Effects of yarn size and blood drop size on wicking and bloodstains in textiles.

Bloodstain pattern analysis (BPA) for stains found on non-porous surfaces has matured into a powerful forensic science tool based on fluid mechanics principles. The same cannot be said when bloodstains are found on porous substrates, such as textiles. This is partially due to the complex nature of textiles with tens of thousands of different materials in addition to unknown wear characteristics. In this study, three single jersey knit fabrics were manufactured from 100% cotton ring-spun yarns of linear densities of 12, 20, and 30 Ne (492, 295, and 197 dtex, respectively) and nearly identical twist multipliers. Single drops of porcine blood of 2, 10, 30, and 60 µL were allowed to fall 1 cm (to eliminate the impact of blood velocity) onto each fabric to understand the effects of yarn size on wicking and bloodstains. The size of the stain was then measured and compared for different fabrics and blood drop sizes. Wicking of blood into the fabric was fastest for the largest yarn fabrics, but more extensive wicking occurred on finer yarn fabrics resulting in much larger stains. All stains were highly altered due to wicking of blood. The findings from this paper might help the forensic scientists in understanding wicking in textiles and comparing stains on different textiles to gain a better understanding of bloodstains on textiles.

Fundamental study of porcine drip bloodstains on fabrics: Blood droplet impact and wicking dynamics.

The underlying physics in bloodstain formation on fabrics is not well understood, despite its importance in bloodstain pattern analysis (BPA). This paper presents a fundamental study of the formation of drip bloodstains on fabrics, by focusing on blood droplet impact and wicking dynamics. The bloodstains were created on plain woven fabric by the perpendicular impact of a single blood drop with seven different impact velocities. The whole droplet impact and wicking processes were captured by multiple cameras. Fabric properties were characterized in detail at different levels. The bloodstain formation process was classified into distinct stages, including the inertial impact, initial absorption, first wicking and second wicking stages. The subsequent wicking process greatly alters the impact-induced bloodstains, in terms of bloodstain area. The dimensionless impact-induced stain factor (ßi,e) is strongly dependent on the impact velocity while the final stain factor (ßf,e) after the second wicking stage is not. The contribution of the subsequent wicking in altering the stain factor (or stain area) is quantified and found to decrease with increasing impact velocity. The blood wicking dynamics on the fabric in the majority of the first wicking stage can be well described by a simple scaling: [Formula: see text] , where ti marks the end of the inertial impact stage. The wicking coefficient C, which represents the influence of droplet impact on the subsequent droplet wicking, is found to scale as C∼We-0.34. In the end, brief comments are provided regarding (1) the influence of the evaporation on the blood drop post-impact wicking dynamics and (2) the shape of bloodstains formed on fabrics, with a few suggested research directions for future work.

Impact Spatter Bloodstain Patterns on Textiles.

There are few reports of studies of impact spatter on textiles even though bloodstained textiles are found at many violent scenes. Impact spatter was deposited at 90° impact angle onto three knit fabrics of different yarn sizes and on paper. The resulting stain areas and number of stains were measured using ImageJ and compared with stains on paper using one-factor ANOVA. The number of stains observed and their areas on the knit fabrics decreased as the yarn size increased. It was also found that blood that deposited on the fabric wicked only in the direction of the fibers at that location within the fabric which led to distorted stain shapes. Fewer observed impact spatter stains were found on cotton jersey knits for fabrics made with larger yarns than on paper. As the yarn size became smaller, the number of stains became the same as on paper.

Impact of carpet construction on fluid penetration: The case of blood.

Bloodstains and bloodstain patterns are often observed at crime scenes and their analysis through bloodstain pattern analysis (BPA) can assist in reconstructing crime scenes. However, most published work related to BPA only deals with hard, non-porous surfaces and none of the studies have carefully characterized carpets. Soft and porous carpets are often encountered at crime scenes since they are common in American homes accounting for 51% of total U.S. flooring market; this has motivated the research described herein. To assess fluid penetration into tufted carpers, a new method for determining porosity and pore size distribution in tufted carpets has been developed for bloodstains on carpet. In this study, three kinds of nylon carpet were used: a low, a medium and a high face-weight carpet. Each carpet had an antistain treatment, which was removed from half of each carpet by steam-cleaning with a pH 12 NaOH solution. This resulted in six carpet samples. Yarn twist, carpet weight, pile height, water contact angles on carpets, water contact angles on individual fibers, and fiber cross-sectional shapes were characterized. Porosity and pore size distribution were analyzed using confocal laser scanning microscopy (CLSM). Porcine blood was used as a human blood substitute at three liquid volumes (30µL, 10µL, and 2µL). Analysis showed that porous carpet construction and antistain finishing both affected penetration. The depth of blood penetration decreased with the increase of carpet face-weight but increased with increased drop height. The removal of antistain treatment increased blood penetration into the carpets and changed the pore size distribution. Effects of antistain treatment, porosity and pore size distribution of tufted carpet, and blood wicking behaviors on carpets were found to strongly affect blood penetration into the carpets.

Effect of yarn structure on wicking and its impact on bloodstain pattern analysis (BPA) on woven cotton fabrics.

Bloodstain pattern analysis (BPA) of bloodstains on hard, non-porous surfaces has found widespread use in crime scene analysis and reconstruction for violent crimes in which bloodshed occurs. At many violent crime scenes, bloody clothing is also found and may be analyzed. However, to date, there are no definitive methods for analyzing bloodstains on textiles, even for simple drip stains. There are two major classes of textiles used for apparel and household textiles, weaves and knits. In this article, drip stains on two 100% cotton plain weave fabrics representative of bed sheets are analyzed. Since it is common practice in the manufacture of bed sheeting to use different types of yarn in the warp and weft direction to reduce cost, custom weaves were made from yarns produced by each of the three most common staple yarn production techniques to control this variable. It was found that porcine blood wicked into the fabrics made with ring spun yarn, but not into those made with open end or vortex spun yarns. The uneven wicking of blood into the different yarns resulted in elliptical-shaped stains on commercial bed sheeting that can be misleading when performing bloodstain pattern interpretation based on the stain morphology. This surprising result demonstrates that it is not sufficient to analyze the structure of the fabric, but one must also characterize the yarns from which the fabric is made. This study highlights the importance of a deeper characterization of the textile structure, even down to the yarn level, for BPA on textiles.

Alternative method for determining the original drop volume of bloodstains on knit fabrics.

Bloodstains are often observed at violent crime scenes and on the skin and clothing of persons involved. The diameters of the blood drops that created these stains are related to the force or energy that caused these drops to become airborne. This has resulted in several attempts to determine the diameter of the original drops, beginning with the methods reported in the pioneering work of Henry Lee [6]. However, his methods destroyed the bloodstain during the measurement. Other methods described in the literature cannot be applied to bloodstains on textiles. A new, rapid, reliable, non-destructive method for determining the diameter of the original drop of blood that results in a stain has been developed for bloodstains on cotton single jersey knit (tee-shirt) fabrics, which is one of the most common fabrics analyzed for BPA both at crime scenes and in forensic laboratories. In this method, a drop of known volume of an appropriate artificial blood substitute is applied to a region similar to the stained region but in an area away from any stains/areas of interest. The areas of the original stain and the artificial blood substitute stain are determined, from which the original drop diameter can be calculated. Errors in the drop diameters, the Reynolds numbers and the Weber numbers resulting from this procedure are less than approximately 6%. This procedure has only been verified on cotton single jersey knit fabrics with 30µL≤drop volume≤80µL. It should not be applied to other materials.

Impact dynamics of porcine drip bloodstains on fabrics.

As a passive blood drop impacts a hard surface, it is observed to collapse and spread laterally, then retract and settle. During the spreading phase, the edge of the drop may rise forming a crown extending into spines and breaking up into secondary drops. When a similar drop falls onto a textile surface these same processes may occur, but the process of blood wicking into the fabric complicates stain formation. These processes are described within for passive drip stains collected under controlled conditions using anticoagulated porcine blood. Three stages of this impact process were identified and could be separated into distinct time zones: (1) spreading (time t≤2.5ms) and (2) retraction (2.5≤t≤12ms) on the surface with potential splashing at the periphery, and (3) wicking (30ms ≤t≤30min) of the blood into the fabric. Although wetting and wicking may also occur for t<30ms, the vast majority of wetting and wicking occur after this time and thus the short-time wicking can be ignored. In addition, the number of satellite stains correlates with the surface roughness with the number of satellites for jersey knit>plain-woven>cardboard. Conversely, the size of the satellite stains correlates with the amount of wicking in the fabric with the satellite stain size for plain-woven>jersey knit>cardboard.

Synthesis of Antifungal Agents from Xanthene and Thiazine Dyes and Analysis of Their Effects.

Indoor fungi growth is an increasing home health problem as our homes are more tightly sealed. One thing that limits durability of the antifungal agents is the scarcity of reactive sites on many surfaces to attach these agents. In order to increase graft yield of photosensitizers to the fabrics, poly(acrylic acid-co-styrene sulfonic acid-co-vinyl benzyl rose bengal or phloxine B) were polymerized and then grafted to electrospun fabrics. In an alternative process, azure A or toluidine blue O were grafted to poly(acrylic acid), which was subsequently grafted to nanofiber-based and microfiber-based fabrics. The fabrics grafted with photosensitizers induced antifungal effects on all seven types of fungi in the order of rose bengal > phloxine B > toluidine blue O > azure A, which follows the quantum yield production of singlet oxygen for these photoactive dyes. Their inhibition rates for inactivating fungal spores decreased in the order of P. cinnamomi, T. viride, A. niger, A. fumigatus, C. globosum, P. funiculosum, and M. grisea, which is associated with lipid composition in membrane and the morphology of fungal spores. The antifungal activity was also correlated with the surface area of fabric types which grafted the photosensitizer covalently on the surface as determined by the bound color strength.

Photodynamic activity of nanostructured fabrics grafted with xanthene and thiazine dyes against opportunistic fungi.

Fungi are an important class of human pathogens for which considerable research has gone into defeating them. The photodynamic effects of rose bengal (RB), phloxine B (PB), azure A (AA), and toluidine blue O (TBO) dyes to inhibit Aspergillus fumigatus, Aspergillus niger, Trichoderma viride, Penicillium funiculosum, and Chaetomium globosum were investigated grafted to nano- and micro-structured fabrics. Three antifungal tests conducted: broth microdilution test of free dyes, zone of inhibition and quantitative antifungal assays on fabrics grafted with dyes. In the broth microdilution test, free RB displayed the lowest MIC at 32 µM to inhibit visible hyphal growth and germination but the antifungal ability of MIC for other photosensitizers below 63 µM was insignificant. RB and PB showed lower MIC than AA and TBO. In the inhibition zone tests, nanostructured fabrics grafted with RB and PB did not display fungal growth on the surface. Most microstructured fabrics grafted with AA and TBO showed little inhibition. In quantitative antifungal assay, nanostructured fabrics grafted with RB has the largest inhibition rate on T. viride and the lowest inhibition rate on P. funiculosum and the results showed the increasing inhibition rate in the order of AA < TBO < PB < RB.

Symmetric and asymmetric capillary bridges between a rough surface and a parallel surface.

Although the formation of a capillary bridge between two parallel surfaces has been extensively studied, the majority of research has described only symmetric capillary bridges between two smooth surfaces. In this work, an instrument was built to form a capillary bridge by squeezing a liquid drop on one surface with another surface. An analytical solution that describes the shape of symmetric capillary bridges joining two smooth surfaces has been extended to bridges that are asymmetric about the midplane and to rough surfaces. The solution, given by elliptical integrals of the first and second kind, is consistent with a constant Laplace pressure over the entire surface and has been verified for water, Kaydol, and dodecane drops forming symmetric and asymmetric bridges between parallel smooth surfaces. This solution has been applied to asymmetric capillary bridges between a smooth surface and a rough fabric surface as well as symmetric bridges between two rough surfaces. These solutions have been experimentally verified, and good agreement has been found between predicted and experimental profiles for small drops where the effect of gravity is negligible. Finally, a protocol for determining the profile from the volume and height of the capillary bridge has been developed and experimentally verified.

Profiles of liquid drops at the bottom of cylindrical fibers standing on flat substrates.

Based on Carroll's derivation that describes a symmetric liquid drop sitting on an infinite cylindrical fiber and the shape of the drop, we have extended the derivation to describe a drop located at the bottom of cylindrical fibers standing on flat substrates. According to our derivation, the shape of the drop forms a bell as predicted by Carroll but is cut off by the flat substrate. This theoretical prediction was verified experimentally using water, ethylene glycol, and Kaydol drops on glass, nylon and polypropylene cylindrical fibers, and on polytetrafluoroethylene (PTFE) and polyester (PET) flat substrates. We found that only four parameters are required to obtain agreement between the theoretical shape and the observed shape: the drop volume, the fiber radius, the liquid-fiber contact angle, and liquid-flat substrate contact angle.

Gibbs free energy of liquid drops on conical fibers.

Small drops can move spontaneously on conical fibers. As a drop moves along the cone, it must change shape to maintain a constant volume, and thus, it must change its surface energy. Simultaneously, the exposed surface area of the underlying cone must also change. The associated surface energies should balance each other, and the drop should stop moving when it reaches a location where the free energy is a minimum. In this paper, a minimum Gibbs free energy analysis has been performed to predict where a drop will stop on a conical fiber. To obtain the Gibbs free energies of a drop at different locations of a conical fiber, the theoretical expressions for the shape of a droplet on a conical fiber are derived by extending Carroll's equations for a drop on a cylindrical fiber. The predicted Gibbs free energy exhibits a minimum along the length of the cone. For a constant cone angle, as the contact angle between the liquid and the cone increases, the drop will move toward the apex of the cone. Likewise, for a constant contact angle, as the cone angle increases, the drop moves toward the apex. Experiments in which water and dodecane were placed on glass cones verify these dependencies. Thus, the final location of a drop on a conical fiber can be predicted on the basis of the geometry and surface energy of the cone, the surface tension and volume of the liquid, and the original location where the drop was deposited.

Profiles of liquid drops at the tips of cylindrical fibers.

In 1976, B. J. Carroll derived the equation to show that a symmetric liquid droplet sitting on a thin cylindrical fiber would acquire a bell shape at equilibrium. We have extended his derivation to describe a drop located at the top end of a vertical, cylindrical fiber. By minimizing the Gibbs free energy of the drop at the fiber tip, it was found that the drop consists of two portions, a spherical cap on the fiber tip and a full, symmetrical bell located on the fiber body adjacent to the fiber tip. The experimental verification of the predicted shapes was performed using water, ethylene glycol, and Kaydol drops on nylon cylindrical fibers. Only four parameters are required to obtain agreement between the theoretical shape and the observed shape: the drop volume, the fiber radius, the surface tension of the liquid, and the Young contact angle of the liquid on a flat surface of the same composition as the fiber.

Influence of surface modification on the adhesion between Nitinol wire and fluoropolymer films.

PURPOSE: One of the current challenges for the medical device industry is how to manufacture and assemble biomedical implants consisting of a metallic wire component and a fluorocarbon film without the use of an adhesive. In an attempt to answer this question, samples of Nitinol wire and fluorinated ethylene-propylene (FEP) film were surface modified by various treatments before being thermally bonded into a composite pull-out strength test specimen and mechanically tested to determine their adhesion strength. METHODS: The two surface treatments for Nitinol wire included mechanical roughening with sandpaper, and adding a fluorocarbon coating followed by polymerization and curing by a helium plasma treatment. The two surface treatments for FEP film included helium plasma and helium-oxygen plasma under atmospheric conditions. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and contact angle measurements were also taken to characterize the appearance and chemistry of the surfaces before and after modification. A unique pull-out strength test method was developed to assess the level of adhesion between these various candidates. RESULTS: The pull-out force for untreated Nitinol bonded to untreated FEP film was 30.5 +/- 2.4 N. Significant improvements of up to 14% in this level of adhesion were obtained with the mechanically roughened Nitinol wire bonded to the helium plasma treated films. However, coating the wire with a liquid fluorocarbon monomer mixture (TG-10) was not successful and after thermal bonding to FEP film the level of adhesion decreased by over 80%. CONCLUSIONS: Thus, the bonding strength between the wire and the film can be significantly improved by mechanically roughening the Nitinol wire and treating the FEP film with helium plasma prior to thermal bonding.

Design of a superhydrophobic surface using woven structures.

The relationship between surface tension and roughness is reviewed. The Cassie-Baxter model is restated in its original form, which better describes the most general cases of surface roughness. Using mechanical and chemical surface modification of nylon 6,6 woven fabric, an artificial superhydrophobic surface was prepared. A plain woven fabric mimicking the Lotus leaf was created by further grafting 1H,1H-perfluorooctylamine or octadecylamine to poly(acrylic acid) chains which had previously been grafted onto a nylon 6,6 woven fabric surface. Water contact angles as high as 168 degrees were achieved. Good agreement between the predictions based on the original Cassie-Baxter model and experiments was obtained. The version of the Cassie-Baxter model in current use could not be applied to this problem since the surface area fractions in this form is valid only when the liquid is in contact with a flat, porous surface. The angle at which a water droplet rolls off the surface has also been used to define a superhydrophobic surface. It is shown that the roll-off angle is highly dependent on droplet size. The roll-off angles of these superhydrophobic surfaces were less than 5 degrees when a 0.5 mL water droplet was applied.