Stuart L. Cooper

Interactions between dendrimer biocides and bacterial membranes

Dendrimer biocides have been shown to be more potent than their small molecule counterparts. In this study, several techniques were utilized to investigate the interactions between quaternary ammonium functionalized poly(propylene imine) dendrimers and bacterial membranes. Both Gram-positive and Gram-negative bacteria were tested. The techniques employed include UV-Vis spectroscopy, differential scanning calorimetry, and bioluminescence. When treated with dendrimer biocides, release of 260nm adsorbing materials from Escherichia coli strains quickly increased and reached a plateau afterwards, while release of 260 nm absorbing materials from Staphylococcus aureus increased monotonically with the concentration due to the difference in cell structures. The different release behavior also correlates with the antimicrobial properties against these two types of bacteria. Bioluminescence experiments using bacteria containing stress-responsive bioluminescent reporter gene fusions provided information suggesting that damage to the cell membranes is the primary mechanism of the antimicrobial action for dendrimer biocides. High concentrations of calcium ions can limit the efficacy of the dendrimer biocides, although the tested concentration range is much higher than most practical applications. Differential scanning calorimetry studies showed at high concentrations that dendrimer biocides formed precipitates with phospholipid vesicles, suggesting a strong interaction with this model of bacterial membrane. These results provide insight about the antibacterial action of dendrimer biocides and establish the basis for their mode of action.

Biomaterials, interfacial phenomena and applications

New updated! The latest book from a very famous author finally comes out. Book of biomaterials interfacial phenomena and applications, as an amazing reference becomes what you need to get. Whats for is this book? Are you still thinking for what the book is? Well, this is what you probably will get. You should have made proper choices for your better life. Book, as a source that may involve the facts, opinion, literature, religion, and many others are the great friends to join with.

Effect of segment size and polydispersity on the properties of polyurethane block polymers

Abstract The dynamic-mechanical and thermal scanning behaviour of a series of specially synthesized linear segmented polyurethanes is presented. These materials possess a well defined segment molecular weight and molecular weight distribution and no possibility of intermolecular hydrogen bonding. The dynamic-mechanical transitions observed are assigned to specific molecular motions and the effect of segment size and molecular weight distribution is described. The results are explained in terms of hard segment domain perfection. Differential scanning calorimetry (d.s.c.) curves of annealed samples indicate that domain morphology may be affected by thermal treatment. A comparison of dynamic mechanical and d.s.c. results to hydrogen-bonded polyurethanes is made.

Protein adsorption on polymeric biomaterials I. Adsorption isotherms

Abstract the equilibrium adsorption of seven purified human proteins to four different biomaterials was studied at different protein concentraitons under in vitro conditions. The proteins studied were albumin, transferrin, three monoclonal antibodies of different net charge, fibrinogen, and α2-macroglobulin. The biomaterials used in the adsorption studies included a polyether urethane urea, polyethylene, silicone rubber, and plasticized polyvinyl chloride. The equilibrium adsorption data for these protein-biomaterial combinations could be fit by a protein adsorption model assuming two or more adsorbed protein layers. The monolayer concentrations of adsorbed protein agreed closely with the theoretical monolayer concentrations based on the macromolecular dimensions of the proteins. Protein binding constants decreased for protein layers further away from the surface, and, for the series of biomaterials, protein binding constants decreased with decreasing biomaterial surface-water free energy. From these studies, it is apparent that the magnitude of the binding forces at the liquid-polymer interface is a function of both the biomaterial composition and the individual protein.

Block Polymers and Related Heterophase Elastomers

Abstract Recently, there has been considerable interest in heterophase polymer systems which possess enhanced physical properties in the elastomeric state. These systems, with their improved properties, greatly expand the list of available engineering materials and the possibility of designing a material to perform in a given situation. It is the intention of this article to review a significant portion of the literature pertinent to the physical properties and structure of a specific heterophase system: block polymers. In this undertaking we shall first consider work dealing with the morphology of the two-phase block polymer systems and the variety of techniques used to elucidate this structure. Then the mechanical and viscoelastic properties will be examined in terms of the structural changes which occur as a result of changes in chemical composition, physical modification, and deformation history. A review of this type is important at this time to collate and summarize the large volume of literature av...

Infrared thermal analysis of polyurethane block polymers

Abstract Infrared (IR) thermal analysis was used to study the extent, distribution, and the thermal behavior of hydorgen bonding in MDI-based segmented polyurethane elastomers. Two series of polyurethane elastomers were studied; one was based on a polytetrahydrofuran soft segment (ET series), while the second was based on a poly(tetramethylene adipate) soft segment (ES series). The hard segment in these materials was formed form p, p′-diphenylmethane diisocyanate (MDI) extended with butanediol. Bonded and free NH and C=O infrared absorbances were resolved as a function of temperature using a nonlinear least squares analysis for the fitting of Gaussian curve shapes. Results of this analysis revealed that at room temperature, about 80% of the NH groups in the ET and ES polyurethanes formed hydrogen bonds. In the ET polyurethanes, about 65% of the urethane carbonyls were hydrogen-bonded at room temperature. The extent of interurethane hydrogen bonding was found to be higher in the materials having better pha...

Annealing-induced morphological changes in segmented elastomers

Abstract Thermal analysis has been used to study annealing-induced ordering in segmented elastomers. Twelve segmented elastomers were studied each having approximately 50% by wt hard segment content. Seven general classes of materials were examined including polyether and polyester polyurethanes, polyether polyurethane-urea, and polyether-polyester. Materials were slow cooled (−10°C min−1) from the melt to an annealing temperature (−10°, 20°, 60°, 90° or 120°C) where they were annealed (16, 12, 8, 6 or 4 days, respectively). Annealing was followed by slow cooling (−10°C min−1) to −120°C after which a d.s.c. experiment was run. In general, annealing resulted in an endothermic peak at a temperature 20°–50°C above that of the temperature of annealing. This phenomenon was observed in both semicrystalline and amorphous materials. The closer the annealing endotherm was to a crystalline endotherm without exceeding it in temperature, the larger its size. Annealing endotherms resulted from hard or soft segment ordering. Only one annealing endotherm was observed for a given annealing history, even though in some materials hard and soft segments could exhibit annealing-induced morphological changes. Hard segment homopolymers were studied yielding results similar to the block polymers containing shorter sequences of the same material. This suggests that annealing-induced ordering is an intradomain phenomenon not associated with the interphase between domains, or necessarily dependent on the chain architecture of segmented elastomers.

Endothelial cell adhesion on polyurethanes containing covalently attached RGD-peptides

Peptides based on cell-adhesive regions of fibronectin, Arg-Gly-Asp-Ser (RGDS), and vitronectin, Arg-Gly-Asp-Val (RGDV), were covalently bound to a polyurethane backbone via amide bonds. Nuclear magnetic resonance (NMR) and Fourier-transform infrared (FTIR) spectroscopies were used to monitor the reactions. The amount of grafted peptide was determined by amino acid analysis. X-ray photoelectron spectroscopy (XPS) suggested the presence of the grafted peptide at the polymer-air interface in vacuo. Dynamic contact angle analysis showed that, in water, the peptide-grafted polyurethane surfaces were more polar than the underivatized polyurethane indicating enrichment of peptide groups at the surface. The attachment and spreading of human umbilical vein endothelial cells (HUVECs) on the underivatized and peptide-grafted polyurethanes was investigated. The GRGDSY- and GRGDVY-grafted substrates supported cell adhesion and spreading even without serum in the culture medium. The GRGDVY-grafted substrate supported a larger number of adherent cells and a higher extent of cell spreading than the GRGDSY-grafted substrate. These RGD-containing peptide-grafted polyurethane copolymers may be useful in providing an easily prepared cell-adhesive substrate for various biomaterial applications.

Surface properties and blood compatibility of polyurethaneureas.

A series of polyurethaneureas of varying soft segment type and hard/soft segment ratio were synthesized, and their bulk and surface properties evaluated. A canine ex vivo arteriovenous series shunt was used to monitor initial thrombus deposition. Significant levels of surface hard segment components are apparent in these materials. Polymers with poly(tetramethylene oxide) and poly(propylene oxide) soft segments showed blood compatibility variations with changes in hard/soft segment ratios: the more well-phase-separated materials showing lower platelet and fibrinogen deposition levels. Those trends apparent in polymers synthesized with poly(dimethylsiloxane) or poly(ethylene oxide) soft segments, but poly(dimethylsiloxane)-based materials showed higher levels of thrombus deposition than the poly(ethylene oxide)-based polymers.

Sequential protein adsorption and thrombus deposition on polymeric biomaterials

A canine ex vivo arteriovenous shunt model was employed to investigate the effect of preadsorbed blood plasma proteins upon platelet deposition. Albumin and fibrinogen were singly, sequentially, or competitively adsorbed on polyvinyl chloride (PVC), polyethylene (PE), and crosslinked silicone rubber (SR) tubing. Results indicate that platelet deposition and thrombus formation are strongly influenced by the sequence of protein adsorption. The platelet response appears to be determined by the first protein which is preadsorbed to the surface. This response does not appear to correlate well with the total amount of preadsorbed albumin or fibrinogen. To clarify how the sequence of protein adsorption affected the blood response, the sequential adsorption phenomenon was studied using 125I-labeled proteins, Fourier transform infrared spectroscopy, and immunogold particle labeling techniques. It was observed that in the sequential adsorption of albumin followed by fibrinogen, there is a linear correlation between the surface concentrations of fibrinogen and albumin on PVC. On PE and SR, a linear correlation between the fibrinogen and albumin concentrations exists only below a monolayer coverage of albumin. On SR, the initial fibrinogen adsorption rate correlates linearly with the submonolayer concentration of adsorbed albumin. When fibrinogen adsorption is followed by albumin adsorption, no linear correlations in protein adsorption are observed.