Stem Cell Proliferation and Differentiation Observed Within Hydrogel

CWRU research developing technique with promise to guide formation of complex tissues

Friday, 12 April 2013

Stem cells can be coaxed to grow into new bone or new cartilage better and faster when given the right molecular cues and room inside a water-loving gel, researchers at Case Western Reserve University show.

By creating a three-dimensional checkerboard — one with alternating highly connected and less connected spaces within the hydrogel — the team found adjusting the size of the micro-pattern could affect stem cell behaviours, such as proliferation and differentiation.

Inducing how and where stem cells grow — and into the right kind of cell in three dimensions — has proven a challenge to creating useful stem cell therapies. This technique holds promise for studying how physical, chemical and other influences affect cell behaviour in three-dimensions, and, ultimately, as a method to grow tissues for regenerative medicine applications.

"We think that control over local biomaterial properties may allow us to guide the formation of complex tissues," said Eben Alsberg, an associate professor of Biomedical Engineering at Case Western Reserve.

"With this system, we can regulate cell proliferation and cell-specific differentiation into, for example, bone-like or cartilage-like cells."

Oju Jeon, PhD, a postdoctoral researcher in Biomedical Engineering, pursued this work with Alsberg. Their work is described April 11, 2013 in the online edition of Advanced Functional Materials.

Hydrogels are hydrophilic three-dimensional networks of water-soluble polymers bonded, or cross-linked, to one another. Crosslinks increase rigidity and alter the porous structure inside the gel.

Alsberg and Jeon used a hydrogel of oxidized methacrylated alginate and an 8-arm poly(ethylene glycol) amine. A chemical reaction between the alginate and the poly(ethylene glycol) creates crosslinks that provide structure within the gel.

They tweaked the mix so that a second set of crosslinks forms when exposed to light. They used checkerboard masks to create patterns of alternating singly and doubly cross-linked spaces.

The spaces, which varied in size at 25, 50, 100 and 200 micrometres across, were evenly singly and doubly cross-linked.

Human stem cells isolated from fat tissue were encapsulated in the singly and doubly cross-linked regions. The doubly cross-linked spaces are comparatively cluttered with structures. The cells grew into clusters in the singly cross-linked regions, but remained mostly isolated in the doubly cross-linked regions.

The larger the spaces in the checkerboard, the larger the clusters grew.

Cells were cultivated in media that promote differentiation into either bone or cartilage.

In both the singly and doubly cross-linked spaces, stem cells increasingly differentiated according to the media composition as the space size increased. The results were more dramatic in the singly cross-linked spaces.

"Potentially, what's happening is the single cross-linked regions allow better nutrient transport and provide more space for cells to interact and, because it's less restrictive, there's space for new cells and matrix production," Alsberg said.

"Cluster formation, in turn, may influence proliferation and differentiation. Differences in mechanical properties between regions likely also regulate the cell behaviours."

The researchers are continuing to use micro-patterning to understand the influences of biomaterials on stem cell fate decisions. This approach may permit local control over cell behaviour and, ultimately, allow the engineering of complex tissues comprised of multiple cell types using a single stem cell source.

Source: Case Western Reserve University 

Contact: Kevin Mayhood

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ZenMaster

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For more on stem cells and cloning, go to CellNEWS at

http://cellnews-blog.blogspot.com/

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Growing Cartilage – No Easy Task

New nanoscopic material enables cartilage to do what it doesn't do naturally Monday, 01 February 2010 Northwestern University researchers are the first to design a bioactive nanomaterial that promotes the growth of new cartilage in vivo and without the use of expensive growth factors. Minimally invasive, the therapy activates the bone marrow stem cells and produces natural cartilage. No conventional therapy can do this. The results will be published online the week of Feb. 1 by the Proceedings of the National Academy of Sciences (PNAS). "Unlike bone, cartilage does not grow back, and therefore clinical strategies to regenerate this tissue are of great interest," said Samuel I. Stupp, senior author, Board of Trustees Professor of Chemistry, Materials Science and Engineering, and Medicine, and director of the Institute for BioNanotechnology in Medicine. Countless people – amateur athletes, professional athletes and people whose joints have just worn out – learn this all too well when they bring their bad knees, shoulders and elbows to an orthopaedic surgeon. Damaged cartilage can lead to joint pain and loss of physical function and eventually to osteoarthritis, a disorder with an estimated economic impact approaching $65 billion in the United States. With an aging and increasingly active population, this figure is expected to grow. "Cartilage does not regenerate in adults. Once you are fully grown you have all the cartilage you'll ever have," said first author Ramille N. Shah, assistant professor of materials science and engineering at the McCormick School of Engineering and Applied Science and assistant professor of orthopaedic surgery at the Feinberg School of Medicine. Shah is also a resident faculty member at the Institute for BioNanotechnology in Medicine. Type II collagen is the major protein in articular cartilage, the smooth, white connective tissue that covers the ends of bones where they come together to form joints. "Our material of nanoscopic fibres stimulates stem cells present in bone marrow to produce cartilage containing type II collagen and repair the damaged joint," Shah said. "A procedure called microfracture is the most common technique currently used by doctors, but it tends to produce a cartilage having predominantly type I collagen which is more like scar tissue." The Northwestern gel is injected as a liquid to the area of the damaged joint, where it then self-assembles and forms a solid. This extracellular matrix, which mimics what cells usually see, binds by molecular design one of the most important growth factors for the repair and regeneration of cartilage. By keeping the growth factor concentrated and localized, the cartilage cells have the opportunity to regenerate. Together with Nirav A. Shah, a sports medicine orthopaedic surgeon and former orthopaedic resident at Northwestern, the researchers implanted their nanofibre gel in an animal model with cartilage defects. The animals were treated with microfracture, where tiny holes are made in the bone beneath the damaged cartilage to create a new blood supply to stimulate the growth of new cartilage. The researchers tested various combinations: microfracture alone; microfracture and the nanofibre gel with growth factor added; and microfracture and the nanofibre gel without growth factor added. They found their technique produced much better results than the microfracture procedure alone and, more importantly, found that addition of the expensive growth factor was not required to get the best results. Instead, because of the molecular design of the gel material, growth factor already present in the body is enough to regenerate cartilage. The matrix only needed to be present for a month to produce cartilage growth. The matrix, based on self-assembling molecules known as peptide amphiphiles, biodegrades into nutrients and is replaced by natural cartilage. ......... ZenMaster

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For more on stem cells and cloning, go to CellNEWS at http://cellnews-blog.blogspot.com/

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