hair and fiber analysis n.
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Hair and Fiber Analysis

Hair and Fiber Analysis

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Hair and Fiber Analysis

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  1. Hair and Fiber Analysis

  2. Morphology of Hair • Part of Integumentary System • Grows out of hair follicle • Hair consists of • Root/bulb • Shaft • Tip end

  3. Morphology Cont. • Hair Shaft is the focus of most forensic analysis • 3 Parts • Cuticle-the scale structure covering exterior of the hair • Cortex-the main body of the hair shaft • Medulla-a cellular column running through the center of the hair

  4. The Cuticle in Detail • Resistance to decomposition and retainment of structural features are due to cuticle • Overlapping scales made of hardened cells • Scale pattern not useful in distinguishing humans but can be utilized for species identification

  5. The Cortex in Detail • Main body of the hair shaft made of cortical cells • Embedded with pigment granules that give color to hair

  6. The Medulla in Detail • Central canal of the hair • Medullary index- measures the diameter of the medulla compared to diameter of hair shaft • Written as a fraction….humans less 1/3 animals ½ or greater • Medulla can be continuous, fragmented, interrupted, or non exsistent

  7. The Root in Detail • Allows for hair growth (three phases) • 1. Anagen phase- initial growth phase during which the hair follicle actively produces hair • 2. Catagen phase- a transition stage between the anagen and telogen phases • 3. Telogen phase- the final growth phase in which hair naturally falls out of the skin • Follicular tag is the most important part because it contains the “richest” source of DNA for the hair

  8. Misconceptions of Hair • Hair CANNOT be used to identify a single head or body through its structural characteristics • Only if DNA is present can it be matched • Can determine the area of the body that the hair came from • Some racial origins can be determined from hair • Age and sex cannot be determined (exception infant hair or dye)

  9. Fiber History • Most fibers originally came from natural resources: plants and animals • Post 1920 scientist created dozens of new fibers

  10. Types of Fibers • Natural Fibers—animal or plant sources • Sheep—wool • Goats—mohair, cashmere • Camels, Llamas, Alpacas, mink, rabbit, beaver, and muskrat • Cotton

  11. Types of Fibers • Manufactured Fibers—fibers derived from either synthetic or natural polymers • First of these were made from materials derived from cotton or wood pulp • Pure cellulose is extracted from them • Also called regenerated fibers • Rayon, acetate, tracetate (all come from cellulose) • Currently many are made solely from chemicals and are called synthetic fibers • Nylons, polyesters, acrylics

  12. Rayon

  13. Natural and Synthetic Manufactured • Cellulose—natural carbohydrate polymer • Synthetics– polymers are the basic unit of these fibers

  14. Identification and Comparison of Manufactured Fibers • Origin of the fiber is key in utilizing it as a piece of evidence • First step is a microscopic examination • Look at the color, diameter, and longitudinal striations • Cross sections of the fibers can also be beneficial to tying fiber back to the manufacturer

  15. Cross Section

  16. Identification and Comparison of Manufactured Fibers • Microspectrophotometer- compare colors of fibers through spectral patterns • Chromatographic- analyze the dye composition by extracting dye from fibers themselves

  17. Identification and Comparison of Manufactured Fibers • Fibers need to have the same chemical composition • Nylon and subgroups of nylon • Acrylic fibers can be broken down into 24 different groups

  18. Identification and Comparison of Manufactured Fibers • Birefringence-- polarize white light passing though a synthetic fiber is split into two rays that are perpendicular to each other • Infrared Absorption– polymers that make up fiber selectively absorb infrared light in a characteristic pattern

  19. Collection and Preservation of Fiber Evidence