Biomedical subjects

Robert Pelton

Publications and source records attributed to Robert Pelton.

13 recordsLinked to original sources

PubMed2006

Photocatalytic paper from colloidal TiO(2)--fact or fantasy.

Photocatalytic paper encompasses a range of materials based on paper and nonwoven fabrics which performs a function based on the light-activated catalytic activity of colloidal TiO(2). The literature describing photocatalytic paper is surveyed, including mechanisms, applications, limitations and future opportunities. The technology is in its infancy with less than 10 patents and as many scientific publications appearing over the last decade. The main applications described are the destruction of organic molecules (mineralization) and photo-disinfection (sterilization). These disclosures build upon a much larger literature describing photochemical properties of TiO(2) both supported on non-cellulose substrates or simply as suspended particles in water or air. Current photocatalytic paper developments include methods to fix TiO(2) to cellulose substrates to minimize photochemical damage to the paper. Another theme is the use of multiple approaches, such as zeolites, for enhanced mineralization, and metals, such as silver and copper, for enhanced photocatalytic disinfection.

Catalysis↗

PubMed2006

Titrametric characterization of pH-induced phase transitions in functionalized microgels.

The chain and radial functional group distributions in carboxylic acid-functionalized poly(N-isopropylacrylamide)-based microgels have significant impacts on the types of swelling responses exhibited by the microgels upon the application of a temperature and/or pH stimulus. Potentiometric, conductometric, and calorimetric titration approaches are used in this work to characterize the chain distributions of -COOH groups in five microgels prepared using different -COOH-functionalized monomers. A direct correlation is observed between the kinetically predicted formation of functional monomer blocks within the microgel, the excess Gibbs free energy of ionization, and the apparent pK(a) versus degree of ionization profiles generated from potentiometric titration. Isothermal titration calorimetry (ITC) can be used to quantify the relative number of functional groups present in microgels prepared with the same functional monomer and/or identify differences between microgels with the same bulk -COOH content but different chain distributions. In particular, microgels prepared with diacid-functionalized monomers exhibit a characteristic two-step ITC profile. For microgels with the same bulk -COOH content, the heat of ionization measured via ITC increases systematically with the overall change in both the pK(a) and the excess Gibbs free energy for microgels prepared with monoacid-functionalized monomers. Diacid monomer-functionalized microgels have lower ionization enthalpies attributable to the break-up of hydrogen-bonded intramolecular ring complexes upon carboxylic acid ionization. The inferred chain functional group distributions can be used to understand differences in microgel swelling across the pH-induced phase transition.

Acrylamides↗

PubMed2006

Dimensionless plot analysis: a new way to analyze functionalized microgels.

A novel dimensionless plot strategy is developed in which multiple, independently measured macroscopic variables characterizing the same microgel phase transition are reduced onto a zero-to-one scale and simultaneously plotted. This strategy allows for direct comparisons to be made between changes in these variables over the phase transition, generating graphical "fingerprints" characteristic of specific radial and chain functional group distributions. This method is applied to study the swollen state properties of pH-induced phase transitions in five poly(N-isopropylacrylamide)-based microgels with significantly different but well-understood COOH functional group distributions. Radial functional group distributions identified based on this method match the distributions observed via electron microscopy, while the impact of functional group clustering on the ionization-driven swelling response can be directly identified. Change ratio plots in which the percentage changes of two different variables are plotted as mutual functions are also applied to generate semi-quantitative diagnostic parameters for probing radial functional group distributions and gaining insights into the mechanisms of gel phase transitions.

Journal Article↗

PubMed2006

Interactions of hydrophobically modified polyvinylamine with pluronic triblock copolymer micelles.

The heats associated with the addition of triblock copolymers of ethylene oxide and propylene oxide (PEO-PPO-PEO pluronics) to solutions of linear polyvinylamine, with N-substituted pendant octyl groups (HMPVAm), were measured as functions of pH and pluronic structure. The interactions were exothermic with the overall enthalpy decreasing with increasing pH from 5 to 10. Surprisingly, the heat effect increased with increasing pluronic hydrophilicity; however, no enthalpy change was observed in the absence of micelles. The results were quantitatively modeled by assuming two competing processes-micellar dissolution and HMPVAm coating of micelles, preventing dissolution.

Journal Article↗

PubMed2006

Polyvinylamine boronate adhesion to cellulose hydrogel.

The adhesion of polyvinylamine to wet cellulose was significantly enhanced by the presence of pendant phenylboronic acid groups. It is proposed that adhesion results from boronate ester formation with cellulose at pH > 8. Experiments with phenol derivatized polyvinylamine gave low adhesion supporting the fact that the boronate moiety was responsible for strong adhesion to never-dried cellulose surfaces.

Biocompatible Materials↗

PubMed2005

pH-dependence of the properties of hydrophobically modified polyvinylamine.

A series of N-alkyl or N-benzyl substituted polyvinylamines (PVAm) were prepared and the properties of aqueous solutions were measured as functions of pH. The polymer solutions showed almost no surface activity under acidic conditions whereas surface tension was reduced to 40-50 mN/m around pH 9. Increasing either the degree of hydrophobic substitution or the hydrophobic chain length lowered the pH at which surface tension lowering was observed. Hydrophobic substitution also shifted plots of the degree of ionization versus pH toward lower pH which means lower pH values were required to achieve a given value of polymer charging. The hydrophobically modified PVAm associated in water giving species whose apparent diameter measured by dynamic light scattering decreased with increasing pH, whereas the electrophoretic mobilities of the associated species increased with decreasing pH. Although many hydrophobically modified and pH sensitive polymers have been described in the literature for applications in biomaterials, drug release and as pH sensitive surfactants, the hydrophobically modified PVAms are particularly attractive because they are easily prepared from commercially available polyvinylamines.

Journal Article↗

PubMed2005

Hydroxypropyl guar-borate interactions with tear film mucin and lysozyme.

The interactions of hydroxypropyl guar (HPG) with boric acid, lysozyme, and mucin were characterized by rheology, light scattering, electrophoresis, and isothermal titration calorimetry to help understand how HPG interacts with tear film components. Borate binds to guar under pH, temperature, and ionic strength conditions representative of those found in the eye. The HPG-borate complexes behave as anionic polyelectrolytes and thus interact with cationic lysozyme, a major tear film protein, whereas HPG-borate does not appear to bind to mucin, an anionic glycoprotein. The interactions of HPG, borate, lysozyme, and mucin can be explained by two physical interactions: (1) pH-dependent binding of borate to carbohydrates and (2) the electrostatic attraction of oppositely charged macromolecules.

Animals↗

PubMed2005

Flocculation with poly(ethylene oxide)/tyrosine-rich polypeptide complexes.

New insights into the mechanism for the flocculation of aqueous colloids by the sequential addition of a water-borne phenolic polymer, called cofactor, followed by very high molecular poly(ethylene oxide) (PEO) are presented. It is proposed that PEO/cofactor complexes form in the aqueous phase and adsorb onto the surfaces of the target colloidal particles. Flocculation will occur if PEO/cofactor complex on one particle will bind to adsorbed complex on a second particle; i.e., if the complexes are sticky. The proposed mechanism was illustrated by flocculation experiments with precipitated calcium carbonate, very high molecular weight PEO, and a polypeptide cofactor called PEY1 which was a 1:1 random copolymer of l-glycine and l-tyrosine. Independent measurements of the PEO/PEY1 complex properties, in the absence of calcium carbonate, were used to support the mechanism. In order for PEO/PEY1 complexes to be sticky, they must simultaneously have unbound PEY1 and polymer segments. With time the complexes deactivate (i.e., lose their stickiness) by a reconfiguration process which results in elimination of either unbound PEY1 or PEO segments.

Adsorption↗

PubMed2004

A new route to poly(N-isopropylacrylamide) microgels supporting a polyvinylamine corona.

Poly(N-isopropylacrylamide) thermoresponsive microgel particles with an amine-rich corona were prepared by the copolymerization of N-isopropylacrylamide with N-vinylformamide, NVF. Hydrolysis above the volume phase transition temperature converted the surface formamide moieties to the corresponding amine. The surface amine concentration was enriched by coupling iodine-terminated polyNVF oligomers (DP=7) to the microgel amines, followed by a second hydrolysis to give the corresponding polyvinylamine. Microgel swelling and electrophoretic mobility values as functions of pH and temperature were consistent with published results for amine-containing microgels.

Journal Article↗

PubMed2004

Factors influencing the size of PEO complexes with a tyrosine-rich polypeptide.

Aqueous complexes of PEY1, a 36 100 Da random synthetic peptide of tyrosine (50 mol %) and glutamic acid (50 mol %), with poly(ethylene oxide) (PEO) were studied as functions of PEO molecular weight, mixing ratio of PEO and PEY1, and the presence of calcium ions. Without calcium ions, the complexes were water soluble, with each complex consisting of a single PEO chain with many bound PEY1 chains. In the presence of 1 mM calcium ions, PEY1 formed colloidal aggregates with intermediate molecular weight PEO (10(5) to 10(6) Da). By contrast, very high molecular weight PEO (8 x 10(6) Da) with calcium ions formed large hydrogels when mixed with PEY1. It is proposed that PEY1 molecules completely bind to low molecular PEO and thus are deactivated from causing the coupling of multiple PEO chains, whereas deactivation of PEY1 on very high molecular weight PEO clusters is a slower process, giving an opportunity for cluster-cluster aggregation.

Calcium↗

PubMed2004

Functional group distributions in carboxylic acid containing poly(N-isopropylacrylamide) microgels.

Control of the functional group distribution is of fundamental importance in the design of functional polymer particles, particularly in biological applications. Surface-functionalized particles are useful for bioconjugation and medical diagnostics, while internally functionalized particles may have applications in drug delivery. We have prepared a series oftemperature-sensitive poly(N-isopropylacrylamide) (PNIPAM)-based microgels containing carboxylic acid functional groups via copolymerization with methacrylic acid and acrylamide, which was selectively hydrolyzed under optimized conditions to generate the carboxylic acid functionality. The resulting microgels were analyzed using conductometric and potentiometric titration, dynamic light scattering, and electrophoresis. Acrylamide-containing microgels hydrolyzed below the volume phase transition temperature (VPTT) show broad particle size versus temperature profiles, relatively low electrophoretic mobilities at basic pH, and time-dependent base titration profiles, suggesting the presence of internal functional groups whose titration is diffusion-controlled. Methacrylic acid containing microgels show sharper particle size versus temperature profiles, higher electrophoretic mobilities at basic pH, and time-independent base titration profiles, suggesting the presence of a "core-shell" structure with primarily surface functionalization. Similar results were obtained when acrylamide-containing microgels were hydrolyzed at temperatures above the VPTT. Thus, through selection of comonomer and hydrolysis conditions, we have developed strategies to control and characterize the number and distribution ofcarboxylic acid functional groups in PNIPAM-based microgels.

Journal Article↗

PubMed2003

The influence of PEO/poly(vinyl phenol-co-styrene sulfonate) aqueous complex structure on flocculation.

Colloidal suspensions were flocculated with complexes formed from high molecular weight polyethylene oxide (PEO) and a cofactor. Poly(vinyl phenol-co-potassium styrene sulfate) (PKS) or poly(styrene-co-styrene sulfonate) (PS-co-SSS) copolymers were used as the cofactors for this work. The larger the PEO/cofactor complex species, the better the initial flocculation. Factors such as increasing temperature or ionic strength that gave smaller complexes also gave poorer flocculation. Cofactor performance was sensitive to the balance of hydrophobic phenolic groups and hydrophilic styrene sulfonates. If there are too few phenolic groups, the PEO/PSK complexes are large but are too weak to give shear-resistant flocs, whereas complexes formed with high phenolic content PSK are relatively small, giving poorer flocculation but more shear-resistant flocs. Both phenyl and phenol groups are effective as the hydrophobic component in the cofactor. The hydrogen-bonding potential of phenolic cofactors does not seem to offer much advantage relative to phenyl groups. A crucial step in the flocculation is the adsorption of PEO/cofactor complex onto the target colloids. Thus, flocculation is sensitive to the target colloid surface chemistry. Positively charged precipitated calcium carbonate and surfactant-free polystyrene latex are particularly easy to flocculate because adsorption is driven by electrostatic and hydrophobic interactions, respectively. By contrast, the latex coated with hydrophilic poly(N-isopropylacrylamide) (PNIPAM) does not flocculate because the PEO/cofactor complex does not bind to PNIPAM. Finally, the flocculation of highly negatively charged, dextran sulfate coated calcium carbonate seems to be stimulated by the presence of soluble calcium ions that make the complex less soluble and more likely to adsorb.

Journal Article↗

PubMed2002

PEO flocculation with phenolic microparticles.

Polystyrene latex and precipitated calcium carbonate (PCC) with and without dextran sulfate pretreatment were flocculated by the consecutive addition of high-molecular-weight poly(ethylene oxide) and a novel composite latex microparticle consisting of a polystyrene core and a poly(p-vinylphenol) shell. Good flocculation of polystyrene latex and PCC was obtained, whereas the PCC coated with dextran sulfate was not flocculated. The interaction of the composite microparticle with the target colloids was governed by electrostatic forces, whereas hydrogen bonding and hydrophobic interactions drove the PEO adsorption onto the composite particles.

Journal Article↗