Modeling of metamaterial based incision patterns for generating high expansions in skin grafts

BACKGROUND

Split-thickness skin grafting is a widely used treatment for burn patients. It requires removing a small portion of healthy skin, making parallel incisions on it, stretching it, and surgically implanting it into the burn site. Although skin graft mesher companies claim to significantly expand the size of the skin graft, in reality, the amount of expansion achieved is much smaller.

METHODS

This study aimed to improve the expansion potential of skin grafts by designing new incision patterns with auxetic properties, using a skin simulant material and additive manufacturing. The mechanical properties and digital image correlation was used to analyze the strain, effective Poisson's ratio, local strains, void area, and meshing ratio of the auxetic skin graft simulants.

FINDINGS

The results showed that the Y-shaped skin graft simulant had the highest effective negative Poisson's ratio, largest areal expansions, lowest maximum induced stresses and strains, and uniform strain distribution properties, making it the best choice for generating high expansions in skin grafts.

INTREPRETATION

The study found that the expansions were highly strain sensitive, with higher auxeticity observed at lower strains. The novel findings with auxetic skin graft simulants are expected to provide valuable insights for developing skin grafts with higher expansion potential in the future.

Production of artificial fingermarks. Part II - The use of a modified inkjet printer for the deposition of synthetic secretions

This study is the second part of a larger body of research dedicated to the production of synthetic secretions and the use of an inkjet printer to deposit realistic artificial fingermarks. An artificial emulsion combining eccrine and sebaceous compounds, which was described and tested in the first part of this research, was used as it showed a promising compatibility with common detection techniques. An inkjet printer was modified to print the emulsion on two different substrates: paper (porous) and acetate (non-porous). After optimisation of the printing parameters, multiple fingermarks were printed and processed with a range of standalone detection techniques: 1,2-indanedione-zinc, ninhydrin, Oil Red O, and physical developer on paper, and cyanoacrylate fuming, rhodamine 6G, gold/zinc vacuum metal deposition, and silver black powder on acetate. The detection techniques were also applied in sequence, which is considered one of the biggest advantages of the emulsion over simpler amino acid mixtures that are usable with amino acid reagents only. Natural fingermarks deposited by a single donor were processed with the same techniques for comparison. The effect of water immersion was also investigated, where fingermarks printed on paper were immersed in water for 15 min, before being processed with 1,2-indanedione-zinc and Oil Red O. The results showed that realistic-looking fingermarks could be printed on paper and that printing on acetate was also possible albeit of lower quality due to the nature of the substrate. The artificial fingermarks were successfully enhanced by all the detection techniques tested, at the notable exception of physical developer. The results obtained were very similar to what is generally observed with real fingermarks, and it was observed that the impact of water immersion on the artificial fingermarks was comparable as well. These findings open new perspectives for the development of multi-target quality control test strips or for the standardisation of proficiency testing and interlaboratory collaborative exercises where ground truth is crucial to guarantee comparable results and objective assessment.

Production of artificial fingermarks. Part I - Synthetic secretions formulation

Fingermark variability is a critical parameter. To mitigate the effects of this variability, synthetic secretions in the form of simple mixtures of target compounds found in eccrine sweat have been described in the literature, but they are usually reactive towards only a minimal range of detection techniques. If this approach is acceptable for the production of single-technique test strips, such artificial secretions cannot be considered as reliable fingermark simulants because they do not reproduce the complex matrix that makes up real secretions. Research has shown that sebaceous and eccrine compounds are probably present simultaneously in fingermark residue in the form of an emulsion. This paper is the first part of a research project that aims at producing realistic artificial fingermarks containing an extensive range of eccrine and sebaceous compounds. This first study aimed to reproduce and compare two synthetic fingermark residues formulations and assess their potential to be used as fingermark simulants. Spot tests of the artificial secretions were deposited on paper substrates, and their reactivity with four common detection techniques was tested: 1,2-indanedione-zinc, ninhydrin, oil red O, and physical developer. Both formulations showed very good results when processed with the two amino acid reagents, as well as oil red O, and no obvious differences were observed between the two versions. The results obtained with the physical developer were inconsistent and demonstrated that the fundamental working principle of physical developer needs to be further understood. The results were extremely promising as they showed the potential of such reproducible artificial secretions to be used to assess an extensive range of detection techniques, which would be highly beneficial to guarantee better research and quality control in fingermark detection. The use of spot tests to deposit the simulant was shown to be unreliable and a more controllable and reproducible deposition method using an inkjet printer will be presented in the second part of this research.

Practical application of synthetic head models in real ballistic cases

In shooting crimes, ballistics tests are often recommended in order to reproduce the wound characteristics of the involved persons. For this purpose, several "simulants" can be used. However, despite the efforts in the research of "surrogates" in the field of forensic ballistic, the development of synthetic models needs still to be improved through a validation process based on specific real caseworks. This study has been triggered by the findings observed during the autopsy performed on two victims killed in the same shooting incident, with similar wounding characteristics; namely two retained head shots with ricochet against the interior wall of the skull; both projectiles have been recovered during the autopsies after migration in the brain parenchyma. The thickness of the different tissues and structures along the bullets trajectories as well as the incident angles between the bullets paths and the skull walls have been measured and reproduced during the assemblage of the synthetic head models. Two different types of models ("open shape" and "spherical") have been assembled using leather, polyurethane and gelatine to simulate respectively skin, bone and soft tissues. Six shots have been performed in total. The results of the models have been compared to the findings of post-mortem computed tomography (PMCT) and the autopsy findings.Out of the six shots, two perforated the models and four were retained. When the projectile was retained, the use of both models allowed reproducing the wounds characteristics observed on both victims in terms of penetration and ricochet behaviour. However, the projectiles recovered from the models showed less deformation than the bullets collected during the autopsies. The "open shape" model allowed a better controlling on the shooting parameters than the "spherical" model. Finally, the difference in bullet deformation could be caused by the choice of the bone simulant, which might under-represent either the strength or the density of the human bone. In our opinion, it would be worth to develop a new, more representative material for ballistic which simulates the human bone.

Printed artificial sweat as replacement for natural fingermarks: Qualitative and quantitative approach considering an amino acid reagent

The study presented in this paper aims at assessing how printed fingermarks can be used to generate realistic latent marks bearing varying quantities of materials to be detected. Considering dilution series of artificial sweat (eccrine secretion) and 1,2-indanedione/zinc as amino acid reagent, we assessed how printed marks behave in comparison to natural fingermarks provided by a set of 30 donors. The results were assessed in terms of relative intensity (contrast, luminescence) and expert grading (ridge details, overall quality). With regards to the set of 30 donors, this study brought a quantitative look to the influence of intra- and inter-variability on the relative intensity values observed when processing natural fingermarks. This provided new data to further understand the concept of "donorship". With regards to the use of printed marks, it has been illustrated how dilution series of a concentrated solution allows covering a range of cases: unnatural marks (intensity values well above those obtained with donors), rich marks (corresponding to fingermarks left by good donors), and faint marks (associated with the kind of results observed with poor donors). Such a range of detection performance offers the possibility to generate fine-tuned detection exercises of varying difficulty levels. Printed items made of artificial sweat could hence constitute a valuable alternative to natural secretions in the context of education and proficiency testing.

A study into the viability of Synbone® as a proxy for Sus scrofa (domesticus) ribs for use with 5.56-mm open tip match ammunition in ballistic testing

BACKGROUND

In ballistic testing and forensic reconstruction, there is a need to use repeatable and consistent simulants. While synthetic bone is mechanically similar to human bone, it does not have the same viscoelastic properties. In high-energy impact such as ballistic impacts, bone acts as a stiff, brittle material and fails instantaneously. Therefore, a suitable simulant for use in ballistic testing should have comparable energy deposition to mammalian bones. This preliminary study aims to determine if Synbone® could be a viable proxy for Sus scrofa (domesticus) ribs in ballistic testing.

METHODOLOGY

Three thickness of Synbone® were embedded into 10% ballistic gelatin and shot using 5.56-mm ammunition. The models were then analysed to compare the Synbone® to a previous Sus scrofa (domesticus) rib study and focused on the number of fragments within the block, energy deposition, onset of yaw, angle of deviation, the temporary cavity as a percentage of the block and the depth to the temporary cavity centre, depth to maximum gelatin disruption and the permanent wound channel, including shear planes and wound tract diameter.

RESULTS

There was no significant difference in the metrics that were compared between Sus scrofa (domesticus) ribs and the three thicknesses of Synbone®, except for a significant difference in the depth to maximum gelatin disruption between the 6 mm (p = 0.009) and 12 mm plate (p = 0.007) and the Sus scrofa (domesticus) ribs.

CONCLUSION

This study indicates that the 5-mm Synbone® plate is a suitable proxy for Sus scrofa (domesticus) ribs for use with 5.56-mm OTM ammunition in ballistic testing.

Validation of Roebuck 1518 synthetic chamois as a skin simulant when backed by 10% gelatin

INTRODUCTION

Synthetic skin simulants are used both in wound ballistics and forensic investigations and should display similar mechanical properties to human tissue and therefore need to be validated. It is recognised that skin simulants may have a significantly different performance when different backing combinations are used; therefore, it is essential to specify and control the backing material. Roebuck 1518 synthetic chamois (RBK) backed by 20% ballistic gelatin has been validated as a suitable skin simulant; this study looks at validating the RBK simulant when backed by 10% ballistic gelatin.

METHODS

Two layers of RBK synthetic chamois backed by calibrated 10% ballistic gelatin were placed onto the long face of the block and secured. Steel spheres with various sectional densities were fired using a custom-made gas gun to determine the V₅₀ of the simulants and compared with the predicted V₅₀.

RESULTS

The results demonstrate that for a sectional density between 2.1 and 6.6 g/cm², the skin simulants backed by 10% gelatin are within the 35% error bounds predicted by James' patent equation. All samples had a close fit to the regression line (R² = 0.9738), and a Spearman rho test indicates that there is a "strong" negative correlation between sectional density and the V₅₀ (Rs =- 0.957, p = 0.00).

CONCLUSIONS

This validation study confirms that RBK synthetic simulant backed by 10% gelatin is a suitable skin simulant when testing non-deforming projectiles with sectional densities ranging from 2.1 to 6.6 g/cm². A predictive trend line also indicates that the skin simulant is suitable for non-deforming projectiles with sectional densities ranging from 0.6 to 20 g/cm² although this needs to be confirmed.

GC-MS/MS quantification of benzyl salicylate on skin and hair: A novel chemical simulant for human decontamination studies

Human studies investigating the efficacy of emergency decontamination protocols for chemical incidents require the use of non-hazardous chemical simulants. Methyl salicylate (MeS) has almost exclusively been used for this purpose. Whilst MeS is a simulant of the chemical warfare agent (CWA) sulphur mustard, it is not an ideal simulant for many other chemical threats with greater persistence and lower volatility. Benzyl salicylate (BeS) has been investigated here as a low toxicity simulant for lower volatility, persistent chemical threat agents and toxic industrial chemicals (TICs). To evaluate the suitability of BeS as a simulant for human decontamination studies a gas chromatography-triple quadrupole mass spectrometry method was designed, optimised and validated, for the analysis of human skin and hair. Quantification was achieved using isotope-dilution, EI and collision-induced dissociation and multiple reaction monitoring for both qualifier and quantifier ion transitions. The mass transitions were m/z 285 → 91 and m/z 210 → 181, respectively for the quantifier and qualifier ions of BeS, and m/z 289 → 91 and m/z 214 → 185 for the quantifier and qualifier ions for the BeS-d4 internal standard, respectively. The method exhibited excellent coefficients of determination (R² = 0.9992-0.9999) with LOD and LOQ values at 0.023 ng/ml and 0.23 ng/ml. Across three Quality Controls (QCs), 11.5 ng/ml, 115 ng/ml and 1150 ng/ml) average accuracy (intra-day 95.6-100.3%, inter-day 98.5-104.91%) and precision (intra-day RSD (%) 2-13.7%, inter-day RSD (%) 3.3-8.8%) were determined. The validated method was applied in a proof of principle volunteer study for the determination of total BeS recovered from skin and hair. The average total BeS recovery after 70 min was 37.9% from skin and there was a significant increase between baseline and post-intervention levels for hair. These data demonstrate that BeS is an appropriate simulant for persistent chemicals and that the analytical method employed here is suitable for BeS analysis in human studies.

Optimisation and validation of a GC-MS/MS method for the analysis of methyl salicylate in hair and skin samples for use in human-volunteer decontamination studies

Methyl salicylate has a long history of use as a chemical warfare agent simulant for volatile lipophilic compounds such as sulphur mustard. An improved isotope dilution GC-MS/MS method was developed, optimised and validated for the analysis of methyl salicylate in human skin and hair samples, for use in emergency decontamination volunteer studies. Following derivatisation, quantification was measured on a triple quadrupole mass spectrometer, set to EI mode and conducting multiple reaction monitoring of target ions. The mass transitions were 209 → 179 and 213 → 161 for quantitation of methyl salicylate and methyl salicylate D4, respectively whereas qualifier ion transitions used to verify identity were 209 → 169 and 213 → 89. The method achieved excellent coefficient of determination (R² > 0.9968 to 0.9999) over the range of 0.5-5000 ng/ml and the LOD and LOQ were 0.05 ng/ml and 0.5 ng/ml. The method was further validated for accuracy (intra-day and inter-day average 100.28% to 102.03% and 99.48% to 102.33%, respectively) and precision (intra-day RSD 1.43% to 2.35%, inter-day RSD 1.91% to 2.97%) at three concentrations (25, 250 and 2500 ng/ml). The validated method was successfully used to identify methyl salicylate in samples of human skin generated during volunteer studies of emergency decontamination systems and in hair of staff conducting these studies.

Comparison of ballistic impact effects between biological tissue and gelatin

Gelatin is commonly used in ballistic testing as substitute for biological tissue. Comparison of ballistic impact effects produced in the gelatin and living tissue is lacking. The work in this paper was aimed to compare the typical ballistic impact effects (penetration trajectory, energy transfer, temporary cavity) caused by 4.8mm steel ball penetrating the 60kg porcine hind limbs and 10wt% gelatin. The impact event in the biological tissue was recorded by high speed flash X-ray machine at different delay time, while the event in the gelatin continuously recorded by high speed video was compared to that in the biological tissue. The collected results clearly displayed that the ballistic impact effects in the muscle and gelatin were similar for the steel ball test; as for instance, the projectile trajectory in the two targets was basically similar, the process of energy transfer was highly coincident, and the expansion of temporary cavity followed the same pattern. This study fully demonstrated that choosing gelatin as muscle simulant was reasonable. However, the maximum temporary cavity diameter in the gelatin was a little larger than that in the muscle, and the expansion period of temporary cavity was longer in the gelatin. Additionally, the temporary cavity collapse process in the two targets followed different patterns, and the collapse period in the gelatin was two times as long as that in the muscle.

Dual-Function Metal-Organic Framework as a Versatile Catalyst for Detoxifying Chemical Warfare Agent Simulants

The nanocrystals of a porphyrin-based zirconium(IV) metal-organic framework (MOF) are used as a dual-function catalyst for the simultaneous detoxification of two chemical warfare agent simulants at room temperature. Simulants of nerve agent (such as GD, VX) and mustard gas, dimethyl 4-nitrophenyl phosphate and 2-chloroethyl ethyl sulfide, have been hydrolyzed and oxidized, respectively, to nontoxic products via a pair of pathways catalyzed by the same MOF. Phosphotriesterase-like activity of the Zr6-containing node combined with photoactivity of the porphyrin linker gives rise to a versatile MOF catalyst. In addition, bringing the MOF crystals down to the nanoregime leads to acceleration of the catalysis.