Glass sponges inspire: Hybrid material made of collagen fibers and silica as possible substrate for bone tissue culture

Biomineralization is a very complicated process that is not so easy to mimic. The silicate precursors required for the synthesis of the cell walls of diatoms are in a stabilized form, which prevents their uncontrolled polymerization. Special proteins then control the polymerization to make the highly complex structures of the resulting scaffold. Researchers would also like to control biomineralization processes to repair damaged teeth or to make synthetic cartilage and bone tissue. In order to culture bones, scientists would like to seed osteoblasts (bone building cells) from the patient’s own body onto a substrate, where they would attach and multiply. This scaffolding would be implanted to help damaged bone, in cases of osteoporosis-induced or highly complicated fractures for example, to regenerate. Osteoblasts release collagen, calcium phosphate, and calcium carbonate as the basis for new bone material.

Collagen fibers would be an ideal substrate, but they are not solid enough for bone repair. The researchers once again turned to nature for inspiration: in glass sponges, a collagen matrix is one component of the silica scaffolding. Would it thus be possible to strengthen a collagen structure with silica (silicon dioxide)? Although many teams have previously failed in their attempts, the team led by Tay and Chen has now been successful.

They used collagen fibers as both a “mold” and a catalyst for the polymerization of the liquid phase of a silica precursor compound to make solid silica. The silica precursor is stabilized with choline to prevent an uncontrolled polymerization. This leaves enough time for the liquid precursor to fully infiltrate the space between the microfibrils of the collagen fibers before it polymerizes to form silica—one secret to the success of this new approach. After the polymerization the solid silica reflects the architecture determined by the collagen fibers. After drying, the original sponge-like, porous structure of the collagen fibers is maintained. In contrast to pure collagen, the scaffold of the hybrid compound is stable and could, the researchers hope, be used to repair bones.

More information: Franklin R. Tay, Infiltration of Silica Inside Fibrillar Collagen, Angewandte Chemie International Edition, http://dx.doi.org/ … ie.201105114

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New method to grow synthetic collagen unveiled: New material may find use in reconstructive surgery, cosmetics, tissue engineering

In a significant advance for cosmetic and reconstructive medicine, scientists at Rice University have unveiled a new method for making synthetic collagen. The new material, which forms from a liquid in as little as an hour, has many of the properties of natural collagen and may prove useful as a scaffold for regenerating new tissues and organs from stem cells.

"Our work is significant in two ways," said Rice's Jeffrey Hartgerink, the lead author of a new paper about the research in Nature Chemistry. "Our final product more closely resembles native collagen than anything that's previously been made, and we make that material using a self-assembly process that is remarkably similar to processes found in nature."

Collagen, the most abundant protein in the body, is a key component of many tissues, including skin, tendons, ligaments, cartilage and blood vessels. Biomedical researchers in the burgeoning field of regenerative medicine, or tissue engineering, often use a combination of stem cells and collagen-like materials in their attempts to create laboratory-grown tissues that can be transplanted into patients without risk of immunological rejection.

Animal-derived collagen, which has some inherent immunological risks, is the form of collagen most commonly used in reconstructive and cosmetic surgery today. Animal-derived collagen is also used in many cosmetics.

Despite the abundance of collagen in the body, deciphering or recreating it has not been easy for scientists. One reason for this is the complexity collagen exhibits at different scales. For example, just as a rope is made of many interwoven threads, collagen fibers are made of millions of proteins called peptides. Like a rope net that can trap and hold items, collagen fibers can form three-dimensional structures called hydrogels that trap and hold water.

"Our supramolecules, fibers and hydrogels form in a similar way to native collagen, but we start with shorter peptides," said Hartgerink, associate professor of chemistry and of bioengineering.

With an eye toward mimicking collagen's self-assembly process as closely as possible, Hartgerink's team spent several years perfecting its design for the peptides.

Hartgerink said it's too early to say whether the synthetic collagen can be substituted medically for human or animal-derived collagen, but it did clear the first hurdle on that path; the enzyme that the body uses to break down native collagen also breaks down the new material at a similar speed.

A faculty investigator at Rice's BioScience Research Collaborative, Hartgerink said scientists must next determine whether cells can live and grow in the new material and whether it performs the same way in the body that native collagen does. He estimated that clinical trials, if they prove warranted, are at least five years away.

The paper's co-authors include Rice graduate students Lesley O'Leary, Jorge Fallas, Erica Bakota and Marci Kang. The research was funded by the National Science Foundation, the Robert A. Welch Foundation and the Norman Hackerman Advanced Research Program of Texas.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Rice University.

Journal Reference:

Lesley E. R. O'Leary, Jorge A. Fallas, Erica L. Bakota, Marci K. Kang, Jeffrey D. Hartgerink. Multi-hierarchical self-assembly of a collagen mimetic peptide from triple helix to nanofibre and hydrogel. Nature Chemistry, 2011; DOI: 10.1038/nchem.1123

Note: If no author is given, the source is cited instead.

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