Medical implants are devices or tissues that are placed inside or on the surface of the body. Many implants are prosthetics, intended to replace missing body parts. Other implants deliver medication, monitor body functions, or provide support to organs and tissues.

Some implants are made from skin, bone or other body tissues. Others are made from metal, plastic, ceramic or other materials.

Implants can be placed permanently or they can be removed once they are no longer needed. For example, stents or hip implants are intended to be permanent. But chemotherapy ports or screws to repair broken bones can be removed when they no longer needed.

The risks of medical implants include surgical risks during placement or removal, infection, and implant failure. Some people also have reactions to the materials used in implants.

All surgical procedures have risks. These include bruising at the surgical site, pain, swelling and redness. When your implant is inserted or removed, you should expect these types of complications.

Infections are common. Most come from skin contamination at the time of surgery. If you get an infection, you may need to have a drain inserted near the implant, take medication, or even have the implant removed.

Over time, your implant could move, break, or stop working properly. If this happens, you may require additional surgery to repair or replace the implant.

If you learn that you need a medical implant, you should ask your doctor the following questions before agreeing to the procedure:

• Will my implant be permanent or removable? If the device is permanent, find out how long it should last. If the device is removable, find out how long it will be implanted in you and what factors will determine when it can come out.
• What material will the implant be made from? Make sure you are not allergic to any of the components in the implant.
• How many of these procedures have you done? The more experience a doctor has with inserting implants, the better the outcome may be.
• What are the complication rates from the procedure? Make sure you understand the risks of the surgery, infection, and device failure.
• What are the benefits of the procedure? Make sure you understand how the device will benefit you and if it will affect your quality of life.

A look at how prosthetics have changed over time and how NIH supports innovation

Millions of people in the United States are currently living with limb loss. This number is expected to grow as the population ages and rates of diseases such as diabetes that can cause dysvascularity (poor blood circulation in the legs) increase.

For people with limb loss, prosthetic devices improve quality of life by providing movement and independence. Early prosthetics were uncomfortable to wear, but they may have helped people return to work and feel accepted in their daily lives. We’ll explore how these devices have changed over time, from clunky, early designs and materials to modern innovations—some of which NIH-supported researchers are developing.

When were prosthetics invented, and what were they used for?

Historians don’t know for certain if the first prosthetics were functional or for appearances. According to Katherine Ott, Ph.D., curator for the Division of Medicine and Science at the Smithsonian Institution’s National Museum of American History, this is partly because different cultures have their own ideas about what makes a person whole.

The oldest known prosthetics are two different artificial toes from ancient Egypt. One prosthetic toe, known as the “Greville Chester toe,” was made from cartonnage, which is a kind of papier-mâché made from glue, linen, and plaster. It is thought to be between 2,600 and 3,400 years old, though its exact age is unknown. Because it doesn’t bend, researchers believe it was cosmetic.

The other prosthetic, a wooden and leather toe known as the “Cairo toe,” is estimated to be between 2,700 and 3,000 years old. It is thought to be the earliest known practical artificial limb due to its flexibility and because it was refitted for the wearer multiple times.

Approximately 300 years later—300 B.C.—in Italy, an ancient Roman nobleman used a prosthetic leg known as the “Capua leg.” The leg was made of bronze and hollowed-out wood and was held up with leather straps.

Other known early prosthetics include artificial feet from Switzerland and Germany, crafted between the 5th and 8th centuries. These were made from wood, iron, or bronze and may have been strapped to the amputee’s remaining limb.

How war—and the U.S. military—inspired prosthetic advances

Soldiers who lost their limbs in battle often used early artificial limbs made of wood or iron. For example, about 2,200 years ago, the Roman general Marcus Sergius Silus lost his right hand during the Second Punic War. He had it replaced with an iron one that was designed to hold his shield. Knights of the Middle Ages sometimes used wooden limbs for battle or to ride a horse. And in the 16th century, the French surgeon Ambroise Paré designed some of the first purely functional prosthetics for soldiers coming off the battlefield. He also published the earliest written reference to prosthetics.

Then came the American Civil War in 1860. The record number of amputees from the war caused the number of patents for prosthetics to almost quadruple. One of these patents was for a wooden leg called the “Hanger limb.” It was the first to use rubber in the ankle and cushioning in the heel, showing that inventors understood they needed to make prosthetics less painful for amputees to wear.

Today, the U.S. Department of Veterans Affairs is a major provider of prosthetics and a leader in rehabilitation treatments for veterans who lose their limbs during their service. These patients are at risk for polytrauma, meaning they have injuries on multiple body parts, usually from blast-related events.

When this happens, these veterans need multifaceted clinical care and a support network. The Rehabilitation Medicine division at the NIH Clinical Center and the National Center for Medical Rehabilitation Research at the Eunice Kennedy Shriver National Institute of Child Health and Human Development help treat prosthetic users and conduct research about limb loss.

Improvements in design

While prosthetics were still made of combinations of wood, metal, glue, and leather even up to the 20th century, they were becoming more functional. From the late 15th century to the 19th century, France and Switzerland were making artificial limbs that could rotate and bend using cables, gears, cranks, and springs. However, these devices still needed to be adjusted manually. For example, an artificial hand could be cranked shut around a fork, but the person still needed another hand to operate the crank.

During the 1900s, manufacturers started to build more functional prosthetics by swapping wood and leather for plastics and other artificial materials. Still, some of the best prosthetics were out of reach for most people, including veterans. Many of these devices were only designed for specific tasks such as piano playing. They would not become more accessible to veterans until World War I, when prosthetic manufacturing for soldiers with limb loss increased in Great Britain. According to Jeffrey S. Reznick, Ph.D., Chief of the National Library of Medicine History of Medicine Division, such wartime manufacturing (and repair) sometimes occurred in military hospitals. Soldiers recovering in those facilities were fitted with artificial limbs as part of their care.

Today’s prosthetics look and work very differently from those made before the late 20th century. More lightweight and durable materials such as plastic, aluminum, titanium, and silicone are common in today’s prosthetic devices. They also fit closer to the user’s remaining limb. The Walter Reed National Military Medical Center will even tattoo service members’ prosthetics to help them look and feel more natural.

But what if a prosthetic could move without the user consciously controlling it? That is what the next generation of artificial limb technology aims to do.

NIH-supported innovations in prosthetics

Scientists are developing robotics, 3D printing, artificial intelligence, virtual reality, and motion-sensing technologies for prosthetics. Over the last decade, NIH has funded several projects that harness the brain’s electrical activity to move prosthetic limbs using electrodes implanted in a person’s remaining muscles. These electrodes send signals to the brain and allow the prosthetic limbs to move more freely.

One example of research funded by the National Institute of Biomedical Imaging and Bioengineering is a robotic lower leg prosthesis that creates a more natural walking motion. Researchers at Vanderbilt University created the device with powered knee and ankle joints and with software that can anticipate how the user wants to move.

In addition to these technological advances, it’s also important to track how many people use prosthetics and what treatments work best for these patients. That’s why NIH, together with the U.S. Department of Defense and the Mayo Clinic, helped create the Limb Loss and Preservation Registry in 2020. This registry uses electronic health records to measure how many people in the United States have limb loss and understand the costs and treatment outcomes for these patients.

People can lose all or part of an arm or leg for a number of reasons. Common ones include:

• Circulation problems from atherosclerosis or diabetes. They may cause you to need an amputation.
• Traumatic injuries, including from traffic accidents and military combat
• Cancer
• Birth defects

If you are missing an arm or leg, an artificial limb can sometimes replace it. The device, which is called a prosthesis, can help you to perform daily activities such as walking, eating, or dressing. Some artificial limbs let you function nearly as well as before.

What is the pancreas?

The pancreas is an organ in the body that secretes several hormones, including insulin and glucagon, as well as digestive enzymes that help break down food. Insulin helps cells in the body take up glucose (sugar) from the blood to use for energy, which lowers blood glucose levels. Glucagon causes the liver to release stored glucose, which raises blood glucose levels.

Type 1 diabetes occurs when the pancreas produces little or none of the insulin needed to regulate blood glucose. Type 2 diabetes occurs when the pancreas does not produce enough insulin or the body becomes resistant to the insulin that is present. Patients with type 1 diabetes and some patients with type 2 diabetes inject insulin, and occasionally glucagon, to regulate their blood glucose, which is critical to lower their risk of long-term complications such as blindness, kidney failure and cardiovascular disease.

When managing diabetes, many patients must vigilantly test blood glucose with a glucose meter, calculate insulin doses, and administer necessary insulin doses with a needle or insulin infusion pump to lower blood glucose. Glucagon may be injected in an emergency to treat severe low blood glucose. Some patients benefit from additional monitoring with a continuous glucose monitoring system.

What is an artificial pancreas device system?

The Artificial Pancreas Device System is a system of devices that closely mimics the glucose regulating function of a healthy pancreas.

Most Artificial Pancreas Device Systems consists of three types of devices already familiar to many people with diabetes: a continuous glucose monitoring system (CGM) and an insulin infusion pump. A blood glucose device (such as a glucose meter) is used to calibrate the CGM.

A computer-controlled algorithm connects the CGM and insulin infusion pump to allow continuous communication between the two devices. Sometimes an artificial pancreas device system is referred to as a "closed-loop" system, an "automated insulin delivery" system, or an "autonomous system for glycemic control."

An Artificial Pancreas Device System will not only monitors glucose levels in the body but also automatically adjusts the delivery of insulin to reduce high blood glucose levels (hyperglycemia) and minimize the incidence of low blood glucose (hypoglycemia) with little or no input from the patient.

The FDA is collaborating with diabetes patient groups, diabetes care providers, medical device manufactures, researchers, and academic investigatorsto foster innovation by clarifying agency expectations for clinical studies and product approvals. These efforts have accelerated the development of the first hybrid closed loop system, the Medtronic's MiniMed 670G System

The FDA's guidance, The Content of Investigational Device Exemption (IDE) and Premarket Approval (PMA) Applications for Artificial Pancreas Device Systems, addresses requirements for clinical studies and premarket approval applications for and artificial pancreas device system, and provided a flexible regulatory approach to support the rapid, safe and effective development of artificial pancreas device systems. (See below).

The Artificial Pancreas System (An Autonomous System for Glycemic Control)

The illustration below describes the parts of a type of artificial pancreas device system and shows how they work together.

1. Continuous Glucose Monitor (CGM). A CGM provides a steady stream of information that reflects the patient’s blood glucose levels. A sensor placed under the patient's skin (subcutaneously) measures the glucose in the fluid around the cells (interstitial fluid) which is associated with blood glucose levels. A small transmitter sends information to a receiver. A CGM continuously displays both an estimate of blood glucose levels and their direction and rate of change of these estimates.
   • Blood Glucose Device (BGD). Currently, to get the most accurate estimates of blood glucose possible from a CGM, the patient needs to periodically calibrate the CGM using a blood glucose measurement from a BGD; therefore, the BGD still plays a critical role in the proper management of patients with an APDS. However, over time, we anticipate that improved CGM performance may do away with the need for periodic blood glucose checks with a BGD.
2. Control algorithm. A control algorithm is software embedded in an external processor (controller) that receives information from the CGM and performs a series of mathematical calculations. Based on these calculations, the controller sends dosing instructions to the infusion pump. The control algorithm can be run on any number of devices including an insulin pump, computer or cellular phone. The FDA does not require the control algorithm to reside on the insulin pump.
3. Insulin pump. Based on the instructions sent by the controller, an infusion pump adjusts the insulin delivery to the tissue under the skin.
4. The Patient. The patient is an important part of Artificial Pancreas Delivery System. The concentration of glucose circulating in the patient’s blood is constantly changing. It is affected by the patient’s diet, activity level, and how his or her body metabolizes insulin and other substances.

Should I get breast implants? Should they be saline or silicone? Which style? How much monitoring is needed after surgery? Those are common questions people have when considering breast implants.

The FDA has approved implants for increasing breast size (known as augmentation), for reconstruction after breast cancer surgery or trauma, and to correct developmental defects. The FDA has also approved breast implants to correct or improve the result of a previous surgery.

There are two types of FDA-approved breast implants: saline-filled (saltwater solution) and silicone gel-filled. Both have a silicone outer shell and vary in size, shell thickness, shell surface texture, and shape (contour).

Know the Risks of Breast Implants

FDA-approved implants undergo extensive testing before approval to demonstrate reasonable assurance of safety and effectiveness. Still, there are risks associated with all breast implants, including:

• Additional surgeries
• Breast implant associated-anaplastic large cell lymphoma (BIA-ALCL), which is a cancer of the immune system
• Systemic symptoms, commonly referred to as Breast Implant Illness (BII)
• Capsular contracture (scar tissue that squeezes the implant)
• Breast pain
• Rupture (tears or holes in the shell) of saline and silicone gel-filled implants
  • Deflation (with visible change to breast size) of saline-filled implants
  • Silent (without symptoms) rupture of silicone gel-filled implants
• Infection

The silicone used for breast implants is different than injectable silicone. Injectable silicone is not FDA-approved for breast augmentation, breast reconstruction, or for body contouring.

Breast Implants Are Not Lifetime Devices

The longer you have breast implants, the greater the chances are that you will develop complications, some of which will require more surgery.

The life of breast implants varies by person and cannot be predicted. That means everyone with breast implants may need additional surgeries, but no one can predict when. Patients can also request additional surgeries to modify the size or shape of their breasts.

Understand Product Labeling for Implants

To help patients be aware of the risks of breast implants before their surgery, the FDA requires that all FDA-approved breast implants include labeling with easy-to-understand information about the benefits and risks associated with the product. This requirement is intended to enhance the discussions patients have with their doctor about the benefits and risks of implants. The mandatory labeling information includes a patient decision checklist that highlights key information about risks; warning information formatted in a box to make it noticeable; and a patient device card with information specific to a patient’s implant, such as the serial or lot number and the style and size.

The FDA restricts the sale and distribution of breast implants to only health care providers and facilities that provide information to patients using the patient decision checklist. The patient must be given the opportunity to initial and sign the checklist before agreeing to surgery and it must be signed by the physician implanting the device.

Additionally, the FDA advises that patients read the Summary of Safety and Effectiveness Data and product labeling for each implant to learn about the materials used to construct the device, device characteristics and the fillers used. The Summary of Safety and Effectiveness Data have been produced for all approved saline and silicone gel-filled breast implants. The Summary of Safety and Effectiveness Data and the product labeling provide information on the indications for use, risks, warnings, precautions, and studies associated with the FDA’s approval of the device.

The Summary of Safety and Effectiveness Data also provides information on clinical study used for device approval. The most serious complications are those that lead to further surgeries, such as ruptures or capsular contracture, or BIA-ALCL diagnosis.

Communicate with Your Surgeon

Surgeons will discuss the shape, size, surface texture, placement of the implant, and the incision site for each person. Ask your surgeon questions about their experience in performing breast implant surgeries, the surgical procedure, and the ways the implant might affect your life.

Tell your surgeon about previous surgeries and your body’s response. For example, discuss whether surgeries resulted in a more than expected amount of scar tissue. Also, discuss your expectations. These discussions will help you and the surgeon make decisions that achieve the desired appearance, including decisions about incision location and size, as well as implant size, material, texture, and placement.

Many patients have additional operations to change implant size. To achieve the best results after the first procedure, careful planning and reasonable expectations are necessary.

Know the Long-Term Risks of Breast Implants

The FDA has identified an association between breast implants and the development of breast implant-associated anaplastic large cell lymphoma (BIA-ALCL), a type of non-Hodgkin’s lymphoma. Patients who have breast implants may have an increased risk of developing this cancer which mostly develops in the fluid or scar tissue surrounding the implant.

Breast implants have either smooth or textured surfaces (shells). BIA-ALCL develops more frequently in patients with textured implants than in those with smooth-surfaced implants. Like other lymphomas, BIA-ALCL is a cancer of the immune system and not of breast tissue.

Some patients with implants have also reported health problems such as connective tissue diseases (such as lupus and rheumatoid arthritis), trouble breastfeeding, or reproductive problems. There is currently insufficient evidence to support an association between breast implants and those diagnoses.

Additionally, some patients receiving breast implants have reported a variety of systemic symptoms such as joint pain, muscle aches, confusion, chronic fatigue, autoimmune diseases, and others. Individual patient risk for developing these symptoms has not been well established.

Monitor Your Breast Implants

In general, follow your surgeon’s instructions on how to monitor your breast implants.

If you notice any unusual signs or symptoms, report them promptly to your surgeon or health care provider. Health care providers and patients are encouraged to report adverse events or side effects related to the use of these products to the FDA's MedWatch Safety Information and Adverse Event Reporting Program.

Also, follow your health care provider’s instructions for imaging for screening for breast cancer as this may be different for those patients who had breast augmentation and for those patients who had breasts reconstruction. If you are making an appointment for mammography, inform the mammography facility that you have breast implants, and ask them what you can expect regarding mammography with breast implants.

Your surgeon or health care provider may also recommend other tests, such as ultrasound or magnetic resonance imaging (MRI). The FDA recommends that patients with silicone implants get regular screenings to detect silent ruptures.

If you have specific questions about breast implants, ask your surgeon or health care provider.

When you lose the use of a limb, even the simplest of daily tasks can turn into a challenge. High-tech devices can help restore independence. New technologies are even making it possible to connect the mind to an artificial limb. These artificial limbs are called bionic prosthetic devices.

“To get back some of that lost function, you need some sort of assistive tool or technology to either enhance recovery or restore the capability of the anatomy that’s missing now,” says Dr. Nick Langhals, who oversees NIH-supported prosthetic engineering research.

This fast-moving research aims to improve people’s lives by restoring both movement and feeling.

Prosthetic Control

Traditional prosthetic devices use a body-powered harness to control a hand device. These are easy to use. With a shrug of your shoulder, the prosthetic hand or hook opens. With the release of your shoulder, the prosthesis closes. Through the feel of the cable tension across your shoulders, you know whether the prosthesis is open or closed without looking at it.

Newer, motorized hands are not as easy to learn how to use. To close the device, you contract the remaining muscles in your arm. An electrical sensor placed over those muscles detects the contraction and tells the hand to close. Since the original muscles that controlled the hand are gone, the remaining muscles must be retrained. Learning how to open and close a prosthetic hand in this way takes some time. And you still need to watch the device to know what it’s doing.

To make motorized hands more intuitive to use, researchers are developing ways to detect the electrical signals in your brain and nerves to help control advanced bionic prosthetics. This can be done many ways, such as by implanting tiny sensors in the parts of the brain that control movement or by attaching small electrodes to the amputated nerves. Either way, the patients simply think about moving their hand and computers translate it into the movements of a bionic prosthetic hand.

Two-Way Communication

To regain a sense of wholeness, a person with a bionic limb needs to do more than control the device. They also need to “feel” what it’s doing. New bionic devices can send sensation from the device back to the brain. This allows a person with a bionic device to feel like they are using their own limb.

“The most important thing about the research that we’re doing is this sense of wholeness,” says Dr. Paul Marasco, a biomedical engineering researcher at Cleveland Clinic.

One way to help a person feel their prosthetic hand is to move the remaining sensory nerves from the amputated hand to the skin of the upper arm. You can then use small robots to press on the skin of the upper arm when the hand is touching something.

Marasco’s team devised a similar system to restore the feeling of movement, too. The bionic hand sends signals to a computerized control system outside of the body. The computer then tells a small robot worn on the arm to send vibrations to the arm muscle. These vibrations deep in the muscle create an illusion of movement that tells the brain when the hand is closing or opening.

Marasco’s team tested this feedback system with several people who had a hand prosthesis. The study participants were able to operate the bionic hand and know what position it was in just as well as with their natural hand. With this feedback system, they didn’t have to look at the bionic hand to know when it was open or closed, or when it was reaching for an object.

“We fool their brains into believing that the prosthesis is actually part of their body,” Marasco says. This advancement directly taps into the way that the brain senses movement, which helps improve the two-way communication between prosthetic device and mind.

Wearable Robots

Research teams are also trying to help people who have lost the use of their legs. By wearing a robotic device called an exoskeleton, some people with leg paralysis have been able to regain the ability to walk.

A group led by Dr. Thomas Bulea, a biomedical engineer at the NIH Clinical Center, created a wearable exoskeleton for children with cerebral palsy. Cerebral palsy is a brain disorder that makes it hard to stand up straight, balance, and walk. The motorized, robotic exoskeleton changes the way the children walk by helping them straighten their knees at key points during the walking cycle. While the exoskeleton can make walking easier, children must be able to navigate at least small distances on their own to use it.

“The ultimate goal really is to have a person wear this outside of our lab, or even outside of the clinical setting,” Bulea explains. “To do that you have to have a really robust control system that makes sure that the robot is behaving properly in all different kinds of environments.”

The team is now writing software so that the robotic device can be worn while navigating bumps in the terrain and other real-world conditions.

Finding the Right Device

“What I try to emphasize to people is that there are a lot of potential tools and technologies at our disposal to try and make people better, and they should explore them and consider embracing them,” Langhals says.

Many types of prosthetic devices are now in development. If you’d like to find a clinical study to help test one, you can search for one in clinicaltrials.gov, a database of both NIH-supported and other studies around the world.

If you’re interested in taking part in a study, talk with your doctor about the possible risks and benefits.

Ask Your Doctor

If you’re interested in a clinical study for prosthetic devices, ask:

• Why is the study being done?
• How long will I be in the study?
• What kinds of tests and treatments are involved?
• What are the possible side effects or risks of the new treatment?
• What are the possible benefits?

What is a cochlear implant?

A cochlear implant is an implanted electronic hearing device, designed to produce useful hearing sensations to a person with severe to profound nerve deafness by electrically stimulating nerves inside the inner ear.

These implants usually consist of 2 main components:

• The externally worn microphone, sound processor and transmitter system.
• The implanted receiver and electrode system, which contains the electronic circuits that receive signals from the external system and send electrical currents to the inner ear.

Currently made devices have a magnet that holds the external system in place next to the implanted internal system. The external system may be worn entirely behind the ear or its parts may be worn in a pocket, belt pouch, or harness.

Who uses cochlear implants

Cochlear implants are designed to help severely to profoundly deaf adults and children who get little or no benefit from hearing aids. Even individuals with severe or profound "nerve deafness" may be able to benefit from cochlear implants.

What determines the success of cochlear implants?

Many things determine the success of implantation. Some of them are:

• How long the patient has been deaf--as a group, patients who have been deaf for a short time do better than those who have been deaf a long time
• How old they were when they became deaf--whether they were deaf before they could speak
• How old they were when they got the cochlear implant--younger patients, as a group, do better than older patients who have been deaf for a long time
• How long they have used the implant
• How quickly they learn
• How good and dedicated their learning support structure is
• The health and structure of their cochlea--number of nerve (spiral ganglion) cells that they have
• Implanting variables, such as the depth and type of implanted electrode and signal processing technique
• Intelligence and communicativeness of patient

How does a cochlear implant work?

A cochlear implant receives sound from the outside environment, processes it, and sends small electric currents near the auditory nerve. These electric currents activate the nerve, which then sends a signal to the brain. The brain learns to recognize this signal and the person experiences this as "hearing".

The cochlear implant somewhat simulates natural hearing, where sound creates an electric current that stimulates the auditory nerve. However, the result is not the same as normal hearing.

Why are there different kinds of implants?

Current thinking is that the inner ear responds to sound by at least two separate ways.

One theory, the place theory, says the cochlea responds greater to a simple tone at one place along its length. Another theory is that the ear responds to the timing of the sound.

Researchers, following the place theory, devised implants that separated the sound into groups. For example, they sent the lower pitches to the area of the cochlea where it seemed more responsive to lower pitches. And they sent higher pitches to the area more responsive to high pitches. Thus, they used several channels and electrodes spaced out inside the cochlea. Since there were also timing theories, researchers devised implants that made the sound signals into pulses to see if the cochlea would respond better to various kinds of pulses.

Most modern cochlear implants are versatile, in that they are somewhat capable of being adjusted to respond to sound in various ways. Audiologists try a variety of adjustments to see what works best with a particular patient.

How long have cochlear implants been available?

The first commercial devices were approved by the FDA in the mid-1980's. However, research with this device began in the 1950's.

Dental implants are medical devices surgically implanted into the jaw to restore a person's ability to chew or their appearance. They provide support for artificial (fake) teeth, such as crowns, bridges, or dentures.

When a tooth is lost due to injury or disease, a person can experience complications such as rapid bone loss, defective speech, or changes to chewing patterns that result in discomfort. Replacing a lost tooth with a dental implant can significantly improve the patient's quality of life and health.

Dental implant systems consist of a dental implant body and dental implant abutment and may also include an abutment fixation screw. The dental implant body is surgically inserted in the jawbone in place of the tooth's root. The dental implant abutment is usually attached to the implant body by the abutment fixation screw and extends through gums into the mouth to support the attached artificial teeth.

When someone loses a leg or other limb, a prosthetic device (a tool designed to replace a missing part of the body) can play a role in improving their quality of life by helping with mobility and stability. However, while most prosthetic devices are beneficial, current lower-limb devices can’t provide continuous control of balance or posture. Without proper neural (brain and nerve) control, people with lower-limb devices are more likely to fall or have difficulty walking on certain surfaces.

Researchers funded by the National Institute of Biomedical Imaging and Bioengineering (NIBIB) are working on an ankle prosthetic that can use the remaining muscles—and the muscles’ neural signals—to improve amputees’ stability and ability to hold an upright position.

How important are lower-limb prosthetics?

About 2 million people in the United States are living with an amputation, with lower-limb amputations being the most common. Many people choose to use a prosthetic device to help with walking and other types of movement.

What types of prosthetics are there?

There are a few kinds of lower-limb prosthetics:

• Passive devices are designed to support the body, but they generally do not move on their own. They can be static or adjustable and are usually designed to look like a natural limb. These devices are not powered and do not have a natural range of motion. Most lower-limb prosthetics are passive devices.
• Powered devices are designed to function more naturally. They can be controlled to move based on the movement of an amputee’s residual limb (the part of the limb that remains after an amputation) or based on other signals from the body. These signals are measured with sensors, which feed information to a computer model to control balance and movement.

What is the research?

Electrical, or neural, signals that travel from our muscles to our brain help us move our entire body, including our limbs. Even after amputation, these neural signals play a major role in moving residual limbs. He "Helen" Huang, Ph.D., and her research group are developing a new computer model to control a lower-limb prosthetic device that anticipates the person’s intended balance or motion. This system uses direct electromyographic (dEMG) control. In 2021, the research team released a case study report that evaluated how well a dEMG-controlled ankle prosthetic worked on a person with a transtibial amputation (where the limb is removed below the knee).

After an amputation, a person no longer has neural signals that once moved the entire limb, so they will generally need to build new signals to use their muscles in the residual limb differently. In Dr. Huang’s system, dEMG sensors detect these new neural signals from the residual limb muscles. When initially using the dEMG-controlled ankle prosthetic device, the limb will move unnaturally while the computer model learns how the person intends to move it. People using a dEMG-controlled prosthetic would work with a physical therapist to help “train” their residual muscles to work with the device. This training will help the computer model better control the device to create a more natural balance and movement.

How does this dEMG prosthetic work?

• Researchers place surface electrodes (sensors) on the person’s residual limb. These sensors detect electrical signals—the EMG—in a person’s residual muscles.
• When the person contracts their residual muscle (like flexing their foot), the EMG activity is sent to a computer model.
• The computer model learns how to interpret the person’s movement intentions to create a tailored dEMG prosthetic system.
• The dEMG controls the pneumatic artificial muscles (part of the prosthetic device that uses pressurized air to contract or extend), which allows the person to naturalistically control their ankle based on their intentions.

What were the study results?

The research team evaluated one person’s stability when he used his passive prosthetic ankle and, after finishing physical therapy, when he used the dEMG-controlled prosthetic ankle. The study found that his stability while wearing the dEMG-controlled prosthetic ankle noticeably improved. He even had improved control when standing on a foam surface and with his eyes closed. The synchronization between his residual limb and the dEMG prosthetic was also much higher than it was with his usual passive device.

Researchers are now expanding this study to include several more people who have lost their lower limbs.

How can you mend a broken heart? Or repair a damaged liver, kidney, or knee? NIH-funded scientists are exploring innovative ways to fix faulty organs and tissues or even grow new ones. This type of research is called tissue engineering. Exciting advances continue to emerge in this fast-moving field.

Tissue engineering could allow doctors to repair or replace worn-out tissues and organs with living, working parts. Most important, tissue engineering might help some of the 120,000 people on the waitlist to receive donated kidneys, livers, or other organs.

Doctors have long used tissue-engineered skin to heal severe burns or other injuries. But most tissue engineering methods are still experimental. They’ve been tested only in laboratory dishes and sometimes in animals, but only a few new approaches have been tested in people. Several clinical studies (involving human volunteers) are in the early stages of testing newly developed tissues.

“With this approach, scientists are combining engineering and biology to restore a damaged organ or tissue, whether it’s been damaged by disease or injury or something else,” says Dr. Martha Lundberg, an NIH expert in heart-related tissue engineering.

Some scientists are creating special net-like structures, or scaffolds, in desired shapes and then coaxing cells to grow within them. Some use a mixture of natural substances called growth factors, which direct cells to grow and develop in certain ways.

“Other scientists are using different 3-D bioprinting technologies—some are like fancy inkjet printers—to create new tissues or organs,” Lundberg says. They’ve printed 3-D kidneys and other organs that look like the real thing. But while most of these printed body parts have the right shape, they’re not fully functional.

“Scientists haven’t yet figured out how to print an organ that includes the correct blood vessel patterns, nerve connections, and other components that come together in a mature organ,” Lundberg says. “When creating a new organ, if it can perform the right job and functions, it may not need to look like the real thing.”

Many tissue engineering methods use stem cells, which can be nudged to turn into different cell types. One research team guided human stem cells to become a 3-D structure that can respond to light. The method might one day lead to new therapies for eye disorders. Other stem cell approaches may lead to improved treatment for spinal cord injuries, diabetes, and more.

Another approach, called decellularization, involves removing all the cells from an organ. What’s left behind is a thin, pale framework that contains the organ’s natural structural proteins, including the pathways for tiny blood vessels and nerves. By infusing new cells into this mesh-like matrix, some researchers have successfully created working animal kidneys, livers, hearts, lungs, and other organs.

The decellularization technique was used by Dr. Martin Yarmush and his colleagues to create a functional rat liver that included a network of working blood vessels. Yarmush is a biomedical engineer at Rutgers University and the Massachusetts General Hospital. The engineered livers his team created were kept alive in the laboratory for days and functioned for several hours after transplantation into rats. The researchers are now working to help those transplanted livers survive even longer. They’re also scaling up the methods to create a decellularized human liver that can be repopulated with functional cells.

“A parallel effort we are pursuing involves taking a donated organ that is not considered transplantable for a particular reason, and then using a reconditioning solution and perhaps even stem cells to revitalize the organ so it becomes transplantable,” Yarmush says.

Other researchers are working to repair damaged body parts that are still in the body. At the University of Washington in Seattle, Dr. Charles Murry and colleagues are searching for ways to fix injured hearts. One of their latest studies used human stem cells to repair damaged hearts in monkeys. The stem cells were coaxed to become early-stage heart cells, which were then infused near the heart injury.

The new cells made their way into the damaged heart muscle and organized into muscle fibers in all of the treated monkeys. The infused stem cells replaced nearly half of the damaged heart tissue and began beating in sync with the heart. Still, the scientists note they need years of research before this type of therapy might be tried in people.

Some methods are already being tested in humans. Dr. Martha Murray, a surgeon at Boston Children’s Hospital, is exploring new ways to heal a common knee injury known as a torn ACL (anterior cruciate ligament). Athletes who do a lot of twisting and turning, as in basketball or soccer, are at risk for damaging the ACL.

“Typical treatment today, called ACL reconstruction, works well, and it gets patients back to the playing field at a relatively high rate,” Murray says. But the surgery involves removing a piece of tendon from elsewhere in the body and using that to replace the ACL. “So it involves making 2 injuries that the body has to heal from. And even with this treatment, patients still develop arthritis in the knee 15 to 20 years later,” Murray adds. “We wanted to find a better therapy—something less invasive.”

After testing several biomaterials, Murray’s team found that stitching a bioengineered sponge between the torn ends of an injured ACL allows blood to clot and collect around the damaged ligament. Because blood naturally contains stem cells and growth factors, the blood-soaked sponge acts as a “bridge” that encourages ACL healing. The sponge is made of some of the same proteins normally found in ligaments, and it dissolves after a few weeks.

Studies in large animals showed that the bioengineered sponge was much less likely to lead to arthritis, and it healed ACL injuries as well as standard reconstruction surgery. The U.S. Food and Drug Administration recently approved human safety testing of the sponge in 10 people with ACL injuries.

Metal, plastic, and other non-biological devices can also replace or enhance malfunctioning body parts. One promising possibility still in development is an artificial kidney that could be implanted in the body and used in place of dialysis to treat end-stage kidney disease. Scientists are also studying a synthetic glue modeled after a natural adhesive that might help to repair tissues in the body.