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How fingerprints get their unique whorls

This Q intrigued both scientists and common people for ages.

Now an international team of scientists with a myriad of backgrounds has revealed the process by which unique fingerprints develop. In their research, published open access in the journal Cell, the group studied the development of fingerprints in mice and humans.

Prior study of fingerprints has shown that their purpose is to provide added grip and to enhance sensitivity. Scientists and lay people alike have known for a long time that in humans, they are unique—even identical twins have different prints. Why this is the case has remained a mystery. In this new effort, the researchers have solved the mystery.

Graphical abstract. Credit: Cell (2023). DOI: 10.1016/j.cell.2023.01.015

To better understand how fingerprints develop and why they differ between people, the group tracked their formation in fetal mice and studied the genetics behind their development. They found what is known as a Turing reaction-diffusion system.

Back in the 1950s, Alan Turing proposed a development process by which leaves grow in unique arrangements. He suggested that some molecules in a developing system promote cell growth while others actively work to prevent growth. The result was two forces acting against one another on adjoining cells. That led to the creation of ridges, which led to unique formations, such as stripes on a zebra or whorls on fingertips.

By watching as fingerprints developed on fetal mice (and human cells in a petri dish), the researchers could see that ridges developed and worked against one another in three different parts of the end of the finger—the tip, the center, and the part closest to the top knuckle. As different cell groups pushed against one another relative to their physical location, whorl patterns emerged.

The random placement of the fingers in the womb as the cells push against one another to form ridges is what makes the patterns so random. And that is why even identical twins have different prints. The team also found that the initial stages of fingerprint development were nearly identical to those of hair follicles. The only difference was that with hair follicles, cells deeper below the skin surface were involved in the process.

James D. Glover et al, The developmental basis of fingerprint pattern formation and variation, Cell (2023). DOI: 10.1016/j.cell.2023.01.015

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Revised: Fingerprint classification based on gray-level fuzzy clust...

https://www.researchgate.net/figure/Major-Fingerprint-Types-Whorl-A...

The 8 Types of Fingerprints ( used in crime detection)

People have various types of fingerprints, including loops, whorls, and arches. Each type is unique and can be used to identify someone to grant them access to sensitive information and secure areas.

loop-fingerprints

Loop Fingerprints

Loops are the most common type of fingerprint, accounting for around 60% to 70% of all prints. They are characterized by a circular or oval-shaped pattern.

The prints recurve to form a loop shape. There are three subcategories of loop fingerprints:

Radial Loops: Named after the radius bone, these loops join the hand on the same side as the thumb, flowing in a downward slope from the little finger toward the thumb.
Ulnar Loops: This name refers to the ulna bone. The loop has a circular pattern, running from the thumb toward the pinky.
Double Loops: As the name suggests, these loops have two separate loop formations and at least one recurving ridge within the inner pattern.

whorl-fingerprints

Whorl Fingerprints

Whorls are the second most common type of fingerprints, making up around 30% of all. They are characterized by a spiral-like pattern.

There are three different groups of whorl prints:

Plain Whorl: These include concentric circles, with one complete circle and two deltas.
Central Pocket Loop Whorl: This is a loop with a whorl at the end of it, which can be oval, spiral, or circular.
Accidental Whorl: As the name implies, this type is irregularly shaped.

Arch Fingerprints

Arches are the least common type of fingerprints, making up around 10% of all. They are characterized by a wave-like pattern. They occur in two different styles:

Plain Arch: The pattern starts on one side and slightly cascades in an upward direction.
Tented Arch: The arch lies in the center ridges and does not show a continuous arch.

As you can see, there are several types of fingerprints. And given the uniqueness and accessibility of fingerprints, the process of using fingerprint identification technology is easy and effective for enhancing the security protocols you have in place.

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(The above article 's written by me. As I found another one related to this written by another person, I added it below)

Your fingerprint is actually 3D—research into holograms could improve forensic fingerprint analysis

Fingerprints have visible ridge structures, such as arches (left), whorls (middle) and loops (right), but at the microscopic level they have much finer patterns and structures. Credit: ValeriyPolunovskiy/Wikimedia Commons, CC BY-SA

When you use your fingerprint to unlock your smartphone, your phone is looking at a two-dimensional pattern to determine whether it's the correct fingerprint before it unlocks for you. But the imprint your finger leaves on the surface of the button is actually a 3D structure called a fingermark.

Fingermarks are made up of tiny ridges of oil from your skin. Each ridge is only a few microns tall, or a few hundredths of the thickness of human hair.

Biometric identifiers record fingermarks only as 2D pictures, and although these carry a lot of information, there's a lot missing. A 2D fingerprint neglects the depth of the fingermark, including pores and scars buried in the ridges of fingers that are difficult to see.

I'm an educator and scientist who studies holography, a field of research that focuses on how to display 3D information. My lab has created a way to map and visualize fingermarks in three dimensions from any perspective on a computer—using digital holography.

Fingermark types

Scientists categorize fingermarks as either patent, plastic or latent, depending on how visible they are when left on a surface.

Patent fingermarks are the most visible type—bloody fingerprints at crime scenes are one example. Plastic fingermarks are found on soft surfaces, such as clay, Play-Doh or chocolate bars. The human eye can see both patent and plastic fingermarks quite easily.

The least visible are latent fingermarks. These are usually found on hard surfaces such as glass, metals, woods and plastics. To make them out, a fingerprint examiner has to use physical or chemical methods such as dusting with powder, creating chemical reactions with appropriate reagents or cyanoacrylate fuming.

Cyanoacrylate makes super glue in its liquid form, but as a gas it can make latent fingermarks visible. Researchers develop the prints by letting cyanoacrylate vapor molecules react with components in the latent fingerprint residue.

The geometric details on fingermarks are categorized into three levels. Level 1 encompasses visible ridge patterns, so loops, whorls and arches. Level 2 refers to minutiae or small details, such as bifurcations, endings, eyes and hooks.

Finally, Level 3 features, such as pores, scars and creases, are too small for the human eye to resolve. This is where optical techniques like holography come in handy, since optical wavelengths are in the order of microns, small enough to make out small details on an object.

Developing fingermark holograms

Since fingermarks are usually collected as 2D pictures, and holograms display 3D information, my team wanted to develop a technique that can show all the 3D topological characteristics of a fingermark.

To do this, we've been collaborating with Akhlesh Lakhtakia's group at Penn State. They developed a specialized technique that deposits a nanoscale columnar thin film layer, called a CTF, on top of the fingermark to develop and preserve it.

Columnar thin films are dense pillars of glassy material that uniformly cover the fingermark, like a dense growth of identical trees in a forest. Just as the tops of these trees would reflect the topology of the ground, the tops of these columnar thin films replicate the 3D structure of the fingermarks on which they are deposited.

To make a hologram of something like a 3D fingermark, researchers split light from a laser into two parts. One part, called the reference wave, shines directly on a digital camera. The other wave shines on the object, in this case the fingermark.

If the object is reflective, the reflected light is also directed to the digital camera and superimposed on the reference wave.

The superposition of waves—both from the reference and the object—creates an interference pattern, which is called a hologram. In digital holography, this hologram, which is a 2D picture, is recorded in the digital camera. Researchers then import the hologram to a computer, where they can use the physical laws of wave propagation to figure out where the light waves from the laser bounced off different parts of the object.

This process allows them to reconstruct the object as a 3D picture.

So, the reconstructed hologram has all the 3D details of the object, and you can now visualize the 3D object on a laptop from any perspective.

Picking up fingermarks

In 2017, our collaboration reported our first results, where we made 3D pictures of latent fingermarks using the CTF technique. We recorded holograms of the CTF-developed fingermarks with two different wavelengths of light—green and blue—generated from a laser. Using two different wavelengths allowed us to make out tiny details such as pores in the 3D reconstructions.

Lakhtakia's research group has deposited hundreds of fingermarks on glass, wood and plastic. They've then let them age in different environments, at various temperatures and humidity levels, before coating them with CTF film to pick up the fingerprint. My group records the digital holograms of these fingermarks and visualizes them in 3D on a computer.

We have also started working on a better 3D fingermark analysis plan to help identify crime suspects.

The Miami Valley Regional Crime Lab in Dayton, Ohio, has graded the quality of the fingermarks captured by Lakhtakia's research group. It will also help us develop a new method for grading the 3D holographic reconstructions, something that does not currently exist. This may involve creating categories to classify how clear the 3D renderings of the fingermarks are.

The use of fingerprints as unique identifiers has a long history, going back to ancient Babylonian and Chinese civilizations. They've been used for forensic purposes since the late 1890s, starting in Calcutta, India. Our work aims to build on this rich history and use cutting-edge technologies to improve fingermark analysis.

Author: Partha Banerjee

This article is republished from THE CONVERSATION under a Creative Commons license. Read the original article.