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regenerative medicine

3D Printing a Human Heart Valve

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It is now possible to pull up the design of a guitar on a computer screen and print out its parts on a 3D printer equipped with special metal or plastic “inks.” The same technological ingenuity is also now being applied with bioinks—printable gels containing supportive biomaterials and/or cells—to print out tissue, bone, blood vessels, and, even perhaps one day, viable organs.

While there’s a long way to go until then, a team of researchers has reached an important milestone in bioprinting collagen and other extracellular matrix proteins that undergird every tissue and organ in the body. The researchers have become so adept at it that they now can print biomaterials that mimic the structural, mechanical, and biological properties of real human tissues.

Take a look at the video. It shows a life-size human heart valve that’s been printed with their improved collagen bioink. As fluid passes through the aortic valve in a lab test, its three leaf-like flaps open and close like the real thing. All the while, the soft, flexible valve withstands the intense fluid pressure, which mimics that of blood flowing in and out of a beating heart.

The researchers, led by NIH grantee Adam Feinberg, Carnegie Mellon University, Pittsburgh, PA, did it with their latest version of a 3D bioprinting technique featured on the blog a few years ago. It’s called: Freeform Reversible Embedding of Suspended Hydrogels v.2.0. Or, just FRESH v2.0.

The FRESH system uses a bioink that consists of collagen (or other soft biomaterials) embedded in a thick slurry of gelatin microparticles and water. While a number of technical improvements have been made to FRESH v. 2.0, the big one was getting better at bioprinting collagen.

The secret is to dissolve the collagen bioink in an acid solution. When extruded into a neutral support bath, the change in pH drives the rapid assembly of collagen. The ability to extrude miniscule amounts and move the needle anywhere in 3D space enables them to produce amazingly complex, high-resolution structures, layer by layer. The porous microstructure of the printed collagen also helps for incorporating human cells. When printing is complete, the support bath easily melts away by heating to body temperature.

As described in Science, in addition to the working heart valve, the researchers have printed a small model of a heart ventricle. By combining collagen with cardiac muscle cells, they found they could actually control the organization of muscle tissue within the model heart chamber. The 3D-printed ventricles also showed synchronized muscle contractions, just like you’d expect in a living, beating human heart!

That’s not all. Using MRI images of an adult human heart as a template, the researchers created a complete organ structure including internal valves, large veins, and arteries. Based on the vessels they could see in the MRI, they printed even tinier microvessels and showed that the structure could support blood-like fluid flow.

While the researchers have focused the potential of FRESH v.2.0 printing on a human heart, in principle the technology could be used for many other organ systems. But there are still many challenges to overcome. A major one is the need to generate and incorporate billions of human cells, as would be needed to produce a transplantable human heart or other organ.

Feinberg reports more immediate applications of the technology on the horizon, however. His team is working to apply FRESH v.2.0 for producing child-sized replacement tracheas and precisely printed scaffolds for healing wounded muscle tissue.

Meanwhile, the Feinberg lab generously shares its designs with the scientific community via the NIH 3D Print Exchange. This innovative program is helping to bring more 3D scientific models online and advance the field of bioprinting. So we can expect to read about many more exciting milestones like this one from the Feinberg lab.

Reference:

[1] 3D bioprinting of collagen to rebuild components of the human heart. Lee A, Hudson AR, Shiwarski DJ, Tashman JW, Hinton TJ, Yerneni S, Bliley JM, Campbell PG, Feinberg AW. Science. 2019 Aug 2;365(6452):482-487.

Links:

Tissue Engineering and Regenerative Medicine (National Institute of Biomedical Imaging and Bioengineering/NIH)

Regenerative Biomaterials and Therapeutics Group (Carnegie Mellon University, Pittsburgh, PA)

FluidForm (Acton, MA)

3D Bioprinting Open Source Workshops (Carnegie Mellon)

Video: Adam Feinberg on Tissue Engineering to Treat Human Disease (YouTube)

NIH 3D Print Exchange

NIH Support: National Heart, Lung, and Blood Institute; Eunice Kennedy Shriver National Institute of Child Health and Human Development; Common Fund


Skin Cells Can Be Reprogrammed In Vivo

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Daniel Gallego-Perez
Credit: The Ohio State University College of Medicine, Columbus

Thousands of Americans are rushed to the hospital each day with traumatic injuries. Daniel Gallego-Perez hopes that small chips similar to the one that he’s touching with a metal stylus in this photo will one day be a part of their recovery process.

The chip, about one square centimeter in size, includes an array of tiny channels with the potential to regenerate damaged tissue in people. Gallego-Perez, a researcher at The Ohio State University Colleges of Medicine and Engineering, Columbus, has received a 2018 NIH Director’s New Innovator Award to develop the chip to reprogram skin and other cells to become other types of tissue needed for healing. The reprogrammed cells then could regenerate and restore injured neural or vascular tissue right where it’s needed.

Gallego-Perez and his Ohio State colleagues wondered if it was possible to engineer a device placed on the skin that’s capable of delivering reprogramming factors directly into cells, eliminating the need for the viral delivery vectors now used in such work. While such a goal might sound futuristic, Gallego-Perez and colleagues offered proof-of-principle last year in Nature Nanotechnology that such a chip can reprogram skin cells in mice. [1]

Here’s how it works: First, the chip’s channels are loaded with specific reprogramming factors, including DNA or proteins, and then the chip is placed on the skin. A small electrical current zaps the chip’s channels, driving reprogramming factors through cell membranes and into cells. The process, called tissue nanotransfection (TNT), is finished in milliseconds.

To see if the chips could help heal injuries, researchers used them to reprogram skin cells into vascular cells in mice. Not only did the technology regenerate blood vessels and restore blood flow to injured legs, the animals regained use of those limbs within two weeks of treatment.

The researchers then went on to show that they could use the chips to reprogram mouse skin cells into neural tissue. When proteins secreted by those reprogrammed skin cells were injected into mice with brain injuries, it helped them recover.

In the newly funded work, Gallego-Perez wants to take the approach one step further. His team will use the chip to reprogram harder-to-reach tissues within the body, including peripheral nerves and the brain. The hope is that the device will reprogram cells surrounding an injury, even including scar tissue, and “repurpose” them to encourage nerve repair and regeneration. Such an approach may help people who’ve suffered a stroke or traumatic nerve injury.

If all goes well, this TNT method could one day fill an important niche in emergency medicine. Gallego-Perez’s work is also a fine example of just one of the many amazing ideas now being pursued in the emerging field of regenerative medicine.

Reference:

[1] Topical tissue nano-transfection mediates non-viral stroma reprogramming and rescue. Gallego-Perez D, Pal D, Ghatak S, Malkoc V, Higuita-Castro N, Gnyawali S, Chang L, Liao WC, Shi J, Sinha M, Singh K, Steen E, Sunyecz A, Stewart R, Moore J, Ziebro T, Northcutt RG, Homsy M, Bertani P, Lu W, Roy S, Khanna S, Rink C, Sundaresan VB, Otero JJ, Lee LJ, Sen CK. Nat Nanotechnol. 2017 Oct;12(10):974-979.

Links:

Stroke Information (National Institute of Neurological Disorders and Stroke/NIH)

Burns and Traumatic Injury (NIH)

Peripheral Neuropathy (National Institute of Neurological Disorders and Stroke/NIH)

Video: Breakthrough Device Heals Organs with a Single Touch (YouTube)

Gallego-Perez Lab (The Ohio State University College of Medicine, Columbus)

Gallego-Perez Project Information (NIH RePORTER)

NIH Support: Common Fund; National Institute of Neurological Disorders and Stroke


Regenerative Medicine: Making Blood Stem Cells in the Lab

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Endothelial cells becoming hematopoietic stem cells

Caption: Arrow in first panel points to an endothelial cell induced to become hematopoietic stem cell (HSC). Second and third panels show the expansion of HSCs over time.
Credit: Raphael Lis, Weill Cornell Medicine, New York, NY

Bone marrow transplants offer a way to cure leukemia, sickle cell disease, and a variety of other life-threatening blood disorders.There are two major problems, however: One is many patients don’t have a well-matched donor to provide the marrow needed to reconstitute their blood with healthy cells. Another is even with a well-matched donor, rejection or graft versus host disease can occur, and lifelong immunosuppression may be needed.

A much more powerful option would be to develop a means for every patient to serve as their own bone marrow donor. To address this challenge, researchers have been trying to develop reliable, lab-based methods for making the vital, blood-producing component of bone marrow: hematopoietic stem cells (HSCs).

Two new studies by NIH-funded research teams bring us closer to achieving this feat. In the first study, researchers developed a biochemical “recipe” to produce HSC-like cells from human induced pluripotent stem cells (iPSCs), which were derived from mature skin cells. In the second, researchers employed another approach to convert mature mouse endothelial cells, which line the inside of blood vessels, directly into self-renewing HSCs. When these HSCs were transplanted into mice, they fully reconstituted the animals’ blood systems with healthy red and white blood cells.


Snapshots of Life: Healing Spinal Cord Injuries

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Nerve cell on a nanofiber gel

Credit: Mark McClendon, Zaida Alvarez Pinto, Samuel I. Stupp, Northwestern University, Evanston, IL

When someone suffers a fully severed spinal cord, it’s considered highly unlikely the injury will heal on its own. That’s because the spinal cord’s neural tissue is notorious for its inability to bridge large gaps and reconnect in ways that restore vital functions. But the image above is a hopeful sight that one day that could change.

Here, a mouse neural stem cell  (blue and green) sits in a lab dish, atop a special gel containing a mat of synthetic nanofibers (purple). The cell is growing and sending out spindly appendages, called axons (green), in an attempt to re-establish connections with other nearby nerve cells.


Regenerative Medicine: The Promise and Peril

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Retinal pigment epithelial cells

Caption: Scanning electron micrograph of iPSC-derived retinal pigment epithelial cells growing on a nanofiber scaffold (blue).
Credit: Sheldon Miller, Arvydas Maminishkis, Robert Fariss, and Kapil Bharti, National Eye Institute/NIH

Stem cells derived from a person’s own body have the potential to replace tissue damaged by a wide array of diseases. Now, two reports published in the New England Journal of Medicine highlight the promise—and the peril—of this rapidly advancing area of regenerative medicine. Both groups took aim at the same disorder: age-related macular degeneration (AMD), a common, progressive form of vision loss. Unfortunately for several patients, the results couldn’t have been more different.

In the first case, researchers in Japan took cells from the skin of a female volunteer with AMD and used them to create induced pluripotent stem cells (iPSCs) in the lab. Those iPSCs were coaxed into differentiating into cells that closely resemble those found near the macula, a tiny area in the center of the eye’s retina that is damaged in AMD. The lab-grown tissue, made of retinal pigment epithelial cells, was then transplanted into one of the woman’s eyes. While there was hope that there might be actual visual improvement, the main goal of this first in human clinical research project was to assess safety. The patient’s vision remained stable in the treated eye, no adverse events occurred, and the transplanted cells remained viable for more than a year.

Exciting stuff, but, as the second report shows, it is imperative that all human tests of regenerative approaches be designed and carried out with the utmost care and scientific rigor. In that instance, three elderly women with AMD each paid $5,000 to a Florida clinic to be injected in both eyes with a slurry of cells, including stem cells isolated from their own abdominal fat. The sad result? All of the women suffered severe and irreversible vision loss that left them legally or, in one case, completely blind.


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