Repairing Nerve Pathways With 3-D Printing

The peripheral nerves extend from the brain and spinal cord out to the rest of the body. They can be damaged in various ways, including disease and traumatic injuries such as car accidents and battlefield wounds.

A 3-D printed nerve scaffold made to mimic the geometry of the original nerve. Separate biochemical cues were incorporated into the structure to act as guides for sensory neurons (nerve growth factor, green dye) and motor neurons (glial cell line-derived neurotrophic factor, red dye). Image by the researchers, courtesy of Advanced Functional Materials.

Treatment for peripheral nerve damage depends on the specific injury. Nerve regeneration requires a complex interplay of physical and chemical cues. Current techniques for nerve repair center on grafts, in which a portion of a healthy nerve is taken (harvested) from another part of the body to replace the damaged section. However, grafts require harvesting surgery and are also limited by size and geometry. They can cause a host of problems at the donor site as well, including harmful immune responses, chronic pain, and sensory loss.

A team led by Dr. Michael C. McAlpine at the University of Minnesota, Blake N. Johnson at Virginia Tech, and Dr. Xiaofeng Jia at the University of Maryland and Johns Hopkins University has been investigating techniques for guiding nerve regeneration. Previous attempts have been limited to linear structures that don’t mimic naturally branching nerves. To create complex, customized structures, the team turned to 3-D printing, in which an object is “printed” by laying down successive layers of material in a pattern based on a digital model. The work was funded in part by NIH’s National Institute of Neurological Disorders and Stroke (NINDS) and National Heart, Lung, and Blood Institute (NHLBI). It appeared online in Advanced Functional Materialson September 18, 2015.

The team selected the sciatic nerve in rats as a model for regeneration, as it contains a complex, mixed nerve (sensory and motor) system. The researchers removed a section and prepared a cast of the nerve to image using a 3-D light-scanning technique. After conducting scans from various angles, they assembled the images into a 3-D model of the nerve pathway. This model then served as a template for a specialized, custom-built 3-D printer to manufacture a structure mimicking the exact geometry of the original nerve tissue.

The team demonstrated they could use the approach to create anatomically accurate nerve pathways. They verified they could use various materials known to be safe for use in the body, including silicone. Incorporating microgrooves in the structure helped guide nerve fiber growth. They found they could also help direct sensory and motor nerve branches to grow along separate paths by incorporating specific biochemical cues into different parts of the structure.

Once they developed the approach in laboratory experiments, they tested how well the technique could regenerate complex nerve gaps in a rat model. They created 10 mm gaps in the sciatic nerve and treated the animals with customized, 3-D printed nerve scaffolds. Over a 3-month period, the rats’ ability to walk improved significantly.

The team also showed that conventional imaging technologies, such as CT scans and MRI, could be used to make 3-D models of nerves in the body.

“This represents an important proof of concept of the 3-D printing of custom nerve guides for the regeneration of complex nerve injuries,” McAlpine says. “Someday we hope that we could have a 3-D scanner and printer right at the hospital to create custom nerve guides on site to restore nerve function.”

—by Harrison Wein, Ph.D.

Children's Health: Babies' lives were saved by 3-D printing ♦ Childhood bullying causes long-term mental health problems ♦ Breast milk sharing risky

Childhood bullying causes worse long-term mental health problems than maltreatment Bullying adversely affects children in later life more than being maltreated, according to new research. A new study shows that children who have been bullied by peers suffer worse in the longer term than those who have been maltreated by adults

Maternal obesity increases risk of type 1 diabetes in children   A study of more than 1.2 million children in Sweden has concluded that children of parents with any type of diabetes are more likely to develop type 1 diabetes (T1D), and that maternal overweight and obesity increases the risk of the child developing T1D when neither parent has diabetes.

Toxic combination of air pollution and poverty lowers child IQ Children born to mothers experiencing economic hardship, who were also exposed during pregnancy to high levels of PAH (polycyclic aromatic hydrocarbons), scored significantly lower on IQ tests at age 5 compared with children born to mothers with greater economic security and less exposure to the pollutants.

How babies' lives were saved by 3-D printing A new study reports outcomes for three boys who became among the first in the world to benefit from 3D printed devices that saved their lives

Breast milk sharing among friends, relatives increasing, but still risky A new study offers insight into the attitudes around the growing -- and unregulated -- practice of breast milk sharing. Results indicate that friends and relatives are sharing breast milk with each other, but that many may not be aware of the risks, even when the milk is from someone they know. The study also found that healthcare practitioners are being left out of the milk-sharing dialogue-- and that there are untapped opportunities to encourage women to donate desperately needed, extra breast milk for premature babies.

Engineering New Tissues and Organs

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.

3-D Gel-Nanoparticle Device Detoxifies Blood

Researchers developed a liver-inspired 3-D device made of hydrogel and nanoparticles that can remove toxins from blood. Designed for use outside the body, the device provides a proof-of-concept model for new detoxification techniques.

The 3-D structure of the detoxifier, measured by laser confocal microscopy.Image by the researchers, courtesy of Nature Communications.

Toxins from animal bites and stings or from bacterial infections can damage cells, leading to pain and illness. Conventional treatments, such as antisera, may not completely neutralize the toxins.

Scientists have previously developed nanoparticles that can bind certain types of toxins and neutralize them. Nanoparticles, however, can’t be given directly to patients because the particles may accumulate in the liver, creating an additional health risk.

An international team led by Dr. Shaochen Chen at the University of California, San Diego, set out to develop a nanoparticle-based detoxification device that wouldn’t be hazardous to patients. Their study was funded in part by NIH’s National Institute of Biomedical Imaging and Bioengineering (NIBIB) and other NIH components. Results appeared on May 8, 2014, in Nature Communications.

The team made nanoparticles out of the polymer polydiacetylene. The chemical characteristics of polydiacetylene cause it to change its fluorescence pattern when it binds to toxins. Toxin binding changes its color from blue to red, and the intensity of red fluorescence increases with the amount of toxin bound.

To test the nanoparticles, the researchers mixed them with red blood cells and melittin, the main toxic component of bee venom. As expected, the nanoparticles bound the toxin and exhibited red fluorescence that increased with the amount of melittin bound. Using computer simulations, the researchers were able to characterize the interactions between the nanoparticles and toxin.

The group next used 3-D printing to create a device that could capture and remove melittin from a solution. They formed scaffold structures composed of the nanoparticles embedded in a non-toxic gel often used in biomedical applications. They tested several 3-D scaffold patterns with different surface areas. A hexagonal pattern with a very large surface area, which mimicked the hexagonal organization of a liver lobule, trapped the toxins best.

To further test the ability of the scaffold to remove toxins, the scientists mixed red blood cells with melittin treated with the detoxification device. The device neutralized the toxin by capturing and separating it from the cells.

“The concept of using 3-D printing to encapsulate functional nanoparticles in a biocompatible hydrogel is novel,” Chen says. “This will inspire many new designs for detoxification techniques since 3-D printing allows user-specific or site-specific manufacturing of highly functional products.”