Scanning Electron Microscopic Analysis of Skin Resolution as an Aid in Identifying Trauma in Forensic Investigations

Abstract

The forensic investigator is frequently confronted with cases that present with wounds and blunt force trauma. Presently, the forensic investigator depends upon previous experience and further investigative deduction of the crime scene to analyze these injuries. Although not readily apparent to the naked eye, many skin tissue injuries can be visualized with scanning electron microscopy (SEM). This study was designed to establish skin trauma resolution using SEM in various skin preparations. Tissue trauma was induced on leather, preserved skin, fresh skin, and living skin using dies of varying thread size. Calibrated pressure forces in pounds per square inch (psi) were applied and impressions made using vinyl polysiloxane. Positive replicas of the tissues were prepared for SEM using isocyanate resin. After sputter coating the cast with 35 nm of gold-palladium, electron micrographs were generated using a Jeol JSM-5310L V scanning electron microscope. To establish resolution, thread widths of 52, 104, and 208 threads per inch (tpi) and trauma forces of 150, 200, and 250 psi were used to produce the impressions. Microgrooves that were identified on the die threads were analyzed. The optimum pressure for resolution studies was 150 psi using the 52 tpi die on the leather sample (4.67 + 0.88 µm, p = 0.046 and 0.025, respectively, by ANOVA). The resolution was compared to that of leather using preserved, fresh, and living skin. The resolution in preserved and fresh skin was less than for leather (9.00 ± 1.73 and 10.5 ± 4.5 versus 4.67 ± 0.88 µm, p = 0.09 and p = 0.20, respectively). Living skin resolution was 3 µm at 52 tpi and 100 psi. Various implements of blunt force trauma were also examined using the leather sample. Time after trauma resolution was examined at 0 (3 µm), 5 (6 µm), 10 (8 µm), and 20 (9 µm) min in living tissue. A comparison between the microgrooves on the die replicas and the tissue trauma impressions revealed striking agreement for both linearity and resolution. Analysis of the microgrooves suggests that discrete morphological characteristics are seen in skin tissue traumas. This method could expand the tools available for the forensic investigation of blunt force trauma.

Analysis of experimental cranial skin wounding from screwdriver trauma

“…7), and the difference is only clearly visible at the SEM level. Thus, while we share the optimism of Rawson et al [8] about the usefulness of SEM comparisons of wounds and the instruments that inflicted them, our results suggest that caution is warranted in interpreting the morphology of screwdriver wounds to the skin. Posidriv 3 3 0 0 0 50 Square 0 0 6 0 0 100 Star 1 0 2 3 0 50 Straight 0 0 0 0 6 100 Total 8 3 10 3 6 73 …”

“…In other words, can different types of screwdriver be recognised by the pattern of skin trauma they inflict? Both Rawson et al [8] and Sitiene et al [10] emphasise the importance of the assessment of wound characteristics in the identification of the wounding instrument. Our study shows clearly that wounds inflicted by different types of screwdriver may be grouped into three categories.…”

“…Yet, screwdriver stab wounds are often described in the surgical and traumatological literature [1][2][3][4][5][6], which has prompted the call by Trutton et al [7] for an increased awareness of such injuries to the skin. Moreover, a number of recent reports [8][9][10] have highlighted the importance of a careful analysis of dermal stab wounds in forensic investigations.…”

“…Often, such trauma is not readily identifiable with the naked eye and has to be magnified through photographic processes. Rawson et al [8] have underlined an inherent limitation in the use of photographs, in that they fail to capture details of the third dimension or depth of a wound, and have advocated the use of scanning electron microscopy (SEM) in such cases. The question arises, can skin wounds inflicted by different screwdriver types be characterised?…”

The biomechanical modelling of non-ballistic skin wounding: blunt-force injury

“…The ability to reconstruct a wounding event hinges on the use of as many lines of evidence as possible. Historically, most inferences of non-ballistic, blunt force wound reconstruction have relied on visual examination, photography, and experience [1][2][3], whereas more recently, techniques such as X-ray examination, scanning electron microscopy, and optical 3D surface digitization have been used [4][5][6]. Concomitantly, our understanding of molecular biological phenomena associated with wounding has advanced, fuelled by the availability of ever more sophisticated laboratory techniques and tests [7,8].…”