Objectives

Laboratory Instruments for Processing

A. Open vs. Closed Tissue Processors

Open Systems — Autotechnicon

The lecture identifies the Autotechnicon Mono, Duo, and Ultra as open processors.

Key characteristics:

  • Tissue is transferred from one reagent station to another.

  • Notched discs serve as the timing mechanism.

  • Reagents and tissues are exposed to the air.

  • Vacuum is available only on the Ultra model.

  • Heat is available on all three models but only at limited stations.

HTL+4312+P%26E+Lecture+2021.pptx

Closed Systems — VIP / Shandon PathCenter

Modern closed processors are:

  • Computerized and digital

  • Designed to minimize fumes

  • Move reagents to the tissue rather than moving tissue through reagent stations

  • Allow heat and vacuum to be programmed at different stages

  • Have dedicated paraffin chambers

HTL+4312+P%26E+Lecture+2021.pptx

Why closed systems are advantageous

Think:

Computerized + enclosed + programmable + controlled

They provide better control of processing conditions and reduce exposure to reagent fumes.


B. Factors Affecting Tissue Processing

The lecture emphasizes five major factors:

Agitation → Temperature → Viscosity → Pressure → Vacuum

These influence the interchange of fluids between tissue and processing reagents.

HTL+4312+P%26E+Lecture+2021.pptx

1. Agitation

Agitation increases the rate of reagent exchange with the tissue.

Examples include:

  • Rotation

  • Oscillation

  • Pumping systems

⚠ Agitation should not be excessively slow or excessively fast.

2. Temperature

Increasing temperature generally increases reagent penetration.

However:

  • Highly flammable reagents must be considered.

  • Processing temperature should be limited to approximately 45°C according to the lecture.

  • Higher temperatures may negatively affect staining and IHC assays.

HTL+4312+P%26E+Lecture+2021.pptx

3. Viscosity

Viscosity = resistance of a fluid or semisolid to flow.

  • Excessively viscous reagents → slower penetration.

  • Reagents that are too non-viscous may not properly prepare tissue for sectioning.

4. Pressure and Vacuum

According to the lecture, pressure and vacuum are not effective with dehydrating and clearing reagents.

They are useful during paraffin impregnation, particularly for porous tissues, because they assist infiltration.

HTL+4312+P%26E+Lecture+2021.pptx


C. Embedding Center / Modules

An embedding center is a modular apparatus that supplies:

  • Molten paraffin

  • Warm storage for embedding molds

  • Hot plate

  • Cold plate

  • Paraffin dispenser

HTL+4312+P%26E+Lecture+2021.pptx

Paraffin temperature

Molten paraffin is maintained approximately 2–4°C above its melting point.

Most manufactured paraffin has a melting point around:

58–60°C

Therefore, if paraffin melts at 58°C:

Instrument setting ≈ 60–62°C.

HTL+4312+P%26E+Lecture+2021.pptx

Cold plate

The cold plate rapidly cools the paraffin and helps produce a firm block while maintaining proper tissue orientation.


D. Laboratory Accessories

The lecture lists these accessories:

  1. Paraffin dispensers/baths

  2. Vacuum apparatus

  3. Forcep warmers

  4. Decalcifier

  5. Gross/dissection instruments

  6. Hydrometer

  7. Automatic cassette labelers

  8. Solvent recyclers

  9. Exhaust/fume hoods

HTL+4312+P%26E+Lecture+2021.pptx

Paraffin dispenser

Supplies molten paraffin during embedding.

Vacuum apparatus

Used to provide vacuum when applicable, particularly to assist paraffin infiltration of porous tissues.

Forcep warmer

Keeps forceps warm during embedding so the forceps do not prematurely cool or disturb the paraffin/tissue.

The lecture specifically instructs using warm forceps when selecting and orienting tissue.

HTL+4312+P%26E+Lecture+2021.pptx

Gross area

The area where tissue is initially examined, described, and appropriately placed into cassettes.

Gross examination involves describing the specimen and placing all or part of it into a plastic cassette for processing.

HTL+4312+P%26E+Lecture+2021.pptx

Hydrometer

Used to measure specific gravity of solutions.

Automatic cassette labeler

Provides identification/labeling of cassettes, helping maintain specimen identification and tracking.

Solvent recycler

Allows solvents to be recovered/recycled, improving efficient solvent use.

Exhaust/fume hood

Provides ventilation and helps maintain a safer working environment when handling reagent fumes.


2. Dehydration Principles and Actions

Definition

Dehydration = removal of water from tissue after fixation.

HTL+4312+P%26E+Lecture+2021.pptx

Why is dehydration necessary?

The tissue must eventually be infiltrated with an embedding medium.

Important concept:

Paraffin, celloidin, and plastics do not mix with water.

Therefore, water must be removed before infiltration.

HTL+4312+P%26E+Lecture+2021.pptx


Principle of dehydration

Dehydration is performed using a gradually increasing concentration of dehydrant.

Example:

70% ethanol → 95% ethanol → 100% ethanol

This gradual progression removes water while minimizing excessive tissue distortion.

HTL+4312+P%26E+Lecture+2021.pptx


Common Dehydrating Agents

The lecture lists:

  • Ethanol / ethyl alcohol (ETOH)

  • Methanol / methyl alcohol

  • Isopropanol / isopropyl alcohol

  • Butanol / butyl alcohol

  • Acetone

HTL+4312+P%26E+Lecture+2021.pptx


Universal Solvents

Universal solvents can perform two functions:

Dehydration + Clearing

Therefore, instead of using separate dehydrating and clearing reagents, one reagent can perform both functions.

Advantages

  • Saves time

  • Saves money

  • Miscible with:

    • Water

    • Dehydrants

    • Clearing agents

    • Most infiltration/embedding media

Disadvantages

  • Rarely used

  • Not recommended for delicate tissue

  • Tissue distortion may occur

  • Diffusion rate is relatively slow

The lecture attributes the slower diffusion to the molecular makeup of universal solvents.

HTL+4312+P%26E+Lecture+2021.pptx

Universal reagents listed

  • Dioxane

  • Tertiary butanol

  • Tetrahydrofuran (THF)

HTL+4312+P%26E+Lecture+2021.pptx


Quality Control — Dehydration

Watch for:

1. Reagent concentration

Dehydrating solutions must remain capable of removing water.

2. Tissue size

Large/thick specimens require appropriate processing schedules.

3. Reagent contamination

If dehydrant becomes excessively saturated with water, it becomes ineffective.

HTL+4312+P%26E+Lecture+2021.pptx


3. Clearing Principles and Actions

Definition

Clearing occurs after dehydration.

Some clearing solvents have a high refractive index that approaches that of dehydrated tissue proteins.

As tissue becomes immersed in the clearing agent, it becomes transparent or “clear.”

Important QC clue:

Opaque tissue = possible incomplete dehydration.

HTL+4312+P%26E+Lecture+2021.pptx


Purpose of clearing

Clearing replaces the dehydrating reagent with a fluid that is:

Miscible with both the dehydrating reagent AND the infiltration medium.

This is important because most dehydrants are not miscible with paraffin wax.

HTL+4312+P%26E+Lecture+2021.pptx

Easy way to remember:

Dehydration removes WATER.

Clearing removes the DEHYDRANT and prepares tissue for WAX.


Clearing Agents

The lecture lists:

  • Benzene

  • Toluene

  • Xylene

  • Chloroform

  • Cedarwood oil

  • Limonene derivatives

  • Aliphatic hydrocarbons

HTL+4312+P%26E+Lecture+2021.pptx


Universal vs. Non-universal clearing

Universal solvent

One reagent performs dehydration + clearing.

Non-universal approach

Uses separate reagents:

Dehydrant → Clearing agent → Infiltration medium


Quality Control — Clearing

The major things to watch:

  • Complete dehydration before clearing

  • Adequate clearing time

  • Appropriate reagent volume

  • Reagent contamination

  • Tissue appearance

Remember:

Opaque areas can indicate incomplete dehydration.


4. Problem-Solving in Dehydration & Clearing

The lecture specifically focuses on:

TIME + VOLUME + CONTAMINATION

A. Time

Processing schedule should be selected according to the tissue type.

Examples include:

  • Surgical tissue

  • Clinical biopsy tissue

  • Fatty tissue

HTL+4312+P%26E+Lecture+2021.pptx

If tissue isn’t adequately processed, consider whether the schedule is too short.


B. Volume

The lecture recommends reagent volume approximately:

15–20× the volume of the tissue.

HTL+4312+P%26E+Lecture+2021.pptx

Exam memory:

Tissue volume × 15–20 = reagent volume


C. Contamination

Dehydrant contaminated with water

→ becomes saturated with water
→ becomes ineffective at removing additional water.

Clearing agent contaminated with ethanol

→ becomes contaminated with water
→ becomes ineffective as a clearing agent.

HTL+4312+P%26E+Lecture+2021.pptx


5. Infiltration & Embedding

Infiltration — Definition

Infiltration = saturation of tissue cavities and cells with a supporting substance.

Usually, this substance is the same or related to the final embedding medium.

For paraffin processing, tissue is immersed in wax while it is fluid/hot; the wax becomes solid when cooled.

HTL+4312+P%26E+Lecture+2021.pptx

Purpose

Replace the clearing reagent with the infiltration medium and prepare the tissue for embedding.


Embedding — Definition

Embedding = surrounding tissue with a medium that becomes sufficiently solid to provide external support during sectioning.

Examples include:

  • Agar

  • Gelatin

  • Wax

HTL+4312+P%26E+Lecture+2021.pptx

Purpose

To provide a solid matrix with enough rigidity to allow thin sections to be cut without damaging the tissue.


Infiltration & Embedding Media

The lecture lists:

  • Paraffin

  • Carbowax

  • Celloidin

  • Glycol methacrylate (GMA)

  • Agar & gelatin

  • Epoxy resins

  • Double embedding

  • OCT / frozen sections

    Medium

    Key point

    Paraffin

    Routine histology embedding medium

    Carbowax

    Alternative embedding medium

    Celloidin

    Provides firm support; useful in specialized processing

    GMA

    Plastic embedding medium

    Epoxy resin

    Plastic/resin medium; associated with TEM

    Agar/Gelatin

    Can provide support, including double-embedding approaches

    OCT

    Used for frozen sections

    Double embedding

    Uses more than one embedding medium/process

    Quality Control — Infiltration & Embedding

    Important checks include:

    Before embedding

    * Verify specimen identification.

    * Check tissue pieces against the worksheet.

    * Select the correct mold.

    * Ensure sufficient wax surrounds the tissue.

    During embedding

    * Keep tissue and forceps warm.

    * Maintain correct orientation.

    * Prevent tissue from cooling prematurely.

    * Use the cold plate to solidify the block.

    After embedding

    * Verify the block.

    * Verify the label.

    * Cross-check with the worksheet. HTL+4312+P%26E+Lecture+2021.pptx

    ⸻

    Problem Solving in Infiltration & Embedding

    Remember:

    TIME + VOLUME + TEMPERATURE + CONTAMINATION

    Time

    Insufficient processing/infiltration can prevent adequate penetration.

    Volume

    There must be sufficient reagent/media relative to tissue volume.

    Temperature

    Paraffin must remain appropriately molten during infiltration/embedding.

    For most manufactured paraffin:

    MP ≈ 58–60°C

    Instrument setting:

    MP + 2–4°C. HTL+4312+P%26E+Lecture+2021.pptx

    Contamination

    Contaminated processing reagents/media can interfere with proper tissue processing and embedding.

    ⸻

    Paraffin Embedding Procedure

    This is especially important to know for an exam.

    Step 1

    Open cassette and compare the tissue pieces with the worksheet.

    Step 2

    Select an appropriate mold.

    Allow approximately 2 mm of surrounding wax.

    Step 3

    Fill mold with paraffin.

    Step 4

    Use warm forceps to select the tissue.

    Don’t allow tissue to cool in the air.

    Step 5

    Place/chill mold on cold plate while orienting the tissue.

    Step 6

    Insert the identifying label or labeled cassette/embedding ring.

    Step 7

    Cool the block on the cold plate.

    Step 8

    Remove the block from the mold.

    Step 9

    Cross-check:

    BLOCK + LABEL + WORKSHEET HTL+4312+P%26E+Lecture+2021.pptx

    ⸻

    Specimen Orientation

    Your objective specifically requires proper orientation of:

    * Skin

    * Tubular structures

    * Structures with walls

    * Bone HTL+4312+P%26E+Lecture+2021.pptx

    The lecture contains an Embedding Orientation section, but the extracted text does not provide the detailed orientation diagrams/labels. HTL+4312+P%26E+Lecture+2021.pptx

    For your exam, this is an area where the actual slide image/diagram matters, so I would study the orientation figures from the PowerPoint rather than relying on text alone.

    ⸻

    ⭐ HIGH-YIELD EXAM MEMORIZATION

    If you are short on time, memorize these:

    Processing

    Agitation + Temperature + Viscosity + Pressure + Vacuum

    Closed processor

    Computerized + digital + enclosed + programmable heat/vacuum + dedicated paraffin chambers

    Dehydration

    Removes water from fixed tissue.

    70% → 95% → 100% ethanol

    Why dehydrate?

    Embedding media such as paraffin, celloidin, and plastics don’t mix with water.

    Universal solvent

    Dehydrates + clears

    Advantages:

    Time + money saved

    Disadvantages:

    Slow diffusion + possible tissue distortion + not ideal for delicate tissue

    Clearing

    Replaces dehydrant with a fluid miscible with both dehydrant and infiltration medium.

    Clearing clue

    Opaque tissue → incomplete dehydration may be present.

    Reagent volume

    15–20× tissue volume

    Dehydrant contamination

    Too much water → ineffective dehydration

    Clearing contamination

    Ethanol/water contamination → ineffective clearing

    Infiltration

    Fills/saturates tissue spaces with supporting medium.

    Embedding

    Surrounds tissue with a solid-supporting medium.

    Paraffin

    58–60°C melting point

    Set instrument:

    2–4°C above melting point

    Embedding QC

    Correct tissue + correct orientation + correct label + correct worksheet