Tag Archives: hydrogel

Assembly-line 3-D tissue engineering

It looks as if the researchers at Singapore’s Institute of Bioengineering and Nanotechnology (IBN), have developed a template for producing complex tissues such as those in liver and in fat, from an Aug. 20, 2013 news item on ScienceDaily,

Researchers at the Institute of Bioengineering and Nanotechnology (IBN) have developed a simple method of organizing cells and their microenvironments in hydrogel fibers. Their unique technology provides a feasible template for assembling complex structures, such as liver and fat tissues, as described in their recent publication in Nature Communications.

According to IBN Executive Director Professor Jackie Y. Ying, “Our tissue engineering approach gives researchers great control and flexibility over the arrangement of individual cell types, making it possible to engineer prevascularized tissue constructs easily. This innovation brings us a step closer toward developing viable tissue or organ replacements.”

The Aug. 19, 2013 A*STAR’s (Singapore’s Agency for Science and Technology Research) IBN  press release, which originated the news item, offers a detailed explanation of how this discovery could make tissue and organ replacements much easier,

IBN Team Leader and Principal Research Scientist, Dr Andrew Wan, elaborated, “Critical to the success of an implant is its ability to rapidly integrate with the patient’s circulatory system. This is essential for the survival of cells within the implant, as it would ensure timely access to oxygen and essential nutrients, as well as the removal of metabolic waste products. Integration would also facilitate signaling between the cells and blood vessels, which is important for tissue development.”

Tissues designed with pre-formed vascular networks are known to promote rapid vascular integration with the host. Generally, prevascularization has been achieved by seeding or encapsulating endothelial cells, which line the interior surfaces of blood vessels, with other cell types. In many of these approaches, the eventual distribution of vessels within a thick structure is reliant on in vitro cellular infiltration and self-organization of the cell mixture. These are slow processes, often leading to a non-uniform network of vessels within the tissue. As vascular self-assembly requires a large concentration of endothelial cells, this method also severely restricts the number of other cells that may be co-cultured.

Alternatively, scientists have attempted to direct the distribution of newly formed vessels via three-dimensional (3D) co-patterning of endothelial cells with other cell types in a hydrogel. This approach allows large concentrations of endothelial cells to be positioned in specific regions within the tissue, leaving the rest of the construct available for other cell types. The hydrogel also acts as a reservoir of nutrients for the encapsulated cells. However, co-patterning multiple cell types within a hydrogel is not easy. Conventional techniques, such as micromolding and organ printing, are limited by slow cell assembly, large volumes of cell suspension, complicated multi-step processes and expensive instruments. These factors also make it difficult to scale up the production of implantable 3D cell-patterned constructs. To date, these approaches have been unsuccessful in achieving vascularization and mass transport through thick engineered tissues.

To overcome these limitations, IBN researchers have used interfacial polyelectrolyte complexation (IPC) fiber assembly, a unique cell patterning technology patented by IBN, to produce cell-laden hydrogel fibers under aqueous conditions at room temperature. Unlike other methods, IBN’s novel technique allows researchers to incorporate different cell types separately into different fibers, and these cell-laden fibers may then be assembled into more complex constructs with hierarchical tissue structures. In addition, IBN researchers are able to tailor the microenvironment for each cell type for optimal functionality by incorporating the appropriate factors, e.g. proteins, into the fibers. Using IPC fiber assembly, the researchers have engineered an endothelial vessel network, as well as cell-patterned fat and liver tissue constructs, which have successfully integrated with the host circulatory system in a mouse model and produced vascularized tissues.

Here’s a citation for and link to the published paper,

Patterned prevascularised tissue constructs by assembly of polyelectrolyte hydrogel fibres by Meng Fatt Leong,    Jerry K. C. Toh, Chan Du, Karthikeyan Narayanan, Hong Fang Lu, Tze Chiun Lim, Andrew C. A. Wan, & Jackie Y. Ying. Nature Communications 4, Article number: 2353 doi:10.1038/ncomms3353 Published 19 August 2013

This article is behind a paywall although you can preview it with ReadingCube access.

More than human—a bionic ear that extends hearing beyond the usual frequencies

It’s now possible to print a bionic ear in 3D that can hear beyond the human range and all you need is off-the-shelf printing equipment—and technical expertise. A May 2, 2013 news item on Azonano provides more detail,

Scientists at Princeton University used off-the-shelf printing tools to create a functional ear that can “hear” radio frequencies far beyond the range of normal human capability.

“In general, there are mechanical and thermal challenges with interfacing electronic materials with biological materials,” said Michael McAlpine, an assistant professor of mechanical and aerospace engineering at Princeton and the lead researcher. “Previously, researchers have suggested some strategies to tailor the electronics so that this merger is less awkward. That typically happens between a 2D sheet of electronics and a surface of the tissue. However, our work suggests a new approach — to build and grow the biology up with the electronics synergistically and in a 3D interwoven format.”

McAlpine’s team has made several advances in recent years involving the use of small-scale medical sensors and antenna. Last year, a research effort led by McAlpine and Naveen Verma, an assistant professor of electrical engineering, and Fio Omenetto of Tufts University, resulted in the development of a “tattoo” made up of a biological sensor and antenna that can be affixed to the surface of a tooth.

The tooth tattoo is mentioned in my Nov. 9, 2012 posting; I focused more on Tufts University than Princeton in that piece. As for the ear (from the news item on Azonano),

The finished ear consists of a coiled antenna inside a cartilage structure. Two wires lead from the base of the ear and wind around a helical “cochlea” – the part of the ear that senses sound – which can connect to electrodes. Although McAlpine cautions that further work and extensive testing would need to be done before the technology could be used on a patient, he said the ear in principle could be used to restore or enhance human hearing. He said electrical signals produced by the ear could be connected to a patient’s nerve endings, similar to a hearing aid. The current system receives radio waves, but he said the research team plans to incorporate other materials, such as pressure-sensitive electronic sensors, to enable the ear to register acoustic sounds.

Here’s the technique the researchers used to create their bionic ear (from the news item),

Standard tissue engineering involves seeding types of cells, such as those that form ear cartilage, onto a scaffold of a polymer material called a hydrogel. However, the researchers said that this technique has problems replicating complicated three dimensional biological structures. Ear reconstruction “remains one of the most difficult problems in the field of plastic and reconstructive surgery,” they wrote.

To solve the problem, the team turned to a manufacturing approach called 3D printing. These printers use computer-assisted design to conceive of objects as arrays of thin slices. The printer then deposits layers of a variety of materials – ranging from plastic to cells – to build up a finished product. Proponents say additive manufacturing promises to revolutionize home industries by allowing small teams or individuals to create work that could previously only be done by factories.

Creating organs using 3D printers is a recent advance; several groups have reported using the technology for this purpose in the past few months. But this is the first time that researchers have demonstrated that 3D printing is a convenient strategy to interweave tissue with electronics.

The technique allowed the researchers to combine the antenna electronics with tissue within the highly complex topology of a human ear. The researchers used an ordinary 3D printer to combine a matrix of hydrogel and calf cells with silver nanoparticles that form an antenna. The calf cells later develop into cartilage.

Here’s an image of the ear,

Scientists used 3-D printing to merge tissue and an antenna capable of receiving radio signals. Credit: Photo by Frank Wojciechowski

Scientists used 3-D printing to merge tissue and an antenna capable of receiving radio signals. Credit: Photo by Frank Wojciechowski

For interested parties,a link to and a citation for the published research,

A 3D Printed Bionic Ear by Manu S Mannoor , Ziwen Jiang , Teena James , Yong Lin Kong , Karen A Malatesta , Winston Soboyejo , Naveen Verma , David H Gracias , and Michael C. McAlpine. Nano Lett., Just Accepted Manuscript DOI: 10.1021/nl4007744 Publication Date (Web): May 1, 2013

Copyright © 2013 American Chemical Society

This article is behind a paywall.

At this point, the ear is strictly for use in the laboratory they have not run any ‘in vivo’ experiments, which would be one of the next steps and a prerequisite before  human clinical trials are considered.

I have written about human enhancement before, notably in my Aug. 30, 2011 posting where I highlighted this excerpt from an article by Paul Hochman,

“I don’t think I would have said this if it had never happened,” says Bailey, referring to the accident that tore off his pinkie, ring, and middle fingers. “But I told Touch Bionics I’d cut the rest of my hand off if I could make all five of my fingers robotic.” [originally excerpted from Paul Hochman’s Feb. 1, 2010 article, Bionic Legs, i-Limbs, and Other Super Human Prostheses You’ll Envy for Fast Company]

The Bailey quote stimulated this question for me, what would you choose if you could get an ear that hears beyond the human range?

Squishy knees and tissue engineering at Johns Hopkins

Researchers at Johns Hopkins University School of Medicine’s Translational Tissue Engineering Center (TTEC) have developed a material (a kind of hydrogel) which they use with a new technique they’ve developed for growing new tissue and cartilage in knees. From the Jan. 15, 2013 news release on EurekAlert,

Proof-of-concept clinical trial in 18 patients shows improved tissue growth

In a small study, researchers reported increased healthy tissue growth after surgical repair of damaged cartilage if they put a “hydrogel” scaffolding into the wound to support and nourish the healing process. The squishy hydrogel material was implanted in 15 patients during standard microfracture surgery, in which tiny holes are punched in a bone near the injured cartilage. The holes stimulate patients’ own specialized stem cells to emerge from bone marrow and grow new cartilage atop the bone.

“Our pilot study indicates that the new implant works as well in patients as it does in the lab, so we hope it will become a routine part of care and improve healing,” says Jennifer Elisseeff, Ph.D., Jules Stein Professor of Ophthalmology and director of the Johns Hopkins University School of Medicine’s Translational Tissue Engineering Center (TTEC). Damage to cartilage, the tough-yet-flexible material that gives shape to ears and noses and lines the surface of joints so they can move easily, can be caused by injury, disease or faulty genes. Microfracture is a standard of care for cartilage repair, but for holes in cartilage caused by injury, it often either fails to stimulate new cartilage growth or grows cartilage that is less hardy than the original tissue.

Here are more details from the Johns Hopkins Jan. 15, 2013 news release,

Tissue engineering researchers, including Elisseeff, theorized that the specialized stem cells needed a nourishing scaffold on which to grow, but demonstrating the clinical value of hydrogels has “taken a lot of time,” Elisseeff says. By experimenting with various materials, her group eventually developed a promising hydrogel, and then an adhesive that could bind it to the bone.

After testing the combination for several years in the lab and in goats, with promising results, she says, the group and their surgeon collaborators conducted their first clinical study, in which 15 patients with holes in the cartilage of their knees received a hydrogel and adhesive implant along with microfracture. For comparative purposes, another three patients were treated with microfracture alone. After six months, the researchers reported that the implants had caused no major problems, and MRIs showed that patients with implants had new cartilage filling an average 86 percent of the defect in their knees, while patients with only microfracture had an average of 64 percent of the tissue replaced. Patients with the implant also reported a greater decrease in knee pain in the six months following surgery, according to the investigators.

The trial continues, has enrolled more patients and is now being managed by a company called Biomet. The trial is part of efforts to win European regulatory approval for the device.

In the meantime, Elisseeff says her team has begun developing a next-generation implant, one in which the hydrogel and adhesive will be combined in a single material. In addition, they are working on technologies to lubricate joints and reduce inflammation.

The study has been published in the AAAS’s (American Association for the Advancement of Science) Science Translational Medicine journal,

Human Cartilage Repair with a Photoreactive Adhesive-Hydrogel Composite

Surgical options for cartilage resurfacing may be significantly improved by advances and application of biomaterials that direct tissue repair. A poly(ethylene glycol) diacrylate (PEGDA) hydrogel was designed to support cartilage matrix production, with easy surgical application. A model in vitro system demonstrated deposition of cartilage-specific extracellular matrix in the hydrogel

Sci Transl Med 9 January 2013:
Vol. 5 no. 167 pp. 167ra6DOI:10.1126/scitranslmed.3004838

This article is behind a paywall and for some reason the authors are listed only in the news release,

Jennifer Elisseeff, Blanka Sharma, Sara Fermanian, Matthew Gibson, Shimon Unterman, Daniel A. Herzka, Jeannine Coburn and Alexander Y. Hui of the Johns Hopkins School of Medicine; Brett Cascio of Lake Charles Memorial Hospital; Norman Marcus, a private practice orthopedic surgeon; and Garry E. Gold of Stanford University

From Cornell University, a liquid that remembers its shape

Sometimes one experiences a frisson (shiver) when reading about a piece of research. Let’s see how you do with this Dec. 4, 2012 news item on Nanowerk,

A bit reminiscent of the Terminator T-1000, a new material created by Cornell researchers is so soft that it can flow like a liquid and then, strangely, return to its original shape.

Rather than liquid metal, it is a hydrogel, a mesh of organic molecules with many small empty spaces that can absorb water like a sponge. It qualifies as a “metamaterial” with properties not found in nature and may be the first organic metamaterial with mechanical meta-properties.

The Dec. 3, 2012 Cornell University news article by Bill Steele, which originated the news item,goes on to explain the interest in hydrogels and what makes this particular formulation so special,

Hydrogels have already been considered for use in drug delivery — the spaces can be filled with drugs that release slowly as the gel biodegrades — and as frameworks for tissue rebuilding. The ability to form a gel into a desired shape further expands the possibilities. For example, a drug-infused gel could be formed to exactly fit the space inside a wound.

The new hydrogel is made of synthetic DNA. In addition to being the stuff genes are made of, DNA can serve as a building block for self-assembling materials. Single strands of DNA will lock onto other single stands that have complementary coding, like tiny organic Legos. By synthesizing DNA with carefully arranged complementary sections Luo’s [Dan Luo, professor of biological and environmental engineering] research team previously created short stands that link into shapes such as crosses or Y’s, which in turn join at the ends to form meshlike structures to form the first successful all-DNA hydrogel. Trying a new approach, they mixed synthetic DNA with enzymes that cause DNA to self-replicate and to extend itself into long chains, to make a hydrogel without DNA linkages.

“During this process they entangle, and the entanglement produces a 3-D network,” Luo explained. But the result was not what they expected: The hydrogel they made flows like a liquid, but when placed in water returns to the shape of the container in which it was formed.

“This was not by design,” Luo said.

See the material for yourself,

Hydrogels made in the form of the letters D, N and A collapse into a liquid-like state on their own but return to the original shape when surrounded by water Provided/Luo Lab

Nature Nanotechnology published the team’s research online Dec. 2, 2012 and, unusually, the article is open access (at least for now),

A mechanical metamaterial made from a DNA hydrogel by Jong Bum Lee, Songming Peng, Dayong Yang,  Young Hoon Roh, Hisakage Funabashi, Nokyoung Park, Edward J. Rice, Liwei Chen, Rong Long, Mingming Wu & Dan Luo in Nature Nanotechnology  (2012) doi:10.1038/nnano.2012.211 published online Dec. 2, 2012

Depending on your reading interests and time available, Bill Steele’s Cornell University article has more detail than I’ve provided here or you can check out the well illustrated article in Nature Nanotechnology. As these things go, it’s quite readable as you can see with the abstract (Note: I have removed footnotes),

Metamaterials are artificial substances that are structurally engineered to have properties not typically found in nature. To date, almost all metamaterials have been made from inorganic materials such as silicon and copper, which have unusual electromagnetic or acoustic properties that allow them to be used, for example, as invisible cloaks superlenses or super absorbers for sound. Here, we show that metamaterials with unusual mechanical properties can be prepared using DNA as a building block. We used a polymerase enzyme to elongate DNA chains and weave them non-covalently into a hydrogel. The resulting material, which we term a meta-hydrogel, has liquid-like properties when taken out of water and solid-like properties when in water. Moreover, upon the addition of water, and after complete deformation, the hydrogel can be made to return to its original shape. The meta-hydrogel has a hierarchical internal structure and, as an example of its potential applications, we use it to create an electric circuit that uses water as a switch.

For anyone not familiar with the Terminator movies, here’s an essay in Wikipedia about the ‘franchise’. Pay special note to the second movie in the series, Terminator 2: Judgment Day which introduced a robot (played by Robert Patrick) that could morph from a liquidlike state into various lethal entities.

New hydrogels make greater elasticity in tissue engineering possible

A team from Harvard University have developed a technique for creating hydrogels that could be used effective in tissue engineering projects. From the Sept. 5, 2012 news release on EurekAlert,

A team of experts in mechanics, materials science, and tissue engineering at Harvard have created an extremely stretchy and tough gel that may pave the way to replacing damaged cartilage in human joints.

Called a hydrogel, because its main ingredient is water, the new material is a hybrid of two weak gels that combine to create something much stronger. Not only can this new gel stretch to 21 times its original length, but it is also exceptionally tough, self-healing, and biocompatible—a valuable collection of attributes that opens up new opportunities in medicine and tissue engineering.

Here’s an image of the hydrogel provided by the researchers,

The researchers pinned both ends of the new gel in clamps and stretched it to 21 times its initial length before it broke. Credit: Photo courtesy of Jeong-Yun Sun

The Sept. 5, 2012 news item on ScienceDaily has some comments from the researcher,

“Conventional hydrogels are very weak and brittle — imagine a spoon breaking through jelly,” explains lead author Jeong-Yun Sun, a postdoctoral fellow at the Harvard School of Engineering and Applied Sciences (SEAS). “But because they are water-based and biocompatible, people would like to use them for some very challenging applications like artificial cartilage or spinal disks. For a gel to work in those settings, it has to be able to stretch and expand under compression and tension without breaking.”

To create the tough new hydrogel, they combined two common polymers. The primary component is polyacrylamide, known for its use in soft contact lenses and as the electrophoresis gel that separates DNA fragments in biology labs; the second component is alginate, a seaweed extract that is frequently used to thicken food.

Separately, these gels are both quite weak — alginate, for instance, can stretch to only 1.2 times its length before it breaks. Combined in an 8:1 ratio, however, the two polymers form a complex network of crosslinked chains that reinforce one another. The chemical structure of this network allows the molecules to pull apart very slightly over a large area instead of allowing the gel to crack.

The alginate portion of the gel consists of polymer chains that form weak ionic bonds with one another, capturing calcium ions (added to the water) in the process. When the gel is stretched, some of these bonds between chains break — or “unzip,” as the researchers put it — releasing the calcium. As a result, the gel expands slightly, but the polymer chains themselves remain intact. Meanwhile, the polyacrylamide chains form a grid-like structure that bonds covalently (very tightly) with the alginate chains.

Therefore, if the gel acquires a tiny crack as it stretches, the polyacrylamide grid helps to spread the pulling force over a large area, tugging on the alginate’s ionic bonds and unzipping them here and there. The research team showed that even with a huge crack, a critically large hole, the hybrid gel can still stretch to 17 times its initial length.

Importantly, the new hydrogel is capable of maintaining its elasticity and toughness over multiple stretches.

Anyone can see that the ability to stretch, self-heal and stretch mimics the body’s own processes and that materials which can mimic those processes are very promising. From the news item on ScienceDaily,

Beyond artificial cartilage, the researchers suggest that the new hydrogel could be used in soft robotics, optics, artificial muscle, as a tough protective covering for wounds, or “any other place where we need hydrogels of high stretchability and high toughness.”

If you’re interested, there are still more details in the news release on EurekAlert or in the news item on ScienceDaily.

Printing jello and conducting electricity

The July 4, 2012 news item on ScienceDaily about a gel that behaves like biological tissue but conducts electricity is another one of those pieces of research which illustrate the idea that the boundary between the behaviour of biological and nonbiological materials is wavering,

The material, created by Stanford chemical engineering Associate Professor Zhenan Bao, materials science and engineering Associate Professor Yi Cui and members of their labs, is a kind of conducting hydrogel — a jelly that feels and behaves like biological tissues, but conducts electricity like a metal or semiconductor.

That combination of characteristics holds enormous promise for biological sensors and futuristic energy storage devices, but has proven difficult to manufacture until now.

The ScienceDaily news item originated in a June 27, 2012 article written by Max McClure for the (University of) Stanford Report,

Bao and Cui made the gel by binding long chains of the organic compound aniline together with phytic acid, found naturally in plant tissues. The acid is able to grab up to six polymer chains at once, making for an extensively cross-linked network.

“There are already commercially available conducting polymers,” said Bao, “but they all form a uniform film without any nanostructures.”

In contrast, the new gel’s cross-linking makes for a complex, sponge-like structure.  The hydrogel is marked with innumerable tiny pores that expand the gel’s surface area, increasing the amount of charge it can hold, its ability to sense chemicals, and the rapidity of its electrical response.

Still, the gel can be easily manipulated. Because the material doesn’t solidify until the last step of its synthesis, it can be printed or sprayed as a liquid and turned into a gel after it’s already in place – meaning that manufacturers should be able to construct intricately patterned electrodes at low cost.

Here’s more about the electrical conductance properties from the McClure article,

The material’s unusual structure also gives the gel what Cui referred to as “remarkable electronic properties.”

Most hydrogels are tied together by a large number of insulating molecules, reducing the material’s overall ability to pass electrical current. But phytic acid is a “small-molecule dopant” – meaning that when it links polymer chains, it also lends them charge. This effect makes the hydrogel highly conductive.

The gel’s conductance is “among the best you can get through this kind of process,” said Cui. Its capacity to hold charge is very high, and its response to applied charge is unusually fast.

The substance’s similarity to biological tissues, its large surface area and its electrical capabilities make it well suited for allowing biological systems to communicate with technological hardware.

The researchers envision it being used in everything from medical probes and laboratory biological sensors to biofuel cells and high-energy density capacitors.

“And all it’s made of are commercially available ingredients thrown into a water solution,” said Bao.

The July 4, 2012 ScienceDaily news item provided this citation for the paper,

L. Pan, G. Yu, D. Zhai, H. R. Lee, W. Zhao, N. Liu, H. Wang, B. C.- K. Tee, Y. Shi, Y. Cui, Z. Bao. Hierarchical nanostructured conducting polymer hydrogel with high electrochemical activity. Proceedings of the National Academy of Sciences, 2012; 109 (24): 9287 DOI: 10.1073/pnas.1202636109