Splitting hairs (and fibers): 4 Methods of Cross-sectioning

Sandra Koch, Ph.D.Senior Research Microscopist

Cross-sections

• A cross-section is made by cutting a material at 90° to its main axis to study the morphology of the material you are analyzing

• Take care not to alter shape by the method you choose

What can a cross-section reveal?

How to determine the cross-section of hairs and fibers:

• Hot plate and polyethylene

• Cross-section plates

• Ultramicrotome

• Optical sectioning

Methods:1

How to determine the cross-section of hairs and fibers:

• Hot plate and polyethylene

• Cross-section plates

• Ultramicrotome

• Optical sectioning

Methods:1

2

How to determine the cross-section of hairs and fibers:

• Hot plate and polyethylene

• Cross-section plates

• Ultramicrotome

• Optical sectioning

Methods:1

2

3

How to determine the cross-section of hairs and fibers:

• Hot plate and polyethylene

• Cross-section plates

• Ultramicrotome

• Optical sectioning

Methods:1

2

3

4

Cross-Sectioning Method #1

Supplies:

• Disposable pipette (or sheets of

polyethylene film)

• Hot plate

• Two glass microscope slides

• Single-edge razor blade

• Double sided tape

Cross-Sectioning Method #1Method:• Cut a section of a disposable

polyethylene pipette• Thread hair/fiber inside pipette tube

Place between slides on hot plate till pipette melts – turns translucent

• Remove and slice sections with razor blade

• Double-sided tape helps to orient sections for viewing

• Can also use polyethylene sheets

Cross-Sectioning Method #1

• Polyethylene sheets

Cross-Sectioning Method #1

• Remove and slice sections with razor blade

Cross-Sectioning Method #1Double-sided tape can be useful to help orient sections for viewingBenefits:• Quick and easy method• Supplies typically on hand• Can observe internal microstructure

Limitations:• Material may not be oriented at 90° to fiber

length• Dull razor blade may alter hair/fiber

morphology

Moose hair cross-section

Cross-Sectioning Method #2Supplies:• Cross section plates• Thread• Packing material (suggest

different color than hair/fibers)• Razor bladeMethod:• wrap fiber packing around

material of interest• Pull bundle through hole with

loop of thread

Cross-Section Plate Demo

Cross-Sectioning Method #2Cross sectioning plates:• wrap fiber packing around

material of interest• Pull bundle through hole with

loop of thread• Cut flat along back surface with

razor blade• Coat with clear nail polish to

hold in place• Flip and cut top surface with

razor blade• Use as slide and place on

microscope stage to examine

Cross-section samples (fibers)

Cross-section examples (hairs)

Cross-Sectioning Method #2Benefits to cross-section plate:• Material prepared for direct analysis using

a microscope• Once coated with clear nail polish sections

are preservedLimitations:• If too much packing material is used

around hairs/fibers may not be able to pull through plate

• If too little packing material is used, sections may not stay in place

• Be careful of altering morphology

Cross-sectioning Method #3

Supplies:• Ultramicrotome• Glass or diamond boat to cut

sections• Resin and resin mold to hold

samples• Oven to cure resin

Cross-sectioning Method #3Ultramicrotome• Sample oriented in holder perpendicular to

cutting blade • Sections float off blade onto water

Cross-sectioning Method #3Ultramicrotome• If sections wrinkle, chloroform can

be used to help flatten sections• Staining can help reveal structure

Cross-sectioning method #3

Benefits:• Lower potential for distortion of

sample by cutting blade so measurements more precise

Limitations:• Must orient samples prior to

embedding and sectioning• Resource and equipment dependent

– Resin cures in oven– Glass or diamond boats to section

Cross-sectioning Method #4

Optical sectioning• Train your eye to recognize

different shapes by focusing up and down on a longitudinally prepared sample that you have images of the known cross-sectional shape

Cross-sectioning Method #4

• Microscopy training should involve examining known samples in longitudinal view and cross-section to be able to recognize features

Physical Cross-sectioning

• Direct observation of sample morphology

• Embedding methods differ in how samples are packed, oriented, and their potential for distortion

• Choice of sectioning method is dependent on equipment, time, sample size, and data needs

Thank You

Fiber Cross Sectioning Sheet-Pack of 50SKU: 315-PK50https://www.mccrone.com/product/fiber-cross-sectioning-sheet-pack-of-50/

Sandra Koch, Ph.D.Senior Research Microscopist

skoch@mccrone.com • (630) 887-7100

Thank you for joining us.