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Topic 10 - Tissue Simulants in Terminal Ballistic Analysis (What is a…
Topic 10 - Tissue Simulants in Terminal Ballistic Analysis
Fragmenting rifle bullet
Larger and heavier bullet is stable for longer, less tumbling.
Can exit body sideways.
Temp cavity is related to energy transfer. Therefore is biggest at entry site.
Tumbling bullet
Rifle Ammunition
Ballistic gel is used as a simulant, is more elastic than human tissue but it still comparable.
Creation of Permanent Wound Path
Debris is distributed along wound path
If projectile remains inside the body, it will be found slightly behind its ultimate penetration depth.
Radial fissures (cracks) are typically found along the length of the wound path where tissue has been taken beyond its elastic limit by temporary cavity formation.
Temporary Cavity
Pulsation:
After cavity reaches max diameter it begins to retract, after this the cavity
re opens
which is called
recavitation
and a pulsing effect is seen.
What is a ballistic penetration simulant?
any material, biological or synthetic, that is able to give comparable and reproductive wound data in relation to the human body when penetrated with a projectile.
Why?
overcome ethical issues with testing on human tissue.
comparative penetration data between different projectiles.
understand potential wounding effects of projectiles.
fairly reproducible results (accuracy not always considered most important).
Desirable Properties:
non-cadaveric (not dead human body), non-biological so biological variation is avoided.
ethically sound
reproducability
stable during storage
readily available and easy to handle
similarity in the deformation behaviour of projectiles
similarity in the deceleration of projectiles
similarity in kinetic energy dissipation
elastic behaviour similar to living tissue.
Ballistic Gelatin
flesh penetration simulant. Made of:
collagen from bones of pigs by acid.
10% gelatin at 4 degrees celcius
20% gelatin and 20 degrees celcius
density of gelatin is extremely temperature sensitive, different temps must be used to give similar penetration properties at different concentrations.
Biological material lacks reproducability as biological organisms vary due to variety of coding sequences in DNA. No two are the same except for twins, where lifestyle will cause variation. Therefore there is no standard attribute to any material property of this tissue. Averaged values have a v high associated error.
Problems:
variability
methods cant be used as too soft
sample prep often tricky
material are viscoelastic
ethical issues
Soap
Plastic material. Allows observation of the profile of the temp cavity produced during penetration of the body. Size of cavity not a direct representation of that expected in human tissue, but can be used to predict it from calibrations.
Leather
Collagen is supposed to be represented by grain structure of leather. But there are highly variable properties by body region and age of cow.
Head Models
"Skin-Skull-Brain" Model by Thali et al.
multi-layered polyurethane bone structures made up of elastic, compact tabula externa and tabula interna, which sandwich cancellous (mesh-like) spongy diploe centre.
silicon skull cap
clay support during impact which is analogous to the neck supporting the structure.
10% gelatin at 4 degrees celcius
not realistic geometry
, doesn't look like or have the same geometries as a real human skull.
Shepherd Model:
Cheap skull models filled with ballistic gel, surrounded by silicon skin layer.
has realistic geometries.
10% gelatin at 4 degrees celcius
