Storability of porcine blood in forensics: How far should we go?

The effect of the anti-coagulant EDTA on the deposition and adhesion of whole blood deposits on non-porous substrates

An investigation into whether the addition of a commonly used anti-coagulant agent like ethylenediaminetetraacetic acid (EDTA) has an impact on the adhesion potential of blood to non-porous substrates was conducted. Two non-porous substrates (aluminum and polypropylene) exhibiting six different surface roughness categories (R1-R6) were used as test substrates upon which either whole blood or blood treated with EDTA was deposited. Samples were exposed to different drying periods (24 hours, 48 hours, and 1 week) before undergoing a tapping agitation experiment in order to evaluate the adhesion to the surface. Clear differences in adhesion potential were observed between whole blood and blood treated with EDTA. Blood treated with EDTA displayed a stronger adhesion strength to aluminum after a drying time of 24 h pre-agitation, while whole blood presented with a stronger adhesion strength at the drying time of 48 h and 1 week. Both EDTA-treated and EDTA-untreated blood was shown to dislodge less easily on polypropylene with the only difference observed on smooth surfaces (0.51-1.50 μm surface roughness). Thus, when conducting transfer studies using smooth hydrophobic substrates like polypropylene or considering the likelihood of transfer given specific case scenarios, differences in adhesion strength of blood due to hydrophobic substrate characteristics and a decreased surface area need to be considered. Overall, whole blood displayed a better adhesion strength to aluminum, emphasizing that indirect transfer probability experiments using EDTA blood on substrates like aluminum should take an increased dislodgment tendency into account in their transfer estimations.

Alginate/xanthan gum hydrogels as forensic blood substitutes for bloodstain formation and analysis

Understanding the behaviour of human blood outside of the body has important implications in forensic research, especially related to bloodstain pattern analysis (BPA). The design of forensic blood substitutes (FBSs) can provide many advantages, including the incorporation of multiple physiological components for use as safe and reliable materials for forensic applications. In this work, we present the design of synthetic alginate and xanthan gum-based hydrogels that contain electrosprayed microparticles (MPs) with and without crosslinked DNA. In addition to the MPs, the alginate/xanthan gum FBS materials include fillers to alter the physical appearance and fluid properties of the material. The optimized FBS consisted of alginate (1% w/v) and xanthan gum (5.0 × 10^-3% w/v), 2 mM CaCl₂, ferric citrate (0.5% w/v), magnesium silicate (0.25% w/v), Allura Red dye (2% w/v), 0.025% v/v Tween 20 and 9.5% v/v MPs. The FBS was tested in passive dripping experiments relevant to BPA scenarios at various impact angles. The spreading ratio (D_s/D₀) was determined for 90° stains made on a paper surface and compared to bovine blood where the FBS was shown to simulate accurate and predictable spreading behaviour. In addition, we simulated other common BPA scenarios (e.g., impact patterns) and evidence processing potential. The FBS could be swabbed, and the DNA could be extracted, amplified, and genotyped analogous to human blood evidence. A stability test was also conducted which revealed a shelf-life of over 4 weeks where the material remains relevant to human blood at physiological temperature.

Cow blood - A superior storage option in forensics?

Given the use of modified blood products (e.g. leucocyte depleted erythrocyte concentrates in SAG-mannitol, dehydrated blood powder, defibrinated blood), drawing blood from conscious animals while minimizing their stress is a good option to obtain blood for bloodstain pattern analysis. Nevertheless, the blood must be well described since individual differences in quality can occur, and storage will influence blood components qualitatively and quantitatively. Cow has been discussed as a suitable source of blood supply, but current data lack hematological and full rheological perspectives. This project includes the respective parameters in combination with passive drip pattern experiments during refrigerated storage in multiple study arms. Cow blood displayed a constant increase in viscosity (at high shear rate: 1000s^-1), reflecting the expected reduction in red blood cell (RBC) flexibility. RBCs shrank but remained intact with very few irregular shapes, therefore there was no evidence of hemolysis. Influence of storage on stain size in passive drip pattern experiments with different substrates was minimal. However in cows, it is not hemolysis but an early change in suspension properties that indicates storage lesion. Viscosity (at low shear rate: 1s^-1) of some blood samples increased three-fold (peaking at day 14), transitioning sharply to near-Newtonian (almost shear-independent) behavior thereafter. The higher this increase in viscosity, the greater the increase in the number of satellite spatter on glass. In order to ensure high quality simulations in the future, comprehensive rheological analyses to detect gradual changes in blood pseudoplasticity should be implemented in the forensic discipline of bloodstain pattern analysis.

The role of plasma in the yield stress of blood

BACKGROUND

Yielding and shear elasticity of blood are merely discussed within the context of hematocrit and erythrocyte aggregation. However, plasma might play a substantial role due its own viscoelasticity.

OBJECTIVE

If only erythrocyte aggregation and hematocrit would determine yielding, blood of different species with comparable values would present comparable yield stresses.

METHODS

rheometry (SAOS: amplitude and frequency sweep tests; flow curves) of hematocrit-matched samples at 37°C. Brillouin Light Scattering Spectroscopy at 38°C.

RESULTS

Yield stress for pig: 20mPa, rat: 18mPa, and human blood: 9mPa. Cow and sheep blood were not in quasi-stationary state supporting the role of erythrocyte aggregation for the development of elasticity and yielding. However, pig and human erythrocytes feature similar aggregability, but yield stress of porcine blood was double. Murine and ruminant erythrocytes both rarely aggregate, but their blood behavior was fundamentally different. Pig plasma was shear-thinning and murine plasma was platelet-enriched, supporting the role of plasma for triggering collective effects and gel-like properties.

CONCLUSIONS

Blood behavior near zero shear flow is not based solely on erythrocyte aggregation and hematocrit, but includes the hydrodynamic interaction with plasma. The shear stress required to break down elasticity is not the critical shear stress for dispersing erythrocyte aggregates, but the shear stress required to fracture the entire assembly of blood cells within their intimate embedding.

Animal blood in translational research: How to adjust animal blood viscosity to the human standard

Animal blood is used in mock circulations or in forensic bloodstain pattern analysis. Blood viscosity is important in these settings as it determines the driving pressure through biomedical devices and the shape of the bloodstain. However, animal blood can never exactly mimic human blood due to erythrocyte properties differing among species. This results in the species-specific shear thinning behavior of blood suspensions, and it is therefore not enough to adjust the hematocrit of an animal blood sample to mimic the behavior of human blood over the entire range of shear rates that are present in the body. In order to optimize experiments that require animal blood, we need models to adapt the blood samples. We here offer mathematical models derived for each species using a multi linear regression approach to describe the influence of shear rate, hematocrit, and temperature on blood viscosity. Results show that pig blood cannot be recommended for experiments at low flow conditions (<200 s-1 ) even though erythrocyte properties are similar in pigs and humans. However, pig blood mimics human blood excellently at high flow condition. Horse blood is unsuitable as experimental model in this regard. For several studied conditions, sheep blood was the closest match to human blood viscosity among the tested species.

Whole bovine blood use in forensic research: Sample preparation and storage considerations

Mammalian whole blood sources are often used for forensic research and training when human samples cannot be sourced. While porcine, ovine and equine blood have been shown to be viable alternatives to whole human blood for forensic purposes, procurement can still pose a problem, especially for smaller and remote institutions. This work explores the use of whole bovine blood for basic bloodstain simulation. Sample preparation through the addition of ACD-A anticoagulant was optimized and storability was explored. Viscosity, surface tension, density, and packed cell volume, four fluid properties relevant to bloodstain pattern analysis, were monitored over four days and in two temperature conditions. Linear mixed models accounting for variation in the donor demonstrated that these fluid properties of the bovine blood changed predictably over time and with temperature. Whole bovine blood with 12.5% v/v ACD-A was found to be viable for use in basic bloodstain simulation at ambient and physiological temperature.