Difference Between Freeze Fracture and Freeze Etching

The key difference between freeze fracture and freeze etching is that freeze fracture is the breaking of a frozen specimen to reveal internal structures, while freeze etching is the vacuum-drying of an unfixed, frozen and freeze-fractured biological sample.

Freeze fracture and freeze etching are two procedures that are helpful to study details of three-dimensional structures of biological samples. Freeze fracturing is always followed by freeze etching. Freeze fracturing involves the breaking the frozen biological sample, while freeze etching involves making a platinum-carbon replica of the fracture face through frozen cells.

CONTENTS

1. Overview and Key Difference
2. What is Freeze Fracture 
3. What is Freeze Etching
4. Similarities Between Freeze Fracture and Freeze Etching
5. Side by Side Comparison – Freeze Fracture vs Freeze Etching in Tabular Form
6. Summary

What is Freeze Fracture?

Freeze fracture is a technique of fracturing a frozen biological sample. This procedure helps to understand the structure of different cell structures with a detailed analysis of their functions. In freeze fracturing, the frozen sample is cracked using a microtome. A microtome is a knife-like instrument that cuts thin tissue slices. Freezing of the sample is done using liquid nitrogen.

Figure 01: Freeze Fracture Device

Freeze fracturing split membranes into two layers, visualizing the internal details of the membrane. Once the sample is fractured, it is necessary to employ freeze etching in order to preserve the fractured surfaces.

What is Freeze Etching?

Freeze etching is a technique of vacuum drying the frozen fractured biological sample. It involves making a platinum-carbon replica of the fracture face through frozen cells. Generally, freeze etching is done after freeze fracturing the biological sample. Once the replica is made, it is examined under electron microscopy. The freeze etching process is similar to the normal freeze-drying process of fruits and vegetables selling at grocery shops. Fixation and dehydration are not involved in freeze etching.

Figure 02: Freeze Etching

The vacuum prevents the contamination of the sample. Moreover, the ice of the surface evaporates away, exposing the fractures surface. Then a thin metal shadow is created on the surface. The metal film on the frozen fracture surface is reinforced with a carbon layer. In this way, the details of the fracture surface are revealed.

What are the Similarities Between Freeze Fracture and Freeze Etching?

• Freeze fracture is followed by freeze etching.
• They are done to biological samples.
• Moreover, the sample needs to be frozen prior to fracturing and etching.
• They are electron microscopy sample preparation procedures.

What is the Difference Between Freeze Fracture and Freeze Etching?

Freeze fracture is the procedure for breaking apart a frozen biological sample. Freeze etching is the making of a platinum-carbon replica of the fracture face through frozen cells. So, this is the key difference between freeze fracture and freeze etching.

Below is a summary of the difference between freeze fracture and freeze etching in tabular form.

Summary – Freeze Fracture vs Freeze Etching

In freeze fracture, a frozen biological sample is fractured or cracked. In freeze etching, the sublimation of surface ice under vacuum is done, and a platinum-carbon replica of the fractured surface is made. Thus, this is the difference between freeze fracture and freeze etching. Both procedures are done during the sample preparation for electron microscopy. These procedures help to understand the internal structures and three-dimensional structures of biological samples.

Reference:

1. WP; Chandler DE;Sharp. “Freeze Fracture and Freeze Etching.” Methods in Molecular Biology (Clifton, N.J.), U.S. National Library of Medicine, Available here.
2. “Freeze Fracture and Freeze Etching.” Radiology Key, 4 Mar. 2017, Available here.

Image Courtesy:

1. “BAF 060 Freeze Fracture Device (8513545772)” By NIAID – BAF 060 Freeze Fracture Device (CC BY 2.0) via Commons Wikimedia

2. “Freeze Fracture Replicas” By NIAID (CC BY 2.0) via Flickr

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