The Life-Changing Future of the Prosthetic Hand Development

Prosthetic hands are not just engineering designs; they are always a sensitive topic for those requiring them. A prosthetic hand means the replacement of a missing hand for a hand amputee. It will give them a second life and give them hope to come back to a normal life again.

Over the years, different developers have developed prosthetic hands in different ways. Some are focusing on mechanical engineering designs like mechanisms, new concepts, and new actuation methods. Some are working on controlling things like active and passive motions. Signal conditions also played a major role in the development of prosthetic devices like electromyograms (EMG), electroencephalograms (EEG), and multi-model or hybrid control. However, everyone is trying to develop underactuated devices with a low number of actuators and a higher degree of freedom.

Throughout this article, the anatomy of the human hand, grasping patterns of human hands, prosthetic hand development, challenges, and the future of prosthetic hands will be discussed.

Anatomy of the Human Hand

The anatomy of a human hand is a complicated and impressive creation created by nature. A single hand has 27 bones and 19 joints, and those can be classified into three layers. Carpals are the first layer of the human hand, and metacarpals are the second layer of the bone structure. The third layer is the phalange bone layer. To actuate these bone structures, there are tendon and muscle systems. The biological wrist hand has combinations of 27 degrees of freedom for obtaining different grasping patterns.

Finger motions and hand motions are very important for day-to-day life. The human hand has different motion patterns, like “Flexion and Extension” and “Abduction and Adduction” motion for all five fingers. The thumb finger has a special motion pattern compared to the other four fingers called the “Retroposition and Opposition” motion. Other than these basic motion patterns, “bending and flattening” motion and finger “hyperextension” are also important finger motion patterns for activities in daily living.

Types of Upper Limb Amputations

Upper limb amputation is determined by the hand’s lost location. The following are the amputation types:

• Partial Hand Amputation: Loss of fingers or portion of the hand
• Wrist Amputations: Loss of the hand at the level of the wrist
• Transradial Amputation: Loss of the hand below the elbow

Other than these types, transhumeral, shoulder disarticulation, and forequarter amputations are the other upper limb amputation types.

Based on the amputation type, prosthetic hand designs are also changed, and it can be a single finger or a complete hand prosthesis. However, the size of the fingers and hand depends on the amputee’s body scale and body dimensions. Most of the time, prosthetic devices are developed for the average body dimensions of humans. Human Body dimensions are always related to ergonomic data.

Grasping Patterns of Human Hand

Grasping means how we feel about the nature around us and it’s just not a finger motion pattern of the human hand. It connects with the human mind and feelings.

However, there are different classifications of grasping patterns, like power, lateral, and precision patterns. To obtain actual human hand motions, obtaining different grasping patterns is essential for prosthetic hands. When we are performing grasping patterns in our day-to-day lives, all fingers are moving simultaneously.

So, different developers were trying to get all the grasping patterns with different mechanical and actuation methods. Linkage mechanisms are the most common and popular methods for finger flexion and extension motions. Other than that, gear systems, pneumatic muscles, and hydraulic systems are also popular methods.

Prosthetic Hand Development

Prosthetic hand development is a challenging project due to various factors. Whether a prosthetic hand is a commercial hand or an R&D project, it should have human hand anthropometry. Meeting the human body’s dimensions is challenging work with mechanical designs in most of the prosthetic device designs.

The cost of the hand should be less, and the weight of the hand should also be less. To reduce the hand’s weight, cost, and complexity, passive and underactuated mechanisms are very popular in the prosthetic industry.

Most of the designs are developed using CAD software for stress and motion simulations, and those play a critical role in designing. Motion simulation gives the range of motion of the prosthetic hand and all the movements of the fingers. Stress simulations are used to identify the stress-critical parts. Most of the Prototype Prosthetic Hand are developing using Additive Manufacturing Processes, Modern Advance Manufacturing Processes and CNC Machining Technologies.

Challenges of Prosthetic Hand Development

The major challenge that developers are facing is the size of the standard components (ex. motors and actuators) and the number of actuators. There are 27 DOFs in the wrist, and 27 actuators cannot be used due to the size of the components and control difficulties. So, it’s always trying to go for underactuated and passive mechanisms like linkage mechanisms, spring systems, and many other pneumatic, hydraulic, and shape memory alloy systems.

Over the years, different finger mechanisms for flexion and extension motions and other mechanisms have been developed. Linkage mechanisms (Four Bar, Five Bar, and Multi Bar) and tendon base systems are prevalent in flexion and extension mechanisms. The thumb-finger mechanisms also have different linkage mechanisms.

Future of Prosthetic Hands

Almost all the finger motions have been identified and replaced with different mechanisms and actuators. But the human hand has two things: grasping capability, which is needed for daily activities. The other one is feeling the grasping of objects. For example, Feeling the Shape of the grasped object, temperature difference, Feeling of solid and liquid, vibration, etc. These feelings are very important, and they will give the real feeling of living to hand amputees.

Most prosthetic hands have been developed to address grasping capabilities, but very little research has been done on the sensible part of the prosthetic hand. However, grasping feelings is just as vital as grasping ability.

Another thing is controlling the prosthetic hands. Almost all the novel prosthetic hands are controlled with EMG and EEG signals. Extracting biosignals and controlling them are challenging due to the varying signal strengths of the amputees. Before implementing prosthetic devices, amputees should have the proper training for biosignal extraction, control, and calibration of the devices.

Now it is time to change the prosthetic hand development for touching and feeling. It will be very challenging because it is very complicated with the human nervous system. But it will be a game-changing step for the industry and all humans.

Thank you to everyone who read my article regarding prosthetic hands. There are a lot of subjective words in this article. However, I am trying to deliver on the current development and future direction of prosthetic hands.