 1-butyl-2,3-dimethylimidazolium hexafluorophosphate [bdmim][HFP] at different temperatures was measured. The pseudo first order rate constant for the reaction of O2•- with benzhydrol in [bdmim][HFP] at T= 49, 57, 65, 84 C were found to be 60, 72, 92, 148 L mol-1 s-1. The pseudo first order rate constant for the reaction of O2•- with benzhydrol in [bmim][HFP] at T=27, 40 and 80 °C were found to be 53,74, 201 L mol-1 s-1.The Arrhenius plot was then used to determine the activation energy and pre-exponential factor for the corresponding reactions.
    No preview · Article · Dec 2013 · Analytical and Bioanalytical Electrochemistry
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    ABSTRACT: Stable superoxide ion O2•- is electrochemically generated in five room temperature ionic liquids namely 1-hexyl-3-methylimidazolium hexafluorophosphate [hmim][PF6], 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [bmim] [btfmsi], 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide [bdmim] [btfmsi], N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [N-Bu-N-MePyrr] [btfmsi], 1-butyl-2,3-dimethylimidazolium tetrafluoroborate [bdmim] [BF4]. Cyclic voltammetry studies were used to check for the short-term stability of O2•-in these RTIL's. In the absence of impurities, especially water, the O2•-is stable in these three RTIL's in the timescale of the cyclic voltammetry. The formal potential for the O2•-couple is found to be -0.86 V vs. Ag/AgCl reference electrode. Hydrophobicity, Viscosity, Oxygen Solubility and Electrical Conductivity were found to be key parameters in the generation of stable superoxide ions in RTILs.
    No preview · Article · Dec 2013 · Analytical and Bioanalytical Electrochemistry
  • Ping Li · Lin Yu · Michael A. Matthews · Wissam A. Saidi · J. Karl Johnson
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    ABSTRACT: We report a theoretical investigation of H2O adsorption on the NaBH4(100) surface based on first principles density functional theory with inclusion of dispersion corrections in order to explore the initial stages of deliquescence at the molecular level. In the zero coverage limit, H2O is found to bind strongly to sodium sites on NaBH4(100) through O··· Na and O–H···H–B attractions. As the coverage increases H2O molecules adsorb on boron sites. H atoms in the adsorbed H2O monomer adopt tilted down (15°–20°) configurations with respect to the NaBH4(100) surface, which undergoes reconstruction in response to adsorbed H2O by rotations of BH4– groups of up to 90° and slight distortions of the positions of Na+ and BH4–. The adsorption energy per H2O is roughly independent of water coverage up to at least a coverage of four monolayers, suggesting that it is energetically feasible for water to condense on the surface, in agreement with experiments. We have experimentally studied the deliquescence of a mixture of NaBH4 with 10 wt % CoCl2. We found that CoCl2 lowers the deliquescence temperature compared to that for pure NaBH4 at a given vapor phase mole fraction of water; i.e., the deliquescence relative humidity is increased because of addition of CoCl2. Thus, while CoCl2 is a catalyst for aqueous phase hydrolysis of NaBH4, it actually inhibits deliquescence and hence delays the onset of steam hydrolysis.
    No preview · Article · Sep 2013 · Industrial & Engineering Chemistry Research
  • Rajasree Retnamma · C. M. Rangel · A. Q. Novais · Michael A. Matthews
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    ABSTRACT: Liquid-phase catalytic hydrolysis of sodium borohydride (NaBH4) for hydrogen production necessitates long-term stability of base-stabilized NaBH4 solutions at higher temperatures. The present paper reports the kinetics of aqueous-basic solutions containing 20 wt% NaBH4 with 1-15 wt% sodium hydroxide (NaOH) at 80 0C. The established kinetic model employs a modified isoconversional method assuming single-step kinetics. The estimation of kinetic parameters is performed by gPROMS (general PRocess Modeling System) parameter estimation tool. The reaction kinetics differs from low to highly-concentrated NaOH solutions. In highly-basic (≥10 wt% NaOH), aqueous solutions of NaBH4, the rate is independent of NaOH concentration, while for lower-basic (< 10 wt% NaOH) solutions, the dependence is -0.57, confirming the inhibition of hydrolysis kinetics by NaOH.
    No preview · Conference Paper · Jun 2013
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    ABSTRACT: We show that the superoxide ion (O2 ) generated electrochemically from oxygen dissolved in room temperature ionic liquids (RTIL's) reacts with primary and secondary alcohols to form the corresponding ketones and carboxylic acids, respectively. Specifically, we study the conversion of benzhydrol to benzophenone and benzyl alcohol to benzaldehyde/benzoic acid. The kinetics (e.g., rate, selectivity and yield) for these reactions are also determined as a function of the variations in the structure of the ionic liquids. The RTIL's used here are imidazolium-based cations where the functional groups on the imidazolium ring are modified. Specifically, 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF6], 1-butyl-2,3-dimethylimidazolium hexafluorophosphate [bdmim][PF6], 1-hexyl-3-methylimidazolium hexafluorophosphate [hmim][PF6] are used as the reaction medium. These results are compared to an ammonium-based RTIL (N-butyl-N-trimethylammonium bis(trifluoromethylsulfonyl)imide). The results show that the nucleophilic attack by the O2 of both the RTIL and the alcohol, especially that of the H atom at the R2 position of the [bmim][PF6] and [hmim][PF6] greatly affects the yields. No RTIL degradation products were detected for the reactions in [bdmim][PF6] and N-butyl-N-trimethylammonium bis(trifluoromethylsulfonyl)imide ionic liquids. For the benzyl alcohol oxidation reaction in the RTIL, N-butyl-N-trimethylammonium bis(trifluoromethylsulfonyl)imide, benzaldehyde formed did not undergo further oxidation to form benzoic acid, which may be due to the greater hydrophobicity of this RTIL. The competitive reaction kinetics between the alcohol and RTIL component must be considered in the selection of the RTIL solvent system.
    No preview · Article · Dec 2012 · Synthetic Communications
  • Michael A Matthews · Chris Long · Nancy Thompson
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    ABSTRACT: The benefits of active learning in the traditional classroom setting are well established among engineering educators; however, this learning model can thrive in other settings, namely in a research group. This work presents findings from an educational research project specifically designed to foster active learning among undergraduates and graduate students. Observations and data were collected in the Research Communications Studio (RCS), which uses the research group as a forum for active learning. Distributed cognition is a key concept behind the structure of the RCS. Specific practices that facilitate active participation are described, and a quantitative analysis of group discourse is used to confirm activity levels and to characterize the nature of the group interactions. The methods used to foster active learning can be adapted to a variety of research group settings. This approach has been adapted and institutionalized via several professional development seminar courses, and observations from these courses will also be presented. (William Corcoran Award paper, 2008.)
    No preview · Conference Paper · Oct 2012
  • R.Retnamma · L.Yu · C.M. Rangel · A.Q. Novais · K.Johnson · M.A. Matthews
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    ABSTRACT: Hydrolysis of sodium borohydride (NaBH4) over metal catalyst is being accepted as a potential technology to deliver H2 for portable fuel cells. However, unresolved issues such as minimizing the amount of water and nature of hydration by-product limit the hydrogen storage capacities of NaBH4. An alternative method, steam/water vapor hydrolysis, can enhance the hydrogen storage capacities without catalyst, if operating conditions can be optimized. In this approach, solid NaBH4 absorbs water and deliquesces, forming a highly concentrated viscous solution at near boiling point of water and hydrogen evolution occurs from this concentrated solution. Self or spontaneous hydrolysis also occurs even at room temperature when NaBH4 is mixed with water and becomes significant at elevated temperatures and needs to be arrested for increasing the shelf life of the solution. Thus the knowledge of self-hydrolysis of concentrated solutions at elevated temperature is crucial for: (1) developing steam/water vapor hydrolysis technology; and (2) storage of NaBH4-based fuel tanks. These conditions have not been studied in detail so far and the reported studies, except two, were for buffered dilute solutions of NaBH4 (< 0.4 wt%) at low temperatures (< 250C ). The present study reports the kinetics of self-hydrolysis of unbuffered, unstabilized concentrated NaBH4 solutions (10-20 wt %) at elevated temperatures (25-80 0C). The evolution of metaborate formation and NaBH4 consumption were measured in-situ by 11B NMR to determine the reaction kinetic parameters. The reaction order with respect to borohydride concentration is independent of NaBH4 conversion (%) and decreases with temperature, i.e., the reaction order decreases from first-order to 0.24 for an increase in temperature from 25 to 80 0C. The activation energy is found to be NaBH4 concentration dependent and increases with increase in NaBH4 conversion (%). A power law kinetic model in borohydride concentration which accounts the effect of temperature on reaction order and the effect of NaBH4 conversion (%) on activation energy has been developed to represent the self-hydrolysis rate.
    No preview · Conference Paper · Oct 2011
  • Lin Yu · Michael A. Matthews
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    ABSTRACT: Sodium borohydride is being commercialized to provide hydrogen storage for portable fuel cells. Prior kinetic studies have focused on catalytic hydrolysis of dilute aqueous solutions at room temperature. This work reports on a new NMR method for studying the kinetics of non-catalyzed sodium borohydride hydrolysis in highly concentrated solutions. The effects of initial NaBH4 concentration, temperature and pH on conversion are studied. It is found that higher initial NaBH4 concentration and higher temperature both improve the reaction rate. The reaction rate is slowed down with increasing pH of basic solutions and is accelerated with decreasing pH of acidic solutions. In addition, temperature effect seems to be more important than that of the acidic pH on the reaction rate.
    No preview · Article · Jul 2011 · Fuel and Energy Abstracts
  • Hong Liu · Christopher M. Boyd · Amy M. Beaird · Michael A. Matthews
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    ABSTRACT: Complex chemical hydrides are a means to store hydrogen in the solid state near ambient temperatures and pressures. Hydrolysis of hydrides has the potential to provide high gravimetric and volumetric energy densities if water consumption can be minimized. At low temperatures (110∼140 °C), the product of NaBH4 hydrolysis is NaBO2·2H2O (dihydrate), consuming 2 mol of unutilized water. The objective of this work was to conduct water vapor hydrolysis of NaBH4 at elevated pressure and temperature above 150 °C. It was hypothesized that this would yield a solid borate with decreased water bound in the crystal structure. A series of batch reactions were conducted to verify the hypothesis. Experimental characterization of the sodium metaborate byproducts indicated that the primary product of water vapor hydrolysis was NaBO2·1/3H2O (hemihydrate) under a variety of reaction conditions. For the most cases, the conversion of NaBH4 approached 100%.
    No preview · Article · Jun 2011 · Fuel and Energy Abstracts
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    ABSTRACT: Sodium metaborate hydrates are a class of compounds represented by the stoichiometry NaBO2·xH2O. Recently, sodium metaborate has received attention as the byproduct of sodium borohydride hydrolysis, a reaction that is under consideration for hydrogen storage applications. The aim of this work was to understand the disposition of water in the crystal structure of hydrated sodium metaborates and to characterize the thermal stability and dehydration of the various hydrated species to optimize hydrogen storage efficiency as well as recyclability of the borate. Observations from a suite of analytical techniques including thermal analyses (thermogravimetric analysis/differential scanning calorimetry), X-ray diffraction, and Raman spectroscopy were correlated to characterize the dehydration mechanism of commercially available sodium metaborates, with an emphasis on the dihydrate (x = 2). A transformation from tetrahedrally coordinated boron to trigonal boron occurs when NaB(OH)4 (x = 2) is heated between 25 and 400 °C. The first dehydration to Na3[B3O5(OH)2] (x = 1/3) releases 5 mol of water between 83 and 155 °C. The final mole of water is released between 249 and 280 °C, and Na3B3O6 (x = 0) is formed. Raman spectra are reported for x = 2 and 1/3 for the first time. First-principles density functional theory was used to compute Raman spectra of the x = 1/3 and 2 material in order to assign the modes. We found reasonably good agreement between the experimentally measured and calculated vibrational frequencies.
    No preview · Article · May 2011 · Industrial & Engineering Chemistry Research
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    Pedro J Tarafa · Eve Williams · Samir Panvelker · Jian Zhang · Michael A Matthews
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    ABSTRACT: Bacterial endotoxins have strong affinity for metallic biomaterials because of surface energy effects. Conventional depyrogenation methods may not eradicate endotoxins and may compromise biological properties and functionality of metallic instruments and implants. We evaluated the solubilization and removal of E. coli endotoxin from smooth and porous titanium (Ti) surfaces and stainless steel lumens using compressed CO(2)-based mixtures having water and/or surfactant Ls-54. The CO(2)/water/Ls-54 ternary mixture in the liquid CO(2) region (25 °C and 27.6 MPa) with strong mixing removed endotoxin below detection levels. This suggests that the ternary mixture penetrates and dissolves endotoxins from all the tested substrates. The successful removal of endotoxins from metallic biomaterials with compressed CO(2) is a promising cleaning technology for biomaterials and reusable medical devices.
    Full-text · Article · Jan 2011 · Journal of Supercritical Fluids The
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    ABSTRACT: Hydrolysis of sodium borohydride (NaBH 4) solution over metal catalyst is a potential technology for delivering H 2 to portable fuel cells. However, unresolved issues, e.g., minimizing the amount of water and the nature of hydration of metaborate byproducts, limit its hydrogen storage capacities. The NaBH 4 self-hydrolysis process is analyzed using a differential isothermal isoconversional method based on a single-step kinetic approximation. The overall process is described by a reaction order model with temperature dependent reaction order in a wide practical operating window. The apparent activation parameters are conversion dependent and interrelated through the kinetic compensation effect. The apparent activation parameters obtained provide some insight into the theoretical kinetic mechanism. This is an abstract of a paper presented at the 2011 AIChE Annual Meeting (Minneapolis, MN 10/16-21/2011).
    Full-text · Article · Jan 2011
  • Lin Yu · Amy M. Beaird · Ping Li · Karl Johnson · Rajasree Retnamma · Michael A. Matthews
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    ABSTRACT: Sodium borohydride is being commercialized to provide hydrogen storage for portable fuel cells. Prior kinetic studies have focused on catalytic hydrolysis of dilute aqueous solutions at room temperature. Kinetic models for both homogeneous acid catalysts and heterogeneous solid catalysts have previously been proposed. We have developed an alternative pathway allowing the reaction of solid NaBH4 with water vapor. In this approach, the hydride deliquesces to form a concentrated liquid phase that reacts to evolve hydrogen at temperatures near the boiling point of water. Hydrated solid borate byproducts are also formed. Characterization of both liquid phase kinetics as well as BH4 and BO2 solid phase is essential. This work reports kinetics of non-catalyzed sodium borohydride hydrolysis in highly concentrated solutions measured with a novel in-situ 11B NMR technique. To further characterize the solid reactants and products, in-situ Raman spectroscopy was implemented. The experimental work was complemented by first-principles density functional theory calculations to gain insight into possible reaction pathways for NaBH4 solutions. Both constant temperature and constant energy first-principles molecular dynamics simulations have been used to characterize the reactivity of NaBH4 under various conditions.
    No preview · Conference Paper · Nov 2010
  • Ping Li · Karl Johnson · Amy M. Beaird · Michael A. Matthews
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    ABSTRACT: Hydrogen storage continues to be a vexing problem for applications like hydrogen powered fuel cell vehicles. Complex hydrides of light elements are attractive as storage materials due to their high gravimetric and volumetric densities. The hydrolysis reaction of sodium borohydride with water releases 10.7 wt% hydrogen. The reaction mechanism and kinetic barriers associated with this reaction have not yet been conclusively elucidated, despite the number of studies on this material. We are developing a fundamental molecular level understanding of the hydrolysis reaction of NaBH4 using a combination of experiments and first-principles density functional theory (DFT) calculations. We first examined the ground state structure of the low pressure cubic α-NaBH4 crystal. Experimental x-ray diffraction data indicate partial occupancy of the hydrogen sites. We have therefore enumerated all possible structures under the constraint that the BH4 group is tetrahedral and from a series of calculations have found the lowest energy bulk structures. We computed the surface energies of the low Miller index surfaces and used the Wulff construction method to find the equilibrium crystal shape. The surfaces are important because the initial step in the hydrolysis reaction is the adsorption of H2O from the gas phase onto the surface. The (001) surface was found to have the lowest energy. We computed the adsorption energy and structure of H2O on the (001) surface with DFT. Possible reaction mechanisms on the surface were investigated with DFT molecular dynamics. We were unable to observe any reactions on the hydrated (001) surface of NaBH4 on picosecond time scales at high temperatures (~1000 K). We have investigated the role of defects on the reaction mechanism and have found that initial hydrolysis reactions can occur rapidly when Na vacancies are present on the NaBH4 surface. Vibrational modes of NaBH4 and related systems were calculated to provide data that directly complement experimental Raman measurements.
    No preview · Conference Paper · Nov 2010
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    Rajasree Retnamma · C. M. Rangel · Augusto Q. Novais · Lin Yu · Michael A. Matthews

    Full-text · Article · Nov 2010
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    Pedro J Tarafa · Michael A Matthews
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    ABSTRACT: It is known that the commercial surfactant Dehypon® Ls-54 is soluble in supercritical CO(2) and that it enables formation of water-in-CO(2) microemulsions. In this work we observed phase equilibrium for the Ls-54/CO(2) and Ls-54/water/CO(2) systems in the liquid CO(2) region, from 278.15 - 298.15 K. In addition, the Peng-Robinson equation of state (PREOS) was used to model the phase behavior of Ls-54/CO(2) binary system as well as to estimate water solubilities in CO(2). Ls-54 in CO(2) can have solubilities as high as 0.086 M at 278.15 K and 15.2 MPa. The stability of the microemulsion decreases with increasing concentration of water, and lower temperatures favor increased solubility of water into the one-phase microemulsion. The PREOS model showed satisfactory agreement with the experimental data for both Ls-54/CO(2) and water/CO(2) systems.
    Full-text · Article · Nov 2010 · Fluid Phase Equilibria
  • Amy M. Beaird · Thomas A. Davis · Michael A. Matthews
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    ABSTRACT: The interaction between sodium borohydride (NaBH4) and water vapor leading to hydrolysis and hydrogen generation has been investigated by a visual technique. In situ video monitoring confirms that reaction is preceded by deliquescence of NaBH4 upon exposure to water vapor, forming a viscous liquid solution that releases hydrogen. A regime of temperature and relative humidity under which the deliquescence is favorable has been determined. A relative humidity threshold exists below which NaBH4 powder does not absorb water vapor into the bulk to form a solution and thereby does not undergo reaction to form hydrogen. The deliquescence behavior of NaBH4 in water vapor provides an alternative reaction pathway that has potential to improve hydrogen storage density by reducing excess water and other additives.
    No preview · Article · Sep 2010 · Industrial & Engineering Chemistry Research
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    Pedro J. Tarafa · Aidaris Jiménez · Jian Zhang · Michael A. Matthews
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    ABSTRACT: Biomaterials must be both sterile and free of contaminants prior to use, and this is particularly critical for the next generation of implants based on tissue engineering. With increasing complexity of tissue engineering scaffolds and multifunctional devices, there is a need for new approaches to decontamination, i.e. cleaning, disinfection, and sterilization. This work presents our recent results on several aspects of decontamination of both metallic and polymeric biomaterials using compressed carbon dioxide (CO2) technology. We demonstrate the removal of a lubricant oil from titanium surfaces with supercritical CO2. In another application, high level disinfection of a model hydrogel contaminated with Staphylococcus aureus has been achieved with liquid CO2.
    Full-text · Article · Jun 2010 · Journal of Supercritical Fluids The