Performance Evaluation of the Solo-T and the Combat Application Tourniquet in a Perfused Cadaver Model.

PURPOSE: We evaluated a 10.2-cm-wide, minimally elastic, adhesive wrap-based tourniquet (Solo-T or ST) alongside a 3.8-cm-wide windlass-based tourniquet (Combat Application Tourniquet Generation 7, or CAT) to determine if the tension wrap-tightened ST could deliver hemorrhage control equivalent to the windlass-tightened CAT. METHODS: A cadaver model was used to simulate lower-thigh femoral arterial hemorrhage at "normal" (146 ± 5mmHg) and "elevated" (471 ± 3mmHg) perfusion pressures (mean ± standard error). Three study participants used the ST and CAT to control hemorrhage during 48 timed trials. Arterial occlusion was established by Doppler ultrasound and tourniquet performance was quantified by under-tourniquet pressure cuffs. RESULTS: Participants achieved 100% (24/24) occlusion success rates and reported similar ease of use for both tourniquets. Occlusion and application times (mean ± standard error) were similar (p > .05) for the ST and CAT under "normal" (occlusion, ST: 25 ± 2 seconds, CAT: 22 ± 2 seconds; application, ST: 27 ± 2 seconds, CAT: 26 ± 2 seconds) and "elevated" (occlusion, ST: 24 ± 7 seconds, CAT: 24 ± 7 seconds; application, ST: 25 ± 7 seconds, CAT: 25 ± 7 seconds) perfusion alike. The ST mean completion pressures (mean ± standard error) were > 40% lower than the CAT under both "normal" perfusion (ST: 110 ± 20mmHg; CAT: 210 ± 30mmHg; p = 0.009) and "elevated" perfusion (ST: 190 ± 50mmHg; CAT: 340 ± 30mmHg; p = 0.03). CONCLUSION: The adhesive wrap-based ST tourniquet delivered equivalent hemorrhage control performance at significantly lower completion pressures than the CAT.

In vitro antimicrobial effects of chlorhexidine diacetate versus chlorhexidine free base dressings.

OBJECTIVE: The aim of this study was to investigate the in vitro antimicrobial performance of a chlorhexidine diacetate dressing and a chlorhexidine free base dressing to determine if the free base form of chlorhexidine has the potential to be an effective alternative to the chlorhexidine salts used in conventional, chlorhexidine-based antimicrobial dressings. METHOD: Dressing samples were inoculated with clinically relevant pathogenic microorganisms including Gram-positive and Gram-negative bacteria, yeasts and fungus, and subsequently evaluated for in vitro log10 reduction at 1-, 3-, and 7-day time points. Chlorhexidine mole content was also calculated as a function of dressing surface area for both sample types to allow for formulation-independent comparison between the dressings. RESULTS: The chlorhexidine free base dressing demonstrated >0.5 log10 superior mean antimicrobial efficacy at 67% of the experimental time points and equivalent mean antimicrobial efficacy (≤0.5 log10 different) at the remaining time points when compared with the chlorhexidine diacetate dressing. The chlorhexidine free base dressing was also found to contain 36% less chlorhexidine mole content than the chlorhexidine diacetate dressing. CONCLUSION: Our results suggest that a dressing formulated with chlorhexidine free base can deliver in vitro antimicrobial performance at both a magnitude and rate that meets or exceeds that of a chlorhexidine diacetate-based dressing, while also allowing for a reduction in total chlorhexidine content per dressing. These findings could be of particular interest to researchers developing new antimicrobial technologies as well as to infection preventionists when evaluating antimicrobial products for use on clinical patients at elevated risk of infection.

An SFG study of interfacial amino acids at the hydrophilic SiO2 and hydrophobic deuterated polystyrene surfaces.

Sum frequency generation (SFG) vibrational spectroscopy was employed to characterize the interfacial structure of eight individual amino acids--L-phenylalanine, L-leucine, glycine, L-lysine, L-arginine, L-cysteine, L-alanine, and L-proline--in aqueous solution adsorbed at model hydrophilic and hydrophobic surfaces. Specifically, SFG vibrational spectra were obtained for the amino acids at the solid-liquid interface between both hydrophobic d(8)-polystyrene (d(8)-PS) and SiO(2) model surfaces and phosphate buffered saline (PBS) at pH 7.4. At the hydrophobic d(8)-PS surface, seven of the amino acids solutions investigated showed clear and identifiable C-H vibrational modes, with the exception being l-alanine. In the SFG spectra obtained at the hydrophilic SiO(2) surface, no C-H vibrational modes were observed from any of the amino acids studied. However, it was confirmed by quartz crystal microbalance that amino acids do adsorb to the SiO(2) interface, and the amino acid solutions were found to have a detectable and widely varying influence on the magnitude of SFG signal from water at the SiO(2)/PBS interface. This study provides the first known SFG spectra of several individual amino acids in aqueous solution at the solid-liquid interface and under physiological conditions.

Curing induced structural reorganization and enhanced reactivity of amino-terminated organic thin films on solid substrates: observations of two types of chemically and structurally unique amino groups on the surface.

Infrared-visible sum frequency generation vibrational spectroscopy (SFG) was used to characterize the structure of 3-aminopropyltriethoxysilane (APTES) films deposited on solid substrates under controlled experimental conditions for the first time. Our SFG spectra in combination with complementary analytical data showed that APTES films undergo structural changes when cured at an elevated temperature. Before the films are cured, well-ordered hydrophobic ethoxy groups are dominantly present on the surface. A majority of hydrophilic surface amino groups are protonated, and they are either buried or randomly oriented at the interface. After the films are cured, chemically and structurally different neutral amino groups are detected on the surface. Unlike the protonated amino groups, a new class of neutral amino groups is ordered at the interface and shows enhanced reactivity.

An investigation of the influence of chain length on the interfacial ordering of L-lysine and L-proline and their homopeptides at hydrophobic and hydrophilic interfaces studied by sum frequency generation and quartz crystal microbalance.

Sum frequency generation vibrational spectroscopy (SFG) and quartz crystal microbalance with dissipation monitoring (QCM-D) are employed to study the interfacial structure and adsorbed amount of the amino acids L-lysine and L-proline and their corresponding homopeptides, poly-L-lysine and poly-L-proline, at two liquid-solid interfaces. SFG and QCM-D experiments of these molecules are carried out at the interface between phosphate buffered saline at pH 7.4 (PBS) and the hydrophobic deuterated polystyrene (d8-PS) surface as well as the interface between PBS and hydrophilic fused silica (SiO2). The SFG spectra of the amino acids studied here are qualitatively similar to their corresponding homopeptides; however, the SFG signal from amino acids at the solid/PBS interface is smaller in magnitude relative to their more massive homopeptides at the concentrations studied here. Substantial differences are observed in SFG spectra for each species between the hydrophobic d8-PS and the hydrophilic SiO2 liquid-solid interfaces, suggesting surface-dependent interfacial ordering of the biomolecules. Over the range of concentrations used in this study, QCM-D measurements also indicate that on both surfaces poly-L-lysine adsorbs to a greater extent than its constituent amino acid L-lysine. The opposite trend is demonstrated by poly-L-proline which sticks to both surfaces less extensively than its corresponding amino acid, L-proline. Lastly, we find that the adsorption of the molecules studied here can have a strong influence on interfacial water structure as detected in the SFG spectra.

Sum frequency generation vibrational spectra: the influence of experimental geometry for an absorptive medium or media.

The influence of experimental geometry on infrared total internal reflection surface sum frequency generation (SFG) vibrational spectra at the water/solid interface has been examined. A detailed analysis of the experimental geometry revealed that the enhancement of SFG signal for the "critical angle" can be much weaker than previously thought if the index of refraction of the transmitted or reflected medium is treated as a complex value (i.e., the imaginary part of the index of refraction is not zero and not neglected). The theoretical analysis outlined here agreed well with the experimental results of the SFG spectra of the silica/water interface in two different geometries. This paper deals with the SSP polarization combination.

A new optical parametric amplifier based on lithium thioindate used for sum frequency generation vibrational spectroscopic studies of the amide I mode of an interfacial model peptide.

We describe a new optical parametric amplifier (OPA) that employs lithium thioindate, LiInS2 (LIS), to create tunable infrared light between 1500 cm(-1) and 2000 cm(-1). The OPA based on LIS described within provides intense infrared light with a good beam profile relative to similar OPAs built on silver gallium sulfide, AgGaS2 (AGS), or silver gallium selenide, AgGaSe2 (AGSe). We have used the new LIS OPA to perform surface-specific sum frequency generation (SFG) vibrational spectroscopy of the amide I vibrational mode of a model peptide at the hydrophobic deuterated polystyrene (d8-PS)-phosphate buffered saline interface. This model polypeptide (which is known to be an alpha-helix in the bulk solution under the high ionic strength conditions employed here) contains hydrophobic leucyl (L) residues and hydrophilic lysyl (K) residues, with sequence Ac-LKKLLKLLKKLLKL-NH2. The amide I mode at the d8-PS-buffer interface was found to be centered around 1655 cm(-1). This can be interpreted as the peptide having maintained its alpha-helical structure when adsorbed on the hydrophobic surface, although other interpretations are discussed.