Prosthetics with a Sense of Touch: The Bridge Between Technology and Sensation

For individuals with prosthetics, experiencing the true sensation of touch has long been a unreachable goal. Breakthroughs in technology have now made prosthetics with a sense of touch a part of today’s reality, unlocking new levels of function and freedom. This article examines how advanced materials and AI contribute to this sensory revolution and the way it is changing lives.

Key Takeaways

  • Advancements in prosthetics now include sensory feedback capabilities through haptic technology, e-skin, and highly conductive nanomaterials, alongside AI that learns user behavior for a personalized and intuitive experience.
  • Researchers face challenges in replicating dense nerve information and are exploring electrical stimulation, myoelectric prostheses, and brain-computer interfaces to improve control and feedback in prosthetic limbs.
  • Despite significant advancements in prosthetic technology, challenges remain regarding cost, accessibility, and the quality of sensory feedback; ongoing research aims to address these issues for broader adoption.

Advancements in Sensory Prosthetics

A robotic hand shaking hand with a human hand
A robotic hand shaking hand with a human hand

The field of prosthetics has seen remarkable advancements, particularly in the realm of sensory feedback. Haptic technology and electronic skin (e-skin) have emerged as advancements, offering a new realm of possibilities for prosthetic limbs. E-skin is embedded with sensors that act as synthetic nerve endings, detecting stimuli such as texture and temperature, and relaying impulses back to the wearer’s peripheral nerves.

These technological innovations have led to the development of bionic skin sensitive to light touches, haptic feedback via vibrations, and pressure sensors for grip sensation. The integration of highly conductive nanomaterials has further improved feedback mechanisms. These advancements are transforming the prosthetic user’s experience, enabling more intuitive and less effortful interaction with their environment.

Machine Learning and Artificial Intelligence

The prosthetics industry has been revolutionized by the introduction of machine learning and artificial intelligence (AI). It have introduced a level of adaptability in artificial limbs, such as prosthetic limbs, that was once unimaginable. Machine learning algorithms incorporated into these devices learn and adapt to the user’s movement patterns and intentions, creating a more personalized and intuitive experience.

AI-driven prosthetics can:

  • Adjust grip strength and dexterity by learning from the user’s behavior in real-time
  • Effectively reduce the cognitive burden on the wearer
  • Enhance the internal models that prosthetic devices learn from feedback
  • Significantly boost their real-time execution and output performance.

Material Innovations

Prosthetic skins made from silicone compounds have revolutionized prosthetics. These skins imitate the look and feel of human skin closely, leading to a more realistic experience for the user. The development of a malleable, self-healing, and recyclable material infused with silver nanoparticles represents an enhancement in prosthetic skin functionality.

The use of rubber and silicone in prosthetic hands, like the Ability Hand’s fingers, provides users with increased flexibility and durability. This plays a key role in empowering users to confidently participate in a wide range of activities, from daily tasks such as carrying a shopping bag to extraordinary feats like playing musical instruments.

The Science Behind Sensory Prosthetics

Sensory feedback as illustrated by AI of two hands making motion
Sensory feedback as illustrated by AI of two hands making motion

The science behind sensory prosthetics is a field that has captured the attention of researchers worldwide. The potential to dramatically enhance prosthesis utility has led to a heightened focus on sensory feedback in upper-limb prosthetics. However, challenges remain. Current sensory interfacing devices face hurdles in replicating the dense information flow and compact size of normal nerves.

Despite these challenges, progress is being made. The majority of clinically available prosthetic devices fail to transmit the vast majority of sensory information conveyed by peripheral nerve axons, including those related to the spinal cord, resulting in a significant feedback gap. Yet, with every challenge comes an opportunity for innovation. And in the realm of sensory prosthetics, these opportunities are being capitalized on through electrical stimulation, myoelectric prosthesis, and brain-computer interfaces.

Electrical Stimulation

Electrical stimulation, particularly in the form of Transcutaneous Electrical Nerve Stimulation (TENS), is one approach being used to induce somatic sensations in amputees. By stimulating the nerves present in the residual limbs, TENS can recreate sensations tied to specific amputation site locations.

The effectiveness of sensory feedback from TENS is significantly enhanced when stimuli are targeted at the phantom hand map (PHM) on the stump. Remarkably, repeatability of induced sensory positions using TENS can achieve 100% accuracy across multiple sessions when applied according to precise PHM distribution.

Furthermore, long-term implanted electrodes that provide natural electrical feedback have shown potential in improving users’ performance in intricate tasks like handling small objects by replicating the sensations of touch.

Myoelectric Prosthesis

Myoelectric prosthetic devices represent another significant advancement in the field. These devices operate based on the electrical activity present in the remaining limb muscles, with electric motors powered by an external source. To harness a myoelectric prosthesis, a certain threshold of microvolt signal from the musculature must be met, alongside a functional evaluation to ensure cognitive ability for daily use.

Educating users on the correct operation within the device’s specifications, including weight limits and environmental conditions, is an important aspect of training. AI is utilized to enhance the interpretation of myoelectric sensor data, creating a sophisticated connection between user muscle activity and prosthesis movement and control. Furthermore, hybrid myoelectric systems extend the functionality to control multiple joints simultaneously for amputations above the elbow.

Brain-Computer Interfaces

The frontier of prosthetics science lies in Brain-Computer Interface (BCI) technology, which connects directly to the human brain. BCIs record movement-related activity from the motor cortex, even after paralysis, permitting control of devices such as robotic arms. Machine learning, a subset of AI, deciphers neural signals from the user’s body, enabling the prosthetic to replicate movements as instructed by the user’s thoughts.

Intracortical microelectrode arrays are being explored for their ability to grant high degrees of freedom in controlling robotic prosthetic arms. At the same time, somatosensory feedback is being tested through intracortical microstimulation, aiming to refine the BCI control of prosthetics. However, a major hurdle in BCI implementation is ensuring long-term biocompatibility for implanted electrodes, as there is potential for adverse body reactions and fibrotic tissue development.

Notable Research Projects and Institutions

Dedicated researchers and institutions are propelling the evolution of sensory prosthetics. Significant contributions have come from institutions such as John Hopkins University, Ossur, and the University of Utah. Driving the evolution of sensory prosthetics through a combination of research, collaboration, and clinical studies.

The University of Utah, for instance, is advancing touch-sensitive prosthetics through collaborations across departments and with neurotechnology companies, backed by DARPA and the National Science Foundation. Companies like Ossur collaborate with top scientists and institutions to gather essential clinical evidence and health economics data. These collaborations are important in ensuring that the performance of hand prostheses in real-life situations is as effective as it is in controlled lab environments.

John Hopkins University

Johns Hopkins University has been at the forefront of developing advanced prosthetics. Their work on the Modular Prosthetic Limb offers human-like strength and sensory feedback capabilities. The Revolutionizing Prosthetics program, established in 2006, is geared towards restoring functional capabilities in individuals with upper-limb amputations.

In addition, the Ability Hand developed by Psyonic provides users with:

  • Touch feedback through vibrations, allowing them to sense when they touch an object and to assess its manipulation strength
  • The fastest bionic hand on the market
  • 32 different grips, which enhances the ability of users to perform a wide array of tasks.

Ossur

Ossur’s current clinical trials include hand and leg prostheses that incorporate sensory feedback mechanisms to offer a more natural experience to users.

University of Utah

The University of Utah has made significant strides in the development of touch-sensitive prosthetics. Dr. Gregory Clark is leading research related to touch-sensitive prosthetics designed for individuals with upper limb amputations. The LUKE Arm, currently under development by Dr. Clark and his team, features touch-sensitive capabilities to provide sensory feedback to the user.

Dr. Clark’s team has plans for future versions of the LUKE Arm which include making the prosthetic completely portable and wireless. This will further enhance wearer independence and mobility.

Real-Life Applications and Benefits

Young person holding an apple between his advanced robotic fingers prosthetic
Young person holding an apple between his advanced robotic fingers prosthetic

Sensory prosthetics have extensive real-life applications and benefits. Prostheses with sensory feedback enhance the psychological integration of the device, with users commonly referring to the prosthetic as ‘my hand’ or ‘my fingers’. Users often experience a sense of completeness and higher self-esteem, fostering stronger body ownership.

Prosthetic users, with the aid of sensory feedback, can:

  • Grasp objects in a more natural and efficient way, thereby reducing the reliance on continual visual hand monitoring
  • Perform delicate tasks with accurate grip force feedback, leading to improved control and user confidence
  • Experience more confident social interactions, such as handshakes, which are integral to personal and professional communication

The ability to feel objects, a basic sense, facilitates these benefits.

Increased Independence

Increased independence stands as one benefits of sensory prosthetics. Users experience more natural and intuitive control, substantially reducing the cognitive burden during many different tasks.

The ability to perceive and apply precise pressures allows users to carefully manipulate objects, enhancing their confidence in engaging in everyday activities.

Moreover, the sensory experience generated by these prosthetics, despite being different from natural sensation, has been reported to improve users’ emotional well-being. This in turn, promotes engagement with a broader range of activities.

Enhanced Social Interaction

Moreover, social interactions are greatly enriched by the presence of sensory feedback. Prosthetic hands with sensory feedback allow for a more natural and pleasant experience of touch, enhancing social interactions that involve physical contact. This feedback improves interpersonal connections by providing users with the confidence to engage in social gestures like handshakes, which are an integral part of the human touch in our daily interactions.

Users of the Ability Hand have reported the following benefits:

  • Feeling that a part of them has come back
  • Enhanced overall experience of social interactions
  • More frequent and confident social engagements

Despite occasional control issues, such as difficulty in releasing a handshake, the Ability Hand, has proven to be a valuable tool for improving social interactions.

Challenges and Future Directions

While sensory prosthetics have made considerable advancements, they are not without challenges. Some of them include:

  • Identifying the optimal amount of sensory feedback required for amputees to use their prosthetic limbs effectively
  • Tackling the concerns of cost and accessibility
  • Enhancing the quality and resilience of the feedback

These challenges need to be addressed in order to further improve sensory prosthetics.

Cost and Accessibility

The cost of advanced prosthetics, such as those with multiple gripping fingers and enhanced functions, can reach up to and excedd $50,000. This renders them unaffordable for many, including those in developing countries. Furthermore, amputees living in developing countries encounter substantial obstacles in accessing proper healthcare and prosthetics due to economic constraints and the scarcity of public health facilities and funding.

Access to advanced prosthetic devices, such as an artificial hand with sensory feedback technology, is currently limited to highly specialized institutions, which excludes a large portion of patients with a missing hand who could otherwise benefit from such innovations. Hence, there is a pressing need for affordable prosthetics, such as the Ability Hand, which aim to empower amputees, including those in need of a prosthetic arm, to resume daily activities that were once thought impossible.

Improving Sensory Feedback

The enhancement of sensory feedback in prosthetics continues to pose a challenge. Innovative materials like self-healing polyamine-based e-skin and hybrid materials with inorganic particles have been used to improve the durability and effectiveness of sensory feedback in prosthetics. However, some users have expressed the need for adjustable feedback intensity.

Strategies like Regenerative Peripheral Nerve Interface (RPNI) show promise for sensory feedback restoration. Some potential benefits of RPNI include:

  • Muscle graft wrapped around peripheral nerves can transmit motor control and sensory feedback
  • Restoration of sensory feedback can improve the functionality of prosthetic limbs
  • RPNI has the potential to enhance the quality of life for individuals with limb loss

However, optimization of the surgical procedure is needed before widespread clinical adoption.

Frequently Asked Questions

Are there prosthetics that can feel?

Yes, researchers have been developing prosthetic limbs that can provide natural sensory feedback, allowing users to better control the device and regain a sense of agency over their robotic limb.

What are the four types of prosthetics?

The four types of prosthetics are transradial, transhumeral, transtibial, and transfemoral, each serving a different function depending on the missing body part.

Can bionic limbs feel?

Bionic limbs can indeed provide sensation to the user, allowing for intuitive control and natural flow of sensation from the artificial device. This is achieved through connection of the remaining nerves or muscles above the level of amputation to the prosthetic device sensors.

What are sensory prosthetics?

Sensory prosthetics are devices that enhance the user’s interaction with their environment by providing sensory feedback, improving natural perception and intuition.

How do machine learning and AI enhance the functionality of prosthetics?

Machine learning and AI enhance prosthetics by enabling them to learn and adapt to the user’s movement patterns and intentions, providing a more personalized and intuitive experience. This helps improve functionality and user experience significantly.

Conclusion

Sensory prosthetics represent a revolution in technology, bridging the gap between mechanical devices and human sensation. Advancements in machine learning and AI, innovative materials, and research efforts by institutions are driving this evolution. These advancements have not only enhanced the functionality of prosthetics but also significantly improved the quality of life for amputees. Despite the challenges that lie ahead, the future of sensory prosthetics is bright, promising to bring life-changing benefits for countless individuals around the world.

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